Manufacture of pitot mast insert

Following some ideas from Pascal Latten's build blog I decided to make the pitot mast removable, ensuring that this removal and replacement can be performed entirely by accessing the nearby small inspection port (modified to be removable). The key step in this is the replace the rivets attaching the pitot mast to the internal brackets with bolts that run through the mast. M4 nutplates will be installed on the far-side mounting brackets, and M4 allen-key bolts will be pass right through the mast with the heads closest to the inspection port. Removal by Allen key should be straightforward, with application of an adequate tightening torque readily achievable with a small right angle Allen key. I favoured using an Allen bolt over a Philips for accessibility reasons, and the awkward angles required to hold a driver to tighten the latter type.

One motivation for making this mast removable is that I am allowing for the possibility of replacing this non-heated pitot with a heated type in the future, in the event I upgrade the aircraft to IFR for example. Also to provide for easier repair in the event of damage.

I used aluminium for this insert rather than plastic or wood, because of the possible temperatures in the immediate vicinity when a heated pitot is used, and also to reduce the amount of combustibles in the aircraft.

For this to work, it is necessary to make an insert that fills the volume of the mast between the mounting holes, in order to prevent crushing of the mast when the bolts are tightened. This insert must also provide channels for the two 3/16" aluminium air tubes to pass. The material used is 6060-T5 20mm x 25mm rectangular rod, purchased from eBay. 4.9mm holes were made for the air tubes, and 4mm holes for the M4 bolts. Hand-filing was used to achieve the shape, the original stock chosen to minimise the amount of material to be used.

I upsized the holes in the mast and brackets to 4.1mm, and will consider upsizing the 4.9mm tube holes to something slightly large as the aluminium tubing tends to bind due to small bends along its length. In retrospect I might have routed the tubes behind the rear face of the block, but I was attracted to the idea of it providing additional support for the tubes. However, this space would be needed in part for routing the wires of a heated pitot tube and I did not want to take the risk of there being too much congestion.