Abstract:
The present work was undertaken in order to extend the existing experimental information on the 30 per cent. Griffith suction aerofoil obtained by Richards, Walker and Taylor (1945), in particular: (a) to investigate the behaviour of the wing when the flap was deflected, (b) to test a wider slot and improved internal ducting system, (c) to investigate further the variation of suction quantity with speed, and (d) to find the variation of CD with suction quantity and with different surface conditions. Tests with zero suction were carried out at a Reynolds number of 2.88 × 10power6 for a range of incidence of 0-20 deg. and for flap angles of 0-14 deg. With boundary layer suction applied, tests were carried out at this Reynolds number to 6 deg. incidence only, owing to insufficient suction head. At a Reynolds number of 0.96 × l0power6 the pump power was sufficient to prevent separation up to an incidence of 16 deg. where the maximum CNF recorded was 2.3 with 14 deg. flap angle. The flap is effective as a high-lift device. A given CL can be obtained at a much smaller angle of incidence when there is a positive flap setting than with zero flap angle, and less suction is required to prevent separation. There is considerable scale effect present between the two speeds at which tests were made, and it is desirable to test the wing in the Compressed Air Tunnel in order to estimate flight performance, particularly in the event of suction failure. The suction quantity is high at R = 0.96 x 10power6 but now shows a continuous decrease with increase of Reynolds number in contrast to the irregular variation found by Richards. With no suction and with laminar flow to the slot, the CD has the low value, for the thickness of the aerofoil, of 0.010.
