Chaplin, Harvey R.

Johnson, Arthur E.

English

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REPORT 1546AERO REPORT39080 02754 3971NAVYTHE DAVID W. TAYLORAERODYNAMICS LAMODELBORATORYWASHINGTON 7, D.C.RESULTS OF GEM III TETHERED TESTSbyArthur E. Johnson and Harvey R.August 1961V393.R46F-1012DEPARTMENTBASINChaplinI rl -- v r I __11111111imp.m.11111111i1SYMBOLSS base area in square feet, measured to outer edge of nozzleh height above surface, (in feet, unless indicated otherwise)measured at center of base to plane containing the loweredges of the nozzleC perimeter of the base in feet, measured at outer edge ofnozzleb length of base in feet measured to outer edge of nozzlea width of base in feet measured to outer edge of nozzle13 nominal nozzle control vane angle in degreesPe effective tangential jet deflection in degreesPt total pressure measured in plenum, pounds per square footQ airflow rate, cubic feet per secondp mass density of air in slugs per cubic footroll angle in degreesa pitch angle in degreesNf fan rpm, or percent (nominal) of rated fan rpmT propulsive thrust in poundsL total lift, or gross weight, in poundsM pitching moment in pound-feetS rolling moment in pound-feetN yawing moment in pound-feetM figure of meritM 1 L 53.7 121; 550 EP 53.7 E S-- 0Y11HINW1,111~---- ------- --- --- ----~  --- ~~r~-cn ranuuna~ ~SYMBOLS (Concluded)fP total shaft power delivered by engines (horsepower)qaoh apparent over-all hovering efficiencyS. total effective nozzle area with control vanes neutral,in square feetA augmentation factor with control vanes neutralq. jet dynamic pressure at nozzle exit in pounds per squareJ footpint internal efficiencyl~eL~lll 113 ~I I I i I I ~s~Report 1546Aero Report 1012AERODYNAMICS LABORATORYDAVID TAYLOR MODEL BASINUNITED STATES NAVYWASHINGTON, D. C.RESULTS OF GEM III TETHERED TESTSbyArthur E. Johnson and Harvey R. ChaplinSUMMARYStatic test results on hovering performance, pitch androll stability, and control effectiveness are presented. Thevehicle hovered at a height of 14 inches with a gross weightof 1850 pounds. Both pitch and roll stability were practicallyneutral at this height. (Weak stability was measured at lowerheights.) Propulsion, braking, and steering controls, accom-plished by means of variable-camber vanes in the main nozzles,were partially effective. Pitch and roll controls, accomplishedby a system of four dump valves bleeding air from the cushion,were completely ineffective. Some data were obtained whichindicated that a simple jet spoiler installation could providesatisfactory pitch and roll control.INTRODUCTIONGEM III is a one-ton experimental manned ground effectmachine constructed for the Marine Corps by National ResearchAssociates, Incorporated. The subject tests were undertakenat the request of the Marine Corps (Reference 1) to provide__  _ 111 -2-static data on the hovering performance, stability and controlof GEM III, preparatory to flight evaluation of the machine byUSMC. Reference 2 provided Bureau of Weapons endorsement ofthis request.TEST RIG AND APPARATUSPrincipal dimensions of GEM III are given in Figure 1.GEM III is an integrated-air-curtain type machine. It is poweredby two nacelle units, each with a Solar YT62-S-2 engine driving aJoy 38-17 1/2 fan through a centrifugal clutch, belt and pulleys,and a shaft. A system of cascade vanes guides the air through a90' bend within the nacelle, after which it is dumped into thehull at a mean velocity of slightly less than half the final jet-exhaust velocity. Controls are engine throttles, aircraft-typecontrol wheel which turns for steering (differential deflectionof variable-camber nozzle control vanes) and push/pulls for pro-pulsion/braking (collective deflection of vanes), four aircraft-type trim crank devices which actuate the four dump valves forattitude trim, and brake pedal which actuates hydraulic brakeson the main wheels. The machine was tested as delivered fromthe manufacturer, except for the addition of the half-roundfairings noted in section A-A of Figure 1.Photographs of the vehicle in its static test rig arepresented in Figure 2. There was a system of six nominallyhorizontal cables, two running to each side, one forward andone aft, which prevented the vehicle from moving in a horizontalplane. The aft and starboard cables ran over pulleys to weightswhich held them taut; the forward and port cables ran overpulleys to strain-gage dynamometers. Also, there was a systemof four vertical cables, running over pulleys to loading pans,by means of which known pitching and rolling moments could be"s~ II II I Il I I I I I "SE-3-imposed on the vehicle. The