It's hard to calculate because it's hard to know the thrust of the engine. I have heard of guys hooking a fishing scale to the plane and try to measure it. But how accurate is the scale? Let's assume you can get an accurate measurement. IF your plane pulls 15lbs on the scale and weighs 10lbs. You have a 1.5:1 thrust to weight. For me I guess at the ratio. If the plane will hover at 1/4 throttle I would say it's 2:1. It's just a guess but I think it's close. This is assuming your engine is tuned and propped right. The more I think about this the more complicated it gets so I am going to quit.

David