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Fuel line bending

LettersFromFlyoverCountry

Well Known Member
It never fails that every year on the day the Lindy Award winners are announced, I go back to the hangar to redo something on whatever plane I'm building that I might have been generally dissatisfied with.

This year it was the fuel tank. I had used EZ Turn on fitting threads (which we used to do and consider it acceptable) and I wanted to fix that. And I did, replacing it with Permatex 2.

But in reinstalling it, I badly nicked the fuel line when trying to get a crowsfoot on the fuel line fitting at the tank. So I pulled it off, ordered new tubing and tried to remember how the heck I made that line in the first place.

Here's why.

PXL_20210801_191050185.jpg


The instructions say:
1. Flare the tank end of the tube.
2. Make the bend
3. Install the nut and sleeve from the pump end of the tube.

The problem is you can't (at least *I*) can't slip a sleeve over a 38 degree bend. And yet somehow I made this line two years ago. I just can't remember what I did. (Yes, I know the sleeve is on backwards in the above photo)

Putting the collar on first and then making the bend seems problematic as the end of the bend line is 21/32" from the end of the tube.

Maybe I put the collar on, made the bend, and THEN flared the tube. I don't know.

What's the secret here?
 
I think you may need to do the flare first then the bend. If you try to do it the other way around you will need the length of the sleeve plus the thickness of your flaring tool to be less than you 21/32" dimension. I don't think that will work. Some folks have modified a bender tool to allow the flare to be positioned back into the bender. Tom had this as a recommendation some years back. This can help getting short bend distances.
 
Just me

I would take the straight tube, put the B nut and collar on, flare it.
Then put it on a union, and hand bend the curve, gently
 
You can shorten the sleeve

I have seen where the sleeve has been cut back with dremel wheel cutoff disc so a minimum is showing outside the BNut. That shortened length allows slipping over curves that would not otherwise be possible. If you have an extra sleeve, give it a try. Otherwise I would do what John recommended and hand bend it last.
 
I have seen where the sleeve has been cut back with dremel wheel cutoff disc so a minimum is showing outside the BNut. That shortened length allows slipping over curves that would not otherwise be possible. If you have an extra sleeve, give it a try. Otherwise I would do what John recommended and hand bend it last.

This is what I did, except I still put the sleeve on before bending - I just trimmed it so that the tube could slide further into the bender. (I can't recall if I thought to try sliding the shortened sleeve around the bend, but if that works it would definitely be easier.) I then inserted a properly sized drill into the end of the tubing to act as an extension. These two steps allowed me to get the bend as close to the end of the tube as possible, ultimately matching the drawing. I obsessed way to much over this one bend.
 
This is not an answer to your question, but what do you mean when you say the sleeve is on backwards in the picture?

It looks like the normal orientation to me.

I also don't follow your comment about using permatex on flared fitting threads. I am not familiar with the -12 fuel tank, so it may be that you are referring to a different fitting than the rest of your post.

Thanks for helping me understand.
 
I also don't follow your comment about using permatex on flared fitting threads. I am not familiar with the -12 fuel tank, so it may be that you are referring to a different fitting than the rest of your post.

I'm starting this section in the next few days and this threw me back into a loop of doubt too.
 
The fitting to which this line attaches.

The NPT threads of the fitting into the tank. Not the threads to which the B nut attaches.

Section 5.27.
 
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HI Bob--
Flare the tubing as normal. For short runs before the bend, I trim the sleeve so it just exits the nut. OR you can do this----do the same procedure with a standard sleeve and reverse the bending operation---instead of having the nut and sleeve against the bender fulcrum, put the long side of the tube there, and bend. Gee---3003 tubing is soft enough that you can bend it with your fingers.

YES I have a couple of modified hand benders that I made that work well, but you can do the same thing with out them.

Tom
 
Unfortunately I'm going broke on tubing. I can't get the start of the bend in the proper location at the tank end even when bending from the other side because the sleeve interferes. That messes up the dimensions at the other end. If you're off even by a fraction, you're screwed.

It's true I can bend it with my fingers, but not at the points called out.
 
I just completed the fuel lines on my project. I had ordered extra tubing ahead of time just in case, and it turns out that I won't need it. It should be here by now, but isn't. I even ordered extra flare fittings just to have around the hangar. I just like having extra stuff around.

That line took me a few tries but I'm confident now I could get another one made up since it's fresh experience for me.

If you don't have this solved by the time my shipment shows up I'll be glad to make one up and send it your way. If that's where we end up, just send me replacement nuts and sleeves.
 
Unfortunately I'm going broke on tubing. I can't get the start of the bend in the proper location at the tank end even when bending from the other side because the sleeve interferes. That messes up the dimensions at the other end. If you're off even by a fraction, you're screwed.

It's true I can bend it with my fingers, but not at the points called out.

Hi Bob - I'd like to attach 3 photos of how I did this without cutting or modifying the sleeve, but I haven't yet done the photo link thing.

I think I may have run into the same problem, if so, just cut a short piece (6" or so) of 1/2" copper plumbing line, secure it vertically in your bench vise, insert the aluminum tube with the sleeve installed against the flair and SLOWLY and carefully bend to shape. Try a combination of using the palm of your hand to make incremental bends, or try very small bends using a grip further out on the tube (longer lever gives more force)- when you think you're getting close, just slip the tube out of the copper to check it against the plans. Rinse and repeat until you have the right angle.

A few important tips: 1) My photos would show Sharpie marks on the aluminum tube delineating the start and the end of bend radius. 2) I also put a few small slivers of pine at the inside edge of the copper tube to ensure no creases to the aluminum tube.

