|
"Tangerine"Scratch-built parkflyer |
| Wingspan | 910mm (36") |
| Wing Loading | 21gm/dm 2 (7oz/sqft) |
| Flying Weight | 260gm (9.3 oz) |
| Motor | Speed 300 direct drive |
| Propeller | Graupner folder 120mm x 60mm (4.7" x 2.3") |
| Speed Control | 10A with brake (no BEC) |
| Battery | 4 x Sanyo KR600AE NiCad (4.8V) |
| Receiver | GWS 4P |
| Servos | 2 x Cirrus CS-20BB |
| Controls | Rudder, Elevator, Motor |
| Construction | Balsa, covered with Airspan (lightly doped) |
This is my second scratch-built design. My goal was to produce a light-weight plane that could be powered with a small motor. Originally I intended to use a Mabuchi FK-050SH motor rescued from a broken CDROM drive, geared down to drive a high-pitch prop. However, earlier tests on my "Sandfly" showed that this motor would not deliver enough power. Therefore I decided to fit a Speed-260 motor with direct drive to a Graupner 4.7" x 2.3" folding prop.
The Speed-260 was barely powerful enough to keep the plane aloft. Unfortunately after only three flights the motor overheated and melted its plastic endbell. Driving the 4.7" x 2.3" prop on 4.8V caused current draw to approach 3 Amps, three times higher than the motor's point of best efficiency. I then realised that a better motor was required, so I installed a Speed-300 unit. This motor draws about 5 Amps static, but is efficient at such power levels. The extra power available permits a good climb rate, and it cruises at half-throttle. Hand launching is easy, with plenty of thrust for a steep climbout. Flight duration is from 8 to 14 minutes depending on flying style.
Combining a Speed-300 motor and 4 x 600AE cells has proven to be a good match
for this model. 600AE cells have excellent energy to weight ratio, and are less
expensive than most smaller cells. The only problem I had was finding a speed
controller that would cut off at the required 4.0 volts. I tried a GWS #100A,
but it was heavy and inefficient (frame-rate) and had an awkward arming button.
Therefore once again I built my own
ESC
, this time without a BEC (the receiver and servos run direct from the 4.8V
motor battery).
Replacing the servos and ESC with lighter equipment could trim 15-20gms off the total weight. However, I doubt such a small improvement would be very noticable. An inline gearbox should markedly improve performance, as the motor could then drive a larger prop which would be more efficient at low speeds. I may try this if I can get a suitable gearbox for a reasonable price.
|
|
| a nice snug fit! | Custom-built ESC |
|
|
|
1st April, 2001. Found out air can be stronger than balsa.