RM L56B09

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RESEARCH ME

A BRIEF INVESTIGATION OF TKE EFFECT O F WAVES

ON THE TAKE-OFF RESISTANCE O F A SEAPLANE

By Elmo J. Mottard

Langley Aeronautical Labor at or y Langley Field, Va.

CLASSIFIED DOCUMENT

THLS material contsins information affecting the National Defense of the U y e d State&--ithln the meaning of the espionage laws, Title 18, U.S.C., Secs. 793 and 794, the transmissionior &ela&n of which in any manner to an unautbrieed person is prohibited by law.

NATIONAL ADVIS RY COM M I TTEE FOR AER TICS

WASHINGTON April 24, 1956

https://ntrs.nasa.gov/search.jsp?R=19930089165 2018-05-13T17:32:11+00:00Z

R * NACA RM L56B09

NATIONAL ADVISORY COMMITllEE FOR AJCRONAUTICS

RESEARCH MEMORANDUM

A BRIEF INVESTIGATION OF TI-IE EFFECT OF WAVES

ON THF, !IME$OET' RESISTANCE OF A SEALANE

By Elmo J. Mottard

The resistance of a f a seaplaae with of 17 and a wing loading pounds per square smooth water and three w hts under various

a length-beam r f o o t w a s determined i n conditions of load,

speed, elevator sett ing, angle of dead r i se , and center-of-gravity posi- t ion. water and increased with wave height. The maximum increase due t o waves occurred a t speeds between hump speed and take-off. I n 6-foot waves the maximum increase w a s 63 percent at a speed equal t o 70 percent of getaway speed. r i s e angles of 20°, 40°, and 60'.

In general, the resistance w a s greater i n waves than i n smooth

The ef fec t of waves on resistance w a s about the same f o r dead-

INTRODUCTION

During take-off i n smooth water it is usually possible t o operate a seaplane at trims which give maximum l i f t -drag ra t ios a t all but the low-speed portion of the run. In waves, however, departures are made from these favorable trims during the uncontrollable motions which the seaplane goes through. During these motions the w a t e r load and wetted length-beam r a t i o may become very large; also, spray may become very high, wetting aerodynamic surfaces which would normally be dry. The extent t o which these factors increase the resistance is not known.

In order t o determine the order of magnitude of the resistance increase, exploratory t ank t e s t s were mad.e with a dynamic model of a possible seaplane design. included speed, elevator deflection, center-of -gravity location, load, angle of dead r i se , and wave height and length. used so as t o have the range of water speeds correspond with that of a high-speed water-based a i r c ra f t . required t o w i n t a i n speed w a s measured f o r various speeds up t o take-off i n waves corresponding t o 2, 4, and 6 f e e t high ful l -s ize .

The controlled variables of the investigation

A high wing loading w a s

The t o t a l average horizontal force

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SYMBOLS

Ti

7

'i

r

C r

R

CR

b

t

V

cV

- C

instantaneous trim (angle between forebody keel at s tep and horizontal reference l ine) , deg

)i d t

t average trim, , deg

instantaneous rise (distance of the point of the step above the s t a t i c w a t e r surface), f t

]ri d t

t average rise, 9 ft

average r i s e coefficient, - r b

average t o t a l resistance including air drag, l b

R average total-resistance coefficient, - wb 3

beam, f t

elapsed t i m e interval, sec

speed, f t / s ec

V speed coefficient, - llgb

mean aerodynamic chord, f t

0 gross-load coefficient,

gross load, l b

acceleration due t o gravity (32.2 ft/sec2)

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W

C

specific w e i g h t of water (63.4 lb/cu f t f o r these tests)

speed coefficient at getaway VG

MODEL AND APPARATUS

The basic model, which is shown i n figure l (a ) , w a s a 1/12-size dynamic model of a possible seaplane design having a gross load of 73,000 pounds, a beam of 5.84 feet , a wing loading of 120 pounds per square foot, a length-beam r a t i o of 13, and a dead-rise angle of 20'. This seaplane w a s similar t o that described i n reference 1 except tha t a s m a l l e r wing w a s used giving a w i n g l o a d i y 3 times as great. model w a s t es ted w i t h dead-rise angles of 40 (fig. l ( c ) ) . 120 pounds per square foot axe representative of current values f o r high- speed seaplane designs.

