Hi,

I wondering if anyone out there has a fairly scientific way of measuring a gas or glow engine's power output, other than relying on what any particular manufacturer claims their engine will produce.

Short of having an expensive dyno setup, I've thought about fabricating an engine test stand where the engine mounts on rails that slide in a track, so that the amount of thrust produced could be measured as the engine pulled against let's say a strain gauge. It could even be something as crude as a common fish-scale to start off with, but I think that's a no-nonsense way of evaluating what an engine can actually produce.

Any thoughts?[sm=spinnyeyes.gif]

I'm in New York right now and don't have it to hand but there is a formula you can use based on the max rpms and the prop size and pitch that will get you very close to actual horsepower. Someone on here should know it. What you are suggesting measures static thrust and is done by almost everyone I know. You just run a nylon strap around the tail of your plane, hook it to a Berkeley Digital Fish Scale, and run the throttle up. That's where all of these static thrust numbers are coming from. They provide an initial measurement but the actual thrust in flight is different from static. The static thrust number comes in when you are going to hover. That's what let's you know if you can pull out of a hover, or even do one for that matter.

Each propeller has a specific load/power curve.
The good engine testers had calibrated "props" that acted as air brakes. After a lot of juggling with atmospheric pressure and relative humidity, wielding slide rules, they came up with test power curves, almost as good as sophisticated dyno data.
Taking simplifaction one step further, use the calculator I develloped (not all my work!)
http://www.mvvs.nl/prop-power-calculator.xls

No fair!!!! I use Vess props!! LOL

If you used a strain gage, possibly set up as a load cell you would still need to calibrate it. This may be more accurate than a fishscale, but not enough to make a difference. If you used the strain gage to just measure pure micro-strain you would still need to convert this to pounds of thrust, which would still require a calibration of your fixture. Then the question is, how would you accurately calibrate it.

I used to worry about manufacturers posted horse power, but now I don't care what they post. There is enough information on forums like this to get a good idea about almost all the engines out there. There are so many factors that could affect your testing that I'm not sure how useful it would be compared to the information we already have on forums like this. Also how a engine performs on a test-stand and in the air will probably be completely different. My opinion is to let a dead horse lie.

A dyno is very easy to make for aircraft engines, a simple bearing supported mount with an arm, scale, and tachometer will work. They are great for developing powerplants but tend to create more questions than answers and cause confusion for the end user. We already have a lot of people wasting time with tachometers and spring scales instead of going to the field and finding what actually flys best. Some of these guys will send their engines back or discard props before they ever fly them based on a potentially meaningless measurment. Ive found too many good flying engines and props that did not perform very well on a test stand. Maybe I could create a new sport by producing cheap dynos, engine MFGS would hate me.

Take a look at this thread. It has some dyno info.

http://www.rcuniverse.com/forum/m_56...tm.htm#5639077

Here is a link to one I built, Not NSA quility but will give you readings in pounds of thrust with different props and rpms

Milton


http://www.rcuniverse.com/forum/m_65...tm.htm#6519939