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

Step 1:

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.

Step 2:

The first pieces of the wing together lying flat on the table. The intersection pieces are not glued together yet.

Step 3:

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.

Step 4:

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.)

Step 5:

Making sure both wingtips were the same height.

Step 6:

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.

Step 7:

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!

Step 8:

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.

Step 9:

Put two pieces of wood on each side of the lid to make a better fit.

Step 10:

put another two pieces of balsa front and back of the compartment.

Step 11:

Added magnets to the lid and fuselage.

Step 12:

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

Step 13:

Here some details about the piece of wood that goes across diagonally and where the hinges will be glued

Step 14:

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.

Step 15:

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.

Step 16:

Adding the continuation of the ribs

Step 17:

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.

Step 18:

Here is the finished aileron. It does the job but it can be improved.

Step 19:

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.

Step 20:

I needed a way to get the cable out of the wing, like i said maybe not the most finest work here

Step 21:

Elevator pieces

Step 22:

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

Step 23:

Rudder

Step 24:

Dry fitting the Servos to see where the cables to control rudder and elevator should go.

Step 25:

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

tissue

Step 26:

Glued the empennage to the tail.

Step 27:

Wing and ailerons covered. I gave the tissue a fine coat of easy-dope to give it some strength.

Step 28:

Tail covered.

Step 29:

Gluing the rudder. Used some scrap wood I had lying around to try to keep the rudder straight, worked better that I expected.

Step 30:

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.

Step 31:

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.

Step 32:

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.

Step 33:

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

Step 34:

Time to cover the plane,

Step 35:

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

Step 36:

Painting the canopy

Step 37:

Priming the model with Tamiya spray, fine white.

Step 38:

Painted the whole thing with chrome yellow Tamiya TS-47

Step 39:

Put the decals in place, it really comes alive

Step 40:

Main gear and Tail

Step 41:

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.

Step 42:

I have done some weathering on the plane with dark grey pastels. you can also see it on the fuselage and tail, very subtle.

Step 43:

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

Step 44:

Mold of the engine cowl. I added a couple more layers at the bottom. The grey stuff is putty.

Step 45:

Few plastic cowls made with the vacuum forming machine

Step 46:

Picked the best one and made the engine and vent holes.

Step 47:

Put the engine in place. I Added a 1mm piece of plywood as a firewall, basswood wasn't strong enough

Step 48:

Some more masking to paint the nose.

Step 49:

Cowl finished!

Step 50:

260 grams

Step 51:

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.

Step 52:

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!

Comments

[Crossle32F]

Hello, terrific work, thanks for all the effort here sharing it.
What is the prop?
How many degrees is the prop tilted nose-down vs. the wing bottom surface? It looks like you put some nose-down angle on the motor (seems there is a spacer under the top motor to firewall screw).
My sons and I did an almost identical conversion (materials bought from Burnaby Hobbies & Magic Box), modeled after the same RCAF 671 aircraft at Shuttleworth in the UK. We made the same decal set, covered it in yellow Monokote. Uncanny to independently do almost identical projects.
However, we did a lot more reinforcement, mainly by skinning the wing torque box and sections of the fuse with 1/32 balsa sheet. I overestimated the strength increase required for full RC conversion, and we ended up overweight for the Park 250 we had originally selected. We changed up to a Park 370, but of course then the power system weight snowballs and it is now essentially un-flyable due to wicked torque roll and high wing loading. So, we are re-engineering it now to reduce weight and go back to the Park 250.
Cheers!

[DavidB685]

Hey Crossle32F,

Thanks for liking the work i put on this, honestly I was harder to write all this than making the plane..

the prop I used was an APC 8 x 6 slow flyer.
In the end I removed the spacer after i flew it few times, just felt it didn't need any down anlge at all.

The 3 little washers on the left side mount of the engine are still there, giving the engine some right angle since the prop was quite big.

About weights, yeah I feel your pain. I had actually built 2 more planes before this one, a biplane Dh4, you can see it at Magicbox hanging on the ceiling :) and a Spitfire.

The biplane, didn't fly really well. i should have put ailerons, the rudder was just not enough for a wingspan that big.

The spitfire is still flying (no instructables sorry) but it was a tad heavy.

I realized the lighter the better is going to fly. Since i was putting a park250 (manual said 170-340g models) i was looking at the weight really carefully while building the chipmunk

Thanks again.

