Dh4 Dumas RC Plane

This instructable is to show you how i have built the Dumas Dh4 balsa RC plane and the challenges that i faced and how i figured out a solution for them. I have uploaded a lot of photos showing the build process, although i am not going to explain every little thing that i did to accomplish what you can see in the photo, you should be able to do it yourself by looking at it (thanks to the amount of photos posted) or at least get the idea.

For this i didn't followed the paint schema on the kit box, i wanted to build an after war DH4 (used to transport mail across the US.)

To build balsa planes, you are going to need several tools, but the most important thing is a good flat surface. Mine was a piece of glass with a sheet of homasote glued on top with caulking, so i can replace it easily in case it deteriorates, easier than if it was plain glue.

you are going to need more tools, i always think the more the better, you always going to have a better result when you have the right tool for the right job, at least that is what i think.

This is a list of what i have used to build this plane, some stuff that i have been collecting along the years, you probably don't need all of them but anyways there it goes:

glues:

• white glue
• epoxy 5 min and 20 min
• superglue
• Super Phatic glue (deluxe materials)
• butter stick glue (purple elmers glue)

other products:

• easy-dope (acrylic non toxic!)
• silkspan tissue (which is not the kind of tissue that comes with the kit)

tools:

• razorblades
• x-acto knives/blades
• sanding paper, different grates
• little saws
• files, round/flat different shapes
• drill bits
• dremel with sanding/drilling accessories
• brass/aluminium tube cuter
• heat gun/
• rules
• [90 degree rule?]
• pins, lots of them
• pliers, cutting pliers (small)
• rubber bands
• clamps (small)
• soldering iron

Rc:

• 2 micro servos hitek HS-55, 9gr
• brush-less engine eflite - park 250
• spectrum receiver 4 channel AR-400 (depends on you radio etc)
• ESC 10 amp
• lipo battery, 2 cell
• APC propeller slowflyer 8x6

Rc parts

• hinges
• linkages for the servos

misc:

• brushes
• airbrush
• paints/solvents etc (mostly Vallejo the some enamels and Mig pigments and pastels)
• masking tape.
• clear/glossy/matt varnish cans/bottles..
• wood varnishes/sealers.
• balsa, playwood wood.
• brass/aluminum tube
• silicon tube (the one used on gas Rc cars/planes)
• foamboard , got it on a dollar store
• nuts and bolts.

The kit comes with wood and tissue and some other parts, but i found the wood was pretty bad quality and some of it was bent. The tissue that it came with it wasn't enough to cover the whole plane if you were going to follow the kit paint schema, (blue and yellow) so i used silkspan tissue (white) and got some new wood from my local hobby store.

first i made the foamboard patters, the kit comes with the templates on the instructions

In order to bend the balsa wood I put the 2 pieces in warm water for 5 minutes till it was really soft, then glued the 2 pieces together (white glue) at the same time i was bending the wood around the templates, i put pins around the outlines to keep it in place, also i put wax paper underneath so the wood wouldn't stick to the bench.

let them dry all night, you could use a heat-gun or hair-dryer to speed up the process if you are in a hurry.

There is nothing special here, the kit instructions explain the process really well, I used basswood instead of balsa for the top spars of the wing, those are the ones on the front part of the wing that go across the wing.

one important note is, you have to raise the wingtips 1/16 inch to create *washout, you can see the detail on the first picture, i have added a note for clarification.

once the the top and bottom wings were finished i glued them together putting a block of wood 1 inch high to keep the right dihedral, the plan has the markings where to put the block so you get it right.

I used white glue to build the wings, leaving it to dry overnight.

washout: Washout refers to a feature of wing design to deliberately reduce the lift distribution across the span of the wing of an aircraft. The wings are designed so that the angle of incidence is greater at the wing roots and decreases across the span, becoming lowest at the wingtip. washout

Here you can see the built stabilizer and rudder, the only difference from the kit/plan is that i used thicker wood where the hinges are supposed to go so it makes a stronger fit for them, the kit comes with CA hinges, but i prefer using regular small hinges you can get at your local hobby shop.

after all was glued and dried i took the hinges out and applied the silkspan tissue, i will explain how to apply the tissue in next steps.

