What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Where to Learn About Fuel Line bending and Fitting

Saville

Well Known Member
Is there a document or web page(s) that describes how to cut fuel line tubing so that once the bends and flares are made the ends line up and the length is correct?

For example:

I have to create an L-shaped fuel tube to go from the bottom of an Andair fuel selector to a pre-existing fuel line with an AN fitting. I can't use the one that exists because I'm moving the selector forward. So after flaring the selector end and putting in the 90 degree bend, I need to cut the tube to length so that AFTER flaring, it fits snugly against the existing AN fitting.

So I need to know how much to allow for the flare when I cut the tubing.

I realize a lot of this comes down to practice. But I've found that there is often a lot of lore and help that can be absorbed before starting. I've been through the chapter on Fluid Lines and Fittings in the Aviation Maintenance Technician Handbook but there wasn't much there. Also reviewed Section 5.

Thanks!
 
Youtube

Try a youtube search, there's probably some video explanations there. There might be something on the EAA website too, I'm just not sure. Otherwise, it's a bit of trial and error by flaring and bending a piece so it's snug at one end (the selector end probably best), then lay out the tubing across the fitting you're going to connect to, mark, cut & flare.
 
Try a youtube search, there's probably some video explanations there. There might be something on the EAA website too, I'm just not sure. Otherwise, it's a bit of trial and error by flaring and bending a piece so it's snug at one end (the selector end probably best), then lay out the tubing across the fitting you're going to connect to, mark, cut & flare.

Checked Youtube and ther EAA website already.
Thanks
 
Radius & fitting allowances will vary dependant on what bending & flaring tools you end up using. Best suggestion is allow for some repeat rounds and extra tubing to 'practice' with till you come up with an acceptable fit. A roll of tubing from ACS is cheap, and after the project is done, comes in handy for so many other jobs.
 
You can always cut a 2" length of line, perhaps, put a flare on it and see what its finished length is. Then you'll know.

Dave
 
Tube bending

I have some experience and still had to make some lines several times to get this right. Finished up with a small pile of scrap tubing for other projects. Good suggestion to take a known length of tubing, flare one end and measure again to determine how much length the flare will use up. Sometimes a mockup can be helpful. For this I like to use 3/8? OD clear vinyl tubing with a length of insulated copper house wire inserted inside. It?s easily bendable, holds its shape, is about the same OD as -6 size tubing. Mark bend locations with a sharpie right on the tubing.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
AT0-035X3/8 ?

According to Section 5, Vans suggests 3003 Soft Aluminum tubing for fuel lines.

I take it that it's 3/8" OD and part number AT0-035X3/8? (the only difference in the 4 options being the length). Wall thickness .035 if I'm reading this correctly.


I was told by one A&P that he uses 5052.


Any opinions on 3003 vs 5052?

Thanks
 
Flares

It important to learn flares but Tom @ TS Flightlines makes some really nice fuel lines.
 
Id guess the flare shortens the tube about 1/8 inch.

Estimate how much you need, cut it slightly too long and flare one side. Bend as needed and install the flared side with a fuel fitting. Now you can see exactly where to cut/flare it at the opposite end. Unless it's a very short line there is usually enough play in the lines to be slightly off. Error on the side of slightly too long, then you can cut/reflare it. Good luck !
 
Last edited:
You might already know that automotive flares are 45 deg and JIC/aircraft flares are 37 deg. Therefore you cannot use the flaring tools from HF.
 
You might already know that automotive flares are 45 deg and JIC/aircraft flares are 37 deg. Therefore you cannot use the flaring tools from HF.

I do already know that and I own an aircraft flaring tool (Rolo)

Doesn't hurt to mention it though.

Thanks
 
When it comes to bending 90 deg, my bending tool came with very explicit instructions for initial length vs final (up-right) lengths. Or, you could do the math.
 
When it comes to bending 90 deg, my bending tool came with very explicit instructions for initial length vs final (up-right) lengths. Or, you could do the math.

I have read that even with quality bending tools there can be a slight flattening of the tubing. And there has to be some stretching I would think. I would think that trying to get an accurate value by math would be difficult. But maybe I'm wrong.
 
My observation is that the outside radius does have a small amount of stretching/flatening. But the inside radius is slightly compressed/flattened as well. They seem to average out!
 
Gregg---alot of this is just practice, and knowing what your equipment does. Not a rule of thumb, but a pretty good quide is to cut your tube +- .180 long. That will allow you to square the end of the tube, and flare it with a +- .090 .
Take a piece of scrap tube that you have and bend it to the desired shape and flare one side so it will fit. See how much too long it is on the other side, and know what your flare bar will do, give yourself +- .090 for the flare. Should end up being pretty close.
Different tube benders with different radius will yield a different tube cut length.

Tom
 
humble

Very humble advice Tom.

Only advice I can give you is at least consider TS Flightlines. You'll NEVER have a leak - especially brake lines. I've used TS on my last 2 RVs solely - not a hard line in the plane. AN4 lines aren't too bad and you can muscle then in place if you have to but I can assure you a pretty AN6 line that requires a couple 180 bends is varsity.

If you're set on hard lines I use a copper tube (very thin) or thick soder that I can bend anywhere. You can actually insert it into the fitting and make marks where you want the flares to end up. Then try and replicate it on the bench with a tube bender.

