New Pitot Static Probe

The Pitot Static probe on the Fly Baby Biplane is mounted about 2/3 of the way up the left wing strut.  It's a home made probe similar to this factory one I saw at Oshkosh.  Our old one was made with fairly light aluminum for the mounting braces and screwed to the strut.  The light braces have been bent several times and just like on the landing gear water has gotten into the screw holes.  I decided I needed to make a new one of sturdier aluminum, that clamps to the strut, more like the factory probe.

The old one worked so the original idea was to just make a new mount for it.

As I disassembled it I realized I probably should just make a new one using some of the same concepts.  The old one was taped and safety wired together.

The tube connectors are pieces of 1/4" I.D. brass tubing which was splitting.

The probe tubes are separated by a piece of wood, which I liked.

The static probe was A piece of 1/4" aluminum tubing with the end hammered closed in a bullet shape, with a pattern of air holes.  To make a new one I used an Oak block to support the tube while rotating it and slowly hammered the end closed.  The tube wanted to slide along the block as I hammered so I leaned a piece of wood against my vise as a stop.  It worked fine.

The last, tiny bit of closing was done by hammering straight down on the end.

It was fairly smooth but I decided to lightly file off any slight bumps.  I aligned the tube at an angle with the cutting edges on a smooth mill file.  By gently holding the end of the tube between my fingers I was able to rotate the tube and nicely clean up the hammer marks.

It was easier to form this end than I thought it would be.

I prick punched a pattern of holes, 1/4" on centers, 3 holes on the 4 quadrants and 2 hole between each set of 3.

The smallest drill I have is 3/64".  The only chuck I have that will hold a drill this small is the little chuck on my angle drive.  I had just gotten this chuck a couple weeks before so it was my first chance to use it.  It worked out very well.

The hard part was deburring the holes.  I used a piece of 3/32" welding rod to work the burrs until I was sure I had removed them all.  It was mostly a matter of knocking them off or having them close the hole and then poke the hole clear until they all fell off.

The tube was bent so it would be parallel to the bottom of the upper wing, same as the old one.  The joggle in the tube is to allow a piece of soft rubber tubing as the connector.  I thought about using AN tube fittings but I wasn't sure I could make both tubes fit perfectly.

The Pitot Tube was formed like the old one but with a joggle to the side so the connector tubes would clear each other.  I also made it longer so the connector hoses wouldn't be beside each other.

For the block of wood separating the tubes I used a scrap piece of 1/4" spruce.  I used an Exacto Knife to carve notches for the tubes along the edges.  I also rounded the leading edge to be streamlined.  I just couldn't leave it square.

To help the connector hoses seal I crimped a bead on the end of the tubes using a hardware store compression fitting.  They sell extra rings so you only need one fitting.  You need to drill out the hole in the nut so it will slip over the bends in the tubes or you'll have it stuck on the tube.  You could put the bead on before bending, but I find it easier to bend and then cut the tube to length.

I also Alodined the tubes to give them a little corrosion protection.  I like the Gold Alodine better than clear for these things because I can see it working to judge when it's done.

To hold the tubes in position while I made the remaining parts I glued them and the wood block together with some 5 minute epoxy.  I used a piece of non-stick aluminum foil to wrap everything.  This minimized any trimming of excess glue and held the parts in position while the glue set.

The next piece was the strap which clamps the tubes to the strut.  I worked out the shape with a piece of card stock.  The aluminum is 0.032" 2024-T3.

After Folding it in half, so it would fit snug to the tubes, I Clamped it in the vise with a piece of 1/4" rod.  The piece of Oak has a 1/8" radius on the corner to make the bends to fit the front of the strut.

Back in the vise with a piece of 7/8" tubing to from the sides to the strut leading edge radius.

It makes a nice fit to the strut.

These pieces will replace the fragile side braces with some more 0.032" aluminum.  To help hold the tubes from coming loose in flight, I rolled the edge over to make a "J" shaped piece.  The length of the "J" section is less on the piece which hooks around the bottom than it is for the piece around the top.

The "J" shape fits snugly to the tube.

To form the hook edge I pounded the aluminum around a 1/4" rod to make a 90 degree bend.  Then I clamped the short end in the vise and continued to increase the bend in small increments until I had a 180 degree bend.  For each added bend you have to loosen the vise and rotate the part a little than hammer a few more degrees of bend with the wood block.  It works just be patient.

The aft ends were bent out, like on the clamp strap.

Then the second bend was marked to fit the strap.

The second bend was made to those marks using the piece of 7/8" tubing.  These side braces will get riveted to the strap to stiffen it all.

I trimmed up the braces, Alodined them, and glued them to the tube assembly.

The strap was glued and clamped in position before drilling the rivet holes.

I wanted the probe clamped to the strut without screws and with the ability to tighten the strap so the probe pointed straight forward.  For this I needs some little angle brackets on the sides of the strap, and also on a strap around the back of the strut.  This way I can pull the strap tight and adjust the screw on each side to pull the probe left or right as needed.

