Monday, August 27, 2018

Engine Cowling

 The lower fuselage cowl is fitted so engine oil and rain do not go inside the fuselage.  It is removable to get at the brake cylinders, even with the engine cowl installed.
 Our grandson Duncan visited for 2 weeks to help work on the plane and hang out with old people.
 The engine cowl is on.  It's finally looking like an airplane again.

 We found the belts were not holding the front of the cowl tight enough.  We moved the crew hole about 1/2" at one end and now it's tight.

 In the long run I would like to make some springs like the Ford Model T springs, as on this Pietenpol cowl.  The belts will stretch over time.  We made some but need slightly thicker wire to get the 15 pound load needed to hold the cowl tight, with the spring stretched about 1/2".  The ones we made with .080" piano wire only pull 5 pounds.  I have some 0.125" wire but I think it is too thick.  I may try it any way.
We started fitting the wings but Duncan had to go back home early.  The Cross Country team wanted some pre-season practice.  I'll finish fitting the wings when I get back from the Antique and Stearman fly-ins.

Saturday, August 18, 2018

Windshield Installed

 I went to install the piece of cowling with the windshield and realized it wouldn't go on with the center section installed.  I thought I could split the bottom of the cowl where the rear of the cabane strut attaches so it could get around the strut.  That didn't work either.  I finally realized I needed to remove the rear strut bolt and pivot the strut up around the front bolt. That worked fine and I probably could have done it with the center section still bolted to the struts.  Oh well, we got there.

 Once I had it on I realized I hadn't installed the little tabs to hold the top of the instrument panel from tipping forward with the weight of the instruments, so back off again.

I decided to use some old scraps of 1/8" x 1" aluminum angle.  I thought I would just tap a screw hole in it rather than install a nut plate.  In the end I used a nut plate on each.

 The instrument panel is tipped slightly from perpendicular to the cowl so I had to bend the angle about 3/32" to get a nice fit.

 To get the holes in the brackets to align with the holes in the Instrument panel I riveted the brackets to the cowl and re-installed it. 

I then drew the hole locations on the panel so they would be close to the center of the brackets and drilled through the panel and the brackets.

With the cowl back off I could then install nut plates on the back of the brackets.

 The cowl and center section are finally back on, again, with the panel screwed to the brackets.

 In this process I discovered another small problem.  My clever bracket for the temporary vacuum gauge was bolted to the 2 bolts on the outside of the cowl not the 2 on the inside.  I'll need to make another bracket.
 I also found that some of the screw holes along the top of the firewall don't align with the cowl holes.  I used a circle template to draw where the holes should be.  Then I took out all the screws except the aft screw on each side of the cowl. This allowed me to tip the cowl up just enough to re-punch the holes with the Whitney punch.  I used a punch with the nib ground off and aligned the punch with my drawn marks.  It worked.
 While I had it up I put a bead of high temp. RTV along the cowl with strips of waxed paper on top.  The waxed paper is to keep the RTV from gluing the cowl to the firewall while still forming a nice gasket to keep oil and fumes out of the cockpit.

This time I think the cowl is on to stay.

 I used Contact Cement to glue some anti-chafing strips to the edges of the cowl piece above the engine.  This piece isn't intended to move, but all the engine vibration and air loads do cause it to wiggle slightly.  The 2 access doors are just held shut by belts so they wiggle quite a bit.

Fortunately the holes in this cowl piece all match the firewall and it covers the mis-located holes in the other piece.  We're getting there.

Tuesday, August 7, 2018

Tinnerman Nut Plates on the Firewall Flange for the Cowl Screws

I like the Tinnerman, AN6195-8Z-1D, nut plates.  They get riveted on with 3/32" flat head, countersunk, rivets.  Nut plates with an elastic stop nut are nice where you are not removing the screw very often.  For something like the cowling, sheet metal screws with these nuts keep working longer.

Installing them is easy.  I make a template from a piece of galvanized steel.  I have 3/16 holes in the flange so I made the center hole in the template 3/16".  The rivet holes are 3/32".
I found the Cleco clamp was out of my way in the back.  I used a regular 3/16" washer for a spacer between the flange and my template.

By using the spacer, my automatic center punch fit snugly in the rivet holes of my template.  This way I can just hold the template from moving and mark both holes quickly.

The Whitney punch works perfect for making the rivet holes in the flange.  Normally I would then drill the holes with a # 40 drill to open them to just fit the rivets.  There's no need to do that since The holes open up slightly when dimpling them for the flat head rivets.

The 3/32" dimpling tool for my rivet squeezer has a rivet shaped punch and a matching die.  Adjust them so they are closed tight just before the handle closes completely.

Because the nut plates are dimpled for the flat head rivets we can dimple the holes rather than countersink them with a drill bit style cutter.  Much quicker, easier and no mess.

To squeeze the rivets we just need two flat anvils.
Use a 3/32" Cleco to hold the nut in place at one hole.  The dimple on the other end will keep the free end aligned while you rivet it.

Squeeze the rivet, very easy with 3/32" rivets, and do the second rivet.

I've used a 3/16" long rivet which works nice for the nut plates.  A 1/4" long rivet tends to bend when squeezing it.

There's a screw very couple inches, so there are 32 screw around the flange.

Sunday, August 5, 2018

Primer Line Replaced with new Tubing

I've read some articles about broken primer lines and decided to replace the line to the engine.  It is over 50 years old.  The fitting at the gascolator used a compression ring, prone to cracking copper tubing, so I decided to replace it with the correct AN fittings. The AN4022-1 Discharge Nipple and AN780-2 Straight Connector both use the AN800-2 Union Cone Brazed to the tube, and the AN805-2 Union Nut to hold the Cone to the Fitting.
 The idea with the line to the engine was to make it longer so it could have some bends to flex with engine vibration.  Along with being a fresh, not work hardened piece of tubing, this should make it less likely to crack at the fitting.  The bends are made in 2 perpendicular planes to let it wiggle in all directions and, expand and contract with temperature.

 the same bends were made at the end where it joins the tube from the primer.  I clamped the tube, not the coupling, to the engine mount to again reduce stresses on the tube at the fitting.  This way the weight of the coupling isn't causing the line to move with engine vibrations, etc.

The tube from the gascolator to the primer is also clamped to the engine mount tube.

 I had some trouble brazing the AN800-2 Cone to the copper tube because of some "modern" flux I bought, which I have thrown away.  The first step is to clean the end of the tube with Scotch-Brite.  De-burr the end including the inside edge.  A 1/16" drill bit will open the hole after cutting to make de-burring easier.

In the end I used the same flux and brazing metal I use for brazing band saw blades.  The company has gone out of business so I will have to use it sparingly.

It doesn't take a lot of flux.  I put some on the tube then rotate the Cone on the end of the tube to make sure it gets worked inside of it.

 A small propane torch works fine for heating.  I tried my Butane torch but it wouldn't get it hot enough without the help of the propane torch.  It has to glow Red hot for the brazing material to flow.  When it gets hot enough the brazing metal flows nicely into the joint, just like brazing band saw blades.

 A little cleaning with Scotch-Brite and you're done.  Along with other problems the "modern" flux left a hard residue which I could not clean up.

 I took one of the pieces I tried brazing with the "Modern" flux and cut it in half to see how well the brazing metal flowed into the joint.  I pried the end of the tube loose and pulled it back enough to see where the brazing ended.  You can see it made it more than half way up the tube despite the fact that I thought it was a horrible mess and wouldn't use it.  The good flux flowed so well I didn't cut open a piece brazed with it.