the sideforce on · pdf filethe sideforce on surface piercing hydrofoil struts david w....
TRANSCRIPT
U.S. DEPARTMENT OF COMMERCENational Technical Information Service
AD-A029 456
Methods for Controlling
the Sideforce on SurfacePiercing Hydrofoil StrutsDavid W. Taylor Naval Ship Res & Dev Center
July 1976
p.. W ... . ...
DAVID W. TAYLOR NAVAL SHIPRESEARCH AND DEVELOPMENT CENTER
Bethsda, Md. 20064
Methods for Controlling the
Cq Sideforce on Surface-Piercing
4 Hydrofoil Struts
by
Richard S. Rothbl urnm'CMichael F. Jeffers
CvRussel P. Smith
.a,
C 4,,
U)
~~fO 11 1 JUlIC IIE~ll a ISIBUUOU II 1.,UL l I D
~Ship Performance Department
. Departmental Report
C4J
4.'1. V)
V July 1976 SPD-700-O1
.{ NATIONAL TECHNICAL"INFORMATION SERVICE
U.S. DPARMNr OF COMM,CE. SPRINGFIENL. VA. 221.
MAJOR DTNSRDC ORGANIZATIONAL COMPONENTS
i DTNSRDC
~~COMMANDER 0
TECHNICAL DI RECTOR01
OFFICER-IN.CHARGE OFFICERIN.CHARGECARDEROCK ANNAPOLIS05 04
SYSTEMS VDEVELOPMENTDEPARTMENT
SHIP PERFORMANCE AVIATION AND
DEPARTMENT SURFACE EFFECTS15 DEPARTMENT 16
STRUCTURES COMPUTATION
DEPARTMENT AND MATHEMATICS17 DEPARTMENT 18
[SHIP ACOUSTICS PROPULSION AND
I DEPARTME14T AUXILIARY SYSTEMS19 DEPARTMENT 27
MATERIALS CENTRAL
DEPARTMENT INSTRUMENTATION
28 DEPARTMENT 29
rp
UNCLASSIFIED
SECURITY CLASSIFICATION OF THIS PAGE tWhon Data Entered)REOTDCMNAINPAGE READ INSTRUCTONS
REPORT DOCUMENTATION PBEFORE COMPLETING FORM
1. REPORT NUMBER 2. GOVT ACCESSION NO. 3. RECIPIE4T1S CATALOG NUMBER
SPD-700-01 I4, TITLE (and Subtitle) S. TYPE OF REPORT & PERIOD COVERED
Methods for Controlling the Sideforce on FinalSurface-Piercing Hydrofoil Struts
S. PERqFORqMINU ORG. REPORqT NUMNEIrl
7. AUTHOR(#) S. CONTRACT OR GRANT NUMBER(*)
Richard S. RothblumMichael F. JeffersRussell P. Smith
0. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRi.M ELEMENT. PROJECT. TASK
David W. Taylor Naval Ship iMD Center AREA & WORK UNIT NUMBERSBethesda, Maryland 20084
11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE
Systems Development Department. Advanced Hydro- July 1976foil Systems Office, David W. Taylor Naval Ship 13. NUMBER OF PAGES
R&D Center, Bethesda, Maryland 20084 /47 114. MONITORING AGENCY NAME a ADDRESS(I dillerenl from Controlling Office) IS. SECURITY CLASS. (of thl teport)
UNCLASSIFIED
1S. DECL ASSI FI CA rION/ DOWN GRAOINGSCHEDULE
I. OISTFIBUTION STATEMENT (of thle Report)
APPROVED FOR ?'UBLIC REJ.FASE: DISTRIBUTION UNLIMITED
I?. OISTRIUTION STATEMENT (of the abstrt ontered In Block 20, If different from Report)
IS. SUPPLEMENTARY NOTES
IS. KiE' WORDS (Continue on reverse aide If necesary and Identify by block nuo. ber)
Hydrofoil, Struts, Ventilation, Lift, Drag, Sidefnrce, Aeration, Airbleed,
Air injection, Cavitation, Ventilation fences, 7ences, Cavitation plate,Endplate, Flaps, Split flops, Trailing edge flaps, Nose flaps
20. ASSTPACT (Continue on tooeres side If necesewy and Identify by block m mber)
Possible means of reducing the sideforce due to sideslip angle on a
surface-piercing hydrofoil strut were investigated. An expexfiental programwas performed to test the effect on strut sideforce and venrilation character-
istics of 50-percent chord trailing edge flaps, midchord spoilers (split
flaps), and airbleed (air injection). The effect of fences was tested in com-
bination with the trailing edge flap and airbleed. All syscems were foundto be effective in reducing or changing sideforce. None of the methods
DO IAN,73 1473 EDITION OF I NOV *S IS OSSOLETE UNCLASSIFIED
S/N 0102-014-6601 01 SECURIT" CLASSIFICATION OF THIS PAGE (When Dos Enfred)
UNCLASIFIED..LAIVIlITY CLASSIFICATION OF TMIS PAGE(Whon bae Entered)-
-xigificantly- improved, strut--wesitance-to. ventilation, -but irbleed andspoilers reduced the abruptness Of tren~sition to the ventilated state -ndercertain circumstances. Power requirements were evaluated for the case of
* flapped struts.-Drag penalties varied from nothing. for a midchord spoileron one side to 200 percent of baseline drag for continuous airbiced. -Fencesslightly increased drag, and had a smoothing influence on transition. betweenventilated and unventilated flow states.
ii 'INCLASSIFIED
SECURITY CLASSIFICATION OF THI 1 AOE(Whon Data rnlmted)
TABLE or CONTENTS
Page
ABSTRACT......................................................................................... I
ADMINISTRATIVE INFORMATION ........................................................... I
INTRODUCTION ......................................... ...................................... 2
CONTROLLABLE FLAP........................................................................8
THE FLAP AND FENCE EXPERIMENT ............... ....................................... 14The Model...................................................... ............................ 14Te:;t Conditions............................................................................... 14Sign Conventions ............................................................................. 14Data Collection and Sources of' Error...................................................... 14
RESULTS OF THE FLAP AND FENCE EXPERIMENT ...................................... 17
CONCLUSIONS OF THE FLAP AND FENCE EXPERIMENT .............................. 40
AIRBLEED ...................................................................................... 41
ESTIMATE OF REQUIRED AIR FLOW RATE ........................................... .. 42
THE AIRBLEED AND FENCE EXPERIMENT ................................................ 43Thec Model ................................................................................. 43Air SuIpplY............................................................... ................... 43Test Conditions............................................................................... 43Data Collection............................................................................... 43
RESULTS AND DISCUSSION OF THE AIRBLEED AND FENCE EXPERIMENT ....... 45
CONCLUSIONS OF THE AIRBLEED AND FENCE EXPERIMENT........................10o5
SPOILER........................................................................................ 106
THE SPOILER EXPERIMENT ................................ ................................. 106The Model .................................................................................. 106
RESULTS AND DISCUSSION OF THE SPOILFR EXPERIMENT.......................... 107
CONCLUSIONS OF THE SP~OILER EXPE'.RIMNIT........................................... 112
GENERAL CONCLUSIONS ...................................................................... 112
LIST OF FIGURES
Figure Page
I - Diagram of Sideslip Angle, 3, Induced by Turn .............................................. 3
2 - Apparent Sideslip Angle versus Strut Separation for VariousTurn Rates, 60 kts .......................................................................................... 4
3 - Apparent Sideslip Angle versus Strut Separation for VariousTurn Rates, 50 kts ........................................................................................... 5
4 - Apparent Sideslip Angle versus Strut Separation for VariousTurn Rates, 40 kts .......................................................................................... 6
- F'-p Fffeclveness vs Flap/Chord Ratio (From Reference I) ........................... 8
6 - Pressure Distribution on Flapped Symmetric Foil (r~rom Reference 1) ........... 9
7 - Possible Use of Ventilation Fences to Prevent Fap or Nose %ventilation ...... 10
8 - Theoretical Hinge Moment and Pitching Moment of PlainTrailing Edge Flaps (From Reference 1) ........................................................... 1
9 - Sideforce Coefficient Slope versus Reciprocal of Aspect Ratio forSurface Piercing Struts Without Endplate (From Reference 3) ........................ 12
10 - Histogram of Power Requirement to Exercise a Flap Through aContinuous Linear Cycle, 0 to +13 to -13 to 0 D- g ....................................... 13
11 - Fiapi%.d Model with Fences: Mounting Arrangement, Section.O ffsets, Photograph ......................................................................................... 15
12 - Data Collection Schematic ............................................................................... 16
13a - Sideforce Coefficient vs Sideslip Angle, Flapped Strut, WithoutFences, 0 Degrees, 20, 30, 35, 40, 45, 50 kts ................................................. 18
13b- Drag Coefficient vs Sideslip Angle, Fapped Strut, WithoutFences, 0 Degrees Flap, 20, 30, 35, 40, 45, 50 kts ........................................ 19
14a - Sideforce Coefficient vs Sideslip Angle, Flapped Strut, WithoutFences, 5 Degices Flap, 10, 25, 30, 35, 40, 45, 50 kts ................................... 20
14b- Drag Coefficient vs Sideslip Angle. Flapped Strut, WithoutFences, 5 Degrees Flap, 10, 25, 30, 35, 40, 45, 50 kts ................................... 21
1 Sa - Sideforce Coefficient vs Sideslip Angle, Flapped Strut. WithoutFences, 7 1l2 Degrees Flap, 25, 30, 35, 40. 45 kts .......................................... 22
15b- Drag Coefficient vs Sideslip Angle, Flapped Strut, WithoutFences, 7 1/2 Degrees Flap, 25, 30, 35, 40, 45 kts ......................................... 23
iv
Figure Page
16a - Sideforce Coefficient vs Sideslip Angle, Flapped Strut, WithoutFences, 10 Degrees Flap, 10, 25, 30, 35, 40 kts ...................... 24
16b- Drag Coefficient vs Sideslip Angle, Flapped Strut, WithoutFences, 10 Degrees Flap, 10, 25, 30, 35, 40 kts ............................................. 25
17a - Sideforce Coefficient vs Sideslip Argle, Flapped Strut, WithoutFences, 15 Degrees Flap, 20, 25, 30, 35, 40, 45 kts ........................................ 26
17b- Drag Coefficient vs Sideslip Angle, Flapped Strut, WithoutFences, 15 Degrees Flap, 20, 25, 30, 35, 40, 45 kts ........................................ 27
1 8a - Sideforce Coefficient vs Sideslip Angle, Flapped Strut, WithoutFences, 20 Degrees Flap, 10, 25, 30, 35, 40 kts .......................... 28
18b- Drag Coefficient vs Sideslip Angle, Flapped Strut,20 Degrees Flap, 10, 25, 30, 35, 40 kts ........................................................... 29
19a - Sideforce Coefficient vs Sideslip Angle, Flapped Strut, WithFences, 0 Degrees Flap, 10, 25, 30, 35, 40, 45, 50 kts .................................... 30
19b - Drag Coefficient vs Sideslip Angle, Flapped Strut, WithFences, 0 Degrees Flap, 10, 25, 30, 35, 40, 45, 50 kts .................................... 31
20a - Sideforce Coefficient vs Sideslip Angle, Flapped Strut, WithFences, 10 Degrees Fla,, 10, 25, 30, 35, 40, 45, 50 kts ................................. 32
20b- Drag Coefficient vs Sideslip Angle, Flapped Strut, WithFences, 10 Degrees Flap, 10, 25, 30, 35, 40, 45, 50 kts ................................. 33
21a- Sideforce Coeffiripn, vs Sideslip Angle, Flapped Strut, WithFences, 10 Degrees Flap, 10. 25, 30, 35, 40, 45, 50 kts ................................ 34
21b- Drag Coefficient vs Sideslip Angle, Flapped Strut, WithFences, 10 Degrees Flap. 10, 25, 30, 35, 40, 45. 50 kts ................................. 35
22a - Sideforce Coefficient vs Sideslip Angle, Flapped Strut, WithFences, 20 Degrees Flap, 10. 25. 30, 35, 40, 45, 50 kts ................................. 36
22b- Drag Coeffic;-nt vs Sideslip Angle, Flapped Strut, WithFences, 20 DegrLes Flap, 10, 25, 30, 35, 40, 45. 50 kts ................................. 37
23 - Nomenclature from Lang and Daybell for Use in CalculatingCritical Airflow Rates ...................................................................................... 42
24 - Airbleed Model with Fences ............................................................................. 44
25a - Sideforce Coefficient vs Sideslip Angle. Airbleed Strut, Off,Plugged, Without Fences, 10, 25, 30, 40, 50 kts ............................................ 46
V
Figure Page
25b- Drag Coefficient vs Sideslip Angle, Airbleed Strut, Off,Plugged, Without Fences, 1O, 25, 30, 40, 50 kts .............................................. 47
26a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,35 SCFM (16.5 x 10-3 m3/s), Without Fences, All Holes,Port Side, 10, 25, 30. 35, 40, 45. CA. ,is ......................................................... 48
26b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,35 SCFM (16 5 x 10- 3 m3/s), Without Fences, All Holes,Port Side, 10, 25, 30, 35, 40, 45, 50 kts ........................................................ 49
27a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,20 SCFM (9.4 x 10- 3m 3 /s), Without Fences, All Holes,Port Side Only, 10, 25, 30, 35, 40, 45, 50 kts ........................................... 50
27b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,20 SCFM (9.4 x 10- 3 m3 /s), Without Fences, All Holes,Port Side Only, 10, 25, 30, 35, 40, 45, 50 kts ................................................. 51
28a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut, Atmospheric,Without Fences, All Holes Port Side, 10, 25, 30, 35, 40, 45, 50 kts ............... 52
28b- Drag Coefficient vs Sideslip Angle, Airbleed Strut, Atmospheric,Without Fences, All Holes, Port Side, 10, 25, 30, 35, 40, 43, 50 kts .............. 53
29a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,35 SCFM (16.5-x 10-3 m 3 /s), With Fences, All Holes,Port Side, 10, 25, 30, 35, 40, 45, 50 kts ............................................................ S4
29b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,35 SCFM (16.5 x 10- 3 m3/s), With Fences, All Holes,Port Side, 10, 25, 30, 35, 40, 45, 50 kts ............................................................ 5
30a - Sideforce Coefficient vs Sideslip Angle, Airbloed Strti,20 SCFM (9.4 x l(- 3 m3 /s), With Fences, All Holes,
Port Side Only, 10, 25, 30, 35, 40, 45, 50 kts ............................................... 56
30b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,20 SCFM (9.4 x 10-3m 3 /s), With Fences, All iloles,Port Side Only, 10, 25, 30, 35, 40, 45, 50 kts ............................................... 57
31a- Sideforce Coefficient vs Sideslip Angle, Airbloed Strut, Atmospheric,With Fences, All Holes, Port Side, 10, 25, 30. 35. 40, 45, 50 kts ................... 58
31b- Drag Coefficient vs Sideslip Angle, Airbleed Strut, Atmospl~tc.With Fences. All lloles, Port Side, 10, 25. 30, 35, 40, 45, 50 kts ................... 59
vi
Figure Page
32 - Max Air Runs - All Holes Open on Port Side - Fences on Upper -Lift & Drag Coefficient vs Sideslip Angle. Air Flow Started at- 85 SCFM at Beginning or Run, Decreasing to 35 SCFM TowardsEnd of Run. Lower - Lift & Drag Coefficients vs Sideslip Angle.Burst of Air at - 95 SCFM During Data Collection Where Indicatedby o Circle Around Graph Points, 10 & 40 kts ................................................ 60
33 - Air Off Runs - Lift and Drag Coefficient vs Sideslip Anglewith Air Flow Shut Off at Supply. Holes in Strut All Open,Port Side, Fences On, 10 & 40 kts .................................................................... 61
34a - Sideforce Coefficiert vs Sideslip Angle, Airbleed Strut,20 SCFM (9.4 x 10- 3 m3/s), Without Fences, Leading EdgeHoles, Port Side, 10, 25. 30, 35, 40, 45, 50 kts ............................................... 62
34b- Drag Coefficient vs Sideslip Angle. Airbleed Strut.20 SCFM (9.4 x 10- 3m3/s), Without Fences, Leading EdgeHoles, Port Side. 10, 25. 30, 35, 40, 45. 50 kts ............................................... 63
35a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut, At,nospheric,Without Fences. Leading Edge Holes, Port Side. 10, 40, 45, 50 kts ................. 64
35b-m- Drag Coefficient vs Sideslip Angle, Airbleed Strut. Atmospheric,Without Fences, Leading Edge Holes, Port Side. 10. 40, 45, 50 kts ............... 65
36a - Sideforce Coefficient vs Sideslip Angle. Airbleed Strut, Atmospheric,Without Fences, Leading Edge Holes, Port Side, 10, 25, 30, 35, 40,45,50 kts ........................................................................................................ 66
36b- Drag Coefficient vs Sideslip Angle, Airbleed Strut, Atmospheric,Without Fences, Leading Edge Holes, Port Side, 10, 25, 30. 35, 40.45, 50 kts ......................................................................................................... 67
