Sat Oct 4 2008

Longeron and firewall work

With my dad in town, we started the day by figuring out how to mark the locations where the longerons need to be notched out for the F-711C bars that attach the horizontal stabilizer to the fuselage. Essentially I clecoed them at the end nearest the bottom of the fuselage, then used c-clamps to clamp them to the F-711A & B bulkheads.

I clamped a piece of angle across the front, drew one line, flipped it around and clamped it to the back, and drew the other line. Between these marks is where I need to notch the longeron.

I used a piece of 1/8 thick aluminum to draw the line for the bottom of the notch.

Here's the first notch. There's actually something wrong with the way I did this notch. The plans say 3/32 radius two places. I read this and misinterpreted it as 3/64 radius two places. What I did is drill using a #40 drill bit for the corners whereas I should have just used a #12 drill bit to make a 3/16 diameter hole. If you ask me, the wording on the print is confusing. Oh well, I still think it came out well.

After this, I chopped the aft end of the right longeron on the mitre saw and notched it out.

Here's the left longeron in the process of notching out the aft end. I think these are going to be a little too long even though I cut them according to the plans. I suppose I can always trim some more later if necessary.

The left longeron is all trimmed and notched.

While I was busy with all the filing, my dad was making shavings by countersinking all the skin holes down the length of the two longerons.

Afterward, I moved on to working on the firewall hole for the nose gear access bolt.

First I used a cutting disc in my Dremel to cut a starter hole.

Then it was a bunch of work with a grinding stone to slowly open the hole up to size. Why don't I use a unibit? Basically I'm chicken. I've heard that some folks end up with mushroomed holes and I don't want to take a chance distorting this thin stainless steel.

The result came out pretty well except for a small scratch just above the hole from when I was deburring with the carbide deburring tool.

I had a couple holes in the firewall to dimple, but they were very close to some already dimpled holes. I bought this small diameter dimple die for just this purpose, but it needed to be ground down a little smaller, so I chucked it up in the drill and held it against my running grinding stone followed by the scotchbrite wheel.

My dad was making great progress on the countersinking until the pilot broke off this countersink. Oh well, I'm sure it's not the last countersink I'll go though on this project. Fortunately I had another countersink in my toolbox. I bought it specifically for working on the steel parts, but it still looks pretty sharp. We'll give it a try tomorrow to see if it works.

Next I decided to drill the holes for the brake fluid reservoir. I've decided to use nutplates to hold this on rather than nuts from inside the cabin. I figure it'll make it much more of a one person operation to install and remove. As you can see I've sandwiched the stainless between two pieces of of the firewall stiffeners on the back and this piece of scrap on the front. This is the only way I know of to be sure that the stainless doesn't distort while drilling.

The holes for the bolts and nutplates came out great.

Next I just need to drill the hole for the lower port on the brake fluid reservoir. It's getting late...I'll do that tomorrow. Today was a great day...almost 9 hours on the project!