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Schleicher ASH31 4m

Let us all watch your new project progress.
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Antonia
Posts: 130
Joined: 17 Mar 2015, 22:30
Location: Oxfordshire

Re: Schleicher ASH31 4m

Post by Antonia »

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.
Kenneth Paine
Posts: 12
Joined: 14 Nov 2021, 09:50
Location: Cheltenham

Re: Schleicher ASH31 4m

Post by Kenneth Paine »

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:
  • 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.
I trim my wet cloth flush with the root and trailing edges of the Mylar and let it overhang the LE and tip by 10mm so that the top and bottom skins meet in front of the LE and tip ribbon forming a lip which is trimmed after curing.

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.

Discus 1/5 wing tip
Discus 1/5 wing tip
Discus 1/5 stab
Discus 1/5 stab
Rotor wings
Rotor wings
Rotor stabs
Rotor stabs
MartinE
Posts: 122
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

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?
Kenneth Paine
Posts: 12
Joined: 14 Nov 2021, 09:50
Location: Cheltenham

Re: Schleicher ASH31 4m

Post by Kenneth Paine »

Hello Martin,
MartinE wrote: 31 Mar 2022, 08:56 Thanks for that info, I will try that on the wings.
I am glad to be of help.
MartinE wrote: 31 Mar 2022, 08:56 I have (on previous wings) tried scraping the LE of the Mylar, without much success - probably didn't remove enough thickness.
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.
MartinE wrote: 31 Mar 2022, 08:56 Your surfaces look very smooth, would you say the 350 vs 250micron has a significant influence on that?
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
Kenneth Paine
Posts: 12
Joined: 14 Nov 2021, 09:50
Location: Cheltenham

Re: Schleicher ASH31 4m

Post by Kenneth Paine »

Another super secret :mrgreen:

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.
Kenneth Paine
Posts: 12
Joined: 14 Nov 2021, 09:50
Location: Cheltenham

Re: Schleicher ASH31 4m

Post by Kenneth Paine »

MartinE wrote: 31 Mar 2022, 08:56 Your surfaces look very smooth, would you say the 350 vs 250micron has a significant influence on that?
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
MartinE
Posts: 122
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

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.
MartinE
Posts: 122
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

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.
Attachments
20220403_150856.jpg
MartinE
Posts: 122
Joined: 28 Oct 2021, 14:36
Location: Essex

Re: Schleicher ASH31 4m

Post by MartinE »

Lengths of carbon fibre tow cut ready to fill the spare cap slot.
Kenneth Paine
Posts: 12
Joined: 14 Nov 2021, 09:50
Location: Cheltenham

Re: Schleicher ASH31 4m

Post by Kenneth Paine »

How are you going to tackle the shear web Martin?
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