By the time you do all that, redo it, swear, redo it again the TS lines will be on your doorstep.
 
https://bearhawkforums.com/forum/to...practices/32690-fuel-line-fabrication-pattern

This thread on another forum shows how to make a pattern for fuel line. People with no experience are making fuel lines with 6 bends that fit the first time without doing a trial and error mayhem.

Every bend has three dimensions. A distance, a clocking, and an angle. You must fabricate and quantify those three dimensions before doing it for real.

Brooks
 
Last edited:
I think you just need to jump in and start practicing flaring. Start with your roll of tubing and start learning how to do the flare. Get a magnifier that you can inspect the flare afterwards. Some say that should be 10x. I have a big magnifier lamp that I inspect mine with. Look for cracks or scoring.

I found a nice set of instructions for flaring on the General Aircraft Hardware site.
https://www.gen-aircraft-hardware.com/Flaring_Stainless_Steel_Tubing.asp
It uses a rigid flaring tool on stainless tubing but most of the tubing prep steps are still applicable.

The bending tools are easy to use once you figure out the L and R marks on the tool. Put a little grease on area where the tube is formed around and it?s pretty simple.

I work from one end. Make the flare. If your screw it up cut it off and redo. Once you have a good flare then measure to the first bend. Mark the tubing make the bend. Check the length is correct. Measure to the next bend and work toward the other end. This is a good way to practice too. You will mess up plenting of tubing at least I did.
 
Hi Gregg,

You already have a Rolo so that means you are going to do tubing. I used a tubing bender from HF.... https://www.harborfreight.com/tubing-bender-3755.html?_br_psugg_q=tube+bender you will need to make some bends and waste some tubing and file and sand the rough edges till you can bend a 90 without any marks on the tubing. Applying electric tape in drag locations really helps.

As far as flairs, I found that a flair DOES NOT change the finished length by any significant amount. You can check this yourself.

An easy way to make up lines that fit is to make some parts that will help you. First, take a measured piece of tubing that will fit in your Rolo to flair. Measure it, flair it and measure it again. Do this with a 90 and 45 also. Understand where your bend starts and ends.

A few marks on these bends will tell you how much tubing you are using to make that bend. Mark a start point where it will match the mark on your bender. Make a mark every 1/8 inch the full distance of the bend area plus some so you can see what is consumed in a bend.

To help with your mock-up of a line, consider some made up bends, some flairs with known dimensions (say 1 or 2"), some 3/8 wooden dowel (for runs) and some 3/8 ID vinyl tubing cut into small 1/2" sections to connect the dowel, the flairs, and the bends to mock-up the line you want to make. Then just add up the dimensions of each piece and transfer the bend marks to your project tubing. Make up the longest line first so you can continue to cut the dowel to make the rest.

Do buff the lip of your flairs so they clear the threads of the coupling nut and fit the sleeve. Do not over flair (crush) with the Rolo, stop when you feel resistance.
 
According to Section 5, Vans suggests 3003 Soft Aluminum tubing for fuel lines.

I take it that it's 3/8" OD and part number AT0-035X3/8? (the only difference in the 4 options being the length). Wall thickness .035 if I'm reading this correctly.


I was told by one A&P that he uses 5052.


Any opinions on 3003 vs 5052?

Thanks

5052 is much stiffer than 3003. I used 5052 in some places. It has been long enough ago that I don't remember if I used it everywhere or not. 5052 bends are by tool only. 3003 can be done by hand in some cases. I prefered my flair results on 5052 over 3003.
 
You will quickly learn to appreciate Tom and his beautiful products when you retrofit an AFP boost pump and filter into a flying RV-8. I just don't think I could have done the tube bending and fitting required while wedged into the area of the left rudder pedal. With Tom's products, I was able to do it sitting in the seat (filter) or through the front baggage compartment with the floor removed (boost pump).It wasn't simple but it wasn't terrible either. First flight yesterday after install and ground checks and all is perfect. BTW, replaced all FWF hoses at the same time with Tom's integral firesleeve, lifetime teflon molded hoses. Beautiful stuff!
 
You can always cut a 2" length of line, perhaps, put a flare on it and see what its finished length is. Then you'll know.

Dave

+1 this is exactly what I did to learn with my tools. Short length of tube, and flare union . . . . measured both before flaring and after it was assembled using a dial caliper. To make prototype pieces, I used a length of coat hanger and bent to the start and end point. Then used for a gage against the tube being bent.
 
Well, in the production shop we use a CMM scanner to give the profile of an existing tube, OR a drawing that we can make a prototype of. (RV12, RV14 for examples). WE make one, and compare it to one that fits the application. IF it doesnt fit, thene we adjust it so it does, and re-scan it to do a comparison. ONe we have one that is correct, we have the computer software tell us the tube cut lenghts, and where to start bends and what degree and axis to make those bends.
Yes this is mostly for doing production tubes, like the 12 IS and 14 fuel systems, among others. Somewhat way overkill for 1 tube. But knowing some dimensions, we can do the same thing on single piece tubes. But like I said, different bender with different bend radius heads or dies, will give you different length dimensions.

Just practice on some scrap until you find what your bender will give you.

Tom
 
Back
Top