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USAAVLABS TECHNICAL REPORT 65-83

GEMINI ONE-TONAMPHIBIOUS OFF-HIGHWAYAIR-TRANSPORTABLE VEHICLE-

CONTINUATION OF PHASE I PROGRAM

I

i

February 1966,

..

U. S . A R M Y AVIATION MATERIEL L A B O R A T O R I E S

F O R T E U S T I S , VIRGINIA

CONTRACT DA 44-177-AMC-21(T)

HAWKER SIDDELEY CANADA LTD.

ENGINEERING DIVISION

TORONTO, ONTARIO

Dist r ibut ionof t h i s

document is unl imited.

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DisclaimersThe findings in this report are not to be construed as an official Depart-ment of the Army position, unless so designated by other authorizeddocuments.When Government drawings, specifications, or other data are used forany purpose other than in connection with a definitely related Governmentprocurement operation, the United States Government thereby incurs noresponsibility nor any obligation whatsoever; and the fact that theGovernment mnay have formulated, furnished, or in any way supplied thesaid drawings, specifications, or other data is not to be regarded byimplication or otherwise as in any manner licensing the holder or anyother Dersun or corporation, or conveying any rights or permission, tor'.anuiacture, use, or sell any patented invention that nmay in any way berelated thereto.Trade names cited in this report do not constitute an official indorsementor approval of the use of such commercial hardware or software.

Disposition InstructionsDestroy this report when it is no longer needed. Do not return it to theoriginator.

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DEPARTMENT OF TH E ARMYSNU S ARMY AVIATION MATERIEL LABORATORIESFORT EUSTIS VIRGINIA 23604

This report presents the results of the second phaseof an exploratory development program to investigateth e feasibility of an air cushion assist concept.The contents have been reviewed by th e U. S. ArmyAviation Materiel Laboratories and are consideredto be technically sound. The report is publishedfor the exchange of information and the stimulation ofideas.

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Task 1P125901A14Z03Contract DA 44-177-AMC-2l (T)USAAVLABS Technical Report 65-83February 1966

GEMINI ONE-TON AMPHIBIOUS OFF-HIGHWAYAIR-TRANSPORTABLE VEHICLE -

CONTINUATION OF PHASE I PROGRAM

Final Report

byF.H. Keast

Prepared byHawker Siddeley Canada Ltd.

Engineering DivisionToronto, Ontario

forU.S. ARMY AVIATION MATERIEL LABORATORIES

FORT EUSTIS, VIRGINIA

Distributionof thisd,'o-nent is unlimited.

k_

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This re por t presen ts the furt her r esul ts of testing a ful l -sca le mock-up

chassis representative ofa-ton, amphibious, off-highway, air-t ranspor tab levehicle which utilizes ai r cushion principles to pe rmi t

mobility in low-bearing terrain .

The test vehicle was modified and subjected to tests in water. A ski r t

was fitted and the vehicle was tested in p r epa red clay beds of low cone

index and on a level, hardsurface. Noise l ev e l tests were also carr ied

out. Fu rt her work to improve directional control andspeed in water and

to improve ski rt struct ure i s recommended to attain optirnum perfo rm-

ance.

iii

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PREFFACE

The work described in this report was carried out by Hawker SiddeleyCanada Ltd., Engineering Division during the period from June 1964 toAugust 1965. The principal engineering members of this organizationinvolved in the project were as follows:

Mr. F.P. Mitchell, Vice-President, Hawker Siddeley Canada Ltd.Mr. C.A. Grinyer, Vice-President, EngineeringMr. F.H. Keast, Director of ResearchMr. D.H. Parker, Engineering Laboratories ManagerMr. R.F.C. Tanner, Chief Engineer, Engineering DivisionMr. R.G.A. Chisholm, EngineerMr. N.B, HIerbert EngineerMr. W.U. Shaw, Senior Engineer

Acknowledgement is also made of the assistance rendered by the followingmembers of the Organic and Associated Terrain Research Unit ofMcMaster University, Hamilton, Ontario.

Dr. N.W. Radforth, ChairmanProf. W.R. NewcombeMr. K. Ashdown

This is the final report on the continuation of the Gemini Phase I Programand was prepared by Mr. F.H. Keast.

V

77 FMM57_7n mn`u n

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CON iTENTSi.Page

ABSTRACT iiiPREFACE vLIST OF ILLUSTRATIONS viiiSUMMARY 1CONCLUSIONS AND RECOMMENDATIONS 2DISCUSSION 3

Introduction 3Modifications to Test Vehicle 3General 3Power Plant 3Drive Train 4Ducting 4Skirt 4

Test Results 12Hard Surface Testing with Modified Splitter, without

Skirt 12Waterborne Testing 20Hard Surface Testing with Skirt Installed 23Clay Bed Testing with Skirt Installed 31Noise Testing 35

DISTRIBUTION 47

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ILLUSTRATIONSFigure Page

1 Comparison of Original and Modified SplitterConfigurations 52 Skirt Model Test Rig 63 Underside of Skirt Model Test Box with CylindricalSkirt Installed 84 Details of Model Skirt No.6 105 Details of Model Skirt No.6A 106 Skirt Type 6D and Attachment to Vehicle (Sheet 1) 137 Skirt Type 6D and Attachment to Vehicle (Sheet Z) 158 Underside of Test Vehicle with Skirt Installed 179 Comparison of Velocity Distribution - Original vs.Modified Splitter 1810 Duct Losses vs. Flow 1911 Variation of Lift with Flow Division 2112 Lift vs. Engine r.p.m. - Hard Surface Testing withOriginal and Modified Splitter 2z13 Side View of Test Vehicle with Fan Off During

