-. .. -

SEC-TR-65-53

ci0 EVALUATION OF RAIN-EROSION-RESISTANT MATERIALSTO PROTECT THE HH-43B/F HELICOPTER ROTOR

MATTHEW H. CHOPIN

TECHNICAL REPORT SEG-TR-O5-53

AUGUST 1966

Distribution of this document is unlimited Drip

iq6jSYSTEMS ENGINEERING GROUP

RESEARCH AND TECHNOLOGY DIVISIONAIR FORCE SYSTEMS COMMAND

WRIGItT-PATTERSON AIR FORCE BASE, OHIO

Best Available Copy

NOTICES

When Government drawings, specifications, or other data are used for anypurpose other than in connection with a definitely related Government procure-ment operation, the United States Government thereby incurs no responsibilitynor any obligation whatsoever; and the fact that the Government may haveformulated, furnished, or in any way supplied the said drawings, specifications,or other data, is isot to be regarded by implication or otherwise as in anymanner licensing the holder or arty other person or corporation, or conveyingany rights or permission to manufacture, use, or sell any patented inventionthat may in any way be related thereto.

Many of the materials compared in this report were commercially available andwere not developed or manufactured to meet Government Specifications, to with-stand the tests to which they were subjected, or to operate as applied during thisstudy. Any failure to meet the objectives of this study is no reflection on any of thecommercial r,-aterials discussed herein or on any manufacturer.

/ I

Copies of this report should not be returned to the Research and Tech-nology Division unless return is required by security considerations,contractual obligations, or notice on a specific document.

200 - February 1967 - C0192-22-479

SEG-TR-65-53

EVALUATION OF RAIN-EROSION-RESISTANT MATERIALSTO PROTECT THE HH-43B/F HELICOPTER ROTOR

MATTHEW H, CHOPIN

Distribution of this document is unlimited

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SEG%-TR-65-53

FORI' WORD

This report was prepared as the result of an in-house program to select a suitable materialto protect the servo-flap of the HH-43B/F hlwhcopter rotor system from rain erosion. Workwas initiated by the HH-43B/F Helicopter System Program Office under System No. 976Z.The test report was prepared by Mr. NV!, H. Chopin of the V/STOL Propulsion Branch,Systems Engineering Group, which proviced eTngneering support to the project offino.. Testfacilities were provided by the Propulsion Brstch of the AF Aero Propulsion Laboratory.Both support orgaiizations are under the Research and Technology Division.

During a subsequent series of tests, the tert club separated from the shaft and completelydestroyed itself and the spray rig. This report, therefore, also serves to describe the RTDrain erosion test facility in detail and the tests performed on it prior to its destruction.

This report cover- work from 30 July 1963 to 26 December 1964.

The report was submitted by the author in August 1965.

Figures 6 and 24 are reproduced by peim-lssion of the Kaman Aircraft Corporation.

This technical report has been reviewed and iv approved.

AMIES G. BARRETT

Technic-al DirectorDirectorate of ProrTulsion & Power

Subsystems EngineeringSystems Engineering Group

it

SEG-TR-65-53

ABSTRACT

Tbis report describes the tests of various materials to determine a suitable protectivecovering for the HH-43B/F helicopter servo-flap leading edge when operating in rain.

Nineteen materials were tested and compared on a rain erosion spray rig in the electricmotor whirl stand facility at WPAFB Ohio. Impact velocity varied from 330 to 730 ft persecond.

A description of the facility, test procedures, results and recommendations is presented.Photographs of the spray rig and test specimens are also included.

iii

SE•-TR-65-53

TABLE OF CONTENTS

SECTION PAGE

I INTRODUCTION .. .......................... 1

II TEST PREPARATION. INSTRUMENTATION, AND EQUIPMENT .... 3

HII TESTING PROCEDURES AND FINDINGS ................ 14

1. High Speed Tests (500 mph) . .................... 14

2. Variable Speed Tests ............................. 14

3. Comparison Tests ......................... 22

IV CONCLUSIONS .. ........................... 33

V RECOMMENDATIONS .......................... 34

APPENDIX - DESCRIPTION OF TEST SAMPLES .................. 35

REFERENCES ..................................... 37

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SEG-TH-65-63

ILLUSTRATIONS

FIGURE PAGE

1. Flap Spanwise Locaticn on HH-43 Helicopter Blade ....... ............ 1

2. Typical In-Flight Servo Flap Damage From Operation in Rain ...... 2

3. Closeup View of Damaged Plywood Leading Edge and PeeledAway Nylon Rip-Stop Cloth ............. ......................... 4

