Ultimate Biplane (oz4162)

About this Plan

Ultimate Biplane. Free flight scale rubber model.

Quote: "Ultimate Biplane, by Pat Tritle. With all the RC Ultimate bipes being flown throughout the country, it's about time the free flighters had one too. This modern design has all the right moments for a good flying rubber scale model. Might make a good CO2 job as well.

When the first RC Ultimate biplane kits burst upon the scene a few years back they took the market by storm. My kit was the second to leave the local hobby shop and the first to return framed. I hung it in the shop for display and to maybe help sell a couple more kits. The first thing that happened was that someone offered me more than I could turn down, so I sold it. Later on, I had the opportunity to fly one, and was duly impressed by the stable, steady feel of the airplane, and immediately began to regret selling mine.

In the meantime, my modeling pendulum had swung back to the early roots of my modeling career - rubber power. At the same time, the direction of my interest was again migrating back to scale, which it always does, and I again began thinking about the Ultimate. There are lots of RC kits and plans out there, a couple of CL plans are available, but nothing for FF rubber. It seemed like the time was right.

Rather than get too carried away with a hardcore scale project, I decided to keep construction as simple and light as possible in hopes of producing a durable sport scale model for the weekend flier.

The basic airframe design is a simple stick-and-tissue format. Wing construction utilizes main and sub spars and sliced ribs to keep the weight down, as well as built-up I-struts for further weight savings. The overall outline is not intended to be true to scale, and the horizontal stab has been enlarged for added stability. Though not totally accurate in outline, it's definitely an Ultimate.

Construction: Start by building up the vertical and horizontal stabilizers. When the glue has dried thoroughly, remove the frames from the plan, sand all the edges round and set them aside.

The wings go together next. Pin the leading and trailing edges to the plan, followed by the 1/16 square rib bottoms. Add the main and rear spars, and glue everything in place.

Both wings are of equal and constant chord, so only one rib template is required (I made mine from .040 styrene). Cut all the sliced rib tops from contest grade balsa and glue them to the wings, followed by the 1/32 balsa end caps. When dry, take the wing panels from the plan and shape the leading and trailing edges. Block up the tips and join the panels to the center sections at the proper dihedral angle. The 3 degrees of dihedral may not look like enough, but coupled with the effective 2 degrees obtained by the 10 degrees of wing sweep, it's adequate.

The fuselage is the basic stick side frame type, joined at the top by the formers and cross sticks on the bottom. Note that former 1 is installed to provide at least 4-1/2 to 5 degrees of downthrust. Next add the up-per and lower cowl sheeting. Glue the 1/4-inch balsa noseblock to the fuselage and sand it to shape to complete the basic structure.

Using the front view of the cabane struts as a guide, build up the strut system directly on the fuselage. Cut the rear strut 1/16-inch shorter to obtain the top wing incidence, bei ng careful to maintain the saddle alignment true to the fuselage centerline. This setup goes together easier than it sounds, but care is needed to ensure good alignment. The landing gear is bent from .032 music wire and installed using triangles for reinforcement. The pants are layered from 1/4 and 3/32-inch soft balsa, carved and sanded to shape..."

Direct submission to Outerzone.

Here is Pat Tritle's Ultimate Biplane from Model Builder magazine issue 12-94. Note: this is a different plan to the larger (and later) 22in Ultimate kit for RC from Pat Tritle.

Supplementary file notes

Article, thanks to hlsat.

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