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Dynon heated pitot/AOA mounting question

scsmith

Well Known Member
I am installing a Dynon heated pitot/AOA probe in our tapered composite wings for Bob Mills' Rocket 6. The Dynon instructions are pretty lean on how to attach the probe body to the mount strut. The strut (I think it is from Gretz) has four holes at good locations to put screws into the body of the probe, but the probe itself does not have any threaded holes.

The Dynon instructions say not much, except that it is OK to carefully drill through the outer shell of the probe body. Looking at the probe, it is not clear that the shell is thick enough to match drill with a tap-size drill and thread the probe body for attachment screws. I'm thinking of using 4-40 100-degree flat head screws, but I may not get even two full threads in the shell?

Looking for experience from others - is there enough metal there to get a few threads tapped into it?
 
No real experience with a pitot probe yet.. but would it help to set one of those rounded spring loaded drill stops so the drill tip is just barley poking out? Then the ball of the drill stop will center the bit? Even if the #40 is too big, it could just start the hole so that the tap drill can follow it.. I have used this method to match drill where the skin is already dimpled and it works great.
 
The question here is whether the shell material is thick enough to cut threads into.

I'm not worried about match-drilling a tap drill hole into it, controlling the depth to just go through the shell, on center with the mount hole. I know how to do that.
 
Yes, I did exactly what you are asking about - twice. The original Dynon probe was recalled, they sent me a new one. IIRC I used some thread locker compound. Forces are all shear, so you don’t need much in the way of threads.
 
Yes, I did exactly what you are asking about - twice. The original Dynon probe was recalled, they sent me a new one. IIRC I used some thread locker compound. Forces are all shear, so you don’t need much in the way of threads.

Thanks Bob.
 
Same as Bob, I did mine twice. Both times I drilled the pitot tube on the drill press to precisely control the depth of the hole. In the second picture (recalled pitot tube, hence the cut tubing and wires) you can see there’s plenty of room to thread for the screws. On an aside, that pitot mast was later recalled for a failed weld at the base. Make sure you’ve got the newer mast. Can’t remember the brand but the new one is anodized blue.
 

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If you look closely at the pitot tube itself, you'll see four places where the wall thickness is perhaps doubled relative the rest. Those are the places you drill and tap for the screws that go through the pitot mast. I called Dynon on this because of the thin-to-no instructions on doing this. They confirmed that tapping into the thickened sections of the pitot wall is the way to go. They also said the screws could go beyond the metal of the wall into what looks like bathroom sealant - just be aware of the screw coming in from the other side.

Yes, it seems daunting, but it's really not that hard.

I thought perhaps we'd countersink the screws into the walls of the pitot mast, but in the end thought they were a bit too thin to do that. Little cap head #6-32 screws worked find. But, we probably gave up .01kts right there.
 
Same as Bob, I did mine twice. Both times I drilled the pitot tube on the drill press to precisely control the depth of the hole. In the second picture (recalled pitot tube, hence the cut tubing and wires) you can see there’s plenty of room to thread for the screws. On an aside, that pitot mast was later recalled for a failed weld at the base. Make sure you’ve got the newer mast. Can’t remember the brand but the new one is anodized blue.

An addendum here: a gold mast doesn't automatically mean "bad." The masts referred to here are the SafeAir1 units, which I'm pretty sure are no longer available since Bob Avery retired. A gold SafeAir1 mast is definitely a concern.

However, Dynon also sells a pitot mast, which is also gold anodized, but it is not the same "don't use this" unit as the SafeAir1.

The color looks to be slightly different too, though that could just be different photo lighting. This is my Dynon mast:

img_0939-768x1024.jpg
 
Thanks to all. Our mast is steel, and the weld looks perfect.

Yes I see now that the location for the screws falls in the area where the wall has been substantially thickened to allow plenty of thread depth. On initial glance I thought the holes would miss those 'lands' and go into the thin part, but when I marked the holes, I could see it will be fine.

Thanks again for everyone's tips. Perhaps someone else in the future will benefit too.
 
An addendum here: a gold mast doesn't automatically mean "bad." The masts referred to here are the SafeAir1 units, which I'm pretty sure are no longer available since Bob Avery retired. A gold SafeAir1 mast is definitely a concern.

However, Dynon also sells a pitot mast, which is also gold anodized, but it is not the same "don't use this" unit as the SafeAir1.

The color looks to be slightly different too, though that could just be different photo lighting.

My bad, didn’t mean to imply that all gold anodized masts were bad. Like I said in the original post, couldn’t remember the brand name, it’s been too long since I worked on it. Simply a caution to make sure you’ve got a good mast to support that pitot tube.
You can see the failed weld on the left side of the picture. I discovered it on a preflight a while back when I saw the pitot tube hanging slightly lower than it should have been.
 

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Where Are You Guys Mounting the Pitot Mast?

I planned to mount mine one cavity inside where the plans indicate the pitot tube mounts (yellow arrow), ie, inside the inspection door next to the flap bell crank inspection door.

Pitot Mast Mockup with Tape 2.jpg

Pitot Mast Big Picture.jpg

That said, it positions the tip of the pitot 16 inches aft of the leading edge. The plans from Dynon indicate the tip should be 2 - 12" aft. But, I see no good way to mount the mast any farther forward, at least using the supplied parts.

Does this seem right or am I upside down once again?
 

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Pitot mast

I mounted mine just outboard of the most outboard inspection hole to prevent interference with the wing tie down. I also used 6-40 screws to attach the pitot to the mast using a drill stop. Not my original idea, but seems to have worked well. See Mike Bullocks build log for more details.

http://rvplane.com/?categoryid=7&dayid=901
 
I mounted mine just outboard of the most outboard inspection hole to prevent interference with the wing tie down. I also used 6-40 screws to attach the pitot to the mast using a drill stop. Not my original idea, but seems to have worked well. See Mike Bullocks build log for more details.

http://rvplane.com/?categoryid=7&dayid=901

Same here for the #6 attach screws - but 1000 flight hours later I've got two of the four screw holes stripped and enlarged for #8. Not really a big deal in the long run I suppose.
 
I just replaced my pitot tube with this new one from Dynon.

My mast was drilled for short #10 screws, so that's what I drilled and tapped. Mounted up fine.
 
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