Kyosho Osmose C of G

[Bob Vaughan]

I'm in the process of resurrecting a Kyosho Osmose powered by a OS 55ax and have encountered a c of g problem which someone might be able to help with. The suggested c of g according to the manual is between 210 and 230mm forward of the trailing edge at root. Thinking that 220 might well be a good starting point I then find that the airframe is significantly tail heavy requiring a hefty roll of gaffer tape on the prop to get anywhere near to correct balance.

The model is configured for the location of the fuel tank astride the c of g position, in the case of a 'pumped' engine, but it also has provision for the tank to be fitted right behind the firewall in the case of a normal non pumped 46 - 55 2 stroke. This moves the tank at least 4" forward of the suggested c of g which is quite big discrepancy. Any members previously owning this airframe remember the likely solution please?

many thanks

Bob

[Peter Jenkins]

I've not had an Osmose, but I did have its predecessor the Oxalys. I had the tank forward with that one and had no difficulty with the CG and an Irvine 53. It flew beautifully but needed a fair bit of sticky lead at the back to get the CG to the right position as judged by its flying characteristics.

Just a thought, if you move the balance to the 230 mm point will the aircraft balance? If it does, then I'd stick some lead in the nose for the first flight at 220 mm and see how it feels in the air. If when you roll inverted the nose pitches down quickly, remove a little lead. Keep removing lead until you reach the point when the nose drops slowly when inverted. What ever lead remains will then be there for keeps.

The other issue is whether the rudder and elevator servos are mounted in the centre of the fuselage or have been moved to the tail - or just one has been moved to the tail. That will also have an impact on CG as if my memory serves me right the servos should all be mounted in the centre of the fuselage.

[Bob Vaughan]

Thanks Peter, I think I've sorted it. I was thinking that with such a wide choice of tank locations the trim during flight, with consequent fuel consumption, might be an issue. Searching thru old posts I find its cropped up before and I posted a similar question in 2011 regarding this very same airframe issue. I can find nothing new on this subject anywhere else but have decided to set c of g in a half full tank configuration and then placed rx battery to give a slightly nose down attitude. At least that should keep things in good trim for my normal flight durations even if they do change mid flight -ish.

If that makes sense!.

Bob

[Peter Jenkins]

OK good luck with your flying but remember, it's what it flies like that matters. Make fine adjustments once you have had a successful first flight. Don't make the mistake of just leaving the CG where it flies OK. You will improve the aerobatic performance of the aircraft if the CG is where it suits your style of flying.