37a - Sideforce Coefficient vs Sideslip Angle. Airbleed Strut,35 SCFM (16.5 x 10-31m3 /s). Without Fences,10,, C Holes. Port Side. 10, 30, 45 kts ............................................................. 68
37b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,35 SCFM (16.5 x 10- 3 m3/s), Without Fences,I W r C Holes, Port Side, 10, 30, 45 kts ............................................................. 69
38a - Sideforce Coefficient vs Sideslip Angle. Airbleed Strut,20 SCFM (9.4 x 10-3i 3/s). Without Fences. 10yi( CHoles, Port Side. 10, 25, 30, 35, 40, 45, 50 kts ............................................... 70
38b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,20 SCFNI (9.4 x 10- 3m3/s), Without Fences. 101/ CHoles, Port Side, 10, 25, 30, 35, 40. 45, 50 kts ............................................... 71
vii
Figure Page
39a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,1O SCFM (4.7 x 10- 3 m3/s), Without Fences,I0o C Holes, Port Side, 10, 30, 45 kts ........................................................... 72
39b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,10 SCFM (4.7 x 10-3 m3/s), Without Fences,10% C Holes, Port Side, 10, 30, 45 kts ........................................................... 73
40a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,Atmospheric, Without Fences, 10% C Holes, Port Side,10, 25, 30, 35, 40, 45, 50 kts ........................................................................... 74
40b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,Atmospheric, Without Fences, 10% C Holee, Port Side,10, 25, 30, 35, 40, 45, 50 kts .......................................................................... 75
41a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,20 SCFM (9.4 x 10- 3 m3/s), Without Fences, 25 % CHoles, Port Side, 10, 25, 30, 45 kts .................................................................. 76
4lb- Drag Coefficient vs Sideslip Angle, Airbleed Strut,20 SCFM (9.4 x 10- 3 m3/s), Without Fences, 25% CHoles, Port Side, 10, 25, 30, 45 kts .................................................................. 77
42a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,10 SCFM (4.7 x 10- 3 m3/s), Without Fences, 25% CHoles, Port Side, 10, 30, 45 kts ....................................................................... 78
42b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,10 SCFM (4.7 x 10-3m3/s), Without Fences, 25% CHoles, Port Side, 10, 30, 45 kts ........................................................................ 79
43a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,Atmospheric, Without Fences, 25% C Holes, Port Side,10, 25, 30, 35, 40, 45, 50 kts ........................................................................... 80
43b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,Atmospheric, Without Fences. 25% C Holes, Port Side,10, 25, 30, 35, 40, 45, 50 kts ................................... 81
44a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,20 SCFM (9.4 x 10-3m 3 /s), Without Fences, Midchord Holes,Port Side, 10, 25, 30, 35, 40, 45, 50 kts ......................................................... 82
44b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,20 SCFM (9.4 x 10- 3m 3 /s), Without Fences, Midchord Holes,Port Side, 10, 25, 30, 35. 40, 45. 50 kts ........................................................ 83
45a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,10 SCFM (4.7 x 10" 3 m3/s). Without Fences, MidchordHoles, Port Side, 10, 30, 45 kts ....................................................................... 84
viii
Figure Page
45b.- Drag Coefficient vs Sideslip Angle, Airbleed Strut,10 SCFM (4.7 x 10- 3 m3/s), Without Fences MidchordHoles, Port Side, 10, 30, 45 kts ...................................................................... 85
46a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,Atmospheric, Without Fences, Midchord Holes, PortSide, 10, 25, 30, 35, 40, 45 kts ..................................... 86
46b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,Atmospheric, Without Fences, Midchord Holes. PortSide, 10, 25, 30, 35, 40, 45 kts ...................................................................... 87
47a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut, Atmospheric,Without Fences, Midchord Holes, Port Side, 10, 10 kts.Example of Cleared and Uncleared Holes .............................. 88
47b- Drag Coefficient vs Sideslip Angle, Airbleed Strut, Atmospheric,Without Fences, Midchord Holes, Port Side, 10, 10 kts.Example of Cleared and Uncleared Holes ......................................................... 88
48a - Sideforce Coefficient vs Sides'ip Angle, Airbleed Strut,35 SCFM (16.5 x 10-3m3/s), Without Fences, All Holes Open.Port and Starboard, 10, 25, 30, 35, 40, 45, 50 kts ........................................ 89
48b- Drag Coefficient vs Sideslip Angle, Airbleed Strut,35 SCFM (16.5 x l0- 3m3/s), Without Fences, All Holes Open,Port and Starboard, 10, 25, 30, 35, 40, 45, 50 kts ........................................ 90
49a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,Atmospheric, Without Fences, All Holes Open, Portand Starboard, 10, 25, 30, 35, 40, 45, 50 kts ................................................. 91
49b- Drag Coefficients vs Sideslip Angle, Airbleed Strut,
Atmospheric, Without Fences, All Holes Open, Portand Starboard, )0, 25, 30, 35, 40, 45, 50 kts ................................................. 92
5Oa - Sideforce Coefficient vs Sideslip Angle. Airbleed Strut,35 SCFM, Without Fences, Leading Edge Holes OpenBoth Sides, 10, 25, 30, 35, 40, 45, 50 kts ...................................................... 93
50b- Drag Coefficient vs Sideslip Angle, Airbleed Strut.35 SCFM, Without Fences, Leading Edge Holes OpenBoth Sides, 10, 25, 30, 35, 40, 45, 50 kts ....................................................... 94
51a- Sideforce Coefficient vs Sideilip Angle, Airbleed Strut,20 SCFM (9.4 x 10-3m3/s), Without Fences, Leading Edge HolesOpen Both Sides, 10, 25, 30, 35, 40, 45, 50 kts ............................................. 99
51b- Drag Coefficient vs Sideslip Angle, Airbleed Strut20 SCFM (9.4 x 10- 3 m3/s), Without Fences, Leading Edge lolesOpen Both Sides, 10, 25, 30, 35, 40, 45, 50 kts ................................................ 100
ix
Figure Page
52a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,10 SCFM (4.7 x 10- 3m3 s). Without Fences, Leading EdgeHoles Open Both Sides, 10, 25, 30, 35, 40, 45, 50 ks ..................................... 101
52b- Drag Coefficient vs Sideslip Angle, A:rbleed Strut,10 SCFM (4.7 x 10- 3m 3 /s), Without Fences, Leading EdgeHoles Open Both Sides. 10, 25. 30, 35, 40, 45, 50 kts ...................................... 102
53a - Sideforce Coefficient vs Sideslip Angle, Airbleed Strut,Atmospheric, Without Fences, Leading Edge HolesOpen Both Sides, 10, 20, 25, 30, 35, 40, 45, 50 kts .......................................... 103
53b- Drag Coefficient vs Sideslip Angle, Airbleed Strut.Atmospheric, Without Fences, Leading Edge HolesOpen Both Sides, 10, 20, 25, 30, 35, 40. 45, 50 kts .......................................... 104
54 - NACA 16-012 Strut with Spoilers .................................... 106
55a - Sideforce Coefficient vs Sideslip Angle. Spoiler Strut.Without Fences, Spoiler Both Sides, 10, 25, 30, 35,40, 45, 50 kts ...................................................................................................... 108
55b- Drag Coefficient vs Sideslip Angle, Spoiler Strut,Without Fences, Spoiler Both Sides, 10, 25, 30,35, 40, 45, 50 kts ............................................................................................... 109
56a - Sideforce Coefficient vs Sideslip Angle, SpoilerStrut, Without Fences, Spoiler STBD Side,10, 25, 30, 35, 40, 45, 50 kts ............................................................................ 110
56b- Drag Coefficient vs Sideslip Angle, Sp( iferStrut, Without Fences, Spoiler STBD Side,10, 25, 30, 35, 40, 45, 50 kts ............................................................................. 111
x
ABSTRACT
Possible means of reducing the sideforce due to sideslip angle on asurface-piercing hydrofoil strut wore investigated. An experimental pro-
gram was performed to test the effect on strut sideforce and ventilation
characteristics of 50-percent chord trailing edge flaps, midchord spoilers(split flaps), and airbleed (air injection). The effect of fences was testedin combination with the trailing edge flap and airbleed. All systems werefound to be effective in reducing or changing sideforce. None of the
methods significantly improved strut resistance to ventilation, but airbleed
and spoilers reduced the abruptness of transition to the ventilated stateunder certain circumstances. Power requirements were evaluated for thecase of flapped struts. Drag penalties varied from nothing for a mid-
chord spoiler on one side to 200 percent of baseline drag for continuous
airbleed. Fences slightly increased drag, and had a smoothing influenceon transition between ventilated and unventilated flow states.
ADMINISTRATIVE INFORMATION
This work was funded by the Systems Development Department, Advanced Hydrofoil
Systems Office, David W. Taylor Naval Ship Research and Development Center.
INTRODUCTION
The Advanced Hydrofoil Systems Office of thie David W. Taylor Naval Ship R& D Centeris considering the design of a large, ocean-going hydrofoil ship (HOC) with the following
approximate characteristics:
hullborne displacement 750 - 1200 metric tons
length overall 60 - 80 mlongitudinal strut spacing 50 - 70 inforward strut chord length 5 - 7 m
max turn rate 5 - 6 deg/s
(c.f. PHM, TUCUMdCARI,
8 deg/s, 12 deg/s, respectively)
design -speed 50 knots
It is envisioned that turns will be fully coordinated. That is, the craft will heel in-a turn such
that the-centrifigal and gravitational forces are exact'y compensated by the lift force on the
foil system. It can be assumed for purposes of estimating strut side slip angle during turns
that the craft will pivot virtually on the :fter struts. In these cirzunstances, the forward strut
will experience a sideslip angle even in a-perfectly coordinated, caln water turn. The sideslip
angle, 0, the heel angle, y, the radius of the turn, r, and the apparent sideslip angle at- the
strut (reduced because of the heel) P', are related by straightforward geometric formulas to the
craft velocity, V. the strut spacing, s, and the turn rate. (deg/s) or W (rad/s):
Vr
I
= tan -
tan tan P cos yVW4tan ' -
g
tani=l cos tan "1
A useful approximation. for small heel angles and sideslip angles is
r h h r = (tnits ofr are radians)r
Figure I show.,; tile geometry. Figures 2 - 4 show sideslip angle at the strut. P', versus strut
spacing. s, for various values of V and ,. The corresponding values of -' and r are also noted.
Figure 3 also shows the values of the approximation. P = sir, for comparison with the exact
formula. It can be seen from tie figures that 0' will be well above 10 degrees even for modestvalues of s and ' at the design speed.
2
VaV
j3-TN1 0
FOR AFLAT TURN
TRUEVERTICAL
APPARENT SIDESLIPP' IS REDUCED BYROLL ANGLEy DUTO PROJECTION OF~ON TILTED STRUT
IN HORIZON-I TAL PLANE
Figure I - Diagram of Sideslip Angle, jInduced by Turn
3
C4
LL.1
EE
u. E.
II III N N 1
(3ON dis-ai ini IN1IN 90
F __ _ __ _ __ _ __ _---- -- --------R__
i4ldiC
LI-LL v
U.U
To l -I
?..
0.L
I-
N 0
D30 NI 'A '31ONV dflS 301s iflhis iN3UVddV
LU
I
w4 U.
?-1
4.u
Om~ 4d
N ~ N N
030 NI '31E)NV dlISIUIS 1flu1s iN3UV&IV
6
For sideslip angles of',10 degrees and speeds of 50 kts, it is unlikely that conventionally
shaped surface piercing s'cruts will not become ventilated, with undesirable coisequences of
discontinuous side force. Aside from the problem of ventilation, the large sideslip angle-induced on the forward strut would tend to throw the boat out of the turn, or prevent it
from turning at all. It would be desirable to be able to control the amount of sideforce on
the forward strut as well as to ensure that the force was a well-behaved function of sideslip
anple.
On the HIGHPOINT (PCH-1), theproblem of turn-induced sideslip angle was solved by[steering the forward strut along the course tangent, or true heading at the strut. For HOC,
this may not be feasible because of structural limitations. Therefore it is 'ctessary to examine
alternative solutions. In this study, the following are considered:
1. Controllable flap
2. Air bleed
3. Spoilers
4. Fences
Each of these techniques are evaluated in terms of the following criteria:
1. effectiveness in reducing adverse side forces
2. suppression of ventilationor
smoothness of transistion betweenventilated and fully wetted state
3. drag or auxiliary power penalty
4. potential reliability
5. complexity of implementation
6. adverse or favorable associated effects
In order to resolve some of the unknowns encountered in the study, a rather extensive
experimental program was conducted, the results of which are incorporated herein.
7
FTIM
com'rROLLABLE FLAP
If aligning the entire strut to ihe flow is impractical, a possible alternative is to align a
portion of the strut with the Plow. This could be accomplished by a leading or trailing edge
flap. Generally, moving a flap does not change the force as greatly as moving the entire foil,
per degree of rotation. Figure 5 shows the average effectiveness of several trailing edge airfoil
flaps. 1 Effectivenes. is defined as Aao/A6 where a. is the angle of attack at zero lift and 8
is the flap deflection. In this text, when reference to airfoil data is made, the standard geo-
metric orientation of a wing in air will be assumed, rather than that of a vertical strut.
0.8
0.6
0.4 0<6< 100
0.2
, , I , , I , , , , , , I , , , IX 0 0 0.1 0.2 0.3 0.4 0.5 E
0.8 "
0.6 -
0.4I 0<6< 200
0.2
0 0.1 0.2 0.3 0.4 0.5 E (FLAP/CHORD RATIO)
Figure 5 - Flap Effectiveness vs Flap/Chord Ratio I
iAbbott, I.H., and A.E. von Doenhoff, "Thcor of Wing Sections," Dover Publications, Inc., New York (1959).
8
r WT
Thus, angle of attack is a rather than 3, and tile crossforce is lift rather than sideforce. Thedifference in the physics of the two situations is thereby emphasized. Experience with
flapped hydrofoil has not confirmed the effectiveness predicted by Figure 5. This may be
because the hydrofoil sections were not specifically designed for flap effectiveness. Cavitation
and the higher susceptibility of foils in water to roughness effects may also be significant.
Whether the forward strut sideforce could be reduced to near zero at sideslip angles of 10
degrees at 50 knots will depend upon the effect of cavitation and ventilation on a surface-piercing flap. Chances for success are enhanced since the flap will be working to reducerather than increase lift. Figure 6 shows the pressure distribution on a flapped symetric foil
at at. angle of attack. 2 Notice that the upper surface distribution has crossed over the lower
st face distribution to become slightly positive, and the converse has happened to the lower
surface distribution. Because a region of lower-than-atmospheric pressure is a prerequisite for
spontaneous ventilation inception.3 ventilation as it usually occurs on the low pressure face
of a surface-piercing strut could be prevented by use of a flap, and probably the loads could
be reduced to near zero or made somewhat negative. A more complete-examination of
pressure distribution on flapped-struts 2 reveals that for many conthinations of flap angle and
V- -t. P,-- Re - 35 106
R 3.'56xO-3-
-2
Cp-1 -
0-
+1 -o= 160 -200 20% c FLAP
Figure 6 - Pressure Distribution on Flapped Symetric Foil t
2Jacobs, E.N. and R.M. Pinkerton, "Pressure Distribution oieraSyS t'metrical.AtirjfilSectioni with Trailihg EdgeFlap." Langley Men:- rial Aeronautical Laboratory Report No. 360 (April 1930).
3Rothblum, R.S., D.A. Mayer. and G.M. Wilburm, "Veitilation. Crmitation, and Other Characteristics of High.Speed Surface.PierchigStnts," Naval Ship Research and Development Center Report 3023 (Oct 1072).
9
angle of attack, some sharp anomalies appear in the pressure distribution. This indicates the
possiblity of separation or ventilation at the hinge line. The details of construction of the
hinge line may also be important. since an abrupt break in the contour could provide an air
path.
