Armstrong-Whitworth F.K.8 (oz12396)


Armstrong-Whitworth F.K.8 (oz12396) by Tom Nallen 1989 - plan thumbnail

About this Plan

Armstrong-Whitworth F.K.8 (Big Ack). Peanut scale rubber model.

Quote: "Here's an interesting and relatively obscure WWI machine designed for the Flying Aces Peanut Mass Launch event. Layout and moments are ideal for F/F scale.

This WWI Royal Flying Corps recon ship is simple yet distinctive; obscure but not unknown. Best of all, it has a great nickname: 'Big Ack'.

The design featured in this article qualifies to fly in the Flying Aces Club WWI Peanut Mass Launch event. Built light and true, this ship will give those SE-Ss and D-7s a run for their money. If you haven't yet experienced the thrill of flying shoulder to-shoulder in open combat, grab your helmet and goggles and head for the flight line. But first, to the building board. You've got to build your own mount for this aerial joust.

Here are some hints to help you pull it all together before the next dawn patrol.

WINGS Make a rib template and cut out all ribs from medium 1/32 sheet balsa. Select straight and stiff lengths of 1/16 square balsa for the leading and trailing edges and the spars. Cut out four wing tips from medium 1/32 sheet and begin assembly.

Anyone who has ever built a free flight biplane knows that strut attachments are a key design element. A good approach on small models such as this is to fabricate a 'pocket' in the wing rib at each strut-towing attachment point. This is done by notching the top or bottom of the appropriate wing ribs before assembly and cementing short lengths of 1/32 square balsa alongside each notch. During final assembly, the strut ends are inserted into these pockets and cemented, thus creating a rigid structure. After the wings have been assembled flat on the building board, cut the dihedral breaks in the leading and trailing edges and block up each wing tip 1/2 inch. Cement the dihedral breaks, add gussets and lay in the spars, beveling the ends to ensure a good fit. After the cement has hardened, lift the wings off of the board, shape the leading and trailing edges and fine sand the entire structure.

TAIL: The angular tail assembly is fairly simple to construct. Light wood is used here with gussets added to provide strength. Again, sand the completed structures and set aside for covering later.

FUSELAGE: Begin by building two identical fuselage sides on the board. Use straight and stiff lengths of 1/16 square balsa for the longerons and softer wood for the uprights (and crosspieces later). Gusset where indicated on the plan and fill in the nose section with soft 1/32 sheet balsa. When building the fuselage sides, consider the structural loads involved and select wood accordingly. For example, the rear motor peg support should be hard balsa while the remaining uprights in the aft end can be much lighter. In general, use stiffer wood in the forward sections and softer wood aft. When the cement has hardened, lift the sides off the board and make certain that they are identical. If so, proceed to build the basic fuselage "box,” trying to keep the structure as square as possible. I find it easiest to start from the tail post, working forward with the fuselage upside down on the building board. The straight upper longerons help to maintain a square section as you work forward adding crosspieces. When the fuselage box is completed, fill in the underside of the nose section with soft 1/32 sheet. Also, cement hard 1/8 x1/8 balsa strips inside the nose crosspieces and uprights. These last pieces must be hard enough to withstand regular removal of the nose-block and those inevitable rough landings.

Turtledeck formers are cut from 1/32 sheet. Formers 1 through 5 have no stringers, but are covered in two sections with very thin sheet balsa. I used 1/64 sheet for the decking. The cockpit section is installed first, trimmed and then followed by the front top section. At this time, rough out the nose-block from medium block balsa, cement the 1/4 sheet plug to the rear face, drill out the assembly and insert the 1/16 O.D. brass tube bushing. Drill the block with a few degrees of down and left thrust as shown on the plan. Bring the nose-block to a snug fit and finish shaping. The fuselage is completed by notching and mounting the rear formers and laying in the 1/32 square balsa stringers. The entire fuselage is now sanded and readied for covering.

COVERING: Store-bought green tissue is never quite right for WWI ships. I dye my own using white Japanese tissue taped to a frame and pre-shrunk with a sprayed water and RIT olive drab dye mixture. The results are worthwhile. Use a sturdy frame and masking tape the tissue all around as taut as possible. Spray the dye mixture onto the tissue and gently wipe off the excess with a Kleenex. Be careful not to tear the wet tissue. Let dry, then cut the dyed tissue from the frame and cover the model, shrinking the tissue once again with a light water mist. Cover the undersurfaces of the wings and stabilizer with white tissue to simulate the clear doped undersurfaces typical of Allied machines in WWI.

LANDING GEAR: I prefer the early version of Big Ack with the birdcage landing gear and Venetian blind radiator. However, the plan also shows the more conventional landing gear and detail of the later 160-hp variant. That spidery landing gear is actually quite sturdy. The two main legs are mounted on a bamboo core, while the remaining sections are fine piano wire wrapped with thread and cemented at the joints. All of these 'core' pieces are embedded and cemented into the sheeted nose and then covered with balsa struts. It really isn’t as complicated as it seems.

Start by fashioning a length of 1/32 square bamboo and embedding a section in to each fuselage side at the proper angles. Cement at the fuselage joint and trim each leg to the proper length. Using the plan front view as a pattern, bend and cut the front and rear 'V' sections from .010 music wire..."

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Armstrong-Whitworth F.K.8 (oz12396) by Tom Nallen 1989 - model pic

  • (oz12396)
    Armstrong-Whitworth F.K.8
    by Tom Nallen
    from Model Builder
    August 1989 
    13in span
    Scale Rubber F/F Biplane Military
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 22/07/2020
    Filesize: 311KB
    Format: • PDFbitmap
    Credit*: JanNovick
    Downloads: 613

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