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Is this a reasonable fuel line routing method?

grayforge

grayforge

Well Known Member
I've been refactoring my fuel line routing, initially going from the fuel pump to the servo along the outside of the sump. But then I thought the line might go nicely below the sump. Sure enough, it's shorter and keeps well away from the exhaust.

Next was from the firewall to the engine driven pump. Does Vans have you just install a short section bent 90 degrees? Does it need to be secured to anything along its span?

What do folks think?

1st half of Pump to Servo
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2nd half of Pump to Servo
DSC00458.JPG


Firewall to pump. Secure to engine mount or just loop in a wide 90 degree arc?
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I think it looks good in general, but you may take note of
http://www.faa.gov/regulations_poli...craft/amt_handbook/media/FAA-8083-30_Ch07.pdf

Clearance—The hose assembly must clear all other
lines, equipment, and adjacent structure under every
operating condition.
Flexible hose should be installed so that it will be
subject to a minimum of flexing during operation.
Although hose must be supported at least every 24
inches, closer supports are desirable.

You may check as well the thread of Axel's Fastback 4 to get some ideas on support locations (p. 19). He used a similar routing. Correction: He went on top of the sump.
http://www.vansairforce.com/community/showthread.php?t=39772&page=19
 
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Looks fine, do not secure pump/firewall line to mount as it needs to move around. Servo line needs firesleeve.
 
Yep. The firewall -to - pump hose is exactly how I've been running mine for many hours and has no issues. Pump-to- servo is stainless hardline on mine though. With hardline and it's more defined bends, it made more sense to go over the sump and use the pan studs as attachment points.

2096kad.jpg


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2nautcg.jpg
 
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Russ---its a good mock up. Yep firesleeve for sure, and the farther from heat an other obstacles the better. Firewall to the pump should also have firesleeve, and be free floating.
I do like Michael's stainles hard line, but he is very proficient at bending rigid tubing. In your case, I think it might be ALOT of trial and error. In most of our cases, flex hose is great.
Tom
 
The stainless hardline is very interesting - and well done. I don't believe I've ever seen aluminum hardware on the end of a stainless line before, but the builder obviously knows what he's doing.

Has anyone ever experienced corrosion issues with this combination?
 
It's not standard practice to use aluminum on stainless (for hardlines - you do see it on hose assemblies sometimes), but that's because of the "mission" of the two materials, not the elemental composition. For the pressures we are running here, aluminum is more than adequate. Once you step up to stainless, you "normally" are doing it in a high pressure (meaning several thousand pounds) application which requires steel nuts. However, in this case, the substitution for stainless tube is only for damage resistance, and yes, fire safety. On the point of fire safety, one could argue the use of aluminum nuts. In my mind, the aluminum fuel pump or aluminum servo/carb will fail when the nuts do, so it's a wash. At the very least, a fire that melts through the relatively thick aluminum nuts will take out the paper thin oil cooler long before, or at the very least, give me plenty of time to turn the fuel off. I've taken a calculated risk to save a few ounces. However, even with the use of steel nuts, you will be well ahead of hose in weight (and cost).
 
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TS Flightlines said:
...I do like Michael's stainles hard line, but he is very proficient at bending rigid tubing. In your case, I think it might be ALOT of trial and error. In most of our cases, flex hose is great...
Click to expand...

Thanks for the complement Tom. However, the line bending is not that tough, especially if you use that soft line Van provides as a template first. Another trick to getting it right is to use bends on cardinal angles whenever you can. If you will notice, most of my bends on that line are simple 90's or 45's... Makes it very easy to figure out where the line is going to be without any complex math.
 
Stainless is sometimes a pain, even with a template. I bend .065 wall .375 stainless for my custom fittings, and yes it can still be a hassle, (as one of my very good customers will attest!!! He knows who he is!). For something like what you have, .035 is fine IF you pay attention to the bends and not try to make a real tight radius. Bending .035 really tight will shrink the outside of the bend, and wrinkle the inside.
As for aluminum B nuts and sleeve on stainless, if you had a fire, many other things would burn and cause issues before the B nuts. They look pretty though!
Tom
 
Thanks folks. I think I'll go with the below the sump route. And I'll totally use firesleeve. This is just a prototype run with hose that Tom sent me. :)

For the short 90 degree run between the firewall and pump, my worry is that engine shake will cause the hose to want to twist at the firewall, allowing it to loosen eventually. But this may just be paranoia and the twisting moments are likely way smaller than the torque required to loosen a properly tightened fitting.

