Inverted flight with no flop tubes
 

I had a discussion yesterday about inverted flight with no flop tubes. I was told that an 8 will supply fuel for around 30 seconds inverted with no tubes fitted, assuming sufficient fuel in the tank. This assumes inverted oil system fitted!

True or false? Anyone confirm?

Also assumes you have FI. A carb will stop engine.

Correct. FI.

Well, to the extent that there is about (maybe) 30 seconds of fuel in the lines, sure. Its no different than if you switch your fuel selector to a completely dry tank.

When upside down, the fuel pick-up is in the very highest corner of the tank because of the dihedral. So even a brim-full tank will probably vent the fuel pickup immediately when upside down (unless you keep positive g)

Thirty seconds is probably a stretch. More like 15. I could fly the length of my 3000 foot runway inverted but after turning upright the engine would stumble for a few seconds while the injection servo ingested a slug of air. I have a flop tube installed now.

Practically speaking, you can do most any aerobatic maneuver without a flop tube as you are only negative for less than 3 or 4 seconds. An inverted oil system is a higher priority item in my book.

Interesting to read this. On that note anyone got thoughts on a non inverted oil system and how long could one expect a neg G influence on the oil before some serious damage might result? Yeah I know how long is a piece of string but occasionally when I roll I might get a small amount of Neg G (accidentally) going inverted but only a few seconds, anyone?

During phase 1 I measured without inverted oil or fuel pick up on an IO360 M1B with fixed pitch prop the following oil pressures inverted:

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 Lycoming) )

Below thread shows you this years sportsman without inverted oil or fuel pickup some engine/prop which has small negative portions in it:

http://www.vansairforce.com/communit...d.php?t=156903

So I wouldn't be worried.

Oliver

Has anyone every a header tank in the fwd cargo? It would be easy to service the flop tube and a small 3 gal could be all you need? I know it works well on high wing planes not sure about a low wing? Might need a extra pump somewhere?

I have a 5-gallon fuel tank in the forward cargo compartment. It has a flop tube but I don't fill the tank when doing acro as this makes the plane too nose heavy. I had it plumbed for a smoke oil tank when I did air shows but now just use it for a ferry tank when I need a bit more range.