Upper cowl

While I was waiting for the Roloc disks to arrive and the burnishing to resume, we decided to start on the upper cowling. I figured it would be best to start from the front to back.

The first step - make the cutout for the fuel gauge and fuel cap.



The lip of the opening is bent downward. I made a forming block out of a scrap piece of wood.



Then the lip was bent downwards by stretching the metal around the form.



Flip the form over and bend the other side.



Trim and sand the edge smooth.



The opening is complete.



Another view.



Once the opening was cut and bent, the sides of the aluminum were marked and the pneumatic shears cut off the excess.



We put the original rear cowl in place. We haven't made the new one yet but the old one fits so that is a good thing. The opening for the front cockpit needs to be cut out yet. A decision has to be made. Here is why:



We have a bunch of original Curtiss drawings showing the cowling dimensions. The prints are from the JN4D2 which is different than the JN4D.

The JN4D has two nearly round cutouts with a small windshield.





Here is another view.



Now the Canuck has a bigger opening than the JN4D. If you look under the windscreen, you will see the cowling cut out beneath it. Plus, it is a bigger windscreen.



The extra cutout allows you to see the instruments better. If you sit in a JN4D cockpit, you have to duck your head to see the upper instruments. Not so in a Canuck.



Of course, the JN4D2 cutouts are even different. they have the same rear curve, but the cutout in the front is even bigger than the Canuck! So, our drawings are nearly useless.

Such decisions.

The piece of original cockpit is from a Canuck. I sat in the airplane last night and I must admit, the cutout under the windscreen is nice. I have not made a decision yet, but I am leaning this way.

There is a lot of sheet metal work to come. Stay tuned!

Brian

Burnishing - Jewling - Machine Turning - call it what you wish

The seat cushion arrived from the upholsterer today. We had them put the old style buttons in the cushion, just like the Curtiss drawings.



Hey...the first panel was finished! Four Roloc disks later and four hours worth of work and the entire panel was done.



After the burnishing, the bead roller was used to put the 3/16 in. radius beads into the panel.



Two lines - 15/16 in. apart...according to the Curtiss drawings.



Here is the panel in place.



We also cut out the left side cowling.



More soon

Brian

Cowl Burnishing & Louvers

Continuing with the cowling, I tried my best to decipher the measurements of the louvers from the Curtiss drawings. Many of the numbers were smudged. Luckily, I had an original cowl from which to measure.



Before we can make the louvers, the cowl must be burnished. If you did it the other way around, it would be difficult to put the swirl pattern on the raised or curved parts.

Paul Dougherty at the Golden Age Air Museum lent me his louver making pattern. He used this board with some thick gum rubber to press the louvers into the metal. As you can see in the background, the louvers turned out beautifully.



However, the guys in Minnesota who built the Jenny hanging in the history museum in St. Cloud gave me a louver jig, too. It works a little differently.



The jig is variable - the ends slide left and right to make the different sized louvers.



Then a louver die with a hard wood louver shape presses the metal. Instead of the hydraulic press, a mallet is used.

I wanted to practice making a louver this way.

Two holes need to be drilled at the end of the louver. Then a slot was cut into the sheet metal.



I used a die grinder for the cut. A die grinder not the best way to do this because it is hard to cut a straight line and it leaves a ragged edge. But, this was a test piece and I didn't care too much about the cut.

Paul told me he used a sharp razor blade with a steel guide to cut the slot. He said it took a lot of passes with the razor but it cut the steel just fine. I could tell from the pressed louvers that this method made a prettier line. When we make the final louvers, I will do it this way.

Anyway, the hardwood die was hammered into the jig.



You can see it better here.



A finished louver in about three minutes of hammering.



Brian and I also decided to experiment with burnishing. Burnishing was used back then to hide the machine marks in the sheet metal when it was shrunk, stretched or pounded over a form.



Using some photographs we played with several different patterns and spacing trying to find the look that we liked. Eventually, we came to a consensus. The burnishes would be 1 1/4 in apart.