4. Photograph and Schematic cf RTD 30,000 HP Test Rig With SprayApparatus, Side View ............ ............................ 6,7

5. Photograph and Schematic of RTD 30,000 HP Test Rig With SprayApparatus, Front View ............. ........................... 8,9

6. Detail Diagram of Test Sample Block .......... ................... 10

7. Detail Diagram of Sample Adapter ....... ...................... 11

8. Club Tip, Sample, and Water Spray Photographed Through the Transit . . 13

9. Various Speeds Versus Test Rig RPM ........ ................... 15

10. Time-to-Failure for Samples Tested at High Speed (500 mph) ......... .16

11. Comparison of Neoprene Samples -101 and -103 Testedat High Speed (500 mph) ............. .......................... 17

12. Advanced State of Failure of Sample -105 Stainless Steel Tested at HighSpeed (500 mph) ............... ............................. 18

13. Comparison of Sample -109 Neoprene Sheet and Sample -111 Precured

Urethane Sheet Tested at High Speed (500 mph) ...... .............. 19

14. Time-to-Failure for Samples Tested at Varying Speeds ..... .......... 20

15. Comparisov of Neoprene Samples Te:sted to Failure ................... 21

16. Sprayed Neoprene Sample -115 Tested at Various RPM ...... ......... 23

17. Stainless Steel With Plywood Backing, Sample -117, Tested at VariousRPM.. ................. .................................... 24

18. Precured Neoprene Sheet With Plywood Backing, Sample -119, Testedat Various RPM ................ ............................. 25

19. Cloth Impregnated with Neoprene, Hard Backing, Sample -123, Testedat Various RPM ................. ............................. 26

20. Tradename Material on Plywood Backing, Sample -129, Testedat Various RPM ............... ............................. 27

vi

ILLUSTRATIONS (Cont'd)

FIGURE PAGE

21. Extreme Values for Specific Materials Tested ..... ............... 28

22. Test of Polyurethane Sheet Material, Sample -131. After Initial Failure • 29

23. Comparison of Clear and Impregnated Polyurethane,Samples -131T and -143T .................................. 30

24. Detail Diagram of Recommended Protective Strip of -143T Material .... 32

vii

SEG-TH'-tb.-53

SECTION I

INTRODUCTION

Propulsion and lift of the IH-43B/F rescue 2 mm droplets and a water flow rate of 1helicopter are provided by twin, intermesh- inch per hour. During initial tests, whlcii wereing, counter-rotating, two-blade rotor as- run at 700 rpm (500 mph tip speed), failuresemblies controlled by aerodynamic actiou times were found to be very rapid. Laterof the blade-mounted servo flaps (see Figure tests, which were run Lt varying rpm's1). The cyclic and collective pitch controls from hover to red line tip speeds, producedare linked directly to the blade-mounted curves similar to conventional S-N curves andservo flaps. failure times were more meaningful.

The servo flap of the production modelsof the3e helicopters is constructed of high- Manyo of the materials tested were knownquaitysprceand maple wood, birchplywood,* to provide excellent protection when appliedquality spruce and mhelea oneg over a hard surface. The leading edge of theand nylon rip-stop cloth, and theleaoeingeare servo flap for the HH-43 helicopter, however,is sprayed with a layer of neoprene rubber consists of a spruce core covered with aover the rip-stop cloth. The primary objective 1/32-inch 3-ply plywood, which provides aof this test program was to determine a relatively soft surface. This made the selec-suitable material for protecting the tion of a suiiable protective material veryHH-43 B/F helicopter servo-flap leading edge difficult. The failure of the materials duringfrom rain erosion when operating in a rain this test program, therefore, should notenvironment. Typical damage to the servo reflect upon their usefulness when used underflaps when operating in rain is illustrated the conditions for which they were intended.in Figure 2. Based ipon these test results, a material was

Comparative tests of 19 materials were run selectedl which provided the best protectionunder the same simulated rain conditions of for the given flight conditions.

