Carlson Skunk Works

June 22nd, 2012

AMF 14H MARANDA SN:1026 Making Sawdust June 22, 2012

Posted by Roger in AMF 14H Maranda SN1026, news

This is the first post made from the new Apple Macbook Pro that work has provided for me to use. Let’s see if it works as good as my Linux box.

Things have been pretty busy, so progress has been slow, but progress has been made. Tomorrow I am going out to Cal’s and will weld a couple of parts for the control stick and heat up the joints on the engine mount to release the excess stress.

The engine mount turned out pretty good, but when metal is heated it has a tendency to move around. Therefore, I purchased a piece of steel plate and drilled holes matching the engine end of things, then bolted the engine mount to it. Then I scrounged up some angle iron from an earlier project and drilled holes in that for the fittings on the firewall side of the engine mount. All I “should” have to do now is to heat the joints nice and cherry read and then let them cool while being held in place. When that is done I can check to see how smoothly it fits the firewall.

I also ordered material for the fuel tank last Monday. At the Holdrege fly-in last weekend I showed the plans for the fuel tank to Gary from Marlat Machine Shop here in Kearney. Gary said he was getting ready to order some metal and would add some aluminum sheet for my fuel tank to the order. With a bit of luck (and a few bucks) I can probably get him to make the major cuts on his shear for me. But that will be another day.

So, what I have been doing is building the control stick assembly.

This is what the assembly looks like. There will be another piece added toward the rear of the assembly to transfer movement to the ailerons. I need to get this much done and then figure out how to do the aileron connections.

Everything starts a a bunch of parts. The whole assembly consists of a 1″ diameter tube for the stick, a 1/2″ diameter piece of tube that goes through the stick to act as a spacer and pivot for the stick. The stick will pivot forward and backward on that tube. Then there is a 1 1/2″ tube that runs front to back and has a slot for the stick to fit into. The final piece is a sheet metal yoke that goes around the torque tube and has the pivot hole for the stick. With this arrangement the stick can move forward and backward, and it can cause the torque tube to twist right and left.

The yoke fits around the torque tube and will be welded to the torque tube. The yoke has 1/4″ wide flanges that are bent perpendicular to the yoke surface. These flanges add a huge amount of rigidity to the assembly.

Because I learned that metal moves when it is welded and I have also learned that it is difficult to keep things in place while welding, I drilled a couple of holes through the yoke and the torque tube and inserted screws in them to hold things in place. This also allowed me to disassemble and re-assemble things while I was making adjustments. The main adjustment was the size of the hole in the torque tube where the stick goes into it. This hole is the mechanism that limits the travel of the stick forward and back. The airplane must have some form of mechanical stop to ensure that control surfaces won’t move beyond safe limits. This mechanism limits how far the elevator will be able to travel up and down.

The control assembly needs to ride in some type of bearing, so the plans call for bearing blocks made of Delrin which is a very dense plastic. There is one of these blocks at the front of the assembly and another at the rear of the assembly. The bearing blocks are bolted to the back sides of the front and back bulkheads. The picture above is the rear bearing block.

The front bearing block had and issue. The 4130 rods that transfer the load of the wings and landing gear through the fuselage just happened to interfere with the location of the torque tube. The plans call for a thin piece of Delrin, but I had 3/4″ thick material and decided to use that. This was good because …

… it allowed me to groove the bearing block around the rod. I still have about half an inch of support for the torque tube which is more than what is called for in the plans.

The other thing that is a bit different than I expected is that there is a gap at the top of the rear bearing block. When I built the rear bulkhead the plans said to glue a piece of plywood (I think it was aobut 1.5mm) to the bulkhead below a cross piece. The cross piece has an opening to fit the bearing block, but the plywood doesn’t extend into that opening. This will not be a problem because I will take advantage of it to help secure a bracket. That bracket has yet to be built, so I won’t go into what it is for at this point. You will just have to reference back to here later.

The stick won’t do much good unless the pilot can get a good hold on it. So …

I cut a hole in the floor to allow it to extend into the cabin. The torque tube rides about half an inch below the floor, so the yoke comes up through the floor as well. The stick cannot be installed until the torque tube has been installed. So the process is to bolt the front bearing block into place, then slip the rear of the torque tube through the hole in the rear bulkhead, slip the yoke through the hole in the floor and insert the front of the torque tube into the front bearing block.

Next the rear bearing block needs to be bolted into place to hold things together. Then the stick can be positioned in the yoke and the pivot bolt can be installed.

And it fits pretty good. Full back on the stick doesn’t hit the seat and there is plenty of room to move it full forward as well.

This will probably be the only picture that will ever be taken from this angle. This is a front view that I took by reaching over the firewall. Once the fuel tank is in place I will be putting the top on the nose of the cockpit and I won’t be able to reach down into the plane this way.

Tomorrow is supposed to be 96 degrees, but I am going to weld anyway!