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Aviation History
1958
1958 - 0072.PDF
74 FLIGHT, 17 January 1958 DC GENERATOR RELAY (Above, right) The electrical circuit of the new skid-warning system. (Abovs) The rudder pedals designed by Brooklands Aviation, which in- pororate the oscillated "toe-thum- per" button. (Left) The electric motor, cam, leaf spring and thum- per button. The electrical gener- ating system is buried within the mainwheel axle of the aircraft. TOE-TOUCH SKID WARNING . . . The coil and capacitor of the secondary relay are switched tosupply negative, discharging the capacitor and releasing the relay. This has the effect of cancelling any unused portion of the longhold-in period and thus switching-off the skid indicator motor, which will not then continue to operate when the wheel is rapidlyaccelerating (and requires early re-braking) after a skid. The skid indicator is mounted upon the rudder pedals; it is avibrator device consisting of a small D.C. motor running at 750 r.p.m. which, via a 4 :1 speed changer and cam, oscillatesa leaf-spring-loaded plunger at 50 c.p.s. It does not vibrate the pedal itself or affect the applied brake pressure. The indicatorcontinues to "thump" against the pilot's foot until brake pressure is released. To demonstrate the "foot thumper" skid-warning system,Goodyear had set up at Wallasey a dummy cockpit with a rudder bar and brake pedal of the S.B.A.C. type with built-in skidindicator units. The assembly, which can be seen in the heading photograph, is the prototype of a new Brooklands Aviation design.In front of the seat is a facia panel on which are mounted instru- ments showing brake hydraulic pressure and simulated airspeed,a veeder counter giving runway yards covered, and warning lights "prepare to brake" and "start braking." Behind the pilot's seat is Goodyear's 120in Arrol dynamometerdriven by a 400 h.p. electric motor. To the left and right of the flywheel are movable carriages and ram mechanisms upon whichwheel, brake and tyre assemblies can be "landed" against the flywheel. For demonstration purposes, to make the wheel skideasily, ram pressures were limited to 3,000 lb; a condition in which wet rubber clings to the periphery of the dynamometerflywheel and reduces the coefficient of friction to about that of wet ice. A DC-6 and Bristol Freighter wheel assembly is usedon the demonstration rig with a kinetic energy absorption of less than 2,000,000ft lb (this wheel is rated for use at K.E.s of6,338,000ft lb). As a result, some care had to be taken to release the pedal completely when the foot thumper (which, by the way,does not tickle) comes into operation. The brake-line pressure indicator is blanked-off during a test, as the best pedal force togive maximum retardation without skidding can fairly easily be judged from the dial. To obtain the best results a certain amountof skill (as well as practice) is required; foot pressure needs to be regulated so that the thumper does not quite come into operation.If it does so, the coefficient of friction of the test undercarriage is so low that brake pressure must be relieved entirely for theflywheel to apply enough static torque to rotate the wheel and tyre; but to ensure shortest-distance braking the brakes must beapplied again immediately. These characteristics would not apply to the same extent forlandings made in anything but exceptional runway conditions. Arranged as it is, the demonstration rig lends itself to some keencompetition, and Goodyear have a "names and braking distances" board in the test house to add to the fun. How quickly the system works is a function of pilot and system reaction time; the pilot may take about 0.3 sees to react and the wheel will then remain locked for about 0.4 sees. No damage to the tyre is done in this time. One possible disadvantage of this skid warning system is thatthe warning is a negative arrangement: when the foot thumper operates, too much brake pressure has already been applied. Butpresumably the simplicity of the system would have to be sacri- ficed if, for instance, a secondary frequency vibration indicationwere provided. This might be operated at a lower pre-set capaci- tor/relay current to give warning that with any greater pedalpressure, the skid warning system would function. In any case,: for the electro-mechanical scheme being developed as an alterna-tive to the electrical system, such complication could not be incorporated. The disastrous effect of skidding on aircraft tyres (Goodyearestimate that 50 per cent of all tyres returned to them are rejected because of flat spots and skid burns due to locking wheels) makean anti-skid system a wise safety investment. A system of the type described here may also show a return on increased tyreand brake life, since installation costs are said to be low. While specific examples cannot yet be" quoted, for an aircraft of theViscount type the cost might be £500—a sum that should quickly be re-couped in tyre savings by a short-haul airline. And in pro-viding a skid warning system for non-hydraulic brakes, Goodyear are offering a service that has not been provided before. Perhapsthe greatest advantage of the system is that skid control is under the control of the pilot. BEECHCRAFT'S 1958 PROGRAMME SALES of the new Beechcraft Travel Air are expected to totalapproximately $9m during 1958. This was announced at the company's recent international sales meeting at Wichita, when itwas also disclosed that Timken Roller Bearing Company had brought "the world's first business jet"—the Morane-SaulnierMS 760, U.S. sales of which are handled by Beech under licence agreement with the French company. Among the Beechcraft range of aircraft for 1958, the J35Bonanza is powered by a six-cylinder Continental IO-470-C engine rated at 250 h.p. at 2,600 r.p.m. A simplified continuous-flowfuel injection system is used, and the pneumatically operated Tactair T-3 lightweight autopilot is among the optional equip-ment offered. Economical cruising speed (65 per cent power) is 195 m.p.h.j and top speed is 210 m.p.h. Two versions of theTwin-Bonanza are being offered, the F50 (two supercharged 340 h.p. Lycoming GSO-480-B1B6 engines) and the D50A (two-high-compression 295 h.p. Lycoming GO-480-G2D6 engines). Top speeds are respectively 240 and 214 m.p.h., and cruisingspeeds 228 and 203 m.p.h. The new Model 95 Travel Air, now in full production, isdesigned to fill the gap between the Bonanza and the Twin- Bonanza, and is a four-seater powered by two 180 h.p. LycomingO-360-A1A engines. It cruises at 200 m.pJi. and has a maximum speed of 208 m.p.h. It was first flown in August 1956 and receivedC.A.A. certification in June 1957. The remaining aircraft in the 1958 Beechcraft range is the Super 18 executive transport.
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