Speed 3 Blade Over 2. How to work out?

[Drax21]

So I have been using OSE's calculator to work out what speed I would be getting and usually its pretty accurate but I can only be used for 2 blade props.
How can I work out the speed with a 3 blade? Mathematicians at the ready :help:
Thanks

[jevmax]

Prop pitch is prop pitch, regardless of the number of blades

[Drax21]

But a 447/3 surely would increase speed over a 447/2, no?

[photohoward1]

No. Pitch is like a gear. More blades means less slip though. Kind of like a fatter tire putting more rubber on the road. It may slow you down actually.

[Drax21]

No. Pitch is like a gear. More blades means less slip though. Kind of like a fatter tire putting more rubber on the road. It may slow you down actually.

Thanks this is useful info:thumbup1:

[jevmax]

I agree with Howard. In addition, a multi-blade prop presents a larger surface area in the water and creates more drag. In most cases, a two bladed prop will be faster.

[Chilli]

No. Pitch is like a gear. More blades means less slip though. Kind of like a fatter tire putting more rubber on the road. It may slow you down actually.

And put more load on the motor/ESC.

[Goonboy2]

Granted - a three blade prop should be slower than it's two blade equivalent and put more load on the motor & ESC but it should improve handling since there will be blade in the water at all times.

[jevmax]

Granted - a three blade prop should be slower than it's two blade equivalent and put more load on the motor & ESC but it should improve handling since there will be blade in the water at all times.

Yes. A three blade prop can have a stabilizing effect. It seems to be most noticeable with a mono.

[dana]

ive always found 3 blade to be faster, and 2 blade quicker outta the hole. contrary to others findings. i will agree that 3 blade have less torque roll on a mono or v

[iamandrew]

well 2 blade you have less mass to spin, less heat compared to 3 blade, but 3 blades just seem so smooth in the water compared with 2 blade

[lohring]

The three blade will load the motor more increasing the current draw. If the three blade has the same blade shape, diameter, and pitch as the two blade the power required will increase by 150%. With lipos the voltage won't drop much so the rpm and speed will only decrease a little. This can be compensated for by running the three blade shallower, decreasing the load.

Lohring Miller

[Drax21]

Thanks, great info:thumbup1:

[Chrisg81983]

I was told by someone that a 450/3 would be about the same load on the motor as a 455/2 so I tried it out and my eagle tree data was almost identical for the two props although it had a 2 mph difference the 450 was a tad slower

[dana]

I suppose there are many variables involved... Too many to give a definitive answer.

[lohring]

Propeller scaling is well understood. The power required varies as the diameter to the fifth power, the rpm cubed, and directly as the pitch and blade area. That's why two propellers with the same blade shape, pitch, and diameter will take 150% (3/2) times the power if one is a 3 blade and the other is a two blade.

Lohring Miller