Hatz Biplane Association

Question for Rick (HC85) - I was reading the Poly Fiber manual and looking through the posts on the forum. I came across this picture. I have to ask if the plywood backing around the spar fittings comes from experience. The Poly Fiber manual doesn't say anything about backing. It says to stretch the fabric with ironing then cut the fabric to let the fitting through. A patch is applied after the poly fiber is cut.

So when you put the backing around the fittings, do you cut the fabric and glue it to the backing before the fabric is stretched? And do you add a patch over the area?

I'm not Rick but here are my 2 cents worth.......
On my LB-1, I didn't put the backing around the fittings. I was taught to shrink the fabric before you cut the holes. If you cut the holes first, the holes get REALLY big when you shrink the fabric.
I've also heard where builders shrink, and apply a coat of dope or polybrush around the fitting area, and then cut.
If you do put the backing on, and are going to attach the fabric to it, make sure you apply the "glue" to the backing first. Then when the fabric touches it, and your coat of polybrush is applied, the fibers will be encased.
In either case, a patch is appropriate. If you use a preshrunk patch and a sharp razor blade/knife, you will get a nice looking installation.

Good luck!

Jeff Moore

Thanks Jeff - For sure the Poly Fiber manual talks about shrinking before cutting and preshrinking the patch. Thanks for reminding me. I had a look at a recently restored J3 and a couple of Tiger Moths. The cub had a couple of fittings protruding through like the Hatz with no backing and they looked good. When I pushed on them you can tell they didn't have a backing. The owner of the cub did show me where he used plastic (from a plastic gallon jug) on the fabric with a patch over it where he wanted to stiffen up the area around a bigger hole. I can't see where the Hatz has any of those situations but a good idea for sure.

I'm a long ways from fabric but every time I see a place where there is going to be a hole in the fabric I'm wondering how I'm going to handle it.

Test the plastic jug material with the covering system you are going to use; elsewise, thou mayeth have a gooey mess.

Jeff

Hi Doc,

I have no experience with doing it on a full scale airplanes other then mine here, but when I used to make RC model airplanes ( Which got me down this crazy road in the first place) I used to always support the area around any openings if at all possible, because it just made the cover job look better, and kept the covering from sagging into the area. I saw that other folks building Hatz' have done this (Hanson Hatz Classic), so, I did it as well. I also made little tabs from steel around all the hinges for the tail feathers as well. I saw that Maklan did it on their CD pics.... but this is not shown on the plans.

i hope this info is useful for ya.

Best regards,

RIck ( HC85)

Oh, I forgot to add this. I planned on shrinking the covering enough to make sure it will lay down nicely around the area, then stick it to the pad I placed around the fittings. Then, make and apply a patch around it all.

I plan on using Oratex 6000 on my plane. It reportedly does not shrink as much as Poly Fiber, and has a little different methods for the process. But, that material is a lot closer to what I am used to using on my big RC birds, and I'm looking forward to using it!

Rick

JBMoore wrote:Test the plastic jug material with the covering system you are going to use; elsewise, thou mayeth have a gooey mess. Jeff

Thanks Jeff. Good idea. A person also could use 1/32 plywood with compatible varnish.

Rick - I'm going to explore some of the ideas I see here and on the forum some more. I like the idea of putting a backing even though I haven't seen it except in your pictures. I'll have a look through the Makelan CD pictures again for the tabs on the rudder hinges.

I was just reading Tom Wilson article in Kitplanes; "Builders by Type". He didn't have an OCD category. I probably fit that category best.

I had to see what it was going to look like!