Wednesday, December 1, 2010

Fun with fuel lines

Some years ago, I wrote an essay on determining when "good enough" is good enough on your RV airplane-building project. In matters of firewall forward, however, it's very difficult for a novice airplane builder like me to know when good enough is good enough.

For the last week, I've been building a couple of fuel lines for the RV-7A and I thought things were going OK until I asked a question on Van's Air Force regarding firesleeves. That's when someone noticed that I'm using aluminum fittings.

We went back and forth and I learned that:

-1- Aluminum fittings shouldn't be used.
-2- Aluminum fittings can be used.

Then today came the question about the route my fuel line is taking. See, the problem is I'm building a nose-gear airplane and there are extra "tubes" on the engine mount for a nose gear plane. You people with tail draggers have it easy. See destination, route to destination.

I, on the other hand, have an additional maze to get through.

Anyway, once the aluminum fitting vs. steel fitting debate petered out without a declared victor, the route I took for the fuel line is faulty because my original plan to clamp it to an engine mount is faulty.

Perhaps it doesn't matter in the short term because once I put the firesleeve on, a lot of the slack I depended on to allow me to clamp it (a fuel line needs flexibility because the engine is going to be shaking) disappeared.

So regardless, I've got to build a new fuel line and, frankly, the money is used up and that pretty much kills progress until spring. God love ya, Christmas shopping season! Oh what the heck! It's too cold to be building airplanes anyway.

Here's a video that shows how things are:

4 comments:

  1. Love the videos. I always get a smile from them. I would suggest running your throttle and mix cables first Bob. A few builders on tri gear found the fuel lines had to be redone due to issues they hadnt anticipated, so...might be a good idea to run them first. I did and it was a good move. Rick

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  2. Bob...

    Pull up in a warm chair with a cold beer and pause. You may actually have it right.

    In any event, too much line - as in extra for routing and so forth - is not necessarily good. You could wind up with some "traps" (as in the bathroom sink) as a result of "S" bends in the line as you take it where you want to go. That's definitely not good.

    Over clamping various lines / wires on the front end isn't good - the engine does move around a lot in the mounts and clamping can cause some serious problems (fuel / oil leaks, broken wires, broken primer lines, etc.).

    I know you want to clamp it and it seems right, but I'd suggest two things:
    1) Take a look at some different brand C and P aircraft - you'll probably be surprised. Not to say that's necessarily correct - just that there's some peace of mind you won't come out of the sky for lack of a clamp, and
    2) Take a look at AC 43-13. I get a sense that you want to make build decisions on data and fact and less on anecdotal ideas that various people have. That AC is pretty good and should address most of what you're looking for in terms of authoritative guidance.

    It's downloadable in chapters (free) from http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/99C827DB9BAAC81B86256B4500596C4E?OpenDocument

    Good luck

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  3. I ran the mixture and throttle already. No issues other than the possibility of an over-center prob on the mixture which I'll fix. The bulkhead=to-fuel-pump input line comes close to the throttle cable. Will consider some sort of stand-off/clamp there.

    Baffle kit sitting in the box (and the $800 credit card bill from Van's hasn't come yet; my timing really sucks) but I wanted to get lines run before installing.

    and haven't even talked about that stupid Lightspeed cube on the top of the engine, right up next to where the baffling is going to go.

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  4. Hey Bob...can't comment on the fuel line stuff with the nose wheel tubing, but here's a pic of the Lightspeed cube on my airplane, and the solution I used to route the wires thru...

    http://www.chadandbrittne.com/images/End%20Game/8-23-09-002w.jpg

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