Building the MachNone
A Sky Pup Construction Project
Possible Alterations to the Plans
Although it is strongly advised to avoid making changes to the Sky Pup plans, here are some changes that I recommend.
The plans recommends that the hinge be constructed of two strips of cloth sewn together and then glued up such that each individual cloth strip wraps around alternate edges of the control surfaces leaving only the thread alone holding it together. I recommend rotating the sewn together strips 90 degrees laying it up such that each cloth strip crosses over both surfaces. That way the surfaces are held together with two full layers of cloth rather than just the thread of the stitch line.
I forget now how I discovered it, but at some point I noticed that one or both lower longerons had worked loose from the seat support gussets probably from the twisting imposed when one wheel touches down before the other. Whatever reason, this is a common problem with Sky Pups. In Sky Pup News #11 Cecil Bosworth had the same issue and I recall some others having similar issues. I had to reinforce that area, so I recommend that you should circumvent the issue altogether by reinforcing that area while constructing your Pup.
There are two things I think would work. First, put a short strip of longeron doubler from the front to back of the gusset. That will mean you will have to slightly alter the gusset–basically move things off by ¼ inch but it would give double the gluing area and I don’y think it would ever come loose. By the way, make sure you scarf (taper) the ends of the longeron doubler, otherwise you might have a stress riser with a bkunt cut off.
The other thing you could do is beef up the Fiberglas “anti-peel strips” that the plan calls for over this area. (I had to do this in my retrofit repair.)
I do think that this is a necessary improvement.