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SECTION II

TEST PREPARATION, INSTRUMENTATION, AND EQUIPMENT

Construction of the RTD rain erosion rig The 2 mm droplet size and 1 inch/hour flowresulted from a 1957 study conducted by rate are equivalent to rainfall classifiedCornell Aeronautical Laboratory under Con- between "heavy" and "excessive" and rep-tract AF33(616)-3267. The study concluded resent a world-wide average.the use of the 30,000 HP propeller electricwhirl rig (already In existence at Wright- The method used to produce the desiredPatterson A FB) was a feasible and economical 2 mm droplet size was established during aapproach to obtain high-velocity (up to Mach 2) prior series of tests. Droplets from hypo-rain-erosion test conditions. dermic needles of different sizes were photo-

RTD personnel designed and fabricated the graphed as they passed in front of a screen20-foot-diameter test club for use in the marked off in a millimeter grid. Individualtest facility. (See Figures 3, 4, and 5.) The needles were mounted slightly in front of andtest club was a two-blade solid steelsection, parallel to the plane of the grid. A camerasymmetrical both chordwise and inplanform, was mounted in front of the screen with aand having no camber, twist, or pitch. The spotlight positioned on each side. As thetest samples were attached in a slot machined spray passed across the grid, the individualin each blade tip, and were retained by a droplets were clearly defined and the diam-combination of a wedge fit of the sample eter could be determined by comparing themount and small diameter pins through the droplets with the grid in the background. Asample. (See Figure 6 and 7.) 0.030 inch ID needle was found to produce a2 mm droplet consistently. Droplet size

The circular spray rig system as designed could be varied by using different ID sizeby Cornell contained 16 modified spray needles.nozzles around the circumference of the ring.These nozzles were obtained commercially. The desired water flow rate for this testThe rig was later modified to hold 32 hypo- was 1 in./hr; the flow actually exceeded thisdermic needles, 1-1/4 inches long and 0.030 rate but the exact amount of excess is notinch inside diameter, to provide the proper known. Measurements indicated that the flowdroplet size. rates ranged from excessive to cloudburst.

All tests run on this spray rig were of theSixteen solenoid valves (2 needles per comparative type and the time to failure undervalve) were installed upstream of the hypo- test conditions is not the same as actualdermic needles to provide accurate off-on service time.control of the water flow. (See Figure 4.)These solenoid valves were connected to an Before a test was run the water lines,electric timer and a common switch which sp r e edles t ers an the fr amemeasured water spray "on" time. Pressure spray needles, filters, and spray framemteasurd water ospray "on"eme. Pessdusted were cleaned and flushed to remove sedi-at each pair of spray needles was adjusted ment. Each day the hypodermic needles wereby a small restriction type valve, cleaned and adjusted for spray impingement.

Rain intensities shown in Table I ire Line water pressure range from 25 to 30specified in AFSCM 80-1, Handbook of In- psig. Pressure for individual needle pairsstructions for Aircraft Designers (HIAD). was adjustable at the spray frame. The spray

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SEG-TR-65-53

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frame, supported by two large steel "'A" observer was protected by a series of

frames, wa: poisitioned parallel to and ap- bends in the wall. Light was transmitted

prox.imately 30 inches before the plane to the transit by a series of mirrors and

of the test club. prisms. Two stroboscopes were mounte.below the blade to provide sufficient lightfor viewing the test, as shown In Figures

The 30,000 HP spray rig was equipped 4 and 5. The light was not adequate for

with a precision optical viewing system and taking movies through the transit, however,

a high-speed stroboscopic light which allowed so only still pictures were made of the spray

continuous viewing of the test club tips at passing over the sample. (See Figure 8.)any speed. While a test was being conducted, Synchronization of the strobe lights, relativean observer in the observation room below to the rotating test club, could be variedthe rig could wat'. the progress of a test during operation, allowing observation ofthrough a 20X t.- it and periscope. The alternate blades during any test run.

