LettersFromFlyoverCountry

LettersFromFlyoverCountry

Well Known Member
I took off the fuel tank last week to fix a couple of weepy rivets on the topside and notice when I was putting it back on last night that the flare on the fuel line (the little 3 inch stub) could be better. I sanded it lightly to smooth out some rough spots but it seems to me that this is an area where things could be moving a little bit.

I've made a notation to rebuild that line at next year's condition inspection.

I didn't particularly like bending aluminum back when I built this line and I'm wondering two things: (1) Does anyone use flexible lines here and (2) Rather than run the line out of the fuselage and to the wing, does anyone use a bulkhead fitting here to terminate the line inside the fuselage and then run a shorter line between the two outside fittings? I would think this would be easier for maintenance.

Is there a downside to this?
 
Bob,

There are a lot of us using flexible lines for fuel. I see no downside to this, rather I think it is much better and safer than the hard aluminum lines (though more expensive). Check with Tom at TS Flightlines and he can probably set you up easily.

Mine go straight through with a grommet in the fuselage. I would think trying to get the perfect length of hard line between the bulkhead on the tank and a bulkhead on the fuselage would be difficult, plus the extra fitting and connections add a couple more places where fuel could potentially leak.

Greg
 
And...with our A model, a flex line to the firewall is safer than a hard line in a nose wheel incident where the firewall bulkhead may be compromised from any possible crumple.
 
Bob---
Alot of guys use hose to connect the tanks. Those that use a bulkhead fitting in the sidewall have to do something creative to make the connection, because of the VERY short distance between the 2 fittings. The shorter the hose, the stiffer it is, and almost becomes a rigid tube. In addition, short teflon hoses like that are kinda expensive for the lengths (basically cost of the fittings).
Some of us use 90* hose ends on both sides and make a loop to the tank. International guys put gascolators in both wing roots, and use 180* hose ends to make the routing change.

It can be done, but good planning will help.
Tom
 
I have a single line for each tank from the valve from Tom with the aforementioned grommet in the fuselage. Will do the same for lines forward from the Airflow Performance pump as well.
 
Flex lines here, for both suction from the tank and return lines back to it.
 
I have Bonaco flex in my entire fuel system. The hard lines just bugged me for some reason. I tried to keep connections to a minimum and ran through the sidewall with a rubber grommet. My tank lines ran a little long but make a perfect loop in the root area. Lots of room in the -10. Although not an intention of my design, I jokingly envisioned the extra pint or so of fuel from the line loops as getting me over the fence that one time. It's amazing how many accidents are just a fraction of a gallon short. (Yes, shame on me if that ever became necessary.)
 
Greg Arehart said:
...There are a lot of us using flexible lines for fuel. I see no downside to this...
Click to expand...

How about weight?

I have removed the flex lines from FWF on two airplanes and replaced with SS hard lines (where appropriate) I have also weighed the difference before and after. The difference was significant. Based on that, I'd say running your entire fuel system behind the firewall with hose is going to cost you about 15 pounds - and possibly a bunch more if you run a return system. It might be worth it to you, but there is no denying that weight is a significant design consideration.

There are plenty of people who would cut off a body part to save 15+ pounds on an airplane. Just saying...
 
Michael,

I challenge that assertion. Perhaps Tom can give us real weights on his 3/8" fuel lines, but looking at various other places that sell similar lines (i.e., car racing), a typical weight is considerably less than 0.25 lb/foot. Lets call it half a pound/foot for good measure. I have two feed lines from the wing tanks to the selector, total maybe 5 feet. Another line to the firewall, maybe another 3 feet. Total of 8 feet of line. Double that for return lines (if you have them, I don't) so we are up to 16 feet. That's 8 pounds that could be lost compared to no fuel lines at all.

So while I agree that the flex lines are indeed heavier than either stainless or aluminum, I think you're an order of magnitude off in your calculation of how much the difference is. I would estimate at most 2-3 pounds of excess weight using all flex lines with no return lines.

