NASA Technical Note - Free flight model investigation of a vertical-altitude VTOL fighter - 1975.pdf

8/12/2019 NASA Technical Note - Free flight model investigation of a vertical-altitude VTOL fighter - 1975.pdf

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N A S A T E C H N I C A L N O T E TN D-8 0 5 4_

: RETAFWL TECHP4ICALK 1RTLAND AFB,

AbFREE-FLIGHT MODEL INVESTIGATIONOF A VERTICAL-ATTITUDE VTOL FIGHTE3

Wil l iam A. Newsom, Jr. a n d Erm e L. A n g hLungley Research CenterHumpton, Vu. 23665NA TIO NA L AE RONA UTICS A ND SPACE ADMIN5S;fRATtON WA SH IN GT ON D. C. 1 5PTEMBR W75

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- - - -1. Report No. 2. Government Accession No.NASA TN D-8054 I4. Title and SubtitleFR EE -FLIGHT MODEL INVESTIGATION O F A

VERTICAL-ATTITUDE VTOL FIGHTER7. Authods)

William A. Newsom, J r . , and Ernie L. Anglin9. Performing Organization Name and Address

NASA Langley Res ea rc h CenterHampton, Va . 23665

. .2. Sponsoring Agency Name and Address

National Aeronau tics and Space AdministrationWashington, D.C. 205465. Supplementary Notes

TECH LIBRARY KAFB, NMIllllll IIIIIIllIll0333900- _ . ..3. Recipient's Catalog No.

5. Report DateSeptember 19756. Performing Organization Code8. Performing Organization Report No.

L -1034 5-IO. Work Unit No.505-10-31 -01

11. Contract or Grant No.

13. Type of Report and Period CoveredTechnical Note~

14. Sponsoring Agency Code

Technical Film Supplement L-1186 available on request.-.

6. AbstractThe tests were made in the Langley full-scale tunnel and included a study of the

stability and control cha rac ter ist ics of del ta- and swept-wing configurations from hoveringthrough the transition to normal forward flight. Static force te st s were als o conducted toaid in the analysis of the flight te st s. With conventional art ifi cia l ra te stab ilizati on, verysmooth transitions could be made consistently with relatively li ttle difficulty. Because ofthe lower appa rent damping and a tendency to diverge in yaw, however, the swept-wing configuration was co nsider ed to be much mo re difficult to fly than the delta-wing configuration.With rate dampers off, both configurations were very difficult to control and the controlpower needed for satisfactory flights was substantially higher than with the ra te d amp ersoperating.

. .7. Key-Words (Suggested by Authoris)) 18. Distribution StatementVTOL Unclassified - UnlimitedStability

Subject Category 0219. Security Classif. (of this report) 1 20. Security Classif. (of this page) 21. N Pages 22. Price*Unclassified Unclassified $3.75

For sale by the National Technical Info rmatio n Service, Springfield, Virgin ia 22161


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FR EE -FLIGHT MODEL INVESTIGATION O F AVERTICAL-ATTITUDE VTOL FIGHTER

William A. Newsom, Jr., and Er ni e L. AnglinLangley Resea rch Cen ter

SUMMARYFree-flight tes ts were made using a model of a vertical-att itude VTOL fighter with

a pivoted forebody (nose-cockpit) design. The tes ts we re conducted in the Langley full -sc al e tunnel and included a study of de lta - and swept-wing configurations fro m hoveringthrough the transit ion to norm al forw ard flight. Evaluations wer e al so made of the controlrequi red to hover with and without artif icial damping. Static forc e tes ts wer e als o conducted to aid in the analy sis of the flight tes ts . With art ifi cia l rate stabilization, ver ysmoo th tra nsi tio ns could be made consistently with rela tive ly litt le difficulty. Because ofthe lower apparent damping and a tendency to div erge in yaw, however, the swept-wingconfiguration was co nsid ered to be much m or e difficult to contro l than the delta-wing configuration. With ra te da mp er s off ,both configurations were very difficult to control andthe con trol power needed fo r sat isf act ory flights was substantially higher than with therat e damp ers operating.

INTRODUCTIONDuring the early 1 9 5 0 9 , considerable interest w a s expre ssed in vertical-attitude

VTOL figh ter configurations. The flight pro gra m for the delta-wing X-13 resea rch vehicle (ref . 1) demonst rate d the ability of such configurations to complete tran sit ion s betweenhovering and forw ard flight in a relatively simple, straigh tforward manner. VTOL fighte rsof th is type involve l es s com pro mi se of the nor ma l for wa rd flight configuration to acco mmodate VTOL operati on than do the va rio us horizontal-attitude concepts that have beenstudied. However, the vertical-attitude VTOL concept w a s not developed into an opera tional aircraft at that t ime fo r a number of r ea so ns , including:

1)The thrust r equir ed for VTOL was so much greater than that demanded by anyconventional flight requirement , hat the additional engine si ze c aused unacceptable l os se sin the payload and range;

(2) The nece ssi ty of an elab ora te ground appa rat us fo r take-off and landing wa s consid ere d operationally unacceptable.


