Category Archives: Stern Post

Another GREAT shop day

Two great shop days in a row, how awesome is that?

Another five hours today; that makes ten hours for the weekend. A fantastic way to wrap things up for the week, I think.

I started out the day by sanding the stern post core and preparing it for bonding the ⅛” skins to it. The T-88 did a great job bonding the edges of the core pieces together, and waxed paper works fantastic as a barrier and release paper. I hadn’t worked with T-88 before so this was a trial run for me. T-88 measures out and mixes up easily. The change from two components, clear and honey, mixing to a cream color when stirred together makes it really easy to tell when it is thoroughly mixed. The best part is the smell, or lack there of. I have been doing some work with polyester resins in my day job, and that stuff is really noxious. The T-88 is so easy to work with and so far I am really happy with its performance.

With the stern post core bonding to the skins and clamped up, it was time to move on to the firewall. First I had to remove the strengtheners from the original firewall which took a little longer than I had hoped for. Once all of the hardware was removed and the strengtheners separated it was time to mark out the new firewall. After marking out the cut lines I set up the table saw and did the rip and cross cut for the basic shape. The new firewall matched up perfectly with the old one.

I decided to clamp them together and used the old firewall as a drilling jig for the new firewall which worked out very well. The holes are really snug on the bolts so any misalignment would make life difficult at this point. Fortunately everything lined up spot on and bolted up cleanly. The counter-sink worked much better this time around. With everything torqued up, the bolt heads are just a couple of thousandths below the surface and they look great.

   

   

With the shape cut and the strengtheners attached I started setting up some test boards for the bevels. Both side edges of the firewall have an 8.5º bevel and the top has a 5º bevel. I was concerned about the set up and I wanted to make sure I didn’t hose the second firewall. After a few sample passes through the table saw I had the angle and distance from the fence set up just right. Time for the bevel cuts.

   

After the bevels where cut it was time to cut the parallel notches in the bottom for the firewall that will eventually accommodate the longerons. There are still several things to do on the firewall but it is well under way.

   

If next weekend comes even remotely close to this weekend in productivity I should be able to finish the firewall and maybe even get a good head start on the stern post, at least get the rough blank cut for the stern post. Looks like I need to get my ducks in a row as far as materials go for the spar bulkheads.

Until next time, blue skies and tail winds.
~FlyBoyJon

10 days since my last confession

Ack! I had hoped to get something posted by now. Well here we go, this post will cover a lot of ground, aviation and otherwise.

In the other category… A lot of stuff has been going in my world over the last few years. I started an AS in Aviation Operations degree program at Mountain State University in 2006. With my aviation experience credit and classes completed, I have 50 units out of 60 for my degree. Before I could finish the program my mother passed away. I had to drop out in the middle of the semester so my grades took a nose drive. All of my aviation credits are pass/no pass so thy don’t affect my GPA. My Presidents List earning 4.0 was now a pathetic 1.8. To keep my financial aid I need to maintain a minimum of 2.0 which presents a problem for me.

To get my GPA back in order I decided to go to San Jose City College and take some classes. I made this decision a while ago but recently I had a bit of an epiphany. It became clear that I needed to do more than I had planed back in 2006. I decided to pursue an Aeronautical Engineering Degree which means I need to cover all of my GEs. Very few units at MSU are transferable to San Jose State so I need to fulfill them at SJCC, hence a complete over-haul of my education plan. I still want to finish my AS at MSU, but that will have to be part time while I work on my AA at SJCC. I’m guessing you can see why I have been busy. I start classes again on Monday.

Now for some of that airplane stuff. Today I worked on the firewall bulkhead and the stern post. I started by marking out everything I wanted to cut. The Doug Fir I am using for the core of the stern post was laid out on a piece of 1″ x 6″ board and the skins for the stern post were laid out on a piece ⅛” ply. With the wood for the stern post cut out I turned my attention to the firewall bulkhead.

