LettersFromFlyoverCountry

LettersFromFlyoverCountry

Well Known Member
safe_air.jpg


You probably know that the fitting here is too small for the 1/4" aluminum tube that the plans have you use for your pitot line (at least in an RV-7A). Is there a way to make them play together happily?
 
Bob, a little more info on what you've got there would help, but I'll take a guess that the blue fitting is a AN816-3D (1/8" pipe thread to 3/16" flared tube). If that's the case, then any reason why you can't just swap it out for a AN816-4D (1/8" pipe thread to 1/4" flared tube)?

Anyhow, what are you trying to do? Just curious.
 
There are lots of ways to make that connection (and probably at least as many opinions). I followed Dan Checkoway's lead, using a piece of 1/4" ID silicone hose bought from Aircraft Spruce: http://www.aircraftspruce.com/catalog/appages/siliconehose.php

Another option would be to use an instant tube coupling (the brass fitting in your photo is known in the pneumatics world as an instant tube fitting). For example, McMaster-Carr #51055K129 or similar.
 
roee said:
Anyhow, what are you trying to do? Just curious.
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I want to take the current aluminum tubing that goes to the Pitot tube and get rid of all but about a foot of it. Then I'd like to flare that tube and connect it to the SafeAir kit, and run the tube straight into the fuselage with no breaks at the wing root.

I think this is actually designed for connecting to the Dynon heated pitot tube, which must use a smaller diameter tube. You can see how the SafeAir instructions show the connection here.

What would be ideal is if there were some sort of AN fitting like the above that goes from a -4 flare end to a -3. But I didn't see anything like that when I browsed through the Aircraft Spruce catalog.

I was just reading Stein's article in Kitplanes on static/pitot connections and he notes that this connection is where most pitot errors occur. I can see why.
 
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Bob,
I don't recall which pitot you're using, but Andrew at Angus Aviation (Gretz heated pitot) just told me via e-mail that it's acceptable to use one of Stein's straight fittings to go directly from the pitot tube to the nylon. I think this may be what Lars is referring to above.
 
Scott_F said:
Bob,
I don't recall which pitot you're using, but Andrew at Angus Aviation (Gretz heated pitot) just told me via e-mail that it's acceptable to use one of Stein's straight fittings to go directly from the pitot tube to the nylon. I think this may be what Lars is referring to above.
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Yes, that's exactly what I meant. It's commonplace in industry to connect metal tubing to plastic tubing using instant tube fittings. They are designed for that purpose, though some permutations, the ones with metal gripping sleeves, are better than others.

Bob, I made an assumption in my original post- that the Safeair tubing is 1/4" OD. If it is, then the fitting, known as a coupling, sold by McMaster-Carr that I referenced (or Stein's equivalent) will work. If that green tubing is not 1/4", there are reducing couplings available. Likely there is one that will go from the 1/4" aluminum pitot tube to the green tube.
 
I'm using the lame-oh piece of aluminum tube as a pitot tube. no fancy stuff for me! :rolleyes:

Tony at SafeAir says just grab a -4 fitting and it'll fit in that gold connector. I'll try that this morning and see.
 
Bob Collins said:
I want to take the current aluminum tubing that goes to the Pitot tube and get rid of all but about a foot of it. Then I'd like to flare that tube and connect it to the SafeAir kit, and run the tube straight into the fuselage with no breaks at the wing root.

I think this is actually designed for connecting to the Dynon heated pitot tube, which must use a smaller diameter tube. You can see how the SafeAir instructions show the connection here.

What would be ideal is if there were some sort of AN fitting like the above that goes from a -4 flare end to a -3. But I didn't see anything like that when I browsed through the Aircraft Spruce catalog.

I was just reading Stein's article in Kitplanes on static/pitot connections and he notes that this connection is where most pitot errors occur. I can see why.
Click to expand...

There is a mistake in the drawing "show connection here", airspeed indicator need to be connected to pitot and static.
 
Well, that was simple. Tony was, of course, right. I just swapped the -3 nipple for a -4 nipple. I don't know why I thought the pipe-thread end of the connector would be a different size.

I wonder if I'll ever actually LEARN everything I need to know to build an airplane?
 
Just exactly how much pitot error could be caused by using a simple 2 inch long section of ordinary 1/4" ID rubber fuel hose to join the aluminum line to the green plastic line, and secure the connection with ordinary hose clamps snugged just enough to hold tight without squashing the plastic line?

I know of an RV-10 that was connected using exactly this method, with the joint kept in a straight line, secured in place and hidden inside the wing root fairing. In that plane, both the Dynon and the mechanical ASI both agree with each other and seem to be plenty accurate when compared to the GPS-reported groundspeed and accounting for the headwind/tailwind.
 
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