Introduction: DHC-1 Chipmunk
Dumas KIT NO. 335
30'' Wingspan Scale Rubber Powered Flying model converted to full RC.
Max weight once finished 250 grams (everything included)
RC equipment details:
Engine: E-flite park 250
Receiver: 4 Channel Spectrum AR400
ESC: Talon 15 Amp castle.
Elevator/rudder servo: Hitec HS-55
Aileron Servo: Hitec Digital Micro HS-5055MG
Prop: APC 8 x 6 slow flyer
This plane doesn’t come with pre-cut spar to make sure the wings have the right amount of dihedral, they want you to raise the wingtips to a set height on the plans 2-⅜” and glue the wings together. That would be enough for a free flight plane, but in order to convert this pane into a full RC one I was going to need more strength in the middle of the wing.
With the help of a protractor, I figured out that according to plans the wing dihedral was 9 degrees. I cut a piece of basswood, which is stronger/heavier than balsa wood. later on I realized that indeed 9 degrees was way too much and created another one, more details on this later.
The first pieces of the wing together lying flat on the table. The intersection pieces are not glued together yet.
I realized that 9 degrees of dihedral would make the wingtips pretty much touch each other. I did my research and made the decision to cut another basswood piece, this time with 6 degrees of dihedral. What you can see on the picture is the template I used to cut the wood piece.
The reason the plans use 9 degrees is because a free flight rubber band plane needs to be stable. lots of dihedral means the plane would have tendency to keep the wings level. although the less responsive the ailerons will be.
WW2 planes had a little bit of dihedral. so pilots didn't have to keep their hands on the stick on long missions. but not too much so the plane was still maneuverable during dogfights.
Center part detail. I planked the center bottom. I was thinking to put the aileron servo around that area but I thought it would be a good idea to add some reinforcement (Wings are glued now. You can see the dihedral spar.)
Making sure both wingtips were the same height.
Starting with the fuselage, the hardest part for me is getting both sections (you can only see one here) to align straight together once you are gluing them. I need to find a gadget or something to help me out with that.
I planked the top part of the nose, I decided to add the battery plus ESC there, so I needed some kind of lid/compartment.
Also, I cut out one of the formers so I had space to put the elevator and rudder servos. Trying to keep the weight as forward as possible!
After sanding the nose. I cut/opened the compartment (did that with a little saw) where i am going to put the battery and ESC. You can also see that I added the firewall made of basswood.
Put two pieces of wood on each side of the lid to make a better fit.
put another two pieces of balsa front and back of the compartment.
Added magnets to the lid and fuselage.
I am not super happy about the way I built the ailerons. I could have used way less wood and been more careful on the finish. I put too much unnecessary wood and glue, but anyway they turned out to be alright.
You can see I cut out the aileron from the wing and added a piece of wood across. Couldn't find the right height so i glued a 1/16 at the bottom
Here some details about the piece of wood that goes across diagonally and where the hinges will be glued
I should have used CA hinges, way less heavy and simpler, but for some reason i decided to go with normal hinges. I had to add 2 pieces of wood so the hinges would have a place to be glued.
It might be hard to see, but the aileron is made of 2 pieces of wood. The flat bottom and a square piece right in front, Front piece will be sanded round. More details on next steps.
Adding the continuation of the ribs
Bottom part and the front square piece sanded. Tried to sand 45 degrees bottom and top so the aileron would be able to move once attached to the wing.
Here is the finished aileron. It does the job but it can be improved.
To move the ailerons I ran Sullivan cable through the wing and put the servo in the middle. Wings are thin so this is pretty much the only way, it also saves weight.
I needed a way to get the cable out of the wing, like i said maybe not the most finest work here
Joined both elevator pieces with a U shaped wire. I tried to use a flat piece of wire first and it didn't work out, I had to fill the gap and try again
Dry fitting the Servos to see where the cables to control rudder and elevator should go.
Wing covered with tissue, I would also like to say that I didn't use the tissue that comes with the kit, I really like the tissue Guillows kits come with, you can also buy it separately
Glued the empennage to the tail.
Wing and ailerons covered. I gave the tissue a fine coat of easy-dope to give it some strength.
Gluing the rudder. Used some scrap wood I had lying around to try to keep the rudder straight, worked better that I expected.
For the Elevator and rudder I used CA hinges instead of regular hinges. After my work on the ailerons, I decided to give them a go. This was my first time using them and I have to say that from now on, this is all i am going to be using for these types of planes.
Glued the servos with CA so I could set the cables. I will put some screws at the end to hold the servos in place.
Had to come up with a solution for the canopy so I could take it off to reach the electronics. To do that I added 4 pieces of wood and glued some magnets on them.
Added some washers to the canopy so it would stay in place. Neodymium magnets are freaking strong by the way.
So this is the engine cowl, “for a rubber-band engine”. There is no way I can fit the brush-less engine there. So I decided to add more wood, and make a mold out of it. later I could use the mold on a vacuum forming machine and get a plastic version of it
Time to cover the plane,
I changed the servo on the wing for a digital metal geared one. I found that the cable was putting quite a bit of stress on the old servo. Didn’t want that servo to slip the gears while flying, so I decided to change it for something better. Of course I glued the old one with Epoxy, so I had to break the base where it was sitting and make a new one for the new servo.
I added a little box of wood around it too keep it in place,. Didn't glue it this time, I put a very good double side tape underneath. and surround the servo with a wood
Painting the canopy
Priming the model with Tamiya spray, fine white.
Painted the whole thing with chrome yellow Tamiya TS-47
Put the decals in place, it really comes alive
Main gear and Tail
Masking work to paint the “black stripes” used by the pilots to get in and out of the cockpit. I used an airbrush and Tamiya XF-1 flat black.
I have done some weathering on the plane with dark grey pastels. you can also see it on the fuselage and tail, very subtle.
This is the frame I am going to use to hold the plastic for the vacuum machine. The pieces are put together with those 90 degrees angled pieces and few nuts and bolts.
plastic is styrene
Mold of the engine cowl. I added a couple more layers at the bottom. The grey stuff is putty.
Few plastic cowls made with the vacuum forming machine
Picked the best one and made the engine and vent holes.
Put the engine in place. I Added a 1mm piece of plywood as a firewall, basswood wasn't strong enough
Some more masking to paint the nose.
If I measured correctly the CG should be 5 cm from the leading edge of the wing. The plane looks quite nose heavy in that configuration.
If I move the CG a bit forward until the plane is just a tad less nose heavy the CG is 4 cm from the leading edge.
The finished plane. If you are reading this, thanks for making it all the way through.
now I just need to find some time and a calm day!
Step 53: Finally Flying!
I finally had some time for the maiden flight. I was surprised how well it did, it flies straight didn't even have to trim it. I might add some down angle to the engine so it doesn't go up so easily when adding gas.
Overall, really nice slow plane, I even did a loop!
Grand Prize in the
Make It Fly! Contest 2017