Cockpit fuel lines and fire prevention

[Toobuilder]

Originally Posted by apkp777

Mike,

The 304 seamless? I don't remember the stainless I used in the past being .035 wall thickness. Maybe it was, just seems awfully thick.

I've used the .035 because that is what is readily available. Given the choice I would go a lot thinner on the wall thickness, but the .035 still is fairly easy to work with. The thicker wall does give you a bunch of margin for damage and working out the flare tool bite marks.

[bhassel]

Originally Posted by Mike S

Would you just not run a fuel valve, or do you intend to install the valve outside the fuse also, and remote the control handle inside somehow??

I'm still reading htis excellent thread so please forgive me if someone else has already addressed this.

Andair used to advertise a remote fuel valve. I know that the canard world was very excited about it at the time. I'm just not sure if it was ever produced, etc..

Bob

[rv6ejguy]

Originally Posted by bhassel

I'm still reading htis excellent thread so please forgive me if someone else has already addressed this.

Andair used to advertise a remote fuel valve. I know that the canard world was very excited about it at the time. I'm just not sure if it was ever produced, etc..

Bob

Andair does make a fuel selector with long remote extension. If you really want to move things outside the cabin, electric fuel solenoid valves are available.

[Phil]

Comments are added in-line and in red.

Phil

Originally Posted by Toobuilder

OK, couple of comments, not the least of which is the fact that you are afraid of properly bending and flaring hard line, yet you are constructing a four passenger aircraft... Do you see the irony here?

Nope, I don't see it.... There are far less qualified or less modest folks who are building airplanes today. A good builder is one who recognizes a limitation and addresses it adequately. A bad one is the one who pushes on and says it's okay.

Airplane construction is a terrible time to play hero, pound your chest, and claim you can do more than you can really do. I've yet to meet anyone who knew everything and had mastered all the skills. If they think they do, I try to stay away.

I'm level headed enough to know 1) I don't know it all and 2) I make mistakes. I'm human. A good airplane builder (and pilot for that matter) starts with that understanding and manages against it.

To more practical comments:

If you do "all braided hose" you are signing up to:

1. About a 10-12 pound decrease in useful load;
Not a problem for the mission of my airplane.

2. Significant unnecessary expense;
It's mice nuts in the cost of the RV-10. It's about 0.25% (1/4 of 1%) of the total project cost. There are better places to worry about cutting cost in this airframe. The fuel system is a bad place to start getting cheap anyway.

3. A complete fuel line replacement schedule every few years;
Maybe... Teflon hoses in the tunnel have a different lifespan than those who operate in the harsh environment under the cowling. I agree they should be inspected regularly and replaced upon a condition inspection - but so should a hard line. Everything FWF will be replaced every 5 years; though there are some Teflon pundits that claim you don't need to replace them until they fail a conditional inspection. (I don't share that opinion.)

4. A packaging nightmare;
Been down this path already. It's really no big deal to properly support the lines in the RV-10 tunnel at least every 24 inches per 43-13. The factory supplied supports in the RV-10 tunnel are already 12" to begin with.

5. Decreased reliability (hose does fail, degrade, chafe, cause damage and LEAK!.)
And hard lines don't?
In the past two weeks we've heard of two major failures of hard lines in RV's. One RV-10 in IMC and then this one. (I agree verdict isn't in.)

I wholeheartedly echo those here who call to not "reinvent the wheel". Flex hose has its application in standard aviation practices, (but it's usually a LAST resort), as does other material. We're building aircraft here, so it's best to follow "aircraft standards" don't you think? The standards for proper fluid systems are readily available to all of us and are fairly easy to understand. Most "standard practices" can be found in AC43-13, and the T.O.s 1-1A-1 and 1-1A-8.

43-13 addresses the use of Teflon hoses and in fact reference their use for "superior qualities" relative to other lines (hard & rubber). Their only caution against using them is to avoid bending them too much, twisting them, or attempting to re-shape them after they've been installed and set-up into a specific shape.

The purpose for building amateur built airplanes is to learn... Don't sell yourself short on the experience of learning how to fabricate a few hard lines.

I agree completely. In fact I already built hard lines once and even took them to a couple of A&P's for inspection. They looked great and the skill was gained. But I still don't trust them because I know of too many hard lines that have snapped over the years. I can't say that for a flexible line. I have heard of slow drip leaks and other not-so-catastrophic failures, but nothing as catastrophic or as common as a severed hard line.

[L.Adamson]

In the past two weeks we've heard of two major failures of hard lines in RV's. One RV-10 in IMC and then this one. (I agree verdict isn't in.)

I haven't seen the report of a RV-10 in IMC with a fuel line failure. Only the two accidents you provided links for in a previous reply, as well as a 10 with door problems, and Dan Lloyds. Are there others?

L.Adamson --- RV6A

[Toobuilder]

Phil,

Your lack of concern about 10 extra pounds would get you fired as an engineer at my company, but it's your airplane, so I won't comment further on that. Nor will I comment on your individual responses because it would just take too long. But let me leave you with some thoughts: If flex hose is so superior, why is it in such limited use in the "real" aviation world? Why do military fighters and civilian transport aircraft still use miles of "inferior" hard line?

Running all flex hose may make you sleep better, but as hard as you try to justify it, there's no good engineering reason to do so. I'd encourage you to stick with common aerospace practice.

[Toobuilder]

Originally Posted by L.Adamson

I haven't seen the report of a RV-10 in IMC with a fuel line failure. L.Adamson --- RV6A

http://www.vansairforce.com/communit...ad.php?t=57122

[RV8R999]

I don't get it..

There is nothing at all very challenging or significant in fabricating a solid fuel line. The comments in this thread and others has raised this pretty simple task to some level of artisanship it simply does not deserve.

Riveting solid -4's is harder and requires more skills. Certainly the layup of the windscreen fairing or the alignment of the landing gear is harder..even bending the elevator leading edge is more problematic (IMHO).

The fuel system is no more or less critical than the control system, the landing gear system, the spar, the canopy, blah, blah, blah... they all have to be built correctly and to a standard which matches their function.

The reason most hardlines fail is not because of tiny little tool marks left by the tools having been used for decades but rather the lack of support at the correct points in the line. If the line nor connection pointst move the stress is very low. If you use alum lines, support them very well with adel clamps and don't use them to connect between two points with relative motion and they will last longer than your flex lines. You don't have to polish them to a mirror finish either. That is simply paranoia, akin to worrying about the carbon content in black magic markers causing corrosion..cmon!

[N427EF]

Engine failure in IMC had a hard line break in the FW forward area.
No one in their right mind would install a hard line where that one failed.

As to Todd's explosion. We don't actualy know that a hardline broke.

[flion]

Those cautioning calm and thought before doing anything have a point and are heard, at least by this builder. I've been looking over the -10 fuel system drawings and I don't see a need for a wild redesign. I like hard lines and I think the potential problems can be addressed with careful building - though I don't think it hurts to explore some possible improvements, like tunnel venting. I've also been very happy with the -6A fuel system, except for the transverse lines behind my heels. Unlike the -7/9 setup, where these lines are behind kick panels and have additional ribs to support them, I find the -6A lines to be rather exposed and vulnerable. One way to address this might be to use -7/9-style structure. Another might be flex lines to the wings; they are so exposed that inspection and maintenance would not be difficult. I have not made up my mind and I'm not rushing to a decision. I'm just saying, let's not turn this into a 'pr---r wars' type of issue.