Perhaps the ones you removed were lead-lined?:eek:

Greg
 
Greg Arehart said:
Michael,

I challenge that assertion. Perhaps Tom can give us real weights on his 3/8" fuel lines, but looking at various other places that sell similar lines (i.e., car racing), a typical weight is considerably less than 0.25 lb/foot. Lets call it half a pound/foot for good measure. I have two feed lines from the wing tanks to the selector, total maybe 5 feet. Another line to the firewall, maybe another 3 feet. Total of 8 feet of line. Double that for return lines (if you have them, I don't) so we are up to 16 feet. That's 8 pounds that could be lost compared to no fuel lines at all.

So while I agree that the flex lines are indeed heavier than either stainless or aluminum, I think you're an order of magnitude off in your calculation of how much the difference is. I would estimate at most 2-3 pounds of excess weight using all flex lines with no return lines.

Perhaps the ones you removed were lead-lined?:eek:

Greg
Click to expand...

And I'll add to this that there are some areas to cut to the bare bone in order to save weight, and other areas where you do a little something extra because you've got a weight budget that allows you to. You can choose where and what...
 
I saved over 7 pounds FWF by switching to hardline. I weighed it myself. I'll admit that much of it was also fire sleeved, and the total length was probably close to what is behind the firewall now that I think about it, but the fact remains that there is nothing to be gained from a safety standpoint by going with hose when a hard line will do. Even the lowly 3003 aluminum line (which I think is garbage to work with) is perfectly adequate. And in aerospace, there is no advantage to making something stronger than it needs to be.

The advantage of hose (in this case) is it is easy to work with - but that comes at a price.

Let's not try spin this into a safety issue.
 
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Toobuilder said:
I saved over 7 pounds FWF by switching to hardline. I weighed it myself. I'll admit that much of it was also fire sleeved, and the total length was probably close to what is behind the firewall now that I think about it, but the fact remains that there is nothing to be gained from a safety standpoint by going with hose when a hard line will do. Even the lowly 3003 aluminum line (which I think is garbage to work with) is perfectly adequate. And in aerospace, there is no advantage to making something stronger than it needs to be.

The advantage of hose (in this case) is it is easy to work with - but that comes at a price.

Let's not try spin this into a safety issue.
Click to expand...

Right on post Mike.....
I was so wanting to ask everyone that has posted that hoses are safer, what evidence is available as proof? But I figured what is the point.......
 
Flexible lines might actually be less safe, depending on how long they have been in there. I don't think hard lines have a life limit.
That said, I have flexible lines from the tanks to the selector. Everything else aft of the firewall are hard lines.
I think both are susceptible to the biggest safety issue in equal doses; build error.
 
Greg Arehart said:
Michael,

I challenge that assertion. Perhaps Tom can give us real weights on his 3/8" fuel lines, but looking at various other places that sell similar lines (i.e., car racing), a typical weight is considerably less than 0.25 lb/foot. Lets call it half a pound/foot for good measure. I have two feed lines from the wing tanks to the selector, total maybe 5 feet. Another line to the firewall, maybe another 3 feet. Total of 8 feet of line. Double that for return lines (if you have them, I don't) so we are up to 16 feet. That's 8 pounds that could be lost compared to no fuel lines at all.

So while I agree that the flex lines are indeed heavier than either stainless or aluminum, I think you're an order of magnitude off in your calculation of how much the difference is. I would estimate at most 2-3 pounds of excess weight using all flex lines with no return lines.

Perhaps the ones you removed were lead-lined?:eek:

Greg
Click to expand...

I have outer coated SS carbon impregnated PTFE line that is 2 ounce a foot. so that's 8 FT/LB, Fittings for this line are .8 of one OZ
 
Just to back up a second. I wasn't trying to start a flame war about safety as much as I was ease of maintenance. I'm going to replace the fuel line next year as I indicated so length of service isn't much of an issue here. It's ease of maintenance. I HATED running and bending that tubing when I built this thing and I'm looking for an easier way to replace that line.

Yes, obviously the weight issue is a "thing" but on the other hand I saved a lot of weight (and money) with a fixed pitch prop and I don't have my panel loaded with a bunch of fancy thingamajigs that also add weight. It's a very spartan machine. And I mostly fly alone and I'm a long way from being the RV version of the "Guppy". So I'm good there, especially when I save 11 pounds by getting rid of that big Odyssey PC680 up front.
 