Figure 8. Club Tip, Sample and Wpter Spray Photographed Through the Transit

13

SEG-TR-65-53

SECTION III

TESTING PROCEDURES AND FINDINGS

The test program was divided into three but it also failed after 4 to 12 minutes ofphases -- 1. high speed, 2. variable speed, exposure. Typical failures of Stainless steeland 3. comparisom, tests. The test samples sanm ples are illustrated by Figure 12 and theywere considered to have failed when the appeared to fail from fatigue after the softbackup material, either wood or fabric, spruce back-up material deformed. Typicalshowed through the protective material cov- failure patterns of -109 Neoprene sheet andering enough for the observer to detect it precured Urethane sheet -111 are illustratedthrough the transit. by Figure 13.

The test materials were applied over After initial tests had shown that rapidspruce blocks shaped in accordance with failures were primarily due to deformationFigure 6. Early blocks did not have the of the soft spruce back-up material, newmolded plywood leading edge and presented blocks were constructed with a "hard" lead-a softer backing for the test sample. A ing edge, duplicating the construction usedsample consisted of a soft spruce block on the servo flap of the helicopter. Thiscovered with a sheet of pre-molded birch "hard" block consisted of the same spruceplywood. This was then covered with a core but covered with a 1/32 inch thick 3-plysheet of nylon rip-stop cloth and the pro- molded birch plywood leading edge. Thetective material was then sprayed, bonded, significance of this change is apparent fromor brushed over the nylon cloth. For exact Figure 14. The -103 curve represents theconstruction details of partictlar samples, "soft" block and the -115 curve representssee the Appendix. None of the materials the "hard" block - both were covered withwere aged prior to testing, the exact same neoprene. The difference

between the two curves is attributed to the1. HIGH SPEED TESTS (500 MPH) increased hardness of the backing for the

-115 sample.The tip speed selected for this part of

the program was 733 ft/sec (equivalent to Analysis of these high speed tests indicated500 mph) which was produced by a whirl rig that the test conditions were too severe andspeed of 700 rpm. Various Speeds vs Whirl unrealistic. The 500 mph tip speed is aboveRig RPM are shown in Figure 9. 500 mph is the speed of the advancing servo-flap whengenerally considered a standard for rain tests the helicopter is flying at its 105 knot redas most rain erosion studies in the pasthave line, and therefore would not be encounteredbeen conducted at this speed. in normal operation. The tests did, however,

serve to eliminate from further testingSamples -101 through -113 (see Appendix) several of the materials that had demon-

were tested at 733 ft/sec tip speed and the strated low time-to-failure.time to failure was noted. All of thesematerials were applied over the bare spruce 2. VARIABLE SPEED TESTSblocks and the results are shown plotted inFigure 10. All samples for this portion of the test were

backed by the 1/32 inch 3-ply birch ply-w-oodIn general, these high speed tests revealed leading edge. Test rig speeds were varied

that the materials failed within a very bhort from 465 rpm to 700 rpm, which are equivalenttime. One sample -.101 failed in less tha,% to servo-fiap speeds just slightly below hover10 seconds, and no material lasted lo.ger to above aircraft red line (105 knots), as shownthan 12-1/2 minutes. Samples -101 and -103 by Figure 9 The niajority of the test pointsafter only 4 seconds exposure to simulated were run at a servo-flap speec' correspondingrain are shown in Figure 11. Stainless steel to an approximate belicopter speed of 50 knots,-105 was expected to provide good protection 85 knots, and 105 knots. Only two points

14

SEG-TR-65-53

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Figure 11. Comparison of Neoprene Samples -101 and -103 TestedI atHigh Speed (500 mph)

17

SEG-TR-65-53

a. Sample -105, No. 6 - - Test Time 6 men. 44 sec.

b. Sample - 105 No. 3.- - Test Time 7 min. 25 sec,

Figure 12. Advaiiced State of Failure of Sample -105 Stainless Steel Testedat High Speed Ib00 mph)

18

Sample -109

Sample -1111

Test Time, 6 minutes 48 seconds

Figure 13. Comparisonl of Sample -109 Neoprene Sheet and Sample -111

Precured Urethane Sheet Tested at High Speed (500 mph)

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were run at speeds below hover tip speed and The nmode -f failure for both was for waterthese were o.. Samples -103 and -129. to enter initially formed nin holes in the

material and then for the materia, to separateThe significance of varying the test speed and peel from the nylon rip-stop-cloth.

