New Carbon Wing

I was asked to post about the new, carbon wing, for my self designed U/L, that I'm fabricating. The goal was to improve my climb performance with the tiny CorsAir engine. The challenge was to design the new wing with a much higher aspect ratio and deep undercamber... yet keep it very light. To make it even harder, I decided to make it semi-cantilevered, with wires down to the landing gear that would only take about 1 G of the load. Due to the shortage of carbon cloth, I was forced to fabricate the tubular carbon spar last. I would have preferred to do it first, since everything has to connect to it.

I posted some photos previously in this Light Stuff section, under Self Designed Carbon U/L, including one showing piles of ribs for this new wing. The 1/4" thick balsa ribs, that are scrimmed with very thin fiberglass on both sides, worked out great. I like them better than styrofoam core ribs for the less structural ribs, that only support fabric. I just glued together 1/4" by 3" by 36" sheets of balsa, edge to edge, to form large flat sheets of balsa. Then I scrimmed them with fiberglass on both sides. The ribs were cut out on a band saw.

The stronger ribs, that support the engine, cockpit, etc. are made of 1/4" balsa with two plys of carbon on each side. But and tip ribs are 1+1/2" thick styrofoam, with two plys of carbon on both sides. They needed the extra thickness to take the side loads of the fabric pull.

The carbon leading edge was layed up in 3' sections on a mold I made:

 

Laying up the 30' spar was challenging. First I made a mold of these 4' sections of 1/32" thick plywood. Each section has two 1" thick styrofoam discs inside to keep it round. The sections are glued together into a 30.5' long tube that the carbon is rolled onto. The plywood mold stays inside the completed spar.

 

The spar has about $2,000 worth of carbon and epoxy, including unidirectional tapes on the top and bottom. Then the ribs are slipped onto the spar and glued on with a wet micro/flox mixture. Then the leading edge sections are glued on:

 

Plywood rib caps are glued on with CA glue, and then filletted with epoxy to the ribs. The carbon ribs get thicker plywood rib caps and larger micro/flox fillets:

 

I used preformed aluminum trailing edge. The trailing edge is reinforced with carbon rod and micro between every rib. It's strong enough that you can pound on it with your fist from the top, bottom, or rear:

 

Then hard points are added. This spar is just small enough diameter that I could use through bolts. Areas were reinforced, and blind nut plates were attached. Then the frame is prepped and covered:

 

I used the Stitts PolyFiber system for covering. I used PK screws instead of rib stitching to save time. The concave areas had to be glued and screwed and screwed to the ribs, before the final shrinking.

 

Congrats - beautifully done!

 

I designed the airfoil myself. The upper surface is a modified Gottingen 387.

Before covering, the wing structure weighed 89#. That might seem like a lot. But my plane dosen't really have a fusalage in the normal sense. So the wing structure has to support the empennage, cockpit, fuel tank, engine, etc. My plane should come in a little lighter than it is now, with the new wing. My plane weights 229# empty now.

Here's a cross section of the trailing edge. The white is wet micro the black is carbon rod.

 

Yup, a big deal......

And I thought it would be a big deal to tap out ribs from a set of plans:lex: Sheesh!

CAB
Bearhawk# 862
Inferiority complex setting in:wail:

 

I finished painting the new wing. I skimped on the coatings on the bottom
of the wing to save weight and expense. The yellow paint is quite
transparent. It really could have used a coat of white underneath. So you
can see what's underneath... which is the "silver" UV proofing on top, and
the streaky, red-tinted sealer on the bottom. The top ended up with a hint
of greenish, lemmon-lime look. The bottom varries in color with streaks of
orange-yellow and yellow. The bottom would be unacceptable on a "real"
plane. But it looks kind of wild and cool on an U/L.

Painting was the last step. So the new wing is complete and ready to
install. I'm still thinking about when I'd like to install it on my plane.
My old wing still works fine, so I may wait a spell. I can fabricate the
new fuel tank mount and cover, and a few other small parts in the mean time.

 

Here's a photo of the bottom.

 

It Flys

I finished installing the new wing on my plane. In the process, I improved all the things I felt needed improvement. Many parts were reengineered or substancially modified. The plane is about 2' shorter front to back, but 4' longer wing span. The plane weighs in at 219#, including the ballistic parachute. That's 10# lighter than the plane weighed with the old wing. And about 50# lighter than almost all true ultralights that have a parachute.

I'm quickly working my way through the test sequence. I finished taxi testing, bunny hops, pattern work, stalls, and steep banked turns. The new wing had the desired effect. Climb rate and glide ratio both about doubled. It handles and stalls about like my old wing, except everything happens much slower.

It climbs best between 35 and 40 mph. Cruise speed at half power is about 41 mph. Stall happens at 24 mph indicated, which is a vast improvement. Full throttle in level flight yeilds 58 mph. The plane is perfectly happy flying between 30 and 45 mph. It's not mushy at all at 30 mph. I'm landing around 30 mph, instead of 40.

Negatives: Adverse yaw doubled; Roll rate is about half; The plane will much more easily be flipped over by a gust of wind when it's on the ground.

I'll do some adjusting to get everything just right. But it came out quite excellent. It is much more enjoyable to fly now. Cruising 10 mph slower, the intensity of the breeze and wind chill are much less. It's very quiet and relaxed. The improved glide ratio and lower landing speed make the plane much safer in event of an engine failure... as does the stronger, more shock absorbing landing gear.

 

In a stiff wind I imagine you could get some vertical flight in! Great job!

Jake

 

I improved the windshield and added a partial cockpit enclosure to keep the winter wind off my head and legs. They both work excellent. My plane is up to about 222#, including the BRS parachute, now. I'll paint the enclosure yellow, when/if we get a warm spell. The enclosure is made mostly of 1/32" birch plywood. I think it improved cruise speed a tad. I can't be sure, since the pitot-static system changed along with it.

 

With the new wing, I renamed my plane "U/L". I like to keep things simple. It will be fun to call ATC on the radio, "...Experimental Ultralight, Uniform slash Lima..."

 

Pitch issues?

Looks great Mark.

Does the body shroud / fairing have any noticable affect on pitch or trim?

 

It's been too cold to fly enough to be sure... But I think I'm applying a tiny bit more up elevator to compensate for its weight and/or down force.