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Cockpit fuel lines and fire prevention

Mike S

Mike S

Senior Curmudgeon
I am starting this thread in response to the fire/explosion of Todd Sweezy's rv 10.

Here is a good place to discuss ideas to prevent a re-occurrence of Todd's accident.

Lets try to keep the speculation/discussion out of the original thread, please.

To start, remember fire/explosion needs 3 things,

1. oxygen, 2. fuel, ( in this case, vapors from a leak, not the liquid stuff safely contained in the fuel lines) 3. ignition.

Most discussion has been keeping fuel out of the cockpit, but in reality, unless we want fuel lines on the exterior of the fuse, this is not too practical of an idea.

My thoughts were to eliminate ignition sources as the most practical way to address this issue.

The tunnel design of the 10 is a definite factor in the issue, with fuel lines, fuel pump, fuel filter, fuel valve, all in there, flap motor and fuel boost pump, and usually fuel flow meter also inside. This coupled with the fact that the tunnel is a pretty much closed container is sorta like a design for disaster. Luckily, the way the tunnel covers are designed, the weak link seems to be in the baggage area.

One possible corrective mod I can see is positive ventilation of some kind to the tunnel, and keeping the fuel/air mixture too lean to ignite, should a leak occur.

And some kind of monitoring/sampling of the tunnel for fumes.

On the positive side, 10 have been flying now for a few years, and this is a first to the best of my knowledge. In addition, I believe Todd had a non standard system due to the needs of his powerplant, so this bodes well for the factory design.

O.K., folks, lets hear from you. Please feel free to jump in with any constructive info/ideas for any of the RV line, this is not meant to be just a RV 10 issue.

Thanks in advance.
 
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szicree said:
I vote for drain holes that are checked at preflight and no sources of ignition. That's all that's required to avoid this type of accident, so let's don't pverthonk it.
Click to expand...

Not exactly. The source of ignition is a problem with the 10's tunnel.

The -10 tunnel has fuel lines, brake lines, and a minimum of three electrical devices (per Vans plans) installed in the enclosed space. Those electrical devices are the fuel boost pump, flap motor, fuel flow transducer.

As expected the fuel pump "appears" to be intrinsically safe (meaning it could operate in an explosive environment without being the source of an ignition.) This makes sense for a fuel pump motor; since it knows it will be operating in a volatile environment.

The flap motor on the other hand is not. It has 4 vents on one side of the motor and 4 more on the other. With a fuel leak in the enclosed tunnel and the right air/fuel ratio, it can be an undetected bomb waiting to be lit. All it takes is the application of the flap motor to set it off. Similar to an explosion on an inboard boat with gasoline in the bilge.

That's a scenario very few (if any) of us realized until Todd's event. Todd's source of fuel and ignition might be different, but it doesn't change a potential risk we've now put our finger on. This risk is completely independent of engine type.

Other RV's may be different, I don't know. But now I'm thinking twice about running any electrical items in the tunnel or any O2 lines through it to the front/rear seats.

Another thing to consider is that many people are insulating the tunnel per Van's SB. In a plans-built fuel system the fuel filter is replaced at the annual and some fuel could drain on the insulation and soak it up like a sponge. So it's possible you don't even need a leak in the fuel system to have fuel vapors in the tunnel. Also if you did have a leak, the insulation could retain the fuel and prevent it from ever making it to the proposed drain hole.

A couple of options I'm considering are:

1) Modifying a marine fuel vapor monitor that goes into the bilge of a boat and wiring it to a warning light next to the flap & boost switches. This will at least let you know there are fumes in the tunnel and you shouldn't touch either of those switches.

2) I located the maker of the electric motor for our flaps. I'm trying to contact them and see if the they make an intrinsically safe version of it. If so, it should be really easy to swap the motor out on the flap actuator frame.

Phil
 
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Phil said:
Not exactly. The source of ignition is a problem with the 10's tunnel.