If flap ventilation should prove to be a problem, it could be alleviated by the use of
fences as shown in Figure 7. If nose cavitation should trigger nose ventilation, nose fences as
zI
Figure 7 - Possible Use of Ventilation Fencesto Prevent Flap or Nose Ventilation
10
shown in the Figure may also be required. Previous experience4 ,5 with fences and fence-like
appendages indicated that the use of fences might not add appreciably, if at all, to the total
strut drag. Tlhe power consumption required to activate the flap depends on the control
system and the two-dimensional hinge moment coefficient
M hCh = 1I Vc
"2 flap
as a function of flap angle and 'lift coefficient. For symetric wing sections, the theoretical
hinge moment coefficient is
dCh dChC
where R and -j are given in Figure 8.1 (6 is in radians)
1.0_- dCh
d CM
_ch
0 0.2 0.4 0.6 0.8 1.0E
Figure 8 - Theoretical Hinge Moment and Pitching Momentof Plain Trailing Edge Flaps 1
A rough correction for aspect ratio can be applied by multiplying the theoretical moment
coefficient by the ratio of the empirically derived finite span sideforce coefficient slope to
the infinite span-stope. Figure 9 gives sideforce coefficient slopes for several experimental
cases of finite aspect ratio and a theoretical curve.3
4 Swales, P.D., R.C. McGregor, R.S. Rothblum, "The Influence of Fences on Strut and Fol Ventilatloa,:. " 10thONR Symposium, Boston (1974).
5 Layne, D.E., "Effects of External Stiffeners on the Ventilation. Force and Cavitation Characteristics of a Sur-face-Piercing Hydrofoil Strat," Naval Ship Research and Development Center Report SPD-621-01 (Apr 1975).
11
As an example, consider a strut with a 50% flap, and an aspect ratio of 1. From
Figure 9, dCs/dP -0.02. For a Cs - 0.2, P - 10 degrees. For a 50% flap/chord ratio,
Figure 5 indicates the flap efficiency is about 0.8. To generate or counteract a sideforce
coefficient of 0.2 would thus require a flap angle of about 13 degrees. The hinge momentcoefficient formula then gives
(hO dCh1 1 . 13 dhCh = ° 2 \' +5-7.3 d
d Ch d Ch,From Figure 8, for E = 50%, IdC£ -0.13 and d -0.36.
Then Ch1 -0.2x 0.13 0.36-x 13 0.1157.3
For a one foot chord strut at 50 kts,-M = V2c2flap px 0.11
-Mn = 190 ft lb/ft (860 N m/m)
0.11
0.10
0.08
d Cs(DEG-')
0.05-
0.01
0 '1.O 2.0 2.8
11AR
Figure 9 - Sideforce Coefficient Slope Versus Reciprocal of AspectRatio for Surface Piercing Struts Without Endplate
From Reference 3
12
For a one foot span
Mn = 190 ft lb - 200 ft lb (270 N m)
For a 15 foot (4.5 m) chord strut of AR = 1, since the moment varies as the cube of the ratio
of linear dimensions, -Mn = 656000 ft lbs (890 k N i m).
Assuming that 6 2 10 deg/s, the peak rate of work will be
27r rad 6.5 x 105 lb ft/sec
360 deg X 550 lb ft/sec
= 210 HP (150 kW)
The average power for a complete cycle (i.e. 6 = 0, + 130, 0, - 13, 0) would be just 1/4
the peak power, or about 50 HP, .,s can be seen from the geometry of Figure 10.
HP (kW)
+200-6 10 OEG/S(150 kW)
NO WORK
-130
+200 -
(150 kW)
Figure 10 - Power Requirement as a Functionof a Flap Angle, 6, for 6 = 10 deg/s
Several points in the foregoing calculations were unresolved with respect to the use of
flaps on surface-piercing struts. The flap effectiveness would be influenced by cavitation and
ventilation, for which there is no prediction method. The intersection between the strut and
flap may create anomalous characteristics that override the beneficial influence of the flap on
the pressure distribution.
Besides these unknowns, the effect of fences on these same factors cannot be predicted.
Because of this, an experiment was necessary to establish a rational basis for applying flaps
and fences to surface piercing struts. To this end, a model with flap was constructed and
tested with and without fences, in the Rotating Arm facility of the Center.
13
THE FLAP AND FENCE EXPERIMENT
The Model. A NACA 16-012 section strut with a one-foot chord (c = 305 mm) and just over
4 chords of uniform span was modified to allow the 50 percent trailing section to function
as a flap. The flap extended from the strut tip to a height of 3 chords. Figure I i shows the
model and experimental setup. The strut-flap hinge intersection was smoothed by gluing
0.010 inch (0.25 mm) spring brass to the strut sides, tangent to the section. Four removable
ventilation fences, articulated to turn with the flap, were built to be attached to the strut at
0.25 c intervals from the tip. To the tip was affixed an endplate, 1/8 inch (3 mm) thick with
beveled edges, parallel sided with half-breadth of 0.25 c, semi-circular leading and trailing
section.
Test Conditions. The strut was towed vertically, piercing the water surface to a depth of one
chord, from the six-component Aerojet Dynamometer, mounted at a radius of 120 c on the
Rotating Arm, at angular velocities ranging from 014 to 0.7 rad/s. Linear velocities ranged
from 10 to 50 kt. Flap angle, 8, was varied between -20 and 20 -degrees.
Sign Conventions. As viewed-from above, the Arm rotated clockwise; counterclockwise side-
slip angle, P3, was considered positive. Sideforce to port was positive. Flap angle which would
ordinarily be expected to increase sideforce was positive. T' at is, for positive 6, the trailing
edge of the flap would move to starboard.
Data Collection and Sources of Error. The lift and drag force, were digitized, analyzed, and
recorded by an automatic d.ta processing system, which also controlled sideslip-angle and an
underwater camera and stro,,.. light. The data collection system is shown schematically in
Figure 12. An analysis of t, accuracy of the dynamometer and sideslip angle transducer can
be found in Reference 3. Briefly, that analysis indicated that the forces were measured and
recorded with an error of less -than -1 or 2 percent, assuming the electronics were near-perfect
tor practical-purposes. The sideslip angle was measured independently by three methods which
agreed to within 1/3 degree, which is representative of the overall anguJar error range. The
principal -source of error arose from the imposition of unsteady forces which, at the lower
speeds, created a signal many times as great as the mean signal of interest, in-spite of the useof 10 liz low pass- filters.
The-best judgement of the effect of this factor is obtained by examining the scatter of
the points-plotted on the resulting graphs of force coefficients versus sideslip angle presented
here. Each point on the graphs represents 200 data points averaged over approximately 1/2
second for a particular value of sideslip angle.
14
NACA 16-012
r I 25cCOORDINATESIN INCHES Own)
BAS0.2C0 0I. 150 (3.811 .156(3*3
"' HI. (7.42) .211 (5.51)FLAPOVER0Am(15.24) . 0l (7.64)
1.209 (3045L .415 0.1.800 (45.721 .496 (12.10)
4.8W0(121.9) 1.0 1.15
6.000 (152.9) .720(18.2517.20U086.9 .700(1.7)
ENPAE0.5c FENCES (4) 9.6m 4 ~~i~
IIAW(290.111 :170(4-311
NOE ADUS- M6" (2lh)
ROTATING ARM
fYAOEE
II
Figure I I - Flopped Model with Fences, Mounting Arrangement,Section, Offsets, Photograph
TERMIAL CMPUTR 6.O CAERA
Figre 2-Dat Coletio ShemTic CEV
LIGH
Another factor affecting the reliability of the results was the technique of continuous
running used on the Rotating Arm. The water surface became very disturbed after a few
minutes of rotation. Nelka 7 found that this did not affect ventilation inception but did
influence cavity washout. Because of the exploratory nature of this test, it was felt that the
disturbed water surface would not be a serious detriment. In fact, it was undoubtedly more
representative of actual prototype conditions than a smooth towing tank. Unfortunately, it
did introduce a further undefined quan'cty.
Depth of submergence could be controlled only by raising and lowering the water level
in the Rotating Arm Basin. This was not very satisfactory, as the water level tended to drop
as much as an inch (25 mm) per day. An accurate estimate of the submergence during
operations was difficult to obtain because the lowered water surface rendered the wave
damping beaches ineffective. Thus, the disturbances created by the tests were very persistent.
Therefore, a variation of ±0.08 c in depth of submergence from the nominal one chord
submergence would not be surprising. The gross phenomena affecting the forces acting on
the strut - ventilation, cavitation and separation - would not be measurably affected by such
a small change in submergence. However, the mean values of the forces would be expected
to be approximately proportional to the submergence, and could therefore be ±8% of theirvalues at the proper submergence. The submergence would not change much from run-to-run,
making most comparisons between adjacent runs free from this factor.
RESULTS OF THE FLAP AND FENCE EXPERIMENT
Figures 13 to 22 show the sideforce and drag coefficients, Cs and CD, versus sideslip angle,
P, for various values of flap angle, 6, over the range of velocities tested. The force coefficients
are defined as follows:
Cx--Fx( 1 pV2ch)
where
Fx is force in the appropriate direction
p is density
V is linear velocity
c is chord length
h is submergence to strut tip frommean free surface
7Nelka, J J., "Effects of Mid.Cord Flaps on the Ventilation and Force Characteristics of a Surface.PiercingHtydrofoilStnt." Naval Ship Research and Development Center Report 4508 (Nov 1974).
17
] .. . I-
C A . - I III - - - ll -
4.6 05 1
1_ -
I.0 W 4 io I I&]
4.3 2 - - .t - - - -
S. o I45
0 D"GRE , A, 0 TS- ,1.8.26~- - - - - - 8
-- ---4
...... ... .. . 40vm , ..
- - - - - - .. ..
-l -i ii - - - --- - - - - - - - -
-
.(-- - - --- - - - - - - - -
- --- -
, - - - - - - - - - --. - - - - - -,.,-- - - - -
r,-- - - - -
- - - - - - - - 1 4 4 - --- - - - - - -
0,! 50
- - - - - -4 . .14
ti4
FIGURE 13b DRAG COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT, WITHOUT FENCES,0 DEGREES FLAP, 20, 30, 36, 40,46, S0 KTS.
r19
.. 0 35
2I, 4
,..g -- - - - -
,. :> "-.-., --
"edt -4 -I .l " . - - - -I - -0 l 1
-4.1. --- ---- - 6 . - l --
" -s I I I I-
'".1 -- '"I-wfix r-L-
. -".- -
Mll - - - - - -
t 40
IL.-t: - - -4 o t
-- ... .J'"..I-II - I
1 -- -- -Q 1 -8 * 1? 4 4 1 o 14 114
l.l:v 50e.g - - -
!tt t14 W -IQ .IL I A 6 I 12 1. 16
I,,l
FIGURE 14. SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT, WITHOUT FENCES,5 DEGREES FLAP. 10, 25, 30, 36,40,46, 50 KTS.
20
10 35
Al I-l rr001 -1 -12 -W -8 .- 4 - 2 I 0 11 12 - - -1 a -0 -6 - 6. s - o 2-
.14 -
iJ IIIii , - i Iiit
0.1- - -. ,.
"- 1 - -. 10 . t -2 "4 -
".4 -- t "" -
r-7- !- 0. * *-
130t~
.4 . " 1 I 4414 1 I
1. S i i! -LL 1,I1 0.0IY I I l:.! k ,i;i tH+ r i,[,, ... !, t .. .l ..
FIGURE .4b DRAG COEFFICIENT VS. SIDESLP ANGLE, FLAPPED STRUT, ,THOUT FENCES.5 DEGREES FLAP, 10, 25,X0,35,40,45, 50 KTS.
21
25 40
4.10 ~ -43-t - 0 - 2 4 10 J 4 11 4
300 -0 465, --
o 4 0 -O A a t,,
": 3:
-4.14
l.I °4 -2 *2 *O 4 .6 o 4 2 4 £6O16 11414 | *O° -Ia-214 -1 -4 - 4 - 4 2 4 £ i16| 12 14 2£
,. -- -4-.I I I I I i i T l
4.2 ii - - - -
* I ".,_ 4- - - - - - - - -t l
7A DEGREES Z.22 254 30 3 46, 222424
22
25 4%
lII
0.14 41
III
C41 II 0I 1 I ---
S.1 1. -1 1,
,.,, edt - --"-/
' - -12 -2 , 12 14 1 m I- -1 -I -- - - I I 1 14 1
FIGUR 15b DRA COFIIN VS SIESI ANLE FLPETU. WIHU FNE,7l-4.~I %e DEGREE FLAP 25 30, 5612,1451
2I3
:0:14 -. - -- *-- - - - - - - - -
0.i•[ I.I1 ! 1 -! (-- -- I
liii-
24,.2 2 0i4-?i i i6 2 2
7I, I DEREE FAP,25 3 ,' 6, 40,46KTS.
O''', I, - ' "l "6 ,, " { l 0 2 3 1 '~ f *1 "2 9 I *; 4 " i 2 l (
10 35~
Pt
'"i I I!Lo I ,.,-1 1
141 10 1- -4 -1 -1 -2-0 . 4 . a1 - -9
-0.0 - -
2, 1 40-02 -- -1 -4
I to 2 . 14. ..-
.oA . ,.JI/ L .#1 ,;4 -.- --t -f ii - - V ' l i 4 1 -- S .20 I-o .e + 4 * ,1 ± -• q e 'z
*.20~ . L vl.. ... - -
, , i
___. ...__._-____t j ,...k..,-,.
.D * ! !"' " . ~ - 0
- -~l 4 -- - 20-22t24 20
I TI
-44~~~.44 & * A M
FIGURE 6. SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE. FLAPPED STRUT, WITHOUT FENCES-10 DEGREES FLAP. 10, 25,30, 35,40 KTS.
24
0.0 -G - -- - -
0.14 -
0.20 -
q.2 Ii I
FU1b A& COFIIN VS xIEU NLFAPDSRT IHU ECS
0-10 DEG_ EES A 1 , a, is .
25 1 5 40
0.1o010:
1i
.14 •1-1 -.
.4 :1'
!1 DERE FUP 10 53,3,0KS
"" ii L 2-
IMPT.
20 -IT- - - --
4.-". rl- " -' --
Al I A I A -I
Z-1 14 .12.161 14 II
,! . . ! , , - . . . . . . . . . . . .
• ___ i r1 '" iI.. ~ I I
.2 -1 -1. -it -9 .4 22 22 oI Z*. *4-2 .4 -6 10 12 1. 1"A
SW-'- - .1 14 -1 - . to 12 14 16 -
45 1 1 I1
•- " -2 - - Z 4 1 12
1.I D R IA 2, ,0
26-i-I-I-
---
""" t I ; i II
FIGURE 17. SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT. WITHOUT FENCES,15 DEGREES FLAP, 20, 25,30, 35,40, 46 KTS.
26
"r --t -,.. - - . -"" - - -
20 -- 3
-I-IA
- -~ ' i ~.-f 1 .14 ' 12i i V . .si
I.
cs_4__::.
-I Z - 4 . 1 - 1 . l .- 1 , 4 9 ' I 4 6 6 1 1 1 2 1 4 1
I GUE1bDA OFIN SIES I NL, ,LPE TUWIHU ECS301 5EGESFA,0,2,0,3,0 45[TS
0.27
A-~l I, fi N)
to 1 -,2d A I s 1 t4 4 0 1 4 1
FIGURE 17b) DRAG COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT, WITHOUT FENCES.
15 DEGREES FLAP, 20, 25, 30, 35, 40, 46 KTS.
27
i'l
r
lo~ l 35 1 6~
- .or10
.A[.i I -; - -I.^
_T r I I I I
25 4046621 k .~s..-.
- ,U-- --- -
f 0 to I ! . - - -" " .z2
I~ ~ Ale,(i
.1 'S ..-e. -e-
0 D F 1 - .0 4. -8 -
K I 2
- - 35
- - -- - - I
- - - - --- ts - -T
1.1 -1 -1 -1 -1-. 4: 1
etc -1 -1 .1 @ o t64
0.11
I - -- - -- -
A I .
75 -, -- *61--1.-
6.92 ,
FIUE 0 DRA COI CIN SI DSI AN .LE -LPE ST U ,WT OU E CS.1 1 20 DEGEE FLP 10, ~ li 25, 30, 3- 40 -- .. -
4.2t29
[ ..,. - 35
a.9- 40-
26. 6.U
.,,,. .\.
".4i -I -?-I - e ..... =- "- - -1 - -i -l Z - i4 - . - - t - l .4.. -4 ~ -z 6I 2 1 2 z14 14
0.-1 1 1 1 J I I I
6.,I I
-19 -14- -l-2 le la 1- -Fl
14-1 -1 le .1 - 2 a 4 s I. 22 7 if~
_____..- -i -
,,11 I -j
"- -- 1-I4-- 4-1=:-2- ,.4,,4,14- 41 44 l46 III11I2I42
OI . , F T H 11 !-"L 1, 2 3 , , 0 li i-
S. |I -I - - g30 -,--- • -
-IU6.2SOFO6 OFIIN V.SDSI NGE LPE TUT IHFNP;
FIUR 9.SDEFGRE E FICIEN VS. 2 IDESLIP 3NGLE4 , FLPPD0TRTKWTHS.CE,
30
10 3
41.400J : : : ; ; 1
9.1 4.