is clearly shown in Figures 14 and 15. TIhecurve of a materia! which shifts to the right The mode of failure of the precuredwith increasing tirae-to-failure, and upward neoprene sheet -119 was such that the leadingwith increasing speed indicates a material edge would erode away evenly. If the erosionwhich provides greater resistance to rain were allowed to continue to total failure, theerosion. Results shown in Figure 15 indicate neoprene would completely erode along thegood correlation of the various neoprene center and peel from the wood into two parts.samples with the exception of sample -1.23,Sample -123 was a composite constructionof The time-to-failure for the -123 materialcloth impregnated with neoprene, and cannot was the best for all the neoprene types tested;truly be compared to pure neoprene tapes or however, its mode of failure was such thatsheets. it would create a severe airflow disturbance

if it were to fail in flight. Figure 19 il-A significant point is that (excluding the lustrates this type of failure for amultilayer

-129 material) no material tested at bover tip cloth-neoprene impregnated material.

speed failed after one hour of testing. Examin- Sample -129 (Figure 20) was the poorestation of Figures 14 and 15 reveals that for material tested, with failures occuringbelowmost of the curves a definite boundary or the hover flap speed as shown by Figure 21.area exists, above which failures occur The material was very brittle and portionsrapidly and below which the time-to-failure of it would chip and crack off after onlyincreases or may never fail if the speed is short periods of exposure to water.low enough. This might be ccnsidered anal-ogous to the alternating load endurance limitaad "run out" for metals. The failure curves Figure 21 shows the extremes of protectionare shaped very similar to classical S-N offered by the various materials tested.curves. Thus, use of these materials on an Depending on the speed of operation required,actual aircraft at hover flap speeds should a choice of several materials is available.not result in failures in a reasonable period For an impact velocity of 300 mph, a neopreneof time. As the speed of operation increases, material would be sufficient, for an inter-the time-to-failure decreases proportional to mediate speed of 400 mph one would select athe damage done. A study of Figures 14, 15 polyurethane material and for extended oper-and 21 emphasize this point very well. ation around 500 mph, Stainless Steel would

be required.The fact that some materials provide

better protection at high speeds while othersare ettr a lowspeds s ilustate by Although Stainless Steel -117 (shown inare better at low speeds is illustrated by Figure 17) was the best material tested,

Figure 15. Allowing for obvious scatter, there it was not recommended for this applicationis a strong trend for certain materials such because of its known susceptibility to sandas the -115 material to be better at higher abrasion when applied in very thin sheetsspeeds, although the curve crosses all the (0.005 in.). Figure 14 shows that the thirdothers and is the worst at low speeds. Stainless sample had not failed when the test

was stopped after 1 hour 30 minutes.A comparison of Figures 2 and 16 shows

the similarity and degree of duplication of Polyurethane -131 was second only tothe test sample failures to actual service stainless steel in providing resistance toencountered failures of the -115 material, rain erosion. Figure 14 shows the

22

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Run 39: 650 rpm, Run 43: 550 rpn.,

5 min. 16 sec. 26 min. 58 sec.

Run 40: 603 rpm, Run 44: 525 rpm,

0 min. 19 sec. 30 mrin. 35 sec.

Run 42: 575 rpm, Run 45: 490 rpm,

19 mrin. 26 sec. 51 min. 30 sec.

Figure 18. Precured Neoprene Sheet With Plywood Backing, Sample -119,

Tested at Various RPM

25

Run 57: 550 rpm, Run 54.ý 650 rpm,47 min, 23 sec, 10 min, 5 sec,

Run 5. 575rpnRun 58: 535 rpm,30 min 18 sec.4 m 9sc

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Figure 19. Cloth impregnated with Neoprene, Hard Backing, Sample -123,Tested at Various RPM

26

SEG-TR-65-53

Run 63: 604 rpm, Run 75: 465 rpm,2 min, 49 sec. 40 min. 10 sec.

Run 69: 550 rpin, Rt.n 76: 525 rpm,1 mini. 39 sec., 3 min 8 soc.

Run 70: 500 rpm, Run 77: 575 rpm,12 min. 58 sec. 1 min. 0 sec,

Figure 20. Tradename Material on Plywood Backing, Sample -129, Testedat Various RPM

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c. Initial Failure650 rpm, 11 min. 49 so.

d. Failure After AdditionalRun of 30 Minutes Ot 603

Figure 22. Test of Polyurethane Sheet Material. Sample -131, After Initial Failure

29

SEG-TR-65-53

.143T

-131T

a, Run 78: 650 rpm, Sample -131T failed after19 min. 32 sec,und Sample -143T after11 min. 49 sec.

