Building a solid aluminum model aircraft

davehal9000 · Post by **davehal9000** » Wed Jul 04, 2007 2:05 am

I've got an odd project I'm kicking around, and that's how to make a large scale, about 1/24 scale, model airplane out of aluminum.

My father suggested lost wax. Recently I saw a movie clip online where a guy used plain Styrofoam and sand to cast his own aluminum gun parts. It looked pretty simply. My concern is getting the level of detail I'd want in the casting using ordinary Styrofoam.

In this casting process the master is cast in Styrofoam, then green sand is packed tightly around it inside a mold box. Molten aluminum is poured into the space occupied by the Styrofoam. The foam is melted by the aluminum, with the aluminum forming the former shape of the foam.

My thought is that balsa foam might work in the same manner and allow easier, more accurate shaping than Styrofoam. Anyone worked with balsa foam and have any thoughts either way? Would it melt as I'd need it to?

Lt. Z0mBe · Post by **Lt. Z0mBe** » Wed Jul 04, 2007 10:00 pm

My thought would be this:

If you are going through the trouble of making a master of the balsafoam, why not sheath it in Aves and make it your master for casting?

Am I making sense? I have that problem sometimes.

Kenny

davehal9000 · Post by **davehal9000** » Wed Jul 04, 2007 10:46 pm

I'm trying to make a sacrificial master. The sand creates the mold around the foam master. When the molten aluminum is pour in it melts and displaces the foam, creating an aluminum copy.

I assume you're talking about making a plaster cast, using the skinned aircraft as a master? I've got a wooden master started that I may use if I go that route. I've not had much luck with two piece plaster molds so far, but I haven't messed with them for some time.

Basically I'm trying to create a one of a kind, large scale aluminum aircraft that can be reasonably detailed with panel lines, flap detail and such, be painted and last decades out in the sun. Any suggestions are greatly appreciated.

macfrank · Post by **macfrank** » Thu Jul 05, 2007 9:15 am

davehal9000 wrote: Basically I'm trying to create a one of a kind, large scale aluminum aircraft that can be reasonably detailed with panel lines, flap detail and such, be painted and last decades out in the sun. Any suggestions are greatly appreciated.

Let nme guess - an Su-25? That's good of ya, Dave!

I'm not sure that BalsaFoam will melt the same as insulation foam, since it isn't styrene.

Why not use wax? It's not that expensive and most will burn out without leaving a residue.

Frank

davehal9000 · Post by **davehal9000** » Thu Jul 05, 2007 2:19 pm

Yeah, the ol' Frogfoot. It seems the thing to do. Looking for ideas on how to make it happen. I could finish up the wooden version in a week or so but I'd rather build one that'll survive the elements.

I've never tried carving wax, not that I've ever tried much with styrofoam either. I'd be afraid of coming home from work and finding my fuselage a pile of goo running down the front of my kitchen cabinet.

Kylwell · Post by **Kylwell** » Thu Jul 05, 2007 2:54 pm

Sand casting is rough even at it's best. I'd suggest lost wax or something simular. With it you can get an extremely high level of detail with very little clean-up.

macfrank · Post by **macfrank** » Thu Jul 05, 2007 2:58 pm

davehal9000 wrote:I've never tried carving wax, not that I've ever tried much with styrofoam either. I'd be afraid of coming home from work and finding my fuselage a pile of goo running down the front of my kitchen cabinet.

You could keep the wax in the fridge until you're ready to burn it off (it'll be stinky and generate a lot of smoke, so it's probably best to do it outdoors).

How are you going to add the details? TIG or MIG welding?

I think your wooden model and a two part plaster mold might be the best solution. Maybe with sand to back up the mold.

Frank

davehal9000 · Post by **davehal9000** » Thu Jul 05, 2007 3:49 pm

Wood is definitely a better medium for me to work with anyway. I've just never had any luck getting my molds separated when I've tried two part plaster molds.

