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Inverted Oil ????

T

Tom Maxwell

Well Known Member
OK, I am going to show my ignorance. Can someone please give me the short explanation of the physics of an inverted oil system?

I think I understand the basics -- a pickup tube in the top and bottom of the sump with a checkvalve that switches between the two based on attitude? Or maybe I don't, correct me if I am wrong.

But not knowing the internals of an aircraft engage, I am working from a vision of an automobile engine with a crankshaft sitting above a pan of oil. If a car were to be inverted, the crank would be submerged in oil and the oil would run throughout the engine which I don't suspect would be a good thing.

What happens to the oil in the sump when an aircraft engine is inverted? Does it not fall down on the crankshaft?
 
You're sort of on the right track....but....

When inverter, the oil is "picked up" from either what is normally the "vent" on the top of the crank case, or near there (sometimes the Vac Pump Pad). This is because all of the oil indeed does run to the "top" of the engine when inverted.

There is a "check valve" that consists of a tube with two rather large steel balls in it (about 1" in diameter") that switch the oil pickup from the sump (when right side up) or the top of the engine (when inverted). There is also a "catch can" with a slider inside of it plumbed into the vent part of the system to catch vented oil and keep if from puking overboard, it then gets returned to the system.

In addition to the ball valve and sump can, you also have to modify the pickup in the sump so it's not just a "tube" hanging in the oil. If that were the case, the oil pump would suck air when inverted.

There are a number of schematics floating around the internet that show the plumbing of the system.

Unless you're planning some lengthy inverted flight, it's not really worth the bother. On an RV, all the added hoses (there's quite a few of them), the added ball valve (which must be mounted close to the level of the sump intake), the vent "t" fitting (eliminated with the vac pad pickup), and the coffe can sized breather can take up a LOT of room on the firewall.

I know because I have full inverted fuel and oil on my RV6. I only did it because my engine came with everything (I bought a nearly new engine off a pitts). I probably won't waste my time on it again. I do a decent amount of aerobatics in the plane, but inverted flight is difficult in the side-by-side RV's anyway (due to seatbelt geometry).

Just my 2 cents!

Cheers,
Stein.
 
Engine models

Can someone point me to a good source of engine model descriptions/comparisons? I'm having a hard time with the 0-### IO-### lingo. Can tell what's a 4 cyl, what's a 6. What 4 has more horses than that 6 I'm looking at. Then of course it would be helpful to know which of those little numbers has the best hp/wt ratio but is so rare that I'll never find one etc.

Thanks,
Ken
 
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