The (fig. l(b)) and 60'

The high length-beam r a t i o of 13 and the wing loading of

The apparatus, which i s shown schematically i n figure 2, permitted movement of the model i n the pitch, rise, and fore-and-aft directions. The mass of the moving pa.rts w a s kept at a minimum so tha t their ine r t i a

would be s m a l l , and the spring constant ( Force ) of the rubber spring Deflection

which w a s used t o simulate propeller thr;st w a s madk as s m a l l as w a s pract ical so that variations i n towing force during fore-and-aft movement of the model would be s m a l l . The tests were made using the Langley tank no. 1 towing carriage, which is described i n reference 2. making machine is described i n reference 3.

The wave-

PROCEDURF:

The basic conditions were: elevator deflection, 0'; speed coeffi- cient, 10.1 0 . 7 ~ ; center-of-gravity location, 0.36C; gross-load coef-

f ic ien t , 3.85; angle of dead r ise , 20°; wave length, 180 feet fu l l scale. Variations of each of these conditions were tes ted i n smooth water and i n waves corresponding t o 2, 4, and 6 f ee t high.

( v d

The model w a s f irst accelerated t o a constant speed; then the spring tension w a s adjusted t o keep the model within i t s permitted range of fore- and-aft movement. When t h i s equilibrium w a s established the speed, spring tension, trim, and rise were recorded. The spring tension w a s a d i rec t measure of resistance.

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The average resistance was obtained from the records by direct meas- urement without the need f o r any averaging process because the spring tension remained essent ia l ly constant. This w a s so because of the low spring constant, which resulted i n the application through the dynamometer of a nearly constant towing force; the fluctuations i n resistance caused by waves w e r e overcome mostly by the ine r t i a of the model. The trim and r ise , however, fluctuated greatly, and the averages of these were obtained

by dividing J& d t and l r d t (obtained by mechanical integration of

the records) by the elapsed t i m e t.

RESULTS AND DISCUSSION

The resu l t s are presented i n the form of plots defining the variation of average total-resistance coefficient, average trim, and average rise coefficients caused by changes i n speed, elevator deflection, wave height and length, center-of -gravity location, dead rise, and loading. These data are presented i n figures 3 t o 8.

The average t o t a l resistance, trim, and rise i n smooth water and i n w a v e s of various heights are shown plotted against speed coefficient i n figure 3 . A t low speeds the influence of the waves w a s s m a l l because the model followed the wave contours with l i t t l e angular or ver t ica l motion relat ive t o the water surface. A t the higher speeds the wave impacts and rebounds caused the average values of resistance, trim, and r i s e t o be higher than f o r smooth w a t e r and t o increase progressively w i t h wave height. The average rise coefficient i n waves continued t o increase t o getaway, but the greatest e f fec ts on average resistance coefficient and trim occurred at intermediate planing speeds w h e r e it w a s observed that the most severe impacts and rebounds occurred. of 10.1 (0.7CvG) the increase i n resistance due t o waves w a s 40 percent

f o r the 2-foot waves and 65 percent f o r the 6-foot waves. N e a r getaway speed the observed severity of the motions and the average resistance decreased because the model w a s nearly airborne and only contacted the wave crests occasionally. N e a r getaway speed, the resistance i n waves actually became s m a l l e r than i n smooth w a t e r , probably because afterbody wetting i n waves exists f o r only a short interval during each wave encounter.

A t a speed coefficient

The e f fec t of elevator deflection on average resistance, trim, and rise i n smooth w a t e r and i n waves at a speed coefficient 'of 10.1, which is i n the range of maximum wave effect , i s shown i n figure 4. water, porpoising occurred, causing the t e s t s t o be limited t o the ele- vator range from -15' t o 10'; but, i n waves, elevator sett ings beyond

I n smooth

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this range could be used without encountering divergent oscil lations. I n the larger waves the elevator range w a s limited by the violence of the wave impacts. A s i n the preceding figure, the waves generally increased the average resistance, trim, and rise. The elevator deflection corre- sponding t o trim f o r minimum resistance remained i n the range between 0' and 10' f o r smooth water and all the wave heights tested.

