Select the
MaxNEO
motor for the power and number of cells defined.
Geared motors will generally give better performance for all but
racing applications by allowing the use of a larger diameter,
higher pitch, more efficient prop.
The maximum airframe weight (including the radio and servos) will
be the total weight less the motor/battery/controller (the "motor
power system") combined weight. Can you build it that light and
still achieve the required strength?
Generally, the "motor power system" weight should represent about
one-half of the total flight weight.
Determine the approximate stall speed: Stall speed (mph) = 3.7 x
sq. root of wing loading (oz/sq.ft)
The propeller pitch should give a theoretical "propeller speed"
of at least twice the stall speed, and preferably 3 to 4
times the stall speed.
The propeller diameter should then be chosen to give the required
current draw of about 25 Amps. (The diameter should always exceed
the pitch).
As a final check, when it is all put together, the measured static
thrust should be at least one third of the total model weight.
Note that static thrust measurements are only meaningful if the
propeller diameter is at least 150% of the pitch (e.g. 12x8).
Using the 1700 mAh cells will give a full power duration of around
4 minutes at 25 Amps (1.7 x 60/25).
Going back to the power loading required for level flight (section 4 above) then allows estimation
of the maximum "cruising" time.
Actual flight time will of course be less than this due to the
full power used at takeoff.
Finally, always use thick multistrand wire (no less than 14 gauge
or 2.5 sq. mm), good connectors (e.g. Sermos or Powerpoles) and
a high efficiency, high rate speed controller that can handle the
required number of cells and current.
If you find that you cannot satisfy all of the above rules with some particular
model, BEWARE! That first flight could be quite interesting.
