Yak-9D (oz11952)

About this Plan

Yak-9D. Control line stunt model.

Quote: "YAK-9D. Semi-scale control-line stunter for 5.6 cc engines. Designed by HC Quek.

WHY THE YAK 9D? Unlike the Spitfire, Mustang or the Hien, the Yak 9D has so little to offer in terms of character! However, though simple both in profile and plan form, the Yak 9D was one of the very successful Yak series of Soviet aircraft during the second World War.

From the modeller's point of view, the simple lines provide an ideal subject for an easy-to-build, semi-scale model. The design presented here is far from scale, but well finished and decorated should provide immense eye appeal.

Basically, it is a slab-sided model, with no gimmicks in the design. The prototype model had an overall span of 58 in and used full span flaps. After flight tests the span was reduced by 3-1/2 in and the flaps subsequently reduced to just two thirds of the span - these two vital modifications were found to contribute towards improving both level flight and square manoeuvres. Wing fairings were added to the original model to improve its appearance.

It is always worthwhile making a careful selection of the various grades of wood required. Using very carefully selected wood the weight distribution was found to be just right on the original model no ballast being necessary to achieve the correct centre of gravity position. Carefully cut out all the wing ribs from light quarter-grain wood. The sections used are grossly modified NACA 0018 airfoils varying in percentage thickness from R1 to R14.

The wings are built flat on the building board. Pin the bottom 3/16 sq main spars in position, then pin all the ribs in position. Level up the TE of the ribs with scrap pieces of balsa. Next mark and insert the 3/16 sq top spars. Pin 1/4 in sq to trailing edges of the ribs and 3/8 sq to leading edges of ribs - still without using any glue. Check alignment and when satisfied that it is absolutely true - with no twists etc, spot cement all the cross points and allow to dry thoroughly. Finally, cement top 1/2 x 3/16 in joiner in position.

With the wings still pinned to the board, add the 1/16 LE and TE sheeting to the top surface before cap stripping the ribs with 3/16 x 1/16 soft balsa.

When dry, remove from board, turn over, and preferably pin wings to the board to check alignment. Add the 1/2 x 3/16 in joiner and secure the wing tip weight as shown. Sheet the LE and TE and add the cap strips as before. Sheet cover underside of centre section. When dry, remove wings from boards and build on the wing tip.

Sand TE of wings to section shown. Cut and sand flaps to section, add flap horn, then hinge to wing. Install the bellcrank mount complete with the control assembly. Connect the bellcrank to the flap horn with a 16 swg pushrod, before sheeting the top of the centre section. The complete wing may now be sanded thoroughly all over..."

Yak 9D, Aeromodeller, February 1971.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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