K.18 (oz3172)

About this Plan

K18. A 76inch span A2 glider, from Model Aircraft August 1958.

Quote: "Now let us take a look at the latest model in the series and see what we have (see Fig. 3). A simple A/2; no scientific layout. The fuselage, whilst having ample side area for towline stability, is cut down to the minimum, where area is not needed, at the top and bottom. It is in effect a profile (there is no such thing as a 'lifting fuselage') and is simply 1/8 x 1/8 in hard balsa covered with 3/32 sheet.

The wing is of normal construction and is fixed to the fuselage by means of a 4 mm ply tongue (best birch). Aerofoil is medium-thin own-design based on the Benedek range. The tailplane uses the same section but in this case it is thinned to 80 per cent. Main points about the performance of this model are good stall recovery and an overhead launch every time.

Finally, a few remarks on trimming and flying procedure. The kind of trim used on an A/2 depends to a great deal on the particular modeller; I myself prefer about 100 ft circles, and a slow undulating glide which is just off the stall. This trim is obtained by using about 50 ft of towline and using packing under the tailplane then the model has a slight stall a small amount of extra rudder is given to damp out any prolonged stalling tendencies. A model trimmed beyond this point is not a good proposition, except in very windy weather, when the turn may need to be increased slightly.

Some time ago I used a tuner-operated d/t on a model very similar to the K-4. This set-up worked by means of a wire retainer pin in the rear of the fuselage; this was connected to the timer and passed through a loop of C/L wire fixed to the tailplane trailing edge. On one flight the timer went haywire and did not pull the pin right out of the loop. The tailplane not only became tilted in flight—it also had a decrease in incidence, thereby giving an up elevator effect and increasing the turn.

The resulting flight was quite interesting and afterwards I began to trim the model for a very tight turn. To counteract this turn it was necessary to place 1/8 in of packing at the trailing edge of the tail. The model flew with about 45 deg of bank, and as the turn radius was in the region of 20 ft, it was nearly thermal happy. Then using this kind of trim it is also noted that elevation trim is not critical as the model just refuses to stall, but please don’t try it the other way - that turn is much too steep to go playing around with trying to make it fly in a groove. If it’s thermals you’re after, this is the trim, but remember, it’s hard on wing tips. I have also used the so-called wandering trim and found it useless for our kind of weather..."

Supplementary file notes

Planfile includes article.

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