jmfitzgerald

I am building the AT-6 from the free plans in this months Model Airplane News mag... I calls for a speed 400 motor direct drive and a 5 1/2x3 or 5 1/4x 4 prop... it says with an 8 cell 600mAh+ pack, you can get ~5 min of flight time. just interested in the differences between direct drive and geared setup... i see with most geared setups, a much larger prop is used...is this to compensate for the slower turning shaft? is there more flight time with it geared? do you not have as much power (plane not able to fly correctly)? any lasting effects on the motor? any info would help! thanks!

woodduck-RCU

Using a geared setup should prolong the engine life, draw fewer amps and provide a longer flight time.
You could probably use a 7x5 or 8x4 prop.

Matt Kirsch

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Air is a fluid that becomes turbulent when you sweep something like a propeller blade through it. The faster you sweep that blade through the air, the more turbulent the surrounding air becomes, and the less "bite" the following propeller blade can get.

By gearing down and using a larger prop, you not only get a bigger bite on the air, you get a cleaner bite. That is to say that the transfer of power from propeller to air is more efficient, and you can get the same result from less power.

There are other benefits, such as the ability to trade off top speed for static thrust. A slower-spinning prop may not be able to move the airplane as fast as a high-revving prop, but it will create signifigantly more thrust. This allows you to match the top speed of the power system with the top speed of the plane, and put more power toward thrust, which gives better acceleration.

flash over

OK, but how do the outrunners compare in these respects

Time Pilot

Outrunners are not geared, but they work like they are geared. They provide more torque but less speed so you can use a larger prop for the same reasons Matt said.

Brushless motors are also more efficient, so you get more power transfered to the prop. Some outrunners can also handle enourmous amounts of current that would significantly shorten a 400 motor. More current means potentially more power to the prop--how much depends on the battery.

jmfitzgerald

Thanks for the input, makes more sence now. So really, if i can get a geared set up in there, that would be a better option to go with??? Has or is anybody else building this plane?

Thanks again!

flash over

Are outrunners typically lighter or heavier compared to a normal brushless with a gearbox,what about durability.