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1/4 Scale Charlesworth ASK13**

Posted: 16 Aug 2019, 10:01
by Peter Balcombe
This plan has been around for a while & apparently quite a few built over the years.
As with most other Cliff Charlesworth designs, the plans are available through Cliff Evans (Laser Cut Sailplanes) who has digitised the plans and makes a short kit available.
However, Cliff has recently been made aware that some of the parts don't fit as well as they might, so this build has been requested to investigate and make improvements where necessary.
Also, this build will have the alternative open cockpit (Cabroilet) arrangement.

The supplied plan sheets are big, so you need a bit of space to spread them out ;)
Initial inspection showed that the wings use the Cliff Charlesworth preferred built-up main spar assembly approach (so I will alter the build here to use my preferred build up from lower spar approach), plus the fuselage longerons are balsa (which I will change to spruce & balsa to add more strength).
Also, I felt that a few more build notes would be helpful, especially for a less experienced builder.

Anyway ....
Starting with the fuselage, I first made up a simple fuselage build jig from softwood (bottom rail with vertical end pieces glued vertical at overall fuselage length + 2mm separation). This was marked with centre lines along the bottom strip & up the inside of the end pieces, plus former locations. (I made the end pieces 220mm high to allow a straight edge to be placed along the top, just above the highest former to give an upper sighting centreline.

Next job was to draw a reference line on the plan, just below the keel at F2, with the formers at 90 degrees to this.
The idea is now to fix pedestals at each former position to position the keel strips at the correct height relative to the reference line.
(Note that Cliff's plan has a 'Datum' line marked in the canopy area, but I needed one below the keel).
1_4 Scale Charlesworth ASK13_.pdf
(2.27 MiB) Downloaded 242 times
Next, Cliff arranged for me to receive some keel pieces cut from 1/4" ply, which could then be epoxied together to make up a full length keel, complete with wheel pant surround.
With the keel sat centrally on the support blocks the front & rear formers were glued onto the keel and tacked to the jig end pieces (each spaced off with a couple of 1mm ply strips to allow them to be released later).

All this is hopefully clarified in the pic below.