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Figure 23. Comparison of Clear and Impregnated Polyurethane,Samples -131T and -143T

30

SEG-TR-65-53

results for the -131 material, and Figure 21 The difference in the results for theindicates the results for two -131 samples two samples when comparison tested (onerun an additional 30 minutes at 603 rpm. Pre- sample on each tip of the 3ame test club)viously these samples were considered failed is shown by the curves of Figure 14. Figureafter exposure at 650 and 635 rpm. Thus, it 23 shows the physical deterioration to bothcan be seen that continued exposure of the samples after equal exposure times andmaterial after it has initially failed does various tip speeds. The amount of deterlora-not cause rapid deterioration of the coating. tion was slight for both samples, althoughComparison photographs of these samples are the damage to the carbon impregnated -143Tshown in Figure 22. The outstanding resist- material waq noticeably greater. (Actualance of this material warranted further deterioration of the -131T samples is notstudy and testing and a series of comparison apparent in the photographs because of thetests of various polyurethane materials was transparency of the clear polyurethane).begun. Both materials, however, exhibited outstand-

ing resistance to rain erosion under these3. COMPARISON TESTS test conditions.

The manufacturer believed that the clear-131migh ag rapdly hen Two additional samples were fabricatedpolyurethane -131to evaluate the effect of rip-stop clothexposed to ultraviolet radiation (sunlight) on the material bond strength. Tests onas no experience was available for this on im ated polyureth. Tesam-formulation. Impregnating the polyurethane carbon impregnated polyurethane-125 sam-with carbon would reduce ,',e possibility of ples bonded over rip-stop cloth and carbonthis deterioration from sunlight but woud impregnated polyurethane -127 s amp1 e sbonded directly to the birch plywood were notalso degrade its resistance to rain erosion, conducted at the time the equipment wasTwo additional sample configurations werefabricated, both of which were optimized for destroyed.weight by being tapered (suffix T for tapered)from leading edge to trailing edge. Cne of As a result of the comparison tests ofthese samples was clear polyurethane -131T the -131T and -143T polyurethane, protectiveand the other was carbon impregnated poly- strips of -143T material shaped as shown inurethane -143T. The maximum leading edge Figure 24 were recommended for installati onthickness was reduced from the original -131 on the leading edges of all HH-43B/F hel-thickness (0.045 inch) to 0.038 inch. icopter servo flaps.

31

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SECTION IV

CONCLUSIONS

1. TEST RESULTS of that material at another speed; some ofthese materials were tested at speeds of

a. The Sample -131 polyurethane ma- 500 mph but were to be used at speedsterial was the best one for the specific ap- considerably lower than this (in the rangeplication of those tested, of 400 mph). The curves may cross as the

test speed is lowered, such as occursb. Due to the little degradation in re- for Samples -115 and -135, and -115 and

sistance caused by carbon impregnation and -119, as shown by Figure 15 at 12-1/2 minutesthe unknown effect of ultraviolet radiation and 20 minutes, respectively. Thus, a ma-(sun light), the Sasmple -143T material taper- terial entirely adequate when used at oneed from leading to trailing edge was re- speed may be unsatisfactory when usedcommended, at a different speed. For example, in a

high speed application of approximately 460c. The Sample -101 material is not mph, Sample -135 would be superior and

adequate and the Sample -103 (sprayed Sample -115 would not be competitive; atneoprene presently used on servo flaps) 350 mph, however, both materials wouldis at best marginal. Had the Sample -103 provide essentially the same protection andbeen applied to the bare wood instead of the selection could be based on economics.over nylon rip-stop cloth, a better bondprobably would have been achieved and thetendency for the material to peel awayafter it was initially daynaged would havebeen reduced. The resis.ance of the various a. The water flow rate for these testsneoprenes (,vhether tape or spray) was very was excessive but the results are validnearly the same at lower speeds. Several on a comparative basis. There is no wayneoprenes appeared to be better than the at present to correlate these times-to-others at the higher speedcs. The scatter bhad, failure with those encountered on the air-as shown by Figure 15, points out the craft in actual service. A method to cor-generally good correlation of the test results, relate test time and service time to failure

would be very useful for future tests.d. The resistance of a material to rain

erosion is a function of the hardness ofthe backup material. A given material ap- b. The spray rig should be moved atplied over a soft structure will fail faster least 15 feet from the plane of the testthan the same material applied over a hard club and the water pressure should be main-structur,. tained at 35-40 psi. This will increase the

area of coverage for each needle and wille. Testing a material at an off-design provide a uiore even distribution of water

speed in no way determines the adequacy droplets.