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Interesting that you bring up the C/S prop point. In that particular never ending debate, weight is often cited as a significant factor. While that is true, much like the similar angle valve vs parallel valve debate, the heavier combination will definitely result in a better thrust to weight ratio. So there is a tangible performance benefit to making the choice.

Going with flex hose in this circumstance provides you ZERO improvement in any aspect of performance, yet is many times heavier. Yes, "ease of maintenance" is one of the special cases where flex hose is used in aerospace, but this particular is a line that should only be installed once. This does not fit the standard for an aerospace vehicle.

While I personally find fabricating hard lines one of the more enjoyable aspects of constuction, I understand that many do not. But just consider this- the 2 hours you save by going with flex hose is going to live as dead weight for the rest of the life of your airplane.

And finaly, if you care about resale (yet another oft quoted reason for doing something on this forum), there are likely going to be some potential buyers who will see this as a "red flag" on your airplane.
 
Toobuilder said:
And finaly, if you care about resale (yet another oft quoted reason for doing something on this forum), there are likely going to be some potential buyers who will see this as a "red flag" on your airplane.
Click to expand...

That is a bit of a stretch.
 
Toobuilder said:
Going with flex hose in this circumstance provides you ZERO improvement in any aspect of performance, yet is many times heavier. Yes, "ease of maintenance" is one of the special cases where flex hose is used in aerospace, but this particular is a line that should only be installed once. This does not fit the standard for an aerospace vehicle.
Click to expand...

As I indicated, I'm not happy with the condition of the flare in the current set up, perhaps it got nicked while removing the fuel tank a couple of times; perhaps not. It doesn't matter. It's not presently up to my standards and will be replaced. That's just a fact and the way it is.

Will it be the only time that line gets replaced? Maybe. Maybe not. I don't know. We'll see.

It doesn't fit the standard for an aerospace vehicle? OK. That's cool.

Toobuilder said:
But just consider this- the 2 hours you save by going with flex hose is going to live as dead weight for the rest of the life of your airplane.
Click to expand...

Sure, that's a valid point. I agree. As I said, if it's a big concern, I can save 11 pounds by removing the battery installing the new Sonex battery. We'll see

Toobuilder said:
And finaly, if you care about resale (yet another oft quoted reason for doing something on this forum), there are likely going to be some potential buyers who will see this as a "red flag" on your airplane.
Click to expand...

I doubt very much that's true, actually. I mean, sure, some potential buyer may view it as a red flag -- there are all sorts of people out there. But if people are really going to make decisions based on resale value, they probably ought to sell their RVs now because based on the dropping pilot population, the market for RVs and airplanes is going to be dropping in the next few decades.

Look, I get it. This isn't something you would do. But, how you decided to build your airplane really isn't of any concern to me in how I've built mine.

I built the RV airplane I wanted to build. I love it. You put a c/s prop. I think that's great. I saved thousands of dollars because I work for a living and stuff like that matters to me.

In my asking questions, please don't be under the impression that I'm looking for permission, approval, or blessings for the choices I make.
 
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I can't make a decent flair if my life depended on it. I've tried. That left me with two choices. Getting somebody to make the lines for me or buying hoses from Tom @ Flightlines. I bought the hoses. I'm not worried about the additional ounces I may have added.

I am happy with my decision.

bob
 
Toobuilder said:
And finaly, if you care about resale (yet another oft quoted reason for doing something on this forum), there are likely going to be some potential buyers who will see this as a "red flag" on your airplane.
Click to expand...

Let's be honest - most "buyers" that are not also builders wouldn't have a clue that one would be preferable to another, or why.
 
On an -A model, bending those aluminum fuel tubes past the gear weldments is a rite of passage, not to mention a badge of honor and a trophy of persistence. It took me three tries, but I finally got a result I could be proud of.

They stay.
 
rightrudder said:
On an -A model, bending those aluminum fuel tubes past the gear weldments is a rite of passage, not to mention a badge of honor and a trophy of persistence. It took me three tries, but I finally got a result I could be proud of.

They stay.
Click to expand...

Truth - I took a couple stabs at it and called Tom Swearingen. I don't need the aggravation.
 
