Document
'l'E CHIn CAL NOTES NATIONAL ADVISORY COi'lcn:rTEE FOR A.sEOi:~AUT I CS No . 456 .
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THE AERODY],AMIC EFFECT OF A RETR"~CTA3LE LA:;DBTG GEAR ~ .
I By Smith J . DeF~ance Langley lAeLlorial Aeronautical Laboratory
- -11- ., 61 EERnW
'\7 ashL1g ton l:i ar c h , 1 933 , .
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NATIONAL ADVISORY COMEITTEE FOR AERONAUTIC S TECHN I CAL NOTE NO . 456 THE AERODYNAMIC EFFECT OF A RETRACTABLE LAND I NG GEAR By Smith J. DeF r ance Tests TIEre conduct ed in the N . A:C.A . f ull-sca l e wind tun ~e l at the request of the Army Air Corp s to determine the effect of retractable landing - eear openings in the bot - tom surface of a wing upon t~e ta ~e - off chara c teristics o f a Lockh ee d Altair airplane . The tests pore e xtended to in - clude the determi ~at i on of the lift and drag characteris- tics throughout the angle - of - attack rango with the landing geer both retracted a nd exte~ded .
Cove ri ng the whe~l o penings in the wing with sheet meta l when the wheels ~ere extended reduced the drag only 2 pe r c ent at a lift coefficient of 1 . 0 , which was assume d for the take - off co~dition . Therefore, the wheel opening s i n the bottom side of the uin~ have a negli g ible effect upon the ta ~e - off of the airplane . Retracting t he landing gear redu c ed the minimum drab of the complete airplane 50 per CC:1.t .
Il~TRODUCT ION somcuhat excessive length of run had been required A b y a ce r tain lo p - wing monoplane, a Lockheed Altair , during take -o ff ~ ~ his airplane has a landing gea r that is c om - pletely housed in the wing whe n retracted ; and when i t is extended , o penings having an area equal to the side area of / t he struts and wheels are exposed on the lower surfa c e of the win~ . It was desired to know whether these o pen in g s ) nere ca u sin g the detri~ental effect upon the take - off cha r- acteristics . Consequently , at the re que st of the Army Air Corps tests were conducted u po n this airplane in the H .A . C . A .
full - scale wind tunnel t o determine the effect of the wing openings upon the lift and drag characteris ti cs .
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2 N.A.C.A. Technical Note No . 456 TESTS A ~D APPA RATU S The airnlane was mounted in the wind tunnel as shown in Figure 1. - The lift and drag forces were measured with the wheels re tra cted, with the wheels extended and wheel we lls op en , and w ith the wheels extended and the wells cov- ered TIi th s heet metal. The tests were conduc ted at an air sp e ed of ap ~ roximately 60 miles per hour. Figure 2 shows the landin g gear extended and the wheel TIells open. A de- scription of the tunnel and balance equipment is given in reference 1.
DISCUSSION OF RESULTS The primary purpose of th e investigation was to deter- mine the effect of the landi ng -gear op enings in the wing up- on the lift and dra g char a ct e ris tics during take - off. As- suming an angle o f attack for take-off that w ould give a l ift coefficient of 1.0, and comparing the cu.rves on Figure 3 for conditions with landin ~ gear extended and whee l wells both open and closed, it c an be seen that closing the wells r edu ced tho drag coefficient only 2 per cent . Therefore, ~t can be said that the openings in the wi n g for the retract - able landin g gea r of the Lockheed Altair have a negligible ef£ect u p on the take-off of the airplane.
Be cause of its retrac table feature, the landing gear on the Loc kheed Altair is not aerodynami c ally clean. It is interesting to note, however, that retracting the gear re- duc es t~1e minimum drag of the complete airpla n e 50 pe r cen t.
It is ther ef ore apparent that, if the landing gear proper is streamlined to reduce the drag, the take-off characteristics wil l be improved; but such a chan ge, if carried to the ex- treme , uould have a detrimental effect upon the landing char- acteristics and migh t necessitate the installation of some device to reduce the landing dis t ance required.
CONCLUSIO NS A retractable la ndi ng gear of the type on the Lockheed Altair may , when extended, account for 50 per cent of the minimum drag of an airplane, but the openin6s that house th e N .A.C,A. Technica l Note No. 456 3 gear in th o bottom surface of the wing have a negl i g ible effect u po n the l ift a nd drag c ha racteristics whe n th e g e ar is exte nde d .
La ~g ley liem or ia l Ae ronauti c a l Laborator y , Na tio na l Adv is o r y Co mm i t toe for Aeronautics, Lan g le y Field , Va ., ~a rc ~ 1 6 , 1 933 .
REFERENC E 1 .• DeFrance , Smith J , : Th e N ~A . C.A . Fu ll- Sca le Wind Tun- ne l. T, R. No. 459 , M. A .C.A., 1 933 .
Fi g .l N.A.C.A. Technical Note No.456 ..
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I( , -'8 -4 4 8 12 16 20 Ang le of attack of thrust axis,eXTJdegrees Figure 3.~Lift and drag characteristics of Lockhee d Altair with landing gear both extended and retracted.
Propeller off,stabi lizer and elevator at 0° to thrust axis.
Wing area = 284 sq. ft. Corrected for jet bounda ry .
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