The -10 tunnel has fuel lines, brake lines, and a minimum of two electrical devices (per Vans plans) installed in the enclosed space. Those electrical devices are the fuel boost pump and the flap motor.

As expected the fuel pump "appears" to be intrinsically safe (meaning it's could operate it in an explosive environment without an ignition.) This makes sense for a fuel pump motor; since it knows it'll be in an volatile environment.

The flap motor on the other hand is not. It has 4 vents on one side of the motor and 4 more on the other. With a fuel leak in the enclosed tunnel and the right air/fuel ratio, it can be an undetected bomb waiting to be lit. All it takes is the application of the flap motor to set it off. Similar to an explosion on an inboard boat with gasoline in the bilge.

That's a scenario very few (if any) of us realized until Todd's event. Todd's source of fuel and ignition might be different, but it doesn't change a potential risk we've now put our finger on.

Other RV's may be different, I don't know. But now I'm thinking twice about running any electrical items in the tunnel or any O2 lines through it to the front/rear seats.

Another thing to consider is that many people are insulating the tunnel per Van's SB. In a plans-built fuel system the fuel filter is replaced at the annual and some fuel could drain on the insulation and soak it up like a sponge. So it's possible you don't even need a leak in the fuel system to have fuel vapors in the tunnel.

A couple of options I'm considering are:

1) Modifying a marine fuel vapor monitor that goes into the bilge of a boat and wiring it to a warning light next to the flap & boost switches. This will at least let you know there are fumes in the tunnel and you shouldn't touch either of those switches.

2) I located the maker of the electric motor for our flaps. I'm trying to contact them and see if the they make an intrinsically safe version of it. If so, it should be a really easy swap the motor out on the flap actuator frame.
Click to expand...

I'm not a 10 builder. What does it take to ventilate the tunnel? Whether flying in winter or summer, we usually do have airflow entering the cockpit area as well as exiting. And if not (as with A/C or closed vents), something could be done. Afterall, boat bilges are ventilated too, especially when moving under power, or by using a fan when stationary. And unlike a boat, in which the bilge is below the water line, an airplane has access to a free moving airstream if incorporated correctly.

L.Adamson --- RV6A
 
L.Adamson said:
What does it take to ventilate the tunnel?
Click to expand...


Someone posted an interesting idea on that late last night. They were wondering if we could use the airflow to create a venturi effect and suck the fumes and fuel out the back end of the tunnel.

A very novel idea, but I'm not sure how to pull it off. My sophisticated mind only understands fuel and sparks - not venturi placements. :)
 
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Prior to the -10 fire, I wanted to start a "what's wrong with this picture" type of thread showing various examples of how NOT to do something. My intent was to see how many novice builders would miss these important errors in workmanship and also how many experienced people could point out mistakes. Many have seen the example of how "not" to flare tubing in the "Engine out/IMC" thread, and you have yet to see is a picture of the electrical wires "zip tied" directly to the aluminum fuel line I discovered the other day :eek:...

The reason I bring this up is not because I think this -10 suffered from poor workmanship (I really have no idea), but because in my days as an aircraft mechanic I have seen many examples of "an accident waiting to happen". Many times it's because some just don't know any better. I'd like to find the root cause of the -10 explosion (as would Van, I'm guessing) but I KNOW that there are plenty of RV's out there that are ticking time bombs due to poor craftsmanship. We need to fix that. The -8 under my care is in fact one of these examples, and I think this thread is timely.
 
Just glancing at the plans, it occurs to me that it ought to be possible to isolate the flap mechanism from the rest of the tunnel.

I also like the idea of venting the tunnel. Instead of insulating the tunnel, insulate the hoses carrying cabin heat. Introduce air into the front of the tunnel via a small scoop on the cowl somewhere away from the exhausts (cool, outside air is what I mean, not heated inter-cowl air), and a small louver or cutout to allow it to exit from the rear on the fuselage bottom. The advantage of a remote scoop over a direct louver at the front is you can install a water trap (don't know about you, but I don't really want water in my tunnel) and you avoid hot air or a potential engine compartment fire from entering the tunnel. Just preliminary thinking, so there are doubtless issues I haven't thought of; be gentle.;)
 
My RV6A originally had 4 fuel pumps, 2 low pressure and 2 high pressure for the EFI plus a header tank mounted behind the firewall. As you can imagine, there were lots of aluminum hard lines and AN fittings to connect it all.

