Fitting Flop Tube and Fuel sending units

paulincapetown · #1 10-10-2012, 05:02 AM

Ok so here?s the thing!!

For my 7, I have purchased QB wings , a flop tube and x2 float fuel sender units. I am getting different advice from experienced guys so thought I would post here to find out what the general thinking is.

I expect to do aerobatics up to sportsman level ? i.e. no or very seldom negative G?s. If I want do anything more (aerobatically) I will buy a Pitts ( wish

)

The strong advice I am getting from local builders is not to fit the flop tube on the QB wings in addition to the x2 float sender units. A new hole will need to be created in the fuel tank for the flop tube ( and one for the Fuel sender unit) and unless this is fitted correctly, chances of leaks are increased significaly and the amount of work required for the limited benefit is not worth it. I also hear that the flop tube needs replacing every 3-4 years?

I am now starting to think that the flop tube benefits are inconsequential ( I do not have nor am going to put in an inverted fuel system). Am I alone in this thinking or is there a general consensus that for basic aerobatics, a flop tube is required.

Andy Hill · #2 10-10-2012, 05:32 AM

A Flop Tube is not required.

I would suggest there is no need unless you have a full inverted oil system and plan to use it (and have an IO engine).

I did the Test Flying on a new RV-8, 180HP IO. To test the inverted oil / fuel I flew inverted for ~1min. I then repeated the test on the "non Flop Tube" tank. Engine ran fine for 23s ~ 75% before beginning to hesitate.

Ironflight · #3 10-10-2012, 07:06 AM

I am goign to agree with Andy (as usual) - unless you plan to fly inverted cross-countries, chances are that you will never know that you don't have a flop tube. If you were slow building, it wouldn't make a lot of difference which way you went, but I certainly wouldnt' go through the effort to modify a QB (and I haven't on two so far), given your requirements.

JonJay · #4 10-10-2012, 10:15 AM

I won't disagree with Andy either. However, you don't need an IO engine, just the proper carb or throttle body. My Bucker has an o-320 with an Ellison. Of course, Christen Fuel and Oil systems. Now to fix my brake reservoirs so they can vent without leaking while I am inverted.

pierre smith · #5 10-10-2012, 11:48 AM

Paul, my -6A had an O-360, carbed and no flop tube.

For 5 years, she was rolled, 4 point rolled, barrel rolled, Immelmans and split essed. It never coughed since it was always somewhat positive G.

Best,

paulincapetown · #6 10-10-2012, 01:32 PM

Great to hear - Thanks Gents, another decision made

100 more to go

N355DW · #7 10-11-2012, 05:55 AM

You will want the flop tube. Sportsman still requires some inverted lines be drawn, such as after the roll in a half-cuban, or reverse half cuban. I can't say for sure in an RV, but the engine will cough or even quit at times in all planes without inverted systems I have flown in a Sportsman competition sequence.