I liked the way the drill press burnished the metal rather than how I made them earlier with the hand drill. But, the cowling is pretty deep and most drill presses can't reach that deep so I was resigned to make them by hand.

But after some thinking, I remembered the Grizzly long reach drill press I bought years ago to drill some angled holes in a stabilizer. The throat was deep enough to reach the center of the cowling.

So, I made an extension arm to go underneath the metal.



We marked the spacing on the sheet metal and started burnishing.



We also tried varying the amount of time the Rylok pad spun on the metal. Three seconds produced a feint swirl. Ten seconds made the swirls deep and dark. Holding down the lever for five seconds worked best.

We also tried various drill RPM's. About 900 to 1000 seemed to be the right spindle speed.



This really is a two man operation. The main job of the second person was to help hold the big piece of metal. But later, we found that if one person could sites down the top line and the other person set up the spacing distance between burnishes, things moved along nicely.



This is what the sheet metal will look like !



Let me warn you - this process takes a long time. What you see here was about an hour's worth of burnishing. There are 21 burnishes in each row. It takes 5 seconds to make the swirl plus about the same time to line up the next one. Doing the math, each row took nearly five minutes. We made twelve rows. That's one hour's worth of work. Whew!

Lastly, the oil tank came back from the welder. Some day I want to learn to weld aluminum with a TIG welder. I've always welded with gas because I couldn't afford a TIG welder but eventually I'd like to learn how to do it.



The tank was made using an old photograph as a guide. I found a picture of a Hisso Jenny without the cowling and tried to make it the same way.



I know having the weld flanges face outwards is not as strong (nor as pretty) as having them face inside, but this is how they made them back in 1917.

That's it for now. More soon. Enjoy

Brian

Burnishing

I wanted to try a few things today. We are planning on burnishing the cowl like they did back in the 1920's. They used a wire wheel to burnish back then, but I used a 2 inch Riloc pad - basically a round scotch brite pad!

I practiced a few times with a drill press while I was visiting David Harwell at Barnstormers Workshop. This worked really well, but I got to thinking - How will I be able to burnish deep into the cowl? The throat of the drill press is only a few inches deep.

So, I tried burnishing by hand. That way I could make the neat little swirls anywhere I wanted. Much as I tried to hold the drill still, the pad wandered. The swirls looked awful. Oh, well. So much for that theory.

Paul Dougherty made a really pretty burnished cowl on the Golden Age Air Museum's Winstead. I always admired the cowl, so I called Paul and he told me how he did it.



Basically, you make a 2 inch hole in a thin piece of plywood. This keeps the pad from wandering.



Then, you just move the hole down the line and burnish with a portable drill. I clamped a wooden guide to keep everything straight (like Paul told me to do). This worked really well.

The Jenny cowl has lots of louvers and beads. Before you can do any of that, the flat cowl must be fully burnished. Using the practice piece, I experimented making the 3/16 in. radius bead using an Eastwood bead roller. It worked very well. The beads were 3/23 in high just like the Curtiss drawings specified.



On a more productive note, the first side cowl was trimmed today.



I couldn't resist hanging up the test piece!



Anyway, the perimeter of the side cowl was cut to match the lower longeron.



Here is what the cut out looks like at the lower wing attach point. More hand filing will be done later.



More soon

Brian

Wire roll on lower cowl

Since the bottom of the lower cowl has a gentle curve to let the air flow through the radiator, a wire edge is needed to stiffen the sheet metal.

So, strike a line and using a hand seamer, bend the edge up about 90 degrees.



Then, clamp the wire in place with some vice grips.



With a block of wood, push down on the wire and bend the edge over a little more.



Then bend the edge over the wire.



Once everything is bent, go back and tap towards the wire. This tucks in the edge and gives you a nice finish.



Here you can see the edge rolling around the wire. at the corner of the block is where I stopped for the photo. You can see the unfinished section to the left and the finished section to the right.



Here is the edge of the cowling from the inside.



And the outside.



More soon.

Brian