vehicle's height and attitudewere measured by means of graduated rods and pointers attachedto the vertical cable system. From the strain-gage readings,and the known weights and vehicle attitude, it was possible tocalculate total thrust, side force, and yawing moment, as wellas the secondary interaction of the horizontal cable systemon lift, pitching moment, and rolling moment.Static pressure orifices were installed in the nacelle andplenum on each side of the vehicle, with tubes running to analcohol manometer. From the manometer readings, the airquantity flow and plenum pressure were calculated with theaid of calibration data from test-stand operation of an identicalnacelle (Reference 3).A temporary pilot's seat is visible in Figure 2 at thecenter of the top deck between the nacelles. Provisions weremade to permit all controls to be operated from this position.The vehicle was operated from this temporary seat during alltests, to minimize the danger of injury to the pilot in theevent of fan failure.TESTSAll tests were made with the effective weight of themachine near its normal gross weight of 1850 pounds. Theengine throttles were set in either the 100 percent rpm detentor the 87 percent rpm detent during all tests. The fan bladeswere set at the manufacturer's blade-angle index of -2 at alltimes, to be compatible with power available from the engine.Normally, all variables (dynamometer readings, manometer readings,loading-pan weights, vertical cable movements, and controlsettings) were recorded for each data point. During stabilityI--- ---I - IYII i-4-runs moments were applied to the vehicle through the verticalcables, and the resulting change in attitude was observed.During control runs, the control settings were varied with thevehicle attitude maintained constant, and the resulting changesin forces and moments were observed. No performance runs,as such, were made; performance data were obtained duringstability and control runs.RESULTS AND DISCUSSIONThe following results were obtained:1. Performance - The operating height attained by thevehicle at 100 percent and at 87 percent rpm at various pitchand roll angles is presented in Figure 3. (Note that heightis measured to the center of the base, the base plane beingthe plane containing the lower edges of the nozzles. Thus,the vehicle is at a height of three inches when it rests,power-off, on its wheels.) An indication of the shaft horse-power is provided by Figure 4, based-on data from Reference 3.The effective exhaust area of the vehicle in normal hoveringoperation is approximately seven square feet per nacelle,indicating, from Figure 4, a shaft power of 70 horsepower pernacelle at the -2 blade-setting index. The correspondingfigure of merit is approximately- . LL53.7 IP s1 1850 185053.7 M140 150M - 0.86-r~aL II I II r II II ii I I I Y".-5-The size/height ratio isS 150 2.66hC 1412 (48.3)which gives an apparent over-all hovering efficiency ofaoh = - 0.32hCThis is comparable to the performance of other early-generationGEM's. In Figure 5, on a graph of plenum pressure versus air-flow quantity, is presented a network of nacelle characteristiclines (from Reference 3) and vehicle air-requirement lines.The vehicle air requirements were estimated from semi-empirical theory (Reference 4) as follows:q L2Sj cos 2 e Ajo e ot qj +2S AQ - 29 q. S .jo CosJ Jo eAn appropriate value for S. was estimated to be 16.0 squareofeet. The f llowing estimat s were used for Afeet. The following estimates were used for A :O-- IY IYIIIIuc~~vrr~~-t-~INII 1 , ll 1 14 11LI I 610 111 0IIIIIYY IMiIM ilU kII -6-h Ainches o6 7.378 6.1710 5.3212 4.6314 4.10For heights below 6 inches, the curves were arbitrarily fairedLto the point pt = L, Q = O, at h = 0. Superimposed on thisnetwork are measured data points for (a) 100 percent rpm, controlvanes neutral (b)100 percent rpm, control vanes fully deflected,and (c) 87 percent rpm, control vanes neutral. The agreementindicates that the combination of semi-empirical theory andnacelle test data can be used for analyses of GEM III withconfidence. The 19.3 psf, 880 cfs data point in Figure 5 for100 percent rpm, control vanes neutral, is equivalent to19.3 (880) = 30.9 air horsepower550per nacelle, giving an internal efficiency of30.9 .44int 70These efficiency values correspond very closely to measuredvalues for DTMB Model 472 (Reference 5), which has a similarnacelle design and approximately the same ratio of nozzle areato fan area.2. Stability - The results of pitch and roll stabilitymeasurements are presented in Figures 6 and 7. (All momentsare referred to the center-of-gravity location indicated inFigure 