Greetings!

I'm interested in learning some more about inverted fuel and oil systems (e.g. systems that permit fuel and oil flow/operation while the aircraft is inverted). I should probably be specific about the pieces that I'm unclear on:

- Can anyone explain or point me to some reference that illustrates what inverted fuel tank pickup mechanisms look like?

- I understand the concept of wet and dry oil sumps. Are dry sump oils systems used in high performance aerobatic aircraft like the Extra or is there some other system used? All explanations and/or illustrations most welcome.

Thanks!

Ben

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• RE: Inverted fuel and oil systems,ChipB727, 18:27z, 05-27-03
  • RE: Inverted fuel and oil systems,TomParsons, 20:05z, 05-27-03
  • RE: Inverted fuel and oil systems,Ben_Chiu, 17:37z, 05-28-03
    • RE: Inverted fuel and oil systems,djpacro, 00:13z, 05-29-03
      • RE: Inverted fuel and oil systems,Ben_Chiu, 01:58z, 06-01-03
      • RE: Inverted fuel and oil systems,ChipB727, 21:03z, 07-02-03

It's a weight threaded to the end of a hose with holes drrilled in all directions to pick-up fuel. Check Aircraft Spruce online catalog. It should be there. Not sure how to post a picture, but I can email you one if you wish.

As for the oil sump on the Extra it is a dry sump and uses a 3-way oil valve to pull oil from the sump or the top of the engine (inverted flight) to the oil pump.

During normal flight, the weighted ball valve at the top of the oil separator is open, allowing blowby gasses from the engine crankcase to be vented from the breather port, through the breather tee, to the top of the oil separator, and out through the overboard breather line. The top ball valve of the oil valve is closed, and the bottom ball valve is open, allowing oil to flow from the sump out through the strainer fitting, to the oil valve, back through the sump fitting to the oil pump and out to engine lubrication points.

When the aircraft is inverted, engine oil falls to the top of the crankcase. The weighted ball valve in the oil separator closes, preventing overboard loss of oil through the top of the oil separator. Blow-by gasses from the engine crankcase are vented from the sump to the bottom of the oil separator and out through the overboard breather line. The top ball valve of the oil valve is open, and the bottom ball valve is closed, allowing oil to flow out from the breather port, through the breather tee, to the oil valve, through the sump fitting and the sump screen, to the oil pump and out to engine lubrication points. Any oil in lines which fails to return to the sump during the transition between normal and inverted flight drains into the oil separator. This oil then returns to the sump from the bottom of the oil separator during periods of normal flight.

Best Regards,

Chip Bonner

Chip-
>It's a weight threaded to the end of a hose with holes
>drilled in all directions to pick-up fuel.
I assume you're describing a flop-tube type of inverted fuel pickup. My airplane has a header tank- can you describe how that works?

On the inverted oil system, am I right in saying that you've described the Christen inverted system? Also, one addition to the system that I've heard of is a swinging oil pickup. Is the purpose of the swinging pick to allow oil flow during knife-edge flight? If so, how does that work out if the ball valve is not seated at either end?

Thanks in advance.

Tom P.

Greetings Chip:

> It's a weight threaded to the end of a hose with holes drrilled in all
> directions to pick-up fuel. Check Aircraft Spruce online catalog. It
> should be there.

I couldn't find one online, but I get the concept. It's very similar to the type of tank "clunk" they use in R/C airplanes.

> Not sure how to post a picture, but I can email you one if you wish.

Just FYI, when you post or reply to a message, there'll be a link called Upload file or something like that on the left side of the screen. Follow the prompts and you'll upload the file. As a moderator of this Forum, you'll be able to view the file URL from the Admin panel. If you're interested, I can email you the details of what to do.

> As for the oil sump on the Extra it is a dry sump and uses a 3-way oil
> valve to pull oil from the sump or the top of the engine (inverted
> flight) to the oil pump.

I found a retrofit system in Aircraft Spruce cat:

http://www.aircraftspruce.com/catalog/eppages/christen801.php

It's probably not the same, but I get the idea. It's interesting how such a high tech machine such as an Extra uses such relatively low tech mechanisms. Then again "KISS" (Keep It Simple Stupid) is usually the best way.

Thanks for the insights, Chip!

Ben

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The Christen system is relabelled as the standard Lycoming installation on aerobatic engines. Some more details at
http://musclebiplane.org/htmlfile/builders.shtml

The swinging arm is one feature of the Sky Dynamics Sump (along with their cold air induction system and maybe even a better exhaust system). This overcomes many of the situations resulting in zero/nil oil pressure with the Christen system.
http://www.skydynamics.com/

Regards,
Dave Pilkington

Thanks for the links and info, Dave!

I couldn't find any diagrams of the SkyDynamics system on their site. It sounds like an revolutionary design.

Ben

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Sorry I'm late getting back, been out of town. My only real experience is with the Christen system, I have troubleshot some of the other systems and usually find the flop hose in the engine turns brittle and will no longer flex. A side effect from heat cycles.