"Fuselage to tank" fuel line lengths?

here is how I ran my fuel lines in a 7A

Running the fuel lines from the fuel selector to the wing roots is a pain in the A models because of the landing gear weldments. One method that worked for me was to use a piece of clear nylon hose with an inside diameter slightly larger than the outside diameter of the aluminum tubing. I put a few drops of tool oil in the nylon tubing and ran it from the hole in the brace next to the fuel selector, through the weldment and out the hole in the fuselage. I then put a slight curve in the aluminum tubing and pushed it through the hose from the selector side until it exited out the fuselage. The hose did a nice job of bending the tubing through the weldment. I then slide the hose off the tubing from outside the fuselage. I did both sides in 30 minutes....

fuel lines

Tonny
I just finished mine on an RV9A. I initially left about 5 inches sticking out of the fuselage. I mounted the wings first with the fuel tanks off. I was then able to get an approximate measurement by placing the fuel tank above its mounting location on the wing, you can get a tank to fuselage distance and cut off the tubing a little longer than needed. I then mounted the tanks and bent the tubes slightly out of place with the AN fittings and marked my final cut to match up perfectly with the fitting. Remember you should be able to gain a little by pulling the tube out a little if needed. Cut long and work down to the right length. Good luck
Oldgeezer
RV9A finishing

On my 7A, the fuel line length between the side skin and the tip of the flare was (is) 3 5/8".

tubing kinks. Do kinks ruin a fuel line tube run

What if you get a slight kink in the fuel line tubing? Is that bad? I made a nice run from valve to outside of fuselage but then when I went to bend it slightly at the valve end with my hand and pliers I made a slight kink in the tubing. Dang it. Does a kink or two ruin the whole tubing run?

thanks

No Kinks Allowed.

Besides restricting the flow, a kink weakens the line.
A kink in a fuel line is similar to a scribe line on sheet metal.
Over time it will crack with vibration.

photo of kinks

Are these kinks no good? Or are they scratches that can fly. See third photo on this page.

sglynn said:

Are these kinks no good? Or are they scratches that can fly. See third photo on this page.

Click to expand...

They might work for a long time. Maybe not.
Personally, I wouldn't want them. It's too easy to make new ones without the "scars". Fuel lines in the cockpit is no place for "marginal".

Replace!

I am with Mell on this! That looks bad.

As the starter of this thread, I never received an answer regarding the length of the tubes and gues what? my "guestimated" return line lengths were not correct. So I just orderded a 2' length of tube from Vans for $ 3,48 yesterday.

I would buy new and replace it! Do you realy want to risk getting burned allive, to save as litle as that?

Regards, Tonny.

sglynn said:

Are these kinks no good? Or are they scratches that can fly. See third photo on this page.

Click to expand...

I see scars, not kinks.

Ask yourself, would I want to take off with my loved one over a highly populated area with a know defect in my fuel line?

That being said, if you use a magnifying glass on anything you probably will lose sleep. The tubing is soft aluminum and does get lots of knicks and dings and hold up just fine. Yours seem just a little deep and near the bend which makes it more critical. Plus at this stage of the game, it's just easy to replace it for the sake of piece of mind. You have a nice template to use to bend a new piece. It'll only take 5 minutes to fab a new one (then another 5 when you realize you forgot to put the B nut on, (if you are me). Then 3 hours trying to get the nuts started.

If the plans are bad ...

If compliance with the drawings are causing you to incorporate defects into your airplane, think about a different way of installing the fuel lines. The installation in my RV-6A is totally different than the "suggested" installation by Van's and there are no kinks or system function or performance problems in nearly 6 years of cruise and racing flight operations. A very significant part of building these airplanes is thinking through the problems of manufacturing and future operations. Obviously you are aware that the condition of your fuel lines is not right or you wouldn't make the post. You are listening to what your mind is telling you - solve the problem before pressing on.

Added note: Sometimes the problem is the design, sometimes it is the tools and sometimes it is the process. You need a good tube bender to get nice precise termination alignment and smooth bends between. As far as the process is concerned, you need to know how the bends need to be made before picking up your flight hardware and starting to bend it. I used coat hanger wire to mock up the tubing runs then used the model to determine the bends necessary on the tubing. Just like wiring, the product is very pleasing to the eye if done correctly.

Bob Axsom

I have worked in aviation with the addage "where there is doubt, there is no doubt". Clearly you have doubts as you have posted here. Take the advice posted here, remove the doubt and then build on with peace of mind.

Regards Bob
www.rv-8.co.uk

Hi all,

I have thought about using the elbow bulkhead fitting for the vent outlets instead of the modified straight bulkhead fitting supplied. Should look a bit tidier and be a bit less unaerodynamic.

FWIW

I gave Brett from Bonaco (909) 985-3429, a call and had my lines built from braided SS hose. No muss and no fuss; they made the gear leg transition with no problems. He had the lengths already for my 7A. I did the same thing with the brake lines.

braided fuel lines

Please, Do you have a photo of the braided fuel lines installation? thanks

So no one has answered the original question. How long does the tubing need to be hanging out of the side of the fuselage to meet the tank?

I took some measurements on my 9A and it looks like 2.5" for the fuel line and a bit longer than that for the vent lines (1/4" line fittings are not as long as the 3/8" fittings).

I'd like to cut these to the proper length in order to be able to fit the wings.

Bruce,
Will this thread help?

bruceh said:

So no one has answered the original question. How long does the tubing need to be hanging out of the side of the fuselage to meet the tank?

I'd like to cut these to the proper length in order to be able to fit the wings.

Click to expand...

Bruce, I know it's probably different for a 9A, but here are the measurements for a 7A. Mine are exactly 3-5/8" long. Perhaps this will help someone.

You can always do it the way I did mine if you don't get an answer. Just leave them plenty long and curve them gently downward before you mate the wings, so they're out of the way. Then you can measure and cut to length after the wings are pulled off.

I did find several threads with the measurements all indicating about 2.5" for the fuel line and around 2.625" inches for the vent line on the RV-9A. Nothing definitive (a picture with a ruler would be nice). Van's doesn't seem to call out the length either. Looks like there is sufficient wiggle room for the lines to be moved around as needed to mate up with the fitting on the tanks. The vent line has a lot more give on the length.

Getting the fuel lines through the landing gear weldments takes some major persuasion. My fingers and arms are still sore! I don't want to cut them off too short and have to suffer through that again.