1、 .CA XOTPES TBCEW I YATIOPbL ADVISORY GOHMITTEE FUR AEBOXAUTICS PLATE WETEOD OF GBOVETD REPRESEXTATSOB 3OR WI%D-TUXtiEL IGTLBMIXATIOX OF ELEBATOR . EFFECTIVEBISS II LBDIlG By I. 0, Recant Langley Memaria Aeranautfcal Laboratory . Washington September 1941 Provided by IHSNot for ResaleNo reproduction
2、 or networking permitted without license from IHS-,-,-NATIONAL ADVISORY COMMITTEE FOB AERONAUTICS .-, TECHNICaL NOTE NO. 823 -. . . PLATE ,METHOD OF GROUND BEPRESENTATION FOR WIND-TUNN fing -20 in the wind tunnel and from -21 to -22- with the plate removed, the maximum angle vas about I 160. The tes
3、ts indicated that the maximum lift coefficient of a trimmed model would be decreesed by the proximity Of the ground plate. . . I INtiODUdTION :. . , . 1 Yhen an airplane appioaches the.ground it undergoes a marked increase in static longitudinal stability This I . * Provided by IHSNot for ResaleNo r
4、eproduction or networking permitted without license from IHS-,-,-2 BACA. Technlcal Note NO. 823 . L. . increase in stability results, in a large measure, from the effect of the ground on the downwash angle at the tail. Not only is the downwash angle decreased bat the rate of change of downwash angle
5、 at the tail wfth wing lift coeffi.c.ient issmaller cear the ground than at great heights from the ground. Thuis, at a given airplane atti- tude, the tail is operating at a higher positive (or lower negative) angle of attack near the ground than at a dfstance from the ground, and this difference in
6、tail angle of attack increases as the wing angle of attack increases. The r$te of change of tail lift with wing an- gle of attack and the pitching moment caused by tail lift are therefore increased by the presence of the ground. Another factor contributing to the increase in sta- bility is the.incre
7、ase in the effective aspect ratio of. the tail caused by the proximity of the ground. This factor, however, is probably a second-order effect. . In view of the increase in stability caused by the ground, a muc!h larger elevator deflection is generally required to trim the airplane at maximum lift, p
8、articu- larly with flaps, near the ground than is required to trim the airplane in the same attitude at a distance. from the ground. It is quite possible that the elevgtor, although satisfactory for other flight conditions, may.: not be powerful enough to trim the airplgne in landing, Even when the
9、elevator is powerful enough to trim the airplane, the deflection required ma;y be of such hagni- tude that ths stick force will be prohfbitive. .The landing condition may well be the most severe criterion ,. in the design of the tail. . . A means of determining the elevator effectiveness, when landi
10、ng, from wind-tunnel tests of a model is there- fore desirable. In tests.of this type the ground may be simulated by an image model, by an endless belt moving w$th the velocity ofthe air stream, by a stationary plate, or by a combination of an image model and a plate. Much has been written concernin
11、g the relative merits of each method. (See references 1 and 2.) Obviously, the plate method is by far the simplest. The validity of the re- sults obtained with this method of ground representation, 1s. however, open to question because of the existence of a boundary layer over the plate in the wind
12、tunnel that is not present over the ground. Despite the doubt as to the adequacy of the plate method, it has been use.,d in numerous investigations. (See references 3, 4, and 5.) . Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA Technical Note N
13、o. 823 3 * Although the results of these fnvestigations (refer- ences 5, 4, and 5) are essentially in agreement as regards the effebt of the ground on pitching moment, they present no direct evidence as to the applicability of the tunnel data to the full-scale airplane. In the present fnvesti- gatio
14、n a model was tested over a plate in the tunnel and the tunnel data were compared with flight data for. the full-scale airplane. The results of the tests and the comparison are presented herein. MODEL AND APPARATUS The model used in the wind-tunnel tests was a l/5- scale model of the Curtiss P-368 a
15、irplane, a low-wfng, single-engine type. A sketch of the model wfth its perti- nent dimensfons fs given in ffgure 1, A complete deecrfp- tion of the full-scale airplane may be found in reference 6. The tests were made in the NACA 7- by IO-foot wind tunnel described in references 7 and 8. The ground
16、was simulated by a flat wooden plate ex- tending complet.ely across the tunnel and several feet ahead of and behfnd the model. Details of plate construc- tion and method of mounting are given in reference 9. The plate was set parallel to the longitudinal axis of the tunnel and its height was so adju
17、sted that it was almost tangent to the front wheels of the landing gear with the model at aero angle of attack; the wheels .never made con- tact with the plate. (12O) At the angle of attack for maximum lift coefficient the landing gear was about l. %h$ value of dcm/dit .shou;td not only be larger wi
18、th the- ground plate. in place .but:.should.also ia- crease with model angle of attack, because the distance of.:the:tail above the ground decreases as: the model angle o;f attack increases. If d6,./dit were corrected for this effect, the values“of . smaller thati those; shoti?in near the groud ll.