Building the fuselage, at least at the beginning, looked like an easy job, although as you will see in the next steps. I had to do many modifications to fit the RC electronics in a place so it would be easy to access them once the wings were in place.

I am not really sold on this part, i didn't like the way the kit wanted me to build the battery hatch, which was using a plastic cover, so i built the sides of the hatch with the same shape as the formers. After that i softened a thin piece of balsa wood in warm water and glued all together holding it with elastic bands.

it looks allright, but i could have built this in a better way, on the next hatch I made (next step) is what i should have done, but i am learning too.

you can also see i added a piece of basswood in the front pat of the fuselage, that will be the engine firewall. The engine i am using on this plane is not the same the plane was designed to use so the provided firewall/parts on the kit are pretty much useless.

This second hatch, is in between the two seats. in the war model the front seat was the pilot seat, the other one closer to the tail was the gunner.

The Mail version was flown from the back seat, which is where the plans put the servos. In order to keep the weight closer to the CG I moved the servos one former forward and made a hatch. I couldn't move the servos further forward because the pilot seat is under the wings, so i wouldn't be able to access it easily in case of maintenance once the plane is finished.

I added some more wood around the firewall so the engine cowl (plastic) would fit snug and also make some space for the engine to fit in between.

As you can see the cowl has a big hole in it, that is so the engine can stick out a little bit. i am not totally happy with this but the brushless engine that i am using doesn't have a long shaft coming out of the engine. The instructions that come with the engine say you can reverse the shaft, when I looked on the internet i saw a lot of people bending it, making the engine useless.

you can see what the finished result looks like in the photos.

Like i said, i tried to move all i could closer to the CG, so i had to figure out a way to put everything together in a way that once installed i could access everything without having to rip the pane tissue/balsa apart.

so i built this little box, that would slide up and down so i would be able to remove the receiver in case i need to fiddle with the servo connectors and also giving me some space to work on the servos if they need replacement. Servos are going right beside the box, screwed on the 2 pieces of balsa wood that cross from one side of the fuselage to the other.

Note: the antenna will go back under the servos and attach to a piece of wood you can see in the pictures, i also made a hatch underneath the plane just in case i need to access that area , this is not totally needed. i added some recent photos of this, unfortunately i didn't have any from while i was building it.

I am not really good at soldering, but i manage to make a decent landing gear, nothing much to explain here. My tip is try to keep the sizes of the pieces of metal right while looking at the plans. all metal parts are provided with the kit, one tool that might help you to bend these easy is the dubro ez bender you can see it on the picture, a great tool!

for the landing gear and struts wood i used minwax oil based stain, choose the colour you like or mix them up, i usually rub the mix directly to the wood with my fingers and let it dry, then few coats of varathane with sanding in between them.

In order to put the tissue on, what i do is use a glue stick, (elmers purple) on all the surface of the wing where the tissue is going to go, once applied I lay the tissue, trying to avoid wrinkles, i let the glue dry, then once dry with a pulverizer i spray some alcohol diluted with water so the tissue tightens up a little bit.

after that if i think some edge of the tissue needs reinforcement, i will add white glue diluted with water and a apply it with a little brush.

after it's dry, i start applying eze-dope with a flat brush straight from the bottle, i apply several coats, leaving time to dry in between. apply coats until the tissue has no pores and you see that applying eze-dope doesn't make the tissue wrinkle anymore, that is the sign that all is sealed and ready to be painted.

Using thin strips of balsa i glued the tube along the fuselage

Note: even though this step is about setting the servos, if you look close at the last photo you can see i removed part of the firewall (default firewall that come with the kit) so i can fit the ESC and a bigger battery. this plane is going to be tail heavy so it's better to add a bigger battery than lead or pennies to add extra weight to the front.

The pilot fairing is made with a piece of paper following the shape that comes with the kit. i glued it with the glue stick and once dry i covered it with silkspan and added eze-dope to it for strength. I wasn't sure if the result was going to look ok, but once painted it looks pretty amazing.

the fuselage is covered using the same technique as the wings.

in the last 2 photos i am gluing the lower wing to the fuselage, using some weight.

I painted these parts using airbrush and with vallejo air brush paints, silver color.

