Fuel Tank flop tube

Hi all, I'm building my fuel tanks and am trying to decide whether to add flop tube (s). I will be doing aerobatics but not too harsh - max 10 sec inverted. Any feedback welcome please...

I see various posts about different fuel system fittings. I've got Vans standard stuff. Any added considerations I should take not of please? I'm the only person building an RV in this country so dont get access to seeing other builds.

Merry Christmas everyone!

John---I'll defer to those guys that like to fly inverted, on whether inverted pickups are necessary for what you are planning. But---just in case you like it, you might want to think about at least one tank with the inverted pickup.
Tom

Flop tube

TS Flightlines said:

John---I'll defer to those guys that like to fly inverted, on whether inverted pickups are necessary for what you are planning. But---just in case you like it, you might want to think about at least one tank with the inverted pickup.
Tom

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That's what I did. Left tank is flop. Several reasons.
1. There have been issues with life span of the flop tube. They may be in the past but just in case I felt it better to have one of each. Should it fail at some point, I can switch to the standard. Also, only one to replace.
2. Reliability. The idea is to keep enough fuel in the right for landings and switch to right before starting the landing sequence. This is precautionary.
3. Flop tube is a bit more difficult to install. One was plenty.

One of these days, I'll have the solution.
Tom

I removed my flop tube the other day. I have tubes in both tanks. I have found that I don't do any negative G-maneuvers, so flop tubes are not really necessary. On a positive note, I found the tube in excellent condition (after 14 years), though it was difficult to safety wire it thru the access port in the side of the tank! I would not put them again in my aircraft (for my type of flying).

Miraclechap said:

I will be doing aerobatics but not too harsh - max 10 sec inverted. Any feedback welcome please...

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Once you get into sustained negative G's feeding fuel is only one part of the system to support inverted flight. There's also inverted oil and fuel injection included. If you plan to maintain positive-Gs while flying basic aero (such as loops and rolls, for example), it's probably not necessary.

For any significant negative-G aero you need a flop tube to pick up the fuel, inverted oil system to make sure oil flows where it needs to go and doesn't go overboard via the vent tube, and fuel injection so the fuel-air mixture can actually make it into the engine properly.

I'm building my RV right now, not flying, so take all this for what it's worth of course. When I asked Van's and a couple other long-time RV'ers and designers recently about the flop tube their consistent response was "Why would you want to do that? It's more complicated, extra work and you only need that if you're going to push negative G's." Which is what I intend to do, so all three systems are part of what I'm putting together. It's all about the mission.

I drilled the and cut the left tank and safety-wired/installed my flop tube just a couple days ago. You have to relocate the fuel level sender for the tank with the tube to a different location, one bay outboard, in the rear baffle, which requires cutting a fairly large hole back there, as well FYI.