Pitot Tube what a drag

[davidkarlsberg]

I installed my pitot tube in the pitot mast for the first time. The big screws that hold it in, which came from gretz, look kinda ugly and draggy. I know its the bottom of the wing but whatelse am I going to worry about until my fuse kit comes? Anyone got any ideas for smaller or hopefully flush screws? Here's a picture. Thanks.

 

[gmcjetpilot]

You may be stuck with your (screw) head'(s) sticking out

I doubt the drag is that great. With the camera close up it looks bad but on the plane you will not notice the loss of 0.00195 mph. (made up number but you get the point).

Solution #1: You can find pan heads with less protrusion. There is nothing keeping you from machining (grinding) some of the height of the pan head off. There are slotted pan head screws (not aircraft) that are flatter than the ones you show.

You could consider flush screw with a recess drive: Torx, Allen head, Hex, Star or square. You could machine the head down so the 0.40" thick tube (or what ever the gauge is) will allow the head to seat better. You are weakening the screw but its not structural. All you need is to maintain some wrenching slot to install and remove it. The socket type screw heads are probably better than a phillips or slot head, but consider those standard types as well.​

Solution #2 - Countersink into pitot for flush screw. Obviously the wall thickness is not deep enough to handle a standard countersink fastener, so the countersink would need to extend into the pitot tube.

With the Gretz I guess it may not be possible to countersink into the pitot? I recall Gretz is composite with inserts? It would be hard or impossible to countersink into the pitot. You may be stuck with protruding fasteners. Cessna countersinks the screws thru the mast and into the pitot. The Cessna's pitot is all metal and the mount holes are threaded into the body, so you can countersink into it.​

You may consider a 120 degree countersink head screw. However it still is not enough and you will end up with the edge of the screw head protruding somewhat unless you can use real small screws (#4). The ones in the picture looks like the typical #6 or #8's. Check this page out for "undercut screws". http://www.mutualscrew.com/subcategories.php?pid=552

Caution
When you countersink thin material you end-up with a knife edge and make the hole bigger, so be careful before you decide to countersink the mast, you could distroy it.

This is one of my pet peeves, and why I don't care for heated pitots, they are bigger and draggier

 

[Scott Will]

I used a lower profile screw... go to Home Depot and find some button head socket stainless screws. I think you'll like them better. Thought about countersinking mine but then I looked on every other aircraft out there and they all have pan head screws, at least the ones I saw.