. - - - : : . - ag - -1 - " . Z
4.1I.
0.12 -
0,14 - *01OF A
.1. .9 4 -10606 1644 1j11 1.12
14 4 - 4 9 2 A I g14 1 14 -14 60 -I0 -11 -4 - 9 p a 4 a is 1- 1-
- - l - - I.- --0.e. , ,,.W . ,-
,,,M .= _____... _ 1 L 1LII! iI"I tIL h t7 ..iiii I -
FIGURE 19b DRAG COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT, WITH FENCES,0 DEGREES FLAP, 10, 2, 30,35,40,46, 50 KTS.
,', f i l ' + I I ,,, i I i I I I . i I I 31
lo. 35. -
.4.11LT4 -
. 14 .1 A01A
I I Z =
-ON- --' T
- -, - F- 1 T 1T -• I
ax=-
,.I '"' II-"-1 I.,I- - - - -
4M-. 14 -1 Ae -0 - -4 -I 1 4 I
4,.I I - - - I .- --
-.-I- S,+ I
to. 4Z v A It It 4o 1 4 1
" 0 AI I I I ..
Ii -
."" 1±1H I I I- Ii le -I - .1. , i ,I10i .ERESIFI1 3 0 7 4 0 I
.,.111F 11111> .,32
.. 4 -iLv LWIL 111. ; -I .,II IIIIIIIII IIIIl
FIGURE 20. SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT, WITH FENCES,-10 DEGREES FLAP, 10. 25, 30, 36, 40, 46, 50 KTS.
.32
2053
0.0'' 4" 0
0 .2 2 1.2 -I - -I
11,45
0.20 -- - mI
ii
0.16 - - - -
-.. !1. " - 1 -, . 0 - o 1 1 1
.. 2. . 0.4.. . . . 4: 4 023221 ,oF24.22 |044410 0 22
'-- 4 I I I I i l I
0. L.,. I ! I ! ! I I " ' I I. l. I I 50 1
..4, 4 ".E ! ,1 f: i t ! .4,0 e 121
. ,,c . 4 -4 0 0 I 2 4
, - - - -., __= _- t l! ! 1- . I ,
FIGURE 20 RGCECET VS. SIDSLI ANLE FLAPE SMUWTHFENES
-10o DEGEE FLP 102 , o 30, 36,4, 4,50KTS
. ,- - .. .. I -r-i-- I~ 1 L L.,.ri '1 ., . $.24 * 0 224 2-*DO-I-I I I
24 4" ~ J ,, 4 0 2I 27 1 2 4 I ' II ' 4 ,11 2 ! I I I 1
FIGURE 201b DRAG COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED SRUT, WITH FENCES,-10 DEGREES FLAP, 10, 25, 30, 36, 40, 45, 50 KTS.
33
I IO I I I I II. II
I" .IS. .o. " "~ -
25..-
1 - .V. -1 -- "" r ,o z -
. I. 4 ! 451.,.....
.., .*. 0i l 4,0 1 4 130.
'1.19 .-
... '! !: _ _
-I .9S6 '.' 9v * -4 1 1 t 1 -* I 4 " 14 -12 .,A -, -_ p ' I 14 1.
FIGURE 21a SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT, WITH FENCES,10 DEGREES FLAP, 10, 25,30, 36,40,46, 50 KTS.
34
l., I I 5
Swi -1 2 4 1 le 2 1 1
1.1A- -01 w
' " ' T - ' l l -
Ii j~ so
! ell,
a 1 1 # ,1 - , 1 I 4 I 1 2 I4 Id
KI -t -to-t-I-
Th EcItI I - i
,,.---
.... ,L- . '.".S A I4 ~ :
' l , - , , , , : . i i i i i i
- * .... P1 I
FIGURE 21b DRAG COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT, WITH FENCES,10 DEGREES FLAP, 10, 25, 30, 35, 40, 45, 50 KTS.
35
I..000.-- .., - -
L H+H
.I "0 -4 -41 0 ' 4 4 0 If I1 14 I9 - ,.I2-l 0 -g . 0 o 6 S 14 it
KL - -1- f~1~ '*..o - - -
II I - ,.0 I. --
_1, V10 -9 "9 , ,- I t i__ 1
,. i LiIIIII IL-t 102 -0 4 04 0 to 12 2
-'A , 11 - , -4 .1 v. 44z A t0 to 12 1. 9 6 -1 -1.' -1 . 1 -A 1 ~ - V 1 4 1
-2 ERESA, 10 253,5,04, 0K
SI ,II~3iII6III,
- - - --- - .. 0_
-, - l .-; 4 4 -,1 . • Z O t I ,-I - ,- ,i- - - i. r r- ,,HI - -H - I 4
.'-G.,, 2.- SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT, WITH FENCES,-20 DEGREES FLAP, 10, 25, 30, 36,40, 46, 50 KTS.
36
C o 35i l , 1 I
"--.v .l .. i-
10
... P' I kM A Ll -
0 - L: : "'- w it - --
0 .14 | I ;
- : : :gL .1 .... MilkU."-.-j T
.,14 12 -10 -4 -6 - -2 4 O 1o 12 14 14 408.14 f .L
a*0 49.1 324
2 -Z - -- i a 1I .. ..
'.34 ' -J. .i. ...94 ,- -
o
4 3I - 4 O 12 3 14 04- - .0 , 4 e 14
FIGURE 22b DRAG COEFFICIENT VS. SIDESLIP ANGLE, FLAPPED STRUT, WITH FENCES,.20 DEGREES FLAP, 10, 25, 30, 36, 40, 46, 50 KTS.
37
In Figure 13, for 8 0, the slope of the sideforce coefficient, dCs/d3, for the lower
velocities is dCs/d3 -" 0.2. This is lower than Nelka's value of 0.25 to 0.29 for the same
strut in the same test facility. The only major discrepancy between the two tests was the
flap modification which allowed an air path down the hinge line. Photographs of the sub-
merged strut underway confirmed that partial veatilated cavities fed by the hinge slot were
occurring.
At the higher speeds, the sideforce coefficients were abruptly cut off, rather than
decreased. This was also due to premature ventilation, undoubtedly caused by the hinge slot.
The hysteresis loops were caused by the persistence of partial or fully vented cavities to lower
sideslip angles than the inception angles. Usually, abrupt changes in forces indicate a change
from one flow state to another, such as, flap wetted to flap vented, strut wetted to strut
vented, and combinations of these states.
Figure 14-shows the effect of a small flap angle, 5 = 5 degrees. Note that for 10 and
25 knots, there is evidence that the flap was effective near 13 = 0 where the sideforce curve is
raised. However, the flap quickly became vented with increasing 13 as shown by the sudden
decrease of the sideforce cu Ye to its zero flap value. At higher speeds, the flap had a
negative effect, decreasing the entire Cs vs P curve to predominantly negative values. This
asymmetry was due to the flap being completely within the ventilated cavity when the entire
strut was ventilated on the starboard side.
The same trends can be seen in Figures 15, 16, and 17. In Figure 17, for IS = 1 degrees,
the hysteresis had become more pronounced, but for some reason the asymmetric effect was
not so notable at high speed. The highest speeds were not tested because of spray problems
associated with the larger flap angles.
For i = 20 degrees, shown in Figure 18, significant change had occurred. Although
there was some hysteresis and uncertainty of flow states, the flap still had an effect on the
lift curve at 40kts, the highest speed tested in that series. The photographs of these runs
reveal that the "spike" in the 25 kt coefficient curve was caused by the momentary washout
of the flap cavity. Evidently, at higher flap angles, the flap was always ventilated, which
reduced the possible number of flow states and therefore lessened the hysteresis.
In Figures 19 - 22 are shown the results of re-testing certain values of flap angle with
ventilation fences added to the strut.
Figure 19, for 8 = 0, is about the same as Figure 13, for the saute flap angle without
fences. The sideforce coefficient slope was virtually unchanged at all velocities tested.
Figures 20 and 21 show the results of a test to determine whether the experiment was
symmetric with respect to positive and negative flap angles, considering the curved path of the
38
towing carriage. The flap angle was tested at - 10 and 10 degrees. Except for some variation
in the hysteresis loops, the results were symmetric. Comparison with the unfenced strutresults for the same flap angle, Figure 15, reveals only insignificant differences.
Generally, the behavior of the strut with flap probably would be unsatisfactory forprototype application for the cases examined thus far, especially for 8 AQ 15 degrees, because
of the erratic jumping form one flow state to another as reflected by the force coefficients.However, for 6 = -20 degrees, with fences, the results are promising as demonstrated by
Figure 22. Except at 10 kts, there was almost no hysteresis. The flap was consistently about20 percent effective, (as defined previously) and the sideforce versus sideslip angle curve is
smooth, at least to the maximum values of 113 tested. Unfortunately, the values of 113 I had
to be restricted due to spray problems, wnich were bad enough with the large flap angle andworse with the fences. In this case, as in the unfenced case with 6 = 20 degrees, the flap was
probably fully ventilated under all conditions of velocity and sideslip angle. Because this
limited the number of possible flow .sates, the erratic behavior associated with smaller flap
angles was eliminated.
No doubt the same would have been true of larger flap angles, although none weretested. The implication for craft control is that a "Bang! Bang!" approach would have to be
used with surface-piercing flaps, with flap angles less than 20 degrees or so not permitted.
Above 20 degrees, proportional control would again become possible. Although no flap
angles between 15 and 20 degrees were tested, the momentary washout of the flap vent inthe unfenced case, 6 = 20 degrees, (Figure 18) indicates that 20 degrees is probably close to
a lower bound for proportional control.
The effect of flaps and fences on drag can be seen by comparing the drag coefficient
presented in Figures 13, 18, 19 and 22. The zero sideforce drag coefficient for no flap angleand no fences (Figure 13b) ranged from 0.02 to 0.025, depending on velocity. With fences,
the drag coefficient increased to 0.03 or slightly less. Therefore, the addition of fences alone
caused a drag increase of 50 to 100 percent.
For a flap angle of 20 degrees and no fences (Figure 18b), and ignoring anomalous 10and 35 kt cases, the zero sideforce drag coefficient ranged from 0.02 to 0.025. Thus flap
angle alone did not significantly increase the zero sideforce drag.
However, when flap angle was applied with fences (Figure 22b), the zero sideforce drag
increased to just below 0.04, an increase of 50 to 100 percent. Thus the drag increase due to
flap angle depended upon whether or not fences were present.
To summarize, flap angle caused a relatively slight increase in zero sideforce drag. Fences
created somewhat more, and the combination of fences and flap angle caused the greatest
increase - about double the baseline case.
39
It is unfortunate that the baseline , was somewhat dubious. Dailey et al8 found that
the drag coefficient for the NACA 16-012 strtit wiffiout endplate for the same submergence
aspect ratio was only 0.01, and for aspect ratio 2 and 3 was 0.005 or less. Even adding end-
plate drag to the Dailey et al results would not be sufficient to explain the higher drag in the
present tests. The explanation must therefore be that the drag increase was induced by the
air flow from the flap hinge intersection.
CONCLUSIONS OF THE FLAP AND FENCE EXPERIMENT
a Flap and fence combinations were effective in changing sideforce reliably only for flap
angles of 20 degrees, and in tile presence of ventilation fences.
0 Flap effectiveness, defined as the ratio of flap angle to sideslip angle at zero sideforce, was
much less than predicted by airfoil data.
* Unless air is prevented from feeding down the flap hinge intersection, there will be a drag
penalty associated with flaps even at zero flap angle.
II
8Dailey, N.L., M.F. Jeffers, R.S. Rothblum , "Ventilation and Force Characteristics of the NA CA 16.012Surface-PiercingStrut in Cavitahing Flow," Naval Ship Research and Development Center Ship PerformanceDepartment Report 479-11-03 (Aug 1972).
40
IL o l ' |:°u .,' '" ' - "'; "
AIRBLEED
Baron Hanns von Schertel9 ,10 was the first to apply the technique of deliberate intro-
duction of air in controlled quantities to the otherwise fully wetted flow around a hydrofoil
in order to influence the hydrodynamic forces acting on it. Other investigators have alsoexamined the process, notably Lang, Daybeli and Smith,1 I who published what is probablythe most extensive information correlating the forces generated by air injection with the
chordwise location of the supply holes and the air flow rate.
The airbleed literature indicates that it is possible to change the lift coefficient on a
hydrofoil by quite large values, of the order of 0.6.
There are some potential disadvantages to the use of an airbleed system to compensate
for turn-induced sideslip angles on surface piercing hydrofoil struts. Generally, there is a drag
penalty, although Lang et al found that the lift:drag ratio did not change with air injection.
There is also a hysteresis effect associated even with fully submerged, two-dimensional hydro-
foils, whereby once airbleed is increased, a subsequent decrease in air flowrate does not cause
the forces to return to their former strengths. This hysteresis effect would be expected to be
even more pro:ounced in the case of a surface piercing strut. where it could become ventila-
ted to the atmosphere. Possibly to prevent this, Von Schertel's hydrofoils have fences on
their surface-piercing elements. 12 There is also the possibility of large unsteady forces due to
the collapse and regeneration of partial cavities, as observed by Lang et al. A final possible
disadvantage of an airbleed system is the power, if any, required to drive the air. and the
ducting and controls to direct the proper amount of air to the desired location. This lotential
disadvantage must, of course, be weighed against the disadvantages of alternative measures for
accomplishing the same result.
In order to more clearly define the problems involved in an airbleed system for a surface-
piercing strut, and to clarify the ambiguities arising from the surface-piercing factor, the
experiment in the Center's Rotating Arm facility concerning the flapped strut described
previously was extended to include a test of an airbleed strut.
9Von Schertel, lanns, "Comparative Tests Between an A ir Stabilizer and a Cotventional Supraniar PTSO,"
Supramar, Ltd (1967).0 Von Schertel, Hanns, "lExperimental Investigation ofA iir.".ed IlHdroirdls." Supramar, Ltd (Aug 19641).! Lang, T.G., D.A. Daybell, and K.E. Smith. "Wlater.Tunnel Tests of Ilhdrofoils with bForced Ventilation."
NAVORD Report NOTS TP 2363 (Nov 1959).12Von Schertel, Hlanns, "Hydrofoil Boats as a New Means of Transportation. "paper presented tn New York
Metropolitan Section of SNAME, (30 Oct 1958).
41
ESTIMATE OF REQUIRED AIR FLOW RATE
Lang et al reported that for airbleed on hydrofoils, there is a certain airflow rate above
which the forces are further affected only negligibly. This was called the critical volume flow
rate, QCR, and was characterized by the formation of a stable, aerated cavity which enclosed
the entire side of the foil over which the air was being ejected, from the ejection point to
somewhat beyond the trailing edge. Lang et al presented an empirical formula for QCR,
which encompassed their data. Referring to Figure 23 for definition of geometric terms,
?Q "" 0.09- 0.05 a
QCR
where Q u-R -U t' b'
where U, was the upstream water tunnel velocity, andyp + (c - a) tan o:, t' > 0,
and b' was the measured gas-covered span.
ry
f a
Figure 23 - Nomenclature for Lang. Daybell and Smith Formula
The maximum Q R for their experiment was about 0.1.For an aslpect rotio I strut- such as tkie NACA 16-012 section strut used in the flap
experiment, assuriing that natural ventilation would occur at about 8 degrees of sideslip
angie, .8 then correcting the geometric angle of 8 degrees by the ratio of measured sideforce
at subcavitating speed to ideal two dimensional, 3 ,7 ,8 the critical air flow rate required at 50
kts was predicteI to be about 28 ft3/min (13 x 10-3 m3/s). In actual fact, it would beitinpdsing if tiis airfic v rate were required to trigger full ventilation for a strut on the verge
of natural ventilation. However, this conservative figure was used to select the air supply forthe airbleed experiment.
42
THE AIRBLEED AND FENCE EXPERIMENT
The Model. A strut was chnsen nearly identical to the one used in the flap experiment, except
that the section was somewhat thicker at the nose. Figure 24 shows the model auu gives the
offsets. Air could be supplied from a common manifold to any one or combination of 5
vertical rows of 1/32 inch (8 mm) diameter holes, each spaced 1/8 inch apart (16 mm) andextending vertically from the strut tip for one and one-half chord. The rows were located at
5, 10, 25, 50 and 75 percent of chord aft of the leading edge, on the port side of the strut.