Always worked great but after about 3 years, I started to get faint fuel smells in the cockpit. I chased these for months, each time thinking I'd found the seep. Finally I stripped out some of the foam soundproofing which had absorbed some fuel. I cleaned everything up and waited for the evidence of fuel dye to reveal the actual seep. Nothing, but the faint smell persisted. :mad:

The header tank was almost impossible to reach from underneath for the two top fittings. The smell was annoying me so I finally stripped out the header tank and all the hard lines and the two low pressure pumps. Some others had flight proven a simpler system using the high pressure pumps mounted right on the floor below the fuel selector. I tested the new Walbro pumps for draw and priming. They were excellent in this regard compared to the original Bosch pumps which don't prime well.

I the end, I saved 5 pounds of weight, got rid of about 15 connections and eliminated the fuel smell. I did careful flight testing with low fuel in uncoordinated high banked turns at altitude to make sure fuel feed was solid in all attitudes compared to the old system. Best thing I ever did. The complex system with all those lines and connections had bothered me for some time.

Personally I don't like the idea of pumps on the engine side of the firewall and there have been issues and accidents from heat causing vapor lock and failures. If there is an engine fire, aluminum pump bodies and lines will perish in a matter of seconds. If you must, use steel lines and protect the pump bodies somehow and cool them with an air blast to prevent vapor lock problems.

The 3003 aluminum tubing often used for fuel lines is easy to work but fairly weak. It must be well supported and not subjected to vibration. Serious consideration should be given to steel or braided lines. The weight penalty will be minor. If you used braided steel hoses, consider using steel AN fittings instead of aluminum. They are about twice as strong. I've seen more than a few AN fittings fracture from having relatively heavy and stiff braided hoses hanging on them, not being well supported. The vibration in aircraft can be an additional concern.

I think important lessons can be learned here.

A fuel fire acting on lightweight aluminum structures is devastating in very short order. You don't have minutes in most cases, you have seconds to either get it out or for you to get out. Don't think that the firewall will protect you for long either, in most cases the belly skin burns through in less than 30 seconds and then you are finished.

Consider Nomex clothing and gloves. The vise grip idea is excellent. Just think what would happen if the hard line to the fuel selector broke in an RV, getting 20+ gallons of fuel flowing into the cockpit.:eek:
 
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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.
 
I want to clarify one of my prior statements a bit.

In the first post, I mentioned three things needed for a fire.

One of them is fuel-----but I was thinking/writing as a long time fireman.

The word "fuel" as I used it, was in reference to flammable vapors in this context, not liquid gasoline while still contained in the fuel line. Big difference.

We need to focus on eliminating potential fuel system leaks, which are what produce the flammable vapor that is the real cause for concern.
 
Phil said:
1) Modifying a marine fuel vapor monitor that goes into the bilge of a boat and wiring it to a warning light next to the flap & boost switches. This will at least let you know there are fumes in the tunnel and you shouldn't touch either of those switches.
Click to expand...

I had considered repackaging (for better display, and minimal panel footprint) something like the Fireboy Marine sensors (like this or this) I've seen on boats, when I got to building. Looks like it wouldn't be that hard to build in, and there are others like those.

If you had more than one sensor, where would you put the others?
 
Where there's smoke...

