stunthanger.com
Engine basics => Engine set up tips => Topic started by: Bootlegger on August 26, 2014, 11:53:54 AM
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Guy's when you are trying to determine which engine has the most power, not R P M, and both engines are the same, what method do you use?
I am going to use the same prop, fuel and glow plug and run one right behind the other so that weather conditions will be as close as possible.
I hope that I made myself clear on this, and thanks a lot...
And the engines will be run on a test stand, not on the model..
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That's going to tell you about what RPM a given engine will generate on a given prop, but not about maximum power.
Power is a function of engine speed, and loading the engine too much or too little will not extract the maximum power from it. To really do it right you need a dynamometer that'll measure engine torque, and a means of adjusting the load on the engine, even if it's just a variety of props.
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Gil unless the differences are pretty great and you don't have equipment to measure them scientifically then the laymen's way is to simply fly them both to feel subtle differences. This would also take into account flight loads which won't show up on the test stand. Looking and listening on the bench won't tell you too much. (Unless one pulls the test stand over and the other doesn't)
Dave
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Thanks guy's, I sorta thought that I'd need a way to measure torque.
Again thanks
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Hi Bootlegger:
Now I ain't very smart, but if one has various engines to compare for a power rating, would not using the same prop(s) and taching them determine which engine had the the more, most power?
I think that force times distance divided by time equals power. Would you not have enough information to draw a conclusion?
I have a site on my favourites that presents power ratings for almost any prop and what the airspeed is when using the rpm,pitch and diameter of each prop. This chart opened my eyes when I compared Diesel engines to glow engines as far as HP was concerned!
Stay well,
Frank
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RPM on a test prop works fine to compare engines that are roughly similar in power. Pick a test rpm. 10,000 rpm is probably about right for stunt engines. Don't use a flight prop, they can load and unload from breezes etc. Cut down an oversize prop, leaving big, square tips, until it reliably turns around 10,000 rpm in a 2 cycle. The motors have to run steadily and smoothly. Then pick a day and run the engines back to back. You should be able to hold rpm within a 200 rpm range. If one motor can turn the prop more than 300 or so rpm faster it is more powerful. If the rpm range of both motors overlaps there ain't much if any difference.
If you want to get better comparisons you'll have to get into measuring density altitude during the runs.
Phil C