A sixth row of holes was added on the starboard side at the 5 percent chord location after
the initial tests of this model. Four removable ventilation fences were built to be attached to
the strut at 0.25 c inte. vals from the tip. An endplate similar to the one used for the flapped
model was affixed to the tip.
Air Supply. Air was supplied from a compressor continuously charging an accumulator. Thecoupling to the strut was vertical, through the strut and dynamometer axis, using a rotating
coupling and flexible hose to ensure that the air pressure did not affect the measurement ofhydrodynamic forces. Zero velocity runs verified-this.
Test Conditions. The strut was towed as before, vertically, piercing the water surface to a
depth of one chord, at a radius of 120 c on the Rotating Arm. Angular velocities ranged
from 0.14 to 0.7 rad/s, corresponding to linear velocities of 10 to 50 kts. Airflow rate was
varied between 10 and 35-ft3 /min (4.7 x 10- 3 and 16.5 x 10- 3 m3/s), corrected to standard
(dry air) conditions of 20 degrees Celcius and 101 kPa (standard atmosphere). Bursts of airas high as 100 SCFM were also included in the tests. Air was supplied through each row ofholes separately, 3xcept for the port side 0.75 c holes, which were not tested individually, and
the starboard side 0.05 c holes, which could not be controlled independently of the port
0.05 c-holes. All-port side-holes -were -fed-simultaneously, and all port and starboard holes
were simultaneously supplied. Sideslip angles were varied between ± 15 degrees.
Data Collection. Airflow was monitored using a National Bureau of Standards calibratedventuri throat instrumented with a differential and an absolute pressure gpge, and a platinum
wire thermometer. The computer continuously performed- the calculation of airflow rate,
assuming adiabatic expansion, and recorded this information with the force, sideslip angle and
velocity data.
Otherwise, the data collection system was identical to that described for the flapped
strut experiment.
43
COORDINATESIN INCHES (mm)
00j " .... Y
0 0
.030 (76) .140(3.56)
.060(1.52) .191 (4.85)
.090 28) .227 (576)_ _.1201(3.04) .255(6.47)
I.180(4.57) .299(7.59)II.240 (6.09) .332 (8.43)
.300 (7.62) .359(9.11)S 1 1 1 II .360(9,14) .381 (9.67)
I. .480 (12.19) .416 (10.56)II III.600 (15.24) .443 (11.25)
("I.720 (18.28) .464 (11.78).840 (21.33) .482 (12.24)
Io ,II.960(24.38) .4 112.59)I I- 1.060 (27.43) .508 (12.90)
1.200 (30.98) .519(13.10)ow 1.320 (33.52) .529 (13.43)
I I II I1.440 (36.54) .537 (13.63)I I, II1.560 (39.62) .545(13.4)
I I 1.o (45.72) .559-(14.19)1 .920 (48.76) .,55114.35)2,100I 1 _53.4) .574 (14.57)
""II HI2.400 (60.96) .589 (19.96)I II I I 2.700 (68.58) .603 (15.31)
Ir I I I II 3.000(76.20) 618 (15.69)3.300 (83.82) .632 (16.05)I 3.600(91.44) .9i (16.40)
III III I I 3.900-(99.06) .660 (16.76)i,)r'oA~tls4.200 (106.58) .6730(7.9g)
S .4.500114.7) .68617.42)\ ,,, ,4.800(121.92) .697(17.70)
0 5.100(129.54) .706 (17.93)5.400 (137.16) .714(18.13)
-. .... 5.709) (144.78) .718(18 23)6.000 (152.40) .720 (18.28)
- AO... 1CIRCULARk om~on,; .. ARC,= 2.000 25.36 INCH
-- (644mnm)RADIUS
NOSE RADIUS - .392 (9.95mm)
Figure 24 - Airbleed Model with Fences
44
RESULTS AND DISCUSSION OF THE AIRBLEED
AND FENCE EXPERIMENT
Figures 25 through 50 show the sideforce and drag coefficients, as previously defined,
versus sideslip angle over the range of velocities, hole locations and airflow rates tested.
Figure 25 shows the results of testing the airbleed strut with tile main feed holes for each
row plugged by the insertion of snug-fitting metal rods. This was the technique used to block
-rows of holes so that airbleed from individual rows could be tested separately.
Because this was not a positive method of' sealing air from the ejection holes, some air
still leaked into the flow around the strut. This is probably why dCs/do decreased from
0.021/degree to 0.017/deg when velocity was increased from 10 to 25 and 30 kts, as shown
in Figure 25.
There was no previously published force coefficients for the airbleed strut section with
endplate. The 10 kt values of Cs and dCs/do are in very close agreement with the results of
Rothblum, et al, 3 for a similar test of the same method, but without endplate. Correcting for
the endplate effects by adding the half-breadth of the endplate to the depth of the airbleed
strut, (for purpose of calculating aspect ratio) and extrapolating between aspect ratio 2.0 and
1.0 in Reference 3, the expected value of dCs/dP was 0.023/degree. Compared with the
measured value at 10 kts, dCs/dg = 0.021/degree, this was about 8 percent too low.
The ventilation inception angles for the airbleed strut with plugged holes were between
8 and 9 degrees at 45 kts and 5 and 6 degrees at 50 kts. lower then 9 1/2 degrees at 45 kts
and 8 degrees at 50 kts as given in Reference 3. While this is not a very significant difference,
it supports the contention that the results for the plugged airbleed model may have been
affected by some air injection.
The drag coefficient at zero sideslip angle for the plugged airbleed strut was about 0.02
for the 25 and 30 kt runs. The 10 kt runs are not considered reliable for drag measurements
because of the small magnitud." of the forces at low speeds. There was also a substantial
unsteady signal from the drag force transducer at low speeds which may have been due to
towing accelerations - the mass of the strut and "floating frame" of the dynamometer was
approximately a tonne, compared to measured forces of the order of a few pounds (30 to 40
newtons).
According to ltoerner, 13 the drag of an endplate can be estimated by the formula
CD (endplate) = 0.008 (AEIA) +
0.004/AR
13lloemer, S.F., "hdd.Dyi'nanmie Drag," published by author (1965).
45
10 -.- - - -- - -- ~~5.
- -- -- -- - - -- - - - - - - - - - - -
- - -- - - - - - -- - - - - - - - - -
------ - - - -
-II I 10 .1 4 1 -, ,J' - - - - - - - - - -
POO ;-ON .1
.1 -.6 -O.u -9.30
Ii- 0.- - - *61
46
.10 1 -- --
h1- T
0.U-+L--
1'12l 0 64 ? 4 01$ 12 114 I
-I
25 -I -r1
,4 -- - - -- - -
- .,6- -8f If- 414 -1 .0 .4 S2 4211017 _J_ I I i1
'1 *-1 1K 4
0.0l - 4 T
30l; #"6
11+i4
50
*'' i\ "j.. --
6.19
1 1 2-4 -4 A 4 1i1214 It -14 0- 4-2 82 4.10i8 2214
FIGURE 25b DRAG COEFFICIENT VS. SIDESLIF ANGLE, AIRBLEED STRUT, OFF, PLUGGED,WITHOUT FENCES, 10,25, 30,40, 50 KTS.
47
10 3
- o- -- w6
-. 0 -1 8 .g . s a t - 2 1- 6 !1 - . 1 12. " . 4 . a6 Il 1- 6-" !I " -i-H
..- : I 11: - --- * --- LL I t.II i -
4j 62 4 6 0 233 . 2 . 1 2 . 3 .- 8.4- 7 A 0 1* i14 6
,.5 !. 8 rQ . - I o- I- l e I I
-.4 -1 .0 -4 .4 .1 A-0 I 4 1
.., I, ,L I "" I
50. _' -8 60 I6" t 4 -eN - 4 -4- 2 A 4 1 I I 1 14 ; "14 - l -:e - l "4 . 4 4 f 0 to 12 14 -
FIUE2m0.FRECEFIIN S IELPAGE A3(LE STUT 36 4.31 1 1. X~ 1 - /2
_ JEL -.......6 .W~ .... I I-. -- --
4.48
-,.- ....,L hILL -
.34, .,, .,.., .-8 -. 2. ,2 , 8, , ,, 43 ,, ,. ,,. ; .-- j
IWL"-- -! I -kill i'"V ,tUEK EL 4...' '' " " ' -"".. i i --I _ ._ _____ IL ," ,T
.38 - .8~ _!_ .. i--- - - - t1+ 1 @ " I -1 I 1 I8..I37 I 8 14 2t| I " *A 4 88 It 2 i * 34
FIGURE 26. SII)EFORCE COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 36 SCFM (16.5 X 10"smn3/-),WITHOUT FENCES, ALL HOLES, PORT SIDE, 10, 25, 30, 36, 40, 46, 50 K? S.
48
-1 4 -1.- -6 1 8 A t - i
r I .-I-- --'
S6 - A -I -.0 -0 -4 -6 0
"7<;-i-i
Ii-M.I2.IO - * *- -1 . , t4 6I 14 1i
6 -1 JA- FZ10 t 2 1 t A .. A 9 I 4 1
II2 . iIIli
FIGURE 26b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 35 SCFM (16.5 X 10"3m3/S),WITHOUT FENCES, ALL HOLES, PORT SIDE, 10, 25, 30, 35, 40, 46, 50 KTS.
49
""21 - --
L16, .- - Z - 1- !__
OCIO
- .
- -- -
"e' el¢= =:ij,. --- -' e
-9 I 4 - 4,I .429,-l - - 4. ". - .
"'-! f ! .l..... .. .2 ,., --- - i - - - -1 : i ' : - - - - , - " -: - : - : -- j
4-4-2 9? 1929 2141
-' -I, -I - - "i i
IO
30ii
" I A I
.e. 4-. - 4--- A
FIGURE 27a SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 20 SCFM (9A X 103 m3 is),WITHOUT FENCES, ALL HOLES, PORT SIDE ONLY, 10, 25, 30, 35, 40, 45, 50 KTS.
so
.k I
[ 4 f1 - -s 1 . i !6 t 2-- - . 0 21
45'
W I *OUT . L R S , 354 5 0 .
6.2 _________________
* I
5
1H1 . .4 .1 1 .
-- fi
*. I.-----+- I~~ "i r
____________ -4 -1 -f
• . . .4.,.
__ I__ _ LI,
..... i~ i~1 . .
.44.
II
WITHOU FECS AL MOES MAT SIE 10 25 3D'-, 35'-" 4,5 , 50- TS,
_ I _ _5
*"~ .. . . . .I !I I [-' -
FIGU.RE 28. SIDEF-ORCE COEFFICIENT VS. SIDESLIP ANGLE. AIFRBLEEO STRUT, ATMOSPHERIC,WIIHOUT FENCES. ALL HOLES, PORT SIDE. 10, 25. 30, 35, 40, 45. 50 KTS.
52
II0.16 4tl I III
0.14 { 014 -
e *e r-- eu -
fit'4 '4 A
FIUR 28 DRA COFIIN VS IELPAGE IBL TUAMSHRC
e It- -, - -.
. ........ ~t I1 ... -~l
...32 __ iI I -" ' . !
WITHOUT FENCES, ALL HOLES, PORT SIDE, 10, 25, 30, 35, 40, 45, 50 KTS.
53
** 0 ; 35
W - -,- i1" i _ _____
I ___
"a t foot-~ll l
_"_iii i~ Lii[ Ili..... ' 1 L L .. !. L I
0 ' t O ( 0 Z 4 (P o Idi t l[14 1
WITH- FE C S AL HO ES POR SIDE 10 250 , 350, 4 , 50 K T S
5
________________ ~ t.. - .... ; . . .. .__ "_-__ - ' ______
: !
'" . . . .- - T 2 ) IT T " = ( ___ ___"
* ,* ( :
.FIGURE 29 SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, AIROLEED STRU: 35 SCFM (16.5 X 10 3ms).
WITH FENCES, ALL HOLES, PORT SIE, 10, 25 30, 35, 40, 45, 50 KTS.
54
t
'35-
1 .14 If
-"- "--- .-
I11 -- 1,- - 'w j--25 2 I I-- -- I I I
.24'II+ .4at- l 1* 4 6. 2 Ia 4 £ | 12 1 6 €2-4 12-22 -I -.4-4 * 42 4 442 222 2l I 4I
*1 1 - -- ..".02 2 .. I I 1 1 44
1,14
2414 -01 -0 - .4 - 4 4 0 2 2 4 2 a to 1 1-
FIGURE 29b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 35 SCFM (16.5 X 10-3m 3/s),WITH FENCES, ALL HOLES, PORT SIDE, 10, 25,30,35,40, 46, 50 KTS.
s5
[4
:.r iiiE " :.:t,,O,-. -0 F - 35i
I. I L
:::, i:i, -""i'L+KLiiL iF'-1 .1 a 2 0 .4 i 1 1- i -.. 8 t I1
oil~
45
"- - -I .'01--- -'
t_ _ 'a____ 1 t to_ 12 J4E300
I 5
Cal -- - - - ---
Fa 1
I I FI LI
S -- -- - j ..... . .. .
- . -- -- - - - - - - - - 8.1 --. - - -
f.21 .1 1 -
- -
-- - - - - -I
-1- ,-, -- - - - - -~ I.I- -
w J
0 16 '14 12.88 - 4-4 -2 82 4 1818 12 4 1$ :.$." - - * 1-14 -12 -.l .1.4- 8 2 4 & 91i 12 14 16
0.:-- - Ii I- - 11 - - - - - -.-
I.11 - - - .10 4 -- -
- - -- - - - - 18 - - - - - - - - - - - -
1.8-- - - - -. - - - - - - -4
8.9 1400 .-- - --
Is 824 41 .21 121 4 t 2 4
0.12
5
4.12
L5
+t
FIGURE 30b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 20 SCFM (9.4 X 10-3n Is),WITH FENCES, ALL HOLES, PORT SIDE ONLY, 10, 25, 30, 35, 40,45, 50 KTS.
57
10' I~..'-.. - ..
0 a
,, -- 0, .20
0.14 - -.-
0.t24 4..11
f - 1 6 14 -12 - -6 -4 -2 - -
6.5025' -0 ,,A-
1111 11 -I -' f+
ji < ' 4:::___.I _
o~n *6.20
0.04 -
~ i~i~Ii t o.10 -1 -ld- IL I LLWITH FENESA OLESPRTIE,2 30 35,4 4, 0 KTS 4 s 12 14
545
t I I I
to24 1. ~ 16Ve22I ~1 5AI'0 A- 4 0 1 214 4
e.1.
t4 .-1* .4 II
FIGURE 31a SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, A1RBLEED STRUT, ATMOSPHERIC,WITH FENCES, ALL HOLES, PORT SIDE, 10, 25, 30, 35,40,45, 50 KTS.
58
- ---3
9.1o- 7
---o -E .. J0111 -,
___e___o__
I _
25 41&8~~ A( I A , I? II . .= - *l 4|I DI . i I O |* 1
@.to 4.02=z -ftoo
WIT FENCES A SD 1 d,30,3540,45,s k ...
59 1'r I' ' ' ' '-.' -- --l --L-l'--. l' - -T ' I
FIGURE 31b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEEO STRUT, ATMOSPHERIC,WITH FENCES, ALL HOLES, PORT SIDE, 10, 25, 30, 35, 40, 45, 50 KTS.
59
• iA 1 Ik00,
-2 -a- -- s a1 1 -- 0,0 s -A -
.11 ""~ '
• N -- o| r 515 -
Figure 32 Max Air Runs -- All Hole Open on Port Side - Fm on
Lipr-itf Da fiintv.SdslpAge Air Flo Streda ^8 SUMA
ait Beg;nninq of Run, Decre to 36 SUM Towards End of RunLw - Lift & Drag Ceficient vs. Sideslip Angle Burst of Air at 96 SCFMDuing Dta CoDlection Whe indicated by Circle Around GSaph t 40 Ms .
60
6 70--- 10 Ai -f I
"." 0-M--- " .1 ,
"4 .,- -I- II ! - ! I" .. 1. .,,--- -- :1 I I!.!ItI I I I L
0 2 2 4 * S 11 I I Il 4 44 - S 11
"" -- - - - - - -- 1. .1 I 1. I a"-.2t -_ -I | l - - -
il
| 4 i
______I___! !z ii . ...~ :: _________ _ :-
Figure 33 Alk CM -)m - Lift and Drag Coefficient vs. Sideslip An~gle with Air Flow Shut Off at Supply.
Holes in Strut All Open, Port Side, Fencs On. 10 & 40 ktr.
