A forum about all aspects of the construction and maintenance of the Billy Dawson inspired modified Hatz Classic biplane. Here is the place to ask your questions and get the answers from the real experts.
I couldn't find anything on the plans showing the bottom wing dihedral. Drawing 10 (Wingbow Details) seems to be the only place the top wing dihedral is shown: 1.5 degrees. I just assumed the bottom wing was the same. Turns out it isn't.
Drawing 22 (Interplane Struts) shows the distance between the top spar fitting (RSTW3) bolt hole and the bottom wing spar fitting (FSBW2) bolt hole to be 46.625 inches. If you build the strut to that length the bottom wing will have a dihedral of about 2.8 degrees. This is actually evident on both Drawing 00 and drawing 22. The top and bottom wings aren't parallel on those drawings.
The rest of the measurements are suspect. or maybe they all are. From the drawings of the spar fittings and mounting fittings on both the fuselage and center section line up (level). So the incidence of the wing is level for both the top and the bottom wings. Given that, the bolt holes for the interplane struts on the top wing front and rear spars are also on the same plane. Drawing 22 shows measurements from the upper wing to the same fitting on the bottom wing as 46.139 and 46.625 inches. Something is not correct there.
I'm looking for comments on what measurements other builders used for the interplane struts and if they had any problems fitting it all together.
I built an LB-1 which has no dihedral in the top wing and 2 deg in the bottom.
I squared up the fuselage, attached and set the dihedral and incidence for both wings.
I made the interplane strut ends, put them into the fittings and measured the length of tube needed to connect the dots.
I tack welded things together and checked the fit.
I have no idea what the measurements are.
Thanks Jeff. That would work for sure if there was some indication of the bottom dihedral. I already have the landing and flying wires. Really what I want is to make sure those fit. I got them from another project but I assume they were ordered according to the measurements on Drawing 22. I'll check the lengths.
Taking a cue from your methods but rather than physically setting up the wings I drew the flying and landing wires in 3D with AutoCAD. Using the 1.5 dihedral for the top wing, the length of the flying wires shown on Drawing 22 are 0.44 and 0.61 inches too short. Also if I use the 46.625 measurement the landing wires are 0.32 and 0.39 inches too long. There is probably enough adjustment in the wires to compensate if you want to go that way. Or the lugs could be modified.
I changed the dihedral of the wings in the drawing so that the flying and landing wires fit better. With those changes, the dihedral for the upper wing is 0.7 degrees and the bottom wing is 2.4 degrees. The distance between the wings is 46.087. Add the 2" offset and the length is then 46.13. On the drawings, the closest measurement is 46.139. I'll may use that to layout the jig for the interplanes struts. I also may change the lugs to make the 1.5 degree dihedral work.
Interplane Struts 2.png (71.45 KiB) Viewed 5151 times
Agreed, I'll make the interplane struts work once I have the wings figured out. The flying wires are too expensive to make a mistake so I measured them yesterday. The wires I have are close to the plan lengths but none match the plans. Go figure. I measured the maximum length. They can be adjusted shorter. I haven't done all the calculations, but the front flying wire is too short to get the 1.5 degrees dihedral. The rear ones will work. I think I'll just make the front landing wire lug longer to make it work. The bottom wing dihedral will probably just be whatever it turn out to be with the length of the landing wires as is. But for sure, I think the upper wing maybe should have the 1.5 degree dihedral. Comes more from my OCD than any engineering analysis.
Hi Nick
I'd also like to welcome you to the group.
Billy Dawson's airplane is called a Hatz Classic which has many changes from the original drawings - more rounded fuselage, a mere 1/8" clearance between the top wing root and the center section ,no fairings between the wing and center section, aluminum ailerons, and on and on and on.
Billy used the standard 2 degrees dihederal on the bottom wings and used 1 degree on the top wings. The intent is to
achieve a Waco look.
If you will be building the standard CB1 setting the 1 degree for the top wings is merely a flying wire adjustment but if you build the Classic model you'll need to adjust your root rib ever so slight to correct for the 1 degree - a simples process.
Again welcome and good luck
Ron B
And.......
A lot of things are documented on the Classic plans in places you would not expect or are not obvious. The 1.5 deg dihedral is specified on Page 10 - Wing Bow Details. On the right side of the page are spar drawings calling out the 1.5 degrees.
Doug
HC 093
Hatz Webmaster
And again.....
I see what's happening. You're referring to the dihedral on the bottom wings. The CB-1 plans call for 2 degrees. The Classic plans does not specify a dihredal value for the lower wings -- just the upper wings -- and this is 1.5 degrees per page 10.
My game plan is to build the upper wings with 1.5 degrees dihedral and the interplane struts to specifications and let the bottom wing dihedral fall where it wants. Any problems with this approach?
-Scott
There are links to the old forum on this website. I did a search for "dihedral".
So, good luck.......
If someone were to request the article from Sport Aviation dated October 1997 on the Dawson Hatz Classic, I would bet there is some info in that article. I seem to remember 1.5 degrees both wings. The is the article that gave me the HOTS bad for the plane. Or, try and call Jeff Shoemake and see if he knows something.
hc 162
My results were top wing almost 0 degrees, Lower wing 1.5 each total 3 degrees. This is pretty much standard for a stable flying biplane, pitts ect are built to be unstable.
Hope this helps.
Steve
I had a look at the Dawson Hatz Classic in Sports Aviation October 1997 issue. No mention of the dihedral but great reading to find out where many of the Hatz Classic features came from.
I had a look again at the flying wire lengths. My two rear flying wires are long enough to make the dihedral for the upper wings 1.5 degrees. I have to lengthen one of the front flying wire lugs by 1/2 inch. No big deal. If I use the 46.625 measurement for the interplane strut the landing wires are 0.8" too long. There is plenty of adjustment in the wires for that. The lower dihedral is 2.8 degrees.
I guess in the long run every Hatz is a one off. Starting with how much the paper drawing used to make the rib jig shrinks. Like Billy mentions in the article, one piece at a time.