Monster sized Fock-Wulf FW-42
- Thread starter rockyboy
- Start date
A coat of WBPU mixed with talcum powder filler on the nacelle covers...
And then I tackled molding the cowling. First I coated the outside of the plug with two coats of mold release. Then I mixed up Ultracal 30 per recommendation and it was the consistency of milk. Not helpful. So I added about 25% more powder than recommended till it got to a workable clay like consistency. Then I covered the plug with about 1/4" of Ultracal, wrapped the whole thing with a strip of t-shirt rag to add some strength to the mold, and then added about another 1/2" of Ultracal and some scrap bamboo sticks for bracing.
And it worked!! This morning I used some putty scrapers to try and pry up the mold, but instead popped the whole plug and mold assembly off the acrylic backer. Getting worried, I fired up the air compressor and blew into the seam between the plug and the mold to try and get some sort of release - and I think it helped. I put a big fat lag bolt into the foam plug and with a gentle pull it came right out!!
For my first mold ever, I'm pretty happy with how it looks. I'm going to let it cure for another day before messing with it more, but the next steps are chopping off the parts of the bamboo that are really in the way, gently cleaning out the wispy bits of mold release, and doing a light sanding and sealing inside to repair the thin cracks and make sure the surface is super smooth before doing a fiberglass layup for the cowling.
And then I tackled molding the cowling. First I coated the outside of the plug with two coats of mold release. Then I mixed up Ultracal 30 per recommendation and it was the consistency of milk. Not helpful. So I added about 25% more powder than recommended till it got to a workable clay like consistency. Then I covered the plug with about 1/4" of Ultracal, wrapped the whole thing with a strip of t-shirt rag to add some strength to the mold, and then added about another 1/2" of Ultracal and some scrap bamboo sticks for bracing.
And it worked!! This morning I used some putty scrapers to try and pry up the mold, but instead popped the whole plug and mold assembly off the acrylic backer. Getting worried, I fired up the air compressor and blew into the seam between the plug and the mold to try and get some sort of release - and I think it helped. I put a big fat lag bolt into the foam plug and with a gentle pull it came right out!!
For my first mold ever, I'm pretty happy with how it looks. I'm going to let it cure for another day before messing with it more, but the next steps are chopping off the parts of the bamboo that are really in the way, gently cleaning out the wispy bits of mold release, and doing a light sanding and sealing inside to repair the thin cracks and make sure the surface is super smooth before doing a fiberglass layup for the cowling.
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Mold update...
My shop gets cold at night. And Ultracal 30 shrinks just a wee little bit when it gets cold. And when solid clay / plaster pieces shrink, they crack. More.
After consultation with an expert (wife has an art degree and lots of experience with ceramics and sculpture) I should have kept the mold at room temperature, especially for the first week, but the damage should be repairable with an epoxy fill / coating inside the mold once it warms up.
So the mold has moved into the house until the weekend when the weather will warm up and I can do the epoxy work with a decent ambient temperature.
So it'll be back to working on the aileron control surfaces and painting the other half of the plane until then.
My shop gets cold at night. And Ultracal 30 shrinks just a wee little bit when it gets cold. And when solid clay / plaster pieces shrink, they crack. More.
After consultation with an expert (wife has an art degree and lots of experience with ceramics and sculpture) I should have kept the mold at room temperature, especially for the first week, but the damage should be repairable with an epoxy fill / coating inside the mold once it warms up.
So the mold has moved into the house until the weekend when the weather will warm up and I can do the epoxy work with a decent ambient temperature.
So it'll be back to working on the aileron control surfaces and painting the other half of the plane until then.
I hate those things that are temperature-dependent. I waited weeks in the spring for weather that was suitable to apply primer to my corsair project. It happens.
Yeah, next time around I'll know better on the Ultracal. So far I haven't had problems with the Ironlak spray paints with temps in the 40s, but I'll probably drag a space heater down from the attic before I continue the paint job. Just in case
PsyBorg
Wake up! Time to fly!
I'll have to ask her but my neice makes kid type jewelry out of a kind of resin that gets baked to cure.
From what she has said it does not shrink and the little glow in the dark alien head i got from her is pretty solid.
That stuff may be a viable solution to get away from fragile clay / pottery type mold making.
From what she has said it does not shrink and the little glow in the dark alien head i got from her is pretty solid.
That stuff may be a viable solution to get away from fragile clay / pottery type mold making.
Been getting my butt kicked by a cold the past few days, but I did finally get the nose gear servo and linkage all finished up last night.
And thanks to @PsyBorg suggestion some little 3D printed hole covers for the top. I was going to paint them, but they do look sort of fancy in black too...
When I put on the other wing to do the final bit of camo, I was confronted with this very ugly join line. I should have done a balsa end cap on both sides of the wing prior to fiberglass. But I thought I could get away without it.
Really ugly on the bottom too. So I think I'm going to call a pause on painting and fix this cause I can't ignore it anymore.
And thanks to @PsyBorg suggestion some little 3D printed hole covers for the top. I was going to paint them, but they do look sort of fancy in black too...
When I put on the other wing to do the final bit of camo, I was confronted with this very ugly join line. I should have done a balsa end cap on both sides of the wing prior to fiberglass. But I thought I could get away without it.
