Yellow Bird (oz7648)
About this Plan
Yellow Bird 20. Chuck glider model.
Quote: "A 'How-to-do' feature on high performance chuck gliders. Yellow Bird, by AJ Webber.
Do You Want a contest model you can fly on the village green and not end up in jail? Then Yellow Bird's the answer! The aim at all stages of development has been to obtain a safe launch in rough weather, have ability to recover from gusts and eddies and maintain sufficient altitude to catch thermals, rather than to rely upon fresh patches of low-level lift.
This might be expected to produce poor calm-air duration; but that is not the case. Flown after sunset on three occasions last summer the larger 'YB' 20 recorded a tranquil 90 seconds plus on each outing. Careful trimming on damp evenings gave maxima of 65, 58 and 74 seconds.
The long tail moment, 40 percent tailplane and big fin keep the YB's on the right climbing track in rough weather. Less fin area is fine for the glide but allows swinging-off to one side on the launch. The 4.7 percent wing section is just right. Thinning it down produces no gain in height and sinking speed goes up sharply. Yet if it is thicker the rate of sink is the same; but on go the brakes early in the climb.
Both YB's will go over the 100 ft altitude mark and the adjustments used produce (1) something between 1/2 loop and right-spiral Climb under power, tending to nose up if the turn over-tightens and (2) a very flat, safe left glide circle.
Building the YB's to lower all-up weights than those shown does not improve performance. Increasing the weight may give one extra time, but calls for more force in the throw. Bamboo leading edges are well worth the extra effort, placing tremendous strength where chuck-gliders take all the knocks. If necessary, "borrow" a piece off the neighbour's bean-poles.
The dangle dethermaliser causes a curious descent but landings have been effected safely on roofs, hawthorn trees and other unfriendly objects!
Colour-scheme on the originals was yellow wings, tailplane and black fin with black trim on fuselage. For elegance this takes some beating. Orange, used on two of the later versions, gives remarkable visibility.
Wood Selection: Cut wing, tailplane and fin from quarter grain sticks. This has a shining, mottled look and strong resistance to bending. If you have a choice, pick the lightest. Fuselage for the YB20 needs hardest spruce, straight-grained, without natural bends. Softer spruce (usually lighter in colour) for YB13, or, if you prefer balsa, use the hardest piece of straight-grained wood you can find.
Components: HMG Adhesive was used on the prototypes for all joints involving spruce and all joints are pre-cemented.
Curve the bamboo leading edges over a candle flame and cut for dihedral breaks before cementing in place. Finish - sand the underside of wing and tailplane and add the linen thread edging to all parts. Reduce the wing to the tapered thickness shown and mark the high-point line of the section on the upper surface. Study the section carefully and then carve and sand to shape, restricting sanding action to work from leading edge to trailing edge and at 45 deg. across the wing..."
Quote: "Hi Steve, Here's the Yellow Bird 20in HLG, sheet 1 of 2. Sheet 2 could be the 13in one, as I have both plans. Unfortunately I don't have the Aeromodeller issue. I tried to rework the outline of wing and stab as good as possible, which were overdrawn with pencil in my original plan. Now is the time to stop repairing and send you the plan. Regards, Wan."
Direct submission to Outerzone.
Update: article pages, text & pics added, thanks to RFJ.
Note: It looks like this plan was published along with the smaller 13in span version, see http://www.outerzone.co.uk/plan_details.asp?ID=3479
Supplementary file notes
Article pages, text & pics.
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User commentsI still have one of these in my loft, built about 1976. I took it out about 10 years ago - say 2008 - and something made me light the DT even whilst testing it. I am glad I did - second lob and it snagged a thermal and was away! I've been itching to convert one to micro r/c. Has anyone done so, I wonder?
Dick - 18/11/2018
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