Embry-Riddle CAP 580- Red Bull Challenge

Embry-Riddle CAP 580- Red Bull Challenge

My aircraft design entry started out with an acceptance letter a year ago. I’m a rising sophomore at Embry-Riddle Aeronautical University (ERAU) majoring in Unmanned Aircraft Systems. I’ve always thought the paint designs on our aircraft were amazing! (See above) But, neither the Cessna 172, Diamond 42, or the Piper Arrow fit the bill for the Red Bull Air Race Plane DIY Competition 2018. So, enter Matt Chapman and N580GP.

I’ve been fortunate enough to speak to Matt on campus and at Sun N’ Fun. Each time, I have come back overly inspired. I also have a huge passion for scale civilian aircraft, so I decided to go with a more semi-modern aircraft. The CAP 231EX (top) was built in 1998 and flown by Matt Chapman, the ERAU sponsored pilot. He performed in airshows all over the country through the early 2000’s in 580GP. Then, in 2015 Matt upgraded to the Extra 330LX. (above) An aircraft capable of 220 knots and +/- 10 g’s. While both aircraft are amazing I thought it was only fitting to bring back the infamous Mudry CAP.

I wanted to keep this build as simple as possible. So, I decided not to use CAD or 3D printing since these products are unavailable to most of us hobbyist. My goal was to sit down with a hobby knife, foam board, and poster board to show that complicated tools aren’t necessary for outstanding model aircraft designs. Unfortunately, that did mean I would not be able to create plans for the FT community. I did use GIMP, which is a free photo editing software, to give me a general outline of the aircraft. (Pictured Below) I sized the drawings to ensure the wings would be about 50 inches. Then, I tiled the plans to fit onto a standard 8.5” X 11” paper. Each drawing was printed and put together in the respective order.

I decided to start with the wheel pants as a test. I used the shape from the side view and cut a strip wide enough for the wheels to wrap around the sides. The process is similar to the FT Guinea Pig.Up next was the wing! I first cut out a set of wings which included the ailerons to use the paper as a hinge. (bottom half) I then cut out a second set of wings leaving the ailerons off. (top half) I then attached the left wing at the leading edge and did the same to the right. I attached the two wings together with tape and hot glue, keeping the leading edge straight. Once that dried I peeled the paper off the inside of the wing. This was to aid in keeping the airfoil, not only smooth, but symmetrical. Then a single spar was glued in place. I made sure to take note of the thickness of the wing at the middle and ends of the wing as well as the positioning behind the leading edge. I threw in a couple of spare carbon rods and then beveled the leading edge and ailerons. Lastly, I folded and glued the wing to shape. It turned out super lightweight!

Next was the fuselage. I took the outline from each angle on the plans and transferred them to the foam board. I cut the horizontal outline in half and glued it in the appropriate position on the vertical outline. Once that dried I attached vertical formers to give the poster board the correct shape. I repeated the process on each quadrant of the fuselage.

Once the formers were in place I attached the tail surfaces. A foam board width slot was cut in the vertical stabilizer to position the elevator. Keeping the fuse and horizontal stabilizer perpendicular, it was glued in. The rudder was then installed with packing tape as a hinge.

Elevator and rudder servos were then installed near the tail of the aircraft. Since the elevator is split on each side, two servos were fitted and the proper mix was used in my transmitter. I had 9 gram servos on hand, so those sufficed. Regrettably, I did not fully think through how much weight I would be adding to the tail even though it was the simplest option.

I then connected servo extensions and cut paths to route wires towards the nose. Once that was complete I started covering the aft fuselage in poster board. My thought was to cover the bottom first and then the top to keep the lines as clean looking as possible. It didn’t go so well in the end… Then wing was then glued into the pre-cut slot I had made when the fuselage was cut out. It wasn’t a perfect fit but with a little spare foam I easily filled the gaps. Once the wing was in place I installed the motor and esc making sure I would have room for a battery in the nose. 

Lastly, before I could paint I had to finish covering the fuselage in poster board. This was the most difficult part of the project with all of the complex curves, especially on the nose. It took multiple evenings and numerous “frustration breaks” to complete. 

Once that was finally finished, it was time to start painting. Of course, on the days I needed to paint rain showers were scattered through the afternoon and evenings. To keep it simple I decided to use spray paint. So in between the rain I painted a base coat of yellow on top and blue on the bottom. 

I soon hit my next wall, painting the cowl. Using painters tape I outlined the design to match the full-scale airplane. I sprayed on several coats only to realize areas had bled through. Knowing I was short on time I went back in with a paint brush and touched up those areas. For the canopy I used a black wide-tip sharpie for simplicity. Originally, I had planned to paint the letters and Eagle on the tail. I was running short on time and had access to a vinyl cutter so decided to use that instead. With that, the letters went on like stickers which made the process much simpler. The last item to be finished was the gear. I first cut a slot just in front of the wing spar. I bent a wire to match the shape of my plans and cut a couple pieces of foam to fit over the wire and into the slot in the wing. And with that I was done! Well…almost.

A proper maiden was in order. If you would like to watch, it is on the video in this article. I wanted to keep the center of gravity (CG) at about 30 percent of the chord. Needless to say, that didn’t quite happen. I wasn’t able to get the battery forward enough so the CG was at around 35% or 40%. I figured that would be close enough and decided to fly anyways. With a full throttle punch up she went with a very sensitive pitch axis. Although manageable, it definitely was tail heavy. Simple aerobatics like loops and rolls were accomplished but I didn’t push the envelope on the first flight. I did come in a bit slow during final approach and stalled a couple of feet over the runway. The CAP 580 survived without damage! I’ll call it a successful maiden.

While this definitely isn’t a Flite Test, David Windestal, or Peter Sripol equivalent design, for my first complete scratch build, I thought version one turned out decent. Someday I hope to re-visit this project but for the next few months my education will take precedence. So, for now this airplane will remain a decorative piece and an inspiration. Inspirations can be miracles in disguise. My inspirations from ERAU, Flite Test, and Matt Chapman have done just that. I hope THIS has been an inspiration for everyone! 

SPECS:

Wingspan: 50”

Motor: Turnigy SK3 3536 1400kv (590 watts)

ESC: Turnigy Trust 70 amp (a bit overkill)

Prop: APC 9X6

Battery: 3000mah 4s LiPo

Servos: Hextronik standard 9 gram