Critical Understanding #6, The “Two Minute Test”


The “Two Minute Test” is a critical, required before test flight procedure. designed to insure your planes engine and systems will run at full power for two minutes at full static RPM and climb out angle. This simulates the time and power it will take your aircraft to reach pattern altitude. If it has an issue with power after that, making a precautionary landing from that point is vastly easier than having an issue at 300′ AGL.


This test is nothing new, I published detailed notes on it in our Flight Operations Manual eight years ago, and I wrote stories  about it all the way back to 2002. Unfortunately, I believe less than half of builders do it before taking their first flight. I can think of 5 planes off the top of my head that would not have been damaged or wrecked if the builder had just run this test and discovered he had an issue on the ground instead of at 300′.  I am including this in this Critical Understanding series, because I want to increase the percentage of builders who use it, hopefully to 100%.


With that goal, we will have line entries for the test, in your Hand Book. I will suggest these at the bottom of this article. If everyone does the test, and logs the results in their Hand Book, we can avoid a lot of needless accidents. If a guy doesn’t want to do it, I can’t force him to, but I’ll be blunt with everyone: if a builder doesn’t do the test, I don’t consider his plane to be airworthy for test flying.


If he has insurance coverage based on claiming his engine is “Built and operated to WW standards”, and he has an accident, his insurance company could try to get out of paying the claim. Many companies pay the claim, and then try to go after everyone who produced a product in the plane, even if the accident was obviously pilot error. If the accident could have been prevented with a two minute test, I will have zero hesitation about pointing that out. BTW, that isn’t a hypothetical situation, insurance companies hire bottom feeder lawyers to harass manufactures on pilot error accidents all the time. The other side of the coin is simple: if you are smart and use the test, it is a tool that will offer you great protection, and if you log book and Hand Book have entries confirming that you performed it, neither the FAA nor your insurance company can give you a hard time about it, and I will consider it my duty to tell everyone that you did your due diligence on risk management.


A full, detailed explanation of the Two Minute Test can be found in this story : Understanding Flying Corvairs Pt. #5, Two Minute Test. This is a lengthy article with many good points about testing, I consider it required reading for builders about to start a test program. The Two Minute Test can also be found in our Flight Operations Manual.


Note Book Section:

Make line 6.1 in your Hand Book a entry that reads the full static RPM. It should also note the prop and pitch, and the atmospheric conditions at the time. It must also include the fuel and the timing settings.  


Make line 6.2 in your Hand Book an entry under the same conditions as 6.1, but with But it has to note the CHT of the engine at the end of the Two Minute Test.



Although GM rated the engine at 575F as the CHT redline, under no circumstances should you allow the CHT to Exceed 425F under the spark plugs or 400F on the bottom of the heads. If it does, stop the test. If the engine exceeds the limit in less than 2 minutes, read this: Cylinder Head Temperature measurement and Corvair CHT, letters and notes. There are many links in the stories to further reading on CHT’s in Corvairs. Read them.


If the Engine starts off with a static RPM of say 2750, but during the test the rpm starts coming down to 2740, 2730, 2720, BEWARE, It is detonating. STOP at once. Critical Understanding #4, ANY loss of RPM is Detonation.


Anytime you observe an engines’ CHT numbers move up smoothly, but suddenly get hotter at 2 or 3 times the previous rate, THE MOTOR IS DETONATING. Stop the test, solve the issue. The motor need not exceed 400F to have this issue. If the engine starts off warm at 200F and slowly works its way to 300F in the first minute, but suddenly in 15 seconds adds another 100F, it is detonating, stop.










About William Wynne
I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at and in more than 50 magazine articles.

4 Responses to Critical Understanding #6, The “Two Minute Test”

  1. Stuart C. Ashley says:

    Hi William;
    For full disclosure, I’m the fellow who bought an engine from Bill Clapp. For this reason you didn’t want to deal with me, which is your perogative. However, along with wishing you a Merry Christmas, I would like to state that the series of articles you have been writing about preparation for first flights are invaluable, will undoubtedly save lives, and have erased any animosity I may have harbored because of your judgement about myself.
    Cheers! Stu.
    Oak Harbor, WA

    • Stu,
      I have great admiration for anyone who can change their perspective after consideration and thought. It is a quality we could use more of these days. The articles also give some background on the landscape that I have to operate in, where I can’t make anyone take the care they should, but the legal system wants to pretend that could have directed peoples actions as if they were robots I was responsible for. I am not really judgmental about anyone, I have missed too many opportunities to be a better human to feel judgmental about others. If I ever come across as short, my apologies, a lot of it is driven by the fact that too things that matter to me, people not getting hurt and my Fathers health, are things I can’t control, and they often lead me to feel helpless. Dad instructed us when we were young that very long odds against success we no excuse for you to give less than 100%, that you were never allowed to quit on things that mattered, so I keep going. – ww.

  2. Ron. Lendon says:

    WW, Merry Christmas! These are the articles I was asking about, I feel they need to be placed in the “clear and succinct area” I have been looking for all theses years. Thanks for the effort. Make a place where we can find it quickly and keep it updated. Keep up great work. The two minute test saved me from flying with a fractured float, it manifested after the two minute and appeared at the next run before the first flight.

  3. michael mckosky says:

    Ron Lendon states it well. “clear and succinct”…the way to go!
    I am no where near doing the test, but I expect to be referring to this information when I get there. Thanks!
    And, wish you and Grace a great, happy, and healthy 2017.
    Looking forward to attending the Barnwell college session.

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