Cockpit fuel lines and fire prevention

[pierre smith]

Originally Posted by David-aviator

.......But there's a lot of floor vibration aft of the firewall (at least there is with my airplane). The area going forward from the spar is progressively more "alive" in flight, place your foot on it sometime to get a feel of it if your floor is not carpeted. .

...such as either silicon or dense foam (Tempurfoam perhaps), to lessen harmonics...kinda like touching a tuning fork.

Makes me want to use a braided teflon flexible line up to the firewall.

Best,

[apkp777]

Here again I am not buying into the whole stainless tubing idea as the solution. Aluminum 3003 has been use for fuel lines for decades without problems. It doesn't matter that stainless is "stronger". The fuel lines are not load bearing. Stainless has its own issues. Certainly $$, weight, the flare is more of a challenge. They leak at the flare, the lines crack, etc.

It seems to me that the problems with aluminum lines in our RV's are;

1. Pre-loading the line (pulling it into place)
2. Improper flaring prep (not polishing the tube ends, not using a lube, using an automotive flaring tool )
3. Work hardening (bending them back and forth)
4. Over bending (not maintaining the minimum bend radii)
5. Over torquing (tighten till the nut seats then ONE additional flat only)

These lines are so easy to make if you have any doubt about any of the above, make a new line.

[rv6ejguy]

I agree with Tony's points here. PROPERLY made and installed, 3003 aluminum hard lines are very reliable for behind the firewall. Most failures occur because one or more of his points were not followed.

Firewall forward, steel lines are best (I prefer mild steel over stainless) and aluminum lines should be firesleeved as they have very little fire resistance.

I was going over a thread from a could years ago with some more useful discussion: http://www.vansairforce.com/communit...ad.php?t=12112

[Toobuilder]

Originally Posted by apkp777

Here again I am not buying into the whole stainless tubing idea as the solution. Aluminum 3003 has been use for fuel lines for decades without problems. .

Agree, to a point... "THE" solution is to properly design, fabricate and install the line. This goes for copper, 3003, 5052, stainless or hose. Some materials don't work in some areas, but for the most part, 3003 as used in the RV is ok IF built properly. The problem is people apparently ignore tried and true standard aviation methods and then wonder why they get a failure - As if their installation will be the one that somehow defies the laws of physics.

Originally Posted by apkp777

It doesn't matter that stainless is "stronger". The fuel lines are not load bearing. Stainless has its own issues.. Certainly $$, weight, the flare is more of a challenge. They leak at the flare, the lines crack, etc..

I disagree on most points here. Stainless is far more damage and fatigue tolerant than even 5052, so "strength" certainly does matter in that regard. As to cost, yes stainless is more expensive than 3003, but it is still FAR cheaper than even the most inexpensive braided hose. 3/8 line is only a couple bucks per foot. You could do an entire RV in stainless hard line for less than $75 bucks in material. As to weight, unlike the difference between 3003 and hose assemblies, stainless hard line REALLY is a "minimal" weight increase. The difference is measured in ounces rather than pounds. Additionally, stainless hard line fabrication takes hardly any more effort than 3003. The only downside is the physical force required to bend the tube is a little more than aluminum, but it is still well within the limits of the average homebuilder. It uses the same tools, is far more forgiving of the "bite marks" at the flare, and is easier to dress out and polish. Finally, the fabrication process cold works the material and actually increases its strength slightly.

Anybody who has any doubts about using stainless should buy a stick from Spruce and make up some lines to see just how easy it is.

[flion]

Originally Posted by Phil

Hey Patrick,

.... begin constructive and gentle...

The only issues/unknowns I see with that are:

1) The air you'd be picking up is likely heated exhaust.

2) How much cooling drag is introduced? You'd want just enough to keep the mixture lean but not so much to pressurize the tunnel or add significant drag.

1) ??? I specifically postulated a scoop on the cowl before the exhaust. Or did I miss something?

2) Yeah, that's the kind of thing I meant. Someone with some experience might be able to advise on inlet/outlet ratio. I don't think this would need to be huge to keep the air moving, maybe just an inch diameter inlet?

Regarding other stuff posted, I really like the idea of braided lines. I've been unhappy with the tank-to-valve lines in my -6A and I think I'm going to experiment. Also, looking at the tunnel photos as opposed to the drawings in the plans, I'm more certain than ever that the flap mechanism can be isolated from the rest of the tunnel so the flap motor can be removed from the equation.

The fuel/oxy/ignition formula seems to be key, in my opinion. While I don't make things worse by running O2 in the tunnel (I'm planning an overhead installation), I don't think air can ever be removed from the equation. But the other two factors we can improve and I am not only going to take extra care in building the -10, I am also going to review the -6A to be sure the wiring is trouble free and improving the fuel system.