Really ugly on the bottom too. So I think I'm going to call a pause on painting and fix this cause I can't ignore it anymore.
PsyBorg
Wake up! Time to fly!
Hey Jon....
Is it me or does the landing gear have the shock tilting rearward?
If so I would suggest you change it so the compression is front to back as it will be inneffective and likely to shear on hard landing if it compresses back to front.
Having the wheel side lead into the landing a bit will allow it to compress into a more vertical state putting the load on the towers not on the shaft.
From the angle of the pic I would say mount the assembly 180 or shorten the support rods to get the shock aimed forward.
Is it me or does the landing gear have the shock tilting rearward?
If so I would suggest you change it so the compression is front to back as it will be inneffective and likely to shear on hard landing if it compresses back to front.
Having the wheel side lead into the landing a bit will allow it to compress into a more vertical state putting the load on the towers not on the shaft.
From the angle of the pic I would say mount the assembly 180 or shorten the support rods to get the shock aimed forward.
BS projects inc.
Elite member
I think he does has the wheel compressing front to back, look a little closer, the control surfaces give it away.
Hmm... I didn't think about that...
It's very simple to rotate the whole assembly 180 and that would help line up the forces if it hits hard enough to start flexing the wires too. Good idea!You are correct that the wheel does move in a backwards arc, but I think @PsyBorg point about having the shock point towards the front could help prevent damage to the shock in a less than ideal landing scenario.
Long term (fingers crossed the bird lives to a "long term") I want to replace the whole main landing gear setup with something that looks a lot more like @wilmracer setup for the Sweet Pea - but I want to fly her at least once before putting the hours into that rebuild.
BS projects inc.
Elite member
oh yeah true, that shock absorber is going to do very little at its current state, definitely try to have it facing the other way or else over time it will rip out the landing gear. However I don't think that switching it the other way around will do too much either. The wires won't bend like you think they will and the landing gear wouldn't move at all.Hmm... I didn't think about that...
You are correct that the wheel does move in a backwards arc, but I think @PsyBorg point about having the shock point towards the front could help prevent damage to the shock in a less than ideal landing scenario.
Long term (fingers crossed the bird lives to a "long term") I want to replace the whole main landing gear setup with something that looks a lot more like @wilmracer setup for the Sweet Pea - but I want to fly her at least once before putting the hours into that rebuild.
kilroy07
Legendary member
I'm curious how those decals work out for ya. (I have an alps for water-slide decals and that is totally backwards to how they work.)
What brand is the paper/system?
I've got quite a bit of experience with mold making... I usually use a platinum cured RTV, but if this is a one-off then it might not be worth the expense. I am a tad worried about you getting epoxy to release from ultracal though...
What brand is the paper/system?
I've got quite a bit of experience with mold making... I usually use a platinum cured RTV, but if this is a one-off then it might not be worth the expense. I am a tad worried about you getting epoxy to release from ultracal though...
In de future mon. Way in de future.
I'm using the Hayes stuff - amazon link here - https://www.amazon.com/gp/product/B077TMFVL9/?tag=lstir-20 - will probably be applying them this weekend
I'm a complete noob on the molding stuff, so appreciate all advice. When I sealed up the cracks with epoxy, I figured it would be better to deal with the same surface everywhere inside the mold so I brushed on epoxy across the entire mold. When I'm ready to do the layup, it'll all get about 3 or 4 coats of mold release first to help promote separation. Fingers crossed!
I haven't done an ultracal mold myself (yet) but have seen John Morgan do a ton and I suspect Jon will be able to get it to work. Fortunately he only needs 2.
I agree it has been too cold to get much done lately. I had loaned a pair of space heaters to my brother last year and I had to go and reclaim them last night. Its just been too cold to work in the shop for more than a few minutes at a time. With three heaters running maybe I can get some work done this weekend. Need to get the shop cleaned up so there is room to balance this beast
kilroy07
Legendary member
Ah, okay. I see what you are doing then, I thought what you were doing was the first coat of your layup.
My bad!
Build is looking great BTW! Hope to see her at FF2019!
Lots of holiday distractions in the past week, but I did get a start on the balsa book ends. Shown here are two rough cut pieces of balsa with glue on each wing side (none in the middle) and all held together with some bungee cords to dry.
And after drying I did a quick trim with a razor plane to get it closer to the wing size.
Next will be masking tape to protect the paint job a little, spackle filler for the gaps, sand to the wing profile, install some sort of mechanical wing holding latch, a layer of fiberglass to hold it all together with some strength, fix up the paint job, and then repeat on the other wing.
Yes it sets me back a couple weeks at my current building pace, but it's going to be a much better wing join.
For anyone else considering a big foam build like this, just do the balsa pieces on the wing joints from the beginning. It would have been easier to do this a long time ago instead of having to retro-fit it.
And after drying I did a quick trim with a razor plane to get it closer to the wing size.
Next will be masking tape to protect the paint job a little, spackle filler for the gaps, sand to the wing profile, install some sort of mechanical wing holding latch, a layer of fiberglass to hold it all together with some strength, fix up the paint job, and then repeat on the other wing.
Yes it sets me back a couple weeks at my current building pace, but it's going to be a much better wing join.
For anyone else considering a big foam build like this, just do the balsa pieces on the wing joints from the beginning. It would have been easier to do this a long time ago instead of having to retro-fit it.
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