E-37

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The final design of the airfoil is going to be a modification to an already existing model. The model plane we are basing our aircraft off of is the Multiplex Twin-Jet 480 Racer’s model. This is a fixed wing F-series jet model. The model has a wingspan of 36” and is 31” long. The biggest modification to this model was going to be for the hover design. We cut a 12-inch hole in the middle of the model for the hover fan. The center of this hole is at the center of gravity of the plane. Since the two counter rotating fans are going to be on top of each other, it is going to be approximately 7 inches high. This means that the hover modification will stick out the bottom and the top by an average of a 1.5 inches. In order to cut the drag, we “ramped up” to the top and bottom of the hover fans. This has cut drag.

The final hover design that we are using is a duel system counter rotating hover fans in the center of the aircraft. This concept is different than the first design in a few ways. The first difference is that the hover fan has two propellers that turn opposite of each other located in the same shaft. This will increase thrust and decrease the moment created by the torque we would have experienced with one rotating propeller. The two propellers are going to be 11 inches in diameter. This will provide plenty of lift over a larger area. The engines running these will be Hacker brushless B20 15L motors. The motors produce a maximum power of 222 W and accelerate the props to a tip speed of over 270 mph or 120 m/s. For forward flight the aircraft is equiped with a 9 in. folding propeller that spins in excess of 280 mph or 124 m/s. It has a maximum power rating of 277.5 W.

The construction of E-37 began with the modification of our base model. The Twin jet model was adapted to our needs by cutting a 12-inch diameter hole in the body to make room for the hover assembly. We cut a cardboard concrete form to a height of 7-inches to give us the height we would need for our hover motors, gearboxes, and props. We used modeling clay called plastalina to make a smooth shape from the cockpit of the plane to the top of the cardboard form. Plastalina is an oil based clay the does not dry out which allows you maximum reshaping time. On the back of the plane, we made a smooth, but bulbous segment that we used to house the servos for the munitions deployment units, and the batteries for the hover fan motors. The nose was tailored to be able to take the puller prop we are using. We removed the tip of the nose to make room for the prop and spinner. We also had to modify the shape of the nose for the mold making process. We used plastalina to bring the centerline of the nose to the same height as the rest of the model. This would ensure that the mold we were constructing was would not lock on our model.

The construction of the carbon fiber skin could now begin. The mold was coated with a silicon spray to ensure the resin would not fuse with the plaster mold. The carbon fiber was cut into manageable strips and set into the plaster mold. A polymer bag was placed over the carbon fiber. Builder’s sand was used as a filler to keep the carbon fiber pressed into place. After the carbon fiber set for 2 days, the sand was removed and a heat gun was used to heat the carbon fiber and activate the resin. After the carbon fiber cooled, excess carbon fiber was trimmed. Epoxy was used to smooth the surface of the carbon fiber. The landing gear was then attached to the bottom half of the frame. Basswood was used to add rigidity to key areas such at the hover fan walls, and the cockpit portion of the plane. This wood was also to mount the servos, and to provide screw down points for the hatches. Once the servos were in place, the two halves were tacked together using CA glue. Final trimming was at this time. Strips of carbon fiber were used in conjunction with epoxy to make certain the two halves would not separate, and to make a smooth surface on the seam.

Control surfaces and munitions deployment doors were constructed by sandwiching three layers of carbon fiber with epoxy. These surfaces were attached to the plane using nylon hinges that were glued in place. Control horns were attached to the control surfaces and munitions deployment doors. These control horns were attached using CA glue. Hatches were cut into the top of the plane in four key locations: the nose, the two sides, and the rear. All of these locations allow easy access to the servos in the plane, as well as access to point for storing the payload, and for running the wiring. The Hatch doors were glued to nylon hinges, and the hinges were then glued to the plane. The loose end of the hinge was then screwed into wood that was placed in the support structure for this purpose. The plane was then given to the painter for the custom paint job. Once the paint job was complete, the motors were mounted in the plane, the wiring for the motors, batteries, and receivers were run, and the batteries and receivers were mounted in the strategic places to best balance the plane. The plane was then balanced using small amounts of lead weights.

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