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1/4 Scale ASK21

Let us all watch your new project progress.
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Simon WS
Posts: 280
Joined: 18 Mar 2015, 11:39
Location: Kent, UK

Re: 1/4 Scale ASK21

Post by Simon WS »

Fantastic achievement Peter.

Simon

Geoff Pearce
Posts: 436
Joined: 18 Mar 2015, 09:11
Location: SN11 9EE

Re: 1/4 Scale ASK21

Post by Geoff Pearce »

Well done Peter, will you be challenging Roo for fastest build? :lol:

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Mike Forsyth
Posts: 26
Joined: 14 Jun 2015, 09:30

Re: 1/4 Scale ASK21

Post by Mike Forsyth »

Thanks, Peter. 1.7kg for the fuselage is not too bad, I will be watching this with special interest. You have done a Fantastic job 😃

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Peter Balcombe
Posts: 1098
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Geoff,
I don’t think Roo has anything to worry about 🙂
It’s taken 18 months so far to just get a fuselage.
However, wing & tail designs are done, so maybe have something to maiden by next Spring.

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Peter Balcombe
Posts: 1098
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

With fuselage available, I have designed a tailplane arrangement using DevWing, transferring the output to DevCad to work up the detailed cutting templates and annotated build plan.
Cliff Evans kindly cut some parts for me, so the tailplane has started taking shape as shown below.
The plan is to embed a thin wing servo in the rear of the tailplane, this driving the elevator via a short pushrod to a ball joint on the bottom of the central elevator half joiner. The linkage sits in a slot cut in the top of the fin.
The tailplane is attached using a single bolt and anti rotation pin.
Tailplane internals
Tailplane internals
Last edited by Anonymous on 14 Sep 2018, 09:01, edited 1 time in total.
Reason: Problem with picture.

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Simon WS
Posts: 280
Joined: 18 Mar 2015, 11:39
Location: Kent, UK

Re: 1/4 Scale ASK21

Post by Simon WS »

Looks very neat Peter
Simon

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Peter Balcombe
Posts: 1098
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

After a bit of a delay (to remake the elevator in order to avoid added filler weight), the tailplane top sheeting has been added and the elevator dry hinged to check servo operation.
Everything looks good, so the lower building tabs have now been removed and lower spars fitted ready for application of the lower sheeting.
Note that tip blocks have still to be added to give the final shape.

I will investigate fitting of a servo hatch to allow access, plus fitting the tailplane to the top of the fin.
Rudder construction has also started, so I hope to be able to check the overall fit of the tail feathers soon.
Attachments
Tailplane & Elevator underside
Tailplane & Elevator underside
Tailplane & Elevator top
Tailplane & Elevator top

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Peter Balcombe
Posts: 1098
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

With rudder built up and hinged onto a Liteply/balsa finpost, I finally found time between other builds to fit the tailplane fixing Tee nut at the top of the fin and also cut out the tailwheel slot in order to check that the rudder & elevator were clear with the tailplane in place.
Happily it all fits, so I can now tidy everything up before moving on to the wings.
The tailplane overhangs the front of the fin a little more than true scale, but that is because my fin is a little less deep than it should be (3-view scaling error :o ) - but hopefully no-one will bother to much when it is all done.

Note that the bit projecting above the tailplane in the photos (looks like a flag) is actually a piece of masking tape attached to the rudder hinge pin wire to hold the top of the rudder in place as the fin-post is only dry fitted. The wire will be replaced with a removeable carbon rod in due course.
Attachments
Tail group check.jpg
Tail group check2.jpg

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Peter Balcombe
Posts: 1098
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

A little more progress today after printing off a wing root rib, complete with datum line in order to transfer the datum line to the fuselage root ribs, together with the main joiner & rear incidence tube centres.

With the wing datum defined, I strapped a length of substantial hardwood strip against the wing root, with one side along the datum line. I also made an 1/8” balsa negative tailplane root section template so that with this sat on the top of the tailplane, I had a flat surface parallel to the tailplane datum.

Thus equipped, I was able to check the longitudinal dihedral & was pleased to find that the wing sits at +2 degrees, or just over, wrt the tailplane 🙂

So, out with the P38 filler to make a smooth tailplane bed at the top of the fin (essentially just filling the 1/8” gap at the very rear of the tailplane. Once that had set & been tidied up around the sides, short lengths of 16swg brass tube have been let into the top of the fin & tailplane for an anti-twist peg.

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Peter Balcombe
Posts: 1098
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

After more than a years delay, I at last have the bench clear to get back on this build.
So..... with a wing parts set kindly cut by Cliff at LCS, let the build recommence.

The wings use top & bottom main spars, bonded full length to a central Ply web to form an 'I' beam.
So after making up the main spars, the lower one was laid over the plan, supported on blocks to achieve the correct height. The outer ply web was then glued to the top of the spar, using a few ribs to correctly position it, before adding the remaining outer section ribs, plus Balsa Dummy LE, Dummy TE, Aileron hinge spar & Aileron LE to produce the complete structure apart from LE & stock Balsa TE.
K21 Outer panel start_small.jpg
The process was then copied for the Inboard section, including the rear spar & web to tie everything together and give a pretty complete structure apart from the upper main spar & lower rear spar.
The brake box will be defined by 1/8" Spruce spars yet to be added. The photos also show the carbon joiner tube which slots through the root ribs/spar web. The main joiner will be a 16mm diameter high carbon steel (machine slide) rod, with 5mm rear incidence rod.
Attachments
K21 Wing structure1_small.jpg
K21 Wing build2_small.jpg
K21 Wing build3_small.jpg

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