Bearhawk Construction Log Section of

Drill, Debur, Dimple, Nutplates

admin — Sat, 05 Jun 2010 04:00:55 +0000

Today was a day with lots of hours and not a lot of pictures. I finished the work on the left air intake, which included dimpling the boot cowl and cutting countersinks into the plastic vent. I also dimpled all of the holes in the boot cowl skins that will get rivets, except for the firewall flange. I wanted to wait to commit to fasteners on the firewall flange until cowl time. I added some missing nutplates to the glareshield hatch (the corners that needed single lug nutplates) and started adding the nutplates to the lower boot cowl panels.

Here's a nice row of nutplates (in the wrong place)

Above you can see that I put the nutplates on wrong. I have made this panel 3 times now, so hopefully it is correct (speaking from the future again).

I also cut off some long strips of aluminum to use for the wingtips, and started preparing the stainless tunnel piece for it’s nutplates. It is so thin that dimpling is the only option for the nutplate rivets.

Engine Mounts and NACA Scoops

admin — Thu, 03 Jun 2010 22:30:04 +0000

I’ve been watching the price of the engine mount rubbers for the past few months, and the trend seems alarming. In the 2008 Vans Accessory catalog, they were $40 per lug (for a total of $160). Today Vans sells them for $125 per lug, or $500 plus shipping! Yikes! I was surprised to see the cost go up so quickly. I was looking for some way to spend less, and eventually found that Jeppesen of all places sold them. Their price was well below anything else that I could find, at $88 per lug. My only explanation for this was that their price was outdated, but who knows. I was glad to save so much money. Here’s the data from the box:

Lord J-7402-24 Engine Mounts

Nobody seems to know how long the bolts need to be for attaching the mounts to the engine. I don’t really understand the mystery- the mounts have a center tube that gets compressed to the washers on either side. Now that I have them on hand I can measure the length of that tube and the end washers to come up with a grip length for the bolts. Here are some pictures of my measurements, in case you find yourself wondering how long the bolts should be.

This was just the uncompressed length, not very useful.

Here's the thickness of the end washer. It's just a little bit more than .1 inch

Here's another somewhat useless measurement- the uncompressed gap between the two big pieces.

Here's the uncompressed length of the pair

Here's a much more useful measurement- the thickness of the assembly once it is compressed.

This is the measurement that I took of the thickness of the engine mounting ear on the engine. This one isn't especially accurate, but is pretty close.

For the purpose of ordering bolts, my measurements aren’t especially accurate, since the bolts generally come in 1/16″ increments. I figured that the compressed rubber was 2.03″ and the engine lug was .93″. This makes the required grip length for the -7 bolts 2.96, not counting for any washers (and I’ll need at least one of those at 1/16″). The AN7-34 is 2 15/16″ (2.9375″), so I ordered the 7-35 with it’s 3 1/16″ grip length. That will allow for a washer or two but will keep the bolt’s threads out of the way.

With that bit of research done, I started working on the air intakes that will go on the sides of the boot cowl. These will provide fresh air for the front seats through an eyeball wemac type of vent on the instrument panel. I got the scoops from Vans, their part SV-1 at $6.25 each.

Here's one of the scoops from Vans, along with a cardboard template that I made for marking the aluminum skin.

I wanted to make an aluminum backup ring so that the plastic part would be sandwiched between two layers of aluminum. The cardboard template made that step easy.

Here are the two rings and a nice view of the back of the SV-1

I drew a few lines on the boot cowl to try and figure out where I wanted to put the vent. My primary goals were to make the centerline of the intake horizontal in level flight, and to keep the intake lower than the outlet inside, so that water would be more likely to drain out if we were flying in the rain. I’m curious to see if this works.

Here's the mark on the boot cowl sheet for where the vent will go. I almost oriented the vent backwards! This is the right side of the airplane, with the nose facing right.

Here's a more wide-angle view of where the vent will go.

Here's the boot cowl skin flattened out and ready for cutting the hole.

Now I just need to dimple the skin, countersink the plastic, and put everything aside until I'm ready to permanently attach the intake.