Time out everyone-

This forum is about information and encouragement ? not shining sunlight up people?s backsides. And as soon as you post here the topic becomes bigger than you. It is going to the countless lurkers and/or builders who NEVER post. We have a duty to provide the best info we can ? and Doug has been very clear on this point.

In this particular instance I?m compelled to correct the misinformation that flex hose is a direct trade for hard line. It is not. While hose is functional and no less safe, it has some significant downsides compared with hardline. This is not my opinion ? this is fact. And I would be shocked to hear from an aero engineer who disagreed. I know for a fact that my Chief Engineer would throw someone out of his office who proposed using flex hose here because fabrication or installation of the proper hard line was ?too hard?. So while it is true that no one is compelled to build to ANY aerospace standard, it's kind of nice to know the right way to do it before you decide to ignore it, right?

So in finality (I hope), I have no interest in passing judgment publicly, nor do I believe I have the authority to grant permission, and I?m certainly not going to try talk anyone out of a decision if their mind is made up ? but don?t expect accolades for taking the easy way out either. Not when 10,000 other RV builders made it through just fine.

I will continue to provide the best information I can, and I will also fully support anyone?s right to completely ignore it.
 
Toobuilder said:
In this particular instance I’m compelled to correct the misinformation that flex hose is a direct trade for hard line. It is not. While hose is functional and no less safe, it has some significant downsides compared with hardline. This is not my opinion – this is fact.
Click to expand...

By many standards, "functional and no less safe" indeed does mean that one would be a suitable direct replacement for the other. What has not been mentioned here, speaking of misinformation, is that flex hose also has some significant upsides compared with hardline. Both are specified for use in different applications. Each is superior to the other for certain uses.

Toobuilder said:
And I would be shocked to hear from an aero engineer who disagreed. I know for a fact that my Chief Engineer would throw someone out of his office who proposed using flex hose here because fabrication or installation of the proper hard line was “too hard”. So while it is true that no one is compelled to build to ANY aerospace standard, it's kind of nice to know the right way to do it before you decide to ignore it, right?
Click to expand...

Perhaps your Chief Engineer is unfamiliar with the concept of Design for Manufacturing? Sometimes ease of installation and repeatability are desirable even at the expense of weight and materials cost. Also, please post a reference to the aerospace standard (any published FAA or other CAA guidance, or released specification by any manufacturer of any type-certified aircraft will do) calling out 3003-O soft aluminum tubing for fuel conveyance, anywhere on the airframe. I doubt you will find one, which means that a cadre of aerospace engineers spanning multiple decades actually DO disagree.
 
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krw5927 said:
Also, please post a reference to the aerospace standard (any published FAA or other CAA guidance, or released specification by any manufacturer of any type-certified aircraft will do) calling out 3003-O soft aluminum tubing for fuel conveyance, anywhere on the airframe. I doubt you will find one, which means that a cadre of aerospace engineers spanning multiple decades actually DO disagree.
Click to expand...

There are a lot of other things we would have to apply to this standard as well, because not everything in an RV is designed per FAR 23 of other standards documents.
Does that automatically make all of those things unsafe? Not at all.
FAA documents are full of requirements that have always been followed because..... they have always been followed.
 
Toobuilder said:
but don’t expect accolades for taking the easy way out either. Not when 10,000 other RV builders made it through just fine.
Click to expand...

Your responses have gone from saving weight to judging that a decision other than the one you've recommended is the "easy way out" as if there's a lack of quality in workmanship in a decision process that may involve efficiency of effort , in which case perhaps we should all go back to the pre pre-punched days of the kits. That's silly. It's also Hubris 101.

If there's one constant over the years of RV building, it's that there's always someone -- from the original RV List, the old Yahoogroup, to the VAF -- who posits to speak for 10,000 RV builders as an evangelical of the proper way to build an RV airplane in the manner of redemptive suffering. Old-timers all know the names, very few of whom are ever heard from anymore, oddly enough.

Let's move along.

Should I use primer?
 
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I just wanted to make a quick comment on this thread after speaking with Tom earlier.

