Hatz Biplane Association

As noted in the discrepancies, rib #10 doesn't fit the spar tapers. I also noted that the top of rib #10 matches the Clark Y airfoil and if you rotate the drawing about 2/3 of a degree. This means that the spar openings on the rib template are off 90 degrees by that much. The opening for the rear spar isn't big enough the fit the spar dimensions as shown on sheet seven. The spar opening is about a 1/4" to small. Finally, if you draw lines on the spars from rib #9 to rib #10 the fabric will clear the spars on the top but not on the bottom.

Just wondering how builders resolved these discrepancies. Build rib #10 as shown and taper the spars to fit?

Also there is a false nose piece between rib #9 and rib #10 and one outside of rib #10 shown on sheet 10. Just fudge them to fit?

I built rib #10 as per the print because I was not aware of any problem. I tapered the spar to fit the rib. The aileron spar has a taper on the plans that I also changed.

I made the #10 rib per plans and tapered all my spars as Ed did.

I did not add a false nose rib, between 9 and 10 rib, but I have seen some that have done so.

My wing tip sheeting laid down real nice. I did not need to have a "pie cuts" in the tip sheeting as I have read some folks have had to do in order for them to lay down properly. They maintained airfoil shape, and are plenty strong in my opinion. I did not add any false ribs out side of rib # 10 but some builders have also done that. It is builders preference I guess.

It is worthwhile to note that the Hatz CB-1 does not have ANY false nose ribs, and since the Classic is a direct descendent of that fine aircraft, I think a person would be fine if they did not put ANY false nose ribs between the main ribs, but I did so.

I have seen some folks put "blue foam" in-between main ribs, ahead of the forward spar on CB-1's. This aids in keeping airfoil shape, and also may help in keeping the metal leading edges from being damaged easily from bird strikes or hangar rash.

There are plenty of CB-1s out there flying without any false nose ribs, and the flimsier metal leading edge sheeting, and they are flying fine, So, its up to you.

Best of luck,

Rick
HC85

Thanks guys. I had a look at Ed's pictures again. Great documentation for us a few years behind in our builds. The wingbow does look good in the photos.

I'm going to mess with the tapers and rib #10 in AutoCAD a bit more. There is an end view of the bow on sheet seven. When I draw the spars on the end view the notches in the end of the spars line up with the bow so that is good. Once I redraw rib #10 I can overlay it on the full size ribs to see how the nose and tail line up.

Rick. I made up the false nose pieces from 3mm Swedish birch plywood. It was a mistake in ordering at first but I can't see where the 0.25mm will make a difference. The stack of 36 false noses pieces probably doesn't weight much more than a pound so I think I'll install them as shown on the plans. No weight penalty there. The end ones will have to be be hand drawn if I install them.

So I analyzed the tenth rib and the spar tapers to death. There are a couple of things about the aileron spar as noted in the discrepancies on this forum. The aileron spar can't have the taper shown on sheet seven of the plans. The piano hinge just wouldn't work. From the photos on the CD there is a slight taper to the top of the aileron spar at the outboard end but it is slight. The hinge quits about six inches from the end and the spar tapers off slightly from there. I think Doug (and other builders) had this figured out.

Rib #10 has to match the aileron spar at the top. So the top of the wing doesn't start tapering down until after Rib #10 at the back of the wing. The aileron spar doesn't taper down but the rear spar does. The front of the wing is different. It starts to taper downward from Rib #9. The nose piece makes a slight bend upwards at Rib #9. The bend is visible on sheet ten. Rib #10 is drawn wrong on the cross section on that sheet. It's not that deep. The top of the rib should be down 5/8" or so from the top of the other ribs.

While the back of Rib #10 has to match the top of the aileron spar, the front of the rib can be adjusted to make a nice up sweep of the nose piece. I think the nose of Rib #10 is too high which makes a bend in the nose piece at Rib #9. As drawn on the plans, Rib #10 is slightly skewed. In order to fit it on the spars and have it line up with the aileron spar some modifications have to be made. I think most builders adjusted the spar tapers to make it fit. The CD pictures show a gap between the top of the rear spar and Rib #10 spar opening. It's fixed by adding a wedge piece on top of the rear spar out board of Rib #10.

I think the intent is to have the wing nose start to curve up from Rib #9, peak at the outside edge of the wing bow, then make a gradual curve down all the way around the aileron to where the rear of the wing straightens out. Kind of like a half lazy eight. There is an end view of the bow on sheet seven that shows the curve. Easy to say, but a difficult complex curve. From the pictures, most bows jog up at rib #10 and are flat curves from there.

The good thing is that wing bows look good on all the pictures I looked at.

Redesigned wing bow. Flat spot is for NAV light.

Wow! That looks beautiful. Looks like you have a great place to work also.

Thanks. I'm pretty happy with the redesign of the bow so thought I would show it off. Long story about the big hanger. They were built for amphibs. 14 foot ceilings. My little Glasair looks lost in a corner. Not what I was looking for but definitely happy with it now that I started my build. Lots of working room for sure. It's heated with solar so gets a little chilly for a month or so in the winter.