Waterborne Tests 2414 Front View of Test Vehicle with Fan Off During

Waterborne Tests 2515 Vehicle Speed vs. Average Wheel Speed -Waterborne Tests with Fan Off 2616 Drawbar Pull vs. Vehicle Speed - Waterborne

Tests with Fan Off 2717 Drawbar Pull vs. Average Wheel Speed -

Waterborne Tests with Fan Off 28viii

- --

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J.I.d.L UQ 1. 1,X'- L J.Xi~N ,J \%.JxJAL, %.AJ

Figure Page18 Test Vehicle with Wheels Removed and Skirt Installed 2919 Rear of Test Vehicle with Wheels Removed and

Skirt Installed 3020 Gemini Clay Bed Tests - Cone Penetrometer Readings

July 28, 1965 3221 Gemini Clay Bed Tests - Cone Penetrometer ReadingsJuly 29, 1965 3322 Gemini Clay Bed Tests - Cone Penetrometer ReadingsJuly 30, 1965 3423 Gemini Clay Bed Tests - Cone Penetrometer Readings

August 16 , 1965 3624 Gemini Clay Bed Tests - Cone Penetrometer Readings

August 25, 1965 3725 Gemini Clay Bed Tests - Cone Penetrometer Readings

August 25, 1965 (After Test) 3826 Test Vehicle During Clay Bed Test Run 39

ix 4

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SUMMARY

This report presents the results of further testing of a full-scale mock-up chassis representative of a 1-ton amphibious off-highway air-trans-portable vehicle which utilizes air cushion principles to permit mobilityin low-bearing terrain otherwise impassable to a wheeled vehicle. Itfollows upon, and should be read in conjunction with, TRECOM TechnicalReport 64-34, dated July 1964, entitled "Gemini 1-Ton, Amphibious,Off-Highway, Air-Transportable Vehicle - Concept Evaluation Program -Final Report".The air diffusion structure in the test platform was modified and thevehicle vas subjected to tests in water. The vehicle was then modifiedby the addition of a skirt and tested on a level, hard surface to measureair cushion lift as a function of height and in a prepared clay bed of lowcone index to measure mobility. A noise level test program was alsoconducted.The "paddle wheel" performance of the wheels was measured in water-borne testing. Application of air cushion during these tests increasedvehicle speed. Because of inadequate directional control in water,examination of the use of direct air blast for propulsion and maneuveringis recommended.Performance in the clay bed was not as good as during previous testsconducted without the skirt, probably because the skirt material hadinsufficient flexibility, causing some dragging, particularly at skirtcorners. However, base pressures recorded during tests were com-"parabl.e to those recorded without the skirt. A further program of skirtdevelopment is recommended to overcome the problem of inflexibility.

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CONCLUSIONS AND RECOMMENDATIONS

Waterborne testing demonstrated that the use of wheels alone for waterpropulsion was inadequate for good directional control and speed. How-ever, it is apparent that the considerable energy potential available inthe air cushion system could be partially or completely directed as a jetstream to propel the test platform forward or backward. Preliminarycalculations indicate that thrusts in the neighborhood of 200 poundscould be developed by a suitable exit nozzle at the end of the vehicle.Directional control could be achieved by deflecting the jet stream or bya conventional rudder. For the final, articulated vehicle, directionalcontrol by je t stream and vehicle articulation alone could be adequate.It is recommended that an enginecring, manufacturing and test programbe undertaken to modify the test platform and further examine water pro-pulsion and directional control optimization.Since the final vehicle will be articulated with front and rear portionsincorporating separate air cushions, variations in loading will affectlongitudinal balance. Design and manufacture of an experimental testinstallation for application to the current test vehicle to determine effec-tiveness of balancing means for front and rear air cushions are recom-mended, concurrent with the work suggested above for an air propulsionsystem.Although adequate base pressures were obtained with the skirt presentlyinstalled, investigation of other skirt designs and development of theoptimum skirt configuration to overcome deficiencies inthe present skirtstructure are desirable to attain optimum vehicle performance. Suchinvestigation should place particular emphasis on skirt flexibility inarriving at the optimum configuration, it being established that the fieldproblem of dragging in wet clayadverselyaffects mobility to a significantdegree.Although limited in scope, this program has proved to be effective inestablishing practical design parameters and attention factors relative towater propulsion and terrain mobility of value to any ensuing majordevelopment program.

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DISCUSSION

INTRODUCTION

A proposal was made in November 1963 to USATRECOM* and theCanadian Dept. of Defence Production by Hawker Siddeley Canada Ltd.for continuation of the Phase I program for construction of a 1-tonamphibious off-highway air-transportable vehicle.This document is the final report on this continuation of the Phase Iprogram and follows upon TRECOM Technical Report 64-34 dated July1964, entitled "Gemini 1-Ton, Amphibious, Off-Highway, Air- TransportableVehicle - Concept Evaluation Program - Final Report".Continuation of the Phase I program commenced in June 1964, with theobject of more nearly establishing certain elements of the configurationof the Phase II vehicle betore this latter phase was begun. The work re -quired to arrive at this end was contractually defined in Schedule "D1"Statement of Work, which forms part of the amended contract for thePhase I continuation program.Subsequent pages contain a detailed report on the continuation of thePhase I program, categorized as follows:(a) Modifications to the test vehicle (including skirt design, develop-ment, manufacture).(b) Test results.