First off, it is true that flex lines are heavier than rigid tubing. The question is how much. I will use an RV-12 crossover hose kit that was jointly developed by Aircraft Specialty and TS Flightlines. There are a total of 6 braided stainless lines as well as all the AN fittings to change over to our system.

wpbddeea6f_06.png


This hose kit weighs 1lb 5 oz complete including AN fittings. It does not take into account the fittings/plastic tubing that is not utilized if you install this kit. So, my guess is that it is probably about a 1lb weight gain or perhaps slightly over versus the stock components. This is just for illustrative purposes. The advantages are that you end up with brake hoses that will last for the life of the aircraft, have a 10 year guarantee on them, and require no fabrication.

The disadvantage is that it is an aftermarket component that has a cost associated with it, and there is a small net weight gain.

Another topic that has been brought up in the past is the issue of life limits of flex hoses. The hoses that Tom and I use are only the highest quality teflon/conductive teflon hoses. These hoses have no defined service life and as long as they are not abused should be flying on your aircraft long after you are no longer flying it. In addition, we utilize stainless fittings throughout, rather than lesser quality fittings that may be a different material with a stainless coating over the top. This ensures that both the fittings and the hose are matched from the standpoint of a long service life.

Regarding the rigid tube discussion. Rigid tubes are intriguing because fabrication techniques and enjoyment vary from builder to builder. Some people thoroughly enjoy it while others absolutely hate the rigid tube portion of aircraft. That's one of the reasons we decided to begin fabrication of rigid tubes for select aircraft. Tom and I have a computerized tubing bender as well as a CNC lathe which has allowed us to start bringing new products to market. And, we are able to utilize 5052, 6061 and stainless tubing, depending on the application. These have better properties than 3003 from the standpoint of strength. The other day I took one of our 5052 thin wall rigid tubes to about 4,000 psi for the fun of it and held it there for a few minutes. Below is an example of an Rv-14 valve to wing root hose that is pre bent, flared and ready to drop in.

RV14150123-181120-152p.jpg


In addition, we can utilize the cnc lathe and bender to build custom rigid/flex assemblies where it is the best option. An example is this picture which shows a custom assembly with a rigid section at the andair valve that transitions to a flex hose to go out to the wing root.

http://aircraftspecialty.com/wpimages/wpde9bc9fe_05_06.jpg

By having the capability to do rigid and flex hosing, Tom and I are able to offer solutions for those builders who really do not enjoy the fabrication of these lines and would like to focus their energy on other things.

With that said...everything we do can be done ala carte, to allow our customers the choice of fabricating what they enjoy, and allowing us to assist in the rest.

Happy Building, and thank you all for your support.
Steve
 
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Aircraft Specialty said:
This hose kit weighs 1lb 5 oz complete including AN fittings. It does not take into account the fittings/plastic tubing that is not utilized if you install this kit. So, my guess is that it is probably about a 1lb weight gain or perhaps slightly over versus the stock components. This is just for illustrative purposes.
Click to expand...

Steve,

Thank you for providing some real data.

Greg
 
LettersFromFlyoverCountry said:
Your responses have gone from saving weight to judging that a decision other than the one you've recommended is the "easy way out".
Click to expand...

Nope, you opened that door. See below.

LettersFromFlyoverCountry said:
...I HATED running and bending that tubing when I built this thing and I'm looking for an easier way to replace that line...
Click to expand...

...but the "too hard" sentiment is very typical of these flex hose threads. It is very reasonable to draw the conclusion that ease of installation is a compelling factor in this choice.

LettersFromFlyoverCountry said:
... If there's one constant over the years of RV building, it's that there's always someone -- from the original RV List, the old Yahoogroup, to the VAF -- who posits to speak for 10,000 RV builders as an evangelical of the proper way to build an RV airplane...
Click to expand...

I'll not speak for any other builder, but I certainly will use the overwhelming data that the RV fleet represents.

I guess the bottom line here is that you had your mind made up before you even asked the question. So the only additional advice I can give you is don't ask the question on a public forum if you are afraid of the answer.
 
As I said, I work for a living and cost matters and I haven't talked to Tom yet, so I really haven't decided what to do. I really Don't think your considerable expertise extends to what I'm thinking or what I've decided or even how many fingers I'm holding up right now.

