I am currently getting an X4 cylinder, 150cc, 4 stroke engine 3D CAD Modelled, this engine is initially being designed for Powered Paragliding (PPG), classified as experimental Aircraft, so no certification is required!

I have read several discussions here, that largely relate to large ridged winged Aeroplanes travelling at high ground speed.

PPG is a Low & Slow (22~75kph) Aviation sport, there are obvious differences with this project being;

Most PPG engines max. rev are from 7'000~12'000rpm. Then a Re-drive is used to slow Prop down to approx. .88~.90 mach.

With a PPG, it is the Wing that sets the Speed in flight, not the engine! A larger more powerful engine only provides a higher climb rate or maintain lever flight easier.

Most engines of similar capacity swing a 125cm (49/28") Prop at around 2'700rpm to under 3'000rpm.

The engine we are designing uses a unique engine that has replaced the 100yr old conventional crankshaft with a patented Contra-rotating Trilobe centre drive shaft (CDS) technology, that uses two trilobe cams, that strokes each Piston 6 times on One revolution, thus providing 3 combustions in two revolutions of CDS, this engine will not be revving over 3'500rpm maximum.

Engine is currently 12.5kg and 41cm width x 37cm high x 20cm deep.

I am planing on using Two 100cm (40") Contra-Rotating propellers!

Raptor X4-150

I would appreciate it if anyone could assist/help me if this is an appropriate Sized Prop & what Pitch would be best ?

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    $\begingroup$ "With a PPG, it is the Wing that sets the Speed in flight, not the engine!" This is true of all aircraft. $\endgroup$ – Steve Mar 14 '17 at 12:28
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    $\begingroup$ @Steve Not exactly. In a conventional aircraft, once you select a certain power setting and adjust stab/elevator trim until you are in level flight, the resulting speed is dependent on the power setting. In a PPG, there is no stabilizer, so level flight will always be at a fixed speed. $\endgroup$ – Sanchises Mar 14 '17 at 12:54
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    $\begingroup$ @Sanchises In a conventional aircraft, in straight and level flight, if the power setting is increased (and only this is changed), the aircraft will initially speed up, but then it will start climbing. It should stabilize back at the original speed, which is set by the trim. $\endgroup$ – Steve Mar 14 '17 at 13:48
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    $\begingroup$ Why do you think you need contra rotating propellors for an engine predicted to produce only 20hp? $\endgroup$ – KuangGradeMark11 Mar 14 '17 at 14:00
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    $\begingroup$ The Engine is still in CAD design phase, then FEA testing, and finally the release hopefully will happen before the end of this year. You can see more information on the [Raptor-150 Project here][1]: [1]: poweredparagliders.com.au/_BlackHawk/Engines/… $\endgroup$ – The Raptor Jun 30 '17 at 3:25

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