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360 AIRCRAFT ENGINEERIN G December, 1945 a lower surface strip gives the same increase speed on a very clean aircraft at economical R. & M. No . 1936. Effect on Hinge Moment of in hinge moment as both strips, while on an cruising speed, but not a t top speed. Fitting Strips near Aileron Trailing Edge, of up-going control it reduces the effectiveness (5) Spiral stability was not in itself important, Increasing Aileron Chord and of Extending of the upper strip. bu t the aircraft should be designed as far as Aileron to Wing Tip. July 2, 1940. With an possible to maintain an even keel in bumps. R. & M . No. 1940. Aerodynamic Aspects of f t is not yet known how this can be best Appendix on Pressures over Surface of Control achieved. Blind Flight. May, 1940. By A. V. Stephens. fitted with Strips. By A. S. Batson and J. H. (3s. od.) Warsap. (3s. 6d.) R. & M. No. 1941. Note on the Effect of I t was required to determine whether blind flying This investigation was undertaken to find a Nose Shape on the- Characteristics of Frise techniqu e could be improved by limiting th e opera metho d of modifying ailerons so tha t a machine may Ailerons. August, 1940. By H. Davies and tions of the pilot and relying to a greater extent be more responsive in roll. upo n the stability of the aircraft. E. C. Brown. (2s. 6d.) (1) Hinge moment was measured on a 1/2·25 scale Flight tests were made a t two speeds on a Blen Wind tunnel tests have shown tha t a sharp-nosed "Hurricane " aileron with the following modifi heim, for C.G. positions covering th e available range, Frise aileron on a wing with N.A.C.A. 4415 tip cations:— t o determine its behaviour in bumpy air with eleva section stalled completely at angles of abou t 13 deg. (a) Strips (depth 0·02 in. and 0·04 in.) fitted near tors locked and rudder free, and the effect of lower (up going). A sufficient rounding of the nose of the trailing edge. ing the undercarriage was also noted. Turns of aileron removed this stall; at the same time the (b) Aileron chord increased from 0·18c to 0·22c various rates with elevators locked for trim were also balance was reduced slightly, and the range over and 0·26c. investigated. Blind flying unde r a hood with elevators which constant balance could be obtained was in (c) Aileron chord 0·22c, extended to th e wing tip. locked and/or rudder free was carried out for com creased by about 4 deg. The reduction in balance Strips (depth 0·40 in.) also fitted near trailing parison with normal technique. The results of the produced by cords near the trai ing edge has been edge. experiments arc discussed and a general survey of investigated and tests have also been made on the Rang e of aileron angle 0° t o ±15°; aerodynami c requirements for blind flight is given. effect of hinge height. Rang e of incidence —4° to 8°. Th e tests showed that, if very carefully trimmed, (2) Pressures were measured over the surface of a th e Blenheim would fly continuously through severe R. & M. No. 1947. Calculation of Additional control (0·4c) of an aerofoil (N.A.C.A. 0020 section, bump s with elevators locked without appreciable Mass and Inertia Coefficients for Rectangular 30 in. chord) with and without strips (depth 0·05 in. - loss of height or change of speed. It was, however, Plates in Still Air. November 8, 1941. W. 0·20 in.) or cords (0·09 in. diameter) by means of a essential to maintain full control of the ailerons in stati c pressure tube: Angles of incidence 0°, 4° and bump s or a spiral would develop causing rapid loss Prichard Jones. (1s. 6d.). 8°: Control angles ±10° and ±15°. of height and change of course. Th e additional mass and inertia coefficients for b (dCII/dα) and b (dCII/dξ) are both increased Turn s with elevators locked were unsatisfactory 1 2 rectangula r plates of various aspect ratios have negatively by about 0·2 when strips of abou t 0·8 per in that height was lost and speed gained. The be been determined experimentally by Scruton and by cen t of aileron chord arc fitted to the "Hurricane" haviou r of the aircraft in straight flight with eleva Gracey. For comparison with their results, some aileron. These slopes arc increased similarly when tor s locked was not greatly affected by changes in theoretical values are calculated in the present aileron chord is increased, but by a little under half C.G. position within th e allowable range: turn s were pape r by the use of an approximate form of the th e amount. Extending the aileron to the wing tip less unsatisfactory with C.G. aft. double t distribution method. In this method, the also increases b1 and b , In magnitude this increase After short periods of blind flight under the hood 2 oscillating plate is assumed to be infinitely thin in b1 lies roughly between tha t due to fitting 0·04 in. pilots were of the opinion tha t locking th e elevators an d is replaced by an equivalent sheet of doublets strips, and tha t due to increasing th e aileron chord did not make control easier on a stable aircraft such which induces the same irrotational field of flow in from 0·08c to 0·26c. The value of b is appreciably a s th e Blenheim. They were also of th e opinion that 2 th e surrounding air. Th e appropriate distribution of affected by gap at the nose. thi s device would be of very limited use in service doublet s is such that the normal induced velocity Measurement s of pressure over the surface of a an d likely to be a fruitful source of accidents. is equal to the normal velocity of the plate at all control reveal the following facts:— More generally it was concluded:— points. Formulae are derived for the induced velocities corresponding to certain modes of doublet (a) Increase in magnitude of hinge moment due (1) That for ease of control in cloud longitudinal distribution and the required combination of modes t o strips is due to a boosting up of pressure stabilit y with control column both fixed and can bo obtained by satisfying the normal velocity a t and forward of strip. This is considerable free was essential. The dynamic stability of condition at a number of points on the plate. In for a down-going (positive) control but may th e Blenheim was considered adequate in view of the large number of simultaneous equations be negligible for a small negative setting. tha t the aircraft would ride through bumpy which would have to be solved in this treatment , an (b) If th e diameter of cords and the dept h of strips air with little or no deliberate use of the approximat e method is substituted in which the are the same, and if the cords or strips are elevators. More static stability would, how chordwise distribution of velocity due to any ever, be advantageous. a t the same fore and aft position along con chordwzse mode of doublet distribution is assumed trol, the elfect on hinge moment will be ap (2) The ability to make accurate turns and cor t o b e proportional t o th e chordwise velocity distribu proximatel y the same. rections to course without using the rudder tion as derived by two-dimensional theory. This (c) The optimum position for strip is a t the trail wa s highly desirable. Equally good results assumptio n simplifies the numerical work as it is ing edge. migh t be obtained if full control could be the n sufficient, and most convenient, to satisfy the (d) Hinge moment increases as depth of strip maintaine d without using the ailerons. velocity condition along the mid-chord axis only. increases. (3) Controls should be light, effective and free Th e required doublet distribution is then readily (c) Only the strips on the pressure side of the from friction. found by collocation for any mode of motion. control are effective: on a down-going control. (4) It would be more difficult to maintai n constant
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Dec 1, 1945
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