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1/4 Scale ASK21**

Let us all watch your new project progress.
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Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Many thanks for your tips James.
The LR system you mention appears to be very similar to the Easy Composites pattern coat primer/high gloss system.
I already have some of the primer, so will press ahead with that on this model.

Tom,
The wing section will be as per the full size, so FX S02-196 / FX 60-126 sections at the root /tip. The intention is to achieve the slower scale-like flying speeds.
Yes, the wing root depth is approx. 3", so plenty of room for the joiner system ;)
The wing will be of built-up construction with a commercial top surface spoiler assembly. I haven't designed the wings/tail surfaces yet, but will do this using the DevWing CAD tool in due course, getting Cliff Evans to laser cut the parts for me.
I will probably finish the model as an ATC Air Cadets Vanguard TX.1 example.
roo Hawkins
Posts: 557
Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: 1/4 Scale ASK21

Post by roo Hawkins »

hi peter i am glad you are getting on with it well . your work so far looks realy good .I am glad to have helped. ROO :D :D
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Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Root TE side view
Root TE side view
Root TE plan view
Root TE plan view
Root TE filled
Root TE filled
This project Is still progressing, albeit very slowly, in short bursts between other projects.
I am still slowly getting the fuselage plug profile smooth after having added yet more filler all over the plug and then sanded back with 120 grit.
It now looks a lot better, so I am currently looking at getting a better wing root profile edge, particularly where the thin TE curves back to the fuselage.

After trying unsuccessfully to get a good edge profile with filler, I decided to bite the bullet and cut off the TE section and insert a pre-cut 1/16" epoxy board shape which I could fill to, and then sand back to the epoxy glass edge as shown in the photos below.
A further improvement will be to add an epoxy glass sheet root rib which has been matched up to the correct length FX S02-196 section.
I can then finally fair the fuselage into this rib to get what should be a very good match to the built-up wing at the wing joint.
Jolly Roger
Posts: 573
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: 1/4 Scale ASK21

Post by Jolly Roger »

P1040233.JPG
P1040242s.jpg
P1040306s.jpg
Hi Peter,

I've been following your build with interest.

Here's some photos of our local K21 this weekend, hopefully inspiring. Keep up the good work!

Rog
roo Hawkins
Posts: 557
Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: 1/4 Scale ASK21

Post by roo Hawkins »

hi peter good to see you have started again .I use a thin ply at the root ends . keep the posts coming
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Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Fuz root plates in position
Fuz root plates in position
Root
Root
Thanks for the encouragement Roger & Roo.
Roger, I remember my flights in a K21 at Sutton Bank so 17 or more years ago :)

Two fuselage root plates now added and faired in. Just needs some stopper to finish off that area.
I have another pic of the root rib, but it just will not load!!
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Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Just checking the wing/tailplane mounting relationship in order to correctly form the plug tailplane seat at the top of the fin.
Measurements taken from the Martin Simons 3-view drawing indicate that the wing incidence should be set at +2 to +2.25 degrees with respect to the tailplane.

Does this sound right?

(Both wing and tailplane sections are as per full size)
Jolly Roger
Posts: 573
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: 1/4 Scale ASK21

Post by Jolly Roger »

To some extent it's personal preference.

In practice, a larger angle requires a more forward CofG and results in a stronger stabilising moment in the longitudinal plane. The sweet spot for most glass sailplanes is around 1.5 to 2 degrees, but I have read of 0 degrees for more aerobatic types.

Hope this helps.

Rog
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jimbo
Posts: 293
Joined: 18 Mar 2015, 21:32
Location: Cornwall

Re: 1/4 Scale ASK21

Post by jimbo »

Good work Peter. Watching with interest, hope the mould comes out well.
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Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Many thanks all.
A tiny bit more progress - the top of the fin has been cut to shape.
The front step is as per full size as it allows the LE to curve up to the LE of the tailplane which projects forward of the top of the fin.
The rear part Is cut to the tailplane underside profile.
Thus the tailplane will have a small block fitted to its front underside & it then bolts directly onto the top of the fin.
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