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Safeair1 Pitot Mast Reinforcement

T

tgmillso

Well Known Member
Sponsor
Hi Guys,

I purchased a Safeair1 pitot mast that I plan on installing, but had a question about a side bracket. In the Gretz mast installation manual, it asks that a side bracket is attached to the neighbouring rib for additional reinforcement, however in my case with the Safeair1 mast, if this bracket is in place and you ever want to remove the mast, it makes it next to impossible, because you can't just drill out the rivets from beneath the wing, push the mast up into the bay then pull it out the inspection panel in the next inboard bay. Safeair does not specify one in their instruction manual. I'm going with not installing any additional reinforcement, but I just wanted to make sure I'm on the right page before I take the plunge in case there are issues with cracking etc. in the future because the installation is too flexible. I guess the other option is to make the bracket attach to the rib using some screws and plate nuts, then reaching in blind to remove them if necessary, but really that sounds like a PITA.
I'm installing the Garmin pitot, and it's sure a pity that the aluminium tubes aren't an inch longer so that I can easily get from just inboard of the 11th rib to the mounting bracket I'm installing on the 10th rib (like many others) with a large radius curve so that you can still fit the tubing down the mast for replacement if necessary. I'm definitely concerned about getting everything to fit back down the mast if and when required, but I figure if remove the screws, drop the pitot tube an inch then rotate it 90 degrees I should be able to maneuver everything down. That mast is just so long. I measured the mast on a Cessna 172S and it is 3" from the wing surface to the pitot centerline. A Piper Comanche 400 is 5", and the safeair1 mast is 6.75", and about 1.5" more than the Gretz. I asked safeair a while back why they picked such a long mast, and they said that it was just because it placed the pitot at the same position as Van's original aluminum mast, no other specific reason.
Anyway, after that monologue tangent, if anyone has experiance with cracking due to the lack of reinforcing when installing the Safeair mast, please let us know.
Cheers,
Tom.
 
That's a timely question for me! I am about to install the same mast and wondering where to position it. It seems like it might be smart to place it towards the outboard end of the bay outboard of the aileron bellcrank. That way there is maximum clearance from the tie-down, but I'm also worried about whether it will need reinforcement if it is in the middle of the bay rather than right next to a rib where the skin is supported more?
 
Safeair1 Pitot Mast Mount

I'll post some pix on how I mounted the Safeair1 Pitot Mast mount on my -7 tomorrow (not near the pix right now). It allows you remove the post if you want and provides a strong, stiff mount for the post.
 
AndyWW said:
That's a timely question for me! I am about to install the same mast and wondering where to position it. It seems like it might be smart to place it towards the outboard end of the bay outboard of the aileron bellcrank. That way there is maximum clearance from the tie-down, but I'm also worried about whether it will need reinforcement if it is in the middle of the bay rather than right next to a rib where the skin is supported more?
Click to expand...

Hi Andy. I've seen people put them in the middle of the bay, but they run a C-channel stiffener between ribs 10 and 11 slightly aft of the pitot, providing stiffness to the skin. Unfortunately I can't find right now any pictures of this, but I'll keep hunting. Taking this path was something I was leaning toward for a while because I didn't think I could solve the issue of the pitot tube aluminium hoses only being 13" long and not being able to reach all the way to the 10th rib. I think I can deal with this by building a slightly deeper bracket off the 10th rib, or by shortening the mast a little, given that it is longer than that on a Comanche 400 which cruises even faster. Another option I have found that would allow us to get all the way to the 11th rib, but still allow the mast to be removed for maintenance, is to transition to an aft pointing 90 degree elbow (Safeair Part Number 1) from both the pitot and AoA lines after at least 8" of aluminum tube straight up to meet the thermal requirements. You place one of the elbows slightly higher that the other to ensure they can be pulled down the mast, but have to reach into the bay blind to separate the quick release fittings.
Jeff, I'm definitely looking forward to any photo's you have on this one. I'm of course looking for that elusive pitot silver bullet.
Tom.
 
Me too

It won't be long and i'll be asking the exact same question. I'm all ears on this one as I have the Safeair 1 pitot mast as well, but going with a Dynon Heated pitot.

I like tom's suggestion in the middle of the bay, never seen that installation method yet.
 
Found the stiffener example.

