Upton Baby Ace (oz2323)

About this Plan

Bob Upton Baby Ace. Peanut scale model. Design features scale structure and sliced ribs at scale spacing.

Quote: "MY FIRST INCLINATION with the Baby Ace was to make a fairly simple model with two inch rib spacing, only uprights in the fuselage and sheet tail surfaces. What actually happened can be seen in the photos. All of the fuselage structure, including diagonals, somehow materialised, and then sliced ribs at scale spacing etc. The result weighs 0.433 ounce without the rubber motor.

Careful attention needs to be paid to wood selection to keep the model as light as possible. Tail structure and fuselage frame uprights were sliced from fairly light (4 to 6 pound) 1/20th sheet balsa. Main longerons, tail spars, leading edges, were sliced from firm (8 to 10 pound) 1/20 sheet. All sheet parts were cut from very light wood. Incidentally I suggest that the two root ribs and the two tip ribs be made solid, rather than sliced. During the application of the trim colours, I broke the top cap of one tip rib. The tissue at the tip tends to pull more strongly in the down direction than it does over the other ribs and will tend to collapse the tip ribs if they are sliced and made from fairly lightweight stock. Solid sheet ribs will save you from tedious repairs later.

Use the lightest piano wire available at your local model shop for the landing gear wire and for the propeller shaft.

Two spar, sliced-rib construction is used for the wings. Lay down and glue the leading edge, trailing edge, and the bottom rib parts directly over the plan. Cut the wing spars from sheet balsa. Note that the rear spar, which is not shown on the plan, is to be made with 1/16th more dihedral at each tip. The difference in dihedral will result in some washout in the completed wing, which is desirable for good stall characteristics. Block up the trailing edge at the tip with a sixteenth shim. Cement the spars in place and add the top rib caps. If you use solid root and tip ribs as suggested, the spars will have to be threaded through the solid ribs. When dry, do a similar job on the other wing. If you have done it correctly, you now have a wing with equal washout in each panel and continuous tip-to-tip spars.

The model in the photos was covered with white superfine tissue (condenser paper would be lighter), shrunk with a light mist of water, and when dry, given two light coats of very thin dope over all the tissue. The wood parts were given four coats. For the colour trim I used a Staedtler Lumocolour 357 permanent felt pen. These are designed to be used on acetate sheet and work perfectly over nitrate doped surfaces (they appear to work fine on all plastics). There is simply no way I know of to get a lighter weight colour coat on a model. The real airplane is white with international orange colour trim and a black pin stripe. The ink will run into undoped balsa or tissue surfaces, so be forewarned..."

Update 16/03/2018: added article, thanks to RFJ.

Supplementary file notes

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