Lublin R-XII (oz14034)

About this Plan

Lublin R-XII. Peanut scale model for rubber power.

Subject is a Polish prototype three-seater sports touring aircraft, designed 1930.

Update 27/8/2022: Added article, thanks to RFJ.

Quote: "Lublin R-XII, by Walt Mooney. An interesting Polish Peanut with out-of-the-rut lines. Elliptical outlines are easier to make than they might appear.

The Lublin R-XII is a simple-to-construct scale model airplane, with excellent aerodynamic characteristics. It has a rectangular cross section fuselage, which is about as simple as they come. The wing and tail surfaces have elliptical planforms, which are theoretically as efficient as can be designed for a subsonic airplane. It also has a cantilever wing, which results in a very low drag configuration. The wing and horizontal tail are located on top of the fuselage, which makes for simple, accurate assembly - about the only draggy items on the design are the landing gear struts, the engine cylinders, and the horizontal tail struts.

The model has been built with only three intentional deviations from exact scale. The horizontal tail has been increased in area to help the flight characteristics, and the landing gear length has been lengthened slightly to increase the diameter of propeller that will clear the ground on ROG takeoffs. One other deviation is that although the wing is built flat over the plan, after it is covered and the tissue is shrunk, it warps up to give about 3/16 of an inch of dihedral at each tip.

All the aerodynamic surfaces are built directly over the plan. The tail ribs and spars are made from 1/20 square balsa. The bottoms of the wing ribs are also made from 1/20 square. The spar is cut to the shape shown from 1/20 sheet balsa, and the tops of the wing ribs are sliced from sheet also.

The surface outlines are the most unusual construction details associated with this model, and the method of making them will be taken up in detail. Start making the surface outlines by cutting out a pattern for each surface to the inside of the outline. If you have some cardboard about 1/16 inch thick, use it for the pattern, otherwise, use 1/16 sheet balsa. Make sure the outlines have smooth curves all the way around. Use a wax candle or a color crayon to coat the outline so that glue will not stick to it.

The outlines are laminated from strips of basswood 1/20 inch wide by .012 inch thick (this material is available from Peck-Polymers). Laminate the outlines using thinned-out white glue for an adhesive. Also, wet the sticks so that they will bend easier. Use masking tape to hold the laminations to the forms. It's best to cut about twenty half-inch squares of masking tape before beginning the lamination and stick them lightly to the edge of the workbench where they can be easily detached and handy for use.

Two pieces of basswood are used to make the tail surface outlines. Wet both sticks with water and shake them off so they are damp, but not dripping. Now apply a coat of white glue to one side of one of the sticks. Put the second stick against the first with the glue between. Starting at the trailing edge centerline of the horizontal tail, tape the sticks to the pattern edge. Now, always keeping the sticks against the form, bend the sticks around the form. Use the masking tape to hold the sticks against the form about every inch around the perifery. Go all the way around the outline. Do not try to bend the sticks if they are not against the form, as they will just break if you do. Once the outline is attached all the way around the form, check to see that the sticks are perfectly aligned, and that the form and the outline are flat in the plane of the surface. Now let the lamination dry. It's best if you let them dry overnight.

The vertical tail is done in a similar manner. Its form should extend at least a half inch in a straight line beyond the ends of the outline so there is a place for the end tapes to hold the sticks... "

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