Here we go- yesterday was quite enlightening.

Ok, I knew that the YS 63 was happier on higher nitro, but I got very graphic evidence of that yesterday.

My 63 is on a SIG Somethin' Extra. I'm using 15% Cool Power fuel. I know about the advantages of higher nitro- I use to run 30% heli fuel. I don't WANT to pay the premium for higher nitro, OR go through the hassle of lugging two kinds of fuel to the field. BTDT. If it doesn't work with CP 15%, I don't need it.

This engine just came back from having the piston replaced, so I'm still running rich in case the ring was replaced too. It was quite unhappy with the 14x4W at this rich condition with 15% fuel; spool-up was slow, and the engine was surging at half throttle. The airplane was basically a pig.

So we put it on my pal's 63. This engine is well broken-in, and is fed a home-brew 20% nitro blend. It was turning 10,300 on the ground.

Flight results were nothing short of spectacular. The model is a Dave Patrick Ultimate ARF, and this prop is perfect for it if your engine will turn it.

I went back to the DynaThrust 13x6 on my SE, and am satisfied for now. The wider chord of this prop slows the model down enough to where I want it to be. Perhaps when I lean my 63 out a bit it will like the 14x4W wide better. But there is no substitute for nitro to get the max performance from these engines.

That little Ultimate has a lot of drag, yet now will accelerate while vertical. On the down lines, chopping the throttle is like throwing out a drag chute.

Of course, this means you had better stay on your toes when landing. This model, like most bipes , gives very little warning as you approach Vmc, and when you get there it just quits flying.

But the 14X4W prop did indeed expand it's flight envelope considerably. Moral of the story; if you want the benefits of these "3D" props on a YS 63, you need high nitro (the 91FZ turns the APC 16x4W just fine on 15%).

The added expense is not worth it to me, so I'll continue to muddle about with my 15%.

This has been interesting. Looks like some sort of 13x6 is the best general-purpose prop for the YS 63; but we already knew that, didn't we...<G>

Steve