As far as the aluminum goes, I was looking at engraving the major details, most likely using a sharp instrument and a straight edge.

The original was carved out of wood and although they had the real thing as reference, I'm sure it was fairly crude. The latest rumor is that the memorial may be moved to the Embassy at Kabul. It would be nice to be able to hand them the model to adorn the top. I just need to get on the ball and do it before I deploy again.

davehal9000 · Post by **davehal9000** » Thu Jul 05, 2007 5:16 pm

After some reconsideration I think I'm going to start all over with this project. The size of the model I'd begun carving was based on the best, largest piece of wood I could find over in Afghanistan. Had I been allowed to continue I would have finished the model in a couple of weeks and it would have been a done deal. Unfortunately I was ordered to stop and wasn't able to finish it.

When I look at other projects done elsewhere, say Sci-Fi projects, people are always looking back and asking why the modeler didn't build to a set scale. I think that might be the way to go with the Frogfoot. Not that there's anything in scale to match, but it's the principle of it all.

With that in mind, what's a good wood to carve a model airplane out of? I'm still pondering how many pieces to mold it into. I'd love to cast the wings attached to the fuselage but I don't think it'll be doable in the long run. If I did though, whatever wood I used would have to stand up to it's own weight and not flex during plaster molding.

Hell, the Blasafoam route Lt. Z0mBe recommended may be the easiest. I'd probably have to cast it with the wings separate though.

Kylwell · Post by **Kylwell** » Thu Jul 05, 2007 7:29 pm

Basswood is th eonly one I can remember. THere's Jute or Jutta or something that has an increadibly fine grain but is still a softwood.

davehal9000 · Post by **davehal9000** » Thu Jul 05, 2007 7:49 pm

Looks like it'll be 1/32 scale. When I initially planned the job I based my dimensions on the distance between the nozzles, then adjusted based on the wood I'd found. I figured it was within half an inch of the original size. If I start over again and go with 1/32 scale it'll be about 3 inches longer.

I know what'll happen; as soon as i finish Trumpeter will release a 1/32 scale Frogfoot!

macfrank · Post by **macfrank** » Thu Jul 05, 2007 8:52 pm

Dave, It's old fashioned, but the old 1940s manuals on carving airplanes is still really useful. It's available for free as several PDFs here.

I think a solid wood master with a plaster cast would be the easiest in the long run - if you have a casting mistake, your master remains untouched.

davehal9000 · Post by **davehal9000** » Thu Jul 05, 2007 9:12 pm

Interesting... It's similar to what I'd started, but the tools I had over there were so crude. A table saw was about all I had that was usable for the project, that and a vibra-sander. I'd already been making wooden model planes and helos for the kids outside the wire so I had a decent routine down. It'll definitely be easier doing it with a jigsaw though!

I definitely need to start playing with my plaster molding techniques though. That, and find someone who'll melt some aluminum for me!

Post by **TER-OR** » Thu Jul 05, 2007 10:01 pm

I wouldn't try to use balsa foam as the lost-wax media. It's not wood, but a resin foam.

You might have the best luck casting wax with silicone molds from a master of another media. Sand casting sounds fun, though....

davehal9000 · Post by **davehal9000** » Thu Jul 05, 2007 10:43 pm

This is what got me to thinking about trying the sand technique

http://www.youtube.com/watch?v=T-i1SczkFLE&NR=1

Bottom line though is I'm alot more comfortable carving wood than I am wax or trusting I've got the sand mixture right. I could see me going to all the trouble of making a foam Frogfoot then find out I didn't pack the sand properly and end up with a pretty aluminum asteroid for my trouble.

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Thu Jul 05, 2007 11:08 pm

Create or finish your wood master.

Then create some rubber molds off of those masters.
Use the molds to cast wax positives.
Sand ram the wax pieces and then pour your metal.

