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Aviation History
1956
1956 - 0934.PDF
80 FLIGHT THE Pasotti Airone F.6, designed by Stelio Frati and built bythe Pasotti factory at Brescia, is a four-seat, twin-enginedtouring aircraft, strongly built, equipped with a retractablenosewheel undercarriage and having a high cruising speed and considerable range. The prototype, which is the subject of thisreport, and which I myself tested, is equipped with two Continental C90 engines of 90 h.p. each, fitted with fixed-pitch, wooden air-s;rews. Production aircraft, which are now being delivered, have two Walter Minor IVs of 105 h.p. each, with variable-pitch,feathering airscrews. More powerful American engines had been foreseen, but it was not possible to obtain the variable-pitcha'rscrews for them. Such airscrews are considered vital for a small twin—and even for a fast single-engined aircraft. With thetwo 105 h.p. engines with v.p. airscrews, full power is available at take-off, in the climb and during single-engined flight, so that themaximum weight, cruising speed (161 m.p.h. with the Walter engines) and fuel consumption will be balanced to the best advan-tage. On one engine the full power of the operating engine will bt available and the drag of a windmilling airscrew will be avoided. By contrast, with fixed-pitch airscrews the full power of theengine may only be available at maximum speed in level flight, and the very minor advantages these could offer over engines oflesser power with v.p. airscrews would be a slightly higher maxi- mum and cruising speed. If a 140 h.p. engine, for example, isfitted with a fixed-pitch airscrew, the pitch may be calculated to give the maximum r.p.m., and therefore the maximum power, onlyin level full-speed flight. In this case, at take-off speed, power proportional to the maximum speed will be lost because if engineand airscrew are set to give 2,600 r.p.m. in level flight at 185 m.p.h., at take-off certainly no more than 2,000 r.p.m. would be available;and this, according to the power curves, will reduce the maximum 140 h.p. to 100 h.p. or even less. In a full-throttle climb a similarloss of power would occur. Moreover, there would be an additional loss in the aircraft's aerodynamic efficiency because, with fixed-pitch airscrews, the optimum aerodynamic climbing speed usually has to be increased by five or ten per cent in order to makeavailable more r.p.m. and therefore more power. These arguments hold good either for twin- or for single-enginedaircraft capable of more than about 140 m.p.h.; and the disadvan- tages of the fixed-pitch airscrew can be translated, in proportionto the difference between take-off and maximum speeds, into a reduction of payload capacity, because this, too, directly affectstake-off and climb. For a twin, however, there is in addition the question ofsingle-engined flight. In this case we find not only a reduction in power of the working engine caused by the fact that the resultingreduction in airspeed forces r.p.m. down, but also that a good proportion of the remaining power has to be used to overcomethe drag of the windmilling airscrew. It can be concluded, there- fore, that an aircraft equipped with 140 h.p. engines and fixed-pitchairscrews might well have the disadvantage, in comparison with a powerplant of 105 h.p. engines and v.p. airscrews, of producingthe same or less power in just those flight conditions where maximum power is most important, i.e., during take-off, climband single-engined flight. The fixed-pitch installation will have a higher fuel consumption: the aircraft will have to carry a higherfuel load either in order to obtain the same range or to allow for the higher weight of the more powerful engines. This has proved a very important problem, especially when,as at present, higher and higher speeds are being achieved with comparatively low-powered engines. The Airone is one of manycases in point. As mentioned above, for want of v.p. airscrews, the Aironeprototype was fitted with two Continental 90-h.p. engines with Flight-testing the Pasotti Airone F.6 Thoughts on Airscrew Suitability A Jet Version in Prospect By VICO ROSASPINA THESE notes were contributed by the Italian test pilot who carried outthe test flight programme of the prototype Pasotti Airone F.6. He was also responsible for flight testing the first production aircraft which, ashe relates below, is fitted with slightly more powerful engines and variable-pitch, feathering airscrews. wooden fixed-pitch airscrews. The passenger cabin is comfort-able and visibility in all directions is very good; lap straps are provided for the passengers. Control-column movement isunobstructed and the throttles, carburettor heating controls, mix- ture levers and fuel cocks are arranged below the instrument panelbetween the two pilots and well within their reach. For take-off all levers have to be set upright.On the left-hand side of the panel in front of the first pilot are the undercarriage and flap controls, master-switch, parking brake,engine instruments and hydraulic gauges. Centrally disposed is the blind-flying panel with, from left to right, A.S.I., artificialhorizon and V.S.I., and below them the ball-and-needle slip indicator, gyro D.I. and altimeter. On the right of the panel arethe V.H.F. controller; radio compass; and switches controlling" generator, battery, radios, cabin, navigation and landing lightsand pitot-head heater. On the floor between the two pilots are the two starters, undercarriage emergency lowering control andfire extinguisher actuators. Beside each pilot's feet are inlets for hot and cold air. The independent hydraulic mainwheel brakesare toe-pedal operated and flaps are hydraulically set to any position between 0 and 60 deg, with an indicator on the left.Magneto switches and elevator and rudder trim wheels are in the cabin roof. Ventilation is independently controlled for thefront and back seats. Folding tables are mounted in the backs of the front seats,together with small lockers, and a baggage compartment is acces- sible either from inside the cabin or from outside. A number ofaccessories such as ash trays are also available. Smoking in the cabin is permitted since no fuel lines pass nearby. In the productionAirone all fuel will be carried in permanently attached tip tanks, but in the prototype tanks are in the wings, and high up in the Comfortable, and offering an excellent field of view, the cockpit of the Airone is shown below to be treated in modern style. The layout is described in the text immediately above.
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