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GIANT Cargo Plane from dollartree foam board

Preface: Over the next few months, I will be building a 10 foot wingspan cargo plane with a close friend. This plane will be made almost entirely out of dollartree foam board. I hope to use this thread to document the build and get input and ideas.

Background: This plane will be based on a smaller cargo plane my friend and I built last year. That plane had a 5 foot wingspan, and this new plane will be a 200% scaled version of it. The old plane was built out of DTFB, and powered by two 1100kv NTM prop drive motors swinging 11x4.7 slowfly props.
The five foot plane performs extremely well. It tracks very straight, handles the wind easily, and has respectable vertical performance when not loaded with cargo. We have tested it with up to 3 lbs in the cargo bay, but I am confident that it could hold much more than that.
Here is a video demonstrating dropping a parachute from the bay.

The 10 foot plane: I have started planning the new plane already. I am using sketchup to get a rough idea of how much foam and materials I will be using, as well as how to reinforce the aiframe. Here is an early screenshot.
Screen Shot 2014-11-18 at 10.37.51 PM.png
I currently expect to use about 20 sheets of DTFB for the build, along with a piece of insulation foam for structural support inside the fuselage.
The power system will likely be 6s (two 3s batteries in parallel), and right now I'm looking at the 5000-6000mAh range for the batteries (20C). This limits my total current to around 100A if I go with this power setup.
The plane will be driven by a twin motor setup (with differential throttle). Currently, I have these motors in mind, though I am open to suggestion.
http://hobbyking.com/hobbyking/store/__19610__NTM_Prop_Drive_Series_42_58_500kv_1300w.h tml
Screen Shot 2014-11-18 at 11.01.49 PM.png

Challenges/Problems: I have never built a plane of this scale, so there are several main problems I anticipate.
  • 3 piece wing and sparring.
  • Sufficiently strong cargo bay door.
  • Keeping price low (under $300).
  • Reinforcing the fuselage.
  • Mounting the motors (my usual firewalls aren't gunna cut it).
  • Attaching the landing gear. On the previous plane, after about 30 landings, the fuselage was bent.

I will be adding images and videos as my build progresses, and look forward to advice and recommendations from you guys!
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I've done some additional work on the CAD model and the structure inside the fuselage (which is hard to see so I didn't bother screenshotting it).
I've gotten to the point where I need to decide between a single V-stab in the middle, or dual v-stabs in the propwash. Does anybody know if one would work better than the other?
Screen Shot 2014-11-19 at 8.36.41 PM.png

Also, some estimations based on the model now put the total at one entire crate of DTFB, or 25 sheets.
Two motor choices

A friend just pointed me to another website which has fairly inexpensive motors, so I now have two options. Any idea which might be better? They both will end up costing about the same.

ValueHobby motor (1000W): http://www.valuehobby.com/power-systems/brushless-motors/outrunner-airplane/g46-5055-400kv-outrunner.html
KV: 400
Weight: 10.6oz (300g) for motor only, not including mounting accessories.
Motor Diameter: Approx. 50mm
Shaft diameter: 8mm
Max efficiency: Approx. 50A
Max Load: Approx. 60A

HobbyKing motor: (1300W): http://hobbyking.com/hobbyking/store/__19610__NTM_Prop_Drive_Series_42_58_500kv_1300w.html
Kv: 500kv
Turns: 6T
Poles: 7
Resistance: 0.144 Ω
No Load current: 1.6A @ 10v
Max current: 60A
Max Power: 1300W
Shaft: 5mm
Weight: 319g
ESC: 70A
Cell count: 5~7 Lipoly
That looks promising but I just bought motors.

These were a good bit bigger than I was expecting to buy, but at $29.99 I just couldn't find a better deal! Here are the specs:
Screen Shot 2014-12-05 at 12.21.39 PM.png

I also added the motors and 18 inch props which I will be using. I put a coke can next to the plane for scale. It really gives you an idea of how big the motors are!
Screen Shot 2014-12-05 at 12.20.03 PM.png


Driftin' with the wind...
That thing is going to have gobs of power! Can you drop the coke can?:D

EDIT: Oh wait, you could probably drop a six-pack.;)
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Looks like in the wind it needs help?

Looks like in the wind it needs help? Thanks for the video and nice build!

Maybe a Orange RX 3 axis gyro/receiver would help this out big time.
Mine was like $24 off E-bay.



To strengthen the fuselage for landing gear, a dowel glued lengthwise in each corner in the bottom, and double thickness foam board. Square dowels work best because you can add a piece of hobby plywood for the gear to bolt to.
To strengthen the fuselage for landing gear, a dowel glued lengthwise in each corner in the bottom, and double thickness foam board. Square dowels work best because you can add a piece of hobby plywood for the gear to bolt to.
That sounds like the way to do it. I decommissioned the 5ft plane a few months ago, but for the 10ft version I will certainly use double layered walls. I'm actually thinking 1inch insulation foam on the inside of the wall and DTFB on the outside for the areas of the fuselage that are under higher stress.

For the dowel, do you mean running along the edge?
The Turnigy 5335/10 motors I purchased for the plane were just discontinued, which I supposed explains the super low price tag. Now I'm just wondering why they were discontinued....
So my first batch of parts just came in from Hong Kong. I ordered from Hobbyking, and the total was just shy of $200 for the whole power train and some spare servos. Here it is:
Screen Shot 2014-12-22 at 6.30.34 PM.png Screen Shot 2014-12-22 at 6.30.48 PM.png

The props and motors are huge!!!!!
I tested the motor using a random 35A esc on 3s and everything worked well. Even at this reduce power level it was able to lift itself and the 2x4 I had it mounted on off the ground!

I wanted to test it on 6s so I began to prep the ESCs. They came with 14 gauge wire so I replaced it with 10AWG and added a BEC in parallel with one of the ESCs. Here is a photo after removing the heatshrink and heatsinks from both ESCs.

When I put everything back together and plugged it into the motor, it all booted up just fine, but when I gave it the first bit of throttle the ESC burst into flame!!!! :mad:
And left me with this:

The ESC booted up just fine (6 beeps for 6 cells). Its rated for 70A and 7s, so there should have been no problems. My theory is that either it's just a dud, or the ESC is not designed to work with such a low KV motor.
I checked with the first 35A ESC and the motor is fine. I will test my other 70A ESC on 3s first before 6s and see if I can get a refund from HK (unlikely).