Andrew, I don't know what prop you are using, but I'd suggest more diameter and possibly less
pitch. You need to try and get a 2-4 break as well. What will this help??- If you are running
the motor with very little break, ie: flat out in a steady speed, when the Score goes above 45
degrees the motor gives no more power then in level flight. If the motor is set richer, ie: in a
4 cycle in level flight, the model will fly slower and with less pull. Then, when you go above
45 degrees, more or less, the motor will break into a 2 cycle and give you more tension
exactly where it's needed. Adding diameter to the prop will give you more tension without
more speed, given the same pitch, and will load the motor much more - so you will have to
set the needle for a breaking 2-4 or it will overheat and sag in maneuvers.
This is easier to understand if you think about doing exactly the opposite- set the needle leaner
and use a high pitch prop and less diameter... Doing this would cause the same problems
you are experiencing. -Lots of pull in level flight, but will want to fall out of the sky
when flying maneuvers.
Less pitch will help the model accelerate, you wouldn't want to use 5th gear to climb a steep hill
when you're driving would you?
It takes some experimentation with different props and setting the needle to give the
right performance. I do not use a ST51, so I am not super familiar with how it performs in stock
form, but I do know many send theirs in to be re-timed to give a better 2-4 break.
Moving the leadouts should also help, but I think a prop change is needed, as well as a
richer needle at takeoff. I'd also suggest a uniflow tank if you are not using one, and
LESS nitro if you are not using 5%, and decent oil content. Good fuel helps the 2-4 break.
If the oil content is low and the nitro too high, the engine will not run cool enough to
return to a 4 cycle after breaking into a 2 after a stunt and return to level flight.
You need to give us more info on EVERYTHING about your setup to give a more
definitive diagnosis.
Stan Bidowski