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Adding Flop Tube to finished Tank

A

APicard

Member
Just looking through my plans and trying to figure out the best way to add the flop tube, anti-hangup guides, trap door and fuel sender to a build and sealed tank?

my wings were started by another builder who finished the tanks and leak checked them already.

Has anyone done this? I'm assuming the QB wings dont include Flop tubes by default?
 
I know of one RV8 builder who did the conversion from a quick build wing. It wasn't easy for him.
 
I would really ask yourself if you REALLY need a flop tube.. unless you are intending extended negative aerobatics, they are must not needed. Are you also planning inverted oil? Flop tubes are rubber and need to be changed every few years.. I don’t know anyone who really changes them as preventative maintenance, but over time, they’ll get stiff and reduce your usable fuel. You can still do all the good aerobatic maneuvers without flop tubes, the engine won’t quit from just a momentary negative maneuver.
 
Taltruda said:
I would really ask yourself if you REALLY need a flop tube.. unless you are intending extended negative aerobatics, they are must not needed. Are you also planning inverted oil? Flop tubes are rubber and need to be changed every few years.. I don’t know anyone who really changes them as preventative maintenance, but over time, they’ll get stiff and reduce your usable fuel. You can still do all the good aerobatic maneuvers without flop tubes, the engine won’t quit from just a momentary negative maneuver.
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+1. From this post by Jon Thocker: https://vansairforce.net/community/showpost.php?p=1180965&postcount=1

"A data point for anyone considering fuel tank flop tubes.

Decided to see how long my engine would run while inverted and on the NON inverted tank.

I have a flop tube in the right tank and a standard pickup in the left. From "experience" I've noticed I can fly for quite some time inverted and on the wrong tank!

Today, I decided to find out just how long! With only 4 gallons in the left tank and the left tank selected, I rolled inverted and started a timer. At 25 seconds I rolled upright and at the 30 second mark the engine stumbled for about 2 to 3 seconds then it smoothly regained power.

Hope this will convince guys to bite the bullet and install that inverted oil system. There is absolutely no need to put in a flop tube unless you intend to fly inverted for more than 20 seconds."​
 
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I did it on my RV-8 QB tank.
It wasn’t easy, but not too difficult either.
Istallation of the floptube can be done through the removed tank opening hatch on the inner side of the tank. Sealing the tank penetration inside the tank where the floptube is mounted was the most difficult thing (in my opinion).

You have to move the fuel level sending unit one bay outboard to provide free movement of the floptube.
Cut the opening in the aft wall of the tank and installation is no biggi.
 
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Thank you everyone who replied this information is very helpful and gives me something to think about.

I'm not planning on sustained inverted flight. I just want to be able to loop and roll when I'm up on my own and having fun.

Guess the reading that flop tubes are required for inverted flight should state sustained inverted as I don't plan to be upside-down that long. (which it does when you go to the part on Van's Website.....boy I feel silly....)
 
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As someone else stated, if you’re so inclined. Just do 1 tank and leave the other one without flop tube. 1/2 the work and a safety margin if anything should happen to that flop tube. I have flop tube in left wing and regular pickup In right wing.
 
Absolutely…just one tank

There are a couple of posts that indicate FLOP TUBE is a life limited item as they “ age “ and loose flexibility and as such must be replaced on occasion..
 
Flop tube

My SB took so long, I just removed mine. Never used but it was already stiff enough that it probably wouldn't flop.
I swapped it for a standard pickup.
 
The typical 'flop' tube is a rubber lined Aeroquip 701 (H-83797) hose, or equivelent, or an 'imposter' looking hose. We know that the chemicals in the fuel will attack the liner and break it down internally, but also do something similar on the OD of the liner and make it stiff. So obviously the flop is gone.
Teflon is stiffer than these so its not an option. (we even tried just a convoluted liner as a pickup like the INDY cars use, and at didnt help.) The real solution is a swinging pickup, or a live swivel joint, but they are expensive.

Another possible solution might be to make an enlarged supply port in the tank rib and use a different fitting with a hose and counterweight attached, so you could drain the tank and unscrew the entire assembly out and replace the hose as needed =maybe every other conditional.

Tom
 
Sustained inverted flight means that you are pulling One Negative G, and all the blood rushes to your head. Takes getting used to, and the younger you are, the easier it is. :rolleyes:
 
For one thing I have never needed a flop tube for positive G rolls or loops. Fuel stays where it is supposed to.
And hey if it doesn't then the engine dies for a bit. Adds excitement to the ride.
My luck varies Fixit
 
If all you want to do is Loops and rolls you don’t need a flop tube. In fact with a negative G oil system the only thing you won’t be able to due is sustained inverted flight. The info from Jon Thocker is spot on.
 
wirejock said:
My SB took so long, I just removed mine. Never used but it was already stiff enough that it probably wouldn't flop.
I swapped it for a standard pickup.
Click to expand...

I resealed three tanks with flop tubes. In two cases the hose was firm and took a set in the tank's upright orientation. When flipped, neither would go beyond the half way mark. Had to replace hoses. Use caution out there. Most rubber loses elasticity over time.

Larry
 
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