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Flop Tube Install in Finished Tank

Scotty G

Well Known Member
Is it worth installing a fuel pickup flop tube in a finished wing tank? I only plan on gentleman aerobatics, but if it was easy to install, I'd opt for a fuel pickup tube.

Can someone give me a general idea of what I'd need to do for that type of addition, and do you think it's worth it?

Thanks in advance.
 
Do you have inverted oil? And fuel injection? Without those, I cannot see a flop tube being much use.
 
Flop

If you do install it, add the anti rotation bracket so it can't get loose when you tighten the fitting.
 
No inverted oil, engine is fuel injected. Again, I don’t see flying inverted more than 10, maybe 15 seconds at the very most.
 
I don't think it is worth it or necessary for gentleman's aerobatics because smooth maneuvers like rolls, loops and steep turns are generally positive G.

On a RV-6 the flop tube fitting is close to the leading edge of the tank, and I assume the -8 will be similar. Retrofitting will involve at least removing the tank, if it is fitted to the aircraft, opening the tank to get access to reposition the float sender and install anti-snag guides and a flap valve, and sealing up with Proseal.
 
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I don't think it is worth it or necessary for gentleman's aerobatics because smooth maneuvers like rolls, loops and steep turns are generally positive G.

On a RV-6 the flop tube goes onto the same threaded fitting in the tank and in place of the fixed pickup, and I assume the -8 will be similar. Retrofitting will involve removing the tank, if it is fitted to the aircraft, taking off the cover plate in the wing root, ensuring the flop tube clears the fuel level sender and dealing with sealant.

Interesting, I would have assumed the installation would be similar, but it doesn't sound like it is. In the -8, the feed fitting for the flop tube is drilled through the nose of the inboard tank rib, rather than through the access cover towards the rear. Inside the tank, a couple of anti-hangup guides are added in that inboard bay, as well as a small trapdoor on the second rib. If the fuel sender is a float-type, it must also be relocated one bay outboard.

So long story short, a retrofit would appear to require:

  • Removing the tank from the wing if installed
  • Drilling a new hole through the reinforcement angle/nose attach point for the flop tube's AN fitting
  • Fabricating the two anti-hangup guides and riveting. The inboard one attaches to the access cover mount ring, so this would likely require drilling a couple new holes there
  • Fabricating the trapdoor and riveting it to the second rib
  • Probably just replacing the access cover with a new blank one (if float equipped)
  • Cutting a second access hole in the baffle and adding the rear-mounted float sender (again, if float-equipped)

It sounds like OP's already made his decision, but I figured it was worthwhile to give an overview of the differences.
 
No inverted oil, engine is fuel injected. Again, I don’t see flying inverted more than 10, maybe 15 seconds at the very most.

In 10 or 15 seconds you will lose oil pressure and dump a load of oil out the breather.
 
In 10 or 15 seconds you will lose oil pressure and dump a load of oil out the breather.

Yep, hence it’s not worth the whole process. No prolonged inverted for me.

I appreciate all the feedback and input. Thank you, all!

Scotty
 
Interesting, I would have assumed the installation would be similar, but it doesn't sound like it is. In the -8, the feed fitting for the flop tube is drilled through the nose of the inboard tank rib, rather than through the access cover towards the rear. Inside the tank, a couple of anti-hangup guides are added in that inboard bay, as well as a small trapdoor on the second rib. If the fuel sender is a float-type, it must also be relocated one bay outboard.

The flop tube is installed in the -6 the same as it is in the -8. Never heard of one going in the same place as the standard pick-up. Not sure how that would work.
 
Flop tube location

The flop tube is installed in the -6 the same as it is in the -8. Never heard of one going in the same place as the standard pick-up. Not sure how that would work.

Philip and Mel, you are both right, I checked my construction manual from 1993 and those guidelines from Vans are the same as you say. Apologies my bad (memory), I will correct my original post to avoid potentially misleading anyone.
 
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