I've been looking for a .10 size engine for my shoestring but they seem hard for me to find. I was wondering how can I can a tame down a .15 size engine since they are easier to find. I want it to be easy flying not a speed demon.

I've been looking for a .10 size engine for my shoestring but they seem hard for me to find. I was wondering how can I can a tame down a .15 size engine since they are easier to find. I want it to be easy flying not a speed demon.

Try putting the prop on BACKWARDS, or try one with less pitch.
It will slow the flying speed to a more reasonable lap time AND you don't have to find another engine.

I've been looking for a .10 size engine for my shoestring but they seem hard for me to find. I was wondering how can I can a tame down a .15 size engine since they are easier to find. I want it to be easy flying not a speed demon.

One question is which 15 do you have? I have several Fox 15's, including the ball bearing schneurle version, Os 15FP, and one thing to note is there are large differences in weight. I think the OS15FP or LA are reasonably light and you will have an easier time keeping the balance in check (and thus the total weight too if you don't need to put on tailweight). Of course the Shoestring was also designed before mufflers were standard in CL, so this will add (unfortunately) to the noseweight.

But in terms of power, the prop tricks work, but also you could go to slightly longer lines (like 56 feet or so) to slow down the lap times.