Header tank or return to main tanks?

[Bradrock]

For a system that requires fuel return lines, has anyone used a header tank or is a return to the main tanks the best way forward?

[Battson]

I can't provide any help, but I am curious... Are you looking at a TCM engine, Brad?

[whee]

Mark M and Glenn Patterson used header tanks. I'm returning to the main tanks and I talked to another builder that also returned to the main tanks. Either method works when done properly.

[JimParker256]

I thought about using a fuel-injected engine and a header tank. Ultimately decided I did not want a bunch of fuel sitting in my lap in case of a crash. (Look at the rate of post-crash fires in Cubs, Champs, and other planes with the fuel in the fuselage... Downright scary!)

So I decided if I went with FI, I would use return lines to the wing tanks, which would require a special fuel selector valve to return the fuel to the tank being drawn from...

All that meant more weight and increased complexity, so I'm back to thinking "carburetor" for my Patrol...

[Battson]

Or just use a Lycoming engine which requires none of that non-sense?

[JimParker256]

I believe that depends on which FI system you use. airflow Performance requires a return line, as does ECI's. From my understanding, only the Bendix FI system does away with the return line - and it's the one that makes hot-starts (or even warm-starts) so challenging due to vapor bubbles forming in the fuel lines. Having lived with that for a number of years in my former Commander 114, I'll pass on that option...

[Battson]

Bendix isn't the problem with hot starts - it all depends on the layout of the installation. I have a Bendix FI system and I have NEVER missed a hot start. They are dead easy, even a student pilot would never miss one (in my installation). I can only assume that the hot start problem comes when the electric fuel pump or gascolator is installed on the engine side of the firewall...

[Chewie]

I like your thinking Jim.
On unmanned systems, we use a proprietary pump for fuel injection that pressurizes a dead head system to 3bar with no return line or header tank. Does anything like that exist for manned aircraft?

[whee]

Lycoming uses a system that does not have a return to a header or main tank. I don't recall if it is a deadhead system though.

My snowmobile uses a deadhead FI system and it is pretty slick. In tank pump that pressurizes the fuel to 38psi. Always thought it might work good on a airplane.

A duplex valve isn't all that special and if you don't want to spend the money on a aviation valve there is a marine grade duplex valve that looks just like the valve Bob uses but it's two stacked together. It's like $180.

[Bcone1381]

A simplified a FI fuel system without the duplex fuel valve, or Header Tank has been used by Cessna in their 310 model. The bypassed fuel is always returned to the Main Tank, and the Pilot is expected to create space in the Main Tank for the return fuel by using that tank first for an hour before switching to the Aux Tank.

One might consider having not a Right and Left tank, rather a Main Tank and an Aux Tank, then operate it like a Cesna 310... creating space for the return fuel into the main tank when the Aux Tank is in use. This would become a habit forming procedure.

If the pilot for some reason errors and uses the Aux tank with the Main Tank full, the return fuel exits via the Tank Vent. Kind of a bummer, but no catastrophe.

There are lots of reasons for choosing either a Fuel Injected Engine, or a Carbureted Engine. I am not advocating one over the other. Just be advised that the risk, expense, weight and complexity Header Tanks, Duplex Fuel Valves, and extra plumbing is unnecessary but has a cost. That cost require system knowledge, mandatory procedures, and an additional limitation when writing your aircraft flight manual.

Brooks Cone
Scratch Building Patrol #303

[Bradrock]

Jono - I have an IO-540.

I also feel uncomfortable with putting an extra tank somewhere in the fuse. Return lines to the tanks seems more sensible.

I am a fair way from needing to decide yet, but have also been considering electronic injection/timing. http://www.flyefii.com
I'm sure this comment will spur on some furious debate about electronically-dependant engines! :-)

[jim.mclaughlin924]

The first airplane I owned was a 1958 Bonanza, return fuel always to left main tank, so that is what I did. $25 fuel valve from ACS. Just have to remember to takeoff and land on the left tank.

