FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1935
1935 - 0459.PDF
FEBRUARY 28, 1935- 13 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT •22(lg hord However, at large elevator angles, the greater chord flap contributed a greater hinge moment. 1 ) Comparative wind-tunnel test of inset flaps and external flaps indicated that the two types had approxi mately equal effectiveness even though the inset type had a smaller moment arm. (c.) The inset-type flap can be satisfactorily used as an aerodynamic balance as shown in wind-tunnel tests. The balancing effect of the flap was approximately equi valent to that of a leading edge balance up to control surface angles of 15 deg., the maximum angle to which a control surface is generally moved in high-speed flight when the balancing effect is necessary. 1 W. G. A. Perring, The Theoretical Relationships for an Aerofoil with a Multiply Hinged Flap System. R. & M. No. 1171 (1928). . * George J. Higgins, The Prediction of Airfoil Characteristics, N.A.C.A. Report No. 312 (1929). ONE-WHEEL LANDINGS An Investigation into the Side-load on the Undercarriage of an Aircraft Landing on One Wheel By B. B. WALKER, B.Sc. WHEN an aircraft lands on one wheel (or on all the wheels on one side, if the undercarriage has more than two wheels) or when the wheel (or wheels) at one side are temporarily out of contact with the ground during taxying, a rotation commences about the point of contact with the ground. The centre of gravity must necessarily move sideways in accelerated motion, and this necessitates a force in this lateral direction ; consequently, there must be a side-load on the tyre. In this investigation it is shown that this side-load is a definite proportion of the vertical-load on the wheel for any par ticular aeroplane (neglecting side-slip of the wheel and sideways tyre deflection) and a formula is found giving this proportion. In what follows the simplest case is taken, in which the aircraft is trimmed laterally, but the uneven ground touches one wheel and not the other (see diagram). It .will be seen that the result applies either to the condition of landing or taxying and whether the shock absorber is working, or has come to a position of equilibrium at the centre of its travel. Let 8 = the angular acceleration of the aircraft in radians per second per second. /, = the vertical component of the acceleration of the centre of gravity in ft./sec.2 (considered as posi tive upwards, i.e.. for retardation of fall. /. = the vertical component of the acceleration of the parts of the machine directly above the wheel, excepting those parts which move relatively to the aircraft with the wheel (using the same sign convention). = the radius of gyration of the aircraft in feet about a longitudinal axis through the centre of gravity. J - the weight of the aircraft in lb. - the height in feet of the centre of gravity above ^ the pomt 0f grouruj contact. - the horizontal distance from the centre line of __ "*e machine to the point of tyre contact, in feet. *e vertical component of the ground reaction °n the wheel, m lb. It S = the horizontal component of the ground reaction on the wheel, in lb. The inertia forces of the machine may be divided into a vertical force Fv and a horizontal force FH, each of which is acting through the centre of gravity, and a couple C. These forces, the weight of the aircraft acting through the centre of gravity, and the ground reaction (represented by R and S), form the complete system of forces on the aircraft and are shown on the diagram. Since the aircraft must rotate about the point of tyre contact, we have— W .. F H = — 9h (i) Also, the only horizontal forces acting, FH and S, must be equal, giving— W •• S = Oh .. .. .. . • •• •• (2) Equating the vertical forces gives— W - Fv = R - • • (3) These equations (2) and (3) show that the horizontal forces form a couple, of magnitude Sh, while the vertical forces form a couple, of magnitude R„ of an opposite sign. The complete system of forces, therefore, consists of these two couples and the inertia couple due to angular accelera tion about the centre of gravity. This inertia couple has a magnitude— w... — Bk°- so that f y&2-R0-S, .. .. (4) By substituting the value of S from (2) W.. W.. — »*» = R a —eh°-g g giving— -^ A2+A2) = RS (5) 8 or 6 = Rag W h* + ft2 Substituting in (5) the value S/h of W-— tffrom (2) g %fl + A2) = Ra (6) or S = - Rah (7) is always a definite particular machine *" Thus the side-load on the wheel fraction of the vertical-load for a except for a slight variation of h, due to the working of the shock absorber. In the present strength requirements of the Air Ministry for airworthiness the external force to be considered in the
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