MODIFICATIONS TO TEST VEHICLEGeneralPrior to commencement of the continuation of the Phase I program, thevehicle was cleaned up both inside and outside, the fan assembly wasremoved to facilitate splitter modification, and the hydraulic motorswere removed, overhauled and replaced.Power PlantIn July 1964, new plugs, points a:kd high-tension leads were fitted to theengine at the commencement of the continuation of Phase I program and*Now USAAVLABS (U.S. Army A.-ation Materiel Laboratories).

3

pp

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the engine was brought to optimum operating condition. In July 1965,difficulties with the fuel injection system were overcome by servicingcomponents of the fuel system.

Drive TrainSmall modifications were made to the fan drive train to eliminate oilleakage.

DuctingThe splitter was re-designed to facilitate varying mass flow distributionto forward and rear ducting. The re-design involved elimination of thecylindrical splitter and its radial supports as far as possible, and fit-ment of a streamlined plastic leading edge at the point where division offlow occurred for front and rear cushions. A comparison of the originalconfiguration and the modified configuration is shown in Figure 1.Additional je t gates were fabricated for mass flow tests to enable a rangeof flow divisions to be studied.

SkirtAn engineering investigation of skirt extensions was commenced in June1964. Available literature was studied and discussions were held withpersonnel of the National Aeronautical Establishment at Ottawa. Toassist in establishing design, sketches were issued covering a quarterscale model of the je t platform, to be made of wood. Model skirts ofvarious depths could be fitted to this model. Air was to be supplied fromthe shop service, the required low-pressure mass flow being attained byusing an injector nozzle. Ground plane was to be represented by a roll-ing platform to which obstacles could be attached for passing throughthe skirt walls (see Figure 2). Four versions of possible skirt construc-tion were drawn up covering plenum and extended je t types.In August 1964, a proposed design of skirt construction was issued forsample manufacture in scale form. This design was of the plenum typeincorporating a single extension sheet of rubber, reinforced by internalrubber gussets. Other design proposals for skirt construction were laidout, giving consideration to installation on tie test and prototype vehicles.In the following month, the ribbed plenum model was fabricated, but washeld in abeyance pending tests of inflated types. Two configurations wereproposed. The first consisted of a single circular inflated bag attached

4

-. . .- .- -~ - . - - --- ____________________-..

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4t

- - BROKEN LINESINDICATESPLITTERAND SPACERS*5 REMOVED BYMODIFICATION''i t

SI "'I|i a' ~',

CYLINDRICAL SPUTTER(ORIGINAL CONFIGURATION) _____

PLASTICLEADINGEDGE

_I

MODIFIED SPUTTER(PLASTIC LEADING EDGE)

Figure 1. Comparison of Original and Modified Splitter Configurations.5

- ' 2 2--.....- .-

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MI.4

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to the cushion base across a short chord. The alternative design com-prised a "double cylinder" with a tension web separating the twocylinders. This latter type, altho:igh of the same depth as the z'ngletype, was somewhat narrower, thus providing a larger ground cushionarea.Three-foot lengths of these two models were se t up on a test box. Thecylindrical type was tested with various gaps from 0.1 to 0.5 :.nch.Figure 3 shows the underside of the three-sided test box, the cylindricalskirt forming the fourth side. Static pressure holes can be seen in thebaseboard, and the tube visible is connected to a static hole to measureejector output pressure. Air enters through the peripheral slot from theejector overhead. Inflation pressure was varied from 0.5 to 1.0 p.s.i.Under all conditions the skirt vibrated at a large amplitude. It wasbelieved that this was caused by the flow breaking away alternately fromthe smooth ground board and the curved surface of the skirt. To checkthis, a I/2-inch fence was attached to the ground board to locate the flowbreakaway at the fence. This eliminated the vibration. The "doublebubble" type was next tested, and substantially icdentical results. wereobtained.For these models with a continuous lower surface, the outflowing airwas markedly influenced by a Coanda effect and in some cases turnedthrough a full 90 degrees so that it was directed upwards from theground.Both models were then modified to incorporate a rubber spoiler on thebottom, and were again tested. The spoiler effectively eliminated theCoanda effect and oscillations of the "double bubble" type, but the singlecircular type still oscillated intermittently. Both models deflected later-ally by an excessive amount, at the same time increasing the gap height.Attempts to pass obstacles, which were 1/3 of the skirt depth, throughthe skirt, failed. The skirt was too flexible laterally but too stiff to passover an obstruction.Since one of the objectives was to investigate retraction of the skirt, thecircular section skirt was tested with air evacuated. Left free, it col-lapsed into a vertical shape. When the bottomwas supported, it collapsedinto a horizontal shape. Undoubtedly, if a space had been available abovethe attachment plane, it could have been made to collapse into this; how-ever, the bulkheads would produce a bulge when retracted. During themodel building and testing periods, layouts were made of the applicationof each type design to the test vehicle and to a Phase II vehicle.Design work and testing continued on skirt configurations during October1964. It was decided to modify the original ribbed plenum model (which

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0 -4J

U)/ 04.)

