Scratch Built Cessna 172 Skyhawk

56in wingspan Cessna 172 Skyhawk

Inspiration:

In July 2013, I took my first flight ever, in a Cessna 172. This is what sparked my interest in aviation, and has lead me to the RC hobby. For this reason, the Cessna 172 continues to be my favorite aircraft, making it high on my list of planes to scratch build. One of my first planes I ever built from Dollar-Tree foam board was inspired by the Cessna 172, although it didn't really look much like it. So, now I decided to build a plane that really looked like the 172, using my own building style, which uses home depot pink foam board instead of dollartree foamboard. Also, I have been fortunate enough to attend the Ohio State University, where they have a fleet of Cessna 172 aircraft painted up in the university's colors, so I thought this would be a cool paint scheme to choose. 

Design:

I began with a '3-view' drawing of the Cessna 172 which I found on google, and used Fusion360 CAD software to create a 3D model of the plane from the 3-view drawing. I designed it in inches, and rounded every dimension to an even 1/4 in, since this would make it easiest to build using a standard US ruler. The model is nearly exactly the same proportions of the real plane, with the exceptions of the horizontal and vertical stabilizers. From prior experience, having too small stabilizers causes a model aircraft to fly poorly, so I slightly exaggerated their size when designing this plane. I tried to get the horizontal stabilizer to be about 30% of the wing area, and the vertical stabilizer greater than 50% of the horizontal stabilizer's area. Once the 3D model looked good, I used it to make 2D plans. Here is a link to the pdf plans: https://drive.google.com/drive/u/1/folders/11_D7h9qMzg80kX1qxPoV41qFSrPt2d4T

Here is a video detailing the 3D model I created in Fusion360:

Construction:

With printed plans in hand, I began construction of the fuselage. I started out with a 24"x24" piece of 1" thick Owens Corning foam board. Since I most of the plane was designed with the panel pieces being 1/2 inch thick, I used my hot-wire cutter to cut one of these pieces in half, so I would have 2 1/2in thick pieces.

Next, I used the plans I had made to draw out and cut out all the panel pieces for the fuselage. I then used gorilla glue and masking tape to hold the pieces together to make simple box shapes.

The fuselage was assembled in 3 box sections. After the gorilla glue dried, I removed the tape, and used my hot wire cutter to slice off the edges of each piece which would be glued against the next section. I did this so that each piece would have a smooth and straight face to glue them together. Next, I glued the 3 section together, holding them in place with masking tape and clamps. I made the 'firewall' piece and bottom of the nose as one large piece, glued it in, and then cut the bottom to follow the contour of the nose side panels.

Here is a build update video documenting the build up to this point:

Next I glued on the top panel of the fuselage tail. I glued on a piece of foam onto the rear window area, then cut it to follow the shape of the fuselage side panel.I used 1/2in thick foam for the stabilizers. I used a thin 1x6mm carbon fiber strip as a spar for each stabilizer. These were glued in with gorilla glue into a slot. Then I glued them onto the fuselage.

I designed 3D printed brackets that glue into the fuselage, which the landing gear wire will slide into. This is the nose gear bracket, but the main gear bracket is similar, but has a wider base.I used a sanding block to sand the fuselage and stabilizers. This really helped to blend the 3 sections together and make it appear seamless. I used a knife to cut material from the corners, then sanded it to make the edges more rounded, and less boxy. 

Here is the next build updated video up to this point:

Next, I began constructing the wing. For it, I used 1in thick pieces of foam. I designed the airfoils templates in Fusion360 based off of the Clark Y airfoil, but stretched slightly. These templates were 3D printed, and I used aluminum tape to cover the edge of the templates. I used these templates to cut out the wings using my hotwire cutter. The wing was made from 5 sections, which were glued together. 

Here is a build update video up to this point:

Next, I sanded the wing down using a sanding block. After that, I cut a slot along the entire wing, and glued in a 1x6mm carbon fiber spar on the upper and lower surface of the wing. While the glue for these spars was drying, I propped up the wingtips to create a slight dihedral in the wing. 

I used carbon fiber tubes as the mounting points for the rubber-bands, which will hold the wing on during flight. 

Here is a build update video up to this point:

Painting:

Next, it was time to paint the plane. I used Rustoleum latex paint. First, I put 3 coats of glossy white paint over the entire plane.

The real plane features the Ohio State University "Block O" logo and the Cessna logo on the on the tail. I used 3D printed stencils which I designed in Fusion360 to make these along with the N-number. The red and grey curves and the windows were marked off using masking tape. I used red, black and gray sharpie permanents markers for all of these.

Electronics:

Here are the electronics I used:

Emax 3506 650kv w/ 11x4.7 prop

30A ESC

Readymaderc 5v 6a BEC

5x Emax ES08AII , and 1x Emax ES08MAII Servos

Frsky X6R reciever

The motor was originally inteded to just screw onto the wooden firewall on the nose, but I got the idea to 3d print a motor mount which looks more realistic. I designed this using Fusion360, and 3D printed it out. This made the nose look much better in my opinion.

I glued in the landing gear wire, and added a 3d printed faring to the main gear which makes it look more realistic. I used 2in wheels. 

The final thing I did was make the hatch which goes on the nose. Here is a video update up to this point:

Here are some pictures of the finished plane:

Maiden Flight:

Here is the maiden flight video:

The maiden flight went very well. The plane ended up weighing about 1200g, which was about the same as my last two planes, which also had similar wingspans. So I predicted it would fly similar to those planes. After trimming it out, and reducing the control surface throws, it flew great! here are some pictures of it in flight:

Conclusion:

Overall, this plane turned out looking very realistic in flight, and has good flight characteristics. I plan on revising the design in the future to improve the detail and look of the plane. If you are interested in my other aircraft projects, or updates to this plane, feel free to check out my YouTube channel: www.youtube.com/aplanerc

Thanks a lot for reading my article, I hope you have enjoyed the build, and maybe even learned something new. 

-Brock