33

SE~G-TR-h;5-53

SECTION V

RECOMMENDATIONS

As a result of these tests, recommendations sheet tapered from 0.038 inch leading edge towere made to the HlI-43B/FSystem Program 0.003 inch trailing edge) as a servo-flapOffice to utilize the -143T material (a fabric- leading-edge protective material.b ac k e d carbon-impregnated polyurethane

34

SEG-TR-65-53

APPENDIX

DESCRIPT'OP OF -E'T I AM PLE-

The critical condition for these tests was -115 Same as -103 except basic block istotalweightof the protective material, since spruce faced with 1/32 in. thickthe weight of the material applied to the flaps 3-ply birch plywood covered withmust be limited to avoid aerodynamic in- nylon rip-stop cloth, spec MIL-stability. Therefore, the weight of the various C-7070, Type Isamples was held essentially constant by -117 Same as -105 except Lasic block isvarying 'hu thickness. This accounts for the spruce faced with 1/32 in. thickrange in thicknesses from 0.005 inch for 3-ply birch plywood over layer ofstainless steel to 0.050 for the polyurethanes. No. 120 glass fabricThe maximum weight of leading edge material -119 Same as -109 except basic block isfor which the aircraft manufacturer had sub- spruce faced with 1/32 in. thick,stantiating flight test data was 0.2 pounds 3-ply birch plywood covered withfor the 33.4-inch flap. nylon rip-stop cloth, spec MIL-C-

7070, Type I

The materials tested in this test program -121 Same as -111 except basic blockwere as follows: is spruce faced with 1/32 in. thick,

3-ply birch plywood covered withCode No. Material nylon rip-stop cloth, spec MIL-C-

7070, Type I-101 Sprayed neoprene, 0.005-0.010 thick -123 Neoprene-coated fabric to a thick-

over spruce core coveredwith nylon ness of 0.040 ±0.005 inch at leadingrip-stop cloth, spec MIL-C-7070, edge, and tapering to 0.003 - 0.010Type I at edges (Neoprene impregnated

-103 Sprayed neoprene, 0.025-0.030 thick 0.005 Dacron fabric built up inover spruce core coveredwith nylon layers) over spruce block faced," ithrip-stop cloth, spec MIL-C-7070, 1/32 in thick, 3-ply birch plywoodType I covered with nylon rip-stop cloth,

-105 Stainless steel, 1/4-hard0.005 thick spec MIL-C-7070, Type Iover spruce core coveredwith nylon -125* Polyurethane boot (0.030 in.) overrip-stop cloth, spec MIL-C-7070, spruce core faced with 1/32 in.Type I thick, 3-ply birch plywood, over

-107 Brush-on urethane 0.020-0.030 thick nylon rip-stop cloth, spec MIL-C-over spruce core covered with nylon 7070, Type Irip-stop cloth, spec MIL-C-7070, -127* Polyrethane boot (0.030 in.) overType I spruce core faced with 1/32 in.

-109 P r e c u red neoprene sheet 0.025- thick, 3-ply birch plywood (without0.030 thick at leading edge, tapering rip-stop cloth - bonded to bare wood)to 0.003-0.010 at edges, over spruce -129 "Tradename" material, 0.008core covered with nylon rip-stop ±0.002 in. thick, brushed on overcloth, spec MIL-C-7070, Type I spruce block faced with 1/32 in.

-111 Precured urethane sheet 1/32 thick thick, 3-ply birch plywoodover spruce core coveredwith nylon -131 Polyurethane sheet, 0.045 - 0.050rip-stop cloth, spec MIL-C-7070, in. thick, fabric backed over spruceType I block faced with 1/32 in. 3-ply

-113 Polyethlene tape over spruce core birch plywoodcovered with nylon rip-stop cloth, -131T Same as -131 but tapered fromspec MIL-C-7070, Type I 0.038 in. at leading edge to 0.003

in. at trailing edge*Note - samples not yet tested due to destruction of test equipment.

