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So I'm making an airplane with a motor at the front, do I use CW or CCW props?

Pretty sure this is what counts as a puller plane (is that the right term?).

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The decision between CW (clockwise) and CCW (counterclockwise) propellers has to do with the direction your motor/engine will spin, not really in regard to where you're putting the engine on the plane. CW props will create thrust behind them when spun in a clockwise direction, and CCW props will create thrust behind them when spun in a counterclockwise direction. It's that simple. :)

For an electric motor driven plane, it probably doesn't matter which kind you get because it's highly likely that you can reverse the motor direction in the ESC (electric speed controller), but I'm not aware of any ability to do this with model plane gas engines. If you're using a gas engine, inquire to figure out either what kind of propeller the specs say to use (if this is listed) or what direction the engine spins and get the appropriate CW/CCW propellers.

If the model airplane plans/kit you have calls for a specific kind of propeller, like for example if the plane was designed to fly better with one propeller rotation direction, I'd recommend abiding by their recommendations. There are quite interesting aerodynamic and physical phenomena like P-factor which the designer may have taken into account in the aircraft layout, resulting in the design requiring a specific kind of propeller.

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  • $\begingroup$ One more question, I've seen these shiny things a few times, what are those for and do I need one? $\endgroup$ – Ceramicmrno0b Oct 7 at 20:39
  • $\begingroup$ @Ceramicmrno0b The pointy part in your link is called a 'spinner' and they are used to improve aerodynamics. $\endgroup$ – Kralc Oct 7 at 20:51
  • $\begingroup$ Yep, @Kralc is correct. to improve aerodynamics by making the propeller attachment point more streamlined and a mechanical connection. These spinners also often serve as the nut holding the propeller onto the motor. $\endgroup$ – ifconfig Oct 7 at 21:29
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    $\begingroup$ @Kralc and ifconfig, thanks. $\endgroup$ – Ceramicmrno0b Oct 7 at 21:32
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If a plane has a preference, it's probably for a clockwise prop. This dates back to before electric motors, when people hand-started glow motors. You'd kneel next to the plane, hold the fuselage with your left hand and flick the nearest blade of the prop down with your right hand (or a short piece of wood, if you valued your fingers!). That resulted in a clockwise rotation when viewed from the cockpit of the plane looking forward.

Most glow motors only ran in one direction, and most pilots are right handed, so this became the standard.

The engine torque reaction would then tend to induce a counter clockwise roll to the plane when more power was applied, i.e. a turn to the left. Thus many planes have some right-thrust angle built in to their firewall, so adding thrust will turn the plane slightly right, to counter the roll to the left.

Not all designs have this right thrust built-in, and you can reverse a brushless motor just by switching any two of the wires to the ESC, so it may not matter.

Incidentally, the writing on the prop usually goes on the front. If you fit a prop backwards it still blows in the normal direction but you only get about half as much thrust.

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