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Old 01-15-2009 | 12:22 AM
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BMatthews
 
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From: Chilliwack, BC, CANADA
Default RE: Thrust to weight

I'm not sure anyone has that sort of chart. It would imply that a very large number of engines were tested with a a variety of props to figure out the thrust amounts and that someone tabulated the whole works together.

If it helps I've found that for lazy sport flying you can get away with around a 1:2 thrust:weight ratio. I've got a 1/2A Texaco model using an .049 that is running a big 8x4 prop to slow the engine down. Fish scale testing on the ground showed that the engine generates 10 oz of static thrust. The model is 19 oz and it has a very J3 Cub like climb out. It's not exciting but it gets the model up to thermal country and helps the engine to achieve up around a 4 minute run time. But the thrust to weight is the key here. For a basic sport flyer that will hold around a 40 to 45 degree climb angle you're likely looking at around a 3:4 thrust:weight ratio. And of course 1:1 is perky but won't maintain a proper vertical climb. For that you need up around 5:4 or more so there's some power available after cancelling out the model's weight to fight the aerodynamic drag and ensure enough airspeed to keep the surfaces working if they are not in the prop blast as on a pukka 3D model.