-It-

0l

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was not tested in it s original form), into a tapering extendd je t type asshown in Figure 4-It was evident from previous tests that any skirt of the inflated type inwhich the inflated structure was continucus along the periphery, wouldbe inherently very stiff. In order to obtain sufficient stiffness to preventexcess lateral deflection, internal pressure would be required sufficientto present a very unyielding surface to the passage of ground obstacles.The inverted pyramidal shape with wide attachment base and with the jetorifice at the bottom appeared to offer more promise. The slightlycurved walls almost meeting at the -pex would form a good structure toresist lateral loads, while the large inclined angle of these walls shouldassist deflection over an obstacle. Internal pressure due to cushion airflow would be resisted by the closely spaced diaphragms, and would bebalanced on the inside by the pressure of the air cushion.The first model was constructed as shown in Figure 4 and tested on themodel box rig. With the skirt gap set at 1/2 inch, a base pressure of6 inches of water was the maximum that could be obtained with theavailable compressed air supplied to the ejector. Lateral deflectionswere very small and well within acceptable limits. Due to the shortnessof the specimen and the fact that the ends were free, the inte: nal pres-sure in the skirt produced gaps at the end plates. The ground gap in-creased to 1-1/2 inches due to deflection of the central section of theskirt specimen. It was very difficult to pass obstacles through the skirtspecimen.The above test indicated that the design was too stiff due to the internaldiaphragms and attaching reinforcements between diaphragms and skirtwalls. It was decided to eliminate most of the diaphragm material, leav-ing only enough at the je t exit to restrain the je t lips., This was done asshown in Figure 5.The model shown in Figure 5 was tested in a similar manner to the pre-vious model. Lateral deflections were within limits and the gap increasedas before. It was much easier to pass obstacles through this model.By letter from USATRECOM dated 20 October 1964, to DDP, it wasagreed that the contractor could delete the requirement to conduct labor-atory attrition tests on skirt materials. This allowed more effort to beextended to skirt model evaluation testing.From November 1964 to January 1965, design work and laboratory test-ing of skirt models formed a continuation of the program of previousmonths. In addition, some time was expended in reviewing skirt conceptsagainst existing design patents.

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711 MATERIAL 1/16" THICK RUBBER

12"R

.50114" PITCSECTION A-A

Figure 4. Details of Model Skirt No.6.

SMATERIAL l 16//1 THICK RUBBER

A

7"1

1.50" 4" PI T C HA SECTION A-A

Figure 5. Details of Model Skirt No.6A.10

4- - - -. 7" A E IA -116-HCnR B E

- --- - ------,---4////////,-////

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The type of skirt investigated had the cross-section of a V with the jetopening at the bottom. The two rubber side wails were r.u..."u.e --restrained under cushion air internal loading by bridges or ties ofrubber connecting the sides.

Under previous testing it had been found that, although the model retainedits shape reasonably well, the portion at the je t outlet deflected exces-sively both laterally and vertically. This was partly due to the fact thatthe specimen was relatively short and was not restrained at each end. Atest was carried out with the ends restrained by means of plates boltedto the test frame. Under a cushion base pressure of 6.Z inches of water,the je t moved out 2 inches and the gap to base increased 1 inch. The je toutlet which was nominally 1/2 inch increased in width between thebridging to 1-1/4 inches. The je t efflux was directed horizontally alongthe base plane, and no Coanda effect was present as found with plenumtype skirts.It was decided to reduce the spacing of the bridging pieces connectingthe walls in an effort to reduce expansion of the je t walls under air pres-sure. This modification was carried out using thin fiberglass cloth gus-sets bonded to the sides. Spacing was reduced to 2 inches from 4 inches.The end bulkheads of the test specimen were restrained as in the pre-vious test.Measurements were made of the changes in dimensions under cushionpressure as before. In this case, outward movement of the skirt bottomwas reduced to 1-1/2 inches, the ground clearance increased from 11/16inch to 2 inches, and je t opening increased between bridging from 1/Zinch to 3/4 inch.A pyramidal obstruction was attached to the plywood base, the latterrepresenting the ground, and this was passed back and forth through theskirt while the ground cushion was in effect. The force required to movethis obstruction through the skirt was a small fraction of that requiredunder similar circumstances when tried with the inflated type models.As a result cf the tests on skirt models carried ou t in previous months,a decision was made to submit a skirt design based on the most prom-ising configurations tested, for approval as per contract.A drawing was prepared, No.400C01012, Skirt Type 6D, (Figures 6 and 7)and submitted. This design differed from the test model in that the clothribs connecting tne sides were replaced by small round metal ribs,bolted at each side.Approval of the design was received in March 1965, and action was takento implement the manufacture of the skirt.

