Wight Kema. Radio control sailplane.
Quote: "Latest in the 'Kema' marque, Keith Humber's super 100 inch soarer. Wight Kema.
Wight Kema was developed several years ago as a simple, attractive two-channel 100S soarer for use on the slope on those very quiet days or as a 100 inch on the line. She was deliberately designed as a 'low-tech' model but uses an Eppler 193 modified wing section (I droop the trailing edge slightly) which has worked very well over the years for me. The model still has the 193 penetration and ability to search over a wide area for elusive thermals but it will also slow down and float in a most satisfactory manner.
When the going is tough and the lift light, Wight Kema can still perform as well and sometimes better than the hi-tech machines. The wing is a similar one to those which I have used on all my family of 'Kema' soarers with detachable tips for transporting and flexibility. In fact, one could put larger tips on the model up to about 120 inches with, I think, a fair degree of success. However, this one is 100 inch so I digress. Those of you with keen eyes will note that I have changed the fuselage wing seating arrangement. On the plan I have simplified it by NOT using the 1/4 in saddle across the fuselage - the advantages do not seem to be worth the exacting work involved - which brings me quite nicely on to a brief resume of the construction (very brief, I may say - Wight Kema should present no problems for anyone who's built one or more models before).
Fuselage: Cut the basic sides from 3/32 x 3 in to the outline. Next, cut the front and rear doublers from 1/16 ply and glue them to the balsa sides with contact adhesive. Now cut out F1 and F2 from 1/8 ply and make up the nose block from 3/8 in laminations - note the rebate for the fuselage sides.
Now glue the sides to the front formers over the plan using epoxy. Also glue the 3/16 sq lower and top longerons into place and fit the nose block. Rough cut the 3/8 underpans to outline and glue into position. Cut and glue the 1/4 in tail seat piece at rear to obtain fuselage taper then cut and glue on the rear fuselage top decking. Cut fin, shape and glue into slot.
Next make and install the pushrods, checking for free movement, then cut and glue the rear fuselage 3/32 bottom sheeting. When all is dry, smooth up the fuselage with a razor plane and sand to a streamlined shape - a very enjoyable task this as it is now that the final curves come into being! The towhook on the prototype was sawn and filed to shape from an old offcut of aluminium glazing bar; however, a commercial hook would be equally suitable. The hook is bolted through the fuselage bottom and 1/8 ply plate and held by 6 ba bolts. Its position on the plan may have to be adjusted with individual models to achieve the best overhead launches - if the model weaves or goes over to one side when on the line, the hook is too far back. If she refuses to climb the full height, it is too far forward. However, if you build sensibly and don't add too much weight the position shown on the plan should be fine.
Wings: These are the most tricky parts of the model to build, particularly the trailing edges, so read these notes carefully. The ribs are cut from 1/16 quarter grain sheet, the joint ribs being faced with an additional 1/16 ply. Ribs 16 to 18 are also 1/16 ply (for the 10swg brass wing tip joiner tubes). Pin down the lower 3/8 x 1/8 spruce spar over the plan and glue the ribs into place over it. Now glue on the top 3/8 x 1/8 spruce spar and cut the leading edge oversize from 3/8 sheet. Glue it in position and also the trailing edge lower sheet from hard 1/16. Choose hard 1/16 sheet for both the top and bottom trailing edge components; this will enable the finely chamfered trailing edge of the Eppler section to be formed.
If your model bench is large enough, build the opposite panel to this stage of construction also, then join both together with a very good quality 1/4 ply brace. There should be approximately four inches of dihedral under each panel at the tip dihedral joint. Now complete the rest of the sheeting checking constantly for warps and twists. Build the tip panels in a similar fashion, fitting the joints before finally top sheeting..."
Wight Kema, Radio Modeller, November 1989.
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