19、(See table 4 of reference 3.) : , . . -a . . :- - - “ The averagedownwash angle atthe tail was. computed from the.angle of attack ofthemode$, the-angle of ikci- henc.e bf the fail, ahdthe an ,but unpublished results of previous investigations have shownthat a windmilling propeller has a negligible e
20、ffect onthe maximum lift coefficient or on the slope of the lift uurve,) Data for trim conditions are not available for the model used in the present investigation. The lift of a trimmed model may be expected to decrease -ne.ar the ground because the pitching moment of the model without the tail is
21、practically unaffected by the proximity of the ground (fig. .5(a) I. Consequently, the tail lift required for trim will be about the same whether or not the ground is present, Since the lift of the model without the tail is decreased by the ground (fig. 7(a) and the tail lift is the same with or wit
22、hout the ground, the lift of the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-XACA Tech and for the type of. model tested: - - . 1. The plate method of ground representation for the determination in the Gina tunnel ofelevktor effectiveness !wheh l
23、anding gave rasults in satfsfactory agreement with flfght tests. -. - ; .- . . 2. The presence of the ground phate deSreased. the. maximum average downwash angle at the, tail by more than 50 percent. . .- : . . 3. The maximum lift coefficfent pf a trimmed model. would be decreased by the presence of
24、“the ground-plate; r . . . _ Laagley.Memorfal Aeronautical Laboratory, . National Advisory Commfttee forAeronautics; . Langley Pield,Pa., August 9; 1941; . , . . *. . . , r . . . . * .:. . _ . . . _ -. _ , . - . . . : . . .:, .*. : . l *:, - . . . a . . 8 . Provided by IHSNot for ResaleNo reproducti
25、on or networking permitted without license from IHS-,-,-10 NACA Technical Note No. 823 REFERENCES 1. Le Sueur, Maurice: Ground. Effect onthe Take-Off and Landing of Airplanes. T.M. No, 771, NACA, 1935. 2. Pistolesi, 1.:. Ground Effect - Theory-.anq,Practice. T.M. No. 828, NACA, 1937. . 3. Lyon, H. M
26、., and.Adamaon, 3. E.: TGe Effect 0% Ground Interference on the Trim of a Low Wing,Monoplane. R. 4. Ower, E., Warden, R., and Brown, W.S.g .An Investiga- tion of Ground Effect with a Model of a Mid-Wing Monoplane. R.“NACA, 1941. 7. Harris, Thomas A.: The 7 by 10 Foot Wind Tunnel of the National Advi
27、sory Committee for Aeronautics. Rep. No. 412, NACA, 1931. 8. Wenzinger, Carl J., and Harris, Thomas A.: Wind-Tunnel Investigation of an NACA 23012 Airfoil with Various Arrangements of Slotted Flaps. Rep. No. 664, NACA, 1939. 9. Recant, Isidore G.: Wind-Tunnel Investigation of Ground Effect on Wings
28、with Flaps. T.N. No. 705, NACA, 1939. 10. Brown, W. S.: Wind Tunnel Corrections on Ground Effect. R. wind tarmol. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-xwb Tecknlcal lotsxo.033 .3 I , I I 9 4 0 4 rig.3 Provided by IHSNot for ResaleNo reprod
29、uction or networking permitted without license from IHS-,-,- - * h Zlwdor d4flootLm for ” . . . s P I I I I I Q IO tN i i ,i 0 -. t a mpla of *ttMk a ,d - (a) mods1 rlth uld r1tbOllt td1. %, Ml am e, - ytal1 on) - $tti1 Off) Plglm B.- rfrwt of grmlud on of aur8l*r P-WA rods 1 itolllaent ooeffioisntr
30、 . mpe11ar rindmIlling; lmding Eeb* dcm: lt,noWo;ai,4eo. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-+I 00 *s f k i -6 R Aip Of “sy.pi“, qla-t Al - , Of attrok. 0 ftil. tail of aurtral wB4mrl. PU dom;it,a06a;6f,+s k ;6,o“. rlgue T.- Pfmt of ground on urt omffic Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