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The shops proceeded with fitment of the front and rear skirts in June1965. The front skirt was received from the sub-contractor and wasassembled to the vehicle. Some difficulty was experienced at the corners,where a small tuck had to be incorporated. The rear skirt, received inan unassembled condition so that a better fit could be obtained by fittingand bonding on assembly to the cushion, was incorporated onto thevehicle base structure (Figure 8).TEST RESULTSHard Surface Testing with Modified Splitter, without SkirtTests performed at a cushion height of 1.5 inches showed a gain of 700pounds of lift over the lift of previous tests and indicated lower losseswith the modified splitter. Previous tests had shown flow-breakaway atthe splitter which caused a loss of pressure to the front jets. Traverseswith the new configuration are compared in Figure 9 with that obtainedwith the original splitter, shown by the solid line. As can be seen fromFigure 9, the curves of total pressure are now smooth but do indicate adeficiency of pressure rise at the hub of the fan. Changes to the je t gatesto alter the flow ratio between the front and rear sections seem to in-fluence the fan operation. With the front flow reduced to 1076, the defici-ency in the hub pressure and velocity is greater than in the other twocases where 61% and 90%6 of the flow was directed to the front jets. Thevariation of static pressure from inner wall to outer wall shown inFigure 9 is much less than that measured with the original splitter andcasts doubt on the accuracy of the inner wall pressure measured pre-viously.As a result of the elimination of the pressure loss associated with flow-breakaway from the splitter, the front duct loss was reduced from itsprevious value of 11%6 of the fan pressure rise to a new mean value of7.4%6. Since the flow to the rear ducts was not affected by the flow-breakaway from the splitter in previous tests, no noticeable changeoccurred in the present tests, the pressure loss remaining at about 17%of the fan pressure rise for normal, flow division.Figure 10 shows the results of the analysis of duct losses. The front ductshows scatter about a mean value of 7.4%6 of the fan pressure rise. Someof this scatter is no doubt associated with changes of the fan outlet pres-sure profile near the hub (Figure 9). This would vary the total initialenergy in the flow to the front duct.For the rear duct a correlation between loss and estimated flow is evi-dent, the variation being roughly proportional to the second power of theflow.

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119"1 108" a--- - .... --II I I. .

5.5.. ........... .................. ... ... '/.Z,,lll! .'471ilii1REXI\ss~ 11['CORNER SEE SHT . ".,ltIll CORNER SEE

L._,-.r .- : . - -. E XI TJ .,-.-- "

STIFFENERS SEE DETAILS KIRTOZZLE -VIEWSTIFFENERR SEE DETAIL BELOEXITIN 7" 3.511FA7MING E. STIN.

NE OS ENOSEFAIRING FAIRING

OT CUSHTIONA-A SECTION B-B OSHION

in, - -------.. ., .-- "-

NOSE NOSEARNG. FAIRING . 75"WB-,WEB 4[

WB3. 5" 4. "

I. 5"1. 5"DETAIL OF FRONT CHANNEL DETAIL OF FRONT CHANNELON FRONT CUSHION ON REAR CUSHION

13 Figure 6. Skirt Type 6D an

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4"

SEAL WITHALUMILASTIC i

119. 2"1 . 4."........4 1 14 2 ,.51 iI.,, __._.____ 7::

67" " 67"1 0 NrCD D

jFOR SECTION AT F.. ,CORNER SEE SHEET 2 . j. -- L, . 1.4 VIEW IN DIRECTION -

PLAN VIEW -- - F EXIT"- NOZZLESEE DETAIL BELOW SKIRT

4. 2"

, .75",-- -

SECTION C-C . E O . VEHICLE---------------------------- ------------- Ii FLEXIBLE "- i_ ) . , " .... SKIRT "Si# 5 6 0-1/ 1 6 "NR/ * I I'~~'NEOPREr41f

.7511NYLONo"7K."__ / ,o1 SIDE ELEVATION CONNECTC$),, VIEW LOONING

FORW'*RD

1.55"CHANNEL

CUSHION

6. Skirt Type 6D and Attachment to Vehicle (Sheet 1). -B ___

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SEAL WITH. EXISTINGAL UM!LASTIC STRUCTURE

75"4" -- KTli 4 _ _ 1. z5,, 7-_ 3.575

EXISTING #Gv67STRUCTURE

"-4 , , EXISTING14 VIEW IN DIRECTION .5" STRUCTURE\EXIT~zLsIT OF ARROW I'G'I F~SECTIONc UHoE" E "54-IRT

4 2"1.7511SEXISTING .7.4 VIEW INDIRECION STRURSTRUCTURE

EXIT~~ OFICA R O E G ETO -

- NOZZLE FRONT CFLEXIBLE4. MZ

Sl.-.i-- --------- V-#560-1/16"NEOPRENENYLON .5"CONNECTORS

VIEW LOOKING SECTION F-FFORWARD REAR CUSHION

to Vehicle (Sheet 1). C

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FAIRING FAIIN

SNECTION SH-H' SECTIONE

K .75"1 .551 K . 35"

rH'+ ., , FLANGE -

II- ". ,,--+ 64 ZO1I , -

5.5/ ,

55-_ -_1.4 1 ' . .. ..7511 75515.5" 18" ---FLANGE 1.4-"1.Z" ---119"

L. H. FRONT CORNER - FRONT CUSHION L. H. FRONT CORNER -

Figure 7. Skirt Type tJ and Attachment to Vehicle (ShW15 A

7"5.511

1+IHI

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III

PLAN VIEW

SECTION -J-J'.3 119

i -" 45"' J OZ Ltil FASIRIN

4 SECTION K-K71 FRONT CUSHION

64715A FOR REARUSHION CU

l+ +

- .- j EXITx 311 45 NOZZLED nd SKIRT.75" 1.E 11.4".11

L. H. FRONT CORNER - REAR CUSHIONTYPICAL FOR REAR CUSHION

Attachment to Vehicle (Sheet 2).

7B

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*11

VAVZ'-4

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ki &6 :iPSQ lAIR 017U

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, I I IIIIo_40

35

C.,0

0 I0

00

UeLU.

