Flexible fuel lines to wing?
 

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.)

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...

Hmmm, I wonder which disposable body part weighs 15 lb? :eek:

Bevan

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