I've seen where people have used the facet pump doubler as a pass through for fuel on an injected plane. I added the facet pump doubler before I realized that the plans default to a carburated plane. So I may as well use that doubler instead of installing another.
 
grayforge said:
For the short 90 degree run between the firewall and pump, my worry is that engine shake will cause the hose to want to twist at the firewall, allowing it to loosen eventually. But this may just be paranoia and the twisting moments are likely way smaller than the torque required to loosen a properly tightened fitting...
Click to expand...

2 things:

1 - The engine does not have a bunch of rotation when it shakes. If the hose was a #12 or bigger and very short, you might have reason for concern. At the length you are going to use, it will absorb some radial movement.

2- Because you have a 90 degree bend in the hose, any minor radial movement will be dissipated by causing to hose to try coil slightly. Not a problem.
 
TS Flightlines said:
Stainless is sometimes a pain, even with a template. I bend .065 wall .375 stainless for my custom fittings, and yes it can still be a hassle, (as one of my very good customers will attest!!! He knows who he is!). For something like what you have, .035 is fine IF you pay attention to the bends and not try to make a real tight radius. Bending .035 really tight will shrink the outside of the bend, and wrinkle the inside.
As for aluminum B nuts and sleeve on stainless, if you had a fire, many other things would burn and cause issues before the B nuts. They look pretty though!
Tom
Click to expand...

Compared to aluminum, stainless certainly takes more effort - I agree. However, it should be noted that I'm using standard tube benders and flare tools for my lines... The same exact ones every RV builder has in his shop. With those, the bends pull right around the curve just fine (just takes more muscle).

That said, I have made some tighter bends and also some larger diameter tube than I have a bender for. Since I don't have a mandrel bender like you likely do, I improvise by packing the tube full of sugar. This turns the "tube" into a "bar" and you can really tighten the radius up a bunch. Why sugar? Because it will not scratch the inside of the tube and also disolves in hot water.

I'd really like to point out here that these lines I make are not a result of years of practice, specialized tools or exceptional skill... I'm like everyone else out there. Don't be afraid of these hard lines. Spend $20, grab some raw stock, and give them a shot.
 
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No Firesleeve for SS?

So using hard SS lines means no firesleeving is required? I assume that's what you meant when you said "saves ounces and cost." Correct?
 
Right. The tubing itself is as resistant (more so, actually) to flame as the "firewall".

As for my specific saving of "ounces" - that was concerning the use of alumimum vs. steel nuts. The weight savings for hard line vs. hose is much more significant. Replacing hose with hardline resulted in a net loss of more than 7 pounds (all FWF) on the RV.

As for "cost" - figuring on current catalog pricing for the AN818 nuts ($.91 ea), the AN819 sleeves ($.76 ea) and the tubing at $3.20 per foot, I can make an essentially indestructible 36" fluid line for about $13 bucks. Not sure how that compares with a teflon lined, firesleeved hose assembly, but I'll bet a hardline is considerably cheaper.
 
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Fuel Line

Ditto the firesleeve. I would also use some of those heat deflectors that secure around the exhaust pipe with hose clamps. They are relatively cheap and for me provide a little more piece of mind.
 
Michael, I like your hard fuel line install between the pump and servo... so I decided to give it a try. You're right, besides requiring more muscle, bending hard lines isn't much more difficult than soft aluminum. One difference is that it's not as easy to tweak the tubing one way or another to make small adjustments. After about 90 minutes of work, I ended up with a pretty decent first attempt. I'll be adding an Adel clamp and maybe some fire sleeve later. Photos below...

Thanks for the idea!

Russ

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I like saving dollars and weight as much as the next guy but I also know that these engines are not solid blocks; they do move a bit in service. I know that some governor oil lines are rigid lines,but are there hard fuel lines used in the certified world on with these engines?
After 800 hours I have some cracks in my baffles and aluminum plenum and these hard lines make me a bit nervous.
 
I agree. Nice job!

You now have an appreciation for how much stiffer this material is than aluminum. This is a clue for their general fabrication. Though the servo and fuel pump are not moving relative to one another, there will be slight dimensional change as the engine heats and cools. So in this case, the general rule concerning bends is, the more, the better. In your case, you have several nice 90 degree bends which allow a little bit of flex without over stressing. Same concept applies to hose- you never want it installed "tight".
 
Mr. Martin -

There is some precedent for rigid fuel lines in the certified world, though admittedly rare. I believe this has to do with the fact that engines are supplied to the OEM's as "generic" power plants. It would be difficult to fabricate a hard fuel line that took into consideration every exhaust system, engine mount, nose landing gear, etc. Better to supply a hose and let the airframe manufacturer deal with it.

