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Permalink Reply by Jerry Griego on September 12, 2025 at 3:07pm

Hello Shaun

It's alright to get stuck on a home build. Take a couple days off. Planning you build on paper is important. I fly behind a Rotax 912ULS in my 701. When it comes to fuel, Rotax wants you to include a return fuel line back to a header tank or main tank. I send my return fuel back into the gascolator. I drilled and threaded it to accept a fuel line fitting. I have no issues with that. Good luck on your build. I was told that the best way to eat an elephant is one bite at a time. This is very true to building an airplane at home.

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Permalink Reply by Matt Pope on September 12, 2025 at 5:03pm

This short document has some basics about the requirements of fuel systems in amateur-built aircraft and is a decent starting point: https://www.md-ra.com/docs/C52E.pdf 

It's amazing what you can learn on YouTube. The Homebuilt Help channel (for example) has a bunch of helpful videos teaching about different parts of the fuel system, techniques for flaring aluminum tubing, etc. 

https://www.youtube.com/@HomebuiltHELP/search?query=fuel

Also, to get a feel for a 912 fuel system, a video like this one looks like it goes through a guy's fuel system in detail (I haven't watched it, so I'm not sure how good it is): https://www.youtube.com/watch?v=bjgmFOfybuQ

Cheers

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Permalink Reply by Michael Barrie on September 18, 2025 at 4:35pm

I am building a 701 with 912 as well.

I have the extended range fuel in my build 4x10g tanks. For the fuel return i had a local welding shop just weld a NPT bung into the right hand main tank at the top. 

i think they charged me 20 bucks and it took about 10 minutes.

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Permalink Reply by Oliver Reik on September 19, 2025 at 8:51pm

Plan for a return line to the tank(s), as required by Rotax, to avoid potential vapor lock issues.

A duplex fuel selector with return lines to both tanks would be the cleanest solution; a return line to only one tank is the simplest. If you choose the latter, remember to start on that tank. The flow through the return line is less than 1 gal / hour, a small diameter fuel line is therefore sufficient. 

Do not just return the fuel to the gascolator, as this not only does nothing to introduce cool fuel to the system, but you could also potentially start trying to pump vapor in circles with nowhere for it to go. In fact, no return line at all would be better than returning to the gascolator; vapor could then at least escape through the carbs instead of making its way to the fuel pump, which is obviously not designed to pump vapor.

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