Screw size for Pitot Tube to Pitot mount mast
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swatson999
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Yep. The installation manual for the pitot tube has several links to builders' sites with details on this. Biggest caution is *don't drill into the pitot and AOA tubes inside the pitot tube itself*.
GKC Aviation
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Yes, 6/32 is the go.
I drilled the mast first, then inserted the pitot tube in and marked it.
Then drill the pitot tube in a drill press.
It's a bit fiddly to get the hole angles correct, but as mentioned above, there is lots of good info around.
I drilled the mast first, then inserted the pitot tube in and marked it.
Then drill the pitot tube in a drill press.
It's a bit fiddly to get the hole angles correct, but as mentioned above, there is lots of good info around.
airguy
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And after you've removed and reinstalled the pitot from the mast a few times, you will ultimately strip out one or more of those 6-32 screws - and you'll end up enlarging them to #8 screws. 2 out of 4 on my airplane (10 years and just over 2000 flight hours) now carry #8 screws. 
But yes, 6-32 for the initial holes, and that leaves you enough material to enlarge later when they strip out.
But yes, 6-32 for the initial holes, and that leaves you enough material to enlarge later when they strip out.
swatson999
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A good reason to mount it in a location such that you don't *need* to remove it unless it's failed (or, in my case many years ago, subject to a recall/replacement). That was the only time I've ever removed it, in 1000+ hours.
jakej
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There are obviously differing methods, including mine -
note : the aluminium ‘casting’ of the pitot base, that fits into the mount, has 4 x ‘pads’ that are much thicker than the rest of the oval area - that’s the area that you drill & tap threads through, in a later step.
All below can be done before the tube mount is fitted for the last time.
Eyeball & mark a point (I use a fine point permanent marker) that is at 90deg to the outside of the curved surface, & does not interfere with the tubes when drilling, mark a line vertical down the pitot body (& onto the mount when the pitot is fitted to the mount) need also to allow for a horizontal point after the mount & tube are together for drilling Initially use a 3/32” drill for drilling through the assembled mount & pitot tube. Separate both & drill/ tap as necessary.
Drill the mount to allow for short 6-32 screw.
Drill & tap the TUBE, using a bit sized for 6-32 screw, carefully & use something like Boeshield during the process - you’ll need to do this progressively, by inserting/extracting the tap, cleaning out the swerve & using the boeshield again because of the soft alloy which can be easily stripped out. HTH.
It’s much easier to do this process with the mount & tube off the plane - that’s why I nearly 100% always mount the pitot tube on an inspection panel YMMV
note : the aluminium ‘casting’ of the pitot base, that fits into the mount, has 4 x ‘pads’ that are much thicker than the rest of the oval area - that’s the area that you drill & tap threads through, in a later step.
All below can be done before the tube mount is fitted for the last time.
Eyeball & mark a point (I use a fine point permanent marker) that is at 90deg to the outside of the curved surface, & does not interfere with the tubes when drilling, mark a line vertical down the pitot body (& onto the mount when the pitot is fitted to the mount) need also to allow for a horizontal point after the mount & tube are together for drilling Initially use a 3/32” drill for drilling through the assembled mount & pitot tube. Separate both & drill/ tap as necessary.
Drill the mount to allow for short 6-32 screw.
Drill & tap the TUBE, using a bit sized for 6-32 screw, carefully & use something like Boeshield during the process - you’ll need to do this progressively, by inserting/extracting the tap, cleaning out the swerve & using the boeshield again because of the soft alloy which can be easily stripped out. HTH.
It’s much easier to do this process with the mount & tube off the plane - that’s why I nearly 100% always mount the pitot tube on an inspection panel YMMV
swatson999
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This is decidedly *not* true.nearly 100% always mount the pitot tube on an inspection panel YMMV
airguy
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Except that I live in west Texas with lots of flying insects, and occasionally pick up a bug in the pitot tube. You're not going to dislodge that without removing the tube from the wing and blowing compressed air backwards through it. 10 years and just over 2000 flight hours, I'll bet I've pulled that pitot a dozen times for various reasons.
swatson999
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Point taken. Maybe on a new installation one could route the tubes to the QD in such a way that you could just pull the vinyl tube from the QD and stick an air hose inside via an access panel? Just a thought...
airguy
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I did precisely that on my -10 wings.
jakej
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I did say I, never said you had to do it that way
.There is another reason &, as I’ve done so many installs on “new” aircraft. I realised that the ‘standard’ Vans way can easily result in damage when moving the wings around in the workshop or for painting & also transporting them to airfield for final assembly - much ‘safer’ without a tube mounted permanently. Just saying my idea - not telling you what to do
.ps - the composite Glasairs always mount their pitot on the inspection panel - way too much work to do otherwise.
Btw - the Dynon heater module will fit, long side vertically onto the inspection panel - just use a 3 pin connector for panel removal.
swatson999
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Ah, yes, my apologies...you did say "I", and my aging brain missed that (and read it as saying that nearly 100% of *all* installations used an inspection plate). I'm sorry.
On mine, I installed the pitot mast per the instructions provided by Dynon in my RV-7A, and used screws rather than rivets to attach the mast to the skin/backing plate. Because the wing spent a couple of years stored next to the other one, and then transported to the airport for final installation, without the pitot mast in place.
And if you go by the instructions for an RV, the backing plate *can't* be mounted on an inspection plate, anyway...no way to rivet it to the spar if you do that.
ETA: I just remembered...the pitot mast I have is basically the same as the Dynon one, but I got it from some other source...it's chromed, and I liked that look better. So the mounting holes on the mast may have already been countersunk. Backing plate was identical, though.
On mine, I installed the pitot mast per the instructions provided by Dynon in my RV-7A, and used screws rather than rivets to attach the mast to the skin/backing plate. Because the wing spent a couple of years stored next to the other one, and then transported to the airport for final installation, without the pitot mast in place.
And if you go by the instructions for an RV, the backing plate *can't* be mounted on an inspection plate, anyway...no way to rivet it to the spar if you do that.
ETA: I just remembered...the pitot mast I have is basically the same as the Dynon one, but I got it from some other source...it's chromed, and I liked that look better. So the mounting holes on the mast may have already been countersunk. Backing plate was identical, though.
jakej
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All good here