Scale gun turrets

Model Airplane News, Dec 2001 by Smith, Charlee

MODEL AIRPLANE NEWS

HOW TO

Bringing a WW II bomber to life

I'll admit it: I'm a WW II bomber nut, and my favorite bomber feature has to be the powered gun turret. Turrets give a bomber its character. A B-17 just isn't the same without its top turret, and the addition of a powered turret "made" the A-20G Havoc. A P-61 Black Widow without the four-gun turret just doesn't have the same character. The B-50, the B-32 and the PB4Y-2 are among my favorites because they seem to have turrets sprouting everywhere. And these turrets had function to back up their fearsome looks; the powered gun turrets manufactured by companies such as Martin, Emerson, Boulton-Paul, Sperry and Bendix saved the lives of countless airmen during WW II.

For sheer firepower, I've always felt that the B-25 Mitchell has no equal among WW II aircraft. Its Bendix top turret downed more Japanese aircraft than any other WW II bomber did. When Wing Mfg. introduced its Pro-Series B-25, I knew that my lifelong goal of building an authentic RC B-25 was within reach. But no matter how accurate the rest of the airframe appeared, I knew I wouldn't be satisfied if I didn't get the top turret right. I've collected a library of B-25 information over the years-factory drawings and manuals, and numerous books and magazines-but none of it contained the detailed information I needed to replicate the late-model Bendix turrets used in B-25Fs and Hs. Even direct contact with Bendix was a dead end. To my rescue came Pat Habel, a member of the team that keeps the B-25H "Barbie III" flying. In discussing our mutual interest, Pat was able to provide me with copies of the Bendix turret operation and service manuals and parts catalog! Within a month, I had the last niece of the puzzle I needed to build the plane of my dreams.

TOP TURRET

The most important part of the turret-the clear, molded-plastic canopy-is provided with the Wing Mfg. kit. I wanted the turret to rotate, so I relocated bulkhead F6A 1 1/4 inches farther aft to eliminate interference. The cross-sections from the rear of the canopy to the rear of the bomb bay are constant on the B-25 fuselage, so the bulkheads can bemoved without a problem. The first part to be made is an 1/8-inch lite-ply disc that matches the inside diameter of the plastic canopy base. I rough-cut it with a Dremel jigsaw then threaded a 1/4-inch screw through its center and chucked it into a tabletop drill press that, along with my Dremel Moto-Tool, acted as my lathes for various parts of the B-25. I then carefully sanded the disc to the correct size to be press-fit inside the canopy base.

Next, I laminated a 1/2-inch balsa disc of slightly larger diameter to the life-ply disc using CA. I wrapped the bottom of the clear canopy with masking tape and placed it over the plywood disc. Then I placed the whole assembly in the drill-press lathe. I turned the balsa down with a sanding block so it matched the outside diameter of the canopy. I then cut out three sections from the disc with a Dremel saw, leaving a Y-shaped structure that supports the center portion. I waited until the aircraft was entirely finished and painted to glue the canopy into place.

Using the wooden disc as a guide, mark the position of the turret on the top of the fuselage. Carefully cut away the balsa sheeting and its stringers with a Dremel tool. At this point, I discovered that the 1/4-inch-square spruce stringers get in the way. To get the turret to sit in the proper position, more than half of the spruce stringers had to be removed. To compensate for the loss in strength, I laminated 1/32-inch graphite sheet to the bottom of the remaining spruce with thick CA. If I had to do it over, I would reposition these stringers 3/8 inch lower, between bulkheads F5A and F6A, before I sheeted the fuselage.

The fuselage cutout is made slightly oversize for the turret base. Line the inside of the cutout with two 1/2-inch-long strips of 1/64-inch ply, with their joints on the fuselage centerline. Put masking tape around the balsa turret base (to provide the necessary gap) and apply it to the fuselage to hold the strips in position while you glue them in with thick CA. Then remove the tape from the turret base and sand the ply in the spots that prevent the base from rotating freely (nothing ever comes out perfectly round).

Gums

Wing Mfg. makes a .50-caliber Browning machine gun kit for the turret that's available separately. I glued a balsa block in the center of the two guns during their assembly so that a hole could be drilled in their sides to connect them with a piece of 1/8-inch wooden dowel. This dowel runs through the two 1/8-inch aircraft plywood vertical supports shown in the pictures. The supports have fuel-tubing inserts that provide the necessary friction to hold the guns in any position. By putting the dowel in my Dremel tool, I made two grooves using a small round file that matched the spacing of the supports. This keeps the dowel centered correctly while the guns rotate from horizontal to vertical.