The e f fec t of height-length r a t i o on resistance f o r waves of various heights at a length of 180 feet and various lengths at a height of 6 feet i s shown i n figure 5. For the range of height-length r a t i o covered by these t e s t s (0.011 t o 0.033) independent variations of height and length resulted i n similar values of resistance f o r a given value of height- length ra t io . This result suggests the possibi l i ty tha t the resistance, l ike the ve r t i ca l accelerations, e tc . ( ref . 3 ) , are primarily a function of

i s of i n i s

the wave slope.

The effect of center-of -gravity location on the resistance i n waves Forward movement of the center shown i n figure 6 t o be rather s m a l l .

gravity increased the resistance slightly. I n this figure, and also figures 4 and 8, it i s noticeable that the resistance during porpoising usually about the same as i n waves.

I n figure 7 the resistance f o r 10.5 percent overload ( C h = 6.45) i s compared with the resistance f o r the normal load CA = 5.85). An addi- t i ona l curve formed by adding 10.5 percent t o the normal-load resistance i s also included. These curves indicate tha t no significant additional effect of the waves due t o overload is present.

(

The variation of resistance with dead rise f o r zero height-length r a t i o (smooth water) i n figure 8 appears peculiar i n tha t the resistance f o r 20' and 40' i s very nearly the same, whereas the resistance f o r 60' i s much higher. These resul ts , however, were checked by data (included i n the f igure) a t zero height-length r a t i o obtained from another investi- gation, as yet unpublished, using the same models. sis based upon available data on prismatic planing surfaces i n smooth water ( refs . 4, 5, 6, 7, and 8) the 20' and 40' dead-rise models were operating very near best trim, and the s m a l l resistance increase associated with the increased dead rise, shown i n figure 8, w a s caused by an increase i n the best-trim planing resistance. A s i m i l a r small increase i n best- tr im planing resistance occms with the dead-rise increase from 40' t o 60'; the remainder of the disproportionately large resistance increase which actually occurred seemed t o be attr ibutable t o a disadvantageous operating trim (considerably below best tr im) and insufficient clearance between the afterbody and the w a k e of the forebody. of as high a dead rise as 60' would require an overall design t o permit a higher forebody running trim and a larger depth of step.

According t o ~ u 1 analy-

Apparently e f f ic ien t u t i l i za t ion

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O f principal in te res t i n figure 8, however, i s the ef fec t of waves on resistance. The trend toward an increase i n resistance with wave height-length r a t i o i s similar f o r a l l three dead-rise angles.

SUMMARY OF RESULTS

For a model of a seaplane having a hu l l length-beam r a t i o of 15 and a wing loading of 120 pounds per square foot, the results of variations i n wave height along w i t h variations from a basic s e t of conditions elevator deflection, 0'; speed coefficient, 10.1 0.7C ; center-of- [ ( VG)

gravity location, 36C; gross-load coefficient, 5.85; angle of dead

rise, 20'; and wave length, 180 f e e t were as follows: I 1. The greatest effect of waves on the average resistance and trim

w a s found at intermediate planing speeds where the mopt severe impacts and rebounds occurred. For the model investigated, the increase i n resistance at a speed coefficient of 10.1 O.7C

6-foot waves.

w a s 65 percent i n ( *

2. The elevator deflection corresponding t o tr im f o r minimum res i s t - ance remained i n the range between 0' and 10' f o r smooth w a t e r and a l l wave heights tested.

3 . The increment i n resistance due t o waves w a s primarily a function of the wave height-length ra t io .

J

4. Variations i n the center-of-gravity position had only a small ef fec t on the resistance i n waves.

5. N o change i n the ef fec t of waves due t o increase i n gross load w a s found.

6. The trend toward increase i n resistance with increase i n height- length r a t i o w a s similar f o r dead-rise angles of 20°, 40°, and 60°.