• vallejo model air silver 71063

after al the parts where painted i added a coat of flat varnish

this was a heck of a job, the first wheel you see in the pictures is the first try making one of these, that made me realize some mistakes i needed to correct on my next attempt.

first of all, one you have the rims that are made of of 2 pieces of balsa glued to each other with the grain crossed 90 degrees, you need to seal it with a wood sealant, so once you apply the thread it won't cut into the wood as easily.

here is the webpage i found that explains the process in detail spoked wheels kudos to the owner/writer.

my version is pretty much the same but i cut open the silicon tube and glued around the rim instead of putting it on top.

Note: in order to know where to put the spokes , i used one of the rings to draw the rim on a poster board so i could draw all the lines where the threads were supposed to go, then i transfered those lines onto the wood rim with a pencil.

To paint the fuselage i used painter green mask and used Model Air 71.036 Mahogany colour from Vallejo.

flat varnish after the painting will seal the paint and protect it.

for the letters i used a set of reese interlocking stencils, putting them over the fuselage holding them with painters tape, you can find something similar in an art store.

I made the exhaust pipes out of a piece of wood, carving carefully and using a file until i got the result i wanted, i drew a little template that i pinned to the piece of wood so i could use it as a guide.

for the pipe that follows the exhaust, i used a straw, i melted the end of it so i could give it some shape, the little braces are little thin strips made out of the case of a little candle, for the little pipe joints i use electrical shrink tubing.

i painted the whole thing in black, then drybrushed with copper, aluminum and stainless

for the cowl, i used the same colour i used for the fuselage and added a few black washes then a matt coat of varnish. to give it a wet/grease effect (like little drops) i used a little bit of shiny varnish in some areas.

I added silicon tube to the pilot seat, just so it looked like the leather on the real plane, painted with humbrol brown.

I also 3d printed a radiator lid, which i painted black and dry brushed with aluminum.

colours used:

• Mr Metal color 215 copper
• Mr Metal color 218 aluminium
• Mr Metal color 213 stainless
• humbrol black 33
• humbrol brown 62

Using the template from the instructions, i made a foamboard gig to align the wings. Gluing the wings to the struts wasn't an easy job. I used rubber bands to help me keeping the wings in place, i used epoxy 20 minutes, so i had time to fiddle with the wings to try and get them to the right angles.

lots of eyeballing i am afraid...

Wigging the wings was easier than i thought, i just followed the instructions carefully and added superglue to the struts to fix the thread once tight and in place.

in order to make it look more real in some of the rigging parts, i cut little pieces of aluminium tube, passed the thread through it and then squeezed the tube with a pair of flat pliers.

in order to drive the thread easily i used a sawing needle.

you might have noticed that the fuselage has some kind of weathering effect, in order to accomplish that i sanded the paint off until i was able to see the the white colour (eze-dope coat used to seal the tissue). you have to be careful to not sand too much and rip the tissue. a coat of flat varnish after that would seal the plane nicely.

The plane doesn't need a pilot, but it looks really cool at least for display. I will probably remove it before i fly the plane, just so it doesn't add more weight to the tail.

I 3d printed this pilot from thingyverse: http://www.thingiverse.com/thing:557037

colours i used to paint the pilot:

• Vallejo Game color khaki 72.061
• Vallejo Game color dwarf skin 72.041
• Vallejo Game color elf skin 72.004
• Vallejo Game color leather brown 72040
• Vallejo Game color pale skin 72.003
• Vallejo model color white 70951
• Vallejo model color buff 70976
• Vallejo Model color black 70950
• vallejo Panzer aces New wood 311
• Vallejo model air light grey 050
• silver pen
• 08 black pen

And this is the finished plane.

like i said this is not a 100% detailed guide, i tried to add all the detail that i could but of course i wasn't able to put all the wood, bolts, screws sizes and measurements , because it would take me another year to write this instructable. The good thing is you don't need to use the same specific size i used for any particular piece, in the end you can use what ever you have handy and have the same result. The purpose of this instructable is to give you an idea of how you can solve the problem that you can face building this airplane.

that is one of the reasons i have taken so many photos of the build process, so you can check how i made it if you need to.

building the plane has been a blast, it has taken me approximately a year, working on it on and off, hopefully the plane flies the same as it looks!

thanks for reading!

Cheers.