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The six minutes or so of flying took 1.56Ahr (1,560mAhr) from the batteries, about half the capacity. This meant that the average current draw was about 16A, or 4A per motor, equating to about 175W - not a lot! Eight to ten minute flights will clearly be possible without overstressing the batteries. The following information gives an overview of the static performance of the power system.
2 x 3S 1,500mAh LiPo, 12.48V off load
|Full throttle||Lots !||10||50||500||?|
|Climb throttle||10,000||11.1||18.5||202||41 mph|
|Low throttle||8,500||11.7||6||70||34 mph|
This table was generated from readings taken using fully charged LiPos with the wing balanced on my knee while taking phone calls about a computer problem and switching off the fluorescent lights so that the rev counter would work and drinking a cup of tea and photographing the underside of the fuselage - so I missed a couple of readings! However, the general spread of info is useful, I think. The model flies nicely at or between low to average throttle.
After taking the wings off, I noticed that the Velcro holding the power tray to the fuselage floor had pulled off. This must have happened at the landing of the test glide, so the CG for the test flight was probably at about the 18 - 20% position! It still handled well. By comparison, the full-size Hercules CG figures are 19 - 30% takeoff and 16 - 30% landing - quite a range. A foam block was later cut and glued inside the fuselage front to define and limit the forward position of the power tray.
The second flight was timed at about nine and a half minutes, and the charge quantity required for a full recharge was 2,300mAh or about 76% of capacity so in the interests of prolonging the battery life, the timer will in future be set at 8 minutes to land at 9 minutes.
All in all, this was a very successful and relatively low cost build of what started on not much more than a thought of “I want one of those!” The table below shows the modest expense incurred in building this airframe. I’ve left out the cost of the hardware items because they may well later do service in another model. It’s interesting to realise that the total airframe cost of £14 is about the cost of a single gallon of IC modeller’s glow fuel!
|Motor Wiring||Stripped from 13 Amp household cable||Nil|
|5 Minute Epoxy||Cheap Shop||£2.50|
|Brown Paper||Cheap Shop||£1.00|
|Total airframe cost||£14.00|
The model has attracted a lot of interest from fellow club members. It’s huge, and flies like a dream. I intend to continue flying it, possibly with another set of batteries, and just enjoy seeing the sight of a Hercules in the sky above Thorney Island again.
|Hercules technical data|
(2 x 1,500mAh 3S LiPo)
|Wing Area||0.34 sq m||530 sq in|
|Wing Load||49g/dm||15.9 oz/sq ft|
|Batteries||2 x 1,500mAh LiPo|
|Motors||4 x 7.2V Speed 400|
|Props||4 x Gunther 5 x 4.3|
|Power Loading (max power)||299W/kg||136W/lb|
|Average in flight power||175W, equivalent to 48W/lb|
|Control||Ailerons, elevator and throttle|
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