35

SEG-TR-65-53

-133 Neoprene sheet, 0.040 - 0.043 in. -139 Neoprene sheet, 0.035 in. thickoverthick, over spruce block faced with wood block coated with 1/32 in.1/32 in. 3-ply birch plywood. fiberglass

-135 Neoprene sheet, 0.938 - 0.040 in. -14i Brush-on urethane over wood blockthick, fabric-backed, over spruce coated with 1/32 in. fiberglassblock faced with 1/32 in. 3-ply -143T Same as sample -131T polyurethanebirch plywood except carbon impregnated

-137 Stainless steel, 0.013 in. thick overwood block coated with 1/32 in.fiberglass

36

SEG-lR-65-53

REFERENCES

i. Coating System, Elastomeric, Thermally 4. ARDCM-80-1, HIAD, I Aprii i961, PartReflective Rain Erosion Resistant and Anti- A, Chapter 8, "Environmental Critc.ria,"static, for Aircraft and Missile Exterior and Part C, Chapter 6, Page C6-32, TabblePlastic Parts, Military Specification MIL- C6-3, "Rain Intensities."C-007439C (USAF), 9 December 1959.

5. Helicopter Rotor Blade Erosion Pro-2. Climatic Extremes for Military Equip- tective Materials; TCREC Technical Reportment, MIL-STD-210A, 2 August 1957. 62-111, Prepared by the Vertol Division -f

the Boeing Company, December 1962.3. Warden, Howard R., Rain ErosionTestsof Protective Coatings, Flight and EngineeringTest Report, ASD, WPAFB, Ohio, lOJanuary1963.

37

Secunty Clax,-iticationDOCUMAENT CONTROL DATA - R&D

(S e..eurui *aI.a catlorn of 1i111 bodY' of abotect and ,ndoa tng mirotet, on must b. entered *-Son the overall report tL claoslloef )

SOqCINA TING ArTI"VIIY (Corp rete author) T28 ACPORT S% Cu.TY C LASSrFICAT'O0.

Systems Engineering Group K RUP i

Wright-Patterson Air Force Base, Ohio

RLEPORT TITLE

EVALUATION OF RAIN-EROSION-RESISTANT MATERIALS TO PROTECT THE

HH-43B/F HELICOPTER R101OR

4 DESCRIPTIVE NOTES (Tr," at topodr and Incleu,'- dates)

AUTHOR(S) (Laot n 10..l,/, nais ,. tnlm i .a)

Chopin, Matthew W.

s R'POMNI DATE I7& TOTAIL 6O OF OASES T7b ma op Rtvs

Aug_________ ,45 1 5Sa CONTRACT OR GRA&r NO| a0 ORICINATON'S REPORT Nt.MUIERIS)

b PROJECT NO 976Z SEG-TR-65-53

Ob oTR C NO(S) (An/ other numbo,. that mny be assigneddit. RIWfl

10 AVA IL AlIL 'TY,LIMI CATION K.*)TI",S

Distribution of this docunment is unilmited.

11 SUPPLEMENTAR'I NCTES 12 SPCOSORING MILtTAPY ACTIVITY

Systems Engineering GroupWright- Patterson Air Force Base, Ohio

'3 Ab.5QACT

This report describes the tests of various materials to determine a s'itable protectlv

covering for Tbe HH-43B/F helicopter servo-flap leading edge when operating in ram

Nineteen matcrials were tested and compared on a rain erosion spray rig in the electricmotor whirl sttand facility at WPAFB Ohio. Impact velocity varied from 330 to 7b0 ft persecond.

A description of the facility, test procedures, results and recommendations is presented.Photographs of the s- -ay rig and teot specimens are also included.

DD e 1473 UNCLASSIFIEDSecunty Classzfu ation

UNCLASSIFIEDSecurity Ciassification _______r14 L.INK A ] LINK 8 LINK C

_____KEY_ -OC COE1-OLE fWT MOt.LL W?

Protective Materials

Rain Erosion Tests

HH-43b Helicopter

Helicopter Rotor Blade

INSTRUCTIONS

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