61
0.-
35
-"1 -A -1 -0 - - -1 0 1- It -
r --liI
,.IO
.0.2. L I - -J --
.0-i1' IZ - 1 -4 -t ,2 1 I I 1A IZ 14 1
.,..e -I I ,.,,1 I~
""ii ... _ __[
I 1 ; 'i Ii
34 Is 1 9 - 1 -Z 4 6 39 IZ 1 44 I 14 - A 9 - -4 4 6 ) li 3| 4 te,* * l l - - - - - - - l .. i ~ I
-I• , V.. .1.. V
-" I i . 4 2 L ..
..S i . .- .,. i I- - - -! -
30 !50i ' _L
-4 Ito
= LI Z ] L .l - o t l 4. -
.,. ! .;,. - - 1 -
t 414 14
FIGURE 348 SIDEFORCE C TiCIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 20 SCFM 19.4 X 10-3 m3 1),WITHOUT FENCES, LEADING EDGE HOLES, PORT SIDE, 0, 10. 25, 30, 35, 40, 45, 50 KTS.
62
35
0.1 - - .- - -- - -
. 17to
-2 4 .01. . 1 1 a1141
oI v -f J > 1: : -, - :-
-. . 0.14
- , - ---
S0
4 1;-17 1 it -614 -2 ioe "- -4 0; A 4 1 to 1 2 I 14 16..,. ! i42-K . ... ~ ~ ____-
X-0,_ -- . -
Q 4 • 1
_______-- _-4- V I.JIL-a
A 5 4 4 0 1 It_% t
FIGURE 34b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 20 SCFM 19.4 X 10"3m31s),WITHOUT FENCES, LEADING EDGE HOLES, PORT SIDE, 0, 10. 25. 30,35,40,45, 50 KTS.
63
[.
i o0 45
4 -1 2 1*0 . 4 . t 1 1 . i - - -? -t 0 - - 1 4 i
-1 -- A
' -... .* * l
'"- -eM , - - ." k .. - - -
"''~ ~ 't !_v
' 4 1 I4 -- 4 2 I 4 i 1 Is 14 I "6 14 4--IS 54- -- 4 4 I t , 11 1. 4
1- ij64
I rF - - -
OL, ---" 410 .1::.{tL L - - - ii
_=14-14<4l,,l -. ~ - . . 4 1 Di A U S |I |d4 4 I 14 1 UI , 1 A 4 4 11 4
FIGURE 36a SIDEFOlC COEFFICIENT VS. SIDESLIP ANGLE AllBLEED STRUT, ATMOSPHERIC, WITHOUT FENCES.LEADING EDGE HOLES, PORT SIDE. 10, 40, 45, 50 KTS.
64
is I. 1
4077 s
.. If
,. a 7 14 I
FIC- 3% DRA COFIIN S IELPAGE, n B DSRT TOPEIWT4U ECS
l~~-I4- LEADING EDG HOES POR SIE 10,9 11 4 0, I45,$~ 50 IST 12
C.'.65
" ______ - - i'1 II IIIVEI " 'i' Il
i I
, 6. #.t I , ,
40-FO O E D A
agoP I6 f we
ze is iJL~I ~ T '45
30.~
50~
* __ ____ ____ ____I lIre,
FIGURE( 36 IEOC OFIIN S IELPAGE ARLE TU.AMSHRC IHU ECS
LEADING~~~~~~~~~~~ EDEHLS OTSD,1, 53,3,04,5 T
S V. 66
41111:1: .1
a.*~ to Is - . It .9 -1 l 1 4 -
#144
... . I~i .. ,
I I I Z ,
* -Ii , -.--- 1 --.-- ... - ,
* . - .+ ! lI 4 ... .r + -
.... '- +:-+ -+- + ! i! L L I +
* I - .. .. .
t- I .------- 4 -i_ _
FIGURE 36b DRAG COEFFICIENT VS SIDESLIP ANGLE, AIRBLEED STRUT. ATMOSPHt:RIC. WITHOUT FENCES,LEADING EDGE HOLES, PORT SIDE, 10, 25. 30, 35, 40, 45, 50 KTS
67
I
AA44 Irv a i - - --- :: LttNi
36!-e14-' -*-------*- - --....--- , .--...- 'I-
7Iii -i i i
FIGURE 37a SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE. AIRBLEED STRUT, 36 SCFM (16.5 X 10 m 's),WITHOUT FENCES, 10% C HOLES, PORT SIDE, 10, 30,45 KTS.
k.__ 68
" fTTl IF ll l - "T 5 i FTTi, I I i
*i.°
. -* ** ".I". -b._L .L_4$_7114
304 ~II
FIGURE 37b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 35 SCFM 116.5 X 10 m3 /s),
WITHOUT FENCES, 10% C HOLES, PORT SIDE, 10, 30, 45 KTS.
_ .vr
I
.j.-- ----- ----- ].---A 1-.- I-4.14 - - I - -.2 - -4 I
1.30 -1~ h
*- }- . I_., .I rC o 351 oet
-0. 0 ,-. ,.. 4-,,.- ..-1 -A 0 -- - 1
"", -'-- - ... , "-- L -, --
, I i T
.2 14 1 ! ! !
f. A , 1 .. . . . .. . .12 _ _4 1 I 1 1%
FIGURE i8 I j:FRC OFINj S IELPAGE IgEE TU 0SF 94X1"m/WITHlUT S 114 l HT5,
70
ai
10 31
*Lis
.l I - -lt
i' -. 1 .I.
40_25 - -T 1 112
(I~~~~ T4: i
-445
5002 * 14 12
IGURE 38b DRA COFFCIN VS SIESI ANLE AIBLE STUT, 20 Sa (9. X 1 ] 3 I3 / "
WIHU ECE, 10 C! HOEPR IE 10 , 30 3, 40 5 0KS
'"' - '-.1
-
-" IC '2 - I - * . I -. I '8 | i t ' V 1 4 '44 A
FIGURE 381i DRAG COEFFICIENT VS, SIDESLIP ANGLE, ,AIRBLE.D STRUT, 20 SCFM (9.4 X 10"-m 3/s),WITHOUT FENCES, 10% C HOLES, PORT SIDE, 10, 25, 30, 35, 40, 45, 50 KTS.
71
0, too
I'
Il 1 - - - 'oh|1
2 10 Is "1 It 416 4E, E -0 .6 -Z 4 0 4 I:t1
Z.i A I 1 1 S 9t 4 1
FIGURE 39a SIDFORCF COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 10 SCFM 4.7 X 103m3 /s),WITHOUT I'ENCES. 10% C HOLES, PORT SIDE, 10, 30,45 KTS.
72
Ir -. -- l l
- -- --.- a -. --- ---- ---
I" .. I I I I I
jIL ' l ilLi
FIGURE 39b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 10 SCFM (4.7 X 103IM3/8),WITHOUT FENCES, 10% C HOLES, PORT SIDE, 10, 30,45 KTS.
73
-- -4 ---
a. .1- 1 1. ,l A1 t
T I'
.5 ~ ~ ~ ~ ~ ~ ~ ~ 1 144 1 ~ 4 -$ -, - J I I 4 * i 1
jill.--,- I I'" [ 1I I - . '!
...-- 4 .. :lo
.... I ., - _45_ +____ --
-4--. 4,,-L-~ - . - ,_
0 !* oL L. Li ' .P ' " -I r-
FIGURE 40a SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, AIRBLED STRUT, ATMOSPHERIC, WITHOUT FENCES,10% C HOLES, PORT SIDE, 10, 25, 30, 35, 40, 45, 50 KTS.
7,4
4.1--- - - - - - - -a
*, ~ ~ ----- -. - - - - - - - --1H -
-7I
I I --
T
I IS I
* C. I=
- --- ---------- = - --- q----- -------- '.- ---- -- + -
FIGRE40bDRG CEFICENTVS SIESIP NGEAIR E STUT ATOPHRC WIHU ECS
10% HOLS, ORT IDE 10,25,0,3540,5,50KTS
-754471
10 .f~ll 30
-41 .1 + - -
*~t-- I*I--4-
19 FT 7
Cm 451
zog
-4 IA4
FIGURE 41a SIOEFORCE COEFFICIENT VS. SIDESLIP ANGLE, AIMBLEED STRUT, 20 SCFM (9.4 X l10 m IsJ,WITHOUT~ FENCES, 25% C HOLES, PORT SIDE, 10, 25, 30, 45 KTS.
76
* -- r - ., I l ! f i - -l -. .,20 30~
.. I+-- q -I- ' -++"
,+. 1+ _ 4 . 1 11 t 1, L, 4 . 1
T25 4 I ,
FiGURE 41b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 20 SCFM (9.4 X I m'Is),WITHOUT FENCES, 25% C HOLES, PORT SIDE, 10, 25,30,45 KTS.
7.;
10 IIr
45F 7 T-
' ' ' '- - I 4 -
III
I,-
FIGURE 42a SIDEFORCE COEFFICIENTVS. SIDESLIP ANLE. AIRBLEED STRUT, 10 SCFM (4.7 X 10 3r/s),
WITHOUT FENCES, 25% C HOLES, PORT SIDE, 10, 30, 45 KTS,
78
I' o !*--,--' 1 ! Ii-- 1---. -i "l i I
....... - -..... 4... .,, _ * .. .. - +
° r '130
I
FIGURE 42b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 10 SCFM (4.7 X 10m 3/s),
WITHOUT FENCES, 25% C HOLES, PORT SIDE, 10, 30, 45 KTS.
79
-T 335
'-. ,- --- + -- -- 'a 4 I I L --, Li
.j F . .- -- -"-- -u - - "-. . .. ... - - "
-i-T-'- - --
'30
. ... . . .. -.. - -..aT !
" ° '50
FIGURE 438 SIDEFORCE COEFFICIENT VS, SIDESLIP ANGLE, AIRBLEED STRUT. ATMOSPHERIC, WITHOUT FENCES,25% C HOLES, PORT SIDE, 10, 25, 30, 35, 40, 45, 50 KTS.
80
-. -:. - - --- - --
10 35-- ---- - - - - ---- -------t
14
25 40T
-
T
.., I~
., _ 4- I* -_---
25 C HOLS, POR SIDE.- 1 2 3 KTI.
I8
FIGURE 43b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIReLEED STRUT, ATMOSPHERIC, W'ITHOUT FENCES,25% C HOLES, PORT SIDE, 20, 25, 30, 35, 40, 45, 50 KTS.
81
"'- o - - - ..~ - I ! ! __ _ -
-A-_ , _I____--i ~~ ~ v ,_ Ii i i :
- -I --,--,---,- ,
W E MH , 40
WITHU - , F, PORT , . ... .
_ _ _ _ _ _ _ - _ _ 82
c12,
T
10 _ [ I1 " 35 i i! -T T [ - -
... . .~ - --. . . .. .-- - - 4 . - ---- --
! i . I i I --
Ii I
2 "145
tII
0 5. I
Vzr 4 4.
... ..i i /- . . . ... . . .. . . .
FIGURE 44b DRAG COEFFICIENT VS. SIDESLIP ANGLE. AIRBLEED STRUT, 20 SCFM 19 4 X 10 It, /WITHOUT FENCES. MIDCHORD HOLES, PORT SIDE. 10. 25, 30. 35, 40. 45, 50 KTS
83
"" '" .- "."-'k10 45
-050
-A 9!!
0.
-0.
- 1, -1 -1 - e -4 -1 t 2 4 6 0 1 2 14 14
- ,. , j J-.. 2 .L oiL ..... --
.aS4 1-. . 54 .4", " 2; 4 1 I01|0 1 14;
FIGURE 45a SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, 10 SCFM 14.7 X 10"m /s),WITHOUT FENCES, MIOCHORO HOLES, PORT SIDE, 10, 30,45 KTS.
84
II;
30
14 -1 - -Y-010 I 4 1
FIGURE ob DRAG COEFFINT VS. SIDESLIP ANGLE, AIULEED STRUT, 10 SCFM (4.7 X 1-3M3/91,WIMhOUT FENCES, MIOCHORD HOLES, PORT SIDE, 10,.30,45 KYS.
Bs
100
I5
- J - - -- -
A!.0 .- .8 -1 a 2 I t 1 4 1 - -1. -1 -1 . 4 0 4 t 0 1 4 1
51, 4 . ....
-01 -4.10
" 14.l tl 4 A .1 Z 1 446 1 11 !S .1. -1: - 4,4 v 1 4 it it,4
30 405
:I+ - - - --- - --.
8.- - -II---- - d tag - - -
*8.1 .5"" -""- "- "-" ". ,' ,
-I 1 41 1 1 i- 1 . ,'12 -1 f l .I$*. 2 t t . . . . . :4..4A - 1 .4, 46 to 2 4 16
- -- \-I----o.: ... ....L i i -- - i ::.- - - ..... 1€ '. -: , + , q , . + + o . Pi, v , , - ... ,- 1. + - - . - - -I - . - ,
IF.. I I _
iII I.L .Ll - .-
'545l 1 *5 4 -IZt3 " .. , " 19 I I 16 14 I 4lAI5 'l8 • -4 -,I " 4 + I I I + I* 585,545
FIGURE 46s SIDEFORCE COEFFICIENT VS. SIDESLIP ANGLE, AIRBLEED STRUT, ATMOSPHERIC,WITHOUT FENCES, MIOCHORD HOLES, PORT SIDE, 10, 25,30, 35, 40,46 KTS.
86
0.37 T' --- --- -- ----.
-16 -'-. .0 .0 .4 -6 24 42 4 0413t is1 Is 1 0t' -042I0- .8 4 -2 0 4 0030t2$134314
20,40
0. 1 4 11 19 1 - - - - J$ - 1 1
C-, I-1
O~ll i 1:: z
L ?L
0. 14 -- - -A -1 -i 11 14 0 4 34.3 -13 .4 4-4 -2 1 1 4 4 W 3 1 W
FIGURE 40b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRILEED STRUT, ATMOSPHERIC,WITHOUT FENCES, MIDCHORD HOLES, PORT SIDE, 10, 25,30,35,40,4 KTS.
87
-10 .-
O~sm
4 -14 -1-1 -1 -4, -4 -.2 2 4 6 9I Is 12 14 16 - t4o 4 2 - c .4 .2 p7 4 4 to 12 14 16
FIGURE 47a SIDEFORCE COEFFICIENT VS. SIDESUP ANGLE, AIRBLEED STRUT, ATMOSPHERIC, WITHOUT FENCES,MIDCHORD HOLES, PORT SIDE, 10, 10 KTS. EXAMPLE OF CLEARED AND UNCLEARED HOLES.
'- ' V I0 , .0
'.1 -4 -1 I9 .0 -
"" - [_O . 1 1 - -1
.3N4 -14 .l2 "39 " 4. 4- =6? 4P2 46OIlI 362434 ' .3..0 .... 24433
FIGURE 47b DRAG COEFFICIENT VS. SIDESUP ANGLE, AIRNLEED STRUT, ATMOSPHERIC, WITHOUT FENCES,MIOCHORD HOLES, PORT SIDE, 10, 10 KTS. EXAMPLE OF CLEARED AND UNCLEARED HOLES.
88
io 35
,. -- Z .: - - - - - t
40
:ol
6._--- -- ,. . ,,-- - -. -,.e __ -u..: ,_ __
- ,3
-OIO I II ., I I U l l
:: l ~ llelllm' " -- - -- -
-- - - - - ' ,-
,,.36-- -' -- - I i ! I ! " I* I -
...I~~~ I
30. -'1- ! - .1 1 -1-! 1 1
- -
*3 i ll i - 4,!l!!j-
A cIit ! .2 .6 24 14I!:~ - - "- ! L i -t.. , I I " , --- . , " a . .-
Cu 1 t
-6.U9
I ! I*Zr " " I V i 4: 14 l 4 1 - 1 ?II-4
FIGURE 40m SID ICE COEFFICIENT VS. SIDESLIP ANGL.. AIRBLEE STRUT, 35 SCFM 116.5 X 1030/s),WITHOUT FENCES. ALL. HOLES OPEN, PORT AND STARBOARD, 10, 25,30,35,40,46, 60 KTS,
89
10 35'
ll.1- -- .
4.14 -
1;.1 4 I 0 - 4 o 1 .1 1 Is -1 -1 1 . z A 4 1 9 1
--. . I. - I I- - -
4.)4
:I::iz' i--- t- I I - L -
, 4 1
.. ... i..... .'-
4, i I24 1
.... liii ' "( li l ll l'. .| - I ,-I l II ~
I:' ' - I . -- I I I L _
FIGURE 48b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIR3LEED STRUT, 35 SCFM (16.5 X 10"3 m3 /8),WITHOUT FENCES, ALL HOLES OPEN, PORT AND STARBOARD, 10, 25, 30, 36, 40, 45, 60 KTS.
