Builders:
In two weeks we will be headed back to Oshkosh. Once there we will be surrounded by hundreds of companies that will all attest on a stack of Bibles that they have carefully tested all of their products to protect the safety of their customers. In with these people will be at least 30 companies selling engines. Every single one of these companies will tell you without blinking an eye that their engine power output numbers are the result of careful Dynomometer testing. Almost all (90%) of these companies are lying about this.
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Traditional dyno testing is expensive, and a bit of a production to adapt an aircraft engine to. To learn much, it requires hours of evaluation, and runs at different conditions. Any company that does this would be justified in taking a photo of this milestone in their company history…….except you can politely ask to see a photo of their engine on a dyno, and of course they will not be able to produce a single image of their engine running on a dyno. I actually had one company tell they had done 100 hours of testing, but had forgotten to take a single photo of it. In an era where nearly every human has a cell phone that is also a camera, please tell me who would believe this?
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There are many kinds of dynos. Basically they all apply a load to the engine, and then measure the equal and opposite torque reaction resisting this load. No Dyno measures HP; they measure torque. HP is a calculation based on torque and RPM. If you building a plane, you don’t need to know this, but ideally everyone selling engines would, (but they don’t). A real motor head, like yours truly, knows this stuff. Combine this with some basic fabrication, and “Taa Daa!” the $500 dyno. Our dyno used the prop to generate the load, allowed the engine to rotate on it’s crank axis by using a front spindle from a Corvair car, and measure the torque with a hydraulic cylinder. Later we simplified it further with an electronic scale for measurement. Using a digital optical tach, the accuracy measuring HP was within 2%
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I didn’t invent this kind of dyno, it has been around a long time, pictures of them in 1960s Sport Aviation magazines. This isn’t even the simplest kind of dyno. In one old Sport Aviation there is a picture of a Corvair hanging on a steel cable turning a prop, with a wooden arm touching a scale. Yes that works also. The pictures of our set up have been on our webpage for more than 10 years. It would be very easy for any company selling engines at Oshkosh to have built their own version. Easy, but not as easy as telling people they have hundred of hours of testing, but forgot to take any photos.
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2003- Above, Oil system testing at Spruce Creek airport, 2003. We were testing how much pressure loss the cooler had when the oil in it was cold soaked for an hour at 32F. Testing like this is serious business. Note that Gus Warren liked Becks Dark, and I liked Michelob. Lot’s of companies like to have the appearance that they test products: they put people in lab coats and have them make scientific faces. I don’t care for appearances, I just want results, and the picture shows we drank beer while we let the oil cool off. I can put on a lab coat a lot faster than a salesman can become a motor head and teach builders anything valuable.
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2004- Above, an O-200 on our dynamomemter; test crew from left to right, above: Gus Warren, Detroit Institute of Aeronautics, A&P 1990; Steve Upson, Northrop University, A&P 1976; yours truly, William Wynne, Embry-Riddle Aeronautical University, A&P 1991. While the way we dress may be slow to catch on in high fashion circles, we certainly know our stuff about all types of aircraft powerplants.
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2008- Above, Kevin and I are standing on my front yard, wearing jackets. We were waiting just before sunset for a rare weather phenomena to occur: a perfect standard day of 59F 50% relative humidity and a pressure of 29.92. Any time you read a dyno report and it says “corrected horsepower,” they’re making a calculation, sometimes accurate and sometimes not, to adjust for their test conditions not being at standard atmosphere. Because we live in Florida near sea level, there was actually three occasions in four years when these conditions were met on testing days, and all our results we calibrated against these standards.
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How you can build a Dyno for $500 if you know how they work and you can weld:
Dynamometer testing the Corvair and O-200
A page devoted to all kinds of testing:
Testing and Data Collection reference page
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