>
>Graham,
>
>Perhaps other air-cooled aero engine owners will back me up here, but I'm
>not sure what you mean by "...that it is not possible to optimise the
>performance of any air cooled engine,
>bearing in mind that most of the world's reciprocating aero engines are
>direct drive, air cooled I think your statement needs clarification.
>
>
Hi Andy
most of the worlds pistom aero engines were designed a long time ago and
in spite of advances in materials , have not really advanced much in
efficiency. The highest performance engines were all liquid cooled.
(Rolls Royce Merlin, Napier Sabre, Junkers Jumo, et al) In wartime the
compromise may not be aimed at performance. There is always a compromise.
>Also, the Europa is NOT an aircraft which needs to have a large propeller
>turning less than 2000 rpm for optimum high speed operation. At (even) a
>cruise speed of 160kts a 58" propeller turning 3000 rpm is working very
>well.
>
"There is no substitute for span!" props or wings! Also at 3000rpm
&160kts what is the tip speed? 0'7Mach? ( confess I'm too lazy to work
it out) but with a fat wooden prop section compressibility will
certainl;y be costing energy. Agree wood is the original composite but
it has it's limitations. A mixture of S glass and carbon is the best so
far. (solid carbon is too stiff) (imho) which is why the Arplast is more
comfortable to fly behind than the Airmaster/Warp drive. For some reason
Alain declined to make blades for our NZ friends. Pity, they would have
a good combination of engineering and aerodynamic artistry...
> the VP propeller performance has more to do with the Rotax's
>relatively peaky power and torque curves rather than the wider speed range
>of the aircraft.
>
Andy, it's not the engine that's the problem, it's the prop! At early
take off the prop is largely stalled because of the high angle of
attack. The finer the pitch the quicker it unstalls and starts to work.
With a fixed pitch prop if it works well at start it will over rev in
the cruise.
I like the idea and principle of the Jab but it can never win because of
the basic laws of physics. Here in the UK we hear of warped heads and
other problems but that may well be poor installation design. There is
always a compromise and I am inclined to think that the complication of
liquid cooling is a better alternative. Bear in mind that Rotax 9xx
engines havwe been shown to survive good hour ove the sea even when only
aircooled.
Graham
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