Greetings fellas from a rainy Charente in S.W. France. Advice needed please .

I'm just your ordinary Sunday sport flyer , non-competitive ...... Too old , lousy pilot !

Can I ask , what would you expect to be the launch RPM using a Stunt tuned 40 [ OS FP / Tower ] swinging an 11 x 5 prop' ?

My 'planes are a mixture of the usual profile Twister / Banshee variety. Around 36 oz ready to go .

I'm using 62 foot lines ,  23% lube' in the fuel [ 17%/6% ] , uniflow Dubro plastic tanks.

Very much obliged for all your comments ,

Robin [ ex-pat Brit in the Charente full of ex-pat Brits ]

Sig Champion...10% nitro at 9600-9700 rpm

Robin,
For the heck of it I would try to load the engine with a bigger prop--either go to 12" or perhaps a 3 blade 11".

If the internal guts are limiting you to 8500 rpm on the ground, then let that rpm turn a bigger prop. At these lower rpm's, the engine has more time to pull in a full charge mixture, and so can probably turn a bigger prop. I guess if it tries to run faster, it can't breathe enough air/fuel to supply the power to turn the prop.

Robin -- I am using a "Tom Dixon" modified FP 40 - I don't know all he did to it but it runs smooth like a sewing
machine and has a nice 4-2-4 break - I'd try upping the nitro to see if that would help.

  Gene