61% FLOW TO FRONT25, .. 10% FLOW TO FRONT

RADIUS 9.1" __ _ __ _ _ _ _01 23 4 5 6 7

Figure 9. Com-parison of Velocity Distribution - Original vs.Modified Splitter.18

- -. -- S L I TA-I

to

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20,FLOW AT NORMAL IFULL SPEED OPERATION FRONT DUCT

110 0MEAN VALUE -

0 0 00 -- ___ _ _ I_ _ _ _ I__I__I_ I0 10 20 30 40 50

Li),

,u.Io50," REAR DUCT

ze0~z4

0"x 30U,'Ucc --FAN DELIVERY PRESSURE

20 G AMBIENT PRESSURE0/FLOW AT NORMALFULL SPEED OPERATION

10 00

0 10 20 30 40 50ESTIMATED FLOW/ &(LB/SEC)

Figure 10 . Duct Losses vs. Flow19

-N

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Tests were performned over level concrete using various combinations ofjet gates to assess the effect on lift of varying mass flow between frontand rear cushions. Figure 11 shows the values of lift calculated from basepressure when the flow to the front was varied from an estimated valueof 10 % of the total flow to 9016. The rear lift curve indicates that theestimated value of 9016 flow to the front appears to be excessive and thedotted curve is more to be expected. It was found quite feasible to varythe 1 ft between front and rear cushions, but any departure from optimumje t widths was accompanied by a loss in total lift (Figures 11 and 12).From these tests it was decided that the optimum configuration was thatwith a flow split of 6116 to the front and 391 to the rear. This gave thesame ratio of front to rear lift as the original configuration (Figure 12)and, as this had proved successful in the early field trials, it wasdecided to retain this ratio.

Watei borne TestingOn completion of hard surface testing of splitter modifications, the testvehicle was prepared for water tests to be conducted at Dinner Lake,Parry Sound Proving Grounds.The side je t gates andthrust vanes were removed and the 450 thrust vaneswere installed, together with optimum jet gates.The hydrostatic drive was assembled to the vehicle and adjustmentsmade to relief valves, filters and other related components to ensurecorrect operation. The vehicle was transported by low-bed trailer toDinner Lake on 25 August 1964.First runs of the test schedule were undertaken with rearward thrustjet vanes and optimum jet gates to determine water speed and generalhandling, for various depths of wheel immersion and a range of wheeland vehicle speeds. The vehicle was ballasted to its gross weight for alltests. Recording instrumentation was installed for measurement ofwheel speeds, motor pressures, pump r.p.m. and static pressures.Vehicle speed was measured by fixing one end of the cord from a "fishingreel" transducer, the reel speed signal being fed into a recorder as thevehicle moved off. Drawbar pull was measured by anchoring one end ofa cable to shore and attaching the other end to a dynamometer fixed tothe stern of the vehicle. Signals were fed into the recording gear from thedynamometer.Many runs were necessary, as no directional control is fitted to thevehicle, which yawed considerably and was sensitive to wind forczs.

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Runs were then made with the air cushion fan operating in corjunctionwith the wheels, Speeds and drawbar pulls were measured.The above program was repeated with vertical je t vanes from 1 Septem-ber to 4 September 1964. Twenty runs with recording apparatus activatedwere made. Additional runs were made to check testing techniques. Dueto excessive yaw and directional instability aggravated by wind conditions,readings taken during runs with the air cushion fan operating yieldedunusable data.

Some photographic coverage of these tests was made (see Figures 13and 14).Recorded results with fan off are shown in graphical form on Figures 15,16, and 17.It is apparent that wheel propulsion is inefficient. Present tires used aspaddle wheels have excessive slip and will not absorb sufficient powerfo r propulsion. In view of this deficiency, maneuverability is also poor,since a reasonable speed is required to maneuver the vehicle. Lateralstability is sensitive to the je t cushion. At part throttle, air is ejectedfrom one side of the cushions and tends to roll the vehicle and propel itsideways. With the tires acting as paddle wheels and with the aircushion on, a better speed was achieved, but with less maneuverability,due to uncontrolled forces of the jets.

Hard Surface Testing with Skirt Installed

From 21 to 22 July 1965, hard surface Lests were carried out withwheels removed to determine clearance between skirt and ground forlift-off (Figures 18 and 19). Lift-off was achieved when the clearance,with air pressure in the skirt, was 1/8 inch at the corners and 3/4 inchat the mid-point of each side on both the front and rear skirts, withengine speed at 5500 r.p.m.The maximum base pressures at 5500 r.p.m. recorded during the hardsurface tests were 80.4 pounds per square foot on the front air cushionand 46.25 pounds per square foot on the rear air cushion, for the aboveconditions. Because of deflection of the skirt under air pressure, it wasnecessary to set the vehicle with the skirt riding on the ground, .. I inter-ference of 1.25 inches being necessary to achieve a reasonable air gapunder pressure.During the period 18 to 20 August.additional hard surface tests werecarried out to determine the effect on base pressure of installing wider

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spacers in each corner of the rear skirt and also to determine by Pitotprobe traverse the uniformity of the air flow around the periphery of thefront and rear skirts. The base pressures obtained were essentially thesame as those recorded during the tests carried out in July (Table I).The results of the air flow survey were not conclusive, mainly becausevibration of the skirt influenced the measuring probe.TABLE I

HARD SURFACE TEST RESULTS

StaticEngine Ground Fan Total Base PressureDate Speed Interference Pressure (P.S.F.)

