Thrust to weight
 

Folks:
Please indulge what is probably an uninformed question.

Is there a nomogram, formula, or rule of thumb for determining the likely thrust generated by a given engine (torque / hp) and propeller (dia / pitch / blades) combination?

I'm asking because I would like to be able to size an engine / prop to an airframe for a given purpose. For 3D, obviously thrust:weight must be >1; for other flight paradigms, that might not be necessary, and could be disadvantageous (taildragger trainer, for example. It would help me select a proper powerplant if I had something other than the 1hp/lb rule.

Thanks in advance for answers, tips, suggestions, or links.

RE: Thrust to weight
 

The rule is about as good as it gets
the problem is how much power does it take to lift a given weight
the prop used is simply the tool which has to covert power into thrust
and there are a number of props which will do this .
2/3/4/blades will all work but generally speaking , max diameter which is pitched such that the engine produces max power -is the best combo.

RE: Thrust to weight
 

Thanks
I appreciate your insights

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.

RE: Thrust to weight
 

Use this tool: mvvs.nl/prop-power-calculator.xls
It's as close as you can get to real-world data. Pe Reivers is incredible!!

RE: Thrust to weight
 

The tool that victorzamora mentions in the post above is quite a tool. However, to use it, you need to have it. And to get it, you need the following link. The link will pop up a download box for you. Point the download to wherever you have your tools available for use.
http://mvvs.nl/prop-power-calculator.xls

RE: Thrust to weight
 

Gentlemen, thank you