Flop Tube Installatiion

[SteFree RV-8]

Please forgive me if this is one of those "asked and answered" type questions. I have tried searching but I can't seem to find the answer.

I am installing a FLOP tube in left wing of my RV-8 project. Per the drawings is says to move the float sender to the second bay in the fuel tank and mount the sender on the 702 Baffle. That is all easy enough but Van's does not offer any measurements for this and have told me:

Unfortunately, I don?t have a whole lot of guidance here. The plans for the fuel sender in the second bay are pretty darned vague. At the very least, I?d insure you have sufficient end distance from hole to rivet and rivet to rivet to the adjacent rib.

I would also be very careful about the wire bend. The bend in the plans are for the inboard rib. That likely won?t work for the second bay installation.

I?d suggest looking to Vans AirForce for this one.

I am wondering if any of you guys might have some advice and pictures describing/showing where you mounted your Flop Tube and how (where and what angle) you bent the float sender based on where you placed the sender.

Any help is very much appreciated.

Tanks (no punt intended) guys!

Steve

[RV6_flyer]

It has been over 21-years since I built my RV-6 with inverted pickups in the tank.

I used the doubler that goes on the inside plus the cover place for layout between the top, bottom, and ribs. On the RV-6, I used the same bend on the float that was called out in the plans. While the tank was under construction, I did "calibrate" the two senders by bending the full / empty stops that was part of the sending unit so that both had the same resistance reading.

The airplane has been flying since 1997 and has over 3,300 hours flight time on the hobbs. Have not had any issues with the fuel senders. I did use a ground tab on each sending unit that had a ground wire back to the gauge. I did not want to use the airframe for ground for the sending units.

[N329JR]

Gary
If you would like to share your email address with me, I will forward you pictures that I took last year while building my -8 left tank with flop tube. I have some fair pictures of the bent sending unit wire and the location of the sender in the second bay.
Ian

[Saber25]

My RV4 had the flop tube in the right wing as per instructions. After some 12 years I decided to remove the flop tube since I was concerned about the heavy brass fitting making a wear pattern on the bottom tank skin. Sure enough, the rubber O ring had broken down and the brass fitting made a semi-circular wear pattern deep enough in the skin that convinced me to remove the flop tube. I sleep better now knowing the flop tube was removed 17 years ago and no longer rests and flops about on the lower skin. Replacing or repairing that skin is not something I would look forward to.

Unless you intend to do sustained inverted you really don't need the flopper.

Cheers, Hans

[SteFree RV-8]

Originally Posted by N329JR

Gary
If you would like to share your email address with me, I will forward you pictures that I took last year while building my -8 left tank with flop tube. I have some fair pictures of the bent sending unit wire and the location of the sender in the second bay.
Ian

steve.freeman@syntaxds.com

It would be great if you could send your photos...I would very much appreciate that.

If possible, can you share the measurement and angle for the bend similar to how it is shown in plans for the conventional installation.

Thank you,

Steve

[SteFree RV-8]

Originally Posted by Saber25

Replacing or repairing that skin is not something I would look forward to.

ON the RV-4, are the tanks not easily removable like the later model RV's?

Based on what I am seeing it would not be terribly difficult to replace the flop tube.

In an extreme sense a builder could add a second skin on bottom of tank too...but that does seem like over kill.

I am not planning on doing a lot of upside down flying but why not...just in case.

Steve

[merlin3]

Didnt redline say that the engine would run for about 30 seconds inverted without flop tube?

[Robert Anglin]

Yes we built a very nice set-up in one tank with guides and stainless cladding.
a weighted fuel shut door and air bleed restrictors in the upper vent holes. The flop tube and the sending unit details should be in your plans. The sending unit goes in the middle of the rear baffle just as you have said. Before you put the tanks together for good, you can take the first rib and second rib out and bend the float wire so that the float just touches the top and bottom of the tank while the sender is at its full travel. I think we set ours 1/16" off the skins so they would not quite touch. You will calibrate the gages later after everything is built and ready for fuel fill testing. If you don't have these instructions in your plans, you may wish to call Van's.
Yours, R.E.A. III # 80888

[Saber25]

Getting the flop tube removed and replaced does require removing the tank. My concern was the semi-circular wear pattern on the bottom skin. To add some kind of wear strip, be it of another aluminum layer or wear resistant material was not in my initial build process. Following another web site, the "O" ring on frequently used acro planes does break down thus losing the buffer it was designed for at the end of the brass flop tube. Perhaps some of the other builders with flop tubes installed can chime in as to what they are seeing.

To mitigate this whole issue, a header tank might be a better solution for hard acro and inverted, hence my Pitts S1S.

Cheers, Hans