(r.p.m.) (inches) (P.S.F.) Rear FrontJul 22 5500 1.25 109.0 48.0 80.4Jul 27 5600 1.25 123.0 44.8 85.0Aug18 6000 1.25 107.5 46.2 85.2

Clay Bed Testing with Skirt InstalledOn 26 and 27 July 1965,the west clay bed was reactivated for these tests,to a consistency when measured with a cone penetrometer of 10 averageat a dept-, of 6 inches and 15 average at a depth of 12 inches (Figures 20,21 and 22).During the period 28 to 30 July, several runs were attempted through theclay bed, the skirt ground clearance being varied for each run. It wasnoted that after the vehicle had completely entered the bed it wouldsettle fairly rapidly and stop. At full engine power the vehicle wouldattempt to rise but there was insufficient traction to overcome the dragand excess buildup of wet clay in front of the vehicle.

It was observed that, as the front wheels entered the clay bed, the noseof the vehicle dropped and plowed up a wall of wet clay mixture as thevehicle progressed forward. This nose-down attitude of the vehicle alsocaused excessive loss of the rear air cushion. Wheel ru t depths weremeasured up to 18 inches, and the power delivered by the hydraulicmotors was insufficient to turn the wheels at this depth.

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The tire treads also loaded up with clay during the runs, and on someoccasions considerable wheel spinning was encountered. Wider spacerswere installed at each of the four corners of the rear skirt, but noimprovement in pressure of the rear air cushion was obtained. It wasobserved that the skirt was dragging, particularly at the corners whichdeflected less under ,ir pressure than the side walls.

A comparison of the cone penetrometer readings of the west clay bed asprepared in October 1963 and as prepared fo r the tests currentlycarried out, show the former to be 37 average at a depth of 12 inchesand the latter 15 average at a depth of 12 inches. It was decided to allowthe clay bed to dry a little and then to retest.

Figure 23 shows the penetrometer readings taken on August 16. As aresult of this check, on 23 and 24 August the clay bed was remixed togive cone penetrometer average readings of 20 at 6 inches depth and 35at 12 inches depth.

Several attempts were made on 25 August to drive the vehicle throughthe clay bed, the ground clearance being adjusted throughout the testruns. No completely successful run was made on the firmer clay, bu t theoverall performance was better and the vehicle travelled 3/4 of the bedlength on two occasions. This was achieved by repeated reversing andprogressing in the same ruts. The ru t depth was only 9 inches and con-siderably better traction was obtained than in the July tests. Figure 24is a complete penitrometer plot of the bed before the tests. Figure 25shows the penetrometer readings taken after these tests along the coursecovered by the vehicle. Figure 26 shows the vehicle during a test run inthe clay bed.

With the completion of these tests it was determined that no furtherbenefit would be obtained from continuing this part of the test program;therefore, testing was discontinued. Table IH shows clay bed test results.

Noise Testing

A noise survey has been completed using equipment manufactured byBruel & Kjaer, Copenha-,en, Denmark, and consisting of the followingitems:(1) Type 4135 and 2615 - 1/2-inch microphone plus cathode follower.*(Z) Type 2112 - Audio Frequency Spectrometer.

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(3) Type 2305 - Levei Re(order.(4) Type 4220 - Pistonphone Calibrator,Measurements were obtained over an arc of 100-foot radius from thecenter of the unit and at angular increments of 300 through the right handside. The forward measuring position is given as 00. The ground coverwas sparse, trimmed grass on stony, dry sub-soil. Location of the testsite was such as to ensure that general fret field conditions wereobtained.

Throughout the test, the power unit was maintained at 6000 r.p.m. andcoupled either to the hydraulic system to give an indicated load of 1000pounds per square inch, or to the fan. Two recordings were thus obtainedat each measuring position. The clearance between the skirt and theground was 12-1/4 inches at the front and 15-1/2 inches at the rear.Results are given in Tables V and VI fo r the two test conditions. A 1/3octave presentation has been employed from which the octave valueshave been computed along with the overall sound pressure level. Allresults are referenced to 2 x 10-4 dynes per square centimeter.For convenience, the overall sound pressure level (OASPL) fo r the twotest conditions is summarized in the following tabulation.

TABLE IIIOVERALL SOUND PRESSURE LEVEL COMPARISON

Angle (0 front - through right hand arc)Condition 0 30 60 90 120 150 1806000 r.p.m.power to 92.7 93.7 95.3 97.1 96.6 94.7 88.4hydraulics

6000 r.p.m.power to 97.1 97.3 101.7 97.9 99.6 97.1 95.5fan

It will be seen from Tables V and VI that the main difference in the noisespectra fo r the two test conditions considered occurs in the octave bandcenter:ed on 4000 cycles per second. This comparison is given in thefollowing tabulation.

41

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TABLE IV4000 CYCLES PER SECOND COMPARISON

Angle (00 front - through right hand arc)Condition 0 30 60 90 120 150 1806000 r.p.m.power to 63.4 69.0 72.3 73.6 69.6 3 58.4hydraulics

6000 r.p.m.power to 89.1 88.5 91.1 84.6 89.9 82.6 83.6fan

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Unc las sifiedSecurity Classification

DOCUMENT CONTROL DATA- R&D(Security classification of title, body of abstract and indexing annotation must be entered when the overull report isla; l icd)

I ORIGINATING ACTIVI"Y (Corporate author) 12a REPORT SECURITY C LASIFICAIIONHawker Siddeley Engineering, Division of Hawker UnclassifiedSiddeley Canada Ltd., Box 6001, 2 b GROUPToronto International Airport, Ontario, Canada. I

