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DC-3 small build

#1
I'm just back from a vacation to Cape Cod, where I saw a couple of dc-3s parked at a tiny municipal field. Andy gave me a tour, let me go inside, poke around, and flip the master switch (very satisfying). I've always thought these planes would be a cool RC project, but since the tour, my mind has been churning out ideas for how to build an RC dc-3.

The dc-3 is a VERY curvy airplane, nothing is boxy. But foam board tends to be boxy. So I'm gonna cut the Gordian knot and 3d print the nose and nacelles. I'll flatten the bottom of the fuse, and use paper for the curved top.

I plan to build a small one. I bought a power pak A twin at this years flite fest, and I want to use that. The big problem is that, if the motors swing 6" props, then the scale dictates a 52" wingspan, and I wanted to attempt something with a 32" span. So I've got some 4-blade 4x5 propellers on order. That size will get my design down to a 32" wingspan.

Feedback and advice appreciated!
 

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jfaleo1

Junior Member
#2
I'm just back from a vacation to Cape Cod, where I saw a couple of dc-3s parked at a tiny municipal field. Andy gave me a tour, let me go inside, poke around, and flip the master switch (very satisfying). I've always thought these planes would be a cool RC project, but since the tour, my mind has been churning out ideas for how to build an RC dc-3.

The dc-3 is a VERY curvy airplane, nothing is boxy. But foam board tends to be boxy. So I'm gonna cut the Gordian knot and 3d print the nose and nacelles. I'll flatten the bottom of the fuse, and use paper for the curved top.

I plan to build a small one. I bought a power pak A twin at this years flite fest, and I want to use that. The big problem is that, if the motors swing 6" props, then the scale dictates a 52" wingspan, and I wanted to attempt something with a 32" span. So I've got some 4-blade 4x5 propellers on order. That size will get my design down to a 32" wingspan.

Feedback and advice appreciated!
All sounds good so far. Keep it light and it’s going to work out fine. 👍🏻
 
#3
My prototypes of the nacelle are coming along, but I'm not finished; the motor mount needs to be supported as it prints, and that's made me re-design and print 5 times already. I'll get it, though.

I'm very happy with the center wing I made. Easy, flight test technique.

I slapped a body together; it's too wide, but I'm happy with the build technique. I plan to use paper for the curved top. I really want a big hatch on top, so I can easily reach the electronics. I might take inspiration from the hatches of the mini mustang, or the mini corsair. Still thinking about it.

Then I made an outer wing. I got all the dimensions wrong. Even the spar doesn't match up with the center part. :) Also, making such a small wing with such a pointed tip is hard! I'm gonna make the tip chord significantly bigger, just for ease of building.
 

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#4
Got a new wing and fuse done. The wing isn't nearly as tapered as the actual dc-3, and that could be a problem for the scale. I'm not trying to be super accurate (at least on this prototype), but I do want it to look like a dc-3. :)

I will cut a wing saddle into the bottom of the fuse; I'm just not sure where, til I get the nose and tail on.

I've got 3-blade 4" props for these 1806 FT radials. I hope that's the right choice.

Even though I haven't completely assembled them onto the wing, I'm pretty happy with these engine nacelles. They even have landing gear mount slots in the bottom.
 

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Piotrsko

Well-known member
#5
You do realize there is a class called STANDOFF scale where people stand 50 ft away from the plane and say " YUP, that's a goonie bird". Look at the aardvark FT makes, kinda lumpy before 50 ft.

I do honor the intensity of your effort.
 

Corbarrad

Active member
#6
I'm working on a DC-3 on my own, at around 40" span, using the twin a pack as well. depending onhow yours turns out I might switch to a DC-4 or an Avro Tudor. Interested to see where this is going.
 
#7
Got the tail on, and all the servos installed. I got the nose printed, and it's good, but I'm gonna adjust it.

Then I tried to complete a nacelle and attach it to the wing, but gluing its front and back halves together was problematic. Yes, hot glue works on PLA, but not exceptionally well, and the amount of stuff crammed into the nacelle kept forcing the front part to separate.

I'm thinking about making the nacelle halves screw together, and perhaps making them a bit larger somehow. I'm also concerned about making the nacelles attach securely enough to the wing. Perhaps I need a BBQ skewer (vertically) behind the spar?
 

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#9
I got the fuse pretty complete. The hatch is built. I'll wait to attach it until the wing and fuse are mated. I'm worried I wont have enough room for the battery, wherever it's gonna wind up.

My adjusted nacelle went on the wing very well; I'm sitting next to my other nacelle as it's being printed. I'm most happy about the landing gear mount. Trivial to bend and trivial to remove when I want to. Dubro 1 3/4" wheels.

This is turning out heavy. I still think it'll fly. But foam board, plywood, and hot glue are still lighter than PLA plastic.

I'm also a bit concerned that my wing's trailing edge is too long, and therefore dips below the line of the wing underside. I'm just not sure what that'll do to the flying characteristics.
 

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Seahunter

Active member
#10
Like where you are going with this. Reminds me a lot of my struggles with my current build, a Cessna T-59 Bobcat. Unfortunately I'm very slow typing and composing a thread and twice the system or moderator has deleted my saved draft. Watching your thread with great interest. Great job! Fred :)
 
#11
Done!

