Online Community of Zenith Builders and Flyers
First, you might want to check to see if what you "heard" is accurate. If Aeromomentum really does recommend against a header tank, I would find out why. I cannot think of an engine related reason not to use a header tank.
Hence the forum question.
If I use a header, the return line just needs to go to the header right? Seems like it might actually be easier that way. This is a part of the build where I have very little prior experience to lean on.
Speaking generically, fuel injected engines pump a lot of fuel to the pressure regulator. Only a small portion is routed to the engine. The rest is unused and must be returned to the tank(s).
If you have two wing tanks and no header tank, you must return the unused fuel to the tank that it comes out of. Otherwise, you can easily overflow a tank. This means you must have an expensive selector valve that will select left or right tank and at the same time switch the return fuel system to return the fuel to the tank that is selected. Think of it as two separate valves stacked on top of one another. With a system like this, selecting both tanks is not an option. With a header tank, you can just plumb both wing tanks to the header and then use a simple ON/OFF valve. No possibility of ever taking off on an empty tank, or unwittingly running a tank dry. All fuel is always available to the engine.
While the fuel is circulating in the engine compartment, it will pick up heat. Heat can contribute to vapor lock. This is more problematic with auto fuel than 100LL because auto fuel is more subject to vapor lock. You do not want that heat to build up. If you are returning to a small header tank, you could heat up all of the fuel in the header tank. So a header tank must be large enough to dissipate the heat that is collected.
Mark from AeroMomentum told me that he had seen issues with header tanks, were plumbing issues or operator error, like accidentally shut valves to the header tank, caused fuel starvation and therefore suggested that the potential benefits will not outweigh the risks.
Keep in mind that AeroMomentum is not selling header tanks and that they therefore have no stake in the game whether builders install header tanks or not.
We debated back and forth whether to install a header tank or not. The main reasons for us to install one would have been to be able to have a 'both' setting on the fuel selector and the additional fuel capacity.
Eventually, we however decided against it:
We installed an Andair Duplex fuel selector, which was around $115 more expensive than their simple on/off selectors. This is certainly less than the cheapest header tank system. Fuel lines are 3/8" steel braided hose from the tanks and 1/4" steel braided hoses for the return. Very clean, supposedly unlimited lifetime (doesn't have to be replace every few years like rubber hoses) and a minimal number of connections inside the fuselage.
Are you aware of Mark Pennsenstadler's blog? It is in any case very worthwhile checking, he also has some great details regarding his fuel system. His system is very similar to ours, he also went without a header tank: http://www.zenithowner.com/marks_log.htm
Just to be clear: I am not opposing header tanks at all and can absolutely understand when others come to a different conclusion.
Yeah, I’ve adapted some of Mark’s ideas into my build. He does such a great job.
I’m kinda leaning towards your solution if I end up with an AM15. It’s a toss up now between this and Viking. They are awfully close to the same engine. I really enjoyed hearing Mark talk about the overhaul plan for these.
Any word on the cowling for a Cruzer yet?
I might be wrong, but believe that the Viking needs a header tank, as the engine does not have a fuel return line. Whatever air enters the fuel line to the engine (e. g. after a tank was ran dry or air was sucked in for some other reason) has only one way to go - through the injectors. The header tank is therefore needed to make sure that absolutely no air makes it to the engine.
I am not 100% sure if this is correct, but would recommend that you talk to Viking in case you decide to go with their engine but don't want to install a header tank.
Our cowling is finally in the works and is supposed to be done in the next few months. Mark has posted some pictures of the first cowling, which is made for a RV-12. The basic design will, after some adaption, also be used for the Zenith:
Additional pictures of the installion:
I just noticed you mentioned autopilot servos. Any chance you have pictures and details of what you did there?
We're not quite there yet, I think it will be another few months until we're ready to install the servos.
By the way, what I “heard” I got confirmed by Aeromomentum. They don’t recommend header tank design, but the engine will happily work with one if that’s what you have (obviously).
This is what Mark from Aeromomentum said to me. There's advantages to both, but overall a header tank definitely adds complexity.
"If you are using a header tank you can run the return back to the header tank or to the main(s). But keep in mind that the return flow is higher than the engine's consumption so this favors returning it to the header tank. Having the the fuel return to the main tank(s) helps keep it cool due to the large surface area and volume so this favors returning it to the main tank. I am not a fan of header tanks due to the added weight, complexity, cost and additional failure modes. Duplex valves are just $200 and allow fuel return to the specific tank being used."
Here is a little write up I did a while ago (vendor independent) on using Header Tanks FWIW: