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"Sandfly"Scratch-built parkflyer |
| Wingspan | 865mm (34") |
| Wing Loading | 24gm/dm 2 (8oz/sqft) |
| Flying Weight | 300gm (10.6 oz) |
| CG (percent of MAC) | 34% |
| Motor | Speed 280 FG3 (1:3 gear ratio) |
| Propeller | Graupner Cam Slimprop 200mm x 150mm (8" x 6") |
| Speed Control | 10A with BEC and brake |
| Battery | 7 x Sanyo N270 NiCad (8.4V) |
| Receiver | Hitec HS-04Mi (no case) |
| Servos | 2 x GWS Pico Standard |
| Controls | Rudder, Elevator, Motor |
| Construction | Balsa, covered with Solarfilm |
This is my first scratch-built radio controlled model aeroplane. It started with a 'stick' fuselage, and was intended to be a testbed for small motors and gearboxes. I hoped that using light-weight components and construction would produce a true slow-flyer. However, the tiny motors and batteries I intended to use were too weak for a model of this size, so I fitted a Graupner Speed-280 FG3 with 8x6 prop. This worked OK, but the model had poor climbing ability. This was because the best battery I had at that time was a 6 cell 600AE pack, which was too heavy and yet still not high enough voltage to suit the Speed-280.
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| Flying with Speed-300 motor | Sandfly and Dragonfly |
When I upgraded the motor to a much hotter Speed-300 unit, performance improved dramatically. However, it made the all-up weight a lot greater than I had originally intended. Eventually the high wing-loading and excessive power led to disaster, as during some aerobatics (three consecutive tight loops) the wing's dihedral brace snapped causing the left wing panel to break off, thus changing the plane into a lawn dart from an altitutude of over 50 Metres!
Fortunately the damage was easily repairable, and gave an opportunity to make some improvements. I rebuilt the front end with a proper fuselage, providing better motor and wing mounts, and enclosing the electronics. I then refitted my original Speed-280 motor, and built up some 7 cell 270mAh battery packs. The battery slides firmly into a pocket at the bottom of the fuselage. In the event of a heavy landing, it can move forward to lessen the shock. The motor/gearbox is held in with ordinary dressmakers pins pushed down into the balsa fuselage sides. If the prop touches the ground during landing these pins will simply pull out a bit.
The only other changes I made were replacing the original GWS-4P receiver with a Hitec HS-04Mi (I needed the light-weight GWS receiver for another model), and reducing the wing incidence. Originally the wing was mounted with its flat bottom in line with the fuselage, but this resulted in several degress of positive incidence. Packing up the rear of the wing by 1.5mm helped to eliminate the plane's previous tendency to stall when applying up-elevator at lower throttle settings.
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| pull-pull controls | Receiver and servos |
Flight performance is good, with a typical running time of 7 to 9 minutes. It can easily takeoff from a mowed grass strip, requiring just a bit of right-rudder to track straight. Climbout is strong, and the plane cruises well at 2/3 throttle. There is just enough power to loop from level flight, but I don't like to do that manoeuvre as the wing is not very strong! It can land in a fairly short distance. Glidepath is quite steep so I usually enter my final approach at low altitude with a bit of throttle on.