[Glenn Patterson]

We debated returning the fuel to the tanks or header tanks to death. We elected to go with a header tank. They are used in Cessnas, Maules & many other aircraft. The engine came out of a twin engine 337 version that had a return tank. Both versions of returning to a mains or using a return tank are flying successfully. The header tank is not pressurized and vents to a tank but it saves cycling the fuel back up to the wings. The TCM engine fuel pumps flow a good excess of fuel that is shed off & returned to the tanks. It is easy to recirculate closer to the engine & eliminate the resistances of several feet of fuel lines, valves & gascolator that the fuel has passed through already. The mains supply the burn rate which is a lazy flow. I was told by a veteran aircraft mechanic who did several of the TCM power upgrades for Cessna 170's to put in the return tank as he was adamant that it made for a safer system. Our logic was that Cessna, Maule and others that put in the header tank do not do it to add weight & cost to their aircraft if they could eliminate the excess hardware they would
.
Whee has a practical system of returning to the tank that the fuel is being drawn from. Safe fuel management is important with the TCM fuel injected engines. I am not going to debate this one way or the other. Everyone has to do what meets their own comfort level.

The TCM fuel injection is mechanical & very reliable. The nice thing is that the TCM IO-360 210hp can cruise on 8 - 8.5gph. It was our long range plan to install a header exhaust & a dual set of electronic ignitions. We have the custom header exhaust. E-mag has been teasing for a while so we will stick with the mags. The thought was that the improved exhaust could give 5-6hp and Lightspeed said that the electronic ignition runs cooler & gives a 5%hp increase. The benefits of the electronic ignition is appreciable. We though that with the header exhaust & electronic ignition that the engine could make 225hp that runs cooler, more efficient & no hot mods on a reasonable fuel burn. The power of of 470 & 540's on mogas with a lighter engine. Nice thought.

Glenn
BH727

[patrickh99]

How about including the gascolator function into the header tank? I don't like a header tank inside the cabin, and there isn't much room for both in the belly, so combine the two and reduce weight/complexity further.
Are there any 1-2gal gascolators available?

[Glenn Patterson]

I think the perception of risk with a header tank is greater than the reality.

We over built and pressure tested a small tank similar to the modified Maule return tank used by some in the Cessna 170 conversions to the TCM IO-360. The TCM injection system operates at a very low pressure and regulates the system with the excess fuel returning to a tank. It does not matter whether the fuel is returned to a main tank or a header tank as both are vented to atmosphere. An atmospheric vented tank cannot hold pressure as it would simply overflow. The excess fuel is returned in a line to a vented tank so it begins to lose energy in the free flowing return line & drops any remaining energy in a vented header or main tank. Our header tank is located close within about 4 inches of the firewall between the passenger kick panel and the fuselage skin. The short distance to dump into the tank eliminates the pressure quickly. All the re circulation is within a matter of inches. The header tank vents to the main tank so the entire system including the tank only sees the head pressure of the main tanks. Water head pressure is about .4psi per foot of difference in height so the entire system in any Bearhawk
sees about 1-1/2 psi pressure including those with a header tank.

I spent 37 years designing pressure piping, pressure vessels, overseeing their installation, maintenance & repair on a large industrial site. I was responsible for managing the code repairs in house to meet the provincial regulations for the self managed owner user program. I spent another 3 years after retiring on contract working on a very large petroleum refinery site. In both scenarios any leaks or failures could cause serious injury or worse. Any leaks, burps or farts in a refinery can be an instant fire ball, a scalding event or a release of extremely toxic gases. I know of horrific injuries.

An aircraft fuel system that has a well built, vented & tested atmospheric header tank with tubing operating at 1-1/2psi on a risk scale of 1 to 10 is about a 1. The tube & fittings operating under 1.5psi pressure has an extreme safety factory that is off the scale for its purpose. A good fuel system has to be respected & maintained but not feared.

ASME B31.3 power piping and B31.1 pressure vessels usually are tested to 1.5 x operating pressure. There is no doubt that the aircraft fuel system may comfortably manage a 2.25psi test pressure. The risk is in the tubing not being properly supported and experiencing vibration that can fatigue to failure. Piping & pressure vessels systems are pressure tested 1.5 times so a simple 150 lb system would get an initial squeeze of 225psi and a 1200lb boiler to . . . ..

So it all is a matter of true risk vs. the perception.

Glenn
BH727