Excellent discussion and timely. Having been on fire in an airborne aircraft (F16) I can assure you things happen fast, especially when the fire is fed by fuel or hydraulic fluid under pressure. When I built my RV4 and re-built my HR2 the memory of all this led me to many preventative measures.
The first was all fuel and oil lines made of braided steel teflon fire-sleeved. Second was ceramic blanket insulation (rated to 1200C) between the firewall and me. Third was attention to detail on fuel lines from the tank to the engine and the addition of ceramic insulation in the stick well around the fuel selector.
Most importantly in an emergency involving fire, get on the ground and away from the airplane ASAP, eliminate electrical and fuel sources and wear protective clothing. Been there, done that.

Smokey
HR2
 
DCat22 said:
If you had more than one sensor, where would you put the others?
Click to expand...

I think the tunnel is the sweet spot, so I really can't say I would install any others. I suppose the next spots would be to catch vapors under the seats (near the landing gear mounts).

On the topic of these sensors, pretty much any hydrocarbon will set them off. So if you've got fairly new fiberglass or adhesives, they can set them off too.
 
I wonder if some of those unexplained crashes could bed related to this. If I was ten miles away and this exploded it would have looked like I lost control for some reason and the plane crashed.
 
I like to add that I have many leaks in my canopy, I don't intend to fix any of them. I like the leaks, keeps fresh air coming in at all times. I have flown mine at 5degrees outside temps and I'm just fine. Than again I have mufflers, panel heat to one muffler and floor heat to the other muffler. I occationally have a piece of lint float around and it gets pushed around and out the back. I don't have any sealing out the back on the back panel for the luggage area, nor do I have any sealing at the rear tail at the horizontal. I think I have a passing air system, which is what I think I have is critical for keeping fresh air in the airplane. I have a tip up. The leaks that I have are where the tip up meets the fuse. I thought of putting in some type of weather stripping, but after this, I don't think so. I think it's possible for us to seal up our airplanes, to much.
 
unexplained crashes???

Todd,
Glad to see you and your daughter getting better.
I have always looked forward to reading your posts.

My question:
What unexplained crashes are you talking about?
I am aware of 2 RV-10 crashes. One in bad weather and the other with an engine problem.
What other ones are there?
 
I am not talking about RV-10 crashes just plane crashes where vapor has gotten in and it has exploded. Now I had a ton of fresh air pumping into the cabin also until I landed
 
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Phil said:
Do other RV models have the same design of a shared airspace for fuel and flaps??
Click to expand...

Yes, but as far as I know, the 10 is the only one with the tunnel. In the other models, the shared space is the cockpit itself.
 
I've been thinking a bit over the past couple of days about running my fuel lines outside the cockpit on my -7. The plan was originally to have an electric pump in each wing root similar to Frankh (I think). I've never really been a fan of running fuel through the cockpit anyway, let alone pressurized, so I think with some of the taildraggers, it wouldn't take much more than an oversized gear intersection fairing to cover fuel lines going from the leading edge of the wing to the cowling.

I'm still a ways away from any of that plumbing, but does this sound even remotely feasible?
 
1:1 Scale said:
I've been thinking a bit over the past couple of days about running my fuel lines outside the cockpit on my -7. The plan was originally to have an electric pump in each wing root similar to Frankh (I think). I've never really been a fan of running fuel through the cockpit anyway, let alone pressurized, so I think with some of the taildraggers, it wouldn't take much more than an oversized gear intersection fairing to cover fuel lines going from the leading edge of the wing to the cowling.

I'm still a ways away from any of that plumbing, but does this sound even remotely feasible?
Click to expand...

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 was thinking I'd just have a switch to turn either pump on or off similar to what I've seen someone else post. I think a third pump could be mounted on the firewall, what could pull fuel through a failed pump (possibly. I still have a lot to learn in this area). I thought the vent lines could just use the Rocket coil trick, so no vent lines in the cockpit either.....
 
My Hiperbipe used to have the fuel selector mounted ahead of the firewall. The handle simply had a long tube extension between cockpit and valve.
 
I don't think more connections ahead of the firewall is the answer. Let's face it, a leak under the hood is almost sure to cause a fire, whereas one in the cockpit will probably just stink (as long as nothing ignites it). Try as we might, I don't think we can ever build planes that are guaranteed not to leak somewhere. The trick is to keep heat and spark away from said areas.
 
szicree said:
I don't think more connections ahead of the firewall is the answer...
Click to expand...