However, you are spot on in your caution that the engine does move around a bit when heating and cooling. That movement needs to be addressed in the design of the tube. It is up to the builder to decide just how to allow for that movement. Hopefully people realize that a perfectly straight, 2 foot long hardline would break very quickly if connected between the servo and fuel pump. But the meandering path taken over and around the engine mount, oil pan rails, etc. as shown above gives a measure of strain relief. The key thing is to just make sure the line does not become a structural member - either in tension or compression.

Bit of trivia- There is at least one retractable gear aircraft that uses a single piece of hardline from the wheel mounted brakes to the fuselage. the 90+ degrees of retraction is accomplished with no flex hose or swivel fitting - it's all done with flexing the hard line. On the SR-71, the brake line travels from the wheel, up the gear leg, then coils around the gear trunion about a dozen times and attaches solidly to a fitting up in the wing. As the gear retracts the hardline bends, but it is only a fraction of a degree per inch through the coil. It's an extreme solution to an extreme mission, but does show that properly designed, even solid hard line can be pretty flexible.
 
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The other difference between Tom's baffles/plenum and these hard lines is that his are made of aluminum and these are made of stainless steel. I also used stainless steel end nuts and steel collars.
 
I am interested in this thread as I am always looking for alternate ways of doing things. There is not just thermal movement in these engines, there is actual movement between the parts. It has been well documented that cylinders move relative to each other and that even in the block there are some movements. There is most certainly a lot of vibration. That we have used hoses as the predominate method of moving all liquids north of the firewall does not mean that other methods will not work. It does however mean that we have a well established failure mode with hoses.
I would feel a lot better about this discussion if one of the expert mechanics would step forth and say that a rigid line from the fuel pump to the fuel servo has been used successfully on a Cessna XXX for 30 years with no issue.
The fact that the tubing is stainless does not mean that it is not susceptible to vibration, just that it could take longer to show that wear. Sometimes a more rigid part may be more susceptible to fracture.
A good friend of mine pointed out that the small stainless lines from our flow divider on injected systems are stainless and properly supported, give good service.
Again I am not just being negative here, fuel system issues are the predominate cause of most engine related problems and I would hate for this to be perceived as an industry accepted practice unless in fact it is. If it is an accepted practice with thousands of hours of trouble free hours I will withdraw my concerns.
 
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grayforge said:
Michael, I like your hard fuel line install between the pump and servo... so I decided to give it a try. You're right, besides requiring more muscle, bending hard lines isn't much more difficult than soft aluminum. One difference is that it's not as easy to tweak the tubing one way or another to make small adjustments. After about 90 minutes of work, I ended up with a pretty decent first attempt. I'll be adding an Adel clamp and maybe some fire sleeve later. Photos below...

Thanks for the idea!

Russ
Click to expand...

Where do you plan to put the adel clamps to terminate vibration? It looks like two good spots long the sump. ( like the governor line)
 
Tom Martin said:
...I would feel a lot better about this discussion if one of the expert mechanics would step forth and say that a rigid line from the fuel pump to the fuel servo has been used successfully on a Cessna XXX for 30 years with no issue...
Click to expand...

Not claiming to be an expert, but here's the "certified/TC'd" setup for the -B1E:

photo2_zps43db162d.jpg



Also keep in mind that short= stiff, so the B1E example is a pretty severe case. A longer run with a few bends in it is actually (relatively) flexible (as found in the SR-71 trivia above).
 
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I would feel a lot better about this discussion if one of the expert mechanics would step forth and say that a rigid line from the fuel pump to the fuel servo has been used successfully on a Cessna XXX for 30 years with no issue. .[/QUOTE said:
Actually there is some history to look at relating to the s/s governor line, excluding the AD for replacing aluminum fittings with steel.
Click to expand...
 
That's a good picture Mike - thanks for posting it. To me, it is clear that trying to fabricate a hose with that tight of a bend would have been tough - the hard line looks to me to be the better of the two options because of the closeness of the two ends. So there was a clear engineering trade that had to be made.

I would be careful about the SR-71 analogy though - as we well know, and aircraft like the Blackbird received meticulous attention from mechanics between every flight - lots of eyes on the machinery in case there was something wrong. Most people don't look under their cowlings on a GA aircraft between oil changes - so the comparison isn't necessarily valid. A good example for what it is, but have to remember the limitations/assumptions that go into every aircraft and the way it is operated.
 
BillL said:
Where do you plan to put the adel clamps to terminate vibration? It looks like two good spots long the sump. ( like the governor line)
Click to expand...