I got to the point of dimpling the holes for the first side and had to quit for the day.

Headset Jacks and Door Sill

admin — Fri, 28 May 2010 18:45:57 +0000

I started out today by finishing something from last week.

This is the forward attachment for the top stringer, looking up and slightly forward.

While I had the torch out, I also added a few more parts to the skylight area. First up were some plates for the headset jacks.

This plate will hold the headset jacks for the front and rear set occupant on one side.

This plate goes on the spanwise mini-bulkhead that I’m creating at the aft side of the skylight. This is what it looks like with a couple of the jacks installed temporarily.

The switch is required to specify stereo or mono headsets. I've never seen an intercom that required such a switch.

The holes started out as small pilot holes, as you can see in this left-right before and after picture.

Here it is after welding in place

This location will put the headset plugs and cords up and out of the way, behind the front seat passengers and ahead of the back seat passengers.

Repositioning Door Area Flange

admin — Fri, 21 May 2010 01:45:06 +0000

Today was a two-part day. In the first session, I used a dremel tool to remove the weld on the vertical portion of the door threshold at the forward end. This was to allow for repositioning that piece so that it would attach properly to the aluminum piece that goes there. This also involved cutting loose the piece that I added on earlier.

This is the forward lower corner of the front door. I've removed the weld and the paint in the area so that I can bend the whole vertical piece out some.

This is the same piece that I added earlier in the year. This time I trimmed it and moved it inboard some to allow for the aluminum panel.

I also addressed a small scratch that I made on one of the engine mount tubes. I sanded the area with fine sandpaper to remove the scratch, then sprayed a little bit of temporary primer to keep it from rusting.

Engine Mount Touch Up

In the second session I added on the front tubes for the skylight, cut the chordwise tubes loose, bent them to a slight curve, raised the front piece up, and cut out some new stringer tabs. This is all work that I wrote about a few entries back.

Seats and Engine Mount

admin — Sun, 16 May 2010 00:15:38 +0000

Today Tabitha came out again to finish squeezing some more wingtip rivets. We also tested the glue on the foams to make sure that it wasn’t going to dissolve them. The glue checked out OK, so we glued one of the bottom cushion combinations. Tabitha marked it for cutting and spent some time thinking about how all of that needed to be done.

Tabitha is trying out a few different seat foam combinations and marking them to cut.

While she was doing all of that I worked on more nutplates in the boot cowl/fuselage area. Danny stopped by, and he and I installed the engine mount.

Nutplates on Panels

admin — Mon, 10 May 2010 21:45:18 +0000

Today was a short day, but I was able to spend some time on the nutplates that will hold on the “optional” aluminum panel under the door. I learned about a few complications.

This is a hole for the nutplate that will hold on the aluminum panel under the door.

First, the nutplates won’t work well on the top unless I bend out the steel piece at the bottom of the door. The surface of the panel and the surface of the nutplate’s support have to be parallel. As it is, the steel piece is bent inward to help keep it from chaffing the fabric.

The second problem is that I have way too many holes in that panel! I’m going to spread them out a little on the top, and the door sill plate will help hide the unused holes (and share the used holes).

Here's a test flush #8 screw.

Tailwheel Spring and Wingtip

admin — Sun, 09 May 2010 23:42:31 +0000

Tabitha came out today too and we made some good progress. I was at a stopping point with the tailwheel spring because I didn’t have a drill that would handle larger bits. It had a temporary bolt in place of the AN-7 that is supposed to go in there. With the new drill I was able to get the hole up to size and reinstall the tailwheel spring.

I got this new drill so that I could use larger bits. All of my others have a 3/8\

Meanwhile, Tabitha was dimpling and squeezing the rivets for the wingtip flush mount strip.

Tabitha was dimpling and squeezing.

I also spent some time getting ready to install the engine mount, now that I have the hardware.

Seat Foam Ergonomics

admin — Sat, 08 May 2010 23:15:14 +0000

Today Tabitha came out to help. With the seat pans finished, it was time to start thinking about cutting the foam for them. But first, the flooring supplies came in, both the foam padding and the top layer.

