Gretz Pitot Mast Angle

I laid out and have ready for installation the Gretz pitot mast at the regular pitot mast location on the bottom left wing. Gotta say I'm pretty happy with what I did; might put up pictures if interested.

I fabricated an angle to tie the doubler plate to the adjacent rib. I was planning to fasten the angle to the rib using 4 AN470AD3-4 that I had around. But they seem awfully small.

Can anyone give me advice on whether that is sufficient, or should I move up to a AN470AD4-4; The spacing along the angle length is about one inch, and I have about 3/8 edge distance for the holes. I think that the rib will not be weakened in the process.

I think yes but figured I'd share an opportunity to learn....

JDA_BTR said:

I was planning to fasten the angle to the rib using 4 AN470AD3-4 that I had around. But they seem awfully small.

Can anyone give me advice on whether that is sufficient, or should I move up to a AN470AD4-4

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Dudley - installed on a -10, but the same as a -14 (in fact a friend building a -14 made an extra angle for me when he was installing his mast). The 3-4s are fine. Once the bottom skin/mount is all riveted together it is extremely stout. Feels like I could do a pull up hanging off the mount

Magnus - here is one pic I have while fitting. The instructions are pretty straight forward. Only thing to pay attention to is to make sure you mount the angle to the rib far enough below the rib flange so that the bottom wing skin is flush between mast backing bracket and rib flange.


After riveting:

How I Installed the Gretz Mast

I marked everything to ensure minimum edge distances and checked many times before drilling through the skin.

First I figured the location of the doubler on the spar and match drilled this to locate the doubler properly. I had to increase the joggle a bit to fit it.

I ran lines up the doubler from the lower rivet locations to confirm edge distances were okay. I ran lines up the skin the same way in the same place on the outside of the skin.

I trial fitted the doubler with skin on top, and marked on the inside the doubler location. I also put the angle I fabricated on the inside and marked it's location on the doubler and rib.

Then I took it apart and put the angle in place on the rib using the jig you see in the first picture. The goal was not to set the location on the doubler; it was solely to get the angle placed on the rib properly, offset back to keep the doubler flush. Angle to rib holes were drilled.

Then I put it all together again with the angle on the rib, doubler in place, and skin on top. Marked on inside and then took apart. Confirmed that all edge distances were good and my marks were good.

Put it all together again, and drilled the hole at the top left on the doubler. Took it apart and checked all good. It was. Did same with doubler top right. Checked good. Then drilled the rest of the doubler holes with confidence.

When I disassembled all the overall assembly was perfect with good edge distances and as you can see it is very true and flat.

I will have to modify the washer plate to accommodate the two lower rivets on the upper half but I'm good with that. If the washer plate had been longer I could have incorporated it into the upper rivets but it just wasn't.

Gretz

I used AN470-4 (1/8) rivets to attach the angle to the rib and NAS1097 rivets where the doubler attaches to the skin. We posted a blog on our website that shows step-by-step how we installed the Gretz pitot tube. Take a look at: http://adventuresinaviation.org/pitot-tube-mounting-bracket-kit-installation/

It may be a nitpick but 1097 rivets are not commonly used in structural applications. On a nut plate the threaded fastener provides strength. In this application the 1097 rivet will not have as good grip strength on the skin as a normal rivet in a dimple will.

I don't know if it matters here but I'm glad I dimpled.

JDA_BTR said:

It may be a nitpick but 1097 rivets are not commonly used in structural applications. On a nut plate the threaded fastener provides strength. In this application the 1097 rivet will not have as good grip strength on the skin as a normal rivet in a dimple will.

I don't know if it matters here but I'm glad I dimpled.

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I know of a few hundred jets that have tens of thousands of 1097 rivets holing the pressurized skins on.

Fair nuff! Mike, would you use the 3-4 or the 4-4 in that location?

Gretz angle

I recently installed my Gretz pitot in the next to last outboard bay. It seemed to me this would be the easiest placement because I built my wing several years ago and just outboard from the inspection hole was too tight of quarters for my hands. Besides, my placement avoids the tie down rope. My question is: Does the angle relative to the wing need to be adjusted up or down to match the longerons?

JDA_BTR said:

Fair nuff! Mike, would you use the 3-4 or the 4-4 in that location?

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3-4's would be sufficient.