90
0.4 1- Si 25 It -l1 T 1
0. -ITII0r .0.w
.16 -1 -t 10 -4 4 0 2 0 1 s 2 4 0o.161 4 1 - -1 . -d -2 4 1 0 - 14 1
40
cl 0.910 - -0 .10 O N -f
I I I I 1-6
41.90 -I - -
4511 1 4 14019 1-1 0 -0.014 - 1 ' I V 1 1 1
0.. -t- I.
* . 1412lf If4. 424 41 .1 00a 2 4 6 o i 4
4 . 0 0 1 0 - - -
. !1 -1 .1 -t - 0 ; -1 it -, -, -1 -1 9 -C 4U - It 0 1 1 I
FIGUR -- - -- - - -IEOC COFIIN VS.0 SIESI ANLE ------------- OPHRI, ITOU FNCS
ALHLSOEPRANSTROR,1,230A 4045 W.N - -
913
'"I I F0.2 6 - 4 - 2 -0 - - 4 - 2 I It It 14 ..o U ,7 2-9 -0 - 4 -1 A 2 4 0
.14.4
6.12
..----------------------------
71-
- 4 ' 14 -12-10 -0 *$ .4 -2 0 2 4 4 e i 2 4 ifS I0.04- i
c i - "
.6.lilll ili '" - -) ~ - ___ __
1a",.14 J2 -l0 -S 6 4 -2 0 1 4 6 1 K 122141If
.,26 I -II- --- I e'" -------------
.I- I fi I 0 .I " -J
.2I -
.14--i- *.-lj "- - "--- -*-.o0, , .,o ,,. -
-.- 4 12 0 --4 -4 -2 2 4 9 0l e 2 14 1 4
50
a.60 1 -Li L J,-
IJt
0.60 -
1I 14 -2. . t-. -4 .2 A 2 4 4 61 0 1 2 12424
FIGURE 40b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIR W.EED STRUT, ATMOSPHERIC, WITHOUT FENCES,ALL HOLES OPEN, PORT AND STARBOARD, 10, 25,30,35,40,45,50 KTS.
92
K,°-"l1 f 35
6.2 4 1 .le 2-1-1
451~~ 1 1 1.1-1
.:.1 .- i i - I . imiri - -
. i- I I I I
- i t :1 A -4 -4 .2 - -tO 1 - -d
'11 .1 1 1 1 1 16. l liLI -
-L~~~~ -9~ 91- 0 t... 1 1 If
- r - - - ... - - I I I i
.A, .E.G.. H OPE. BOT "1 5
- -. -...... i.L .... . i _9
FIUEU IEOC FIINTVS lEl IP- LE iI tLED STU,3 CM ITH! 'FECS
LEDN DEHLE PNBT IS , 102530350455 KTS
.,:,t ,. . L! . . ..3
. 14M 2 4 c -s I 1 4- It 1 --4 - 0 t I
I 15
0.14 8.10
I..
it3 3
_I , _ l~h 41.4,'
0.3- _- I| 4 -9 1 I-4 - 2 = s 4030 .3 .4 .i
'"0. . . ..' 4o
0
A A I 4 2 343 4 -.S 00303 36
FIGURE 50b DRAG COEFFICIENT VS. SIDESLIP ANGLE, AIRILEED STRUT, 35 SCFM, WITHOUT FENCES,LEADING EDGE HOLES OPEN BOTH SIDES, 10, 25, 30, 36, 40, 45, 50 KTS.
94
where A is the planform area
E denotes "endplate"
AR isthe aspect ratio, taken in this caseto be the strut submergence aspectratio of 1.0
The area to be considered in the coefficient is the submerged planforn area of the strut. In
the present case AE/A - 0.5, AR = 1.0. Therefore the endplate contribution to CD is about
0.008 and the corrected value for the strut drag alone is 0.0 12. The drag for a similar strut
tested in Reference 3 without endplate, which had the same maximum thickness and the same
section aft of midchord, but which had a slightly finer nose section, was reported to be
CD a 0.0075.
It is possible that some drag may be induced by endplate lift because of the proximity
of the endplate to the distorted free surface.
Both the-drag and the sideforce curve slopes for the flapped model at zero incidence and
zero flap angle (Figure 13) are similar to those for the plugged airbleed strut, including- the
phenomenon of reduced sideforce slope at speeds of 25 kts and above compared to 10 kts.
The ventilation inception angles for the flapped model are much lower, as are the maximum
sideforce coefficients attained at high speeds.
In sum, the value of the plugged airbleed model as a baseline for comparison with other
airblced strut configurations may be somewhat flawed. The drag appears slightly higher than
might be expected, and the sideforce coefficients somewhat lower. The ventilation inception
angles were also slightly lowur. However, the overall behavior was approximately in agreement
with previous tests.
Figures 26 and 27 show the results of 35 and 20 SCFM (16.5 x 10- 3 m3 /s and
9.5 x 10- 3 m3/s) air forced through all the holes on the port side. Figure 28 shows the effect
of allowing the-holes to remain open, with (he- common--manifold open to the atmosphere.
The natural negative pressure at the ejection hole sites was sufficient to draw, at variable rates,
about 2 - 3 SCFM of air through the supply hose and ventun throat for nealy all sideslip
angles. The three Figures are nearly identical in the gross behavior of the force coefficients.
At 10 kts, the sideforce coefficient at zero sideslip was about -0.10. The value at higher
speeds was between - 0.2 .,nd - 0.25. The coefficient slope at 10 kts for starboard sideslip
angles was about the same as for the plugged hole case (Figure 25). For port angles, the slope
was reduced.
95
Above 10 kts, the unventilated port angle coefficients continued to be about the sameas the baseline case, but for starboard angles, ventilation of the starboard side usually occurred,
which caused the sideforce to fall approximately to zero. Partial or f, dl ventilation of the
starboard side can be noted at remarkably small angles. This suggests that somehow the port
side air made its way to the starboard side to provoke early ventilation. Another factor may
have been the unusually low starboard side pressures implied by the large negative sideforcecoefficients at negative sideslip angles. Sideforce coefficient is often a more reliable ventilation
inception boundary than sideslip angle.
An explanation in detail of the ventilation behavior inferred from the force coefficients
may be helpful in interpreting the Figures. In Figure 26, for example, at 10 kts, the runstarted with the port side vented. The situation remained the same a! sideslip angle increasedto 15 degrees, decreased to - 15 degrees, then increased to - 7 degrees. At -7 degrees, the
starboard side became partly ventilated, causing the sideforce coefficient- to approach, but not
reach, zero. The starboard side vent persisted to zero sideslip angle.
The next graph in Figure 26, for 25 kts, shows that the run began with the starboard
side partial vent still existing. Between 6 and 7 degrees, the starboard vent washed off, andthe force coefficient returned to the port side vented value. This situation was stable as sideslip
angle increased- from 7 to 15 degrees, then decreased to - 1'/. degrees. From - 1 /2 to - 14V2
degrees, partial vents, each successively more extensive, occurred until at - 140 degrees, nearly
full ventilation was present on the starboard side. Evidently the starboard vent continued to
grow, or perhaps the portside vent decreawed, even as sideslip angle increased. This was indi-
cated by the sideforce coefficient approaching closer to zero, implying a symmetric flow pattern.The remaining speeds can be interpreted in much the same way. Note that the 30, 35,
40 and 50 kt runs all started with starboard side vents left over from the previous runs. Thesevents washed-out as sideslip- angles became more positive, and were re-established at, mostly,
negative sideslip angles.It is interesting to note that the drag coefficient at zero sideslip angle in all three Figures
was no different whether or not there was lift. For example, the plugged strut had a dragcoefficient (Figure 25) of about 0.06 when the sideforce coefficient was 0.2. For tile port
aerated strut, at zero sideslip, the drag coefficient was about 0.03 whether the sideforce
coefficient was zero or 0.2. In one case the air injection could be considered to increase drag,
and in the other to decrease drag.Figures 29, 30 and 31 show the results of the same conditions as the previous three
Figures, except that four ventilation fences had been added, at the mean ,,ee .,urface and, at
equal intervals of one quarter chord, one above and two below the surface.
96
The general trend, not obeyed in all cases, was for the fences to increase the sideforce
coefficient slope at low speeds, to limit the hysteresis effects by reducing the excursions
(maxima and minima) of the force coefficients, and to increase the drag. The notable
exception to this generalization is shown in Figure 29 for the 35 kt, and to a certain extent,
the 40 kt case for sideforce coefficient. The hysteresis and excursion is equally as large as for
the unfenced case.
A posrible explanation for the fence results is that the fences trapped air cavities, so that
the change from one state to tile next was never quite completed, and the state which resulted
most of the tihe was a nondescript composite, which exhibited few extremes observed in the
behavior of the unfenced airbleed strut. The reason for the exceptions noted in Figure 29 is
probably that these were the initial runs of the fenced strut series, so the starboard side air
pockets had not had-a chance to become established. ii-fact, up to the 35 kt run inFigure 29, there had been no evidence of a starboard side vent. If this type of "damped"
behavior is sought in a full scale craft, the penalty of an increase in drag coefficient of from
0.005 to 0.01 may be justified.
Before emoving the fences and proceding to test the effects of individual rows of air
ejection, some special purpose runs were made. Figure 32 shows the results of charging the
air supply accumulator to near maximum capacity and allowing the air to be expelled at the
maximum rate compatible with the airflow measurement system. This resulted in a maximum
airflow of around 85 SCFM (40 x 10- 3 m3 /s) which declined during the run to 35 SCFM
(16 x 10- 3 m3/s), the maximum continuous rate sustainable by the supply compressor. This
run was performed at 10 kts only. The principal difference between it and the similar runs
was that a starboard side vent was provoked, showing that excessive air on the port side
probably does affect the starboard side.
On the same Figure, the lower graphs show the results of releasing air in one second
"bursts" every 10 seconds or so, a rate of about 95 SCFM (45- x -10-3 1113/s), at a towing
speed of 40 kts. In this case, no significant general differences were observed, although the
points on the graph where the air is released are changed somewhat from the neighboring
points. This shows that greatly increased airflow rates do not change the force characteristics
appreciably. The technique of "bursting" the air may be useful if for some reason it is
necessary to limit the amount of ali ejected by the air bleed system, while still achieving
substantially the same effect as continuous airbleed.
Figure 33 shows the effect of turning off a valve between the air supply accumulator and
the strut. The effect is much the same as for those runs with active air bleed at the same
speeds, 10 and 40 kts. Apparently the air remaining in the manifold and supply hose, plus
97
I _____________
air sucked in through the above-water holes in the strut was sufficient to create substantially
the same effect as vigorous air ejection. The implication for full scale application is that,
while it may be easy to provoke ventilation, it is not so easy to turn it off.
Figures 34 through 47 show the results of ejecting air from between hole rows 5, 10, 25
and 50 percent of chord aft of the leading edge. Again, no major difference in behavior was
noted. The principal minor variations were: the starboard side did not become ventilated at
as small a sideslip angle at the low and intermediate speeds, especially in the case of the mid-
chord holes, with just atmospheric air as the supply, there was somewhat more hysteresis and
the results were more erratic than with all the portside holes open; with atmospheric air alone,
if the midchord holes were not cleared of water before a run, they would not spontaneously
clear until a "natural" vent occurred; no single row of holes functioned as well with atmos-
pheric air supply if is was not cleared prior to the run. A comparison of runs made with
midchord holes cleared and not cleared is shown in Figure 46.
In general, it can be said that, with active air injection, there was little to choose betwen
any hole pattern. With minimal air supply, holes distributed over the chord functioned better
than holes at any specific chordwise location.
For the final airbleed tests, a row of holes was opened up on the starboard side, 5 percent
of chord aft of the leading edge. Figures 48 and 49 show the results of airbleed through all
holes, port and starboard. Figures 51 through 53 show the results of just tile forward 5 per-
cent chord rows of holes on both sides open.
In Figure 48, the sideforce coefficient exhibited the same tendencies as for runs during
which both sides of the strut were ventilated. However, at large port angles, the coefficients
behaved more as if just the port side were vented, indicating that the starboard side was "starved".
Even at large starboard angles, the port side seems to have had the better air supply.
More symmetry is apparent in Figure 49 for atmospheric air supply. At large port angles,
the starboard side seems to have been starved, but the converse was also true. Even in this
case, it is still evident that the port side had the more adequate air supply.
For all cases of starboard and port side airblecd, the drag coefficient was nearly independ-
ent of sideslip angle, and slightly increased above the comparable value obtained with blowing
on only one side at zero sideslip angle. The drag coefficient was about 0.035 to 0.040, com-
pared to a plugged-strut zero sideslip value of 0.02.
During blowing on both sides from the 5 percent chord holes only, the sideforce coeffi-
cients were quite symmetric, showing signs of starvation on both the port and starboard tacks.
This was pronounced ifi the atmospheric supply case, Figure 53. less so for 10 SCFM
(4.7 x I0 3 m3 /s) airflow rate, and hardly noticeable at the 20 SCFM (9.4 x 10-3 m3is) rate.
98
10| 35
-.4~ -1 - - 1 . 4 z 0 4 It 214 1 -:nl 6 .4~~ ~ ~ -1 -10 - - -2 -2 4 6 S-t 1 4 I
6.261 -1 L .2
1 I .1 -Y -1 9 .9 4 4.2 8 1 2 14 ld*gowN
-- !- 4- -
-1 1 1 -1 . 4 4 i it 14 19 -1&4 -2 4 .aIO " - 4 -Z a 4 6 1 le 1? 14 to
''-i I i -i - - - 1' -. .
I ~I - I .26 - -
7111111r
.14: j H : I : I
.i.26121, -
FIG'.,RE 51a SIDEFORCE COEFFICIENT VS. SIDESUP ANGLE, AIRBLEED STRUT, 20 SCFM 19.4 X lp M3 /s),WITHOUT FENCES, LEADING EDGE HOLES OPEN BOTH SIDES, 10, 25,30,35,40,45, 0 KTS.
99
FF1- 1 17
14-1 -o 8 2 s t 1 1 1-1 . I-1- -1- -1 .1 . 4 z 0 4 4 R a 4 i
0.1.
6.4 .
4.00VA 1 1 1: 1 1 1 1 .L .00 -14 -1- .3 .0 .1 4 2 4 4 8 1 1 14 if
.V 014 -. . ..
.IC I " - ICe0.1 4%-L - - __1
-1.16 -T ' -- - :I~42I . - ~4Z4~64.14 -O
4 *I li II4 .l4. .. - - 21
.. ,. ES MGCOPICET S SIEU ANI1 AISEDShT.2 CM(A 0ml1 4
i | -14 -14 -42 -to o1 .6 4 . 2 1 a 6 It It 14 ltc
1,414 f--ac!i
1 .~ -0 - 4 1 4 45 1 . 4 . - o 1 - 1
FIUESbDUOFIIETV.._EL NL , LE STUT 20SF AX1-m 81WITOU FECS LEAOIN EDGE WIE.PN90HSDS1,2,03 ,404,0KS
li t100
____-________________-. ___,- _______ " - +
. -,r s ~' -
1!14 4 -- .10 -9..-. -Z0 6 0 i it1 If -o 1 2 -1- .4 .2 a z 4 0 it i -I
.110 M
.103
0.2 6 4 0-1
4. ' 4.14 T I --
--24 2 .(7* 6~4 c j v 46 *22 It.421 It4 4. 1. is -Ills* e v
301421 - - -- --J H I
I H-
I * |424 |7 -IO "4 *14J 4 a 4 so 6 2 424
.,,j .. L E .. SIDES 10, 2 0
-'r,-- J-- - -0 14 I *4 °J * 4 41241*1426
--•I. ---: ) l~ 12. ' L -~ 4 -4 - -Iil I 4
-e e _-p : . - -dr
"".4 - _________.____ :_ _:~2' 2k + , ,4 * .9 4 42*2424t '2 .2 .2 -* 4 4- , ! 6 62 2 2
FIUE""SOFRECEFIIN S IEIPANL.ARLE TU.1 SCPM 14.7l, X 10 3/
WITHOTFECS LEAiN111 EDEHLE .PN,, IE. 02,0,,04,6 C
'" !li~ lrlr- kk. l ,10 1 il t . .
