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Christen Inverted Oil

949Aviator

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I've been searching for positive vs negative g aerobatics and can't find any information. Will hammerheads, barrel rolls, aileron rolls, loops, etc.. have enough negative g's to matter? I've barely done aerobatics and will need training once my plane is done. Should I wait on the inverted oil system and if I get more advanced with aerobatics, then consider it?
 
Doesn't sound like you need the inverted oil unless you are flying inverted for several seconds. . A little zero g isn't worth the hassle of an inverted system in my opinion. .do you have flip tubes and fuel injection to go with the inverted oil anyway?
 
I’m installing a Half Raven on my RV-14. That’s the air/oil separator portion of their inverted oil system. I will lose oil pressure when negative G but the oil won’t pour overboard through the breather tube as the separator will return oil from there back to the sump. This was a compromise that fits my needs. I really enjoy hammerheads, Cuban 8’s, and other mostly positive-G maneuvers, and I don’t have to do machining on my engine.

I researched this topic (there’s a thread I started somewhere around here, in fact) and it seems that the consensus among pilots is that an inverted oil system takes a couple seconds to flip over between positive and negative G positions, so you lose oil pressure during that transition anyhow. An oil accumulator (pressurized tube with a piston, which the oil pressure of the engine fills with oil against the air pressure on the piston, and the air pressure forces the oil into the engine if the oil pressure drops) will create a buffer against that, whether you have the inverted system or not, to maintain positive oil pressure for a second or two when the engine oil pump is sucking air. I chose not to install an oil accumulator because the complexity was not warranted by the small amount of time I’m ever going to spend in negative G’s. (Part of my research was to get a full introductory aerobatic course and discover which maneuvers motivate me to build and which of them motivate me to curl into the fetal position in a dark room.)

I don’t think it would be hard to install the Half Raven system after you are flying. You won’t even really have to plan ahead for it. I don’t feel that it has slowed my build much but every deviation from the plans will slow you down a little bit.
 
Will hammerheads, barrel rolls, aileron rolls, loops, etc.. have enough negative g's to matter?

I'm not sure about the hammerheads, but the other maneuvers you listed do not generate negative Gs at the level or duration requiring neg-G oil systems or fuel pickups. I tested and approved KELLI GIRL for aileron rolls, barrel rolls, loops, Immelmanns, Split-Ss, and half-Cubans. Of those, only the Immelmann and half-Cuban experience negative G, and then only momentarily. I have had zero interruption of oil or fuel flow/pressure. I ought to go ahead and allow the full Cuban 8 maneuver.
You should be good.
 
I installed a half raven and have had good results. I keep everything positive for the most part. Loops, rolls, immelman, split s, spins, etc. no oil on my belly either.
 
I've been searching for positive vs negative g aerobatics and can't find any information. Will hammerheads, barrel rolls, aileron rolls, loops, etc.. have enough negative g's to matter? I've barely done aerobatics and will need training once my plane is done. Should I wait on the inverted oil system and if I get more advanced with aerobatics, then consider it?

I wrote an article in the August 2016 issue of Sport Aviation on "Equipping your RV for Aerobatics". You can find it in the EAA magazine archives. If you only want to do the occasional light aerobatics you will be fine with fuel injection and perhaps a half Raven system to keep oil off the belly. A flop tube is only necessary for sustained negative G flight. I don't recommend an oil accumulator if you have a constant speed propeller as it can cause the RPM to surge in some applications. You can progress to a full Raven or Christen system if you get serious about aerobatics.
 
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