Double vs Single Flare

[szicree]

I'm a little curious about something and am hoping somebody here knows the answer. Everything I've read indicates that up through 3/8 inch tubing is supposed to get a double flare, but all the tool places sell single flaring tools of this size. I know the double flare tools are available also, I'm just wondering why everybody sells a tool that performs an ill-advised operation.

[rv8ch]

I'm also curious about this. I didn't even know a double flare existed until I was just about finished with all my flares. It seemed kind of silly to spend USD 600 on a tool that I would use for two flares. I'll buy one of those tools for my next airplane.

[Captain Avgas]

Originally Posted by szicree

I'm a little curious about something and am hoping somebody here knows the answer. Everything I've read indicates that up through 3/8 inch tubing is supposed to get a double flare, but all the tool places sell single flaring tools of this size. I know the double flare tools are available also, I'm just wondering why everybody sells a tool that performs an ill-advised operation.

The "bible" AC43.13 definitely states that all flares in aluminium tube up to 3/8" should be double flared. This is because it is very easy to overswage the lesser diameter tubes and render the walls too thin. So I was ready to dump down a bag of money and buy a double flaring tool because I always abide by the "bible". However I made a few enquiries and this is what I found:

1. Of the 3 major aircraft service centres at a large local GA airport not one does double flaring of 3/8" tube. In fact none of them even had a double flaring tool.

2. Bob Avery of Avery Tools says there's a possibility of causing cracks at the fold when using a double flare tool on 3/8" tube. He doesn't sell this tool because he says there's no demand for it.

3. It seems that neither Piper nor Cessna use double flares on their 3/8" or 1/4" tubes.

4. Vans did not use double flares on any tubing in any of their factory planes, nor do they even own a double flaring tool.

As a result I have decided to stick with single flares for all tubes on my RV7A.
If any LAMEs out there have any empirical evidence or data to suggest that this would not be good practice please speak up.

[robertahegy]

I bought a Parker Rollo Flair tool from Avery and made all single flairs. The Parker tool makes excellent flairs without over stretching the edges. None of mine ever leaked in over two years so far. Save your money (and time) and buy the Parker tool.

JMHO

Roberta

[szicree]

Great info Bob. That's sorta what I expected. Also, Roberta's right -- that RoloFlair deally is about the most fool-proof tool I own (and I should know).

[LettersFromFlyoverCountry]

I haven't been able to find where 43.15 says all flares should be double flares. Anybody got a section citation?

[Captain Avgas]

Originally Posted by Bob Collins

I haven't been able to find where 43.15 says all flares should be double flares. Anybody got a section citation?

Bob, it's in the Hydraulic section right near the data on Wrench Torques for AN-818 nuts. See Section 9-30 (b) Tube Connections.