Fuel System Questions

[957DK]

Hi folks. I'm in the process of plumbing the fuel system in my Highlander and have a couple of questions. I don't like the rubber fuel line running through the cabin and really don't like it in the engine compartment. I want to use aluminum tubing but I'm not sure what size to use from the header tank to the fuel valve and then on to the engine. Anybody have any ideas? Thanks and Happy New Years to all.

Dan
Highlander #268

[Familyflyer]

I am plumbing all 3/8 soft aluminum line with all AN fittings. I will not be using the rubber line anywhere. The transition at the wing will be a braided line. Once in the engine cowl, it will be a fire sleeved braided line with AN fittings. Nothing to take pictures of yet.

[danerazz]

I am plumbing all 3/8 soft aluminum line with all AN fittings. I will not be using the rubber line anywhere. The transition at the wing will be a braided line. Once in the engine cowl, it will be a fire sleeved braided line with AN fittings. Nothing to take pictures of yet.

Same here, using 5052-0 3/8" tubing with aeroquip hoses where needed and AN fitting throughout. Not going to get into the aluminum vs. steel fitting debate. Each have an appropriate use.

[User GDS]

I used rubber fuel line from wing tanks to header tank.

3/8" aluminum with AN fittings from header tank, under the floor to the gascolator on the forward side of the firewall.

Used Rotax-supplied fuel lines from gascolator to engine.

For return line, I ran blue fuel line http://www.aircraftspruce.com/catalog/a ... kkey=32455 from the return outlet at the engine to the header tank. The return line is fire sleeved inside the engine compartment.

I have no complaints about the system, everything under the flooring is aluminum, rubber tubing is used where it can be inspected. It's simple. I was going to install shut-off valves close to the fuel tank outlets, but I'm using pinch off pliers instead, works great: http://www.aircraftspruce.com/catalog/t ... key=632991

[gkremers]

GDS,
Where did you install the fuel filter. I want it to be easy to check and clean/replace.

I plan on running aluminum almost everywhere other than from the tank to the header, that will be aeroquip, all AN fittings also.

I'm installing a 912 and Jak said the return line was not necessary, he also said the factory does not use a facet electric pump. I know some do and some don't.

Gary

[User GDS]

I did not install the Just Aircraft supplied fuel filter, I rely on the screen in the gascolator. If I were going to install the filter, I'd put it in the line right below the header tank. (Before it goes under the flooring)

I installed a return line only because Rotax recommends it. and it's real easy. It's clear blue tubing that's visible in the cockpit. Before start up, I like powering up my fuel pump and seeing fuel flow through the tubing.

The Facet fuel pump is good, it's a cheap back up system. (not a necessity for a high wing, back at the hangar if I pull a line from the top of the header tank the fuel shoots up about 4" by gravity feed)

The only thing I will change about my system is adding a fuel flow cube. Until then, my only fuel management is time and GPH.

[User GDS]

I just looked at the picture again, see that little square patch on the belly fabric? That's where the fuel line was routed the first time. I was installing the adel clamp and pushing real hard with a screwdriver and it slipped off. haha, I said bad words...

[957DK]

Thanks everyone. I like pictures.

I spoke with Jak yesterday, he reccomended using 5/16" without a facet pump or 3/8" with one. I like the idea of using Aeroquip hoses for the flexible sections. I'm a little torn about a fuel pump on a high wing aircraft. I recognize the safety aspect of having a pump but I'm concerned about the additional weight. Guess I'll have to sleep on that one.

I noticed the patch in the picture... I'm happy to say I haven't poked any holes with a screwdriver (yet) but lets not talk about sanding through the fabric. I was so angry I made up a couple of new bad words... I just hate that there are repairs before the darn thing is even painted.

Hope everyone has a safe New Years.

My philosophy: Build it like my life will depend on it.