Ti Raven · Post by **Ti Raven** » Fri Jul 06, 2007 7:31 am

The Umi has spoken! Pay heed to her words of wisdom!

macfrank · Post by **macfrank** » Fri Jul 06, 2007 8:42 am

Ti Raven wrote:The Umi has spoken! Pay heed to her words of wisdom! :8)

Yup. Umi's is the best solution so far. You can do true lost wax aluminum casting and you still get to keep your master. AND you can make more than one.

Chacal · Post by **Chacal** » Fri Jul 06, 2007 9:42 pm

Kylwell wrote:Basswood is th eonly one I can remember. THere's Jute or Jutta or something that has an increadibly fine grain but is still a softwood.

Jelutong's the name.

And yes, Umi does make sense, but that's nothing new.

I'd suggest, however, that you go to a profesional metal caster, as it is not only very complicated, but dangerous as well â€“ as a rule of thumb, anything involving more than an ounce of hot, glowing molten anything is too dangerous for a novice to try. Remember, Anakin had to be turned into Vader because of the extensive burns and Palpatine had the best medic droids money could buy. You gots just the Bactineâ„¢, son.

davehal9000 · Post by **davehal9000** » Fri Jul 06, 2007 10:03 pm

I don't have the facilities to even try melting aluminum. I'd have to ask around town and see if anyone would be willing to make the pour for me.

I really don't have the funds to have this professionally done. I'd hoped the aviation community would have jumped in and helped with this. The whole project was set back due to personal opinions of what we were trying to do which I think in the end made people leery of helping out. That, and security issues.

macfrank · Post by **macfrank** » Sat Jul 07, 2007 9:55 am

davehal9000 wrote:I really don't have the funds to have this professionally done. I'd hoped the aviation community would have jumped in and helped with this.

You'd think the Russian government would have expressed an interest; Alexander V. Rutskoi, a former Russian VP, flew Su-25s (or T-8s) in Afghanistan.

davehal9000 · Post by **davehal9000** » Sat Jul 07, 2007 2:44 pm

The pilot I'm in daily contact with is good friends with Mr. Rutskoi.

Some of the pilots and I discussed the issue, and we'd hoped someone could get the design bureau to donate the model but we never had any luck. I figured they'd have things like that just lying around or could make one quite easily.

I had a lot of offers of help but I held them off not knowing the status of the memorial. I didn't want to take anyone's money, period. I didn't want to take anything from anyone until we knew for sure the memorial was going to be saved.

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Sun Jul 08, 2007 3:25 pm

Reading through this again, I became concerned with the suggestions for plaster molds. A plaster mold would be fine for making a wax master.

However do not attempt to pour hot metal into a plaster mold.
Any moisture in the plaster would flash into steam and you could
likely get results something similar to a land mine, or claymore.
With the addition of molten metal.

A boat modeler was pouring excess lead into an ingot mold and had a small explosion of lead shower his arm. He decided to use a ladel to transfer the molten metal to the mold, but when he stuck the ladel into the crucible, it also caused an explosion of molten metal this time 8ft in diameter, which caught his shoulder and Neck. He is ok, but recommendations that followed were to preheat his molds and tools to make sure all traces of moisture were evaporated.

davehal9000 · Post by **davehal9000** » Sun Jul 08, 2007 3:45 pm

I've read you have to bake out all the moisture or you'll have that problem. Doesn't sound like fun at all!

I'm going to order some wood here soon and start carving another master, then press on from there. I really need to get this moving, whether the Russians are able to use it or not. If nothing else I'll give it to Major Fedchenko to do with as he pleases, whether it's a master or an aluminum finished product.

Here's the latest article, one of dozens to make print.

http://www.rg.ru/2007/06/01/pamyatnik-bagram.html

I believe this was published in Fedchenko's hometown of Barnaul, the same town in which he and the other pilots attended aviation school.

Nothing terribly new, other than Fedchenko pushing for resolution on this memorial through Russia's veterans groups. He's got some powerful friends, to include the former Vice President!