[Crossle32F]

Hello, thanks for the response, we got our DHC-1 flying last night. Your info was really helpful. My son made weight reduction and wing redesign of this model his end-of-year school project for Grade 9 STEM and it turned out to be a really interesting exercise. We decided to try making a foam wing, he found that the typical blue Dow XPS insulating foam board was much stronger but only slightly more dense then the cheaper white EPS beadboard. We chose a Clark YH airfoil, downloaded the data free from the U of Illinois airfoil site, drew it up in SolidWorks to find the volume, and made root and tip templates out of aluminum sheet. We increased the span to 15" each side outboard of the fuse, which still looks reasonably scale but gives a bit lower wing loading. Hot wire cutting the tapering section and planform was a challenge but after many attempts we got two good wing panels and a centre section. Following your example, we went with 6 degree dihedral using a 1/16 plywood spar tapering out to about half-span (just outboard of where the landing gear mounts). Also your ailerons were bigger, probably a good idea; ours were originally scale and did not give enough roll control. So we decided to extend the ailerons almost to the root instead, so we could run a single servo in the centre section operating short torque wires to each aileron. This worked OK.
The whole wing assembly (without covering) was 46 grams, vs. 84 for the original. Other weight reduction in the fuse, and going back to the Park 250 motor (with a 6 x 4 APC Speed E prop and a 2S 800 mAh battery) brought the all-up weight down to 270g (0.6 lbs) including landing gear and some nose weight (down from about 400 g without landing gear, which was unflyable!). Static it drew 43 Watts, so watts per pound about 72 W/lb which is marginal. Wing area is 135 square inches, for a wing loading of about 10 oz/sq. ft. eCalc showed no warnings with this setup. Slow-fly prop might have been better? We put the landing gear on to be able to have a takeoff roll and build up some airspeed and control authority before taking off, since we had so much trouble handlaunching out original build.
So, it lifted off well, flew, and landed, but according to my son was very twitchy and hard to fly! Our CG was right on the spar line (centre of lift) about 50 mm behind the leading edge and it should have been 40 mm, as you found, however we were reluctant to add more nose weight and were running out of time for the school project deadline. Given another day, we would have cut holes in the tail to reduce weight and get the nose weight out and the CG forward. This should solve the wild flight characteristics. Main lesson learned is to keep the empennage weight down; we built the tail first, skinning both sides of the vstab and hstab with balsa sheet and adding a lot of gusseting and glue filleting for strength, and this was the main mistake. Should have built the tail light, and reinforced later after getting far enough along to pre-assemble and find out how the balance and overall weight were shaping up.
Anyway, thanks again for posting you project and responding! Hopefully our notes here might help others doing this sort of conversion. Next for us is a 30" BF109 from an old, abandoned kit we inherited.
Cheers!

[АхмедА]

thanks

[JohnM1517]

Hi, Wondering what size prop you used. Thanks John McCorkle

[DavidB685]

The prop I used was an APC 8 x 6 slow flyer

[TomR177]

Please describe the canopy painting, mostly regarding the see thru panels look like to be also painted.

[DavidB685]

Hi, sorry for the late reply i dont think i got notified!

Anyways as Crossle32F says, it was masked and painted from outside. the canopy comes with a protected blue film, I used and xacto knife and removed the windows frame. once was dried i protected the paint with a coat of varnish.

[Crossle32F]

Looks like he masked and sprayed from the outside. I did a similar project, but painted the canopy brush/toothpick from the inside. The canopy is a clear vacuum-formed piece with the window areas indented (ie. the structure parts protrude outwards), so you can carefully lay in the paint and let it flow out to the edges of the window areas. Slight thinning of the paint and prodding it along the edges with a toothpick helps. This way the paint is protected and you get the smooth glossy finish of the plastic on the outside.

[huuduc52]

Congratualtions.

Your product is very careful and beautiful. I am very like. But may I have a question. What kind of motor you use in this project? Thank you very much.

[DavidB685]

thank you!

the engine is a E-flite park 250

[michaelb2]

Congratualtions

[DavidB685]

Thanks!!!

[N36]

Amazing! And great documentation + visuals of the process. Well done.

I would also love to see a video of this flying. As a young kid I tried to do the exact same thing with a P-51 wooden kit like this. I fitted in what ever electronics equipment I could into it and it was horribly off-balance and didn't fly at all. So would love to see a success of it!

[DavidB685]

uploaded video flying!

[N36]

*BIG smile on my face! CONGRATS! Looks ace... :) so nice to see one of those kits flying in a controlled way! Great work...

[DavidB685]

Hi N36,

Thanks for your kind words!

Indeed getting the CG right it is not an easy task. I tried to put all the weight as forward as I could because I always end up building tail heavy planes. this time though plane seems to be nose heavy so will see how it flies.

like they say, a nose heavy airplane will fly poorly, a tail heavy plane won't fly at all.

Thanks again.

[TURBOTECHNOLOGY]

Very Nice work
Do you have video of flying it???
I want to see great RC Plane Flying!

[DavidB685]

uploaded video flying!

[DavidB685]

Thanks TURBOTECHNOLOGY,

Haven't flown the plane yet, the local filed i usually go is having some construction work, I will have to wait a bit, I would think 2/3 weeks.