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GIANT Cargo Plane from dollartree foam board

#21
I'm sorry to hear about the ESC fire.:( I have one question though, how high did you jump when the ESC went the way of the firecracker?
I was pretty jumpy because they are big motors and I've never run anything on 6s. Luckily I was sitting down...

It took me a second to realize that the thing was still burning after I cut the throttle. So that's why you see me pause before I take off the camera and unplug the batteries.
 

Christopher14

Driftin' with the wind...
#22
I was pretty jumpy because they are big motors and I've never run anything on 6s. Luckily I was sitting down...

It took me a second to realize that the thing was still burning after I cut the throttle. So that's why you see me pause before I take off the camera and unplug the batteries.
Yeah, those motors are huge! I'd be nervous to.
 

Christopher14

Driftin' with the wind...
#25
I wish. Each one costs more than the motor! I'm also limited to about 60A because my 3000mAh batteries are only 20C.
You can have a motor that only pulls 50A at full throttle and have a ESC that's rated for 100A and run it no problem. The motor is the part of the system that actually pulls the power, the ESC is only there to give the motor that power. The ESC can't push power into the motor.

Hope this helps!
 
#29
You can have a motor that only pulls 50A at full throttle and have a ESC that's rated for 100A and run it no problem. The motor is the part of the system that actually pulls the power, the ESC is only there to give the motor that power. The ESC can't push power into the motor.

Hope this helps!
Yeah. I was just saying I have no reason to go 40A over the max, because it's just extra price.

Though, this did make me wonder if it would be possible to run two motors in parallel off the same ESC. It doesn't apply for the cargo plane because I need differential throttle, but it would be an interesting experiment.
 
#30
Finally had some time to start working on the beast. We have begun by working on the plane's 10ft long, 18in chord, 3 piece wing.
My friend (Luke) and I began by cutting four pieces of DTFB down to 18"x30". The four of these end to end make up the wing.

We then began to cut out formers for the wing:
IMG_0231 (Formers).JPG

Next was grabbed some of the wood we will be using for spars and cut it to length. Here's some of the sparing laid out on the wing.
IMG_0232.JPG

For scale, Luke is 6'2"
IMG_0234 (Luke next to wing).JPG

With some of the spars glued in, I dry fitted the formers on the center section
IMG_0239.JPG .
 

FAI-F1D

Free Flight Indoorist
#31
This is a really neat build. I never cease to be amazed at what can be done with foam board (I'm a balsa guy myself, so it's a whole other world for me).

I'm curious to know what you intend to do with the differential throttle?
 
#32
So the wing is coming along pretty well and seems to be very stiff the long way. I do not anticipate being able to fold the wings. However, I am noticing that the wing can twist fairly easily around it's long axis. This is not an issue I have encountered on smaller builds.

I think that diagonal struts will help, and also that it should stiffen up when I apply the upper surface of the wing.

Still, before I glue everything shut, does anyone have any suggestions to improve torsional stiffness?
 
#33
So the wing is coming along pretty well and seems to be very stiff the long way. I do not anticipate being able to fold the wings. However, I am noticing that the wing can twist fairly easily around it's long axis. This is not an issue I have encountered on smaller builds.

I think that diagonal struts will help, and also that it should stiffen up when I apply the upper surface of the wing.

Still, before I glue everything shut, does anyone have any suggestions to improve torsional stiffness?
When the top of the wing is glued the strength will really increase. I do usually use two spars in tandem.
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#34
RT,

I'd echo Aiidan -- The micorwave plane had a similar span and chord and once it was glued shut the wing pannels were solid.

That whole thing was built off a single L-channel AL spar (~2x2" IIRC) on the bottom wing with a few 1/2" square dowels for hardpoints and struts but that was more for distributing the load for the microwave and connecting the wings. Everything else was held stiff between the foam ribs and skin glued together. What you've got is more than enough.

in retrospect, if we'd had a better top-spar and joined the struts more carefully to it top and bottom, the flight back in OH would have been more . . . enjoyable, but as a monoplane, that won't be a problem for you at all. Wing struts aren't a bad idea either, but more becasue it will transfer loading out farther on the wing more to the bottom of the airframe than the wing root. Naturally, make sure you tie hardpoint to hardpoint on both ends.
 
#35
I put some more time in on the plane today.
I finished the internal structure on the outer sections of the three piece wing. Here's what they look like now:
IMG_0259.JPG

I finished the sparring throughout the wing, and put it all together to feel the strength. It was very strong, but still susceptible to twisting. As Craftydan and aiidanwings suggested, this will hopefully not be an issue when the upper surface is attached. However, even without me applying any force, I've noticed the wing has developed some twist when laying flat on the table such that opposite corners are off the surface. Hopefully there is away to flatten it out when I glue the wing shut.
IMG_0258 (Izzy w: Wing).JPG

I also started experimenting with how I will be gluing down the the upper surface. I'm trying to decide whether or not to remove the paper on the inside of the upper foam. Without the paper, the fold will be much easier and cleaner, but strength will be reduced. How much and if it will matter I do not know.
Here is a pic of folding a test strip with the paper removed over the formers.
IMG_0260 (Test wing strip).JPG

So my two main questions are:
- Should I remove the paper from the inside of the upper surface?
- And also, how do I make sure that when I glue everything shut the wing is not already twisted?
 
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#36
I prefer only removing the paper in the places where the radius is the tightest. Usually the front 2/3 of the wing.

I layed this flat on the kitchen floor and carefully stacked books on it to help keep it straight while the glue dried. 128 inches and it was cold so I couldn't get it all in frame.


Your plane is looking awesome.
 
#37
I prefer only removing the paper in the places where the radius is the tightest. Usually the front 2/3 of the wing.

I layed this flat on the kitchen floor and carefully stacked books on it to help keep it straight while the glue dried. 128 inches and it was cold so I couldn't get it all in frame.


Your plane is looking awesome.
Thanks for the advice! and Wow, that wing is awesome! What's your power setup? You must get ∞ flight time on a flying wing with an aspect ratio like that!
 
#38
The power system is a Grayson Hobby 40 size gas to electric conversion. I don't know the flight times, but the stall speed is just over 3 mph, and cruise is 7 so it could be a lot.
 
#39
Some more updates on the wing.

Here are some holes I cut to allow easy wiring
IMG_0279.JPG

I decided to peel the paper off the inside of the upper surface of the wing before folding it shut. This seemed to work pretty well.
IMG_0280.JPG

I used hot glue to glue the wing shut, which was probably a bad idea. This works fine for smaller wings, but on this plane, by the time I was folding the upper surface down, a lot of my hot glue had already dried at least partially, so my connections aren't as strong. It seems to hold ok but I'm less than satisfied.

IMG_0282.JPG IMG_0283.JPG IMG_0284.JPG

Fortunately, [Craftydan] and [aiidanwings] were right about the twisting. The two sections of the wing that are now shut don't twist at all! They are verrrrryyy solid. I had a bit of trouble holding them mostly flat during the glueing process, but I think they cam out OK.

The next step is to finish up the center section of the 3 piece wing which will require installing the motor mounts and connecting them to the main spar. There is a massive blizzard on the East coast, so hopefully I'll have some time to do that over the next few days!
 
#40
Yeah, hot glue is a no go for larger parts. I've been using a foam safe aerosol glue for this situation with fair success. The time to dry is a lot longer than I'm used too, but its worth it.