I agree. That's why I moved the valve inside the cockpit.

As to leaks in flight, I read somewhere that during Dick Rutan's record flight from Alaska to Grand Turk (?) in his Longeze, he developed a fuel leak. As I recall, he was fighting a thunderstorm at night at the time, and ended up landing with an inch of fuel sloshing around the fuselage floor. I remember the story relating that he held is breath and closed his eyes when he finally turned off the master switch- as if that would have helped any.
 
Toobuilder said:
I agree. That's why I moved the valve inside the cockpit.

As to leaks in flight, I read somewhere that during Dick Rutan's record flight from Alaska to Grand Turk (?) in his Longeze, he developed a fuel leak. As I recall, he was fighting a thunderstorm at night at the time, and ended up landing with an inch of fuel sloshing around the fuselage floor. I remember the story relating that he held is breath and closed his eyes when he finally turned off the master switch- as if that would have helped any.
Click to expand...
I would think if a person knew he had a fuel issue to just lean the engine to stop it and get the heck out and don't touch anything. That's my thoughts anyway.
 
For those that are interested, here is the spec sheet on the motor itself.

http://www.alliedelec.com/Images/Products/Datasheets/BM/AMETEK_PITTMAN/388-0012.PDF

More info here:
http://www.alliedelec.com/search/productdetail.aspx?SKU=3880012

FWIW, The motor does have (copper-graphite) brushes and I just ran mine in a pitch black room to see if I could get a visual on any spark. No joy on finding one.

I'm guessing a brushless equivalent would be less likely to spark if a sealed version isn't available.

Phil
 
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Dick Rutan

I will reread the Rutan article but I think the fuel leak was on the positioning flight to Alaska or on a test flight in Alaska. He did say something like, close your eyes, put your fingers in your ears and turn off the battery switch with your elbow. I think this was actually an old Air Force joke.
 
I don't think it's just a tunnel issue there are plenty of openings in the tunnel for vapors to get out. And as it builds slowly you really don't smell it.
 
TSwezey said:
I don't think it's just a tunnel issue there are plenty of openings in the tunnel for vapors to get out. And as it builds slowly you really don't smell it.
Click to expand...

Todd, it sounds like your first overall pick is for the vapor warning device more than any other?
 
not just gas

There are things to be learned from accident/incident reports on large airplanes as well as small. Fires other than fuel fed can kill you just as quickly.
Nascar Cessna310, Orlando, July 10, 2007, electrical fire
Swissair 111, wiring, electrical/oxygen fire
Fedex, Sep 5, 1996, unknown cargo fire
Air Canada DC9, Cincinnatti, OH, lav motor/wiring, electrical fire
Beech Debonair, Pittsburg PA, electrical fire consumed cabin. Pilots aborted takeoff and escaped.
The Fedex accident occurred a few months after the Valujet accident. The Fedex accident is a textbook example of the crew making an almost instant decision and doing everything nearly perfect.
 
Vibration can be bad news aft of the firewall.....

I've been thinking, asking, what causes a fuel leak in the cabin?

We assume the area aft of the firewall is ok for solid aluminum lines. No transition to the engine (a vibrating mass) so it should be safe. Up front we use teflon hose and fire sleeve and feel all right about it.

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. It is especially so with an auto engine. Seems there may be a harmonic issue going on here, perhaps from exhaust pulses. Generally the high rpm six cylinder engine was very smooth - except at that floor area. I was so concerned about it with possible lower skin failure, I go rid of external mufflers and installed an internal muffler. It did not eliminate all floor vibration but it was better. With Lycoming it is not as pronounced but the forward cabin floor area definitely is not smooth and calm.

This has to have an affect on aluminum fuel lines mounted on the floor running to the firewall. The lines coming through the fuselage sides from the wing tanks along the spar are in a relatively calm area, but forward of the valve and pump toward the firewall, vibration is on the increase. That's where aluminum can become brittle and crack, IMHO.

