Byron originals WACO UPF-7

Model Airplane News, Nov 1997 by Olivett, Vic

THE WACO UPF-7 was a great primary trainer that was used to train thousands of pilots during WW II. Though often mistaken for a Stearman, the WACO is a smaller plane with a wider main gear. While in Florida this past winter, I saw two new WACOs fly over the beach; you can always tell the sound of a radial overhead! New WACOs are still being built in the Midwest; I guess you can't get enough of a good thing.

Byron Originals'* 1/4-scale WACO UPF-7 kit features injected-molded foam wings and a hand-laid, fiberglass fuselage with all panel lines molded in. It comes with formed steelwire cabane and N-struts; formed aluminum gear struts; and tires, axles and a steerable tailwheel. A fiberglass cowl and wheel pants, dummy 7-cylinder radial engine kit and flexible flying wire kit are also available as options.

THE KIT

The kit comes in two large boxes. All the part bags are numbered for easy identification, and the kit includes just about everything you'll need. The instruction manual is very well done, with each step well explained. The photos are clear and very helpful. One very important step before any construction is to sand all fiberglass gluing surfaces with 80-grit sandpaper and clean them thoroughly with white vinegar. While doing so, I found several imperfections in the fuselage: the seams weren't bonded correctly and were very weak. Byron sent me a new fuselage and has since corrected this in its kits.

FUSELAGE

Construction of the fuselage is not easy, and a second pair of hands will come in handy. Use a hot-glue gun to tack the formers into place and polyester resin to glass in the formers. Trial-fit all the parts in each step before glassing them in place (this is where the hotglue gun comes in handy). Since the alignment of all the formers is so critical, they should be double-checked. After installing the blind nuts, I used a drop of thin Zap* to secure them in place. The F-1, F-2 and F-3 formers are all tied in together and support the landing gear and the cabane struts. Again, this is why the alignment is very important. Maple rails add support to the area.

The foam stabs are supported by an 1/8-inch plywood spar and a 1/4-inch aluminum spar tube. Setup is critical, so take extra time. The elevators are also made of foam and have to be glassed. The hinges are epoxied into the stab, elevators and rudder foam parts. The rudder post is reinforced with 1/4-inch balsa. I glassed the rudder post in with polyester resin and cloth.

Installing the landing gear is difficult, but it's a work of art when completed. I used medium Zap to fasten the ply formers to the aluminum landing gear. Take great care when forming the fairings around the formers on the landing gear. The center section of the landing gear is for show but has sliding parts that should be lubricated to prevent them from binding, which could cause them to bend out of shape on takeoff and landing.

The horizontal stab, elevators and rudder are all made of injected foam and must be glassed, primed and painted. The foam parts must be very carefully sanded to retain the molded-in ribs. Z-Poxy finishing resin works very well for this procedure. It sands well and gives a great finish. All these parts have dowels installed to support the flying wires.

A word of caution: check the inside of the fuselage, back by the vertical fin. I found split seams on both the first and second fuselages. Reinforcing tape worked well, but the joint opened up when slight pressure was applied to the sides. I repaired this by forcing the joint open and applying a liberal amount of resin with a small brush. Release pressure and wipe off the excess resin with a paper towel.

WINGS

The wing panels are injected-molded foam with simulated ribs. When sanding, be very careful not to remove the rib lines. Each wing panel has two aluminum spars. The 1/16-inch root caps are epoxied on with 30-minute Z-Poxy and are glassed. The servo-wire channels are covered with 1/16inch balsa, and covers are supplied for the servos to be mounted on the side. The counter-balance assembly did need some extra support. I used a piece of 1/4-inch dowel in the ailerons and then tapped them for the counter-balance shafts. The 1/8-inch ply blind nut retainers are used for the N-struts. The 4-40 blind nuts placed on the backside of the ply circles are glued into the wing with Z-Poxy. A little piece of Scotch tape will protect the blind-nut threads.

After all the panels were completed, I glassed the wings with Z-Poxy finishing resin and glass cloth. This is the time to ask a friend for some help. The valley between the ribs is a little tough to handle by yourself.

The center section of the top wing is glass and has great detail. I found that slight pressure on the top and bottom of the wing caused the rear seam to open. Again, polyester resin worked well for this repair. The two spars are glassed in, with the aluminum extrusions bolted and epoxied in. Alignment is very important. You'll also have to install the hardwood blocks for the cabane cross-brace anchors.