[DanH]

Originally Posted by TSwezey

Guys I don't think this is just a tunnel issue. I think this an entire fuel system issue.

Let's not run off a cliff. There is no evidence to suggest an RV-10 redesign is required.

Todd, you had a fuel leak. With all due respect, a fuel leak is usually a craftsmanship issue.

In any case, we're not discussing a Vans design. Your fuel system was modified. Have any photos or diagrams of the complete system?

Those mods are not trivial. For example, a stock LS1 runs something like 58 psi fuel pressure. You installed high pressure pumps in the wing roots so the entire system was at rail pressure?

[L.Adamson]

Originally Posted by DanH

Let's not run off a cliff. There is no evidence to suggest an RV-10 redesign is required.

Todd, you had a fuel leak. With all due respect, a fuel leak is usually a craftsmanship issue.

In any case, we're not discussing a Vans design. Your fuel system was modified. Have any photos or diagrams of the complete system?

Those mods are not trivial. For example, a stock LS1 runs something like 58 psi fuel pressure. You installed high pressure pumps in the wing roots so the entire system was at rail pressure?

Yes, I'm reading all this, and just want to "SCREAM"!!! People are running towards the cliff, and paranoia has set in. Now we're down to the point to where 3003 being vibrated by the floor board or side panel is possible cause for alarm.

Yet..................in the real world, 3003 tubing has been used for decades in vibrating air conditioning units (condensors), and with much higher pressures than we'll ever encounter in an RV. In fact, due to corrosion in various locality's, more air conditioning coils are going to all aluminum.

links to look at -- regarding tubing types, wall thickness, pressures...

http://www.mechanicsupport.com/tube_strength.html

Notice the "high pressure" part....

http://www.lyonsperformance.com/3003...ing-p-246.html

L.Adamson --- RV6A

[TSwezey]

Originally Posted by DanH

Let's not run off a cliff. There is no evidence to suggest an RV-10 redesign is required.

Todd, you had a fuel leak. With all due respect, a fuel leak is usually a craftsmanship issue.

In any case, we're not discussing a Vans design. Your fuel system was modified. Have any photos or diagrams of the complete system?

Those mods are not trivial. For example, a stock LS1 runs something like 58 psi fuel pressure. You installed high pressure pumps in the wing roots so the entire system was at rail pressure?

I meant that we have to make sure all parts are properly ventilated and checked not just the tunnel parts. Now our boost pumps were after the valve running at 60 PSI. But if/when I do build another -10 there will be no gas lines inside the cockpit. Gas leaks I have learned are problems in all types of planes. A friend just bought a 182 a couple of days ago and was checking the fuel system and found that one tank would leak two gals of gas in to the baggage area.

[David-aviator]

Originally Posted by L.Adamson

Yes, I'm reading all this, and just want to "SCREAM"!!! People are running towards the cliff, and paranoia has set in. Now we're down to the point to where 3003 being vibrated by the floor board or side panel is possible cause for alarm.

Yet..................in the real world, 3003 tubing has been used for decades in vibrating air conditioning units (condensors), and with much higher pressures than we'll ever encounter in an RV. In fact, due to corrosion in various locality's, more air conditioning coils are going to all aluminum.

links to look at -- regarding tubing types, wall thickness, pressures...

http://www.mechanicsupport.com/tube_strength.html

Notice the "high pressure" part....

http://www.lyonsperformance.com/3003...ing-p-246.html

L.Adamson --- RV6A

Larry,

I looked at the links you recommend and from the first one

"Some experimental and light-sport aircraft have hydraulic and fuel lines built with 6061-0 or 3003-0 tubing. Low ultimate tensile strength and low fatigue strength provide a narrow safety margin in dynmic (vibration or impulse) applications. Take extra care in clamping and preventing tube vibration."

And from Lyonsperformance,

....3003 is not recommended for high pressure fuel injection systems.

I remain concerned about floor vibration and 3003 fuel lines. There is nothing in these links to lay those concerns to rest. We use 3003 primarily because it is cheap and easy to work with, not because it is a superior product.

Granted, we do not know what caused the fuel leak and fumes in Todd's airplane, but something did. An observation that vibration and fatigue failure could be a factor is not new news in the aviation world, nor is it running off the cliff over the matter.

[L.Adamson]

Originally Posted by David-aviator

I remain concerned about floor vibration and 3003 fuel lines. There is nothing in these links to lay those concerns to rest. We use 3003 primarily because it is cheap and easy to work with, not because it is a superior product.

There are always concerns, but I've been around many high hour RV's in the last 15 years that don't seem to have fuel sytems coming apart suddenly. There are two, that I'm around regularly.........that are 14 years old and flown often.

Just an observation.

L.Adamson --- RV6A