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Old Apr 12, 2012, 06:11 PM
"Free" in Christ! #F3P
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Question
2 or 3 Blade Propellers?

Hi Guys,

I am wondering why everyone uses 2 blade propellers instead of 3 bladed on there F3P planes?

Wouldn't 3 blades lower amps and torque?

Free
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Old Apr 12, 2012, 07:16 PM
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Basic science: the most efficient prop has only one blade, therefore add blades wastes power.
2 blades is the engineering compromise to answer the dynamic balance issue. We see more than 3 blades to further address compromise, ie: 4 blades to allow the CV Corsair to have reasonable ground clearance without a long landing gear which would not hold up to carrier use. In multiengine planes more blades allow motors to be closer to fuselage and each other, reducing wing stress, and power out issues etc
Or in models, 3 blades in IMAC to limit prop noise.
So in F3P we go with the best 'available' efficiency since we dont need to compromise
much. Check out F1D to see single blade props in use
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Old Apr 12, 2012, 08:24 PM
"Free" in Christ! #F3P
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Thank you Crossup,

Would a three blade prop reduce torque?

Free

P.S. If I use a 2 blade 8x4.3 prop, what would the three blade equivalent be?
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Old Apr 13, 2012, 01:49 AM
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53859 Niederkassel, Germany
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Quote:
Originally Posted by Free View Post
...
Would a three blade prop reduce torque?
...
That depends ...

Power is proportional to Torque x rpm. Using a less efficient prop, you would need to increase the power to achieve the same thrust.

This can either be achieved by an increase in torque, rpm or a bit of both.

This is also independent of the type of prop (2-, 3-, 4-blade) . You can achieve a certain amount of thrust bei either running a big prop at low rpm (high torque) or a smaller prop at higher rpm (low torque). A bigger prop is more efficient and it also helps to slow down the model in those vertical down figures.

Jürgen
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Old Apr 13, 2012, 10:38 AM
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Thank you Crossup and Jurgen,

Now I understand why people use 2 blade props!

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