flop tube | Andrew's RV-7 Build Log

Sealed Right Tank’s Inboard Rib

July 4, 2011

Well, after stopping by Lowe’s today to pick up some latex gloves (I picked up latex instead of nitrile…I like the latext better), I got to work on sealing the inboard rib in.

For this rib, things were a little different. First, I can squeeze all of the skin to rib rivets (which is nice). Second, I have to pay attention to the reinforcement plates that need to go in place, and third, I have some fittings that can be installed once the rib is in place.

After buttering up the rib and riveting the 43 inboard AN426AD3-3.5 rivets, I ended up with this.

The clever readers will see the uppermost rivet on the right side is NOT SET. I caught it when I ran back outside later to count how many rivets I had set. (I knew counting rivets was a good idea.)

After getting the rib riveted in, I can now slide the reinforcement plates into place. (Like it says in the instructions, if you install these first, you won’t have room to squeeze the skin to rib rivets in the nose.) There’s a thick angle on the outside of the rib (shown below) and a thin .032 plate on the inside.

After lathering that guy with some pro-seal, I snapped this picture and got it installed.

That fan I bought a few weeks back is worth its weight in gold. It was 95°F today.

Fast forward a few minutes and some loud noises, and I had 6 AN470AD4-8 rivets set in the nose reinforcement area.

Perfect. (Well. Not perfect, but once I cover those smileys with proseal, you will never know.)

Fast forward another few minutes, and I got the flop tube installed with the -6 fitting on the inside and the nut on the outside, then I installed the vent tube (just flared) to the -4 fitting on the outside, you can see the aluminum washer and nut on the inside here. I made sure everything had a good bead of proseal around it before torquing everything down.

Nice.

All that’s left to do on the right tank is installed the anti-hangup brackets, rivet a An470AD6- rivet in the tooling hole of the outboard rib, and then close that bad boy up.

Oh, and fit the access plate with some stainless cap screws, instead of machine screws. More on that later.

2.0 hours. 43 rivets on the inboard rib. 6 rivets for the reinforcement plates. 1 drilled out (Easy as PIE!) Hope everyone had a good fourth. (It’s storming here. Boo.)

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Posted by Andrew

Matchdrilled Right Tank Ribs and Baffle

May 26, 2011

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Not many pictures tonight, but I did get the tank matchdrilled.

But first, I got some things ordered from Van’s today in preparation for the tank sealing process:

60 x BUSHING SB375-4 Snap Bushings, 3/8 (1/4)
1 x DUCT NT 5/8-25 Nylon Conduit
30 x BUSHING SB437-4 Snap Bushings 7/16 (1/4)
2 x IF-4/6 RV-4/6/6A/7/7A/8/8A Wing tank flop tube
1 x MC-236-B2 Tank sealant with accelerator QUART KIT
1 x FUEL TANK TEST KIT Fuel Tank Test Kit

Of course, once I placed the order, I remembered that I buggered up the inboardmost rib of the right leading edge and needed a new one. I need to remember to order that one, and BEG Van’s to send it in the same shipment.

I decided to go with 2 flop tubes. (Flop tubes allow the fuel pickups to flop around in the tank, and therefore sustained inverted flight.)

One school of thought is that if you have two flop tubes and they get stiff, you could increase your unusable fuel (they don’t flop good no more) in either the upright or inverted attitudes. People therefore put one flop tube in and one rigid pickup. This means you have to switch tanks to your “aerobatic” tank before doing negative-g aerobatics. (How often will I do sustained inverted flight? Probably not very much.)

Anyway, I weighed the pros and cons, and came to the conclusion that the aesthetics of not having a single tank for aerobatics, and therefore a checklist item or a special placard, outweighed the possibility that after 10 years, my tube wouldn’t flop as floppily as it did when it was young.

Every couple years, I’ll open up the tanks and verify adequate flopitude. They are only $38, so it’s probably worth replacing them every 5 years anyway.

So, now that I’ve settled on duel flopicity, let’s get back to building.

I decided while matchdirlling, it would be easiest for me to do it while it was on the spar, so up on the spar the tank went.

(Be careful though, Van’s notes to matchdrill off the spar to avoid damaging the spar. This is really only a concern with the baffle holes (about the 10 most inboard ones). Take the tank back off the spar do matchdrill those.)