Inverted Oil Question

I bought an RV-4 a few years back. It has an IO-360/CS Prop/Christen Inverted Oil. It is an amazing airplane, but heavy by RV-4 standards. I do some light aerobatics, but nothing with sustained zero or negative Gs.

I am considering removing the inverted oil system and placing in storage pending completion of my RV-8 build. I would like to get some feedback from those that have added or removed an inverted oil system from their airplane. I would to know your opinions of the + or - of removing the system. A couple of questions that have popped up are:

Is there more or less oil loss overboard with or without the system?

Is there any noticeable difference in with the C/S prop doing vertical maneuvers (e.g. loop, immelmans, hammerheads)?

In your opinion, is it worth having the system is you do only light aerobatics as I described above?

Any other comments or considerations are welcome.

Thanks,
Scott

Unless you're doing negative G stuff, there's not much reason to have an inverted system for oil loss reasons. An inverted oil system also does nothing for oil pressure issues on a zero G vertical line. Inverted oil systems still require either positive or negative load on the airplane to maintain normal oil pressure. If your oil level in the sump is high enough to pick up some oil pressure on a vertical line, the inverted system won't have an affect on that either way. And inverted ball valves can float around at zero G unless they are installed at an angle on the firewall. But that's a separate issue from the ability to draw oil from the sump at zero G in the first place.

Oil Pan

I think the oil pan is modified with some welded portals too. If you remove
the system.....What do do with them. Been a couple of years since I maintained a inverted oil system.
Never had oil pressure "loss" on verticals, did knife edge, and the slobber pot dumps out 1/2 qt. in 20 min(mine did). Any heavy acro, keep oil full, 8 qts.
Eric is right, tilt the ball valve on firewall, and clean ball system every few years so it does not stick.
If you take out the inverted oil and keep fuel..hmmm not good.
John

Just as one data point in my RV-8 with an io-360m1b pretty much factory standard with fixed pitch prop I measured:

80psi->50psi = 3 seconds ( min for continues ops at full power )
80psi->25psi =15 seconds ( stopped at 25 psi as that's factory min )

For oil pressure in inverted flight without an inverted oil system ( used my Dynon logs to work that out ). Note that the fuel pressure stayed at 30 psi the entire time without an inverted fuel system. So if you don't have inverted oil inverted fuel is just a waste of effort.

Right now I am putting 1/2 an inverted Raven system in not because I am worried about oil pressure but because I am tired of having oil dripping of my belly when I land. Depending on what I do I can easily dump 1-2 qt of oil without it. I never fill my engine to 8 qt but usually I start between 6-7.

Oliver
P.s. As said just take that as a data point don't complain to me if your engine breaks.... .

Scott,

Removing the system not prohibit you from doing positive G aerobatics but the occasional zero or negative G maneuver would definitely cause oil to vent overboard. By maintaining the oil canister (slobber pot) you would have the best air/oil separator on the market and no worries about keeping the belly clean. Before removing the shuttle ball valve and associated hoses you should pick up some necessary parts: a new finger strainer for the sump (the old one was shortened to make room for the sump plug), plug for the sump fitting, perhaps a cover for the vacuum pump boss (depending on type of installation).

Caution: When you remove the finger strainer don't forget to remove the plug which was installed in the strainer cavity. You will need a long AN3 bolt to retrieve the plug.

On the other hand, if the inverted oil system is working well and you don't need the room for it, why mess with it?

Finger strainer

If you remove the finger strainer you will need a new one. The finger strainer for the Christen system is shortened to accommodate the plug. The extra ports on the sump, if installed, can be plugged with standard pipe plugs.
The Christen oil system on my 0 360A4A Pitts only lost oil pressure during sustained negative G, such as pushing over from the vertical at zero G, and in left wing down sustained knife edge. With the recovery pot mounted on the right side oil pressure will be maintained in right wing down knife edge. Opposite is true if pot is mounted on left.
Lycoming with custom sump with swivel oil pick up will allegedly maintain oil pressure in all attitudes. Sukhoi uses this principle and the oil pressure never drops below the green.

jrs14855 said:

If you remove the finger strainer you will need a new one. The finger strainer for the Christen system is shortened to accommodate the plug.SNIP

Click to expand...

Interesting - it was not different on my O360. The plug I have has a boss for the screen which somehow preserved the length of the screen. The plug had an oring on the outside, and a blind threaded hole which is used to push the plug in or remove it.

Screen

I think if you buy a new screen, they are only $10 or so from Superior and ECI, you will find that your screen is slightly shorter. The shorter screen might function properly but it will be sliding back and forth slightly between the bore in the sump and the cap.
Thinking about this some more, the flange on the Christen plug must be at least 3/16" long and the screen must be shortened by this amount. If the stock screen were used it would be crushed when tightening the cap. The only other possibility I can see is that Christen modified the cap to work with a stock screen.

Thanks for the info. I think Ron is probably right. While the extra space would be nice, it is not overly obstructing.

Scott