Double vs. Single Flares

[szicree]

I'm beginning to sort out my fuel system and am thoroughly confused about whether I need to double flare the fittings. I've heard and read what seems to be a lot of contradictory advice on the issue and am hoping to get it resolved. What say ye, oh wise rv-ators?

Also, I haven't decided for sure whether I'll have a carb, Ellison, or injectors. What can I get done now, and what has to wait? Thanks.

[tacchi88]

According to the "bible" AC43-1a-2b, double flares are required for soft metal tubing, copper, aluminum from 1/8" to 3/8" tubing, The reson given is to prevent cracking of the tubing near the flared portion which meet the fitting. Not bad advice to follow. My own of those sizes mentioned are all double flared.
See AC43.231B Ch 9-30 and AC65-9a Ch.4.
T88
RV10

[tonyjohnson]

At the risk of sounding way behind the power curve...can you explain the double flare as opposed to a single flare? I am just about to start the plumbing phase of my project and have not yet gotten up to speed on those issues.


Thanks,

Tony

[Captain Avgas]

Originally Posted by tonyjohnson

At the risk of sounding way behind the power curve...can you explain the double flare as opposed to a single flare? I am just about to start the plumbing phase of my project and have not yet gotten up to speed on those issues.


Thanks,

Tony

Take a look at this. http://www.phi-tulip.com/images/flaredr.gif

[Bob Axsom]

There are no double flares or leaks in my airplane. I have never seen one and I cannot imagine a substantive advantage of such an application in an RV.

Bob Axsom

[rv6builder48138]

Any suggestions from anyone on a source for a reasonably-priced double-flare tool? The one that I looked at was rather...um...expensive...it's been a while since I looked, but if I remember correctly it was three figures.

[robertahegy]

I have the usual low pressure carby system, boost pump and engine pump, all low pressure (under 8 psi). Like Bob, I have no double flares either and no leaks. A good flaring tool and good cleaning and finishing is all that is needed for this system. I used a Parker Rolo-Flare.

Roberta

[avpro56]

Originally Posted by szicree

I'm beginning to sort out my fuel system and am thoroughly confused about whether I need to double flare the fittings. I've heard and read what seems to be a lot of contradictory advice on the issue and am hoping to get it resolved. What say ye, oh wise rv-ators?

Also, I haven't decided for sure whether I'll have a carb, Ellison, or injectors. What can I get done now, and what has to wait? Thanks.

Steve:

It all depends upon how tight you torque the B nuts on your aircraft plumbing. It's very easy to work harden the soft aluminum tubing by overtightening single flares; and that's very easy to do. Double flares are more durable, resist cracking and are technically the correct way to flare tubing as per AC 43.13. Very few builders bother with double lap flares, and most get away without doing them. This seems to justify not buying the expensive tool. All the same, the double lap flare is superior in durability and sealing when compared to single flares.

The Double Lap Flaring Tool is expensive, so it's a good EAA chapter tool, or you can borrow one from any good maintenance shop. After you make a few double lap flares you'll be impressed with the quality of the flare.

I'm in Bayport, NY and if you're local I'll be happy to loan you my Double Lap Flaring Tool and teach you how to use it.

Anyway, my 02c.

Jon Ross
RV-8 N207RV
A&P IA
EAA Technical Counselor

[osxuser]

Well yeah, but doublt flares are only correct for small diameter tubing, single flares are still appropriate for larger tubing (-4 and larger I believe). It could be cheaper just to put hoses in anything that is -3 or smaller instead of buying the double-flare tool.