Half Raven Inverted Oil Separator
 

I recently installed a "Half-Raven" oil system on Miss Izzy.

Basically, the Half-Raven system is just the oil separator part of the Raven inverted oil system. It does not include the inverted oil check valve. It is the oil check valve that directs oil from the top of the sump to the oil pump during sustained inverted flight. The oil separator redirects the oil vent from the top of the engine to the sump during inverted flight and collects some oil in the tank for return to the sump after returning to level flight. Here's a link to pictures:

http://www.ravenaircraft.com/Parts.html

Sustained inverted flight is expensive! You would need to have a full inverted oil system, inverted fuel pickup, fuel injection and a counterweighted constant speed propeller (if not fixed pitch). For the momentary negative or zero "G" maneuvering that we typically perform in the RV all of the above is not required. A second or two of oil pressure loss is not detrimental to the engine. The standard fuel pickup is sufficient, as there is adequate fuel in the lines to sustain engine operation for several seconds. While fuel injection is nice, a carbureted engine may sag or quit during some maneuvers but will quickly return to full power when positive "G" is applied. A standard CS propeller will rarely lose enough oil pressure to drive the blades to fine pitch and if this does occur it is easily recognized in time to reduce power to avoid an overspeed.

I light of all of the above, all I wanted was something to keep massive amounts of oil from flying out my vent and onto the belly of the airplane. A few weeks ago five of our Team RV pilots spent two days practicing and performing aerobatic routines to secure our aerobatic competency cards. (We are intent on interjecting some aerobatics into the Team RV airshow routine.) One of our pilots told me he lost over four quarts of oil during one training session! I flew virtually the same maneuvers as he did and didn?t lose a measurable amount of oil and the belly was clean.

Here is what I bought for the Half-Raven system:

Raven Oil Separator Tank with mount and clamps. Sump fitting. (Direct from Raven Aircraft): $326.71

AN842-12 Brass Hose Elbow (2) (Aircraft Spruce): $15.50 each.

AN816-10D Straight Fitting (Aircraft Spruce): $3.10

6000-12 Oil Hose, 3 feet (Aircraft Spruce): $6.75/foot.

#10, 36-inch braided hose with straight end fittings. (Local race shop): $68.43

The installation took about five hours. You need to mount the separator tank high on the firewall so the bottom of the tank is at least two inches above the top of the sump. It should be at least ten inches to one side of the engine centerline, opposite the side you mount the sump fitting. The sump fitting goes into one of the bosses on the bottom of the sump. (Same place you drain oil.) There are three ports on the tank. The top #12 hose comes from the normal oil vent. The middle #12 hose goes out the bottom of the cowling. The bottom #10 hose goes to the sump fitting. Clamp all the hoses down. Refill the oil sump and go fly!

Now, some of you will question my assertion that a few seconds without oil pressure isn't harmful to the engine. I have no documentation or test results to confirm this and my statement is only supported by statements from several pilots with considerable aerobatic experience. Having said that, my next job will be to install a small oil accumulator to supply several seconds of oil pressure when required. I am going this route rather than installing the Raven oil check valve because my aerobatic routine does not involve extended negative "G" flight. I will only have momentary periods of negative or zero "G" exposure. The Raven oil check valve is basically a ball check valve that re-directs oil flow when in inverted flight. It cannot maintain pressure in zero "G" flight because the ball check valve is unseated. Here's where an oil accumulator will supply pressure.

I have ordered an Accusump one quart accumulator.
http://www.hrpworld.com/index.cfm?tp...action=product
Once I get it installed I'll let you know how it works out.

tired of cleaning my belly too
 

Any pics of the installation?

Don,
I didn't take any pictures, but I will try to remember to do that when I have the cowling off to install the oil accumulator. Give me a few weeks and I'll git 'er done!

Hard to argue with results like that!

Wondering how your half-Raven setup is different from other oil separators like Airwolf, Andair, RMJ, etc. Looks to me like basically the same deal, but maybe I'm missing something. Would you expect any of these to work as well?

--Paul

Paul,

I don't know how the others work. The Raven uses a ball valve to select either the top vent when upright, or the sump vent when inverted and then it returns any collected oil to the sump during normal flight. This is 1/2 of the full Raven inverted system, designed to vent the engine when upright and inverted. Most oil separators are only designed to collect oil from the upper (normal) vent. I don't remember seeing any that even have a sump connection. What they do with that collected oil is the issue. Do you have to empty the tank once in a while or is it somehow returned to the engine. Biggest question I have is: "why are they so expensive and why do so many people have trouble with them?"

Pictures of Raven/Accusump Installation
 

OK, it took more than a few weeks to get some pictures. It's really hard to take the cowling off when you're having so much fun flying! :D

Here's the Raven oil separator on the left. The top 3/4-inch rubber hose comes from the engine vent. The middle 3/4-inch rubber hose goes overboard. The bottom #10 braided hose goes to the sump. The oil accumulator (Canton Accusump ) is on the right (blue cannister). It is about 12-inches long and 3 1/4 inch diameter, without the meter and fittings. Here it is precharged to 10 psi. When the engine is running it will fill with one quart of oil and read normal oil pressure. Any loss of pressure will cause the accumulator to discharge it's contents and maintain oil pressure for a short time. Great for the occasional zero or negative "G" excursion.



This is the Raven fitting for the bottom of the sump. It has a standpipe that goes to the top of the sump. This is where vented oil is returned to the sump after returning to normal flight.




This is the "T" fitting that I used to connect the accumulator to the oil system. It has a 3/8 NPT and two #8 AN flare fittings. You can plumb this into the oil port on the accessory case of the engine or onto one of the ports on your oil cooler, whichever is more convenient.



You may ask "why didn't I just install the Raven inverted oil check valve". Answer: I don't do sustained inverted flight. I may pull a few seconds of negative "G" during immelmans, cuban 8's, hammerheads, slow rolls, etc. The oil accumulator provides oil pressure during these brief periods. Plus, the oil accumulator will provide pressure during zero "G" flight where the Raven oil check valve will not. The Raven valve relies on a heavy ball bearing to change the oil pickup port during inverted flight. At zero "G" the ball bearing doesn't seat firmly in either port so the oil pump may cavitate in this instance.

Wise move to avoid the check valve...I know of a few engines that have been trashed by said devices.

The P-51 has a dry sump oil system. In the oil tank there is a J-shaped casting that swivels on a bronze bushing so that when inverted, the weight of the oil pickup keeps it in the oil. Lycoming has produced dry sump engines that use a similar mechanism for sustained inverted flight.

Inverted Oil Pressure
 

I have had some experience with my "Half Raven" oil separator and the Accusump oil accumulator (described in above posts) now and can report that I consistenly get a full seven seconds of oil pressure when inverted before it drops to 25 psi. That's plenty of time to do any of the IAC aerobatic routine maneuvers with a comfortable safety margin. :D

This "half" option is great for anyone wanting to fly IAC Primary or Sportsman in their RV. Both of those categories have only a few maneuvers with very brief zero or negative G exposure.

We've had an identical system to Ron for nearly 2 years... i.e. the (small) Raven Tank + sump return, no Accumulator.

As he says, markedly reduces Oil loss to belly, but can still be defeated ;)

Andy
RV-8 G-HILZ