Add a Bomb
Aaron Baldwick
ONE THING that adds excitement to any model is a functional bomb-drop feature, especially on World War I biplanes. Dropping a bomb is the ticket to add insult to injury after you've defeated your adversary in an exciting dogfight.
There are many simple servo-activated systems around, but I wanted one I could remove and switch from one airplane to another. As I was trying to come up with a spring-loaded system that would allow quick attachment and removal of the droppable bomb load, I learned about WingSpanModels.com, which had developed an answer to all my requirements.
Originally designed for use in WingSpanModels.com's large B-17 bombers, this programmable system allows various bomb-drop sequences. The unit can be set up to drop between one and six bombs and it can be set to drop the bombs one at a time, three at a time, sequentially, or simultaneously—all with the flip of a single switch.
The type of drop sequence is adjusted with small switches on the unit. The unit comes with two bomb-attachment pylons that plug into six pylon ports (you must supply your own 6- to 7.2-volt battery pack). The bomb releases are activated with electrical solenoid, so you need to use a high-capacity pack to supply the power needed to fire the solenoids.
For a single bomb setup as I have, you can get by with a 1500 mAh pack, but the instructions suggest at least a 2500 mAh pack for multiple-bomb operation.
Though not used in my simple biplane, another great feature of the WSM.com electronic bomb release unit is that it can be set up to control a servo to open and close bomb-bay doors.
Installation: For a simple removable setup, I installed a single pylon onto a plywood belly hatch. Here's how it goes together:
The model used in this article is a recovered Hangar 9 Fokker D.VII .60-size ARF. The bottom of the fuselage, exactly where you would want to install a bomb drop, is already cut away. All you have to do is remove the covering in between the two lower wing panels.
To make the plywood hatch cover stiff and warp resistant, I glued two 1/32-inch thick layers together with the grains 90° to each other. Once the hatch was cut to size, giving a 3/8-inch purchase all around the fuselage opening, I used six servo-mounting screws, as shown in the photo, to secure the hatch cover in place. Two attachment screws fasten the release pylon.
To attach the pylon to the hatch cover you have to add two plywood doublers to provide additional thickness to thread the screws into. These are installed in front of and behind the slot cut into the hatch for the power wires to pass through. Feed the pylon wire through the slot and screw the pylon base to the hatch cover. Once secured in place, snap the top part of the pylon over the base piece.
The WingSpanModels.com electronic bomb-release system comes with everything you need.
To install the release control unit, simply use a length of double-sided foam carpet tape and stick the unit to the plywood structure above the hatch opening. Make sure the wire connectors do not interfere with the hatch cover.
Once in place, run the input lead to the receiver and plug it into an auxiliary channel (I used the retract switch). Connect the battery pack and install the battery in a convenient place in the fuselage, packing it with foam to secure it in place. I used a standard Futaba airborne battery harness to turn the bomb release unit on and off and to charge the pack.
Bomb Building: The parts for two vacuum-formed bombs with laser-cut, light-plywood tail fins come with the basic unit package. It is fairly easy to build the bombs, but take your time.
Start by trimming away the excess plastic from the bomb halves and sand the edges smooth. Glue the two halves together with epoxy or plastic cement and install the tail-fin assembly. Finish by painting the bombs and installing the latch plate and release hook as shown.
Keep the seam straight and smooth using the raised trim lines as a guide. A light plywood profile piece is also included to give the bomb's body strength. Slip it into place in the bottom half of the bomb and position it so half of its thickness is above the top edges. Use thin CA and glue in place.
Before attaching the top half, cut two slots in it and glue the attachment bracket in place from the inside, with the tabs sticking through the slots. Use CA and glue into place. Add a layer of paper towel over the bracket and glue it with more CA for additional reinforcement. After the glue has set, place the top half over the plywood profile and fasten with CA.
Sand the joint seam with 220-grit sandpaper, and then use a few applications of Squadron White Putty to fill in the seal. Sand it smooth and use as many applications of the putty as needed to produce a smooth, invisible seam.
Spray on a layer of primer to seal the light plywood tail fins then paint the bomb to your liking. If you use a glow engine for power, use a fuel-proof paint.
Now attach your bomb to the release pylon by sliding the spring-loaded latch tab back to open the release pins. Turn on the radio and switch on the release system. Then flip the switch to check the unit's function. It should release your bomb with a satisfying "click!"
Bombs Away! Once you are ready to make your first bombing run, tell everyone on the flightline that you intend to drop a bomb—no need to surprise anyone. It is also a good idea to have a caller stand next to you to keep an eye on any traffic and call out your intentions.
Fly a normal traffic pattern and at approximately 100 feet up, flip your release switch 50 feet before your target area. Here's the big, very important part—do not watch the bomb! Continue to look at your airplane and fly it in a straight line after the release. Let your caller watch the bomb. There have been more than a few cases where a modeler has watched the bomb until it hit the ground, only to see the model hit the ground shortly after as well! Keep your eyes on your airplane.
That's it! Functional bomb drops are great just for the fun of it. The WingSpanModels.com release system makes it easy to install a bomb drop on many different airplanes, including scale models and trainers. There are additional release pylons and spare bombs available separately as well.
Have fun! MA
Aaron Baldwick [email protected]
Sources:
WingSpanModels.com (404) 944-0028 www.wingspanmodels.com
Squadron White Putty (877) 414-0434 www.squadron.com/ItemDetails.asp?item=SQ9060
Transcribed from original scans by AI. Minor OCR errors may remain.
