Critical Understanding #8, Required Engine Warm Up.

Builders,

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The Required warm up period of a Corvair is set by one single limitation: The oil must be warm enough that the oil Pressure does not exceed 60 PSI on the engine run up to Full static RPM (Critical Understanding #2, Absolute Minimum Static RPM.)

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The normal desired regulated warm oil operational pressure on a Corvair Flight engine is 45 PSI. That means, in normal cruise operation, with the oil warm, it will be regulated to 42-47 PSI at any power setting that will maintain level flight or better. ( If the aircraft is gliding, and the engine is idling, the pressure will be lower)

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When the oil is cold, the regulated pressure will be higher, because the oil is thick, and there is a limit to how much will flow through the bypass. If an engine is at 35F and started and carelessly revved up, the oil pressure will go well over 60 PSI. This is damaging for the engine, and if a person tried this, there is a good chance they will blow the oil filter gasket out, and all the oil will be pumped overboard in 90 seconds.

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If your flight instructor said something like “Warm it up until the oil temp is off the peg” or “Warm it up for X number of minutes” he was actually feeding you BS, because he didn’t care enough about you nor his profession to actually read Lycoming and Continental’s procedures, which are very close to the ones I present here for Corvairs.

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If you would like to read both Lycoming and Continental’s info on why the both require hours of pre-heat below 20F, read the articles at this link: http://www.reiffpreheat.com/Articles.htm

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To understand the factors of cold weather operations, read, study and understand the following story: Thoughts on cold weather operation, minimum oil temps, etc. Notice the story is many years old, and it is made of information that has been on my website for more than a decade. I have long done my homework and presented the data; I am goin a step further to gather it again here, But I can’t make anyone read it. If you just skim it and then go back to watching TV or FB, you are making a judgement error on how to use your time to best manage your risk in aviation.

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The proper procedures:

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Preheat the engine anytime the temp is below 30F.

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Follow the starting instructions:

Starting procedures on Corvairs, 2,000 words of experience.

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Let the engine warm up at 1,000 rpm.

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After an appropriate number of minutes, dictated by personal observation, you can perform the run up procedures.

During the Full Static RPM check, note that the oil pressure does not exceed 60 PSI

If it does, return to 1,000 rpm until the oil is warmer, and re-test.

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If oil pressure exceeds 60 PSI in flight, i.e. on a climb out in cold weather with insufficient warm up, or any flight condition where oil pressure fails to regulate below 60 PSI, a precautionary landing is warranted.

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From reading the procedures above, two things should go without saying, but I am going to say them anyway, just so everyone gets it.

The oil pressure is taken on the gold oil filter housing in the 1/8″ NPT port. If your oil line or sending unit is connected to the 1/2″ NPT port, it is in the wrong location, and it will read incorrectly. If you don’t have it in the correct location, or you don’t have a Gold oil Filter housing, your engine is not built to my specification, and you are on your own for procedures, I don’t advise people on systems I don’t recommend.

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You must have a RELIABLE oil pressure gauge. If it doesn’t work accurately 100% of the time, eventually when it does indicate 75 PSI because something is wrong, the type of person who tolerates instruments that fluctuate or lie, is prone to saying “That can’t be right, it’s just my instrument” If you think I’m kidding about bad instruments causing issues, we had a Cleanex builder sweat out his first flight and make a precautionary landing, nothing wrong with the plane, but his MGL gauge gave erroneously high readings. Eight years ago, we had a builder destroy his aircraft on the third flight: He ran it out of gas, because his “Instruments” were on an I-Pad, and the fuel senders in his tanks didn’t work with the I-Pad.  Think about that the next time someone tells you how brilliant they are for adapting an entertainment device for a flight task.

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“OK, let’s get this point fixed in everyone’s mind: They made 1.8 million Corvairs If they made on 70,000 miles each and drove this at a 35 mph average, then each car made 2,000 hours on average, which means the fleet made it to 3.6 Billion hours of operation. If only 5% of the operation was done below 32 degrees as a starting temp, I would be stunned, but lets use that as a conservative number. That means 180 Million hours of operations we done under these conditions.”

-Taken from the cold weather operations story above. While UL and Jabbaru make fine motors, realize they will never have that kind of hours on their basic engine design. My work with Corvairs is built on the GM experience base, and the advice I offer takes advantage of it.

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Note Book Section:

Make line 8.1 in your Hand book a hand written entry, to seal in your mind that you recognize 60 PSI oil pressure is the flight limit. Make a note that you have marked your gage in the cockpit with this redline.

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Make line 8.2 in your Hand book a notation on what the indicated oil temperature is in your engine, when it will first regulate below 60 PSI. In many engines it is 130F, but each Corvair will be slightly different, and in no way should anyone fall back on a temperature as the determinate of sufficiently warm for flight. . Your Hand Book should also note typical warm up periods in minutes at different OAT’s. Include a not on which oil this was measured with.  

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Make line 8.3 in your Hand book a notation that 1,000 rpm is the warm up RPM for the engine.

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Make line 8.4 in your Hand Book a notation That any cause of oil pressure in excess of  60 PSI is cause for a Precautionary landing.

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Make line 8.5 in your Hand Book a not saying the engine must be preheated below 30F.

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Above, a photo from my website that is 15 years old. The engine in the test went on to service in Gary Coppen’s Stits Skycoupe. (2,700cc-Skycoupe-2002 Photos) The test being done is to measure the drop in oil pressure across the oil cooler when it is submerged in a bucket of ice. Most people never notice the beer in the bucket with the oil cooler. Gus Warren and I did this test at the Spruce Creek airport. Note that it pre-dates welded on head pipes or any of the Gold systems.  I have been testing a long time, but still, this week, someone will get on an internet discussion group and take the contrary advice to what I offer. I accept that some people will do that. But if you want to succeed at this, just make sure that person isn’t you.

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-ww.

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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 www.FlyCorvair.com and in more than 50 magazine articles.

One Response to Critical Understanding #8, Required Engine Warm Up.

  1. Brent Mayo says:

    Keep em coming William I’m learning something new everyday. Thanks

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