Fly Electric!

Stearman PT-17

Ascot Racecourse 22-Apr-01
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Ascot Racecourse 22-Apr-01
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Two years to build and five years dormant, my PT-17 has at last flown! Started as a scale project and intended for a 120 Four Stroke motor, but IC no longer appeals to me and it just had to be electric. Fortunately the firewall is removeable otherwise it would have been impossible to convert. 6 minute flight times may not seem very long, but this is better than having the model lying idle. The pictures above show the model at its first public outing at the Ascot airshow in April 2001.

The direct drive brushless Actro motor is turning a 16x8 at 40A. Despite extensive use of throttle, the motor is only warm to the touch on landing. Having a direct drive motor saves the weight of a large belt drive mechanism, and the brushless technology should be more efficient than brushed. Performance with these power levels is very pleasing. Consecutive loops are easy. Rolls are a bit sluggish so I need to find a way to increase throws. The stall is predictable and is easy to hold with rudder.

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Wing span: 73" (1854mm)
Wing area: 1620 sq"
Wing loading: 24 oz/sq'
Weight: 17.1 lb (32xRC2400); 18.5 lb (30xCR3000)
Motor: Actro 40-5
Gearbox: Direct drive
Prop: Airflow 16x8 Wood
Prop speed: 7000 RPM (all measurements with 32x2400's unless otherwise stated)
Batteries: 32xRC2400 or 30xCR3000
Motor current (full power): 40A
Motor power: 1300w (after drawing off 0.4Ah)
Power loading: 77 w/lb (input)
Static thrust: 4.75kg / 10.5b (after drawing off 0.4Ah)
Flight times: 6 minutes
Receiver: Futaba 8ch dual conversion PPM changing to PCM for safety reasons
Servos: 2 x Futaba S9202 (Rudder/Elevator); 2 x Futaba S3001 (Ailerons)
Speed control: Actronic 32-70
Rx battery: 700mah 4 cell nicad
Model design: Scratch built
Airfoil: NACA 2213
Wing construction: Conventional built-up. Plug-on wings using one 6mm carbon spar for each wing. Velcro retainers.
Fusalage: Fibreglass; plug made from balsa/cardboard, covered, sprayed and them moulded.
Undercarriage: 5mm piano wire.
Covering: Coverite Fabric; sprayed.
Extra features: Scale rib tape (1mm pitch). The machine to make these can be found on my Rib Tape Cutter page.
Real panels on front section of fuz and top deckings (very thin fibreglass).
Many moulded components (eg: u/c fairings, struts, dummy motor, etc.).
Dummy air intake is functional as it is used to feed cooling air to the ESC.
What would I do differently?: Need to increase roll rates.
Undercarriage is too floppy (will probably make one from carbon fibre).
Flying wires take too long to rig; now modified for carbon spars with dummy wires.
2-part epoxy paint on top of Humbrol enamel Silver is not a good idea as it flakes off! (only did this on under surfaces, fortunately).

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