Langley Aeronautical Laboratory, National Advisory Committee f o r Aeronautics,

Langley Field, Va., January 30, 1956.

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REFERENCES

1. Carter, Arthur W., and Haar, Marvin I.: Hydrodynamic €&talities of a Hypothetical Flying Boat With a Low-Drag H u l l Having a kngth-Beam Ratio of 15. NACA TN 1570, 1948.

2. Tmscott, Starr : The Enlarged N.A.C.A. Tank, and Some of Its Work. NACA TM 918, 1939.

3. Parkinson, John B.: NACA Model Investigations of Seaplanes i n Waves. NACA TN 3419, 1953.

4. Weinstein, Irving, and Kapryan, Walter J.: The High-speed Planing Characterist ics of a Rectangular F la t Plate Over a Wide Range of Trim and Wetted Length. NACA TN 2981, 1953.

5. Kapryan, Walter J., and Weinstein, Irving: The Planing Characterist ics of a Surface Having a Basic Angle of Dead R i s e of 20' and Horizontal Chine Flare. NACA TN 2804, 1952.

6. Chambliss, Derrill B., and Boyd, George M., Jr.: The Planing Char- ac t e r i s t i c s of Two V-Shaped Prismatic Surfaces Having Angles of Dead R i s e of 20' and 40'. NACA TN 2876, 1933.

7. Blanchard, Ulysse J.: a Basic Angle of Dead R i s e of 40° and Horizontal Chine Flare. TN 2842, 1952.

The Planing Characterist ics of a Surface Having NACA

8. Springston, George B., Jr., and Sayre, Clifford L., Jr.: The Planing Characterist ics of a V-Shaped Prismatic Surface With 50 Degrees Dead R i s e . Rep. 920, David W. Taylor Model Basin, N a v y Dept., Feb. 1933.

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(a ) Dead rise = 20°. L-83527 Figure 1.- The model with length-beam r a t i o of 15 and wing loading of

120 pounds per square foot.

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(b) Dead rise = 40'.

Figure 1. - Continued.

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L-84065

(c) Dead rise = 60 0 . L-84066

Figure 1.- Concluded.

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Wave height, f t smooth rater

0 2 4 6 8 10 12 14 16 Speed coefficient, Cv

Figure 3.- The effect of speed on resistance, t r i m , and r i s e i n smooth water and waves. 0.36~; angle of dead rise, 20°; gross-load coefficient, 7.85; wave length, 180 feet.

Elevator deflection, Oo; center-of -gravity location,

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- 30 -20 -10 0 10 20 Down Elevator deflection, deg 1 UP

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4.- The effect of elevator deflection on resistance, trim, and rise in smooth water and waves. Speed coefficient, 10.1, center-of-gravity location, 0 . 3 6 ~ ; angle of dead rise, 20'; gross-load coefficient, 5.85; wave length, 180 feet.

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.02 He ight-length ratio

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Figure 5.- The effect of wave height and length on resistance. Speed coefficient, 10.1; elevator deflection, oO; center-of-gravity loca- tion, 0.365 angle of dead rise, ZOO; gross-load coefficient, 5.85.

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3 .G

2.0

I

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Center-of-gravity location, percent 7?

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28 20

I ,- Porpoising

.02 Height-length ratio

Figure 6.- The effect of wave height on the resistance for three locations of the center of gravity. Speed coefficient, 10.1; elevator deflec- tion, Oo; angle of dead rise, 200; gross-load coefficient, 5.85; wave length, 180 feet.

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Figure 7.- The effect of wave height on resistance a t two load conditions. Speed coefficient, 10.1; elevator deflection, 0'; center-of -gravity location, 0.365; angle of dead rise, 20'; wave length, 180 feet.

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.02 He igh t - 1 e ng t h r a t i o

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Figure 8.- The effect of wave height on resistance f o r three dead-rise angles. of-gravity location, 0 . 3 6 ~ ; gross-load coefficient, 5.83; wave length, 180 feet.

Speed coefficient, 10.1; elevator deflection, 0'; center-

NACA - Langley Field. Va.