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Calculating Efficiency of Electric Motors

(Example Motor)

Volts = 14.2
Amps = 28.0
Io = 1.1A (no-load amps at the operating speed)
Rm = 0.055 Ohm (internal resistance of motor)

Input Watt = V x A = 14.2 x 28 = 397.6 Watt

Copper Loss = Amps ² x Rm = 28 x 28 x 0.055 = 43.12 Watt

No-load Losses = Volts x Io = 14 x 1.1 = 15.62 Watt

Total Losses = 43.12 + 15.62 = 58.74 Watt

Output Watt = Input Watt – Total Losses = 397.6 – 58.74 = 338.86 Watt

Efficiency = Output Watt / Input Watt = 338.86 / 397.6 x 100 = 85.23%

Please note that we calculated the efficiency of the motor with a given prop. After calculating the efficiencies with a few different sized props (on the same motor), it will be evident how copper loss is mainly responsible for heat buildup and consequently lower efficiencies

Prop Rule of Thumb to Minimize Torque Roll Tendencies

Whenever you are building a pusher prop, jet type plane, to minimize the effects of torque roll, always keep the prop diameter 1/3 (33%) of the wingspan or less. With a 28" wingspan, a 9" prop is 32% of the wingspan and would be a good choice. A 12" prop is 43% of the wingspan and will generate a large amount of torque roll.

On the larger models, if you can keep the prop down to 25% of the wingspan, there will be almost no discernable torque roll tendancies. My 166% F-18 has a 48" wingspan, and I am running an APC 11x8.5 prop on it. In this case, the prop diameter is 23% of the wingspan, and it has almost no torque roll coupling.

Lucien

Installing magnets: (In Foam)

Locate and glue in all the single magnets flush on the fuse bottom. Cut small squares of saran wrap and place on top of them for a glue barrier. Now place the matching magnets on the ones you glued into the fuse with the saran wrap trapped between them.
Carefully place the fuse on the wing and make sure it is perfectly lined up. Apply pressure to the fuse at all magnet locations to make an indentation of the magnet into the wing. Remove fuse, dig out all the indented places so that the magnets will fit flush. Fill the dug out places with glue ( I always use epoxy for this) and refit the fuse to the wing. Weigh down or tape securely untill the glue cures. After the glue has set, pull the fuse off, remove the saran wrap squares and you have the magnets all glued in and perfectly aligned and never a problem with aligning the correct polarity.

JMorgan

Some GREAT tips on building a cockpit, canopy making, and fiberglassing
Jet Hanger.com Construction Tips

Mr Boogies Basic Steps to Fiberglass Mold Making
Be Sure to Visit R/C Groups Composite Forum

: "TP recommends no more than 3-5c average discharge for breaking in new packs" ... "overdischarging on the first flight will ruin the battery permanently".

TP also recommends never storing a fully charged pack for more than a week, which is a sensible rule often repeated by other manufacturers.

Gerd Giese of Elektromodellflug.de recommends, based on his experience of testing hundreds of packs, the follwing slightly more elaborate procedure to remove the discharge inhibitor:

0.5C charge - 1C discharge to 3.5V/c
0.5C charge - 2C discharge to 3.5V/c
1.0C charge - 3C discharge to 3.3V/c
1.0C charge - full power use

He claims the above general rules have given him the best results... But my observations would be that it almost certainly depends on the cell type/manufacturer.