FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1934
1934 - 1476.PDF
SUPPLEMENT TO FLIGHT 1382b 90 THE AIRCRAFT ENGINEER DECEMBER 27, 1934 STALLING SPEEDS 04 06 OS 10 IZ 1-4 MAXIMUM UFT COEFFICIENT 1-6 SPLIT FLAPS VARIATION OF MAXIMUM LIFT CO£FFlCI£Nr WITH FLAP ANBIE Ob IOJ 01 0 , FI6.2. r / •f— X 4. a - O SCHRCNK X TN42 (CkrkY) + TN47ifaar/<Y) A CAT./&AI4S) N 20* 20' 40' 60' 80' 100' BO' FlAP ANGLE ore 010 0-08 006 0-04 0-02 SPLIT FLAPS VARIATION OF DRAB COEFF. AT CONSTANTKi-O-5 (FLAPCHORD-OZc) 7 20' FLAP ANGLE 60" FIG.3. 8IT100' IM' LOCATION of SPLIT FLAP 05c 0-4c 0-3c 0-2c 0-lc 0 DISTANCE FORWARD OF TRAILING ED6E 0-5 0-4 ,0-3 0-1 OSCHKNK «w<a + W47Z 1 1 f ——_ 60'SPLIT FLAP VARIATION OF CHORD FIG.5. 0-1 c 02c 0-3c 0-4e FLAP CHORD HINGE MOMENTS of SPLIT FLAPS •020 •015 r 010 •005 •020 •015 •010 •'.05 0-lc 0-2e 0-Sc FLAP CHORD FIG 6 45'- • M Pcsv1 y / / > / 0-2SC ~ 0IS< 20' 40" 60" FUP ANQLE TO deg. Estimates of the effect of the flap on the Douglas D.C.2 suggest a reduction of stalling speed from 68 to 59 m.p.h. and increase in gliding angle of 3 deg. The minimum distance to come to rest after clearing a Tooft. obstacle is calculated to be reduced from 2,000 to 1,350ft. This calculation is based on the assumption that the approach is made at the minimum speed from which complete flattening out is possible in each case and that the coefficient of friction on the ground is 0.3 with brakes. It should be noticed that any excess of speed on the approach will result in a greater increase of run for the unflapped aeroplane. It appears, therefore, that in order to make a clean, heavily loaded aeroplane reasonably easy to land it should not be necessary to have full-span flaps. This conclusion would appear to have been justified in practice since no full-span flap is believed to be in use commercially now except on the Pander Postjager. Special Ailerons for Use With Full'Span Flaps If a split trailing edge flap is run right out to the wing tip some unconventional form of aileron must be employed. One method is to use ailerons in the normal position but so arranged that they move upwards only, through a large angle. American model tests show that the angle has to be about 70 deg. to give rolling moments comparable with those of conventional ailerons. Ailerons of this pattern have been tried in flight on the Fairchild F.22 monoplane with a full-span split flap and are believed to have been abandoned on account of excessive hinge moments. An alternative developed by the N.A.C.A. is a retractable curved plate aileron which need involve no aerodynamic hinge moment; these ailerons have been used successfully on the F.22, but they must involve considerable extra weight. Leading edge spoilers or interceptors appear very pro- mising from model tests, but when tested in flight by the N.A.C.A. they gave an initial reversed control equivalent to a half second lag. The only remaining solution is an auxiliary aileron mounted above the trailing edge of the wing, a type TYPES of LANDING FLAP christened " Park bench " in the U.S.A. According to the Zap Corporation, who use this type in conjunction with a full-span Zap flap, the exact location of the aileron and its zero setting is very critical. A feature of this type of aileron is that its rolling moment coefficient is increased when the lift flap is down so that adequate control should be preserved at low speeds. Possible objections to this type are its extra weight, drag at high speeds, and likelihood of causing torsional distortion of the wing owing to its far back location, but full-scale tests in this country will shortly settle these points. Pitching Moments Due to Split Flaps The effect on longitudinal trim when a flap is pulled down is rather complex since it involves three factors, the backward shift of the wing centre of pressure, the lateral shift of the &L ~a curve, and a change in downwash over the tail. There is also the possibility of the turbulent wake causing a drop in tail efficiency. The simplest con- dition to consider is that of unaltered speed when the flap is down, i.e., kL is kept constant, which means that the incidence is reduced. Consequently there is a nose up' pitching moment produced by the reduced incidence of the tail. At constant kL the downwash at the tail should be practically unaltered for a full-span flap. From model tests on split flaps of chord varying from 15 to 30 per cent.,
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
