Radial engine

The engines with cylinders out of star are a family of spark-ignition engine where the Cylindre S are placed the ones beside the others around the axis. The engine can be fixed or rotary; in this last form, the crankshaft is fixed compared to the frame and in fact the cylinders and the casing turn. In its traditional version, the crankshaft, very short, comprises one crank pin to which is connected one of the rods known as " rod maîtresse" , on which come to articulate the " rods secondaires" , so that the races are equal (makes some, the race of the secondary rods is not completely equal to that of the main rod, but it is negligible). Star architecture, in general, was very much used in Aviation. The number of cylinders is obligatorily odd for reasons of balancing and of cyclic regularity, for an engine simple star is 3,5,7,9.

The radial engines are also to use in a rotary way (case of much of engines of the years 1914-1918); this architecture has certain advantages in particular on the level of the Refroidissement and the uniformity, but presents the disadvantage of very important gyroscopic effect and a more delicate distribution to develop (certain engines had an inlet valve integrated into the piston). The rotary engine most powerful which was built (Gnome and the Rhone) developed approximately 240 cv realities. The adjustment of the power was done by cut of lighting on a group of cylinders - for example, the procedure used with this last engine: 3 cylinders with the idle, 6 cylinders on takeoff, 9 cylinders with full power. Without action on the orders, the plane left in Roulis by the simple gyroscopic effects when the 9 cylinders were engaged! In addition to this dangerous gyroscopic effect, the oil consumption of these rotary engines was prohibitory.

Two of the main advantages of these Moteur S are that they are easier to cool by air, more especially as they are assembled on Avion S, that the engines in V which require, in the strong powers, a liquid cooling (ex: famous V12 Rolls Royce Merlin). A radial engine is also simpler, lighter and less expensive than of other architectures. On the other hand, the Food in Fuel, which must be made in an identical way for all the Cylindre S, and the Torsion due to the movement are more difficult to manage than in a conventional engine, and frontal surface is relatively important with the detriment of aerodynamics, which explains the preference with the linear motors (out of V or flat) more compact on the frontal surface on the very fast hunters.

Sometimes, the cylinders can be arranged in several columns, from one to four. The power of the Moteur depending directly on the cubic capacity (on a plane, to avoid exceeding the Mur of the sound in blade tip of Hélice, the engine must necessarily turn to a modest mode of about a 2000 to 3000 tr/min to avoid as much as possible to have recourse to a reducing heavy and greedy in power), to avoid the cubic capacities unit (each cylinder) too important, this organization made it possible to place to 28 cylinders in 4 columns (engine Wasp Major of Pratt & Whitney), but on this level, cooling became very problematic, which has meant the abandonment of this configuration. Indeed, the most powerful radial engine which was built in series was the Wright Cyclone R-3350 with 18 cylinders turbo compound (with turbine of recovery of pushed exhaust fumes) in double star of 3750 cv in its ultimate version, which was in particular assembled on the Lockheed Constellation besides (on this plane, the engine, in version 3250cv, had a direct gasoline injection). The last plane which flew in regular service with this engine is the Lockheed P2V-7 Neptune of the French National marine.

Another French apparatus celebrates recently withdrawn of the active service (there remains about it only one maintained in-flight status by an association), the Noratlas, was been driven by radial engines 14 cylinders without valves built by the SNECMA under license Bristol: the distribution of the without-valves was ensured by rotary shirts which discovered lights: this device was very effective and reliable but caused an important oil consumption.

Currently, only of small radial engines are still manufactured, in particular in Australia by Rotec (one 7 cylinders of 110 cv and one 9 cylinders of 150 cv) and by HCI Aviation in the USA (one 5 cylinders of 75 cv and one 7 cylinders of 125 cv: the latter are with side valves to reduce cost, obstruction and weight). The largest engine still in manufacture is one 9 cylinders of Russian manufacture Vedenyev M-14 from 360 to 450 cv which is used in particular on planes of Aerobatics, or on planes the nostalgic ones of the radial engines, in particular American. These engines, famous extremely reliable, can now also be equipped with an electronic injection (not certified) which improves of it considerably fuel consumptions and the facility of starting.

There also existed of the radial engines Diesel 2 times, the famous Clerget prewar with the completely astonishing performances and reliability. Their development was stopped by the war and after the second world war, the time of the piston engines seemed completed, research being directed towards the turboshaft engines certainly much greedier while carburizing and of a not very pleasant noise, but less heavy and cumbersome, without vibrations and requiring much less maintenance.

External bonds

Seen ''' Wasp Major '''

See also the List of the aeronautical motor mechanics

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