Garmin AOA pitot retrofit

maus92 · #1 03-24-2015, 08:14 PM

I'm installing the unheated Garmin AOA pitot using a Gretz mount in my flying RV-8A. The existing pitot is the bent tube that I assume was standard in the circa 1998 kit. It attaches to the hard line with an elbow, and exits the wing into the airstream just forward of the middle inspection plate (bell crank access) adjacent to the forward inboard corner of the plate.

Question: Where should I install the new pitot? There is some consideration of potential interference with the tie down eye, therefore should I move the pitot to the vicinity of the inboard inspection plate, or is that too close to the prop wash?

Question: Since this is a retrofit, should I drill out some rivets and try to fasten one side of the doubler plate to the rib, or is it OK just to use the doubler on a field of skin without attaching to some structure?

Question: Generally, what color tubing is used for the AOA and pitot lines?

Pat Hatch · #2 03-24-2015, 08:54 PM

We placed the Gretz mount in the next bay outboard of the old pitot tube and used the pitot hole to mount the Garmin OAT probe. Access for riveting is through the inspection access just outboard and adjacent to the old pitot tube. It's requires a few improvisations but very doable.

Yes, we drilled out some rivets so that we could mount the doubler plate (joggle) to the wing spar flange (per the drawing).

We used red tubing for pitot, white for AOA, but that's entirely at your discretion. I don't think there's a standard, that I'm aware of anyway.

I'll try to take a picture for you tomorrow when I'm out at the hangar.

maus92 · #3 03-24-2015, 09:04 PM

Thank you!

So you went for the outboard inspection plate... was that to avoid the prop wash?

How did you extend the pitot hard line? Soft tubing mated to the hard line, or an entirely new run?

I was thinking about using the old hole for the OAT... glad to hear that it works!

Pat Hatch · #4 03-24-2015, 09:15 PM

Not just to avoid prop wash, but generally it's a good idea to go outboard, but just to get it out of the way of the bellcrank, etc.

Used the old pitot plastic tubing for the AOA and ran a new red plastic line for the pitot. Stein has all of the transitions you need, P515, AN816, 818, 819. The photo will definitely make things clearer, so I'll make a note to put one up tomorrow evening for you.

Pat Hatch · #5 03-25-2015, 04:20 PM

Here's the photo taken today. Let me know if you have any questions.

maus92 · #6 03-25-2015, 04:51 PM

Thanks for the photo. Did you shorten the metal air tubes on the pitot? Also, the OAT probe looks like you added a washer to cover the old pitot tube hole. Is it a shoulder washer or a flat washer? Was it difficult to buck the rivets when working through the inspection port? How did you mark the holes on the doubler plate? Did you remove the existing rivets and mark through the holes?

Thanks!

Chkaharyer99 · #7 03-25-2015, 06:25 PM

Quote:

Originally Posted by Pat Hatch

We placed the Gretz mount in the next bay outboard of the old pitot tube and used the pitot hole to mount the Garmin OAT probe. Access for riveting is through the inspection access just outboard and adjacent to the old pitot tube. It's requires a few improvisations but very doable.

Yes, we drilled out some rivets so that we could mount the doubler plate (joggle) to the wing spar flange (per the drawing).

We used red tubing for pitot, white for AOA, but that's entirely at your discretion. I don't think there's a standard, that I'm aware of anyway.

I'll try to take a picture for you tomorrow when I'm out at the hangar.

Pat,

Great job and thank you for posting. I too have the old style pitot and want to upgrade so as to install AoA.

You indicate you placed the Gretz in the next outboard bay.

Question 1: How did you know exactly where to cut the airfoil shaped hole for the Gretz mount in the bottom of your wing while still ensuring the doubler plate (Joggle) holes would still correctly line up with the rivet holes in the spar and the lower skin?

Question 2: Did the doubler plate come pre-drilled for attachment to the wing skin and the spar or did you have to drill those holes?

Question 3: Is there sufficient room to stick your hand and the Gretz though the inspection hole and the rib hole and get it in there or did you have to use a tool or jig?

I really like the idea of placing the OAT probe in the location of the old pitot.

Thank you for the picture and response.

Pat Hatch · #8 03-25-2015, 07:15 PM

Charlie,

Bob actually did the install, but I can tell you basically how it was done. You want to position the doubler against the wing spar flange and drill through the previously drilled-out rivet holes. Once you have drilled all the #40 holes through the doubler on the inside, reposition the doubler on the outside and cleco it to the outside wing skin. This will allow you to roughly trace the airfoil shape of the cutout on the wing skin. Cut out this hole but leave a little for final trim with a file when you put the doubler back inside the wing.

As for drilling through the pre-drilled doubler holes (yes, it comes with the holes pre-drilled), we used an angle drill on the inside, and, yes, there's pretty good access through the two holes. We positioned the doubler right up against the rib and added a small .032 X 3/4 X 3/4 angle against the rib and the doubler to further support the Gretz mount. You can probably see the rivet pattern in the photo.

When it comes time to mount the pitot tube, you can easily reach in with your hand and guide the 3/16" aluminum tubes and gently bend them as you feed them into the mount. We gradually shaped the aluminum tubes to the position shown in the photo. We reached in with the flaring tool and easily were able to flare the end of both aluminum tubes as shown.

Pat Hatch · #9 03-25-2015, 07:36 PM

Quote:

Originally Posted by maus92

Thanks for the photo. Did you shorten the metal air tubes on the pitot? Also, the OAT probe looks like you added a washer to cover the old pitot tube hole. Is it a shoulder washer or a flat washer? Was it difficult to buck the rivets when working through the inspection port? How did you mark the holes on the doubler plate? Did you remove the existing rivets and mark through the holes?

Thanks!

We did not shorten the tubes, no reason to, they are about the right length after the bend (as shown in the photo).

The OAT probe is actually smaller than the hole, so we took an AN960 flat washer that fit perfectly in the hole, was just the right thickness, and acted as a shim. We did have to slightly enlarge the hole in the washer so the probe would fit.

First you have to figure out how many rivets you have to drill out where the doubler will nest on the wing spar flange. Once you have drilled out these rivets, put the doubler in position and you can use a Sharpie to mark these holes on the doubler and check them for proper spacing. Once satisfied of the spacing, you can drill through the removed rivet holes into the doubler and cleco as you go. Setting the rivets is not difficult. It helps to use a small tungsten bucking bar.

Hope this is clear.

Chkaharyer99 · #10 03-26-2015, 09:34 AM

Pat,

Thank you very much for your very detailed response to the questions regarding the pitot install. This looks doable, even for someone who didn't build the plane (me).

I'm still trying to decide between the AFS Pro and the Garmin AoA, but either way I go this gives me perspective on the pitot mod.

I have a retired fire fighter friend with a beautiful RV-10 who's been schooling me letting me follow his panel upgrade and teaching me along the way. He would be a tremendous resource for me on this modification.

Mike...

Thanks again Pat.