   

The work operations for the firewall bulkhead included cutting out the block shape and drilling the holes to attach the stiffeners. Once the stiffeners are in place the beveled edges on the sides and top can be cut as well the curves in the upper corners and drilling all of the holes. I cut the rough shape and drilled the stiffeners. Then I bolted it all up.

   

The aft side of the bulkhead looks good, the forward side however, didn’t come out the way I was hoping it would. The countersinks are a little too deep, so the screw heads that are supposed to be flush are a bit deeper that they should be. The only solution for this predicament is to cut out a new firewall. While I’m not happy about it, I would rather hold myself to a higher standard than let something slide.

I didn’t feel like pulling out the table saw again so I decided to wait until tomorrow to redo the firewall. I still had some time to keep working so I bonded the Doug Fir lumber for the stern post core. Another to-do for tomorrow will be to bond the skins to the core.

   

Since I don’t have any bar-clamps *hint, hint* I had to come up with another solution to keeping the wood firmly in place. This is where my improvised cord clamp comes it. It is just some nylon cord with the ends tied together. Take a piece of scrap wood, put in between the work piece and the cord and start twisting. Simple but effective. The T-88 structural adhesive does not need a lot of pressure to hold the joint together, in fact you need to be sure not to apply too much pressure or the adhesive will squeeze out of the joint, so the cord clamp works well.

That wraps it up for today. Tomorrow is another day in the shop so we’ll see how much gets done.

Until next time, blue skies and tail winds,
~FlyBoyJon

More on the subject of bulkheads

The day job and a clingy head cold have been less than accommodating this last week. That is not to say I have been idle on the project, though.

A day after my last post I got back down into the workshop and was planing on diving in with the rough cut on the firewall bulkhead, then I thought maybe I should get a little further ahead on the parts ordering. The weather has been funky as of late and I wanted to be sure I have small shop work to do that can stretch out over a couple of weeks, so I dug in with building out some parts lists. Sure enough the weather got colder and wetter yesterday and today.

The next part on my build list is the Stern Post. As far as materials go, it is a very simple part. Two pieces of Douglas fir laminated together on the narrow edge to make a wider board, then sandwich the laminate between two pieces of 1/8” plywood. The complicated part is in the beveling and drilling. The biggest concern here as far as the parts is the adhesive for laminating the wood. By far the most recommended adhesive was T-88. On to the order list it went.

The next assemblies in the construction are the spar/strut bulkheads, forward and aft. It really doesn’t make any difference which one I do first. The materials lists for each are very similar, and aside from the lumber and the T-88 for laminating, the only hardware I need is four aluminum bushings for each bulkhead. While that sounds really simple, there was a complication. Well, more of a learning opportunity than a complication.

6061 T6 aluminum Bushing StockThe bushings called out for in the plans are not an item that you buy, they are something you make. You could call up a machine shop and have them made for you, but where’s the fun in that. The plans call for four different sizes of bushing. They are paired two on top and two on bottom for the forward bulkhead and two on top and two on bottom for the aft bulkhead. Between the bulkheads, the bushings on the forward one will be subjected to greater loads than the aft and between the upper and lower bushings, the upper will be subjected to the greatest loads than the lower. Sounds complicated, don’t it?

I posed the the question what if I used the same sized bushing in all eight? on a couple of aviation forums. There were some legitimate questions, for which I had answers. I’m not going to go into all of the finer points, but all boils down to this, there does not appear to be any structural reason for four different sized bushings. In fact, using the largest/strongest bushing in all eight places reduces the aircraft weight rather than add to it. A net benefit I think. Aluminum for bushing stock, added to the parts order.

Parts OrderWhile I was at it I also ordered the bolts that will be going through those bushings. I will still need to order the washers and nuts, but there are some variables with them.

The lumber still needs to be picked up. Fortunately Doug fir and white pine are not hard to come by locally, nor is the plywood I will need for those parts. Once the firewall is roughed out and the bevels cut I will head out and pick up the remaining lumber for the bulkheads.

Sadly I have not made any sawdust so far this week. Hopefully I will be able to get at least one shop day in before turning this week’s time card over.

Until next time, blue skies and tail winds.
~FlyBoyJon