The brackets are made form some scraps of 1/8" x 1" 6061-T6 aluminum angle.  I drew cut lines and punched all the rivet and screw holes before cutting.

I didn't cut the parts off until I cleaned up one edge on the belt sander.  It's much easier to hold the stick than the little parts, which easily get very hot while grinding.

After grinding the first side, the part was cut off, the second side ground, the next part on the stick ground, etc.

When I Fit the first bracket on the strap, I realized the bracket on the back strap needed the screw hole 0.032" further from base because there is only 1 layer of aluminum vs 2 on the front strap.  Normally I make drawings to avoid remaking parts, but this was one of those figure it out as you go projects.

I needed to use flush rivets from the inside of the strap so I dimpled the aluminum and countersunk the bracket holes.  The dimpling would have been better with all the pieces apart but the front rivets had to be in place to hold the pieces tight enough.

The front half of the probe almost done.  I added a screw through the side braces and the block of wood to assure nothing comes apart in flight.

When I made the rear strap I realized I needed the front strap cut off at the back of the brackets to leave some gap for adjustment.

The finished probe.  I added a small piece of aluminum tape in front of the static holes.  I had done this on the old one to give a little turbulent flow past the holes.

Temporarily in position on the struts to make the tubes which connect the probe to the tubes in the wing.

The tubes were formed, and Alodined.

To secure them to the struts I lashed them on with cotton cord like I did on the landing gear legs.

3 coats of varnish fills the cords and glues them to the struts.

I filled the old screw holes and varnished over them.

To keep the probe from moving, I applied friction tape under the strap pieces.

To hold the Connector hose to the tubes, and assure a good seal, I wrapped them with safety wire on both sides of the bead.

I found it best to start at the free end of each to to assure I was close to the bead and still on the end of the aluminum tube.  I snugged the twisting just tight enough to slightly squeeze the rubber.

A few twists are enough to get to the other side of the bead and repeat the snug twisting.

The ends of the safety wire, as always, are folded over to help prevent injury on the sharp end.

I probably could have made the end of the Pitot Tube a little longer since the rubber tubes overlap slightly, the mistakes of not having a drawing.

In the end I like it.  It's solid.  There are no screw holes in the strut and I can adjust right or left if needed.  I also like the Industrial look, very cool.

Aileron Gap Fillers and Hinge Problems

I've always thought the ailerons on the Biplane Fly Baby were slightly inadequate.  I've run out of aileron trying to hold the wing down on crosswind landings and had to go around.  The wings on the Bi-Baby are shorter so the ailerons are a little less effective.  We've never had gap fillers between the 5 sections of piano hinge, which I'm sure contributes a little more to the problem, by letting air flow through from the bottom of the wing.

I've thought about ways to add gap fillers which are simple and easily replaced if needed.  The idea I settled on is to use strips of clear vinyl, taped to the wing and the aileron, and held secure by the hinges.

 My first plan was to cut strips of vinyl 2 3/8" wide with 1" double sided tape along each edge.  When I went to install them I realized I needed a bigger, 5/8", gap at the moving part of the hinge because of where the tape actual touches the fabric.

 I cut out the screw holes in the fabric before installing the tape, to make it easier cutting the holes in the tape.

The tape was applied to the aileron first.  It seemed to make installing the aileron easier.  I realized I needed to hold the wing side of the vinyl strip to the hinges to keep from wrinkling it.  I used a strip of 1/2" wide double sided tape to hold it to the hinges.  The vinyl was taped to the hinges with the hinges folded closed.

 The screw holes were cut through the vinyl and tape before installing to the wing so the screws could be easily positioned.

I played with the idea of slowly removing the paper backing as I installed the aileron.  That didn't work.  The better idea was to remove it all and install the aileron starting at one end.

 I used washer head screws to give a good bearing area with a thin screw head.  I put the screws in the first hinge and pushed them into the wing holes while keeping the other end of the aileron a couple inches out so the tape wouldn't get stuck in the wrong place.

I worked one hinge at a time installing the screws until they just engaged the nut plates, then on to the next hinge.  As each hinge was added I tightened the screws on the earlier hinges, a little, to slowly pull the tape and aileron to the wing.

 It worked out well with a nice even gap filler.  Once the tape was in place I used a squeegee to make sure the tape was tightly adhered.

A fairly simple gap filler.  We'll see how it works in flight.

 While installing the gap filler on the left wing I realized there was a problem with some of the screw heads hitting each other.  This prevents the aileron from having full down deflection and puts a strain on the hinges.  Some of the screws should have had more offset so the heads would miss each other.  The Right wing screws were all well spaced,  Some learning must have happened with the left wing.  To get more travel I replaced the offending screws with flat head screws and stainless steel countersunk washers.  I had to take the hinges back off and countersink the screw holes.  The washers assure the crews will not pull through the hinge and add a little better clamping force.

