FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1949
1949 - 1795.PDF
FLIGHT, 27 October 1949 BEECH TWIN-QUAD POWER PLANT American Arrangement for Coupled Engines IN the light of recent British developments with pairedand coupled-engine installations, the advantages ofwhich have been known to designers for many years, the approach to the problem adopted by the Beech Aircraft Corporation in their development of the Model 34 Twin- Quad, a 14-20-seater feeder-line aircraft, is of interest. Mr. T. A. Wells, Beech's Chief Engineer, and Mr. J. W. Massey, Test Engineer, were primarily responsible for its development. The American installation differs mainly from the British methods in that, unlike the angular or side-by-side disposi- tion of engines used in the Brabazon I and Fairey 17 respectively, and the arrangement proposed for ihe Saro Princess, the small coupled Lycomings of the Twin-Quad are horizontally opposed with their axes parallel to the main spar. Each pair of engines is coupled to drive a single airscrew, rather than the coaxially arranged double airscrews favoured in British designs. A brief description of the Twin-Quad's aerodynamic characteristics, evolved as the result of over 100 flight tests, is necessary in order to understand the various considerations which have governed the arrangement of this installation. It is generally accepted that an essential characteristic of any four-engined aircraft is that it should be able to continue take-off and climb with one airscrew windmilling in the event of an engine failure; this problem is, of course, non-existent in the Twin-Quad, as the single airscrew con- tinues to be driven by the remaining "live" engine, thus relieving the crew of the necessity for identifying and feathering the inoperative one. Tests have shown that when the Twin-Quad "loses" an engine there actually The clutch Is shown in the disengaged position. Rotation of thecrankshaft causes the engaging splines to move towards the engine, thus compressing the clutch discs to provide a direct drive. OVERRIDE CONTROL SLEEVE OVERRIDE CONTROL SPRING OVERLOAD SLIP SPRING SPHERICAL SPLINE COUPLING TO MAIN GEARBOX PINION MALE SPIRAL SPLINE This exterior view of the Twin-Quad installation shows the cleanlines permitted by such an arrangement, and gives a deceptive impression of the aircraft's being " underpowered". remains more than three-quarters of its available thrust power, as opposed to less than three-quarters thrust horse- power for the same condition in a conventional four-engined . aircraft. This is due to the extra power required to over- come the drag which is still produced although the airscrew is in a feathered condition. Beech also claim that the minimum safe air speed is considerably lower than that of an equivalent four-engined aircraft flying on only three engines. Use of the horizontally opposed installation also permits complete submergence of the engines within the wing, thus materially reducing the parasitic drag and aerofoil disturbances usually associated with normal engine nacelles. The general relation of the main components of a Twin- Quad power plant, as developed to date, are shown over- leaf. They consist of two 400 b.h.p. engines (standard Lycoming GSO-58os), two clutch assemblies, main gear box, drive shaft, nose assembly and the airscrew. The clutches are arranged to drive bevel pinions through annular splined couplings which permit movement of the engines in their rubber mounting. Inside the main gear box the bevel pinions mesh with the main input gear on the transmission shaft, and the gear box itself is rigidly mounted in the wing structure. Drives for ancillary equip- ment such as generator, starter, governor, oil pressure- and scavenge-pumps are provided by spur gears driven from a spur pinion carried on the main spiral bevel gear. The two multiple disc clutches provide direct connection between the engines and the main gear box pinions. Axial force necessary to compress the discs in order to provide a direct coupling to the airscrew is derived from the action of engine torque on a spiral spline. In order to avoid damage to the drive system from shock loads the torque transmitted by the clutch is limited by an adjustable stop. If engine torque fails altogether the spiral splines act in reverse, separating the clutch discs and disengaging the dead engine without affecting the drive from the live one; automatic re-engagement occurs if the engine again becomes operative. In order to ensure a " flywheel" action during conditions of starting, idling and gliding, a mechanical override is provided which is operated electrically by changes in engine manifold pressure. With this arrangement the clutch is in the "automatic disengage" position under all powered flight conditions, and the clutches are mechani- cally locked so as to transmit torque in either direction when operating at or near " closed-throttle." The whole trans- mission, including the nose assembly, is pressure-lubricated by a dry-sump system—two spray jets being incorporated to cool and lubricate the spiral bevel gears. Both the air- screw shaft, which, incidentally, also drives the nose- PARTS COUPLED TO ENGINE X/////A A ir>e/-nfrw
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
