How to choose and electric motor for your plane/Heli

so one question i often get asked is, how do i choose a electric motor for my plane. cos MOST electric motors(with the exception of Eflite) do not give the equivalency rating to a glow motor. they say a motor is a 41/50/8 or something which to most guys means...dick.

ok. its quite simple

Firstly se the table below to work out the power requirements roughly that you will need for your particular plane

Glider - Powered Glider. Eg lone Ranger 60-80watts per pound of weight
Trainer = High Wing Kyosho Calmotor. Thunder Tiger Pegasus etc 80-90watts per pound of weight
Sport Plane = Ugly Stick 100-120watts per pound of weight
Aerobat/Pattern = 120-150watts per pound of weight
Fighters/Scale = Spitfire, Harvard, Tiger Moth 120-160watts per pound of weight
3D = Any 3d Aircraft(Foamies included) 200+watts per pound of weight

Ok youve got a trainer. it falls into the 80-90watts per pound of weight category. lets say you work it out that your plane is going to weigh roughly 2.5kg when its ready to fly. this is equal to 5.5 pounds
So you would need a motor that can supply 440watts(5.5 x 80) at LEAST. but its better to er on the side of cauting and go for slightly more power.(you can always throttle back)
so lets use 5.5 x 90 = 495w, call it 500w

ok so now we know the power we need. but how does this compare to a .40 size glow motor.
ok quite simple. MOST 40 size motors put out roughly .8hp, this equates to 600w, remember that glow aircraft are generally heavier due to fuel and extra batteries so ignore the subtle difference.
so off you go now and look for a electric motor putting out 500-600w of power.
but now you see that there are 20 different motors putting out this power. and the only difference between them is something called a KV Rating??????

Ok this means RPM per Volt. so if you have a KV Rating of 1000kv it means that for every volt the motor receives it will turn at 1000rpm so if youre using a 3cell lipo pack which is 11.1v then the motor will turn at 11000rpm(under ideal conditions)

great. how does this equate to glow? between the .25 to .60 size area the rpm range is between 14000rpm and 10000rpm more or less. so go somewhere inbetween and you get 12000rpm

so now you now that to fly your .40 trainer you need a motor which can supply between 500 and 600w of power and a kv rating that will spin whatever prop it recommends at between 10000 and 12000rpm

so please dont go buying a motor with a kv rating of 4000 this means it will spin at 44000rpm on a 3 cell lipo pack. useless for aircraft unless youre flying ducted fan.

most aircraft use 3 cell packs. if you want to use a bigger pack, for a larger aircraft. say a 4 cell(14.4v) pack. then bear in mind it will UP the rpm of the motor. so when considering motor choices you have to look for one with a slightly lower KV rating say 750kv
this means 750 x 14.4 = 10800rpm? you see how it affects it?

anyway. post some comments if it sounds greek but the process can be summed up in the following steps

1.) Find out the type of plane youre flying(should be pretty obvious)
2.) Find out its weight in pounds
3.) establish how much power you need to fly it
4.) look fore the appropriate motor with the necessary power and appropriate kv

voila. done.