 I also found that the right hand aileron was positioned 1/8" high relative to the wing.  I have no idea how I missed this when I made the new hinges.  The only practical solution was to make new hinges moving the holes on the aileron side down 1/8".  The hinges were well positioned on the wing side so there wasn't any benefit to moving them.  The original hinge holes were easily made with the fabric off the wings.  This fix had to be done without getting into the wing or aileron.

I decided to only make new Aileron halves so I wouldn't accidentally mess up the holes on the wing side.  The wing side pieces were crimped on the ends to trap the hinge wire.

 To get the wire out I rounded the end of a 3/32" pin punch and used it to remove the crimp on the ends.  Then the pin could be driven out.

 With the pieces separated the trick was how to move the holes down 1/8" on the aileron piece without accidentally moving any of them in another direction.

 I used the belt sander ground the loops of the old hinge piece thin enough to break them off.  I didn't want to accidentally grind off too much since the plan was to use the remaining ends of the loops as stops to position the piece as a pattern for punching the new holes.

 Using needle nose pliers I rolled the old loops to break them off.

 I then used the belt sander to carefully grind the loop ends to a perfect length.   It took a few passes at the sander to get them just right.

 I clamped the old piece on the the new one and then measure the offset, and reground the ends until I got the offset to 1/8" +- .002".

 With the old part clamped on as a pattern, the screw holes were punched in the new piece.  Each hinge was reassembled and reinstalled.  The aileron now fits perfectly.

Post Painting - Wing Assembly

I've been up to my ears with work for the past few months.  I have gotten a few little things done and Thanksgiving Weekend seems a good time to get caught up and back to work on the Fly Baby.

 I decided to use wing walk tape rather than the gritty paint.  I wasn't sure how the paint would work with Poly-Tone.  I cut pieces 24" long and a little narrower than the wing walk.  I also rounded the corners so they wouldn't tend to come loose.  I heated the tape to about 150 degrees so it would stick well and conform to any bumps.  To help stick it down I made a roller from a piece of foam noodle the grandkids had in the summer.  I used a piece of tubing in the center, which was setting on my work bench, but a piece of dowel would work well to give it some stiffness while pressing the tape down.

 I've bolted all the strut and brace wire fittings back on the wing panels.  I have a plan to paint all the inspection covers with Poly-Tone to match the wings better but it's a fussy process of priming with epoxy primer than spraying the first coat of Poly-Tone while the last coat of primer is tacky.  I'll work on them when warm weather returns.  For now I've found some spray cans with colors close enough.  I only have a few covers needed until the first annual inspection.

As I put the fittings back on I mounted the wing strut to each wing to make sure all the fittings were on correctly and the bolts would fit.  Much easier to resolve any problems in the attic then while assembling the whole plane.

Better Paint Mix and Second Coat on the RH Upper Wing

When I mixed a new batch of light green, I realized I had made some mistake with my spreadsheet for calculating the pigments.  It was causing the quantities of pigments to be so low the paint was watery.  I had seen this with the red, blue and black, but it was much worse with the green.  I spent the morning re-measuring all my pigments by weight and volume to determine their density.  I needed this to correctly convert my weight (gm) measurements into volume (ml) measurements so I could use measuring scoops.

When I first mixed the colors I had access to a very accurate scale.  All I have now is a small kitchen scale which is not accurate enough to measure such small quantities.  Most of the pigments come in 175 ml jars so I have large enough quantities to work out the density with the kitchen scale.
The densities are:
Lamp Black                     0.17 gm/ml
Aluminum Powder           0.27
Prussian Blue                  0.55
Alizarine Crimson            0.66
Litopone                         0.83
Burnt Sienna                   0.87
Chrome Yellow                0.87
Chrome Orange               1.18

 When I mixed the colors I used about 4 times as much pigment as my attempt with the Light Green, which was what I found with the black.  The colors still match and the paint covers much better.
The color mixes here are for Light Green, Beige, Red and blue.  Each has about 25 ml of pigment for a quart of Poly-Tone.  The Alizarine did not want to mix well with the Poly-Tone but the color seems to match my old samples.

 We had another warm dry afternoon so I started the numbers on the lower left wing, and did the red and blue on the roundels.

The upper right wing got a second coat on all the colors.  The red and yellow need another coat and then I can outline the numbers.

After 26 years it's nice to see this paint job getting close to being done.  I really like the look.

Colors on Wings

 The afternoons yesterday and today were both nice and dry for painting.  Yesterday I got the second coat of all the colors on the top of the lower wings.

I also got started on the red in the roundels.  The green stripes are squadron stripes for the 103rd Areo Squadron.  They still need red stripes between the green.

 In the evening when it was too damp to paint to paint I drew all the color boundaries on the top of the upper wings.

Today I was able to get the first coat on the top of both wings.  When the colors are done I'll add a black border around the numbers.

 The upper right wing gets the same green and red stripes as the lower left.

I got the numbers drawn on the lower right in the evening today, but it was too damp to paint them.  Odds are I won't get to do any more painting until mid September.

I did get the gasket set for the engine so I can pull the cylinders to check for rust.  I've only got about 125 hours since the overhaul so I don't want to risk damaging the engine.