3 nEp'OnT TITLEGEMINI ONE-TON AMPHIBIOUS OFF-HIGhWAY AIR-TRANSPORTABLEVEHICLE - CONTINUATION OF PHASE I PROGRAM

4 DESCRIPTIVE NOES (Type of report and inclusive dates)Final Report - June 1964 to August 1965S AUTHOR(S) (Last f.ms.rs t name, initial)

Keast, Francis H.6 REPORT DATE 78 TOTAL NO OF PAGES 7b NO OF REFSFebruary 1966 47 ONE8a CONTRACT OR GRANT NO. 9a ORIGINATOR'S REPORT NUMBER(S)DA 44-177-AMC- Zl(T)b PRojEcv NO. Task 1P125901A14203 USAAVLABS Technical Report 65-83c 9b OTHER REPORT NO(S) (Any other numbers that may be axs~rmnedthis report)d

10 A V A IL ABILITY /LIMITATION NOTICES

Distribution of this document is unlimited.It SUPPLEMENTARY NOTES 12 SPONSORING MILITARY ACTIVITY

US Army Aviation Materiel LaboratoriesFort Eustis, Virginia13 ABSTRACT

This report presents the further results of testing a full-scale mock-upchassis representative of a 1-ton, amphibious, off-highway, air-transportablevehicle which utilizes air cushion principles to permit mobility in low-bearingterrain.The test vehicle was modified and subjected to tests in water. A skirt wasfitted and the vehicle was tested in prepared clay beds of low cone index andon a level, hard surfaLe. Noise level tests were also carried out. Furtherwork to improve directional control and speed in water and to improve skirtstructure is recommended to attain optimum performance.

DD A 1473 UnclassifiedSecurity Classification

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-. UnclassifiedSecurtt CI.,ssif'c,.l lollR-' J

14 LINK A LINK E3 L'NKC

KEY WO ---.-- _ --- -1 --

AIR CUSHION VEHICLEGROUND EFFECT MACHINELOW BEARING TERRAIN MOBILITYSKIRTED VEHICLEGEMINI AMPHIBIOUS VEHICLE

I 'INSTRUCTIONSI. ORIGINATING ACTIVITY: Enter the name and address 10. AVAILABILITY/LIMITATION NOTICES: Enter any lim-of the contractor, subcontractor, grantee, Department of De- stations on further dissemination of the report, other than thosefense activity or other organization (corporate author) ssuing imposed by security classification, using standard statementsthe report, such as :2a. REPORT SECURITY CLASSIFICATION: Enter the over- (1) "Qualified requesters may obtain copies of thisall security classification of the report. Indicate whether report from DDCr ""Restricted Data" is included. Marking is to be in accord- repor fron ofChiance with appropriate security regulations. (2) 'Foreign announcement and dissemination of this2b. GROUP: Automatic downgrading is specified in DO D Di- repor by DDC is not authorizedUrective 5200. 10 and Armed Forces Industrial Manuel. Enter (3) "U. S. Government agencies may obtain copies ofthe group number. Also. when applicable, show that optional this report directly from DDC. Other qualified DDCmarkings have been used for Group 3 and Group 4 as author- users shall request throughized.3. REPORT TITLE: Enter the complete report title in all (4) 1U. S. military agencies may obtain copies of thiscapital letters. Titles in all cases should be unclassified. "U. S iry aecs mayOtain es osIf a meaningful title cannot be selected without classifica- shall request throughtion. show title classification in all capitals in parenthesia stimmediately following the title.4. DESCRIPTIVE NOTES: If appropriate, enter the type of (5) "All distribution of this report is controlled. Qual-report, e.g.. interim, progress, summary, annual, or final. ified DDC users shall reques" throughGive the inclusive dates when a specific reporting period iscovered.covere.A If the report ha s been furnished to the Office of TechnicalS. AUTHOR(S): Enter the ha'me(s) of author(s) as shown on Services, Department of Commerce, for sale to the public, indi.or in the report. Enter last name, first name, nmiddle initial. care this fact and enter the price, if known.If military, show rar* and branch of service. Th e name ofthe principal author is an absolute minimum requirement. II. SUPPLEMENTARY NOTES: Use fo, additional explana-6. REPORT DATE: Enter the date of the report as day.month. year. or month, year. If more than one date appears 12. SPONSORING MILITARY ACTIVITY: Enter the name ofon the report, us e date of publication. I the departmental project office or laboratory sponsoring (payrt ing for) the research and development. Include address.7. . TOTAL NUMBER OF PAGES: The total page countshould follow normal pagination procedures, ie., enter the 13 AIBSTRAC'i Enter an abstract gi% ng a brief and factualnumber of pages containing irno.l .ion. sur-irary of the document indicative of the report, even thoughit mav also appear elsewhere in the body of the technical re-7b. NUMBF.R OF REFERENCES: Enter the total number of p.rt. If addttiona! space is requtred. a continuation sheetreferences cited in the report. shall be attached.8a . CONTRACT OR GRANT NUMBER: If appropriate, enter It is hiri 1v desirable that the abstract of classified re-;he applicable number of the contract or grant under which I p..rts be uncl,,ssified. Each paratlraph of the abstract shal!the report wa s written. i end with an indication of the military security classification8b, 8c, & 8d. PROJECT NUMBER: Enter the appropriate of the infor-nation in the p,,ragrap.h r..presented as (TS). (S).military department identification, such as project number. (C). or (U)subproject number, system numbers, task number. etc. There i no limitati .n on the length of the abstract. How-9a . ORIGINATOR'S REPORT NUMBER(S): Enter the offi- ever. the suggested len*th is fron IS0 to 225 words.