chronos333
Posts: 26
Joined: 10/8/2004
From: longueuil,
QC, CANADA
Status: offline
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From experience,
Electric motors are able to efficiently turn at high rpms even more naturally than big props at low rpms. Remember: The lower the winding, the higher the kv (rpm per volt), the higher the amp rating.
There are scientific reasons to that but lets keep everything down to earth.
FYI, I am preparing a crazy flying wing, the motor (electric) will spin a 5.25X6.25 @ 42-43K rpm... talk about rpm!!!
Inrunners have a natural tendency to spin at high rpms (even higher than glow's) which is good for EDF/cars/boats/helis but not for airplanes or sailplanes. Thus people:
1. matched high kv inrunners to gearboxes
or
2. created low kv inrunners like Neu's ORK/Mega/ Plettenberg all of these are good stuff by the way, but they don't like spinning at rpms below 10-20K
Then people came with the idea of a rotating case, and here came the outrunners. They have more torque, but can also spin at high rpm depending on the winding. To reliably spin at high rpms, an outrunner should have a well balanced cage and at least 2 ball bearings to support the cage. They are less efficient than inrunners but doesn't need a gearbox (which eats part or all of the inrunner's advantage in efficiency)
So why people are putting oversized/low pitch props on their electric model? I have an opinion based on facts, thus we can't infer it is a fact as it is a mere interpretation of observations.
Before lipos battery packs were heavy to fly a .45 plane, you needed a 18sub-C cells pack weighting 42oz. To be able to fly it securely, you needed a lot of thrust thus an underpitched prop.
Nowadays big props are mostly for 3D flyers, parkflyers or everything needing thrust like sailplanes (I will use a 18.5X12 on a new project).
my 2c
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RE: Aurora 60 Build Thread - Electric Power - 
