Carlson Skunk Works

March 2nd, 2012

AMF 14H MARANDA SN:1026 Making Sawdust March 2, 2012

Posted by Roger in AMF 14H Maranda SN1026, news

Progress has been focusing on the landing gear this winter. I need to get more pictures for in here and maybe I will be able to do that this next week. However, I did remember to take a few of the current project which is the shock struts.

Cal has been gracious enough to allow me to use his gas welder setup to learn to weld, and Fred has kindly shown me the basics. Then they turned me loose and let me burn metal! I still burn holes in my tubing, but my welding is going better each time I work on a new part.

So far the front legs of the main landing gear are done. I did the gas welding which was the majority of the work, then Fred took them to TIG weld the axle mounting plates to the lower gear tube. Both of these parts are fairly heavy, so he thought it would have better penetration using the TIG than using the gas welder.

The way this has worked is that during the week I have been cutting and fitting metal and building jigs to hold the parts while I welded them. Then on either Saturday or Sunday afternoon I would go to Cal’s place and do the actual welding. This has worked quite nicely.

This week I have been making the parts for the shock struts. At lunch today I cut the last few parts and took some pictures.

So, here are all the pieces that go into the shock struts except the springs and a few bolts. I am waiting for my checking account to recover a bit before I order the springs, but that should happen next week. I have the bolts, washers and nuts that I will use.

Even though these parts seem to be pointing down, they are the parts for the top section of the shock strut.

I guess what you need to understand is that the shock strut is sort of like a shock absorber. It is basically three parts, an upper tube, a lower tube that slides inside the upper tube, and a spring. There will be a big washer welded to the lower end of the upper tube. The spring will slide over the top of the upper tube and sits against the washer. Then a collar with another big washer slides over the upper tube and sits against the top of the spring. The lower tube extends through the inside of the upper tube far enough beyond the end of the spring that a hole can be drilled through the collar and lower tube to allow a bolt to secure them together. If this is all that happens then we would just have a solid assembly and that would not give us any suspension at all. Therefore, slots will need to be cut in the upper tube to allow the bolt to slide. I will try to remember to add pictures as this all goes together.

The next issue that I had to deal with was that there is a slight discrepancy between some of my sub assemblies. The assembly where the upper end of the shock strut fastens was built according to the plans. The shock struts are being built from the plans in an article by Tony Bingelis in one of his books that I have. The upper tube is 7/8″ in diameter. However, the assembly where it will be fastened will accommodate nothing larger than 3/4″. Therefore, I had to find a way to make the reduction.

This is why I have a 4″ piece of 3/4″ tube inserted into the top end of the 7/8″ tube. To provide the most possible welded area between the two tubes, I cut a “fishmouth” in the top end of each of the 7/8″ tubes, then I drilled a 5/16″ hole through the larger tube at the bottom of the fishmouth. The plan is to weld all along the edge of the fishmouths and in the inside of the hole. I think that should secure things pretty well. These techniques are used when repairs are required on a steel tube fuselage, so they should be acceptable.

Here are the parts that will make up the spring retainers. At the bottom of each upper tube I will weld one of the big washers. However, the washers have a hole diameter of just over 1″ and the upper tube is 7/8″ outside diameter. Therefore I cut a couple of short pieces of the 1″ tube to put inside the washer holes and over the tube. The plan is to weld them all together securely.

The upper collar consists of a 2″ piece of 1″ tube with a washer welded to it. The washer sits against the top of the spring and a hole is drilled through the tube to allow an AN-5 bolt (5/16″ diameter) to go through.

At this time I do not have the springs. I will need to wait a week or so before my checkbook is able to handle the purchase. The springs that I will use cost about $50.00 each. However, Fred has the same setup on his plane and it is currently out at Cal’s. So when I go to do my welding I can find out exactly where the washers need to be welded on the tubes and where the holes have to be drilled.

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