Ok, so I found the one with the stiffener to the rear. It appears however that the plate is still mounted to a bracket that in turn is mounted to the stiffener, which creates the same situation should you ever need to remove the mount, that is where the bracket stops you pushing the pitot mount up into the wing bay after you have drilled out the rivets. The builder (Jeff who posted earlier) gets around this by putting nutplates on the stiffener, then screwing the bracket to it. This still leaves you in the situation where you have to remove the screws blind, although if you used the cap head type screws people are using on the fuel tank inspection plates, or these beauties (if only they were available in #6 size) you should be good taking them off blind.
http://www.aircraftspruce.com/catalog/hapages/nas1801.php?clickkey=2951075
Alternatively you could just rivet the stiffener to the skin, then rivet the safeair mast to the skin surface only. Here's the link to Jeff's post. The stiffener pictures are about halfway down.
http://www.vansairforce.com/community/showthread.php?t=120231
 
Tom found my previous post!

Looks like Tom found my previous post on this subject. No need to add any more on the details of the mount.

However, for my installation I decided not to bend the aluminum tubing coming from the pitot 90? towards the fuselage but instead just kept them straight and plugged the 0.25" OD plastic pitot and AoA tubing directly onto the 0.188" OD aluminum tubing from the pitot. This allows me to reach in thru the access panel, thru the rib opening and "unplug" the plastic tubing from the pitot tubing. Then all I need to do is unscrew the four countersunk screws from the pitot/mast and remove the pitot. If you bend a 90? bend in the aluminum tubing you'll have to straighten the aluminum tubing back out to remove the pitot. I'm not sure how many "cycles" you'll get from this before you work harden the tubing to the point it cracks.

If I ever have issues with this leaking I can just get some 1/4" to 3/16" push to connect reducing coupler (I found some on Amazon) and that should solve any problems.

I hope this helps.
 
The aluminum bend and serviceability

I too have been concerned about making the 90 degree bend from the pitot tube through to the mounting bracket on the 10th rib, and the ability to pull it back out later, especially given the length of the Safeair1 mast and it's limit on possible bend radi. I am leaning toward going straight up with the AoA and Pitot aluminum tubes at least the minimum 8" from the pitot tube itself to allow for heat, but probably a little more (keeping in mind that some type of bushing may be required around the aluminum tubes at the top of the mast to stop vibration of such a long unsupported length), attaching AN fittings with female threaded ends, then connecting to 90 degree male elbows (part #1 on the Safeair1 website). According to safeair, this fitting should still be able to swivel even after it is torqued up to the AN fitting.
http://www.safeair1.com/averytools/pitotstaticplumbingkit.php
"NPT Fitting Installation
Threaded fittings; (Example: Part No. 1, 2, and 3 shown in the listing above), swivel. In other words, after reaching the appropriate torque value, you can rotate the fitting and point the port(s) in the desired direction. You can also use this feature when installing a fitting in confined spaces. The port can stay stationary as the threaded base is rotated."

This should mean that I can just reach in with one arm, unplug the plastic line from the 90 degree fittings, then swivel the 90 degree fittings aft, which should then allow them to pull down through the pitot mast comfortably, especially if one is staggered slightly higher than the other (i.e. one tube is longer than the other. I'll put together a mock-up and post some pics once I have things in place, however I'm pretty confident it will work. All I have to do now is find an AN fitting with a female thread on one end, and the ability to connect to the aluminium pitot/AoA tubes at the other. I'm no guru on AN fittings, so I was hoping someone could point out how I achieve this. The AN fittings on the Aircraft Spruce site may be found below.
http://www.aircraftspruce.com/menus/ha/an.html

Regarding the mast position, I'm definitely going with it all the way out to the 11th rib for tiedown clearance, now that I'm using the 90 degree bend and plastic tubing which I can run from that point onwards and I'm no longer limited by aluminium tube length. Given that Derek is flying without any additional brackets on the rear or side of the mast plate (there I am making decisions based on a single data point again...) and that Safeair1 doesn't stipulate one, I think I will just go without to keep things simple and place it as close as possible to the 11th rib for stiffness. This is my brief attempt at not over complicating things. I'll be pretty stoked once we get this sorted as it should make the journey a lot easier for anyone with the same combination of mast/tube/lines in the future.
Cheers,
Tom.
 
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