Dan

[danerazz]

I am not using a Rotax, and do not plan on using an engine driven pump. That being said, your head pressure at a climb pitch angle will be very low due to the geometry of the tank to firewall. I am expecting everything to work fine without a pump, but am going to use a facet for "critical" phases of flight and have a check valve bypass for redundancy should the pump become blocked. I do not plan on using the pump during normal cruise and maneuvering, just takeoff, landing, priming for start, emergencies, and any time an engine out would be exceptionally bad.

Probably not needed but cheap insurance.

[User GDS]

One more thing, I suggest a short length of flexible tubing beneath the header tank. (as in the picture)

If you fly in rough country and test the performance margins, you can flatten the tailspring, break off the tailwheel or damage a main gear leg. When the AC ends up on its belly, the tubing will bend instead of breaking.

[FlyerChief]

My philosophy: Build it like my life will depend on it.

Dan

I think you have your answer then... Install the electric fuel pump for takeoffs and landings!

I ran a short length (about 12-14") of 3/8" rubber from the wing tanks to front of the cargo area to allow the wings to fold and 3/8" aluminum from there to the header tank. From the bottom of the header I ran 3/8" aluminum to the fuel shut-off valve and aluminum to the firewall where the fuel pump and gascolator are located and the supplied fire sleeve covered braided line to the 912. The return line is a short length of 1/4" fuel line covered by a fire sleeve going to a through firewall AN fitting and a 1/4" aluminum all the way back to the top of the header for a fuel return line.

Dan O.

[R Rinker]

I have a question that I've wondered about since I saw the header tank mounted behind the seat on the Highlander/SS...The header tanks I've seen in the past have been mounted at the top of the firewall. I can't see how putting it back behind the seat can provide a head for the fuel flow in nose up attitudes or hardly even in level flight or normal climb. With maybe a 6' arm from the engine it could easily lose a foot or two of height relative to providing a head for the fuel flow in nose up attitudes. If so, then in reality, the main tanks are providing the head for a flow in all configurations and the Highlander style header is simply a little aux tank that complicates the fuel system with no benefits, and that is why they want a pump. So please enlighten me as I assume there is an explanation for it. I believe AC43-13 has the formula that specifies the fuel flow volume that has to be measured/demonstrated with the nose jacked up in a maximum climb position with a gravity fed fuel supply, and I believe it also has the formula for calculating the size of the fuel lines. I don't have my AC 43-13 handy..it's been years since I've used it and I don't have my kit yet. My understanding is that the lines shouldn't be larger than is necessary for the maximum flow that will be needed because they'd dump fuel about twice as fast if a line got broke or loosen up. I do want to add my disclaimer...there are those who know a lot more than me on this. I do respect AC 43-13 and believe it should be the reference point that we diverge from on all this.

[FlyerChief]

Hi Rodger,

I am certainly no expert, as this is my first build, but I believe the answer to your question is that until you enter a steep banked turn or a long descent that would cause one or both of the wings to un-port, the header tank and lines are full of fuel. This allows the fuel line to the engine to act like a siphon hose would... as long as air does not enter the line, the only things that matter are the friction losses (determined by the size of the lines and any restrictions such as valves, fittings etc.) and the head (which is determined by the highest point of the fuel in the wings relative to the inlet of the carburettors). Theoretically, as long as fuel remains in the line without air entering, the hose could run all the way to the tail and back as long as the friction loss in the line does not exceed the fuel head pressure. After a steep bank or long descent that un-ports the wing tanks, when the plane enters level flight again any air in the header tank should 'burp' back up into the wing tanks and restore the closed loop of fuel from header to carbs.

I'm speaking purely from the physics perspective, not practical experience, so maybe someone else has another answer based on real life experience with rear-mounted header tanks.

Happy New Year!
Dan

[jak]

The header tank is there to give the wings a place to burp when unloading and loading fuel in a banked turn also its the lowest place for the water trap and drain . Jak

[danerazz]

Header height has no impact on head pressure unless the wings are both un-ported (due to attitude) or you only have fuel in the header (probably not a great idea).