Scratch Built Cessna Trainer

Hello! This is my first posting here on Flite Test so I wanted to show you this Cessna I built from $Tree Foamboard. I built it over the course of about 2 weeks

Here is an Overview Video:

Here are the SPECS:

Length: 36"
Wingspan: 52"
Wing Chord: 10"
Horizontal Stabilizer: 20"x7"
Elevator: 20"x2.75"
Ailerons: 16"x3"

Weight: 1100g

Motor: Turnigy Park 480 850kv w/ 10x4.7 prop
ESC: Turnigy 30A Plush
Receiver: OrangeRX R620
Servos: (4) Turnigy 9018MG

Battery: Turnigy 1800mAh 3S LIPO

Radio: Spektrum DX6i

Flight time: 7-8min

Background Info

My inspiration for this plane came after I was commissioned to build a Trainer styled plane for my Grandfather. He had recently gained an interest in RC planes while watching me fly my first plane, the HobbyZone Super Cub. After a few months of scratch building, he asked me to build him a plane rather than buy one. I went with a simple high wing trainer design with a square fuselage and kfm-3 wing. Only being my 3rd scratch built plane, I was weary as to how well it would suit a beginner. It turned out to be a great success! I flew it at my local park to have fun...I mean "Test" it before delivering it to my Grandpa. I found that the thing I enjoyed most was landings and touch and gos. At this time my primary plane was a prop-and-slot jet without landing gear, so I had'nt had the chance to experiment with landing. I decided that my next design would incoorporate landing gear. 

Another thing I liked about my Grandpa's plane was the removable wing. So now I had two parameters to design the plane out from. I knew I wanted more than enough control to fight the wind, and perform aerobatic manouvers, and 3 inch wide control surfaces were added to the design. The actual look of the plane was inspired by the Cessna 172, but is not acurate to the real plane. I also wanted this plane to be as big as possible, and still be able to fit in the back seat of a car without a multi-piece wing. I measured my cars width, and found that 52 inches was the max size it could hold. I then came up with a number for the fuselage length from the size of the wing. 32 inches looked to be a good number, so I set off to sketch the design. I came up with a plan on some grid paper.

Design

Construction

I started out by extending a normal piece of Adams foamboard purchased from the Dollar Tree by 2 inches in lenght to make it 32" total. Next, I drew a line down the middle as a center of the plane to work out from. I measured out the bottom plate and two side plates as a reflection from this center line. The width would be 4 inches tapering to 1/2 inch at the tail.

I cut out the piece and hot glued only one side to the bottom plate. I did this so I could install the firewall and rear bulkhead more easily. The paper on the nose where the firewall will go was removed to make a stronger connection between the 2 foams. The green cube in the upper left is the firewall, made of two, 1" thick foam from Lowes.

After glueing the firewall, and folding the other side up, I drew out the tail and horizontal stabilizer. The HZ was originally 16" long, and 7" wide at the root, but I had to change it (as you will see later). The movable elevator is 3" wide. I drew this by tracing the tail of the fuselage upside down and then adding in the stabilizer.

Here is the plane with the tail glued on. You can almost see the rear builkhead in the center of the image. And the green foam is the firewall at the nose.

Next I cut out the Verticle stabilizer. It has a movable rudder that is 2 inches wide. The size of it also was changed later in the build. the landing gear were installed using a plastic slit that I cut out of my Super Cub, and the wire was from the Super Cub float set. I have two 2" wheels on it.

Now it was time for the wing, the most intimidating part. I had to make it 52 inches long, so I used 2 pieces of foamboard cut to 26 inches long a piece. I wanted the plane to have plenty of lift, so I went with a 10" wide wing. That gave me 520 Sq.In of wing area. I first measured out 10" from the edge of the foam. Then 7. I traced these lines across the entire board. (The 3" less for the bottom of the wing is for the aileron and camber which decreases the length). I removed 5 inches in length from the tip of the bottom to give undercambered wingtips. I cut out the wing half, and traced it onto another piece for the second half. 

It's hard to tell, but I glued in 3 foam strips on top of one another as the main spar. I also added plenty of wooden sticks of about 5mm thickness for extra strength. I folded the wing over itself but forgot one crucial step. I forgot to install the aileron servos & wires inside the wing! 

Here is the shell complete with no electronics installed.

For the Motor mount, I used 2 layers of popscicle sticks hot glued, and gorilla glued onto the foam firewall. I drilled out small holes for the 4 screws, and cut out the hole on the bottom for the motor wires to run into the fuselage. 

Here you can see the Park 480 Motor, and 30A ESC are screwed in, and glued on. The Reciever and Elevator/Rudder servos are also glued in (bottom 2 pictures). 

I had to run about a foot long pushrod for the rudder and elevator to keep the servo weight toward the Center of Gravity (near the middle of the fuselage). Having the 2 servos out on the tail would require the wing to be moved back past its desired position.

Here is the plane nearly completed. All that is left to do is add in the 2 Aileron servos, and some colored tape for the paint scheme. Note that I have it configured as a tricycle gear. I added 2 spots for the landing gear so I could go with a tricyle or taildragger configuration. Though I found that the nosewheel is not strong enough to support landing forces, so I only use the Taildragger configuration. The wing struts are just for show, and are only held on with velcro. 

Now it was time to feed the aileron servo wires through the wing. This was by far the most challenging part of the build. I first just tried letting gravity pull the wires through to the center hole, but it did not work. My second try was adding weight to the wire to help pull it down through the wing. This also failed. I ended up pushing a stick through the ends of the wing to push the wires in. Always remember to put those servos in before finishing the wing! 

Now the plane was all finished and ready to fly! I used red and black Duck tape for the paint scheme.

After the first flight, it pitched up violently when I increased the throttle. I first thought it was tail heavy, so I kept moving the battery farther forward. Eventually It actually became nose heavy and was quite tricky to land due to my inability to slow it down. I realized that adding downthrust to the motor may solve this issue. In addition to downthrust, I also increased the size of the Horizontal, and Verical stabilizers just to be safe. 

With these modifications, it flew great! It can go fairly fast, but also can slow down for nice landings! Althought I originally built this plane to practice landing, it does'nt perform too well on the grass, so I have had to find new paved places to fly at. Overall, I am very happy with this plane, and plan on keeping it until it becomes unflyable (crashes). 

 Here is a flight video. 

Thanks For Reading! 

-Brock C.

www.youtube.com/aplanerc