Yep, one of the sump studs along the top of the sump. In fact, if you use a magnifying glass, you can see a sump stud under the straight stretch of line above the sump that already has its nut removed, ready for installing the adel clamp.

DSC00540.JPG
 
Ironflight said:
...I would be careful about the SR-71 analogy though - as we well know, and aircraft like the Blackbird received meticulous attention from mechanics between every flight...
Click to expand...

I'm aware of the care the Sled received as I was one of the many who provided that "meticulous attention"... ;) That said, this was a working military aircraft, not a fragile show pony. That particular line was no more subject to failure than anything else on the airplane, and in fact the method was used because of its (relatively) high durability.

Anyway, the point was merely to illustrate that hard lines should be designed to have some "give" - and in the case with the Sled, a whole lot. So if you can accommodate a 90+ degree retraction cycle with hard lines, then the slight relative dimensional change from one end of a Lycoming to another CAN BE well inside the properties of the material. I say ?can be? because you will have to design in allowance for movement. If you don't, then the tube becomes "structural" and something is going to break. It's not a complex concept, but those that don't have this clear in their minds and/or are unwilling to learn about it should certainly stick with hose.
 
Vans specifies hard lines in a scenario with relative movement too: The brake lines going down the gear legs to the caliper. And these are with less durable aluminum. :)
 
Don't fly over my house!

Learned that saying from an old saw who didn't like the EXP world much. My take is I don't see much differrence between any of the pre-war stuff and our birds in the FWF area. Heck, even the post-war stuff gives good examples of how to do it, and extended hard lines ain't part of the SOP anywhere until Lyc finds a way to make it work (cheaper) on their gov lines. That hard lne on that B1E is not an example of engineering now, is it? Same thing on my 550-N, but each end is screwed onto a steel fitting - haven't seen THAT referred to anywhere in this thread.

Steel line should be attached to steel fittings.

Hardline in the airframes - well supported - are a completely different matter. As for flexiblke brake lines on an SR-71 - are you really gonna recommend such on an RV? Are the lines on the Sled SS, or aluminum, or more likely made from that very springy Ti stuff?

Let's consider an engine anomaly, like a bad plug, or worse a dead cyl, or worse yet - a cyl that comes loose from the case (broken rod?). Vibration from such will shake the **** out of everything, and if it's not held down (or flexible), it's gonna break. Maybe a hard line that runs under the cyl (flopping around after the studs let loose) migh get hit by the flopping cylinder....it cracks...and where might that fuel go?

How about the FI spider lines and their associated AD? I know a dead guy who didn't follow that AD...

Fellas: hard line might be easier in fact, but consider what else might happen when stuff starts moving around - maybe in only fractions of an inch, and then consider if you want your family member in the plane when the fit hits the shan.

But, what do I know? So far, so good..for me.

carry on!
Mark
 
I mentioned using steel nuts and collars in post 24. The fittings this tubing is attached to are what came from Vans and Precision: Steel or Stainless Steel.
 
Mark,

Let's talk about vibration for a second.

I've seen my share of aircraft hydraulic systems that vibrate, shake and pulse every component in the system much worse than that little aircraft engine could ever hope. When a solenoid opens and the system goes from 0 to 3,200 PSI in a fraction of a second, I can tell you that flex hoses react like a snake dropped into a pot of hot oil, and hardlines jump like they've been hit with a hammer. Just the power pulses from that multi piston hydraulic pump will cause the hardline to vibe so bad you can't even touch it without pain. Sometimes the lines will buzz so much you can't even see them except for a blur.

And they live like this hour after hour... Flying right over your head.

And how about our automotive experience - Remember when cars had carburetors? Remember that 3 foot long steel hardline connecting the fuel pump to that Holley sitting on top of the engine? How about those steel transmission cooler lines solidly connected to the transmission and the radiator... Lots of relative movement between the rubber mounted engine and frame mounted radiator. When was the last time anyone broke those?

Look, if the fabrication and design of hardlines scares you, then go with hose. But don't try to paint those of us who know better as reckless.
 
Message recieved and understood SIR!

Toobuilder said:
Mark, Let's talk about vibration for a second.

SNIP

Look, if the fabrication and design of hardlines scares you, then go with hose. But don't try to paint those of us who know better as reckless.
Click to expand...

Hey Mike:

"Reckless" is your term, not mine. Don't put words in my mouth, please. Cautious would be a better word to use.

Many builders, with a lot less experience than yours, are reading this "How to build your RV-X" forum. Do you want these folks fabbing up their own hard lines without knowing the lessons learned? I do not, and will not, advocate hard line use where hose is the norm. In some cases, it still might not work out, even when the installer knows exactly how to do it. Hoses are much more forgiving.

