Engine Dynomometer
01-31-2002 | 08:51 PM
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From: Doylestown, PA,
Engine Dynomometer
Does anyone know where to purchase a dynomometer that will accurately test our size engines? Our Company has a Dynomite which is designed for 3 HP and up. We are considering purchasing a smaller version. Thank you for the input!
01-31-2002 | 09:30 PM
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From: Houston, TX
Engine Dynomometer
For sure you can find one, but I seriously doubt you'd be willing to pay for one. 
For RC applications, torque and horsepower are not direct measurement for performance - thrust is.
I've been using a digital fishing scale (15lbs works good for up to 1.20) to measure engine output. The trick is to secure the engine to movement ONLY along the trust line while minimizing friction. I've had good results using HD ballbearing drawer guides. The digital scale is nice because the engine doesn't need to move much, so a short drawer guide (<12") works just fine. Cost is around $25 for a decent fish scale and $20 for a good drawer guide, less if you can salvage one from a broken file cabinet.
I ususally get pretty good correlation with the ThrustCalc(?) program.
For RC applications, torque and horsepower are not direct measurement for performance - thrust is.I've been using a digital fishing scale (15lbs works good for up to 1.20) to measure engine output. The trick is to secure the engine to movement ONLY along the trust line while minimizing friction. I've had good results using HD ballbearing drawer guides. The digital scale is nice because the engine doesn't need to move much, so a short drawer guide (<12") works just fine. Cost is around $25 for a decent fish scale and $20 for a good drawer guide, less if you can salvage one from a broken file cabinet.
I ususally get pretty good correlation with the ThrustCalc(?) program.
02-01-2002 | 07:18 AM
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Accurate thrust measurement
Like Volfy I have my engine test stand mounted on a drawer slide, and have the drawer movement limited to 2 inches back and forth. To the back of the drawer I attach a small nylon chord that runs over a ball bearing mounted pulley and drops 90 degrees towards the ground. I hang a plastic bucket on the end of the string. Start the engine and bring it to full power, and the drawer slides to the front stop. Add weight to the bucket until the drawer just starts to move rearward. Shut the engine down, remove and weigh the bucket with contents. Now you know exactly how much static thrust your engine / Prop combo has. The rolling resistance of the drawer is 2 oz, which I add to final weight. You can easily compare prop performance by seeing if you have to add a little or take out a little from the bucket for a different prop.
Thrust HP gives very optimistic results, and assumes all props are 100% efficient (none are). Also, notice that if for a given RPM you change only the prop pitch, the thrust reading does not change, only the speed in MPH does. We all know this is not the case in real life.....
Thrust HP gives very optimistic results, and assumes all props are 100% efficient (none are). Also, notice that if for a given RPM you change only the prop pitch, the thrust reading does not change, only the speed in MPH does. We all know this is not the case in real life.....