Let's move on and if you Don't mind I'd like to continue conversing with some of the people supplying useful data now. It's really interesting what they're providing and I'm anxious to hear more from them.

Thank you for your insight you've shared thusfar and I believe you have made it clear.

Thanks for understanding.
 
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Happy to help Bob.

Next time I'm up your way and have a spare 30 minutes I'll build a set of lines for you.

Cheers
 
airguy said:
Truth - I took a couple stabs at it and called Tom Swearingen. I don't need the aggravation.
Click to expand...

I did the same thing Greg! I own two expensive flare tools that are almost new, and will never be used by me again!

Thanks Tom for the great lines. I need a couple more so I will be getting with you shortly.
 
Well since I too have a vested interest in this thread, with your permission I'd like to comment.

YES ---we build alot of teflon hoses. Started out with engine hoses, mainly to replace the old and heavy 303 series Aeroquip hoses. At one time, the factory was selling components for fabricating 701 hose. After seeing some pictures on this forum of some of the assemblies (how about stems BARELY screwed into the collar because it was 'too hard"), I felt that I might be able to offer some assistance to those builders that enjoyed the process, but felt that they would rather not make their own assemblies.

Builders then began to ask about brake hoses, and the possibility of replacing their aluminum tubing with teflon hoses. Certainly, was the answer. I think we all can agree that in alot of areas, rigid tubing is infact a better option than teflon, especialy where bends are concerned. You can bend a piece of 3003, or 5052O alot tighter than a comparable teflon hose. Just because we build hoses, doesnt mean that we dont use rigid tubing also. The fuel line package for the RV14 is a great example. Yeah, we could have used hose for the valve to wing lines, but after playing with it for a while we decided that YES, aluminum tubing was probably a better product for this application. Yes, a builder can make his own, thanks to some very good plans. We chose to make ours from 5052O instead of 3003, for strength and appearance.

This does bring up a point on the 'other' RV models and tubing versus teflon. I would imagine that if the plans showed a specific pattern of the tube to be bent, many builders would or could do it. Some, however, choose to accomplish the same thing a different way, by using hose.
Tom
 
My parents were born and raised in Theif River, so consequently I spent many a Christmas back there. Though it has been many years, I vividly remember that particular brand of cold. No thanks. I'll hold of until Summer and take my chances with the mosquitos.
 
pristine aluminum fuel tubes, Not dents and scratches

What about the dents, scratches, kinks in the rigid aluminum tubes due to less then perfect bending?

I made two ship sets of aluminum fuel lines for my RV-7A and each time saw scratches or a dang kink that I worried would be a stress concentration and potential failure point.

I think I read in the plans, "don't kink them." So I went with flexible fuel hose from valve to wing. I would have preferred the stiff aluminum but only if I could do it pristine, without any flaws.
 
sglynn said:
What about the dents, scratches, kinks in the rigid aluminum tubes due to less then perfect bending?

I made two ship sets of aluminum fuel lines for my RV-7A and each time saw scratches or a dang kink that I worried would be a stress concentration and potential failure point.

I think I read in the plans, "don't kink them." So I went with flexible fuel hose from valve to wing. I would have preferred the stiff aluminum but only if I could do it pristine, without any flaws.
Click to expand...

I don't have a good answer, but I did not accept any kinks, dents, or creases on mine. I recently changed all of my hoses due to life limits to TS Flightlines Teflon (thanks again Tom).
However, I went back and replaced my main fuel line hoses from the tanks to the fuel selector with 5052 hard line. My reasoning, as dumb as this may sound, was to challenge myself. I am much better at bending tubing now than I was when I built the airplane more than ten years ago. It still took me more than one attempt. One was perfect, except as I was installing it I notice a minor crease and rejected it.
So, I now have hard lines and I am glad I went through the exercise for no other reason than I am proud of the accomplishment.
24dq89e.jpg
 
Return lines

A little off topic but I see several builder logs show a return line to the tanks. Did I miss something? I built mine with only one main line out and a vent line. :confused:
 
Some injected systems need a return line, others don't.
Carbed engines don't.
Building my 7, I made provision for return lines but ended going with Precision Airmotive's RSA5 servo, so didn't need them.
 
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