Twin Motor Coast Guard Plane - Scratch Build

Here is a video about this plane on my Youtube channel:

INSPIRATION

This project was inspired when my then-current plane stalled and crashed. It was a twin motor plane with twin vertical stabilizers. The nose was wrinkled up and fuselage smashed beyond repair. So I saw this as a time to build a new and improved version 2 of the air-frame. Having been flying the old one for a couple months, I had a running list of things I wished I had made differently. I compiled all of these changes and began designing a version 2. I wanted the fuselage to be longer in comparison to the wing, because the old plane seemed to wag the tail a lot in flight. Having a longer distance between the tail and wing should yield a more locked in pitch and yaw. Additionally, I thought that larger Vertical Stabilizers would help with this issue. I also wanted to go with a different paint scheme. I've always loved the look of a U.S Coast Guard C-130, so I decided that was what I'd go with.

Since the old plane was destroyed due to the fuselage being made from white foam board, I really wanted to build the entire plane from solid pink insulation board. I already have been using solid foam and a hot wire cutter to make the wings and tail surfaces.

DESIGN

These were the criteria I used to design the plane by. The wing and tail dimensions were based on the old plane, which can be found here: https://www.youtube.com/watch?v=057RGNs91cI.

Wing: 57inches long w/ 7.75 inch chord

Horizontal Stabilizer: 16 inches x 6.25 inches

Vertical Stabilizers: 8 inches x 6 inches

Fuselage Length: 40 inches

Fuselage width: max 4 inches.

Ailerons: 16 inches x 2.17 inches

Flaps: 9 inches x 2.75 inches

Elevator: 16 inches x 2.25 inches

No rudder. Differential thrust.

INITIAL BUILD

The build began by first cutting out the shapes that would form the fuselage. The fuselage is a rather simple design, Just a rectangular prism and a stretched pyramidal prism fastened together. All of the shapes were cut from solid 1inch foam insulation. Then these pieces were cut in half, so that each "wall" of the fuselage was only 1/2inch thick. The pieces were then glued together with gorilla glue as the main adhesive, whilst using hot glue to hold the pieces in place while the gorilla glue dried.

Nose

The nose was created by drawing the outline of a C-130 nose on one piece of foam. I cut it out with my hobby knife, then traced this shape onto 2 other pieces of foam. All 3 pieces were glued together, and I finished off the shape with my knife and some sand paper.

The fuselage frame is fully assembled here, and below is it pictured next to the old plane which I based this plane off of.

The horizontal stabilizer was cut out and sanded down to round the leading and trailing edges, and the 2 vertical stabilizers were made similarly, then glued onto the sides of the h-stab. 2 diagonal pieces of carbon fiber were glued into the h-stab and the v-stabs to strengthen them. The elevator was attached to the h-stab using 5 nylon hinges.

Wings

The wings were cut out of the 1 inch thick foam using my homemade hot wire cutting bow. The templates were based off a symmetrical airfoil I found online. The templates were cut out of thin aluminum, then attached to the sides of the foam using nails.

The 3 sections were glued together initially with gorilla glue and hot glue. No spars were put in yet. The tips were propped up to create some dihedral. The middle of the wing was weighed down to keep the tips higher than the center.

Next, the slots for the wing spars were cut with my hobby knife. The spars are 10mm x 1mm carbon strips which are placed in vertically so they do not bend easily up and down. Multiple of theses were used to make the wing very stiff. These were glued in with gorilla glue, and the wing was held down with wood blocks while the glued dried.

PAINTING

The paint scheme was inspired by a C-130 Coast Guard plane.

I began by painting the entire plane and all surfaces glossy white with 2 coats of Rustoleum Latex Paint. I then used masking tape to tape off the red areas, and painted 2 layers of red latex paint. Next, the blue stripe was painted which goes on the fuselage in front of the wing. The US COAST GUARD lettering and logos were printed out on plain paper, then cut out and hot glued onto the plane.

WIRING

The main power lines from the batteries connect to a power distribution board, which distributes the 4s lipo voltage to both ESCs, the 10A BEC and to the positive side of the lights. The 10A BEC is connected to the receiver which then powers all of the servos. The negative side of all the lights are connected in series to a NPN transistor which can be switched on and off with an Arduino NANO micro-controller. The Arduino NANO gets a signal from one of the receiver channels which allows me to switch on the lights from my transmitter.

Final wiring with PDB(left) 10A BEC(Middle), and Arduino Nano(right) with X8R RX underneath it.

Motor Brackets

On each nacelle, I glued a small square piece of plywood using gorilla glue. I then used thin aluminum bars and drilled out holes for the motor screws and motor shaft to turn. I bent the aluminum pieces into a little more than 90 degree angle. Then, I screwed them onto the plywood on the nacelles.

Next, I used a block of foam with slots cut on the edges as a battery tray. A velcro strap goes under it through the slots, and I glued it into the fuselage after the correct CG was determined.

Two carbon fiber tubes were glued into the fuselage so that the wing can be held down with rubber bands. I used the same aluminum wing stencil to cut out a relief for the wing to sit in on the fuselage to keep it aligned correctly.