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3) The vert ica l attitude of th e cockpit during low-speed VTOL operations res ult edin objectionable pilot attitudes which we re judged to be unacceptable fo r an operatio nalenvironm ent, part icul arly during landing.As a result of these shortcomings, in ter est i n the concept greatly diminished.

Recently? however, advances in fighter r equ ire me nts and technology have res ult edin configuration feat ure s which may m inimiz e o r even eliminate s om e of th e previousshortcom ings of ver tical-atti tude VTOL vehicles . For exampl e, rec ent lightweight fighteprototypes have uninstalled thrust-weight ra ti os of about 1.5 - th is level of thr ust beingrequ ired to mee t the combat perform ance requirem ents. Also available are fly -by -wirecontrol sy ste ms . Thes e fea tur es suggest the possibility of a vertical- attitude VTOLfigh ter which is essential ly a conventional air pla ne with conventional landing ge ar whichcan be u sed whenever a conventional landing is possible. Added fe atu res needed fo r VTOwould be a jet-reacti on control syst em for control in hover and at low speeds, a landinghook fo r ver tic al landing on an apparat us such as that used for the X-13 , and a pivotednose-cockpit section so that the pilot could rema in in a norm al attitude as the airplanetilted to a ver tic al attitude for take-off and landing. The fly-by-wire control syst em wougreatly facilitate this latter design feature as well as provide any particular controlphasing required during the transit ion. In view of the foregoing co nsid erat ions , it appeathat a new look at the vertical-attitude VTOL fighter concept is warranted. Figure 1 shoa ske tch of the concept under disc uss ion.

The pr ese nt investigation was conducted to study the dynamic stability and controlchar acte rist ics of a free -flight model of ve rt ic al -attitude VTOL fight er configurationshaving such a pivoted fuse lage forebody. The investigation wa s conducted in the Langleyfull-sca le tunnel and included hovering and transit ion flight tests and static forc e tests.Since delta wings ge nerally have good high angle-of -attack cha rac ter ist ics ? the p res en tinvestigation included a delta-wing configuration, but a ls o included a sweptback wing inor d er to investigate the ef fec ts of planform. The flight tests included an investigation of:1) stabil i ty characterist ics at sev era l attitudes during the transi tion fro m hovering to

forw ard flight, (2) the c ontrol power use d during the hover , and 3 ) the need for artificialrate damping.

Selected sc enes fr om a motion pict ure of the free-fligh t te st s have been prep aredas a film supplement availabl e on loan. A requ est ca rd and a desc ript ion of the filmL-1186 ) a r e included at the back of t his re por t.

SYMBOLS

Al l static longitudinal for ce s and moments are re fe rr ed to the wind-axis syst em andall stat ic lateral-directional for ces and moments are ref err ed to the body-axis system2


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shown in fi gure 2. Stat ic moment da ta for th e delta-wing configuration are pres ented withrespect to a center of gravity located at 37 perc ent of the wing mean aerodyn amic chordand static moment data fo r the swept-wing configuration are presented with respec t to ace nt er of g ravi ty located at 25 perc ent of the wing mean aerodynam ic chord. In or de r tofacilitate intern ational usage of data pres ented , dimensional quantities are prese nted bothin the Inte rnat iona l Syst em of Units (SI) and in the U.S. Cust oma ry Units. Me asu rem ent swe re m ade in the U.S. Cust omar y Units and equivalent dimensi ons we re d etermined byusing the conversion facto rs given in ref erenc e 2.

spa n, m (ft)mean aerodynam ic chord , m (ft)dr ag coefficient, FD/q,Srolling-moment coefficient, MX/q,Sblift coefficient, F ~ / ~ _ spitching-moment coefficient, MY/ qSCyawing-moment coef ficient, MZ/q,Sbsi de -fo rce coefficient, Fy/q,Sdrag force , N (lb)l i f t force , N (lb)s ide force , N (lb)mom ent of i ne rt ia about X body axis, kg-m2 (slug-ft2)

mome nt of in er ti a about Y body axis, kg-mz (slug-ft2)moment of ine rti a about Z body axis, kg-m2 (slug-ft2)rolling moment, m -N ( f t -1b)pitching mom ent, m-N (ft-lb)

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yawing moment, m -N (ft -1b)

fr ee- st rea m dynamic pre ss ure , N/m2 (lb/ft2)

wing area, m2 (ft2)angle of a tt ack of fu sel age , deg

angle of si de sl ip , degailero n deflection (pe r surf ace ), positive for left roll , deg

wing leading-edge fl ap deflection, positive f or leading edge down, deg

forebody -deflection angle, positive fo r nose down fro m fuse lage re fer enc eline (se e fig, 2) , deg

rudder deflection, positive for left yaw, degincrem ental rolling moment

incremental yawing moment

incremental side force

- - I ZCz sin aCnP,dyn - cnP Ix p

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NASA Technical Note - Free flight model investigation of a vertical-altitude VTOL fighter - 1975.pdf