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  #1  
Old 08-07-2018, 04:32 PM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
Posts: 97
Default IO-390 Inverted oil system

I am trying hard to talk myself into ordering an engine on the Oshkosh special. I plan to have an inverted oil system in my RV-14 so that I don't have to worry about the engine every time I get bored and fly a half Cuban 8.

Has anyone already done this to an IO-390? What is required beyond having the parts? Will I be removing and drilling holes in my brand new engine's brand new sump?
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  #2  
Old 08-07-2018, 04:35 PM
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mjanduda mjanduda is offline
 
Join Date: Jul 2018
Location: Munich, Germany
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Just pull a little on the stick and you'll keep positive g
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  #3  
Old 08-07-2018, 04:55 PM
iamtheari iamtheari is offline
 
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Location: ND
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Technically true. But not workable for all maneuvers. Slow rolls are a good example where you are going to have some period of time with negative G at the engine and where an inverted oil system is probably a valuable investment.
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  #4  
Old 08-07-2018, 06:16 PM
wawrzynskivp wawrzynskivp is offline
 
Join Date: Feb 2018
Location: san jose
Posts: 8
Default Oil Accumulator

Often used by race car drivers who corner hard, the oil accumulator is there to provide momentary oil pressure while the pickup accesses air.

Also nice to have oil pressure before you crank the engine, and when the valve is closed in flight you know you have a squirt in reserve.
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  #5  
Old 08-07-2018, 07:50 PM
Aluminum Aluminum is offline
 
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Location: San Jose, CA
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Quote:
Originally Posted by wawrzynskivp View Post
oil accumulator is there to provide momentary oil pressure while the pickup accesses air.
The main concern with gentlemen's aerobatics is cleaning up the mess on the belly, not starvation.

I'm planning on a half-Raven with the OP's setup but don't have my engine yet.
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  #6  
Old 08-07-2018, 07:52 PM
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Danny King Danny King is offline
 
Join Date: Dec 2004
Location: Southlake, Texas
Posts: 572
Default Inverted oil system

The Doll is equipped with inverted fuel, and Christen inverted oil. I put it on because I owned a Christen Eagle II. I knew I would be selling the Eagle when I started flying the 8. I didn't want my new 8 to limit me to positive G flight since I had been putting the Eagle through everything for the previous 12 years.

Fast forward 18 years....... If I had it to do over again, I would saved the cost and the weight. The Christen Eagle is equipped with an aerobatic propeller. If oil pressure is momentarily lost during zero G, the prop will move to a higher pitch, thus decreasing RPM until pressure returns. The props we fly are spring loaded to move to a lower pitch when zero G causes an oil pressure interruption!

During hammer head turns in the Doll, I had the RPM runway twice even equipped with Christen inverted oil. When the oil feed shuttle valve stalls in-between positive or negative G position, the oil flow will be cut to the pump. I installed a small oil pressure accumulator that prevented all future runways.

Save your money and the weight. Install an oil pressure accumulator, and plan on positive G aerobatics. The accumulator will take care of momentary negative or zero G flight.
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  #7  
Old 08-07-2018, 08:19 PM
sandifer sandifer is offline
 
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Quote:
Originally Posted by iamtheari View Post
Technically true. But not workable for all maneuvers. Slow rolls are a good example where you are going to have some period of time with negative G at the engine and where an inverted oil system is probably a valuable investment.
"Slow rolls" even at RV roll rates are fast enough that an inverted oil ball valve has insufficient time to properly reseat and redirect oil pressure under negative G before the roll is finished, so you really don't need to worry about that. Inverted oil is primarily for sustained negative G oil pressure, not negative G transitions. Preventing a little oil from pumping out the breather during brief negative G transitions is another matter. I agree w/ Danny's post above, however a full inverted oil system does allow you to expand your flying should you eventually want to do more. Acro can be addicting.
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  #8  
Old 08-07-2018, 08:20 PM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
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Thanks for the oil accumulator tip.

Is an aerobatic prop basically a twin-engine prop on a single-engine plane, so that loss of pressure feathers it rather than flattening it out?
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  #9  
Old 08-07-2018, 08:27 PM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
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Quote:
Originally Posted by sandifer View Post
"Slow rolls" even at RV roll rates are fast enough that an inverted oil ball valve has insufficient time to properly reseat and redirect oil pressure under negative G before the roll is finished, so you really don't need to worry about that. Inverted oil is primarily for sustained negative G oil pressure, not negative G transitions. Preventing a little oil from pumping out the breather during brief negative G transitions is another matter. I agree w/ Danny's post above, however a full inverted oil system does allow you to expand your flying should you eventually want to do more. Acro can be addicting.
Any tips on the breather issue? I noticed that the "slobber tubes" on the Great Lakes planes that I got to fly for my introductory aerobatics lessons last winter made a lot of "slobber" after the inverted lessons, so I inferred that the inverted system kept oil going to the engine but didn't keep it off of the belly of the plane (without help from the tube to the tail, that is).

Talk about addiction...I had 10 hours of aerobatic lessons in December and I'm still twitching for more. But until the RV is flying, the only plane I have that is remotely capable of aerobatics is a J-3 Cub and...well, the advice I am getting on that is that, if you have to ask the entry speeds for loops and such, you shouldn't do them, and I have to ask. So I have been constrained to the boring old Normal Category for months now. I will say that I didn't get addicted to sustained inverted flight or inverted spins, but I would really enjoy a hammerhead right about now!

I'm now torn on the inverted oil system. Probably the right thing to do is finish the 14 and fly it a thousand hours without sustained inverted flight and, if I need more, build an RV-8 or buy something already set up for such foolishness.

For now, I'm shopping for oil accumulators and information on how to get them hooked up to an IO-390.
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  #10  
Old 08-07-2018, 11:57 PM
Aluminum Aluminum is offline
 
Join Date: Jul 2017
Location: San Jose, CA
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Quote:
Originally Posted by Danny King View Post
I installed a small oil pressure accumulator that prevented all future runways.

Save your money and the weight. Install an oil pressure accumulator, and plan on positive G aerobatics. The accumulator will take care of momentary negative or zero G flight.
Danny, is your oil accumulator plumbed in addition to the inverted scavenging, or did you remove the inverted system entirely?

From the apparent size of the oil accumulators google brings up it seems that they would provide a fairly short burst on a Lycoming before they run out?
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