Back in the shop today. Got back to work on the second wing, continuing with the fit up of the pitot static tubes.
I was going to leave the tubes braze welded where they join inside the nose skin, but decided it would be better to braze weld it on the outside portion as well to give it more strength. Flipped the tubes around and braze-welded the tubes on the outside portion of the plate:
To get the tubes in the correct position is a bit challenging The centerline of the static tube (the lower one when the wing is upside down like it is now) needs to be 64mm above the wing skin, but it also needs to the perpendicular to the nose skin surface and perpendicular to the wing spar. This ensures the air flowing across the wing enters the pitot correctly leading to more accurate airspeed readings. If the tube faces slight down/up or sideways to the relative airflow, that can induce airspeed indication errors.
I grabbed a short block of wood from the scrap pile and drilled a 1/4 inch hole close to the end of it:
Used the bandsaw to cut off the end of the block, giving a resting groove for the tube, then trimmed and sanded the opposite end so the block is exactly 64 mm long:
The concept was good, but very hard to make it stay still as there was no easy way to balance or attach the block to the skin and keep the measurements accurate:
Grabbed another board from the scrap pile and created a jig to simulate the wing skin surface.
Drilled a hole similar in size to the one in the nose skin to pass the tubes through:
I like using wood as a base for jigs because you can cleco things to them (I've done this in the past for things I need to duplicate accurately. In this case, it's just to simulate the flat surface of the nose skin:
The picture isn't in best focus, but you can see the concept. The tube is supported by the block which is secured to the wood by a screw from underneath. This places the tube exactly 64 mm from the "skin" and I can also confirm the tubes are square to the plate and parallel to the "skin":
I used a scrap piece of 016 aluminum to strap down the tube in the groove of the block. This holds the tube exactly where I need it and gives me the freedom to secure the tubes to the plate where the tubes pass through:
For years I've seen JB Weld on the shelf of the hardware store and never thought I'd have a use for it. After Ron recommended it as a way to bond the tubes to the plate, so I thought I'd give it a try. Brazing the aluminum plate to the steel tubes would be difficult as each material heats/cools are different rates and heating the joint up enough could compromise the strength of the brazing I'd already done.
JB Weld is very easy to use. Squeeze out a small amount of each part of the epoxy onto a piece of cardboard:
Use a small stick and mix the two parts together until they completely blend to an even colour:
With the epoxy blended, use the stick to apply around the joint and let sit. It takes about 4 to 6 hours to set up and another 12-24 hours to fully cure. It cures extremely hard and strong and can be shaped with grinding and sanding and accepts primer and paint:
I also applied a liberal amount to the end of the static tube which by design has the end plugged (it reads static pressure from the 3 tiny holes drilled radially along the length, perpendicular to airflow). Once the epoxy hardens, I will carefully grind this tip into a more acceptable aerodynamic point, probably a bullet shape or maybe just rounded off.
So of course after all those years of seeing JB Weld on the shelf and not thinking I would ever use it, I can now thing of dozens of uses!
While I Iet that set up and begin to cure, I turned my attention to the front strut pick-up angle. I remembered how I did the other wing, so was able to fairly quickly bend the angle to shape, fasten it to the assembly and drill out the 3/8 hole to match the strut pick-up:
Brought the second wingtip down from storage and did the preliminary cutting out from the mould and trimming the edges. Lots more to do here with outboard skins and nose skin before final trimming will be complete.
Started to layout the curve of the outboard edge of the nose skin. The templates I made are very helpful to make this wing an exact opposite of the other wing.
Thanks again for following along and special thanks to my girls Brenda, Caitlyn and Natalie for giving me the time on Saturdays to work on this dream of mine.
More to come.
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.