Or, am I wrong about that?

Carry on!
Mark
 
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F1Boss said:
Hoses are much more forgiving.

Or, am I wrong about that?

Carry on!
Mark
Click to expand...

For the average builder the above is most definately true. From what I've seen "in the field", many builders have trouble making a good bend/flare on soft aluminum tube.

The chance of failure of a properly constructed, proof tested flex line is practically 0.
 
True, you did not say "reckless", but you did say "don't fly over my house" and...

F1Boss said:
....consider what else might happen when stuff starts moving around - maybe in only fractions of an inch, and then consider if you want your family member in the plane when the fit hits the shan...
Click to expand...

... So what message am I supposed to hear, Mark?

So here we are using the same old "...save the poor builder from themselves..." junction. Yep, Cessna does not use a lot of hard lines FWF, but they are absolutely appropriate if fabricated properly.

I can show with certainty that:

- hard lines work for the governor line on a Lycoming;
- it is acceptable practice to use aluminum nuts and fittings on steel lines (and vice/versa;
- hard lines are used reliably in a variety of applications substantially similar to the fuel delivery on a Lycoming;
- hard lines are used for FWF fuel supply in some certified Lycoming applications;
- I use hardlines FWF wherever possible and have had no failures.

So with all this direct evidence that hardlines work, I still get a bunch of pushback ONLY because Cessna doesn't have a million flight hours on them. Well you know what? Cessna doesn't use plastic brake lines and rod end fittings for flight control hinges either.

So I thought this was an information forum, a place where we could share our collective experience and learn things. Apparently it's nothing more than a customer service counter for Vans Aircraft.

But you are right about one thing. It's possible (likely) that someone will try fabricate a set of lines, do it poorly, and that will be "proof" that they don't work. Never mind all the complete hack jobs that are flying around right now - supposedly "built to plans". I've seen battery cables zip tied to fuel lines, braided hose kinked, chafing and zip tied to the engine mount, Flight control cable rubbing on structure, hinges loose, and a myriad of other obvious maintenance sins. Heck, I just found a 2 pound bucking bar in the wing of my Rocket. Don't know how many flight hours it's been there, but I know at least 20.

Anyway, if there is going to be no sharing of information, nor any "logical" debate, then I will seriously curtail my input to this site. We don't want anyone getting hurt (in the airplanes they're building in their garage).
 
I'm going to throw another data point out there. The DC-9/MD-80/MD-90 series of airliners use hard lines with 3 or 4 coils bent into them for the spoiler actuators on the wings with no flex line at all. Also, all of the current generation of commercial jet engines use rigid stainless steel lines for the majority of the fuel system plumbing, which can be very extensive. And, before someone comments that turbines don't vibrate, think again. I've seen lines disappear into a blur on a running engine.
There is more than one way to skin a cat........
 
I appreciate ALL the opinions and input here on VAF. The whole idea of Experimental Aircraft is trying different things (safely, of course).
 
There has been alot of great information on this thread. Just because I happen to build ALOT of teflon hoses, I'll be the first to tell guys when a rigid tube assembly is a better solution. Properly designed and fabricated rigid tube assemblies do in fact have a place in experimentals. The key words here are properly designed, and fabricated.
Flex hoses naturally are 'easier' for alot of builders that may lack the proper tooling to make bends and flares. That's ok, because there is a place for flex hoses. Both Michael and Mark, and others have given excellent examples that state their cases. My advise---for whats it worth, is to be careful, and have someone check behind you IF you have a question.
Tom
 
grayforge said:
...The whole idea of Experimental Aircraft is trying different things (safely, of course).
Click to expand...

Well, the idea is to do it "better" than the factory (and "better" is determined by each of us). Though we do have the freedom to ?try? almost anything on our E-AB aircraft, that is not quite the case here. In this particular case, we are taking a measured approach and applying well proven and accepted aircraft design/fabrication concepts in an attempt to save a few pounds and improve performance. True, Cessna isn?t going to design and stock a different hardline for every model they make in an attempt to eke out a few pounds. Not when they can yank a generic hose assembly off the shelf and it will work perfectly well. But we don't want to settle for the realities of a production line, do we?

Homebuilding is about craftsmanship for some of us, and craftsmanship is finding the ?best? solution to a given problem. This means taking the extra time and care in the construction of our custom made, one off aircraft where the big manufacturers can?t. Cessna has a production schedule to keep - we are not hamstrung by such a requirement. That?s homebuilding at its best, IMHO.
 
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