Oil Pressure gauge options, oil system notes
Builders,
A friend of ours who is building a Zenith 750 wrote in with a quick note asking about oil pressure gauges and senders. I pulled together this general set of notes on oil pressure measurement and instruments as a good resource on the general subject. Over the years Corvairs have flown with just about every kind of oil pressure instrumentation imaginable. Going back to my point of Principle vs Preference. On this subject, it mostly falls in the category of preference.
The Builders specific question was focused on sending units for electrical gauges, and their reliability. If I had to pick one brand over another, I will say that I have never had an issue with the senders that are used in Autometer gauges. VDO is usually trouble free, but I have personally had one mess up, and it caused a lot of work with it’s erroneous information. Goes without saying, I wouldn’t use one from the land of Chairman Mao.
Some people are concerned about mechanical gauges bringing oil into the cockpit, but in actual experience, I have never had an issue with it. The line itself is 1/8″ on the outside, but only 1/16″ on the inside, and I generally put a #80 hole in a restrictor, at the engine, so even if the line came off, the flow rate is about 1/2 gallon per hour. For the record, I have never seen even the poorest mechanical line installations leak. You can take the nut off at the gauge with the motor running, and it does not “spray” oil, it just oozes, and even when the engine is hot, the oil really isn’t after six feet of line.
Below is the close up of the mechanical oil pressure gauge I have in the Wagabond. In addition to all the other things I like about mechanical gauges, I like the fact the needle covers a 300 degree arc, allowing you to see very fine changes. The gauge below is $54.97 from summit racing.
Now get a look at the next part, which is an analog electrical gauge. My primary complaint beyond the fact it is electrical is that this type of gauge is only a 90 degree sweep, making small differences had to see. They also cost about twice as much as mechanical after you get the sending unit. It is priced at $69.97, but the sender is about $40. I buy Autometer because of the tiny letters at the bottom of the instrument that say “made in USA”
Dear Mr Wynn
I’m considering a Hatz C1B as my next project. I’m studying the possibility of Corvair power versus the Jibaru. I like the idea of doing the conversion myself.(I’ll learn a lot more about the power plant that way).
The CB1 is ,as you probably know, is aerobatic. Can the corvair be built with an inverted, dry sump oil system? What are your thoughts?
I appreciate all that you have contributed to home built aviation. One day you’ll be regarded as highly as Mr Poberezny, or Mr Pietenpol for your untiring work.
Thank you again
Glen Schweizer
The argument of Analog vs. Electronic was settled for me as Electronic a long time ago. I knew a couple of friends that went out flying one afternoon and they experienced a failure in the soft copper line to the analog Oil Pressure guage. While that does not sound too bad, the individual whose legs were under that part of the instrument panel did not appreciate the hot oil dripping on his nice clean slacks. As typical for such situations they were no where near the departure airport and not wanting to strand the passanger at a distant location they Bit the Bullet and took the time to fly all the way back.Yes the volume of lost oil was small as WW stated and since it was in the cockpit they could not have been fooled if the pressure guage started reading low.
Personally I do not even like having the fuel lines from the tank to the engine inside the fuselage but very few aircraft offer an alternative without extreme changes.