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Aviation History
1935
1935 - 0456.PDF
SUPPLEMENT TO FLIGHT 226/ 12 THE AIRCRAFT ENGINEER FEBRUARY 28, i935_ 12° lC FIG.10 o z ft m r Ss- -4* -,~ ' 0Cs-t4- FI6.II. Ks-0° .. -10' -20° TRIMMER ANGLE 6 -30 3 z I a 8° FI6.I2 — •4 PI r \A 1 U.lt D B "\ ^\ V M U^V JJ 8' IZ* 16* W 24" 28* ELEVATOR A.NGLE 6 Fig. 10, Lines of flow over stabiliser-elevator-trimming flap unit at large elevator angles. Fig. 11, Angle of trim of balanced ele vator for zero stick force as affected by trimmer angle and angle of attack of stabiliser (aj. Elevator trimming flap configuration as in Fig. 9. Fig. 12, Elevator angle necessary to trim Curtiss-Wright " Condor " with stabiliser fixed at —0.5 deg. to wing chord, C.G. at 26.5 per cent. From wind-tunnel tests of 1/32 scale model. Fig. 13, Types of aerodynamic balances. A, no balance; B, leading edge balance (24 per cent, of overall elevator chord) ; C, inset flap balance cf/cc =0.285, S S^ = 0.070 ; D, leading edge balance B combined with flap balance C ; E, external flap balance c,/ct. = 0.285 ; S/S =0.070 ; AR,.=4, Fig. 14, Hinge moments for elevators with balances shown in Fig. 13. Stabiliser angle as = o deg. from 150 m.p.h. to 130 m.p.h. agrees with the motion that was observed in flight. •In Table I, the effectiveness of the control flap diminishes rapidly at low air speeds and large flap angles. This is due to the reduced effectiveness of both the flap and the elevator as shown in Figs. 11 and 12. This has been observed in flight as well, as is illustrated in Table II, obtained in flights of a two-place Curtiss aeroplane which had both an adjustable stabiliser and an elevator control 3ap. TABLE II.- -Airspeed for balance as function of stabiliser setting and flap a?\gle. Flap angle Airspeed, m.p.h. Stab. -2°. Stab. -6" 0 5 10 15 20 25 137.0 129.0 122.5 116.5 112.0 109.0 112.0 105.5 101.0 99.0 97.5 97.0 Aerodynamic Balances In Figs. 13 and 14 are shown several types of aero dynamic balances and their comparative hinge moments. The moment curves for the flap-type balances were derived from the curves of Figs. 6 to 9 by drawing the curves through the points where e = — 8. It is seen that the inset flap balance C has satisfactory characteristics, being somewhat better than the leading edge balance through the range of elevator angles up to 15 deg. It is in this range that aerodynamic balance is most important because, in high-speed flight when the control loads require a balance, the elevator is never moved over 15 deg. Conclusions (1) The inset-type control surface flap is satisfactory to use as a controllable " trimmer." and its use has resulted in the simplification jof the design of tail surfaces. The necessity of a stabiliser adjustment has been eliminated on aeroplanes where the elevators have been designed to have sufficient power to stall the wings. Furthermore, the use of controllable flaps on the rudders of twin-engined aeroplanes has made it possible for such aeroplanes to hav satisfactory directional control in single-engine flight tfi single vertical tails, a marked simplification over °'"'y£ tails for twin-engined aeroplanes where a fin and ruu was placed in the slipstream of each propeller. . (2) The elevator hinge moments due to an unbala;^ elevator and due to a control flap as observed in the tunnel were approximately 60 per cent, of the theore-j^ values based on thin aerofoils at small angles- observed variation of the angle of the trim of e . $ with the angle of the trimming flap was in aPProX'0!,, agreement, at small angles, with the theoretical varia 1 ^ (3) Wind-tunnel test of inset control flaps all *^^[ same span but with different chord dimensions mm that, with the elevator neutral, there was little dlttece„t, in the elevator hinge moment between a flap 21 P^^of of the elevator chord and one 42 per cent, of the e
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