It's been a year since I installed the Lycoming and have not gotten around to building a new tunnel cover where 2 batteries used to sit above fuel lines and fuel pumps - all enclosed (the single battery now resides forward of the firewall). Everything is currently exposed. The cabin has major air leaks around the canopy and there is a lot of air moving through. It has been on a list of things to work on, the tunnel cover and excess ventilation, but it will stay as is for now.

One thing we don't need in the cabin are poorly ventilated bomb containers with fuel lines, electric wires and arching motors.
 
I have been following both RV10 incidents with great interest, this is specially that I have been thinking about both scenarios even before they happened.

I have a RV7A and since I built it little over a year ago, occasionally I would smell a bit of fuel. I kept looking for it and could not find it till just recently when I found that my transducer (floscan) was weeping a bit of fuel thru the place that wires come out. As a result I was thinking of moving it FWF, of course the replacement one as the old one is not fixable, or I don't know how to fix it. Anyway after long consideration I thought if that was going to fail, there are greater chances to smell the fuel and do some thing about it then not knowing and let it completely fail. Of course a complete failure is not just engine out, the fuel in FWF to me is perhaps far more dangerous then some (emphasis on some) in the cockpit. I was quite surprise to be able to smell the gas as little as it was coming out judging based on the stain that it left behind but then again, Todd's incident is having me rethink that idea.

At the present, I just like to get others thoughts and ideas about this and thinking of replacing the aluminum lines with the stainless steel.
 
If a little airflow will help in the tunnel. How about running an airhose from a radio stack cooling fan.(If one's installed)
 
Tunnel

All Piper Commanches have a tunnel. In the Twin Commanche it is quite crowded. The Commanches have no history of fire or explosion originating from the tunnel area. In the later airplanes, fuel lines, fuel selector, flap motor and boost pump, along with a lot of electrical wiring.
Some automotive electric pumps are installed inside the fuel tank. Various fuel gage senders are installed inside fuel tanks. These do not cause fire/explosion.
This raises the question: are the electrical components in the tunnel of the RV 10 adequate for the installation. A modern flap motor simply should not be a source of ignition. Likewise the electric boost pump.
I believe strobe light power supplys to be very high risk as ignition sources. It would be best to install strobe light components as far as possible away from any fuel. There have been a few cases of strobe components causeing explosions in GA aircraft.
 
Fuel lines

I believe that 5052 O aluminum tubing is the MINIMUM standard for standard category ga aircraft. 5052 is almost twice the strength of the 3003 tubing supplied by Vans. More important, if the 5052 is properly flared with a quality flaring tool, there should not be any significant "tool marks" left by the flaring tool. Fabrication of hard stainless lines is probably beyond the capability of most homebuilders, except in very small diameters.
 
Guys I don't think this is just a tunnel issue. I think this an entire fuel system issue. Who's to say the fumes didn't fill the cabin when I put it into a slip. Or should I say did the slip block the airflow that was pushing these fumes away. I think this is the first time I have slipped it with the flaps down in a while. I have four overhead vents that pump air into the cabin.
 
Dampening can help..

David-aviator said:
.......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. .
Click to expand...

...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,
 
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.
 
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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/community/showthread.php?t=12112
 
apkp777 said:
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. .
Click to expand...

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.

apkp777 said:
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..
Click to expand...

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.
 
Phil said:
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.
Click to expand...

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.
 
TSwezey said:
Guys I don't think this is just a tunnel issue. I think this an entire fuel system issue.
Click to expand...

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?
 
DanH said:
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?
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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-aluminum-tubing-p-246.html

L.Adamson --- RV6A
 
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DanH said:
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?
Click to expand...

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.
 
L.Adamson said:
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-aluminum-tubing-p-246.html

L.Adamson --- RV6A
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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.
 
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David-aviator said:
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.
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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
 
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