Category Archives: Firewall

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

Day 5 or What I Learned About Building Airplanes

Time Card As you might have already guessed, I try to be very organized. Because one of my goals that goes along with building the VP-1 is to get my A&P Certificate, and some of the logged time can be applied towards said certificate, I decided to try and keep very accurate records of time spent on the project, both shop time and administrative time. To that end I picked up a box of time cards. In theory 100 double sided time cards should last 3.8 years.

Why keep time cards? Not only is it a great way of keeping track of how much time I spend on the project but there’s more. For one, it’s a physical record just for tracking time. Sure, the builders log will do that too, along with a bunch of other information, but I think handing over a stack of time cards to an FAA inspector as proof of work as a separate record shows attention to detailed record keeping that is a very important part of an A&P’s job. Also it is an easy record to have signed by an A&P I am doing work with as supervised work.

There is another reason to use time cards. The idea is to have a slot for every day of the year, a new time card every week, staring me in the face ether say “Wow! you worked a lot on the airplane this week” or “Dude! A whole time card and no work on the airplane?“. It is its own incentive to get out to the shop every day or so. If I get hung up waiting for parts to work with, I am still logging admin time, so there is no reason not to do at least something; at least thats the idea behind it.

This first five days I have logged some time and learned a few things. As promised, I started working on Saturday January 1st, 2011. I started by laying out the Doug fir braces for the firewall bulkhead, relatively straight forward, tolerances were tight with the blade kerf and all, but it looked doable. Then I moved on to laying out the firewall itself. Over all I spent two and a half hours laying out everything and measuring everything several times. After that, I called it a day. I have heard so many builders say “Don’t rush things, you’ll only have to do it over.

Firewall Bulkhead LayoutSunday morning, really early, like 2am early, I woke up with a thought, the layout for the bulkhead was wrong. All of the measurements are referenced from one of two places, ether from the centerline/bottom, or from the outside edges. Here in lies the problem, The centerline marks are fine as long as the centerline doesn’t move. The edges however are in-fact going to move due to a beveled edge that trims off a half inch on ether side. So I can ether go back and remark all cuts referenced by the half inch, or, and I think this best, cut the rough, bolt on the Doug fir as is needed before beveling, then recheck the centerline, and only then move in on the edge cuts. It is a lesson in processes. With nothing but schematics and no real guide for process, you have to take a little extra time to think it all the way through.

Another thing I learned was during my shop time on Monday. I only put in an hour, mainly due to disgust with myself. Don’t cut wood with a wrong or bad blade! After all these years of doing workshop type stuff this should be a second nature no brainer. Well, I was a no brainer apparently. I burned up some perfectly good Doug fir and made myself some push sticks for my next time in the shop.

Then Wednesday came. Shop time, two hours. Yup, changed out that blade and made some real nice soft fluffy sawdust. A beautiful sight and smell, much better than the cloud of burning lumber from Monday. Both of the braces came out nice and neat, square and level, and needed only a nice basic sanding to clean off the light saw marks. This really makes up for Monday.

push sticks   Firewall bulkhead braces

Last weeks time card only had two days from the new year. This week is only half over and I have two days with shop time! I am hoping to get the firewall roughed out by the end of the week. Wee shall see if the day-job will accommodate.

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

Firewall Bulkhead

Firewall BulkheadGreetings all you aviation types out there!

After much debate, a few false starts, and some gnashing of teeth, I am actually starting to build the real full-scale VP-2. I was looking for the least expensive assembly to get the ball rolling and decided to start with the bulkheads. The firewall bulkhead seemed like as good a place as any to start. There are a some good reasons to start here too, first off it is frequently station 0 for all of the location references and weight and balance data. The firewall is also the forward most airframe structure, and this assembly doesn’t require any “aircraft grade” lumber in its construction.

There are of course other aircraft grade materials needed for the assembly, but they are relatively inexpensive. In this case it is 10 bolts with corresponding nuts and washers. I ordered the bolts, nuts, and washers from Aircraft Spruce on the 29th, and I already have the doug fir. All I need to do is pick up “a good sound piece of (3/4“) D.F. exterior ply”.

With hardware en-route (I expect it this afternoon!), board lumber in hand, and plywood a short drive and a few bucks away, I started studying the fine details of the firewall bulkhead assembly. I have been going over the plans for the bulkhead with a fine-tooth comb looking at every minute detail, arc, and dimension. This bulkhead is solid unlike the forward and aft spar bulkheads or the stern post. The other bulkheads all have doug fir and white pine cores with aviation plywood (1/4” and/or 1/8“) webs. The firewall is a slab of ply with doug fir reinforcing members bolted on the aft starboard and port sides.

A challenge presented itself with the hardware specifications. The bolts were spec’d on the plans, but the washer and nut were not. With a little detective work I found a vague reference in the “General Assembly Procedure” text in the back of the plans set. The only references to the firewall bulkhead don’t say anything about what hardware is going to be used. There is a brief note that lists a few pieces of hardware but it has no references to assemblies so you are left to your own devices to figure it out. I found the reference after looking up hardware in the Aircraft Spruce catalog and figuring it out there. There needs to be an updated, cohesive plans set for newbies without aeronautical engineering degrees. After I take an AutoCAD class or two I think I’ll get on that.

On several occasions I have heard that when building an airplane on your own you should try not to look at the Big Picture too often. Taking the construction one assembly at a time and looking at the Big Picture only when between assemblies to decide what to do next and for interconnectivity issues. I have been scouring over the whole plans book in detail for a while now and I am starting to see the whole as a collection of smaller independent projects.

I can see now why a lot of builders that jump in feet first without a lot of thoughtful review find themselves feeling in over their heads after a while. I can also see how experienced builders can switch from one area of the aircraft to another or have a couple of completely unrelated assemblies going at the same time. It seems that the secret to keeping a project going and making regular and significant progress is that ability to compartmentalize the structure and focus only on the areas that are currently in progress and always have something to work on. Keeping build time for focused building and planning time for the strategic organizing and advance ordering of materials that may take a while to arrive. The whole process is really three distinct jobs. The Project Manager, the Materials Procurement Specialist, and the Builder/Mechanic. For a project to be efficient and run like a well oiled machine a builder has to keep all of those jobs going independently and up to date while keeping it all synchronized.

As the project manager I have been reading the AMT handbooks and scouring the internet for various upgrades/mods for the VP-1/2. Yesterday I found some drawings from builders for things like landing gear mods, break systems, various trim devices, canopies, fairings, and more.

As the Materials Procurement Specialist I think it’s time to head out an buy a piece of 3/4” plywood, that is if I want the Builder/Mechanic to have something to do tomorrow.

Until next time, blue skies and tailwinds!

~FlyBoyJon

ETA: The delivery came from Aircraft Spruce while I was out picking up the plywood so everything is in place for a sawdust party tomorrow.