Scaling the nacelles up just 3% give me enough room for the ESC and wires to all fit nicely.

The big top hatch doesn't fit as well as I'd like, but it works.

I've filled all 6 slots on my receiver with rudder, elevator, 2 throttles, and 2 ailerons. So I should be able to do differential thrust. So I fiddled, but didn't get it to work right. I'll tackle it tomorrow.

I dialed down all my throws to about 40%, and 40% expo. I really don't want to jerk this thing around like a fighter, especially the first flight. All my control surfaces are much bigger than the full size plane, so I feel I should be careful.

I'm really happy with how well I cut the wing saddle, and how well it socketed together. I had a separate wing section I'd test-built, and it was exactly the same dimensions, so it was an excellent template. I considered adding doublers to the fuse sides, to give more strength to the wing-fuse join. But after the initial gluing of wing to fuse, it seemed really sturdy to me. Still, it's not too late to add those doublers. What do you think? should I worry about the wing coming off in flight?

I'm powering it with a 1300 3s, and the plane seems to balance with the battery right over the main spar. That's exactly what I wanted, a battery that actually wanted to be under the hatch, where I could get to it. :)

I was worried about the thrust from the 4" 3-blade props, but when I ran it up to full (in the comfort of my basement workshop), it seemed to have plenty of power.
 

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jpot1

Well-known member
#12
Beautiful work, really making me want a 3D printer! I built this 737 all from foam and was limited to how I could crease/bend. Looks fine from 10ft but your smooth nose/nacelles look sweet!

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#13
I'm trying to get diff thrust working on my new plane.
transmitter: Spektrum dx-6e
reciever: AR620 6-Channel RC Sport Receiver
ESCs and motors from flite test A twin pack (radials)

After much fussing and consulting the internet, I found what's working for me.
1) extra ESC connects to the GEAR slot on the receiver (slot 5)
2) make a mix that mixes the THR >> GER, so they synchronize
3) make another mix, RUD >> THR, to adjust a motor speed on one side
4) make a third mix, RUD >> GER, to adjust for the other side

Now I just have to fix a problem that just came up. My right motor is suddenly "weaker" than the left motor. It takes more throttle throw to spin up. I'm gonna look into "resetting" the ESC. Just have to figure out how to do that.
 
#14
Okay, I fixed the "weaker" motor problem. During my fiddling to set up the diff thrust, I accidentally went through the process of re-calibrating the ESC(s) with the throttle. Don't know what that is? I didn't either, till now.

Basically, if you 1) turn on TX, 2) set throttle stick to max, 3) plug in plane battery,
then the ESC(s) go into a calibration mode, and you hear lots of amazing beeps from the motor(s).
then you lower the throttle stick to zero, and you get more beeps, and the ESC(s) are now re-calibrated.

This webpage helped me understand:
http://ardupilot.org/copter/docs/esc-calibration.html
 

Wildthing

Well-known member
#15
Okay, I fixed the "weaker" motor problem. During my fiddling to set up the diff thrust, I accidentally went through the process of re-calibrating the ESC(s) with the throttle. Don't know what that is? I didn't either, till now.

Basically, if you 1) turn on TX, 2) set throttle stick to max, 3) plug in plane battery,
then the ESC(s) go into a calibration mode, and you hear lots of amazing beeps from the motor(s).
then you lower the throttle stick to zero, and you get more beeps, and the ESC(s) are now re-calibrated.

This webpage helped me understand:
http://ardupilot.org/copter/docs/esc-calibration.html
All those different sequence of beeps are for different modes of programing for your esc so careful when and how you move the stick back and after any sequence of beeps. I attached the Hobbyking esc instruction sheet, go to page 6 and you will see what I mean.
 

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#17
It flew.

I went to edgewater as I said, but nobody was there. I think Monday evening may have been a bad idea. I know Friday afternoon is a better time/day, cause I've been there at that time.

However, it was dry, and my plane was ready, and I'd driven all that way, so I took the plane to the runway. I did some taxi tests, and found it was nearly uncontrollable; it would constantly jackknife, spinning around instead of tracking straight.

Finally I got impatient, jumped on the throttle, and it did a quick groundloop. :( The only damage was both props broke, and I'd brought spares, so I trudged back to the car and replaced them. Then I went back to the flightline, and got it into the air.

It's got two big problems; it's heavy, and tail-heavy. I got it into the air, but it really wanted to climb/loop, and even when I trimmed elevator max down, it still wanted to raise the nose with full power. But it had plenty of power, and is fast. In fact, I've never flown a plane that wanted to land at such high speed.

I gotta say, the flite-test-style under-cambered wingtips really did the job; there was never a tip stall.

I swapped the battery, moved it forward, adjusted my subtrim and rates, and got it back into the air a second time. And it flew well. It could roll and do immelmans VERY well. Everything held together. It was still tail-heavy, so the elevator felt weirdly mushy, and it had a tendency to raise the nose til it stalled, if I didn't correct it. And after 6 minutes of flight, I landed it again, using the entire runway, sheesh.

Sorry, no video, 'cause I had noone with me to shoot video.