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Old Apr 05, 2012, 07:37 PM
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United States, GA, Centerville
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So, while waiting for parts to come in for the Waco, I ordered and received a little foam model named the Triton

It is constructed from 2mm Depron foam. It occured to me that there are a lot of stick 'n tissue models whose construction time could be greatly reduced by the substition of foam in strategic places. A case in point could very well be the Waco in which the boxy fuselage could be foam sheet. The tail feathers could also be foam. Which, of course begs the question; why not complete the job and fashion the wings out of foam as well.

Make no mistake, I love balsa, but if they had this foam stuff back in the 40's all the planes would have been made of it or at least used it in construction. Even models with stringers could benefit from foam formers. I get that foam would disolve under dope, but we've come a long way from dope as well. Tissue can now run through inkjet printers, afixed with glue sticks, and sealed with water based laquers or even Future acrylic floor wax. That's not even considering the super light plastic coverings now on the market.

So, as I look at the Waco, I have to ask myself, "Can I do this in Depron?"

Thoughts?
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Old Apr 19, 2012, 11:17 AM
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Gulf Breeze, FL
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Quote:
Originally Posted by RayRangel View Post
So, as I look at the Waco, I have to ask myself, "Can I do this in Depron?"
Absolutely! I'd use 1mm Depron/Aero for the tail group, and 2mm for the wings and fuselage for a "robust" model. Some folks, notably "billyjim" (use search) even use 1mm for wings in the 25"size you're going to do. However, I'd go with UNGN's suggestion to scale it down, simply because I like that ~18"size for micros.

If you were going to do Paul's dynamite modular power pack, I recommend using 1/16 balsa here since it's stiffer and will better handle the push/pulls of battery swaps. If you haven't been able to take Paul's recommendation to read his thread on Zeke's UM Monocoupe, I highly recommend you do since you can use a lot of Paul's techniques and Zeke's design for your Waco: http://www.rcgroups.com/forums/showthread.php?t=1595126.

The only challenging area in the Depron Waco would be around the nose in the transition from rectangular fuselage to round cowl - Depron is a little trickier than balsa to round (use packing tape on the outside, roll the foam, then when formed, remove the tape - this eliminates the foam cracking on the outside surface).

There are many good threads on building with foam, in particular those by Pete (mtflyr), so that would be good reading...but be prepared to spend a lot of time - it's all "bet you can't just read one" material.

As for working with foam, I recommend sparing use of foam safe CA, with the main adhesive being UHU Por, a contact type cement which gives a very good, yet flexible bond. The downside to the flexibility is that it's hard to sand, staying rubbery.

I've only recently wandered back to balsa, and enjoy that as much as foam!

Gene K
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Old Apr 19, 2012, 12:31 PM
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Make no mistake; balsa dust runs in my veins. That being said, I also am not one deny technological progress either. I don't have any building experience with Depron. That's one of the reasons that I bought the little Triton kit. My plan is to build it when I finish my DH. 53 balsa kit. That way, in acouple of weeks or so, when I start on the Waco, I can experiment with using a mixture of foam and balsa.

I think I might try 1mm foam wings with a few balsa ribs and a balsa spar for rigidity. My main concern is twist and flutter under load. Rigid (balsa or foam with a carbon rod) interplane struts will help on that account.

A balsa box to accomodate a Paul Bradley tray would be a must both to handle the torque and the stress of repetative PBT (Paul Bradley Tray) removals.

Covering will be a challenge. Dope will probably attack the foam so using tissue would be a problem. Heat shrinks Depron so plastic coverings are an issue. Paint gets sucked up by balsa so thin coats of paint are problematical. Mixing faom and balsa does present some issues beyond the structural. But, problem solving is one of the the things that makes scratch building fun.
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Old Apr 19, 2012, 02:35 PM
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Originally Posted by RayRangel View Post
... I can experiment with using a mixture of foam and balsa.
Sorry, I misunderstood - I thought you were going for all foam vice a mix.

Quote:
I think I might try 1mm foam wings with a few balsa ribs and a balsa spar for rigidity.
If you're sticking with the 25" span, 1mm is pretty thin! The curve of the wing, of course, will add some rigidity, but the 2mm will afford a lot more strength with not too much weight gain (2mm Depron does not weigh 2X 1mm since a lot of the weight is in the skinning). And you may want to consider a CF spar vice balsa.

Quote:
Covering will be a challenge.
If you build all foam ala the Monocoupe build, you don't need covering. The foam readily accepts acrylic paint of which Walmart has a wide variety. You can apply printed tissue to the foam using spray adhesive if you want to add markings or just add some strength.

At any rate, good luck, you're starting on an interesting journey into DepronLand.

Gene K
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Old Apr 19, 2012, 08:13 PM
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Thanks for the good words. Since there are a couple of planes in que ahead of tbe Waco I have time to gather advice and exchange ideas. Keep them coming. All foam exterior with balsa in strategic locations inside is a possibility too. I bought a buncb of sheet foam in 2mm and 1mm to play with. I even have some blue foam for carving. What kind of foam is used for foam wheels?
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Old Jun 17, 2012, 02:59 PM
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Any progress, Ray?

Gene K
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Old Jun 18, 2012, 08:37 AM
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Unfortunately, no. I have the plans and got parts laid out (decided that balsa is the way to go, at least on this one). As yo have seen in the Nieuport thread, I've been considering four channels insted of three. I have rcvr, servos and a motor from a deceased UM Beast. That should be way more power than it needs.

Still working on the planes ahead of it in the queue though: DH53, Triton, and Mini Drake. I'm also flying as much as I can with my three channel Super Cub LP and full house T-28. The DH53 will take another week or so, the Triton is a weekend project, and the Mini Drake shouldn't take but a week or two. So, all things considered, I'll get to it in a couple of months. However, one of the things I've also considered is laminating the wing tips and tail surfaces. If I do that, then I might get a head start by doing those parts right now.
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Old Jun 18, 2012, 09:04 AM
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Still working on the planes ahead of it in the queue though:...
That's a great line up!

Gene K
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