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Schleicher ASH31 4m
- Antonia
- Posts: 140
- Joined: 17 Mar 2015, 22:30
- Location: Oxfordshire
Re: Schleicher ASH31 4m
Hi Martin, thanks for that, thought that might have to happen.
Really looking forward to the wing build when you get there, great project, thanks for posting your progress.
Really looking forward to the wing build when you get there, great project, thanks for posting your progress.
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- Posts: 13
- Joined: 14 Nov 2021, 09:50
- Location: Cheltenham
Re: Schleicher ASH31 4m
Hi All,
Great build Martin.
I have always used 0.35mm (0.014") Mylar and never had issues with getting it to wrap around compound curves at the tip. My secrets are:
Below are some samples. Unfortunately this forum resizes images so you cannot pixel-peep the detail, but if anyone is interested I can place them on the Cloud and provide a link.
Great build Martin.
I have always used 0.35mm (0.014") Mylar and never had issues with getting it to wrap around compound curves at the tip. My secrets are:
- Block-sand a thickness taper to the outside of the first 15mm to 20mm of the Mylar's LE and tip. Sand it down to say half its thickness or whatever feels right to you flicking the edge with your finger. Yes, this is laborious for Mylar is tough, yet you must be careful not to cut through it.
- Cover the sanded surfaces with clear adhesive tape to prevent epoxy sticking to them.
- Set the Mylars 5 to 6mm back from the core's LE and tip. Nothing will conform to such tight radiuses except the bag.
Below are some samples. Unfortunately this forum resizes images so you cannot pixel-peep the detail, but if anyone is interested I can place them on the Cloud and provide a link.
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- Posts: 126
- Joined: 28 Oct 2021, 14:36
- Location: Essex
Re: Schleicher ASH31 4m
Hello Kenneth,
Thanks for that info, I will try that on the wings. I have (on previous wings) tried scraping the LE of the Mylar, without much success - probably didn't remove enough thickness.
Your surfaces look very smooth, would you say the 350 vs 250micron has a significant influence on that?
Thanks for that info, I will try that on the wings. I have (on previous wings) tried scraping the LE of the Mylar, without much success - probably didn't remove enough thickness.
Your surfaces look very smooth, would you say the 350 vs 250micron has a significant influence on that?
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- Posts: 13
- Joined: 14 Nov 2021, 09:50
- Location: Cheltenham
Re: Schleicher ASH31 4m
Hello Martin,
Kenneth
I am glad to be of help.
I agree with your thinking that you did not remove enough thickness. It is hard work. I use a combination of Dremel with coarse disk sander followed by a 15cm sanding bars with 80 and 180 grits. Careful though, if you get carried away with vigorous shoe polishing you may damage your Mylars.
I think 350 micron will do a better job at concealing cloth weave print-through and span-wise hot wire ridges on your foam core than 250 micron, but it will not conceal a uni carbon ribbon laid on the core as a spar.
Kenneth
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- Posts: 13
- Joined: 14 Nov 2021, 09:50
- Location: Cheltenham
Re: Schleicher ASH31 4m
Another super secret
The surfaces in the last two photos were riddled with pinholes which allowed primer through the skins causing localised dissolution of the cores leading to lots of remedial work.. The surfaces in the first two photos had no such problems.
The difference? Having learned my lesson first time round I started my layup with tissue against the Mylars before any cloth. Voila! Also, the tissue becomes invisible in epoxy so if you want to show off a natural carbon skin your panels will look fabulous.
The surfaces in the last two photos were riddled with pinholes which allowed primer through the skins causing localised dissolution of the cores leading to lots of remedial work.. The surfaces in the first two photos had no such problems.
The difference? Having learned my lesson first time round I started my layup with tissue against the Mylars before any cloth. Voila! Also, the tissue becomes invisible in epoxy so if you want to show off a natural carbon skin your panels will look fabulous.
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- Posts: 13
- Joined: 14 Nov 2021, 09:50
- Location: Cheltenham
Re: Schleicher ASH31 4m
Yes, smooth but not wave-free. Mylar is shiny but still has waves and ripples in it which are fine for a slope soarer but, together with core imperfections, not good enough straight out of the bag on a scale model in my opinion. Sure, you can take the wings out of the bag, spray them and have a nice glossy model, but glossy in a FlyFly sense, not wave free in a European mouldy sense which is the standard I aspire to.
Even though my wings looked beautiful out of the bag, my sanding block quickly revealed how far the surfaces were from wave free. For nauseating detail have a look here: Wing contouring starting at post #158.
The long and short of it is that, given the amount of contouring work my Mylar bagged surfaces still needed before painting, why bother with Mylar at all? I have made a decision that for my next scale model I will lay the cloth straight onto perforated release film, kitchen towel on the outside to absorb excess epoxy and spread the vacuum, and straight into the bag the assembly will go. The post bagging work remains the same but the cost and faff of Mylars are avoided.
My 2p for what it is worth.
Kenneth
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- Posts: 126
- Joined: 28 Oct 2021, 14:36
- Location: Essex
Re: Schleicher ASH31 4m
I think if a 'moulded finish is desired then there is no escaping the graft! I'll have a look through your RCgroups thread. Thanks.
Your last point may well be very wise - let us know if you try it.
Your last point may well be very wise - let us know if you try it.
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- Posts: 126
- Joined: 28 Oct 2021, 14:36
- Location: Essex
Re: Schleicher ASH31 4m
I've hot-wire cut the inner wing sections. My cutting board consists of smooth piece of MDF, with a pulley rail attached and a weighted, pivoted lever to pull the boom through the foam.
This way the cut sections do not end up dished in the middle. This wing section is quite long at 820mm.
The spar cap slot was then sanded in, with 12mm wide 100grit, glued to the edge of some plywood. Meter rule to keep is straight.
This way the cut sections do not end up dished in the middle. This wing section is quite long at 820mm.
The spar cap slot was then sanded in, with 12mm wide 100grit, glued to the edge of some plywood. Meter rule to keep is straight.
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- Posts: 126
- Joined: 28 Oct 2021, 14:36
- Location: Essex
Re: Schleicher ASH31 4m
Lengths of carbon fibre tow cut ready to fill the spare cap slot.
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- Posts: 13
- Joined: 14 Nov 2021, 09:50
- Location: Cheltenham
Re: Schleicher ASH31 4m
How are you going to tackle the shear web Martin?