Carlson Skunk Works

June 20th, 2016

AMF 14H MARANDA SN:1026 Making Sawdust June 20th, 2016

Posted by Roger in AMF 14H Maranda SN1026, news

Continuing on with covering the left wing, and with significant assistance from my son, Ben, we are now lacing the ribs. After moving the wing to the wing racks I added an “outrigger” to the workbench to provide support for the wings under both spars at the same time. Then I covered the outrigger with some carpet scraps and got a 2’x6′ carpet runner at Menards and put that on the top of the workbench. The carpeting is to help cushion and protect the fabric an wing surface. When that was done we moved the wing back onto the bench and I proceeded to cover the top of the wing.


The top of the wing is quite a bit easier to cover than the bottom because there is only one opening that needs to be made in it. I marked a three inch overlap with the bottom fabric at the leading edge, per Stewart Systems recommendations. Glue was applied to the leading edge overlap and to the trailing edge overlap. When the glue was dry the top fabric was tacked into place along the leading edge, then stretched across the wing and wrapped around the trailing edge and tacked into place there. The interesting point here is that the fabric was EXACTLY the correct width to fit. I did not have to trim any of the fabric along the trailing edge and there was just enough to cover the glue. On the next wing I am going to wrap the bottom fabric around the leading edge to 12″ instead of 11 1/2″ to get just a bit more working room on the trailing edge of the top fabric.

I am using the non-certified 2.7 oz Dacron fabric from Aircraft Spruce. This comes in 62″ wide rolls while certified Ceconite comes in 73″ wide rolls. Be aware of this when planning your covering work. The difference in price is that the uncertified fabric is about 1/3 the cost of the certified fabric.

Stewart Systems and the FAA require a three inch leading edge overlap for certified aircraft. Sawdust is an experimental airplane, so I could claim to be experimenting with a two inch overlap, however, where I can I like to follow established aviation guidelines. The three inch overlap seam will be covered by a four inch wide tape when the finishing tapes are applied.

The other issue was to provide an opening for the push-pull aileron control cable to come through the top fabric. This is a bit different than the opening required for a regular pull-pull cable. The aileron control cable is mounted to a bracket and secured internally to the compression struts. Therefore the opening needs to be cut as the fabric is applied rather than after it is applied and shrunk.




With the opening cut and the fabric secured to the leading and trailing edges of the wing, I took a look at how much of a bump the cable and bracket make in the wing surface.




The bump is not too bad, but I decided that I really should open the fabric enough to allow the majority of the bump to be eliminated. The resulting hole is really fairly small and I cut it close to the cable and bracket.


Now, how to cover the opening and provide some type of fairing? I am mainly concerned with keeping moisture and bugs out of the wing, so I visited the aviation department at my local Menards and had a brain storm. The bracket that secures the cable has a diameter of 1 1/2″. It doesn’t extend above the surface of the wing more than about half way. Therefore I decided to find something that would provide a round cover with a 1 1/2″ diameter inside. Guess what I found:



With that decided I cut a doily for around the cable opening. The main thing that I want to do is keep water and bugs out of the wing, so I thought it would be a good idea to cover the cable opening as tightly as possible.


I then cut the pipe into a wedge sort of shape that would cover the cable mount and extend over the cable to sort of make a fairing. This is not as elegant as what the Stewart brothers show in their videos, but it works. I found that I needed to rough up any area where I wanted glue to adhere to the pipe. I used my little rasp for this and that seemed to work pretty good.




I coated the pipe and area around it with glue and cut some fabric to provide a good fit to the wing fabric.


After ironing the fabric to get it to fit the contours it seems to fit pretty good.


With the cable opening covered we proceeded to do the final two fabric shrinks. Ben helped with turning the wing over a few times. The fabric is now taught and looks pretty good. Ben and I marked the locations for the rib stitches on both the top and bottom of the wing, then moved it to the wing racks for rib stitching.






Fathers’ Day afternoon provided an opportunity to try out our rib stitching skills. We found that we needed about 21 feet of lacing cord to do each of the long ribs. I estimate that we will be able to get by with about 15 feet for each of the short ribs. Things went pretty well and we were able to complete two ribs in about two hours.


The next effort is to finish the rib stitching, then apply the finishing and perimeter tapes. Then we can move on to the second wing.

June 8th, 2016

AMF 14H MARANDA SN:1026 Making Sawdust June 8th, 2016

Posted by Roger in AMF 14H Maranda SN1026, news

Covering the wings has begun. The bottom of the left wing is covered and now I need to modify my workbench to make it “friendlier” to the fabric as I work on the wings. However, that is what I WILL be working on. What has been accomplished is getting the left wing ready for covering and getting the bottom covered.

The wings have been installed on the plane for a couple of years now. The old hanger was pretty drafty and dusty. Therefore, the top surfaces of the plane were/are really dirty and needed to be cleaned. All surface imperfections and glue joints needed to be fixed and smoothed. This is just like the control surfaces that I covered last winter. I found that a fine rasp worked really well for doing this.


Then I applied anti-chafe tape to the ribs and to the edges of the plywood wherever I thought it might provide an abrasion issue.

Since I have a limited number of extra hands, I decided to cut the fabric at home where I have enough room to roll out the fabric on the basement floor and cut it by myself. I measured the length of the wing and allowed for some excess on each end, then cut a length of fabric 17 feet long. When I was ready to spread the fabric out on the wing there was a pretty stiff wind and I had to close the hanger door.







I forgot to take pictures of the first pieces of fabric that I put on the wing. I started by putting fabric over the ends of the aileron cutout and the wing root. Then I glued the bottom fabric to the wing.


The big decision for me was how to deal with getting the pitot static tubes through the fabric without problems. What I ended up doing was laying the fabric on the wing and tacking the leading edge in place, then I marked where the back side of the pitot static tubes came through and marked a straight line forward as a cutting guide. Then I took the fabric loose and cut a slit in the fabric just long enough to allow the pitot static tube to go through. The cut started at the mark for the back of the tubes and cut forward for about two inches. After the initial shrink of the fabric I made two doilies to reinforce this cut. One doily had a notch cut to fit the back side of the tubes and was installed first. The other doily had a notch cut to fit the front of the tubes and overlapped the first doily. The result seems to be pretty solid.


The lift strut attach fittings needed to come through the fabric as well and I made doilies to fit them, too.


The same went for the jury strut attachment fittings.



Rib stitching will be done where the ribs are open. However, the wing root and the wing tip have plywood covering a rib each. I don’t know how to stitch these, so I decided to glue the fabric to the plywood at those areas. I thought about drilling holes in the plywood to accommodate the lacing needle, but I don’t really like that idea. I will continue to give this some thought.


Figuring out the position of the fabric edge for the leading edge took a bit of thought. I watched the Stewart Systems videos and read their procedure manual several times. What I ended up doing was working backward. The leading edge finishing tape needs to be four inches wide. The top fabric needs to overlap the bottom fabric by three inches. The leading edge tape should cover the fabric joint in such a way that it sort of faces the air as it meets the wing. Anyway … I marked the place where the fabric edge should be glued at 11 1/2 inches forward from the back of the leading edge plywood bottom edge. That works fine for the main length of the wing. I just eyeballed the same type of position toward the wing root on the area where the wing tapers. It seems to have worked out ok.


The bottom fabric was extended to the wing tip. I glued the wing tip fabric on the top of the Hoerner wing tip. I did have to cut out for the wing tip light mount. I am planning to put another doily over this area after the top fabric has been installed.




We moved the wing to the wing racks to allow us to modify the workbench. Once the workbench has been modified I will put the fabric on the top of the wing.