Bearhawk Construction Log Section of

I decided that I didn’t like the idea of using aluminum angle as the aft support for the panel that goes under the door. This was mostly because I couldn’t think of a way to attach the aluminum angle very cleanly, so I figured I’d try to make one out of steel. I would be able to weld the steel to the fuselage, making for a much cleaner attachment. I saw that Bob specified .032 mild steel for the bulkhead at the trailing edge of the boot cowl, so I used .030 for this piece. It took me a little while to get it cut to shape and to bend it on my little toy brake, but I was very pleasesd with the finished product. I bent the trailing edge also, partly to increase the strength of the part and partly to be sure that it doesn’t chafe the fabric.

Aluminum Angle on top, steel blank ready to bend.

Aluminum Angle on top, steel blank ready to bend.

I made a paper template of the flat piece before I bent it.

I was a little bit worried about welding on the longeron. Making hangar doors is one thing, but welding on an expensive fuselage is another. I had a scrap piece of 3/4″ .049 (Bob’s T11) tubing like that of the longeron, so I started practicing. Since the tube is .049 and the tab is .030, it took a little practice to learn how to keep the heat off of the thinner piece. You can see the result.

Here you can see that the longeron sample tube is .049" thick compared to the .030 tab. I wanted to practice dealing with this difference.

It looks pretty good in the middle, but the ends need work.

This is a bad one. I started using narrower pieces just to make it harder.

Here is the end after trimming and ready to fit. Note the clearance for getting the floorboard in and out later

Here you can see the cleco side clamp holding the bottom ready for tacking.

Here is the left side in place

Here is the left side in place

I used a 90 degree die grinder with a scotchbrite pad to remove the paint on the longeron and door sill, which was quite effective. In the end I was pleased with the welding, and now I just have to make the other side.

Here is the inside view of the panel.

I had a surprise morning off from work due to some cancellations, so I spent a couple of hours working on a trailing edge support for the optional aluminum panel that goes under the door. I like the idea of using this panel for two main reasons. One is to make for a place to attach the lower strut fairing. The other is to protect the fabric in a high-traffic area. I didn’t really think of a good way to mount the aluminum angle support that the avipro manual describes. Some other builders have been able to figure out good ways to do it, so I picked up some 3/4″ angle and started working on making a piece.

Here is a mark so that I can trim the panel to match the other one next time I have it off.

Here I am working on it again.

Here is the end of the Aluminum angle. I tapered it some to try and limit the bulge on the longeron. The current shape still needs one more cut to allow the floorboard to be removed later.

Here is the angle rear support stuck in place. I sort of missed when I cut the slot for the tube. I don't really like it.

This is a view looking up from the bottom. The tunnel is on the left, and the aluminum belly piece is on the right. I'd like to bend the aluminum piece a little bit differently so that it lines up with the tunnel at the trailing edge.

I wanted to work on something other than the boot cowl for a little while, so I put together one of the door latches. I’m planning to use Bob’s design for the latch and will add some locks. I found some very compact cylinders at Home Depot for under $5 each. I got 3 that were keyed the same, just because I will probably not be able to buy more with that same lock again. Who knows, I might even use all of them. I also started looking at the optional aluminum panel under the door to see how that should go together.

I was fairly proud of the way the firewall turned out, so I started working on the boot cowl. Richard built the instrument panel top with a removable triangle panel so that the joint is on the inside of the windshield. Bob’s prototype is just the opposite, with the hole for the cabane struts cut from the forward end. I like Richard’s way better, if for no other reason than to keep rain from having a potential leak under the windshield. The top and large side pieces were easy enough to figure out, but when I started working on the small access panels and the tunnel it took a little bit more time to get it all figured out. The panel that goes behind the tunnel is one that I would like to remake, so I didn’t want to count on its holes for guidance. Bob attached the boot cowl with screws on his prototype, but my preference would be for rivets. I asked him what his thoughts were now that he’s been flying for 10 years and 1000 hours or more, and he said that he hasn’t removed the panels once. This was good news, so I’ll plan to use rivets. This is an especially easy decision in the context of the little removable panels that Avipro incorporated. If I take off those panels, the tunnel, and the front floorboards, I would have very easy access to anything in that area.

Today I spent most of the day working in the hangar and it was great fun.  I spent about an hour sorting out the dumped pile of hardware, and this was a good experience.  I got to be pretty fast with identifying the #6 and #8 nutplates.  I also started going through the wing counting hardware and checking on things.  I used the tackle box pictured in the last post to make an inventory of the #6 screws for the wing inspection panels.  There are 94 screws for each of the fuel tank panels… I sure hope I don’t have to take those off very often!

List of contents at the bottom of the tub, awaiting royalties from land o lakes.

I also finished counting hardware for the floorboards and the rear bulkhead.  I put them into a butter tub and listed the requirements for each panel on the bottom of the tub. 

On the topic of floorboards, I disconnected the fuel valve and unhooked a few of the fuel lines.  The Usher gascolator is 3.75″ tall without the quick drain valve on the bottom, which means that it won’t fit between the floorboard and the bottom of the airplane.  It is nice to be able to keep the bottom of the gascolator above the bottom of the airplane for fire protection in the event of a crash that removes the landing gear.  I might try and find another home for the Usher and buy one of Bob’s gascolators since his is short enough to fit by the valve.  It looks like Richard’s solution was to put a quick-drain at the bottom of the fuel valve also.

I would like to do it differently...

I also spent some time working on the elevator trim tab pushrods.  I was concerned about the kinks in the bend, since they might pose as potential stress risers in service.  To address this concern, I considered replacing the entire part, but it made much more sense to just replace the bent section.  I got out the old AC 43.13 to see what it had to say about reparing tubing. I had a piece of tubing on hand that was larger than the 5/16, so I went that route.

Tubing repair with a larger piece per 43.13

I made the calculations using the diameter of the original tube.

Since the OD of the original tube was 5/16, it was easy to make some calculations about how much to overlap.

Look, it’s really me working on the stuff!

Jared Yates building a Bearhawk!

It looks like a hungry fish!

Wait a minute, that's the wrong kind of fish!

That's Better!

Ready to Weld

Here is a bit more time with working on the firewall, with no substantial content beyond the last post. I just got back into town from a nice weekend of fishing, and while I was gone the firewall didn’t trim itself.