I have a slightly scaled up Wayne Ulery Laser 200 89" Span and have just removed a Zenoah G62 and replaced it with an MVVS 58 (Evolution) which will give a substantial power boost with no weight penalty in an already light model (17.5Lbs). The model incorporates plug in foam cored wings instead of the original built up ones. The original plan gives absolutely no indication of where the reccommended CofG should be.

The model was originally built and flown by my son some 9 years ago and we can't remember where the centre of gravity was, but it did fly well. The MVVS is significantly lighter that the Zenoah but it's centre of mass is probably 1/2" further forward than the Zenoah's was, the Ignition unit and ignition battery bring the total weight close to the Zenoah but they are well behind the engine so in theory the CofG should have moved back when the engine was changed. Now to my problem:-

The CofG is now at 24.7% of the Mean Aerodynamic Chord therefore it figures that with the Zenoah it would have been even further forward (way too far forward in my opinion)yet it flew extremely well in ullimited IMAC flying so it must have been reasonably correct.

I have written a fairly complex program to calculate where on the MAC the CofG should fall taking into account the tail volume and tail moment and this tells me that a good starting point would be 31.33%. Now to further complicate this problem I have a Carden 30% Extra amd the recommended CofG is at 26.5%. The bottom line is that I am unsure of a good startine point and to get it back to 30% I will have to put the flight pack in the rear of the fuselage.

I would appreciate any advice as to a good starting point if anybody can make a recomendation or has any experience with models having the Laser's wing planform and tail moment. I don't want to end up with a model that is hard to flare when landing.

Thanks in anticipation