August's L-bird

[K5083]

I'll be attempting the Rare Planes Stinson L-5 Sentinel. Mine is still sealed in the original bag. The white plastic has yellowed but luckily the transparent plastic for the fuselage has not. If successful, this will be my first-ever completed vac model. It is not my first attempt! It will be in RAF SEAC colors if it makes it to the painting stage.




August

[splash]

Welcome aboard August.

That looks like a nice little kit to introduce you to Vac Form models, I like the clear body idea, the only downside is you will have a join dead centre of the windscreen

Regards Splash

[Stuart]

looks like a nice little kit - you're lucky that the clear part has not yellowed.

[K5083]

You are right splash, and not just the windscreen but the top of the fuselage between the wings also was a window. Luckily, both the windscreen and the upper glazed part were split down the middle on the real L-5. But it will be challenging to get the halves together with no more mess than can be hidden by the canopy framing in those areas. I guess I will butt join those parts with clear PVA glue. The structural strength will have to come from the rest of the fuselage join.

Because of all the windows it will also need a full interior built, but that at least is something I'm used to screwing up.

August

[K5083]

Made some plastic dust this weekend. The styrene turned out to be not only yellowed, but very weak and brittle. Just a slight flexing sent cracks everywhere, including through some of the parts. Well, it's always something of a relief to get the first disaster of a project out of the way. Scoring produced still more wayward cracks, and I soon found that the least destructive way of separating the parts was with scissors.



Anyway, I got started on a few things. Rareplanes provided a nice amount of cockpit detail for this bird including a floor with woody detail, some bulkheads, seats and panel. The horizontal stabs are cut out and built. I find the tail feathers some of the hardest parts of building small vac forms because their final thickness is barely that of one sheet of styrene; to build one out of two pieces takes a lot of sanding and it is hard to know when to stop. These came out okay. I plan to finish the wings before turning to the transparent fuselage, which luckily seems to be much less brittle.

August

[rob_van_riel]

The styrene turned out to be not only yellowed, but very weak and brittle.

Now look what you've done, another puzzle to torture my mind with...
There's a reason why plastic becomes brittle, probably either some chemical reaction, or the loss of plastisizers. If the latter, the process might be reversible. Trying to think my way past this is going to cost me some sleep again...

[DH-Drover]

The Gent I spoke to from HPM in SIN. said to GENTLY warm vacform before cutting.

Dai

Living in the land where the crows fly backwards

[K5083]

The styrene turned out to be not only yellowed, but very weak and brittle.

Now look what you've done, another puzzle to torture my mind with...
There's a reason why plastic becomes brittle, probably either some chemical reaction, or the loss of plastisizers. If the latter, the process might be reversible. Trying to think my way past this is going to cost me some sleep again...

I assume it is damage from light. The plastic is yellowed only on one side, which faced outward from the pack, and the cracks start from (sometimes can be limited to) that face of the sheet. My guess is that light broke down the polymers. Maybe the kit faced a window or a fluorescent light for many years in some hobby shop before it found its way to me.

Anyway it is not too difficult to work with now that I've gotten used to it.

August

[K5083]

Sand, sand, sanding the wing halves. It isn't the difficulty of vacuforms that turns me off, it's the tedium.

Eventually I'll get to the fuselage, and I'll want to cut out the nose cooling holes and show part of a cylinder behind them. I have a quick and cheap technique for making cylinders.



Get some oil-based modeling clay from the craft store and some fine-threaded machine bolts. Push the bolts into the clay to make a mold, then pry them out.



Mix up some casting resin. This is the stuff that is available at the Michael's craft store chain in the U.S., same place I got the clay. You can see I'm mixing up a small amount (but still way more than I need for this job) in a disposable picnic teaspoon. Dribble the resin into the depressions left by the bolts one drop at a time with a toothpick. Minimize spillage around the sides (which will become flash on the finished casting) by dribbling the resin into the part of the depression left by the head of the bolt and then carefully spreading it down the length of the depression with the toothpick.

After setting, pop the resin out and clean off any bits of clay with a toothbrush. You now have half-cylinders with realistic cooling rings. Cement them together if you need whole cylinders; I'll probably just need the halves to peek at through the cowling front. The molds are one-shot but the clay is reusable and it takes just a minute to make another one.

August

[rob_van_riel]

The molds are one-shot but the clay is reusable and it takes just a minute to make another one.

I've used a very similar technique for casting dental plaster. Since I typically pushed the masters all the way in, I had to pick them out with just a bit more force than my clay appreciated, and to compensate for this, I would push in the masters after kneading at room temperature, and then pop the lot into the freezer. At -40 Celcius, the clay is rather more resistant to deforming

[K5083]

Very erratic progress on this. However, I got the wings completed and the fuselage prepped.



Then built a basic cockpit on the floor provided in the kit. You know those seats you hate with older kits that are just two planks set at an angle? For the L-5 those would be accurate!



Painted the inside of the fuselage and added some sprue tubing. I didn't go nuts trying to extend the tubing up the windows. This build will be hard enough to finish on time as it is. Then installed the cockpit. The bulkheads and instrument panel are from the kit, but I added the hood to extend the panel out from the front bulkhead and give the poor pilot a chance of reaching it.



Before joining the fuselage I still have to cut out the intake nostrils and put in the cylinder heads.

August

[DavidWomby]

This is interesting to watch. Love the cylinder heads cast from bolts!

David

[lancfan]

Brilliant job August.

David.

[splash]

Great tip with the resin bolts.

[VickersVandal]

This is looking great. Nice of the original designers to make things so easy for you when it came to the interior....

Now look what you've done, another puzzle to torture my mind with...
There's a reason why plastic becomes brittle, probably either some chemical reaction, or the loss of plastisizers. If the latter, the process might be reversible. Trying to think my way past this is going to cost me some sleep again...

I assume it is damage from light.

It would be, yes:
http://en.wikipedia.org/wiki/UV_degradation;

The process isn't really reversible since it involves breaking down of the molecules.