Dyno testing Corvairs, 2008


Below is a story from the spring of 2008, taken from our ‘Hangar Update” on our main page Flycorvair.com It is a good indication of how testing is integrated  everything we do. I am sure than many other companies headed to Sun-n-Fun that year focused their attention on getting spiffy polo shirts ready and glossy brochures. Not us, we were out on the ramp in front of the hangar testing engines.

In the second part of the story, we are running a test on a perfect “standard day” These are set of circumstances that rarely occur in real life, but which all dynos are supposed to be corrected for. By running the test on that day we developed very accurate correction factors for our testing. It is taking the time to do things like that, and not ow you dress that makes testing valid.

The story was shot in front of our house and hangar in northern Florida. Mark Petz and Kevin Fahy are prominently featured. Mark still builds outstanding Corvair flight heads at Falconmachine.net, but Kevin a member of our original “Hangar Gang” is long since retired. Shortly after this story he He married a very attractive woman with a PhD in Aerospace Engineering who long worked for NASA at Huntsville AL.  Kevin  made a tee-shirt that said “Trophy Husband” and set out to lead a life of quiet leisure.

A few days before Sun ‘N Fun, Kevin came up to give us a hand readying the display engine for the show. Above, he’s prepping our Fifth Bearing engine for its run on our Dynamometer We have run more than 50 engines on this dyno. The the run stand we had before the dyno broke in and test ran about 75 more. Research, testing and years worth of study and learning make our recommendations valid.

A week prior to the show, Mark Petniunas of Falcon Automotive drove down from Wisconsin to our North Florida hangar to give us a hand assembling and test running our Fifth Bearing test engine. I told him on the phone I thought it was a day or two away from running. Late into the sixth 18-hour day of his visit, Mark said: “I’m going to have to fire my travel agent. I have yet to see one girl in one bikini on one sunny sandy beach. This Florida vacation is nothing like the brochure.” Above, Mark on the right confers with Kevin right after the first start up of our Fifth Bearing Motor.

Above is our Fifth Bearing Engine at power on the Dyno. The natural aluminum CNC billet Bearing Plate is between the case, Ring Gear and the Gold Prop Hub. It is intended to address both thrust and bending issues.
I came up with this design myself, but the CAD modeling was done by our aeronautical engineer Spencer Gould.  Sharp eyes will notice that this utilizes All Our Regular Production Components. The added 1″ round spacer in front of the CNC Starter Bracketshows the length of the engine. The engine has a Gold Billet CNC Pan on it.

The day after Sun ‘N Fun we were back at our North Florida Hangar conducting more tests and unloading and unpacking the trailer after the show. Here, Kevin, myself and Mark on the other side use all hands on a run of The Fifth Bearing Engine.

Above is the balancer on The Fifth Bearing Motor. The timing scale on the back of the Corvair engine shows 0 to 16 degrees. The length of this scale can be transferred to the balancer to show 16 and 32 degrees BTDC (before top dead center).
As stated in my conversion manual, the proper way to set the timing on your Corvair engine is to know what the full advance is at full static rpm. I have long told people to tie down the tail of their airplane and check the timing advance at its full static rpm. Installing the distributor and not setting the timing this way is foolish. All aircraft engines, including those with magnetos, have their timing checked at maximum advance.

The difference is that aircraft with magnetos have their timing set statically at full advance, and then their impulse couplings retard their timing. The Corvair engine can have its timing set statically at idle for an idle setting, but it must be run to its full static rpm to have the timing checked because distributor ignition has mechanical advance, not retard.

If you’re a builder and you didn’t know this, that’s perfectly okay. That’s why we issue instructions. If you hold an A&P license and you don’t know this, you can stick the powerplant section of your license in an envelope and mail it back to Oklahoma City. This is a good example of how I’ve intentionally patterned the Corvair engine to philosophically duplicate the proven aspects of Lycomings and Continentals.

Dyno calibration after Sun ‘N Fun.
Above, you’ll notice Kevin and I are wearing jackets. We’re 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 have actually been three occasions in the past four years when these conditions were met during daylight hours on testing days.

Our dyno relies on the super accurate optical Prop Tach for the rpm measurement and it will only reliably pick this up in daylight. A few minutes after the photo above was taken, we made a dyno run which required no correction. By testing the same engine later in the week, we reconfirmed our correction factors for this particular dynomometer and we retained accurate measurements all year round.

As the post Sun ‘N Fun work wound down, we stopped for a photo op with Grace’s Taylorcraft. From left above: Dan Weseman, Mark Petniunas of Falcon, Kevin, myself, Grace and Scoob E were on hand for the last hour of tests. Although it marked the end of another Sun ‘N Fun as it became a collection of good memories, friends and fun, the talk already centered on what we were going to do this summer, plans for Oshkosh and good times ahead.
The pace of the Corvair Movement affords little time for reflection. And certainly the best of times are ahead of us. If you are new to the land of Corvairs, there’s time to express creativity, make your mark, enjoy new friends and join the adventure.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.