Hatz Biplane Association

I was very happy with my ultra simple bending jig. I just screwed together 3-4 2x4's and then drew the wing top profile on them, and cut it out on the band saw.
I then soaked about 20 cap strips in a hot bathtub for 1-2 days and put them between the two pieces I had cut out and clamped them together.
Leave it there for a few days and you have plenty of bend.
I have thought that you could do it fine without any bending, but this was very easy, and I was able to bend I think it was about 20 at a time.

Here is a picture of my jig in action.

https://www.facebook.com/TresHatzClassi ... =3&theater

I did some more research on bending wood. Turns out there is a formula for hard wood. Most sources say softwood can't be bent without steaming. The formula is the radius must be 20 to 30 times the thickness of the wood. So 1/4" inch wood can be bent to about a 5" radius or less depending on the type of wood. Seems a bit extreme. I checked the radius of the capstrip on the ribs. It's about 30" so if I was using hardwood capstrips they could be about 1" thick and I would still be able to bent them without steaming. The 1/4" sitka spruce capstrips seem to bend easily to that radius without steaming. or breaking.

I do have a question. I was looking at the bow at the back of the center section. If the wood used is not critical why not four layers of 1/8" birch plywood. It'll probably bend without steaming. There is a weight penalty but not a lot considering the small amount required.

For both the wing tips and center section bow I used pine. I started with popular but it wanted to split when I bent it.
I planed each piece down to 1/8 inch, steamed them and epoxied them in a fixture. Since I ended up with an epoxy composite I was not concerned with the wood choice. They ended up very strong.
I made a form on my work bench that I used to clamp the steamed wood until it dried, about three days. When I took them out of the form the bend stayed in the wood and I used the same form to epoxy them.
I have a bunch of pictures on my site. I was very happy with the result.
http://edwinwhite.com/hatz.html

I had a jig very similar to Ed's, and just soaked the capstrips (did not steam) in hot water overnight. The jig was wide enough for 4 capstrips at a time, so a little planning ahead meant I always had a pre-bent capstrip.

Now to hijack the thread a little bit...
Speaking of bending wood, what type (species) of wood did builders use for the bending of the wingtips and center section bow?
And speaking of types of wood, what did you use for the leading and trailing edges of the wings? All sitka spruce all the time, or something a little less costly?

Thanks.

Thanks guys. I was paying attention to the direction of the rings, using the best ones for the top and bottom cap strips. Anything near a 45 degree cross section I used for cross pieces.

I think I'll skip the heating and bending process and just fit the capstrip in the jig. I don't see how the rib can distort (because of the capstrip recoil) once the gussets are glued down. I believe curved hand railing depends on the glue to hold the curve. I also suspect the cant in gluelam beams is held in place by the glue. So I don't see a problem structurally with building the ribs without putting the bend in the capstrips first.

I didn't heat any of my cap strips.
The strength of the wood lies in the orientation of the growth rings. They should be a horizontal as possible.... like the spar.

Jeff Moore

I made up a simple fixture from a two by four that would bend four or five at a time. I heated them in a teapot and a rubber hose and then over night in the fixture. I, like you, wondered if I needed it but at one rib a night it didn't slow me down.
I didn't do anything to the lower strips.

I was spending time heating and bending the top capstrip for the rib. It doesn't have a lot of curve in it and it springs back some even after heating and clamping so I was bending it some more to fit it into the jig anyhow. The bottom capstip has so little bend that I didn't bother heating and bending it. Just fit it to the jig. I also tried that with the top capstrip and it fits without a lot of effort.

So the question is, do I really need to heat and bend the capstrip before I place it in the jig? Will the rib be as structurally sound as one that has preformed (bend) cap strips?