Laser-cut
I-Beam Ribs
for a Hatz Taperwing
by Todd Mason
The laser-cut rib and taperwing concepts discussed here are just that, concepts. Todd is working through the development of both with an eye toward the possible use of them on his own Hatz. This information is presented here merely as a report on an interesting use of technology. They don't call our planes experimental for nothing.
Todd will be sending me a sample of the laser-cut rib after Biplane Expo, so watch for a review of the rib next month. - Doug
Attached is a file showing
the construction method I have elected to use for the wing ribs.
The ribs are constructed out of 1/8" plywood with 1/8"
x 1/4" plywood cap strip stiffeners glued to each side top
and bottom. Although this makes the rib cap strips 3/8"
thick, the ease of construction ( glue four (4) pieces to the
rib), the dimensional stability, and the added strength pay off.
The best part of all is it takes a half hour to cut out all the
ribs - I had them laser cut from a CADD drawing.
The image shows one rib and the separate
1/8" ply cap strips. The laser cutting made the cap strips
possible. They claim that all cuts are within 0.002"!!!
Fits like a jig saw puzzle.
As an engineer, I just can't
help but mess with the design. I originally took my drawing files
to the laser cutter to have the fittings and bellcranks cut.
When they showed me they could cut paper, cardboard, wood etc.,
the gears were turning fast! I have been too excited about building
all those ribs and cutting all those gussets. I remembered that
Bellanca used full length gussets along the top and bottom of
there built up spars. I understand the thought was that the plywood
would help retain the shape of the airfoil since the spruce cap
strips can have a tendency to creep back or sag out of shape
over the years. Anyway, to make a long story short, I decided
to try a wood "I-beam" design. Then I realized that
with the airfoil shape in the computer, I could easily scale
down the section to create a taperwing.
I have enclosed an image file that
was created from my drawing file. It should print ok. I feel
the taper looks real good with the tapered horiz. stab. A close
look at the fuselage might reveal why I have called Hatz 723
the Hatz T3. More on that latter.
As I'm sure you are aware, anytime a change is made, it creates
changes all along the way. I still have a lot of work to go on
the taperwing. By having the taper, the spars also taper. The
result is that the spar will not be strong enough at the interplane
struts. A rough calculation indicated that the wing tips would
fail at the interplane struts in upward bending at about 5g's.
Therefore, I will have to either reposition the spars more toward
the center of the section to pick up some extra thickness, move
the interplane struts out to redistribute the max. bending moment,
or a combination of both. I am designing the wing so it can bolt
to the standard fuselage. I'll keep you informed of my progress
which might be some time. I am currently building the tail feathers
and will next build the fuselage. I will probably construct the
wings last to save room but will continue to build and design
the components.