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Good productive Sunday in the shop this past weekend. With the JB Weld epoxy well cured on the pitot/static tube assembly, I was able to sand away some of the sloppy clumps and prepare it for priming. The bench top belt sander worked well for this when taking down slowly to the metal.     With most of the end clump of epoxy removed, I rounded the tip of the static port probe:  In order to prime the assembly, I needed to block off the pitot tube end and the small static port probe holes. I found a piece of steel rod and with a bit of electrical and masking tape on the end made a nice tight fit to prevent primer from getting inside the end.  Kind of hard to see in the picture, but I used some 3/16 inch drill bits in the static probe holes, then primed it all.  In no time, the primer was dry, so I flipped the assembly over and primed the inside tubes after taping off the ends where the pitot/static lines will attach:  Primed and ready for install on the wing, very happy how this turned out!  This picture shows the rounded static tip well. The scuff marks in the primer are cosmetic only and look worse from the camera flash. The inside of the tubes have been treated with Crown to protect against rust.  Also primed the front strut pick-up and support angle. These will get rivetted once the lower wing skin is done.  Next up was laying out the 020 aluminum for the outboard and inboard trailing edges.  Lengthwise bends using the 1/8" radius bending shoe:   The bending brake can only bend the aluminum so far, but does a great job of creating a crisp trailing edge radius:  A preliminary test fit onto the rear wing channel showed a need to trim a little length of the forward facing edge to ensure the distance between the rear channel rivet line and the trailing edge is exactly the same as the other wing.  To finish the bend to the 18 degree opening angle as described in the plans, I secured the trailing edge to the bench with a 1/8 inch rod running the entire inside fold. The wood shims are thinner than the rod so they don't crease the aluminum as it is bent flat:  A better look at the overall set-up. The wooden shims are wedged in place between the rod and the securing playwood which is screwed down to the bench.  A long board and c-clamps apply an even squeeze to form the trailing edge:   I needed to slot the trailing edge skin where the rear strut pick-up protrudes through from the rear channel. I marked the location by extending the lines forward when the pick-up was in place, removed the pick-up then transferred the location backwards to the trailing edge skin when it's in place:  Knowing where the slot needs to be laterally, I can created the slot based on the width of the pick-up (the narrow black rectangle represents what needs to be removed):  Two holes drilled at the end of the slot, then cut out the slot using the Dremel tool:  It worked perfectly, the slot is the perfect size (the slot on the right is for the flapperon arm which has been temporarily removed to make positioning everything easier to manipulate for fit-up):  Both trailing edges fit up and ready for A3 match drilling to the lower skin and rear channels. I need to run the plumbing for the pitot/static and the fuel lines before getting to much farther, but the trailing edge is straight and true.  Next up, taking the lower skins off for debur and priming, along with further wing tip fit up. Thanks for following along as always.
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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. Still working when I can on the left wing. I've found it challenging to get to the shop as regularly as I would like, but a little encouragement from Brenda to get moving on Saturday morning was a big help. First thing I wanted to do was inventory and sort some of the partial sheets of rolled aluminum I have on hand. I've very close to having everything I need and certainly everything I will use in the immediate future.  Inboard nose skin installed on the wing. Critical to get it straight for drilling holes on the spar line otherwise the skin will roll over the nose ribs crooked, leading to wrinkles. A long board weighted down helps keep everything flat.  Used some strong twine to gently wrap the nose skin over and down, leaving more room beside the bench to drill the spar out to A3:  This time, before adding the nose skin, I roughed out the measurements of where the slot for the strut pickup, then translated that onto the nose skin:   I did the same thing on the rear channel where the trailing edge skin will need to be slotted for the rear pick-up:  Outboard nose skin added and rolled down like the inboard. This makes it so much easier to reach to the spar:  Attached the strut angle to the lower wing skin and where it extends out over the nose skin. In the picture I've leaned the strut pick-up approximately in place. This will be bent over to act as the doubler for the strut pick-up where it protrudes through the skin from the spar inside:   Here is a picture from the right wing which explains what it looks like completed:  The correct slot in the outboard end of the skin and the tie down ring in place. I'll wait to rivet it until the skin is ready for final riveting.  Strut pick-up slot cut and fit, forward strut pick-up in place awaiting fit up of the doubler angle:  One of the differences with the left wing vs the right one is the addition of the pitot and static tubes. In simple terms, the pitot tube faces into the slipstream and passes that pressurized air entering the tube through a system of tubing to the instrument panel in the cockpit. An airspeed indicator uses changes in pressure in the tube to calculate the speed of the aircraft through the air. The static tube measures atmospheric pressure outside the aircraft which is used by other cockpit instruments to calculate altitude and the rate of climb/descent. Systems vary from aircraft to aircraft, mine is made of simple metal tubing, formed as per the plans. First I needed to add a plate to the location on the lower nose skin where the plans define the pitot/static tubes will be:  In preparation to bend the plumbing for the fuel system, I bought these tube bending pliers:  The pliers were fantastic to bend the 1/4 inch outside diameter steel brake line for the tubes. The two tubes travel parallel to each other. The one on top is the static tube, the bottom the pitot (airspeed):  This is where things get a bit tricky. The plate needs a figure eight shaped hole for the two tubes where they run parallel. Once welded together, I won't be able to slide the plate off the tubes because they diverge at both ends:  Before welding the tubes together, I removed the plate from the tubes and used the hole to trace out a rough location for the hole in the nose skin:  The hole needs to be wide enough that when the tubes are welded together the ends can pass into the nose skin but still be covered by the plate. Corner drilled the proposed hole....  ....then Dremel tooled the lines to create the hole. A bit of filing to clean up the corners and edges:  I taped the tubes back together with the plate and checked the fit in the hole - all good.  The static tube has three holes drilled around the circumference. The end facing into the siipstream is welded closed. Completed this way, the tube measures atmospheric pressure:  I included a photo of the drill bit (3/64") to give some idea of scale:  I cleaned up the tubes with Scotchbrite pads and again with a stainless steel brush. I used a couple of woodens shims to clamp the tubes in proper position relative to each other and actually remembered to re-add the mounting plate:  Gentle heat up of the tubes where they join inside the wing and brazed them together:   With both tubes brazed together I placed them back on the nose skin. I'll need to figure out how to position these accurately later when the wing gets closed up, but very pleased how they turned out. They get some JB Weld epoxy at the hole to seal them up to the plate and primed before paint.  Good progress this last couple of sessions. Next up, trailing edges. Plumbing for the pitot/static tubes needs to be considered soon as the lines that go to the cockpit/panel run through the rear channel and into the trailing edge spaces as does the fuel lines. Thanks for following along, stay tuned for more soon. |
New here? Try starting at:AuthorHusband, 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. Categories
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