Joe’s Mitchell U-2 Web Page

This is my first attempt at a Web page, but my fourth attempt at an airplane. I've built a Piet from original plans (flown a little way back when), an Avid (crashed), a Heath Parasol from 1929 magazine plans (never flown), and a Kolb Firestar (flown once in a while). The plan was to fly these planes from my 900’ one way, approach over trees, dog-legged strip surrounded on three sides by very large, steep hills. The Kolb works the best, but it’s too hairy, really. Hey, but I’ve been there, done that, and can do it when a need the kick in the pants. I need another airplane like a need a hole in the head, but this Mitchell kit came along for cheap, and both boys are in college, so I thought I would take a crack at putting it together. I’ve always loved building the wings the most, and baby, this is mostly wing! Maybe I’ll hang it in the office when I finish it. My business partner would rather have me do that than fly it. But who knows. Let’s get started.

Inboard spar in jig laid out on an old ping-pong table. Note that the rib depth at each station should determine the depth of the spar. Note the little fillets of epoxy and wood powder applied where the wood verticals attach to the spar caps.

Applying the web to the inboard spar. Note that the weights that are finally finding a purpose in life. Note the plastic staple puller strips.

Blurry close up of staple puller strips. Pull the strip and out comes the staples.

Pilot holes were drilled connected by small screws. The screws were removed one at a time and the fittings were line drilled. The entire group of fittings was sanded to a uniform size on a bench sander.

I temporarily bolted all the fittings on one spar, and all but the bottom outboard fittings on the other spar, which remained clamped. Then I put both spars on the table, web-to-web, inboard edge on table and outboard spars rising 6 degrees…

and made a very slight adjustment in the clamped piece so that both dihedrals are exactly the same, IE. spars are mirror images.

Here is the gismo I used to drill perpendicular to the spar. Worked great.

You can’t have too many clamps. I made the ring clamps by sawing rings off a 3” PVC pipe (be careful if you use a table saw) and then cutting the ring. They are cheap and work pretty well.

Here is a very simple rib skinning jig made from 2 2x 8’s. This is not a good jig, as it can twist, which will twist the spar. Make a sturdy one out of plywood.

Here is the inboard spar with the foam done. Note the stiff straight edge on the leading edge. The leading edge tends to deform when the ribs are located unless it is held straight. I installed all leading edges before I added the ribs as it helps hold the ribs in place.

This is a homemade hot wire gizmo, made from a piece of 1.5” PVC pipe with a long 3/8” bolt at each end to which the .040 stainless safety wire is strung, slightly bowing the PVC. A transformer and dimmer switch create the power supply.

Here is an outboard spar trimmed by hot wire and and rough sanded to shape.

Trimming the foam

The sag in the wire doesn’t seem to cause a problem.

Pulling staples from a wing skin splice doubler is pretty easy!

Fitting the skins on the inboard spar. The ratchet type nylon straps work very well.

Gluing the first skin. The straps hold the skin very tightly and uniformly. The plastic at the bottom was to keep the glue that dripped out of the bottom from getting on the straps, but proved unnecessary because glue didn’t drip on the straps (but they get a lot of glue anyway, just like me and all my other tools!).I’m not sure the plywood needs to be stapled into the spar cap, because it seems to be held very tightly by the straps, but I put in a row of staples anyway to be sure.

Here’s a view from the other side. Don’t tighten the straps after stapling the plywood!

Trimming the excess skin. Note the excess glue that dripped down. It took one quart of epoxy to glue the skins on one inboard spar. It takes quite a bit to coat the inside of the skin for moisture protection, and quite a bit to coat the foam ribs. A little winds up as waste. The back-cut saw is essential for this project, and many other projects. Best tool for the buck I ever owned, and one of the most versatile. I love this tool every time I pick it up.

View of right outboard wing section. This section was rebuilt after it was initially built with the ribs upside down. That backcut saw worked pretty good sawing the ribs off the spar with minimal loss of material. Plywood gussets failed by delaminating, rather than at glue joint.

1mm plywood added to capstrip to fair between gussets.

Fittings to hold tip rudder ready for sandblasting and painting.

Fairing in gusset using wood flour mixed with epoxy. West type epoxy works better than T-88 for this cause it’s easier to spread.

I used a butt joint to join wing skins with a 2” wide plywood doubler because I couldn’t get the skins to lie flat against the noseribs when I used the overlap joint described in the plans and instructions.

Typical messy workbench (pingpong table on pool table) and you can’t see all the little puddles of sticky epoxy that get on my hands and my tools. Oh well. Left outboard wing in background.

Inboard wing.

Stabilator torque tube bell cranks cut out of 1” x .065 rectangular aluminum rather than construction as per plans, which involves bending and riveting. Much better and easier to make in my opinion.

Landing gear fittings. Note access hole on top of wing (also on bottom) because I forgot to install the bolts before skinning the wing. Note fillet of epoxy where rib attaches to spar web.

Wing center section. Note idler fitting resting on plywood and look at torque tube installation. I did not slit the PVC torque tube guides as per plans because they were plenty tight anyway.

A view of the right half of the inboard wing.

Wing tip rudder support, constructed of beadboard sanded to shape plus a layer of epoxy-fiberglass cloth.

Stabilator showing horn and hinge fittings.

Fitting cut from 3/4" x 1” x 1/8” T-6061 aluminum channel.

Stabilator ribs in jig ready for sanding to set the twist.

Getting ready to put the ribs on the second stabilator spar. Messy workbench in background.

Clamping on the leading edge skin. Those strap clamps work great for skinning.

Note that 2” space for hinge is not enough to allow insertion of hinge pins. They should be partially installed with the hinge. I will have to drill some kind of hole into spruce leading edge sides.

I shaped the leading edges by clamping them to a ¾” board after soaking overnight in the bathtub.