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WIK Astir CS77

speedy
Posts: 11
Joined: 13 Nov 2019, 08:50
Location: Germany

WIK Astir CS77

Post by speedy »

Hi!

I am just in the progress of rebuilding an 1:4 WIK Astir CS77, one of the first full composite glider models.
The previous owner has done a lot of nasty things to this poor bird (nose cut off and vent holes for motor, cut outs for servos in vertical fin, ...). But the structure is good and I am quit into composite repair.
But I have a few questions:

The fuselage seems to be laminated using gelcoat, because on grinding it shows white colored matrix with glas fibre in it. It smells like polyester when grinding, but seems flexible like epoxy. No problem, but just interesting to know. Anyone knows more about that?

On one wing the laminate seems to be "bleeding" (smelling liquid) under the gelcoat and shows some bubbles especially at the leading edge. Sand off all of the gelcoat and repaint or only fix the bubble spots?
How is that wing built? I can see balsa as core material, is there an inner shell, too?
It seems there are no supporting ribs but the root rib in the wing. Only shell and spar?
Who knows more about these early composite birds?
Regards,
Christian
speedy
Posts: 11
Joined: 13 Nov 2019, 08:50
Location: Germany

Re: WIK Astir CS77

Post by speedy »

Hello Anthony,

Thanks for your reply!
So it is not balsa as core material in the wing? Good to know, so the wing will not have problems with humidity ...
I my bird the airleron servos have already been placed in the wing using those round servo locks.
I'm intending to put the airbrake servos in the wing, too. Buat as you point out: the original air brakes are a bit to small, so it might be better to change them. Which electrical airbrakes did you install?

But I still do not know what to do with the bubbles under the wings gelacoat, where a starnge smelling liquid comes out. I heard that this was a problem of the early composite birds whe getting wet, comparable to osmosis problems on composite boats. So it might be best to carefully sand down the old gelcout.
Regards,
Christian
MDev
Posts: 160
Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Re: WIK Astir CS77

Post by MDev »

If there is an osmotic type problem caused by the resin taking up moisture and turning into an acid and creating the air pockets then the usual treatment would be to drill the spaces, clean and fill with epoxy/bubbles, I hadn’t heard of it happening on model gliders but if the conditions for it exist.... You may find information leaflets at a chandler? I have treated many pinholes that leave the salts on the surface as water dries, in the same fashion. 35 years ago epoxy would have been an expensive option to use?

Have fun.

M
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VinceC
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Re: WIK Astir CS77

Post by VinceC »

I loved my Wik CS-77, but lost it on an aero tow with an over enthusiastic tug pilot. The wings couldn't take the strain and snapped. If you can, it may be worth adding extra fibreglass to the root area
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2002-07-31_19.jpg
speedy
Posts: 11
Joined: 13 Nov 2019, 08:50
Location: Germany

Re: WIK Astir CS77

Post by speedy »

Really beautifull picture! That's why I want this bird flying again!

You don't hav any pictures of the damage to see where the weakness is?
Regards,
Christian
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VinceC
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Re: WIK Astir CS77

Post by VinceC »

Sorry, I don't.Best forgotten, but it was probably, now I think about it, in the area where the wing joiner finishes
Barry_Cole

Re: WIK Astir CS77

Post by Barry_Cole »

VinceC wrote: 14 Nov 2019, 12:49 Sorry, I don't.Best forgotten, but it was probably, now I think about it, in the area where the wing joiner finishes

Other than the pilot, the point of maximum stress....

;) ;) ;) ;)

BC
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VinceC
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Re: WIK Astir CS77

Post by VinceC »

I'm not stressed, I said I'm not stressed, did you hear me :oops: :oops: :oops: :oops:
ColinP
Posts: 3
Joined: 29 Nov 2019, 15:37
Location: Surrey

Re: WIK Astir CS77

Post by ColinP »

Hi, I've actively monitored this forum for many years, but this is my first post.
I acquired a Wik Astir CS 77 at the Headcorn model show a few years ago. Have just got around to starting the renovation. The wings were all in good condition, except the epoxy paint was flaking off both leading edges. I sanded them back, and tried filling with Polyester filler but that seemed to create bubbles under the remaining skin. So I have had to sand back the LEs chamfering the epoxy skin and sealed the edge with Cyano. Then I have primed and sanded ready for spraying. Will probably use rattle cans to do that. I have not encountered and "leaking" but maybe this is where the epoxy skin is delamminating, so I would remove the bubbles, fill with cyano and epoxy and sand back.
When I bought it, it had no tailplane so I have built a new one. But I cannot fathom out how the original linkage worked, especially at the elevator horn. Does anyone have any idea on this. My current plan is to fit a thin servo high up in the fin and use a straight linkage, but there must be a way to put the servo at the base of the fin. Any drawings or plans welcomed. Thanks
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