1, which would be the actual center of gravity for theROOM - I I II I II I Y-7-vehicle operating with the pilot in the cockpit and with half-filled fuel tenks.) To experimental accuracy (approximately±50 pound-feet), the vehicle had neutral pitch and roll stabilityat 100 percent rpm (h = 14 inches) and had positive roll stabilityat 87 percent rpm (h = 10 inches). Pitch stability was notmeasured at 87 percent rpm, but it may be safely assumed thatthe vehicle also had positive pitch stability at this condition.The rather weak stability characteristics of GEM III may beattributed, at least in part, to the fact that the stabilizingnozzles are fed from the main plenum, and exhaust to the aircushion, which, because of the rather thick primary nozzles, isat a gage static pressure of more than half the plenum pressure.3. Propulsion, Braking, and Steering Control - The variable-camber vanes in the main nozzle (Figures 1 and 2) were intendedto be deflected collectively (i.e., in the same direction onthe port and starboard sides) for propulsion and braking controland to be deflected differentially (i.e., in one direction onthe port side, in the opposite direction on the starboard side)for yawing-moment control (steering). The effectiveness ofthese vanes is shown in Figures 8 and 9. The propulsive thrustincludes an estimated 24 pounds of engine exhaust thrust. Theresponse to either collective or differential deflection islinear up to about one-third of the maximum deflection, and thenbends over sharply at higher deflections as the jet flow separatesfrom the convex side of the vanes. This behavior is due toinsufficient vane solidity and to leakage past the edges of thevanes. The effective solidity of the vanes is substantiallylower than the geometric solidity, due to the fact that only aportion of the vane is capable of being deflected (Figure 1).The control effectiveness shown in Figures 8 and 9 corresponds- - IYil-8-roughly to a maximum jet deflection angle of +200. The vanesystem should be capable of jet deflections of perhaps +45* ,if the solidity were increased sufficiently to retard flowseparation, and if leakage past the edges of the vanes wereprevented.4. Pitch and Roll Control - The four dump valves indicatedin Figure 1 were supposed to provide pitch and roll control.For example, upon opening the front dump valve, allowing airto escape from the front part of the cushion, a reduction ofbase pressure was supposed to occur at the front of the vehicle,resulting in a nose-down pitching moment. This system was noteffective. Within the accuracy to which moments could bemeasured (approximately ±50 pound-feet), no change in pitchingor rolling moment was produced by opening or closing the valves,singly or in combination. (Tests were made at 100 percent rpm,control vanes neutral.) Rough airflow measurements indicatedan air escape rate of approximately 70 cubic feet per secondthrough a single fully-opened valve, or approximately four percentof the total airflow through the nozzles. This produced a slightdecrease of height; the operating height was reduced from 14inches to about 12 inches when all four valves were fully opened.5. Simulated Jet Spoiler for Attitude Control - In viewof the inadequacy of the dump valve system for pitch and rollcontrol, an effort was made to obtain an indication of theeffectiveness of a simple jet-spoiler control system whichcould be installed on the vehicle without major modifications.This was done by sealing off sections of the main nozzle withmasking tape, to simulate the effect of a fully-deflectedjet spoiler, and measuring the resulting change in rolling momentand operating height. The results are presented in Figure 10,where maximum effectiveness of a roll-control spoiler is given~a~aa III1IIII 1 II I I I ~-9-as a function of spoiler length. The results indicate thatthis form of attitude control could be highly effective, andthat a control deflection would not produce a serious loss ofoperating height.GENERAL COMMENTSThe following observations may be made concerning thebehavior of the vehicle during the tests:1. Reliability - The accumulated total time of actualoperation of the vehicle was less than ten hours. Accordingly,no definite conclusions on reliability can be drawn. The testexperience was encouraging to the extent that no major structuralor mechanical failures of any kind occurred. One malfunctiondid occur on each engine. These were rather costly in termsof time lost, due to delays in obtaining technical service andspare parts, but were quite minor in nature.2. Steadiness - The vehicle experienced a continual smallrandom