The Rolls-Royce Crecy

Always woundered what whould happened if Rolls-Royce had developed the
utterly INSANE crecy engine, and shoehorned it into a spit!
The Rolls-Royce Crecy was a 2-stroke 90 degree V12 liquid cooled aero engine
of 26.1 litres capacity, featuring sleeve valves and direct petrol
injection. Single cylinder development began in 1937 under project engineer
Harry Wood. It was designed by Sir Harry Ricardo. The first complete engine
was built in 1941 and produced 1400 hp. There were problems with vibration
and the cooling of the pistons and sleeves. The firing angle was 30 degrees
and 15lb supercharger boost was typical. Bore was 5.1" stoke 6.5"
compression ratio 7:1 and weight 820 kg. The thrust produced by the 2-stroke
exhaust was estimated as being equivalent to 30% of the power of the engine,
and was exceptionally loud.
Unlike most 2-stroke engines, supercharging or turbocharging was used rather
than crankcase compression to force the charge into the cylinder. Stratified
charge was used where the fuel was injected into a bulb like extension of
the combustion chamber where the twin spark plugs ignited the rich mixture.
Operable air/fuel ratios of from 15 to 23 were available to govern the power
produced between maximum and 60%. The lean mixtures reduced detonation
allowing higher compression ratios or supercharger boost. Supercharger
throttling was used as well to achieve idling. The supercharger throttles
were novel vortex types, varying the effective angle of attack of the
impeller blades from 60 degrees to 30. This reduced the power required to
drive the supercharger when throttled and hence fuel consumption at cruising
The sleeve valves were open ended rather than sealing in a junk head. They
had a stroke of 30% of the piston and were 15 degrees in advance.
It was named after the Battle of Crécy, battles being the chosen theme for
Rolls Royce 2-stroke aero engines. There were however no subsequent Rolls
Royce engines of this type, and rivers were used for jet engine names.
Sir Henry Tizard was a proponent of the engine as Chairman of the
Aeronautical Research Council. The power of the engine being interesting in
its own right, but also the exhaust thrust at high speed and altitude making
it a useful stop gap between engines such as the Rolls-Royce Merlin and
anticipated jet engines.
Only six complete examples were built when the research was terminated in
December 1945. An additional eight vee twins were built. Serial numbers were
even, Rolls-Royce practice being to have even numbers for clock-wise
rotating engines when viewed from the front. Crecy number 10 achived 2500 hp
on 21 December 1944. Subsequently single cylinder tests achieved the
equivalent of 5000 bhp ( holy shi**! ) for the complete engine.
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Other interesting engines were the Napier Nomad (12 Cylinder horizontally opposed turbo-compound diesel - target HP 6,000!) and the H 24 (two rows of horizontally opposed 12's) Napier Sabre II, which developed 3,500 HP in later versions. The Nomad was never produced, but is considered by many to be the most complex aircraft engine ever attempted.
Reply to
Bob Chilcoat
One of the engineers working for Lockheed designed a mulit-mode jet engine back in 1947, that we would have trouble building even with all the advanced technology we have today. It was a 47 stage tubojet that used automatic controls to convert to a scramjet based on aircraft speed and power needs. As the aircraft sped up and the dynamic pressure in the inlet increased, the engine would decouple a stage of compression and feather the tubine blades as well as the stator blades. This would continue until all stages were feathered and only a single stage in the hot section was turning, only to drive the accessory gearboxes. By this point the aircraft would be well into the supersonic regime of flight and the engine would be operating in the scramjet mode. The data that I've seen suggested somewhere around 20,000 pounds of thrust in an engine case of only about 20" in diameter.
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I'm curious, what do you believe to be the definition of "scramjet"?
I can't see any way that an engine with 47 feathered turbine stages would be able to sustain supersonic flow in the combustion chamber.
Reply to
J. Clarke

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