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Aviation History
1945
1945 - 1341.PDF
FLIGHT JULY 12TH, 1945 same plan-form and size as on the B-17 Flying Fortress, although of different aerofoil section and construction. To prevent tailplane stall at certain altitudes, the leading edge of the tailplane is turned up, rather as though the aerofoil were upside down. Directional stability with the dorsal fin is such that it is claimed as preserved even with two engine failures on the same side at take-off. It is said that the aircraft is easy to fly and that it has no undesirable ground or flight characteristics, the control response in particular being singled out for special note. In this connection, the control surfaces are claimed to require no more effort in movement than those of many smaller machines, due to the painstaking care lavished upon getting the servo and trimming tabs abso- lutely right. Because of this, a high degree of rolling response is obtained, artd, additionally, operation of the rudder is said to require less effort than in the case of the Fortress, which, incidentally, is not a bad thing, for the Fortress's rudder is not exactly light; in fact, comparably to similar size machines, it is rather heavy. Four Wright Cyclone 18-cylinder air-cooled, radial engines of 2,200 T.O. h.p. are fitted, each engine being equipped with two turbo-blowers, one as reserve. Take- off r.p.m. and boost are 2,800 and 8.8. lb./sq. in. respec- tively, and fuel consumption is 99.7 (U.S.) gallons/ hour/engine at 59 per cent, power. Bore and stroke are 6.125m. and 6.3125m. giving a swept volume of 3/347 cu. in. (54.8 litres). Compression ratio is 6.85 : 1, and the dry weight, without hub or starter, 2,670 lb.( giving a sea level power/weight ratio of 1.21 lb./h.p. Speed-Range Indicator New and Valuable Instrument to Mitigate Inadvertent Stalling y* N instrument called the Baynes Speed Range Indica- /-% tor has been evolved by L. E. Baynes, of Alan •*•-*• Muntz & Co., Ltd., Heston, and has been exhaus- tively tested both here and in America, Messrs. R. B. Pullin & Co. having manufactured tie prototype instruments. Mr. Baynes, in giving the reasons which prompted the design of the instrument, suggested that the causes of high-speed stalls were not always fully understood by pilots, especially novices, and even if they were understood, it seemed rather a tall order to expect the pilot to multiply the known steady flight stall- ing speed of his machine by the square root of the increase in g during any particular manoeuvre. Not that the pilot ordinarily has any in- dication of g increase anyway. The inventor also avers that the instrument is. intended rather as an object lesson in what happens under con- ditions of increased g, rather than as a stall warning indi- cator, in that it gives an at-a- glance picture of the decrease in available speed range dur- ing turns or in pull-outs from dives. As is well known, the fctall- ing speed of an aircraft is proportional to the square root of the wing loading, and when in a small-radius turn or pulling out of a dive the wing loading is much increased and, therefore, the stalling speed is also increased. If g represents the gravitational force per unit of mas, and a represents the acceleration force per unit of mass due to turning or pulling out of a dive, the total force per unit of mass to be supported by the wings ia the resultant of g+a and may be called G. Since wing loading is propor- tional to G the stalling speed is proportional to A/G. Thus a high-speed aircraft in a small-radius turn, neces- sitating a steep angle of bank, may have a value for G as much as 6xG during the turn. The stalling speed during the turn is in this case increased in the proportion of ^/6=2.45 times normal stalling speed, which is equivalent on a modern aircraft to about 200 m.p.h., and as the flying Ordinary air speed is indicated by the " white " pointer,and stalling speed by the "red " pointer. The latter also indicates against the outer "G " scale. not much above this speed, there is the danger of a stall taking place without warning. The same thing may hap- pen- when pulling out of a dive ; the stalling speed may increase to two or three times normal, due to the increase in the value of G, with the result that the machine stalls and fails to pull out of the dive. Furthermore, at altitude the stalling speed has increased in the ratio of the square root of the relative density, and as the maximum speed also be- comes less above the altitude to which the engine is super- charged, the speed range be- tween stalling and flying speed is reduced for all values of G. The Baynes Speed Range Indicator comprises a normal A.S.I, with an additional red pointer, concentric with the A.S.I, pointer, which is set at the known steady flight stall- ing speed (engine on, Haps up). This stalling speed i pointer is operated by a;'*"*"* mechanism inside the instru- ment which will turn the pointer to a degree propor- tional to A/G, SO that the correct stalling speed appro- priate to the prevailing G will be shown on the dial, and the margin between the two pointers will thus repre- sent the speed range available between the prevailing stall- ing and flying speeds. If the air-speed pointer moves back to a position in which it overlies or underlies the stalling- speed pointer, stalling speed will have been reached and, by the approach of this superposition of the pointers, the pilot is given an easily visible indication of the approaching danger of stalling. Since the indicated air speed given by a normal A.S.I. does not compensate for change in density at altitude, the indicated stalling speed is constant at all altitudes although 1he actual stalling speed increases as the square root of the relative density. No altitude compensation is therefore necessary for the stalling-speed pointer mechanism if the correct speed range available between prevailing stalling. _, speed and flying speed is to be shown by the instrument, speed during the turn may have been reduced to a figure At altitudes above that to which the engine is supercharged,
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