If you are feeling you want to hand it off, send me a PM, drive over and we'll git er done. I'm just a few miles East of KFCM.
 
Something I’ve done to help make a bend close to the flare is this: flare the tubing, install the sleeve and B-nut, then attach a spare fitting, preferably a straight bulkhead fitting because it’s a little longer. Make the B-nut tight. Then use the bulkhead fitting in your hand to provide leverage to make the bend by hand close to the B-nut and sleeve. It may work for you too.
 
Something I’ve done to help make a bend close to the flare is this: flare the tubing, install the sleeve and B-nut, then attach a spare fitting, preferably a straight bulkhead fitting because it’s a little longer. Make the B-nut tight. Then use the bulkhead fitting in your hand to provide leverage to make the bend by hand close to the B-nut and sleeve. It may work for you too.

Very good tip.
I have done this many times.
 
I'm at this same stage and trying to figure out how to make this part. Lots of great tips above, so I'll start by trying the hand bending technique (with a bulkhead fitting attached to the flare for leverage).

But first I have a simple newbie question: is it really important to have this bend so close to the flare? Since there seems to be plenty of room in the center fuselage channel where this line runs, why can't you just move the bend downline another ~3/4" to make bending and flaring easy (i.e., lengthen the straight part of the line at the tank), and then adjust the subsequent angle as necessary to get the line to mate up properly with the drain valve fitting at the back? Am I missing something?

Steve
 
Sequence...

Collars and bends are incompatible. You can slide the nut on without fear however...

1. Cut tube longer than necessary (1/2" or so.)
2. Bend tube at the right places
3. Cut tube to correct length
4. Install nut
5. Install collar
6. Flare tube end

YMMV of course.

This is what worked for me getting the Andair FS7 valve to fit in the center section of the RV-7 along with all the Airflow performance pump plumbing.
 
Thanks, Brian. That method works if there's enough tube length remaining for the flaring tool, but in this particular case there isn't. My Roto-Flare requires 3/4" of tubing to fit into and past the die, and after you add the 1/2" collar behind it the minimum tube length you can flare is 1.25". But the plans here call for a bend ending just 3/4" from the flare.

That's why I asked if I can just move that bend a bit and then adjust the angles after that to get the tube to still mate up properly at the other end. Just seems easier than struggling with this one difficult bend.

I just tried some of the tips above on some scrap and am still struggling with this. Bending the tube by hand works but leaves the tube flattened and the curve uneven. Using a tube bender (both with the flared end/coupler under the tube holder and the long end under the tube holder) ended up damaging the flare due to the pressure applied on the edges. Perhaps with a bit more practice I can get the hand bending option to work acceptably...
 
Yes, just did an hour ago and that did the trick. Was able to make the piece match the plans without significant flattening of the tube by using the bending spring. Problem solved! Thanks for the tips, everyone.
 
Steven, are you building a 12 or 12iS? If it's a 12iS, which piece of tubing did you use the bending springs on?

Thanks,
 
Unanswered question

I'm at this same stage and trying to figure out how to make this part. Lots of great tips above, so I'll start by trying the hand bending technique (with a bulkhead fitting attached to the flare for leverage).

But first I have a simple newbie question: is it really important to have this bend so close to the flare? Since there seems to be plenty of room in the center fuselage channel where this line runs, why can't you just move the bend downline another ~3/4" to make bending and flaring easy (i.e., lengthen the straight part of the line at the tank), and then adjust the subsequent angle as necessary to get the line to mate up properly with the drain valve fitting at the back? Am I missing something?

Steve

I am starting to bend the first fuel line (F-12127K) on my 12iS and having the common problem listed on this thread. I would like to re-submit JETSET44's question in the quote above "...is it really important to have this bend so close to the flare?" His posting makes sense, however, never received a response.
 
I thought I'd share how I successfully made this bend. I tend to do things the hard way so I bought a cheapo bender and modified it so the flare and sleeve would fit. A 9/32" bit is a very close fit for the I.D. of the tube and I added a little painters tape around the bit to get a snug fit (probably not needed) and cut a short peice of tube to go over the drill bit for a spacer.
I then used a flat peice of metal to push and get the 38 degree bend. Overkill for just one bend but it worked perfectly.

The drill bit method will work great in a regular bender too for bends that are close to the end.
 

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Ive posted pics of my hand bender several times, but for some new members, I'll post them again. I made this probably 10 years ago to solve the issue of getting the bend close to the flare. ( For our production tubes, we have a CNC 3 axis bender).
Basically, I cut a slot at the "0" mark, and relieved it slightly to allow the head of the sleeve to sit flush. I made a mandrel on the lathe to insert into the tube, to support it against the fulcrum post for leverage during bending. Yep, different OD's for different wall thickness ( smaller ID) tubes, of .035, .049, and .065.
The trick is to NOT insert the mandrel past the bent point, and as you are bending, extract it slowly. That way the end of the mandrel isnt pressed hard into the ID of the tube, creating a 'bump' or a blister on the tube OD. That takes patience and practice to do, but it works well. Now granted, some of what I was bending was 5052O and 6061T6, so much stronger than the 3003O provided in the kits, so some greater bending effort was needed.

Other option is to install the sleeve after the bend. MUST shorten the sleeve tail to allow it to pass over the bends, but is stil takes some persuasion.

I still use this for some concept prototype stuff-the production is all done on the CNC bender (http://aircraftspecialty.com/howwemake.html)

Tom
 

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