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Aviation History
1950
1950 - 0029.PDF
FLIGHT, 5 January 1950 modern high-speed design, the Gremlin rough-riders are now beginning to show their hand. Only a few months ago, at the 1949 National Air Races, a North American F-86 Sabre took a sound rattling of its whole tail end, resulting in wrinkling of the fuselage skin and the loss of more than half of the elevators. The pilot, indeed, was fortunate in having sufficient stabilizer trim control in hand to make a spectacular landing. No doubt, a tem- porary solution will be found in beefing-up the tail struc- ture, but the basic treatment must eventually be aero- dynamic prevention, rather than structural half-cures. (So long as the bold, bad Gremlins are encouraged to ride the tail, they will try to pop the rivets.) Somewhat surprising to the advocates of power-operated control systems for jet fighters is the fact that all the con- trol surfaces of the Skyrocket are manually operated through straightforward, low-friction, control circuits ; furthermore, none of them has any form of aerodynamic balance—a design characteristic made feasible, no doubt, by virtue of the narrow-chord movable surfaces. It is in- teresting to note, for example, that the rudder and elevators are simple hinged surfaces provided only with anti-flutter mass-balance weights at their extremities. Lateral Control.—In the case of the ailerons (invariably the trickiest control to get right), mass, or dynamic, balancing is combined with static balancing in the form of a continuous nose-portion forward of the hinge axis and shielded within the wing profile—the dynamic mass re- quirement being met by a series of tungsten balance- weights distributed along the leading edge of the aileron. With this simple construction—a return to pre-war sub- sonics, in fact—both the upper and lower surfaces of the aileron remain cleanly mated with the wing surface throughout the aileron travel. This feature contributes to a very respectable drag-saving at high speed. Dimensionally, the ailerons extend over roughly 45 per .cent of the semi-span of the wing, while their mean chord is only about 15 per cent of the local wing chord—-a very low chord-ratio. Based on a total aileron area of 10 sq ft and the net wing area of 133 sq ft, the area ratio (aileron /wing) is 0.075. If, however, the gross wing area of r75 sq ft is considered more appropriate (a doubtful premise, in the case of low- and mid-wing configurations), then the area ratio comes down to 0.057. Recent statistical data on this point indicate that fighters usually average around 0.060, so obviously the Skyrocket is not shy on aileron area, despite the optical illusion produced by the low-chord effect. Although this type of aileron, per se, is known to possess undesirable yawing moment characteristics at high wing \ Design artist : Mr. Edward H. Heinemann, chief engineer of the Douglas El Segundo plant, takes a look at his handsome r ffspring. (Wing slottery by courtesy of Sir Frederick Handley Page !) This view shows the original model with flush-type windshield, previously illustrated in Flight of February 5th, 1948. A supersonic speed run nea> oeoci t iciti a\. I iuiuv. with WI'UU- jet and rocket motor in combined operation. angles near the stall, the answer to that, in the case under review, is provided by two powerful remedial factors; namely, the installation of Handley-Page-type leading-edge slats over the outer 75 per cent of the wing span, plus a highly efficient vertical tail ensemble. The open slot combs out the burbling air and holds up the rolling moment to higher wing angles, while the combination of sweeping dorsal fin and powerful rudder counteracts the opposing yaw of the down aileron. All of which, of course, is ele- mentary aerodynamics—for those who know where to burrow-sunder the haystack. Mounted on four sliding links from the wing, the slat aerofoil is of the floating type, automatically opened or closed by the air pressure over it. (The resultant pressure vector over the leading edge changes direction, magnitude and sense, with changing wing incidence and speed.) Port and starboard slats are mechanically interconnected so that they operate in unison together, and they can be locked in either the open or closed position. Chordwise flat-plate segments, which act as boundary-layer fences, are mounted on the upper surface of the wing at the inboard end of the slats, model research indicating that they boost the efficacy of the slot action as an anti-tip-stalling device over back- swept wings. While the slat element is very neatly tailored to the wing in the closed position, nevertheless there is a slight, but perceptible, discontinuity where the chamfered trailing edge of the slat nests on to the wing profile, as it is hardly practicable to taper-off the plate thickness to a razor-edge finish. In view of the extreme sensitivity of a laminar- flow wing section, particularly in the region of the leading edge, it would be interesting to know whether, in practice, the Skyrocket wing does actually achieve laminar flow over the slatted portion of the wing. Experience suggests that the transition locus would lie along the trailing edge of the slat (about 13 per cent chord), and hence the profile drag is probably at least double that of the laboratory ideal. Perhaps in view of current fabrication and design tech- niques, this point is somewhat academic at the moment.
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