C. lot -1 - - -
0.1.1
S' - - -t .1 -4 -4 -2 0 -9r a t 2
-.14 -9 W -, -f -9 -4 -2 -0 1 1
5.31_F II I IS.I I -
t 1 0-e 0 -4 . a - - *I.12I so 124 1 44 iA 4 I 4
ROMObDRG CEFAN V. S" NGEAMLE.1 Tff 10- 7 T/
WHO T . 45NM LEDN EDEHLSOE _ WS 1.2,03,04.0KS
- -- -- .102
10 35'-- ~
6.'! 1 1 , -to --- 4 - 1 0 1 2 M 1 - -., . -0 -a 1 2 4 I
-n- p
4. -1 1.10. 4- - S 01 4 1 1 -le -9 -- -4- 4 611 i ;1
25.' 4
-1 . 12 14 -6 -4 - a a 4 6 9 I It14 1. -14.14 -12i 41 9 .4. a 0 2 1a I f If41
20' 4 - - 41 1
-1 .14 .121 1.4 -1.2 @2 47 *1 1 11 1-14 -t.- .. .4 . 6 4 46 1 114 1
25W ft $MO 45FKf VS II NA M S~fAMSMCVnfamDO IM --- OM BM WO 10, Aa X- - +~ 3%A404- U
4.34 - -- - - - - - - - - - - 0.3
1 I17 -2-0 0 . 4 - 6 a t i 4 4 .1-1 1@ . . 4 4 9 I W 1
0114 45.
I I o
Lii jAj IIII .1 f -t -4 -4 -4 y a A- t 1 d 1 4 -4- 1 44 i s
MM Ufhhb 0MG COURPCIENT VS. SIDESU ANGLE. AMKEED STRUT, ATMOSPHERIC, WITUl ENCES.LEADIN EDG HOLES OPEN MOTH SIDES, 10, 2,26,30, 35,40. 46, 50 KTS.
104
An extremely interesting and significant phenomenon occurred at the 35, 20, and 10
SCFM (16.5 x l0 - 3 , 9.4 x 10- 3 , 4.7 x l0-3 m3/s) flowrates at 50 kts. At 20 and 10 SCFM,
on the starboard sweep, large unsteady forces occurred which overloaded the analog-to-digitalconverter and prevented further data acquisition. At 35 SCFM, on the port sweep, extremely
large unsteady forces were registered which not only overloaded the electronics, but were
distinctly and disturbingly felt by the test operators.Since the unsteady forces on the starboard tack were experienced in an angular region
where air starvation is presumed to have been a problem, it is likely that they were caused by
tWe vented cavity shrinking to a length of the order of one chord. This is known to create
severe oscillations (e,.g., Reference Ii).
The unsteady forces encountered at fairly low port angles present more of a puzzle,
particularly since they occurred at the 35 SCFM airflow rate, the maximum generally applied.
It is possible that having so much air exiting at a very forward position created an instability
of the attachment point of the flow, which alternately vented and wetted each side of the
strut in a coupled oscillation. The involvement of both sides of the strut could explain the
subjective sense of unusual severity of the oscillation. Evidently, multiple chordwise positions
of the air holes prevent the oscillations, since they were not observed prior to the 5 percent
chord airbleed runs. This may be a problem that will have to be examined before a full scale
system is designed.
CONCLUSIONS OF THE AIRBLEEDAND FENCE EXPERIMENT
0 A small amount of airbleed can affect sideforce coefficients by an amuunt equal to a change
in sideslip angle of nearly 12 degrees (AC, = ± 0.2).
0 Airbleed on-both sides of a strut can-effectively reduce sideforce-to near zero even for
sideslip angles of 15 degrees.
0 For continuous airbleed from both 6ides of a strut, the drag penalty referenced to a baseline
condition in this experiment was 75 to 100 percent (about A percent of overall drag).
0 Unsteady forces due to cavity oscillations can be a problem if air ejection is limited to a
single chordwise position.
* Chordwise location of air ejection is not a significant parameter, except perhaps for
oscillations.
0 Multiple-row air ejection compared to single row at a single chordwise position gives moreconsistent results and requires less or no blowing pressure.
105
SPOILERS
A device similar in effect to a split flap is the flow "spoiler" shown in Figu c 54. As
suggested by its name, the spoiler derives part of its effect by changing the circulatiorn-by"spoiling" the flow past a certain point. This might prevent the negative pressures from
developing on the low pressure side of an airfoil, for example. Spoilers can be retractable or
permenantly fixed. The advantage of a spoiler-type flap would be the predictability of its
ventilation characteristics. Spoilers of the type shown in Figure 54 applied to a surface-
piercing strut would probably be ventilated at their base as soon as they were depic d. For
fixed spoilers on both sides of a surface-piercing strut, the expected behavior would be similar
to that of a blunt-based strut, as shown by comparing the data of Dailey 6 and Nelka. 7
Figure 54 - Spoilers on NACA-16-012 Surface-Piercing Strut
Spoilers could be applied in two ways. A retractable spoiler could be extended on either
side of a surface-piercing strut as necessary to counteract undesirable forces or to generate a
desired side force. Or, permanent spoilers could be attached to both sides, which would be
expected to limit the maximum sideforce that could be developed in either direction. How-
ever, based on exper;ence with blunt based struts, the sideforce developed prior to ventilation
is likely to be a linear function of sideslip angle.
In applying spoilers to a given situation, there are several unknowns at,,,ng which are:
the sideslip angle at which ventilation takes place; the conditions under which the trailing
part of the strut would be completely enclosed in the ventilated cavity; the effectiveness of a
given spoiler in producing or reducing sideforce; the control power required to actuate a
spoiler. To clarify these points, an experimental program was necessary.
THE SPOILER EXPERIMENT
The Modal. The flapped model was fitted with two spoilers as shown in Figure 54. After
testing, the port spoiler was removed and the strut filled and smoothed to-its original-contour.
The spoilers were identical to those used by Nelka in Reference 7. They were mounted so
that the spoiling effect took place at mid chord, rather than at 70 percent of chord aft, as in
Nelka's experiment. The angle subltcnded by the spoilers was nearly 7 degrees.
106
They were designed to provide a favorable pressure gradient as the flow followed the "ramp"
starting at the spoiler leading edge, so that premature separation would not occur.
Test Conditions. As in the previous test, the strut was mounted at a radius of IO chords
and towed on the Rotating Arm through a range of speeds tested from 10 to 50 ,%s,
corresponding to angular velocities of 0.14 to 0.7 rad/s. The strut was tested wit sloilers
on both sides and on the starboard side alone. The data acquisition system was idntical to
that used before.
RESULTS AND DISCUSSION
OF THE SPOILER EXPERIMENT
Figure 55 shows the results of the test with spoilers on both sides of the NACA 6-012
strut. The sideforce coefficient curve is virtually identical to the 10 kt slope recorded ir the
previous two models tested in their baseline condition. That is, the 16-012 strut with zero
flap and the plugged airbleed strut.
However, unlike the flapped and airbleed strut, the coefficient slope remained practically
unchanged at the higher speeds. Unfortunately, the range of sideslip angles tested was limited
by the tendency of the spoilers to aggravate the spray problem.
The only occurrence o ' 'ntilation that seriously affected the force coefficient happened
4U 15 degrees and 35 kts. This is quite good compared to the airbleed and flap models at
similar speeds and equivalent to the unmodified 16-012 strut as tested by Nelka. 7 The post-
vented sideforce coefficient was less changed compared to ante-vented conditions than either
Nelka's unmodified 16-012 or nis spoiler strut, which had spoilers farther aft.
The behavior of the force ooefficients also compared favorably with a blunt based strut,
similar to the NACA 16-012, truncated at midchord, tested by Dailey. The sideforce coeffi-
cient slope-was not as great as that measured by Dailey for the blunt based strut. In fact, it
was less that half. However, the ventilation boundary angles were greater and the force
changes were much smaller than those associated with the blunt based strut.
The increase in zero sidesh, drag caused by the addition of spoilers was about 50 percent,
comparcd to the previously tested baseline strut. The absolute change in drag coefficient was
about 0.01, less than for continuous airbleed.
Figure 56 shows the results of the tests of the NACA 16-012 with the spoiler on the
starboard side only. The change in lift coefficient at zero sideslip was 0.2, equivalent to a
change in sideslip angle of about 8 degrees. This was about the same as the change in lift
generated by airbleed. The ventilation angle with port sideslip angle was slightly lower than
in the case with the dual spoiler, and the force changes are greater. However, for starboard
107
O~ -.
-'-
10 35
. . - - - - - - -12 . 4 . 6 . 2 4 2 4 a a I t 1 - 6 . 4 -12- - -1 r -. 4 9 I 211.40 " .40i
IA .. - - - - - - -.
. - - - - - - -
Ir,OIPT
459
I 1 I I.
I Al I 4
gP~m -.U - -
.IG.94 6 M4
4 . 4 .1 .4
4
115
1 214 l 4 26 4 • 4 19 2 14 i
v .,. i i - -
S,, 04- -.
-..'- - - :1K0 L1 .j I i I,, I I .o- I t I I 1 j i
-, SM -,
I --It.- I14 i-
i'! 'ii"--- ! . 5 -- - -
_________ LeSOEOC COEFICEN VS94EUPAG SPOiltR STRUJT, WITHOUTFEES
a,-.4.. O SI ES 0 6 0 6 1,4,6 KTS.
108
- -I . 4 to 12 r- - -
2535
*4- - - - j sE * -1 4. 1. 0I 41
-6$4 -- Al I 4
40.14
vall L -. 14 1 -• 1 I - .
"",- .1 1 -i t ! 1,
6.9" 0. 14 "1 it - -4 "1 1 -1 - 1 -I 4 -4 1 4 I f 12 1
- i~j"- 4..ii-- .
FIGURE 55b DRAG COEFFICIENT VS. SIDESLIP ANGLE, SPCVLER STRUT- WITHIOUT FENCES.
SPOILER BOTH SIDES, 10, 25, 30, 36, 40, 46, 50 KTS.
109
..'" - - - - -2 _
"I16 -12 .10
6 "f -. 2 6 2 4 6 0 to 1- If " 1 1 -10 . .- - - a 2 to at 1 i
.-LJ- - J.-, Y ' . .L140,I i 1***.--i -I .. IT A--
... - +.I ;I~ -. ii
.. 6. 1 ! 1 11- -
-111.---l
I w + I'S.-.
-9.10 iv- I
'14 -- -1 -1 -f -4 ______ -- t 1
"4__,,II I I.I... .. .0 2I I
• ,iiiiiI " A
301 IIII • I+ j
1.1 -2 -1 .84IlI- .4 4. 02 42 00 0 21
.::, LtWL -- jilj :'W - -- -i.4.1 -- -. 9
.0.0 - - -- 4.2
is-I ' -4 -12- -* .0 -4 2 a 2 4 LIIs 1114I
" . I i 1. .I 8 - I -4 q I I 14 to"{ I -+la -I .4 '4 Z A 9 I l 2 II 16II I
FIGURE 6U. SIDEFORCE COEFFICIENT VS. SIDESLIP ANGI.E, SPOILER STRUT, WITHOUT FENCES,SPOILER STID SIDE, 10, 25, , 36,40,46, 50 KTS.
110
- - - " --- -- -
-I -- - - -- - - - - --
--1 - - - - - - - - -
6.6 - - - - --- - -
6 .1 - - -- - - - - - - - - - - - - -
4.14.
-.64 -1 -1 -t -1 -4 2 0 -0 I 4 1
I~~ LL - -- -
14 1
250
.4.1
6.6 7 1 i
FI U E S R G C O F I I N S.S D S I N L , M E T U , WI H U E C SSPIE .O IE 1,2,0,54,5,WKS
sideslip angle, which is the postulated condition for the use of a retractable, starboard side
spoiler, either ventilation does not occur until a very large angle, or the forc:e changes
accompanying it are not very great.
Interestingly, the drag penalty compared with the baseline case is nil, even with the
spoiler deployed. Obviously, there would be little or no drag penalty associated with a
properly designed retracted spoiler, but control power would be necessary for actuation.
CONCLUSIONS OF THE SPOILER EXPERIMENT
0 A retrackble midchord spoiler is a feasible method of reducing sideforce on a surface-
piercing strut to nearly zero, and minimizing the adverse effects of ventilation.
a The drag penalty for a single spoiler was below the resolution of the present experiment.
0 Fixed midchord spoilers can minimize sideforce anomalies associated with partial and full
ventilation to achieve a measure of linearity of response of sideforce to sideslip angle.
Spoilers at midchord were more effective than spoilers farther aft.
0 The drag penalty associated with double spoilers was about 50 percent of the baseline value
at zero sideslip angle.
GENERAL CONCLUSIONS
* Flaps, airbleed or retractable spoilers could be used to affect or nearly eliminate the side-
force experienced by a surface piercing strut at an angle of sideslip.
* The flap has the disadvantage that it would be ineffective or detrimental at small angles.
Unless air can be prevented from travelling down the hinge intersection, a substantial dragpenalty will be incurred.
* Airbleed has many potential advantages, including simplicity. There would be a substantial
drag penalty for continuous airbleed. Intermittent airblced poses control problems, which
would be aggravated by the tendency of the air not to cease its effect when shut off.
• Single or double spoilers, while not as positive in reducing sideforce as airbleed, have little
or no drag penalty associated with them. Single-sided spoilers would necessarily be
retractable, an added complication. It is not known whether the response of a retractable
spoiler would be proportional to its extention.
112
LIST OF REFERENCES
1. Abbott, I.H., and A.E. von Doenhoff, "Theory of Wing Sections," Dover~Publications, Inc., New York (1959).
2. Jacobs, E.N. and R.M. Pinkerton, "Pressure Distribution over a Symmetrical AirfoilSection with Trailing Edge Flap," Langley Memorial Aeronautical Laboratory Report No.360 (Apr 1930).
3. Rothblum, R.S., D.A. Mayer, and G.M. Wilburn, "Ventilation, Cavitation, and OtherCharacteristics of High-Speed Surface-Piercing Struts," Naval Ship Research and DevelopmentCenter Report 3023 (Oct 1972).
4. Swales, P.D., R.C. McGregor, R.S. Rothblum, "The Influence of Fences on Strutand Foil Ventilation," 10th ONR Symposium, Boston (1974).
5. Layne, D.E., "Effects of External Stiffeners on the Ventilation, Force and CavitationCharacteristics of a Surface-Piercing Hydrofoil Strut, " Naval Ship Research and DevelopmentCenter Report SPD-621-01 (Apr 1975).
6. Dailey, N.L., "Experimental Investigation of the Ventilation and Force Characteristicsof a Blunt-Based Surface-Piercing Strut," Naval Ship Research and Development Center ShipPerformance Department Report 479-H-01 (Feb 1973).
7. Nelka, J.J., "Effects of Mid-Chord Flaps on the Ventilation and Force Characteristicsof a Surface-Piercing Hydrofoil Strut, " Naval Ship Research and Development Center Report4508 (Nov 1974).
8. Dailey, N.L., M.F. Jeffers, R.S. Rothblum, "Ventilation and Force Characteristics ofthe NACA 16-012 Surface-Piercing Strut in Cavitating Flow," Naval Ship Research andDevelopment Center Ship Performance Department Report 479-H-03 (Aug 1972).
9. Von Schertel, Hans, "Comparative Tests Between an Air Stabilizer and aSConi,entional Supransar PT5O, " Supramar, Ltd (1967).
10. Von Schertel, Hanns. "Experimental Investigation of Air-Fed Hydrofoils,"Supramar, Ltd (Aug 1964).
11. Ling, T.G., D.A. Daybell, and K.E. Smith, "Water-Tunnel Tests of Hydrofoils withForced Ventilation," NAVORD Report NOTS TP 2363 (Nov 1959).
12. Von Schertel, llanns, "llydrofoil Boats as a New Means of Transportation," paperpresented to New York Metropolitan Section of SNAME (30 Oct 1958).
13. Hoerner, S.F., "Fluid-Dynamic Drag," published by author (1965).
113
DTNSRDC ISSUES THREE TYPES OF REPORTS
ill DTNSROC REPORTS, A FORMAL SERIES PUBLISHING INFORMATION OFPERMANENT TECHNICAL VALUE. DESIGNATED BY A SERIAL REPORT NUMBER.
(2) DEPARTMENTAL REPORTS, A SEMIFORMAL SERIES, RECORDING INFORMA.TION OF A PRELIMINARY OR TEMPORARY NATURE, OR OF LIMITED INTEREST ORSIGNIFICANCE, CARRYING A DEPARTMENTAL ALPHANUMERIC IDENTIFICATION.
(3) TECHNICAL MEMORANDA, AN INFORMAL SERIES, USUALLY INTERNALWORKING PAPERS OR DIRECT REPORTS TO SPONSORS, NUMBERED AS TM SERIESREPORTS; NOT FOR GENERAL DISTRIBUTION.
k _ /'