disturbance of its roll and heave modes, apparentlystemming from minute fluctuations in engine rpm. This mighthave no serious significance in terms of normal operation ofthe vehicle, but could be annoying to the pilot. During thetests, these disturbances constituted an obstacle to obtainingaccurate force and moment readings, and were responsible inlarge part for the scatter apparent in the data. The rolldisturbance could probably be alleviated by providing openingsthrough the center bulkhead, which would tend to equalize thepressure in the port and starboard plenums.RECOMMENDATIONSThe following recommendations are based on the test results:1. The following modifications to the vehicle are consideredessential:__.._1 1111-10-a. Modify the variable-camber control vane installationto increase the range of tangential jet deflections.b. Install a jet-spoiler pitch-control and roll-controlsystem on the vehicle.c. Install cockpit controls which give the pilotcontinuous control of pitch, roll and steering, and selectivecontrol of thrust and braking.2. Additional tests should be performed on the statictest rig, following these modifications, to evaluate the changesin vehicle characteristics.3. No effort should be made to operate GEM III in freeflight in its present condition.Aerodynamics LaboratoryDavid Taylor Model BasinWashington, D. C.August 1961REFERENCES1. USMC P. O. No. 1-0018 of 7 Dec 1960.2. BUWEPS Itr RAAD-342:EE of 27 Dec 1960.3. Murphy, Richard D. Subject: Test Stand Investigation ofa GEM III Nacelle Unit. (Data to be reported later)4. Chaplin, Harvey R. Design Study of a 29-Foot GEM. Wash.,Apr 1961. 54 1. incl. illus. (David Taylor Model Basin.Rpt. 1521. Aero Rpt. 999)5. Burgan, Elmer T. Subject: Wind Tunnel Tests of GEM Model472. (Data to be reported later)'-*n.r~--~ --n~- rLrrdlllbi~~ar r-~.~o~ - ~~_1___~~~_____~_~_~_________~~~~_______Joy Mfg. Co.38-171/2 Fans17'0"Fixed PortionVariable-ComberVanes" Dia Half-RoundFairings Added atDTMB Before TestsSection A-Ab= 20' 0"Variable- ComberVanes- -Oa=10'0"s\\At MaximumDeflectionNote: All Vanes6.5" ApartS= 150 Sq. Ft.C= 48'4"Figure I - Principal Dimensions and General Arrangement of GEM IAERO 1012PSD-304, 142(a) Three-Quarter Front View(Note: Inlet screens and cockpit armor werenot present during tests)PSD - 304,141(b) Three-Quarter Rear ViewFigure 2 - Model and Test Set-Up Photograpihs30 June 1961* I- I7 , --- , ~, I -- I--12-AERO 1012PSD-303,595(c) View Showing Temporary Pilot's Seat andRestraining CablesPSD-303,599(d) Pitch and Roll InstrumentationFigure 2 (Continued)26 April 1961_ ~I I ____I_-13-AERO 1012PSD-303,591(e) DynamometerPSD-303,59226 April 1961(f) Loading Pan for Horizontal CableFigure 2 (Continued)__-14-AERO 1012PSD-303,594(g) View Showing Interior of HullPSD-303,596(h) View of Vanes Looking Down ThroughNozzle From Plenum ChamberFigure 2 (Concluded)26 April 1961-15-AERO 1012InCCS5-16--10 -5 0 5/ in degrees(a) Effect of Roll Angle15I0(00-CC€.)O-5 0ca in degrees(b) Effect of Pitch AngleFigure 3 - Hover HeightBWV 17 Apr 1961100% rpm--u-l I I III I I I IAERO 101200o.oI(r0oSu)9'JwIFigure 4- Shaft Horsepower Required by OneNacelle for Several Blade Angle IndexSettings. (From Reference 3)40 Experimental Data oSym Percent fe hNf in degrees in inches0 1OO 0 14O 87 0 106 100 20 12NoC 30 "Figure 5- Mtching of Vehicle Airflow RequirementsBWV 200 400 600 800 1000 1200Q in ft3/sec(per Nacelle)Figure 5- Matching of Vehicle Airflow RequirementsBWV 17 Apr 1961 to Nacelle Characteristics__ I _ II ~l,.~nn**n - --- ---- ----~"sm~~nmnr~--i- ~- --17-00Blade AngleIndex480-26040 2 42002.0 4.0 6.0 8.0 10IEffective Exhaust Areaper Nacelle in sq. ft.AERO 10120.0100.005MLb- 0.005-o0.0105.0-18--2.5Figure 6a in degrees2.5- Pitch Stability0.0100.0050- 0.005O 100% rpm; h=14"O 87% rpm; h 10"a=0-01010 -5 0 5in degreesFigure 7- Roll StabilityBWV 17 Apr 1961100% rpmh 14"q=00 0 O0O 8 OO OO5.00 0 00 00OOa I II 1 1111 I -,--AERO 1012o0C0.c.s0i.--50-19-'-4 5 - 30 -15 0 15 30 45Pv in degreesFigure 8 - Propulsive Thrust Produced byCollective Vane Deflection0.04100% rpm0.03- 0.02Lb0.010 15 30 45Pv in degreesFigure 9 - Yawing Moment ProducedDifferential Vane DeflectionBWV 17 Apr 1961by- 11 1,1AI'lAERO 1012Length of Spoiler(a) Rolling Moment0.2Produced0.3 0.4Length of Spoilerb(b) Effect on Height10- Effect of a Spoiler Completely BlockingBWV 17Apr 1961a Section of the Side Nozzle0.505100% rpm-Ct OFigure0.5---- -------~  I I I I __ ill II rre-20-3 9080 02754 3971- I I -~_

Results of Gem III Tethered Tests

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Results of Gem III Tethered Tests

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