Falcon mkiii Christian Perry Pleasant Grove, Utah November 2009 This is my third build of the Falcon 120 from Nitro Planes. I have really enjoyed this jet and wanted to do the best I could with this build in terms of strength, weight, aesthetics, and functionality. My final build came in at 18.4 pounds dry. It's significantly stronger and I think it looks pretty cool. It flies fantastic!! I hope you enjoy this journal of its construction.
Wings, tail booms, and control surfaces were stripped of covering With a heat gun and scraping. I filled all the cutouts with matching balsa wood for a solid surface. Everything was glassed with 1.5 oz cloth and West Systems epoxy. The fuselage was stripped and sanded as much as possible The formers pop out easily. I then sanded out any remaining glue on the inside. I wanted a smoother blend in the rear so a portion was trimmed out from the fuselage. The hole was filled with a thin piece of plywood and glued in place I replaced the landing gear wood blocks with a U channel of aluminum filled with plywood. The landing gear mounting was covered with 6 oz carbon fiber cloth and epoxied in with the same resin I used with the fiberglass.
To blend and filet the connections I mixed 5 parts phenolic microballoons to 1 part epoxy resin. It is very lightweight and sands well. The wings and booms were glued in place with Hysol. I used the provided nylon bolts for the wings and booms to save weight. I then filled the holes with lightweight spackle The servo wiring for the rudders and elevator were pulled before gluing the wings in place. I wanted a smoother blend from the tail booms to the wings so I shaped a balsa block in the front of the booms. To add torsional strength to the fuselage I added a strip of 6 oz carbon fiber cloth with epoxy resin. The provided wing spars were replaced with carbon fiber tubes. The front spar was relocated to the base of the wing for more tank space. The rear tube is from a TRex 600. It's much lighter and a bit longer. Some trimming of the formers was required. For aesthetics I added a small fin mid wing. I trimmed and sanded a balsa strip then glassed it to the surface. I also added a strip of 3 oz glass to the connection of the tail boom and the wing for strength since this is a weakspot. Additional blending with micro balloon epoxy mixture. It's about the consistency of peanut butter.
After much careful sanding, working down from 220 grit to 400 grit wet. More wet sanding... And more wet sanding I sprayed the entire surface with white gelcoat thinned with hi-gloss additive. More wet sanding of the gelcoat until smooth Ready for primer The entire surface is sprayed with automotive primer. After masking out non black areas I sprayed two coats of automotive black paint. More masking then a red paint pass.
Next comes the white pass. Notice all the control surfaces strung up on a line to the right. Then came a clear coat pass. I used the removed formers to trace and cutout these carbon fiber sandwich panel replacements from protechcomposite.com The panels only added less than one ounce from the balsa formers they replaced. They are.25 mm carbon fiber with lightweight nomex in between. Overall thickness is 7 mm. I wanted the top to be a clean as possible so only things that need constant access are exposed. everything else is mounted below. Ready for former installation. Formers were attached with hysol. You can see the 2 liter fuel tank in the rear (Windex Refill Bottle). I assembled the front landing gear and formers before installation into fuselage leaving holes for air tanks. Front battery compartments wired in for easy access.
Digital air gauge, spektrum analyzer, air and fuel valves and recessed JetCat GSU connection. UAT and fuel tank visible. Bottom access panels open. The mid section contains the fuel pumps, filters, and shutoff valves. The rear section allows access to the fuel and smoke tanks. The front access panel containing voltage regulators, receiver, retract valve, brake valve, and starting gas tank. I built a box for the nose wheel cavity from.5 mm carbon fiber sheet to accept my training link strut. The nose wheel servo is located in the front portion of the wheel well. It provides a short distance for steering cables.
The access panels are covered with a thin aluminum plate painted to match. The carbon fiber plate in the center houses the vent lines for the fuel and smoke tanks. They are capped with festo end caps. In the middle is a mount for a digital camera. It was cannibalized from a small lightweight tripod.
Servos were mounted to the inside of the aluminum plates then secured to the wing. Aluminum cover panels provide access to retracts. The trailing link struts were purchased from altecare.com. The wheels, brakes, and retracts are from airpowernet.com Turnbuckle style pushrods allow easy adjustments. Control horns were purchased from hobbyking.com
Aluminum plate added under tail plane to protect against a hot start. I also added a small aluminum nose wheel panel and a small rubber nose skid (from experience).
The canopy was purchased from NoRay on the RC Universe Falcon build thread. It's secured with two carbon fiber tubes attached to the canopy that lock into four carbon fiber hooks on the fuselage. Simply sliding forward releases it. I added three luxeon LED lights. Since these burn really hot you need heat sinks. You can notice them thermally glued to some aluminum fins and embedded in the wing. These were left over computer parts that were sanded to shape. The nose wheel is simply thermally glued to the front strut since the strut itself acts as the heat sink. The elevator servo is mounted to an aluminum plate then secured to the top of the tail plane surface to avoid any heat damage.
Decals were printed on my ink jet printer with Avery transparent labels. The turbine mount I cut from aluminum L stock and lightened it as much as possible. I added the ability to adjust the thrust angle with four screws on the sides. I pinstriped all the colors for clean lines. This is a JetCat P60SE. I painted the cowling black to match the paint scheme.
I have a small gyro behind the UAT for added nose wheel stability. I use four 1200 mah lipoly batteries. Two for redundant power to the Spektrum 9100 reciever, one for the ECU, and one for the lights. They are easy to slide securely into the foam cutouts. I don't use any switches only direct power connections.