Notes & Comments Fuel System

From "Construction Notes" Falco Builders Letter, September 2003

"The tank band tightening P/N 733-7 is not listed. What screw or bolt?"

P/N 733-7 is a custom screw, same as any fillister head screw but much longer.

Gary Jacob faxed that he was confused by the fuel system drawing and that he didn't understand what the hose (P/N 740-18) is going to and that it terminates with P/N 740-15. On this drawing, there are two installations shown on the same sheet. If you use the header tank, you screw P/N 740-15 into the bottom of the fuel tank, instead of the AN912-8D. And Gary, as you see this, you will doubtless perform the classic gesture of bouncing heel of hand off forehead-which, incidently, is why Italians have flat foreheads.

From "Construction Notes" Falco Builders Letter, September 1993

Fanie Hendriks reported a problem with the A-600-2-4 fitting that screws into the top of the header tank. He initially reported that it had the 'wrong threads', but it turned out to be shallow threads cut into the fitting on the header tank. He opened them up by simply screwing in a similar fitting that apparently had slightly smaller threads, but if you have this problem, you can just use a 1/4" NPT tap. For those of you who are overseas, spelled out that means "one quarter inch national pipe threads".

In looking this up for Fanie, I was surprised to learn that we have not been shipping the 5/16" diameter steel ball that is supposed to be in the vent of the header tank. Brenda didn't know about this, but we're getting some in and will be happy to ship them to any of you who are missing them. The ball becomes a check valve when the opening of the A-600-2-4 fitting and prevents fuel from running out.

From "Construction Notes" Falco Builders Letter, March 1992

There's an interesting new product on the market for temporary repairs of oil and gasoline leaks. It's called Oyltite-Stik, sort of a styptic pencil for engines and fuel tanks. This thing is like an oversized grey crayon, and what you do is rub it into the crack or weeping hole. Dang if I know how it works, but it appears to be a kind of a waxy substance with a lot of clay in it. Apparently, it packs into the crack and stops the leak. It is advertised to work with all types of oils, gasoline, water, dilute acids and alkalies, and is intended to keep equipment running until a complete repair can be made.

No ferry pilot should be without one of these things. It's make by La-Co Industries in Chicago, and you can get it from Aviation Consumables, P. O. Box 27205, 4000 Red Bank Road, Cincinnati, OH 45227. Phone: 513-561-9977, Fax: 513-561-9550. List price is $6.01 each, and they're having an introductory sale for $4.33. Aviation Consumables says they've found the product works well on Lycoming and Continental casing halves seepage.

From "Construction Notes" Falco Builders Letter, September 1992

As some of you may remember, Jimmy Shaw was the third homebuilder to fly his Falco. He was stationed in Mesa, Arizona, at a training base in the USAF, and he had to get the airplane flying within a certain amount of time. He did it, but it was a bandaid-and-baling wire contraption. The nose gear bay was wide open, and he could throw his Twinkie wrappers out the hole.

Jimmy is now settled down north of Dallas, and he's finally getting his Falco fixed up. In attaching some accessories to the firewall, he drilled a hole and put some bolts through frame No. 1. On removing his fuel tank, he found that one of these bolts had been rubbing on the tank and had almost rubbed a hole in the tank. (We're careful to use washer-head screws in this location, but it never hurts to put a piece of rubber over the screw head, just in case.) Also, Jimmy didn't have padding on the straps for the front fuel tank at the upper aft face, and the straps were rubbing and wearing the tanks.

From "Construction Notes" Falco Builders Letter, December 1989

Steve Wilkinson encountered a minor problem with the gascolator-to-firewall fuel line. We supply the tubing with a 15° angle and a single flared end. Unfortunately, the little blue sleeve will not slip over the bend. Steve solved the problem by slightly unbending the tubing and then re-bending it. The nut, sleeve and flared-tube system is designed to work with considerable pressure, and the function of the sleeve is to press the flared end of the tube tightly against the flared fitting. There is virtually zero pressure in this line, and I think it would be perfectly acceptable to file a slight clearance radius on the inside of the non-flared end of the sleeve.

From "Construction Notes" Falco Builders Letter, December 1988

We are changing the fuel selector valve to a variant of the type used by Mooney. The valve that we have used in the past has worked nicely, but the company that makes it now wants a small fortune for the valve. The new valve is just as good and has three positions instead of the four of our previous valve (which had two Off positions). The valve handle will now have the long part of the handle pointing toward the selection.

There is a minor change in the mounting of the valve. The two screw holes will remain unchanged but the hole for handle moves .25" to the right. Our next series production of the pedestal will be correctly machined, but there will be many of you who will have to fudge things. There are a variety of methods that can be used, none of them very difficult, which I will describe in a later memo. I'll also have a few drawings for those of you who will need them. In the meantime, I would suggest that you do not install the rub-on lettering for the fuel selector valve until you have the new drawings.

From "Construction Notes" Falco Builders Letter, March 1987

One of the beauties of nylon tubing is that it is flexible, and that is also one of the problems with it! We use nylon tubing in the fuel system, and there are places where you would like to bend the tubing and have it stay in that shape. There are also places where the tubing doesn't bend to as tight a radius as you would like. John Oliver came up with a solution that is so simple you feel like a complete fool for not thinking of it yourself.

Nylon tubing is made by melting nylon pellets and extruding the tubing. As it cools it is wound on spools and takes the characteristic slight bend. It doesn't hurt to heat and bend it yourself, and it doesn't take much heat. John just took a hair dryer, heated the tubing in his hands and dunked it in some cold water. The tubing now has a new bend. That's all there is to it.