Here's the final color of flooring. It's the Nautolex Decko Dot in the charcoal color.

This is the 1/4\

The plan for the seats is to use one inch of firm tempur foam on the bottom, followed by urethane foam on top of that. I was initially planning on 1 inch of firm urethane followed by 2 inches of medium, for a total of 4 inches.

Mr. T tries out the back seat foam, but he says it isn't thick enough yet.

It looks like the 4″ cushion is going to limit the headroom, at least for me. We’ll keep the 1″ layer separate and use it when needed.

Here's a test of the 4\

Here's a headroom test. Even without sitting up straight, there isn't a headset worth of space between my head and the ceiling structure.

Tabitha tries out the flap handle, demonstrating the need for inertia reels for the front two people.

Welding Skylight Tubes

admin — Mon, 26 Apr 2010 00:00:28 +0000

I started cutting and adding in some of the new skylight tubes today.

Here is a new chordwise tube. Note that it doesn't really fit just right.

I cut a notch into the tube to make it match the mounting area.
Mysterious note from the future!
I learned in retrospect that the following picture shows a tube that is ground a little too much. It should have been a little bit taller.

Now it fits better.

Here you can see the pair.

Mysterious note from the future number 2:
The above and below pictures show another problem. I put the tubes in as straight tubes, and they should have been curved slightly. Can you see what I mean? They should probably match the curves in the channels at the wing root.

From this angle you can see the new spanwise tubes, and the problem with the chordwise tubes.

While I was there, I welded the seatbelt tube in place.

Here's the completed seatbelt support tube, ready for prep and paint.

Skylight Modifications

admin — Sun, 25 Apr 2010 00:00:59 +0000

Today I finished the back seat covering. Now it’s ready for some airplane noises.

Here's the finished back seat bottom.

It's a front seat, in a seat. It and the engine mount are just having a chat.

Here are some details of how I sequenced the overlaps.

Since our back seat has the added headrest structure, I covered the back in two pieces.

I wrapped the front fabric of the seat back around the back side of the bottom tube.

After I finished the back seat I took a little lunch break. Fellow EAA 731 member Kevin Ball stopped by and we spent an hour or so talking about the airplane, then I went over to Bart’s to take a look at his avionics work and to return his bending brake. When I got back, I started preparing the ceiling structure for the skylight.

The first step was to cut the stringers off. I left them a little bit long for final trimming.

I also cut the old stringer supports down a little bit to effectively lower the roof line about 1/4 inch, after accounting for the thickness of the new tube that will be on top of it. I copied the spanwise tube sizes from the plans at station C (T3, 3/8 x.035), and the chordwise tube sizes from the existing tubes in that area (T2 5/16x.058). I chose that size since the spanwise tube at station C serves the same purpose as my new tube at station N- a forward border for the fabric and an aft border for the other than fabric.

I decided to run the skylight back to the aft spar, which is further back than Pat ran his. I'm planning to have three separate panels that each run the full length. This will help reduce the compound curves in that area.

Bob has also specified that another tube be added between station N and the x cluster for supporting the shoulder harnesses for the front seat passengers, if the shoulder harness is going to attach out in the middle of that big tube at station N.

Note the areas that I've cleaned for welding in the seatbelt support tube.

Since the skylight will move the forward end of the stringers aft, I'll need to cut off these tabs.

In this picture I'm cutting away the old stringer supports.

This is looking mostly forward at what used to be the tab that supported the stringer

Here's a nice overview. The two little vertical tubes that used to be stringer supports will now hold the spanwise and chordwise skylight tubes, and the new forward attach tabs for the stringers. The paint is gone in the middle of the large tube for the seatbelt support tube.

I also did some measuring to decide on how far forward to take the skylight. One certainty is that this is a lot of effort to make a big hole in the roof, and I’ll have to carry sunshades to cover it up for a lot of the time.

I still haven't decided on where exactly to end the skylight on the forward side. Here are some options, with the numbers reflecting the number of inches from the windshield track. This shot is looking down at the top of the fuselage with the nose to the right.