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1/4 Scale ASK21

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Peter Balcombe
Posts: 1178
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

With all ribs in place, the joiner tube has now been epoxied in position and then fully boxed in with ply sheet & epoxy to make a solid lump tied to the spars.
The rear incidence tube has also been added & boxed in using hard balsa, faced with 1/16" ply.
Airbrake fitted & pushrod routed through to the servo bay.
Lastly, a 1/8" balsa doubler strip has been fitted around the wing taper break rib in preparation for skinning, which I have decided to do as separate Inboard & outboard sections.
The structure now just needs to be sanded over to get the False LE & TE to profile prior to applying the full width upper skins.
Attachments
Joiner tube_small.jpg
Brake installed_small.jpg
Joiner tube boxedin_small.jpg
R21 Rib doubler_small.jpg

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Peter Balcombe
Posts: 1178
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Upper sheeting has been applied in 2 sections once rib doubler had been fitted at the taper break.
I now need to find the Brake blade outline in the upper sheeting - if I can find the piece of paper I wrote the measurements on ;)
Aileron servo cable threaded though & now awaits more cable to be able install the Brake servo cable.
Photos below show the current state, noting that a 1.5" TE strip will be fitted once the sheeting is complete.
(The front part of the ailerons is already included in the build so far, complete with angled aileron LE spar).
Attachments
Wing top sheet_small.jpg
Wing tops sheet below_small.jpg

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Peter Balcombe
Posts: 1178
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Underside now sheeted & servo hatches opened up.
1.5” TE stock now being applied to the rear edge, starting with outer section - aligning upper surface to wing profile (excess lower surface to be removed later when profiled to wing section).
Attachments
29D2B662-3E9D-4A8B-A943-0CFF4BC2541E.jpeg
5D875D66-EAE4-4B58-B0DE-E34799D7E99B.jpeg

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Peter Balcombe
Posts: 1178
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

With bottom spar tapered as required this morning, the 2nd wing structure is well on its way - with not a drop of Cyano in sight!
The Ply web sitting on the top of the wing is for the rear spars yet to be fitted. (The web fits from the underside anyway).
Attachments
DE72EF6C-FD96-4953-92CD-9AA19FE5731A.jpeg

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Peter Balcombe
Posts: 1178
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

With the top skin now on the 2nd wing & the lower building tabs removed, I couldn’t resist putting the joiner tube in the fuselage in order to try an initial assembly.
Tailplane also sat in position to get an impression of the overall size.
Still a lot of work to be done, but slowly getting there :)
Attachments
3AFC2C4D-E574-457A-ABE7-13C8ED76DE21.jpeg

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Cliff Evans
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Joined: 29 Dec 2019, 15:13
Location: Bristol
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Re: 1/4 Scale ASK21

Post by Cliff Evans »

Looking good Peter.

roo Hawkins
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Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: 1/4 Scale ASK21

Post by roo Hawkins »

Nice mate

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Peter Balcombe
Posts: 1178
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

With both wings now fully sheeted & fuselage joiner installation complete, attention moves to completing the wings.
After profiling the lower edge of the stock TE section to match the distinct undercamber in this TE area, the aileron has now been separated on the 1st wing.
(This involved remembering to mark the hinge line on the top surface - defined by rear edge of vertical hinge spar) prior to adding the lower skin). The aileron could then be cut off by inserting a scalpel blade through the top skin, down the rear of the hinge spar & out through the bottom skin at the ends & centre of the aileron. Join up the lower surface points & cut through skin & ribs using a razor saw. There is room for error at the bottom due to the gap formed by the angled aileron LE web.
Once removed the aileron LE bevel can be tidied up.
Attachments
E3E89C5D-3606-424B-99D9-8B9A1995A279.jpeg

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Peter Balcombe
Posts: 1178
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

With the wings now having had their glass cloth applied & awaiting a final coat of epoxy to seal the cloth weave, attention has passed to preparing plugs from which I can hopefully ask Barry at Sarik to pull the 2 canopies.

When making the fuselage plug a while ago, I made sure that I saved the canopy cutouts, which were glassed to avoid hanger rash etc. The plan was to use these as the basis for the canopy pulling plugs - although at the time, I wasn’t sure how I would go about this!

In order to produce the canopy plugs, I need to extend the canopy shapes by 1.5” or more at front, rear and bottom, and also make the plug capable of withstanding the vacuum pull without distortion.
The final plug will be cast in Herculite plaster in a simple negative mould bath formed around the extended canopy cutouts.
So ... the first job was to cut some foam blocks having the extended canopy dimensions & cut a recess in these into which the canopy cutouts could be fixed. The remaining foam will then be shaped to profile to also include a moulding release draught angle. The pics below show the canopy cutouts in place in the foam blocks.
Hopefully, all this will work out ;)
Attachments
E61E6DDF-136D-4E1F-BEF7-756037CB243F.jpeg
03A4F6EB-E5BE-4A25-8EA3-EC6F17A1E56C.jpeg

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B Sharp
Posts: 750
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: 1/4 Scale ASK21

Post by B Sharp »

I have been patiently for this build to continue Peter. That is an interesting method for making the plugs .
Brian. :)

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