This is handy for installing the fuel system, but don't get carried away and attempt impossibly tight bends. One of our newest Falco builders (we are approaching 500) built and wrecked an RV-3 because of this. The fuel vent line from the wing was bent into a very tight "S" to get from the tank to the fuselage. After sitting in the sun, the vent line softened, and one of the bends took a crimp. This effectively shut off the vent, and the unfortunate fellow put it down in a field.

From "Tool Talk" Falco Builders Letter, June 1987

In the wake of Richard Brown's accident, Jim DeAngelo came up with a common-sense suggestion for a dip-stick for your fuel tanks. Get one of those folding wooden carpenter's rules and cut it off so it's just long enough to dip the two tanks. Scrape the "inches" off the ruler-or just paint the thing white-and then when you fill the tanks for the first time, mark your folding dip stick at each gallon. One side of the dip stick is for the front tank and the other for the aft tank. Put it in your battery compartment and use it whenever you find yourself in doubt about how much fuel you really have in those tanks. It's a good idea-everyone should do this.

From "Construction Notes" Falco Builders Letter, December 1986

John Oliver asked about whether to install a scupper drain for the fuel tank. I don't have such a thing on my Falco, and I don't recommend it. I always do my own refueling and even then I overflow the fuel from time to time, since the production Falco has such small fuel openings-one of the reasons I went to the larger opening for the front tank.

What I have on my Falco and what I recommend is making a ring-shaped bowl to fit around the tank opening. My Falco has an aluminum bowl that is sealed in place with silicone rubber RTV compound. When I spill fuel, I just flip it out with my finger. While this may sound crude, it happens so infrequently and the finger-flip works so well that I can't see any reason to do anything else. Further, the front tank has a recess around the filler neck, which will make it impossible to drain with a tube, so your finger is going to get into the act anyway!

For the front tank, I think you should have a ring of wood extending almost down to the tank and then seal between the tank and the wood with silicone rubber compound or another suitable sealant such as polysulfide rubber. For the aft tank, you might think about adapting a wooden salad bowl, cutting a hole to fit around the filler neck and gluing the bowl in place under the skin. Jan Waldahl went to the ultimate solution, turning a Sitka spruce bowl on a lathe. The opening even has a groove for an O-ring to seal against the filler neck.

Q: I read about using a sealer/lubricant when joining aluminum fittings, but what about nylon fittings? Can they be joined without a sealer? And what about nylon fittings joined to aluminum?

A: I don't think there's any need for a sealant with nylon fittings. Never heard of doing that.

Q: Does the method of tightening Swagelok connections by turning one and one quarter turns apply to both nylon and aluminum connections (nylon connector/nylon tube, nylon connector/aluminum tube, aluminum connector/nylon and aluminum connector/aluminum tube)?

A: I think that's right, but I suspect Nylon will be more forgiving.

Q: I have painted my fuel tanks straps, and now I'm about to attach the neoprene rubber. Will the adhesion to the painted surface be adequate? Have any other builders attached the neoprene to unpainted steel straps?

A: I think all builders have painted their tank straps. I don't think there's any need at all for an adhesive, but if you wanted to use one, I think mastic or contact cement would be fine.

Q: Where do you buy Swagelok fittings? Aircraft Spruce doesn't seem to carry them?

A: First, if you have ruined a few ferrules, we have a supply here and we'll be happy to take care of that. If you want to buy new fittings, then you'll need to contact a Swagelok distributor near you. This is an exceptional company, and each distributor seems to have marching orders from the parent company to be nice to all customers, even those looking to buy only a single fitting. In all my years, I've never encountered a company like this--it's truly exceptional--but please don't abuse them either. To find a Swagelok distributor near you, check out www.Swagelok.com.

From "Construction Notes" Falco Builders Letter, March/June 2002

Richard Clements got quite a scare. In March, he went for a 30-minute flight, then pulled up to the fueling station and found the fuel tank caps hard to get off, and when he finally got the cap off, he heard a 'whoosh' of air pulling into the tank. On investigation, he found that snow/slush from the taxiway had kicked up to the tank vents on the bottom of the wing and had frozen both tubes shut. Richard estimates that the tubes had about a quarter-inch of ice on them.

Our drawings show a small hole drilled on the aft side of the tubes, the standard technique used on general aviation aircraft, and Richard said he didn't have these holes drilled on his Falco. He didn't think they would have helped, and he could be right.

As it happened, only a few days later, Bill Nutt sent us a note. "The fuel vents appear to be directly inline with the left/right main landing gear. As such, they appear to be susceptible to clogging by debris kicked up by the landing gear on takeoff/landing, especially on grass strips. Has this been a problem with anyone to date? We noticed Dave Nason relocated his vents outboard submerged in small NACA inlets. It seems to me that location is not critical, but what is important is orientation to provide a slight positive pressure on the tanks (i.e. no vacuum). Any comments you might have would be appreciated."

I talked to Richard about the possibility of adding or moving the vents outboard. At this point, I don't have a 'new solution', but I agree that location is not critical and that a slight positive pressure is essential. Other than this report by Richard, I have not heard of any other Falco experiencing the problem.

From "Construction Notes" Falco Builders Letter, March 2003

I have managed to seal the front tank now, and found four real 'pin holes' only evident when fluid was in the tank and it had about 3 psi pressure, they just 'drizzled'. But I can just imagine the smell of fuel had I not found them.

I used a weird stuff to seal the holes. It's is called 'Technoweld' over here (amongst other names). It was apparently developed in the US in the last war as a form of field repair for 2024 aluminum airplanes that suffered battle damage. It is an alloy that melts at about 750 degrees, so it can be used with propane torches. Obviously, the tank takes a lot of heating, but as it is used in a similar way to solder, it really does make a great way to seal tanks, provided that they haven't had fuel in them! When solidified, it is tremendously hard and can be ground, filed and machined to a really great finish.

Alan Powell