Scale Build-Off – 140" C-47 Foamy

[Joker 53150]

You may also want to try a random orbital sander or vibrating hand sander. I've done that on another build and it works very well.

This should be a pretty interesting build to watch!

 

[wilmracer]

You may also want to try a random orbital sander or vibrating hand sander. I've done that on another build and it works very well.

This should be a pretty interesting build to watch!

Pick up one of these too. It is my most used rough-shaping tool.

http://www.amazon.com/gp/product/B00002X1ZH/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

 

[ScottyWarpNine]

Look at what showed up today

This one is going in my cub, but if I like it I'll get two more.

This is my first twin motor airplane. I know I'm getting ahead of myself, but how does BEC work with two ESCs? Does it add up, like if each ESC can provide 3A, can the two together supply 6A? On the cub I'm thinking about just using a Castle Creations 10A switching BEC because I don't really trust the cheap Chinese ESCs internal BEC. I'll probably do that with the DC3 as well, especially since I'll be using some big hungry servos.

 

[BanditJacksRC]

EPIC build man.. I'll be watching this one.

 

[Joker 53150]

If I were doing a plane that size I'd probably let the ESCs only handle the motors, and run a separate BEC to deal with the receiver and servos. My thinking is that and ESC powering both a motor and servos could die leaving you without power AND without the ability to control the plane on it's way down. A separate power circuit for the receiver & servos gives you control if you lose power to one or both motors.

Yes, the BEC could also die, so I'd get one with plenty of power to spare, give it lots of cooling, buy it pretty things, and ask it pretty please not to die.

 

[ScottyWarpNine]

Yes, the BEC could also die, so I'd get one with plenty of power to spare, give it lots of cooling, buy it pretty things, and ask it pretty please not to die.

Makes sense. Right Now I'm looking at the HK's YEP 20A Switching BEC. That should be plenty of juice.

 

[willsonman]

Yes, Since you will need beefy (and many of them) servos I would highly recommend a separate power system for the Rx.

 

[wilmracer]

+1 on an external BEC. I don't use the ESC for receiver power on anything other than parkflyers. Like mentioned above... you lose the ESC you lose motor AND control. No opportunity for a dead-stick landing... just lawn-darting.

And lawn-darting something this size is particularly dangerous.

 

[ScottyWarpNine]

I designed a main gear. I designed it around Dubro 600RV wheels.

I'll print one out tonight and we'll see how it works. I need to get working on tracing formers so I have something to build up.

 

[AkimboGlueGuns]

Neat-o. Doing the scale half-tracts? (they only go part way into the nacelles)

 

[ScottyWarpNine]

Neat-o. Doing the scale half-tracts? (they only go part way into the nacelles)

Yup. I hope the geometry of everything works well. I sort of just based all of my dimensions off of numbers in my head, so hopefully the mechanism will fit in the nacelle properly when retracted. When fully retracted, a little more than half of the wheel should be sticking out.

 

[wilmracer]

I designed a main gear. I designed it around Dubro 600RV wheels.

I'll print one out tonight and we'll see how it works. I need to get working on tracing formers so I have something to build up.

Awesome! I'm dying to get a 3D printer for just things like this. What model do you use?

 

[ScottyWarpNine]

Awesome! I'm dying to get a 3D printer for just things like this. What model do you use?

I have a Reprap Prusa Mendel i2 that I've been fighting with for the past couple years. All in all, it prints pretty well on a good day, and it was cheap to build. Calibrating it to print well is one heck of a learning curve though. Lots of great help and support online though on the reprap forums.

 

[ScottyWarpNine]

Does anybody have any ideas for a good adhesive to glue the formers in? I'm out of epoxy, so I could buy more, but I was wondering if there was something easier to work with, faster drying, stronger, cheaper, etc? I was thinking maybe gorilla glue would hold the foam pretty well. I doubt even high temp hot glue will remain hot enough for the amount of time it would take to apply the glue and set the part in place.

 

[wilmracer]

I use the white gorilla glue for most applications, but depending on your epoxy it will almost certainly take longer to cure.

 

[Barron.Barnett]

Another option, use the white gorilla glue or epoxy and tack things in place with hot glue dabs to hold everything in place while the stronger glues cure.

Just a thought.

 

[ScottyWarpNine]

Thanks for the tips. I'm considering just buying a bunch of polyester resin. I'm going to need it when I fiberglass the thing, so is there any huge reason anybody can think of for why I shouldn't use it to attach formers to my fuse frame? Besides the fact that it is about 20% weaker than epoxy resin, according to the internet. I figure I could save a lot of money and complexity doing it with polyester resin.

BTW, I like the idea of tacking parts in place with hot glue. And just out of curiosity, why do you guys prefer the white Gorilla glue?

 

[willsonman]

I prefer white because it fills gaps more. It also sets up a bit faster than the brown. If you use it... the foam will fail before your glue joint. I guarantee it.

 

[wilmracer]

I prefer white because it fills gaps more. It also sets up a bit faster than the brown. If you use it... the foam will fail before your glue joint. I guarantee it.

+1 on that. It doesn't sand as well as the foam though, so be careful if you're working on surfaces that will be visible. On occasion I've had to go back and dig out excess and then back fill with spackle so I wouldn't have a raised line on a seam.

 

[ScottyWarpNine]

Thanks for the tips guys,

I experimented with using hot glue on this foam. On my hot glue gun's high setting, the foam turns into a molten bubbly mess that leaves a hole when the glue finally cools. On the low setting, it bonds perfectly. That is what I have been using thus far to attach the formers and it seems to be holding up well.

First, I apply a bead along the edge of the former and press it into place. Once that glue cools, I apply another bead along each edge of the seam and use my fingers to "break the surface tension" as it has been said. I'm confident that the foam will break before the joint.

I've been using a big hole saw to cut through the larger formers to save a bit of weight and allow for wire routing.
I'm not too proud of the precision of some of the parts so far. I'm going to have to do a lot of sanding and a lot filling before I skin it, but I think that may also be one of the limitations of this material. It says 1/2" on the side, but I've measured it to be off by almost an 8th too thick.
Oh well, I wasn't expecting this to be the most scale build in the world, and when it comes to something of this size, a little variance here and there won't be the end of the world.

I'm toying with the idea of having the center section of the wing permanently attached to the fuse. This would include everything to the inside of the engine nacelles. That would stiffen up that whole section and eliminate a failure point. That would also give me the ability to add a large hatch to the bottom of the wing inboard of the nacelles that would give me access to battery storage, ESCs and radio gear. Each wing panel is 51", so if my math is correct, the center section is only 38" wide. 3'x8' isn't bad. That should fit on top of my Fiat quite comfortably. I'll have to make up some foam blocks and some rigging to hold it all in place, but I'm not too concerned.

That's all for this weekend's update.