what's the speed of blades of ceiling fan in miles/hour,where the RPM of the fan is..

[abhi@eda]

what's the speed of blades of ceiling fan in miles/hour,where the RPM of the fan is 300 RPM and radius of the fan or length of blade is 1.91Feet ?

i calculated the circumference of the circle,then i converted the calculated how much RPM per second,in this case it 300/60 = 5 Revolutions per second

then i calculated the circumference * 5,so i have the speed of the blades per second,i then multiplied it to get speed/minute,then hour,and finally got 41 miles/hour,is it correct?

is it the true speed of the Ceiling fan Blades?

 

[barry]

It's the speed of the END of the blade.

 

[ArNvC]

I think your ceiling fan rpm is quite ok which is 300rpm. Length of blade is 1.91 feet? i think it is the blade span. Then you calculate rps. Ok. You get the data as cm/sec, then convert to miles/hr. Is that right? So you need the Tip speed?

More info here: **broken link removed**

 

[albbg]

Your calculation is correct.

The end of the blade travel 2*Π*1.91*300=3600 feet/minute that means 216016 feet/hour
that converted in miles gives 40.91 miles/hour

 

[abhi@eda]

I think your ceiling fan rpm is quite ok which is 300rpm. Length of blade is 1.91 feet? i think it is the blade span. Then you calculate rps. Ok. You get the data as cm/sec, then convert to miles/hr. Is that right? So you need the Tip speed?

More info here: **broken link removed**

yes,you are right,the 1.91 feet is the Blade span.

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so its ~40 miles/hour at tip ,but at the middle of the blade,the speed is less than Tip.. but i want to know the Air speed the blade is experiencing,any ideas on how to calculate it?

 

[ArNvC]

but i want to know the Air speed the blade is experiencing,any ideas on how to calculate it?

What exactly are you trying to do? A ceiling fan can only circulate the air which is present at its surroundings. Are you trying to harness wind power with it? :wink:

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On a serious note...you can find the speed at the middle of the blade by halving the blade span with highly approximate results. Rather it would be erroneous also because the middle of any given ceiling fan is curved inwards. And there will be some air pressure considerations too.

 

[D.A.(Tony)Stewart]

Meanwhile the disks in your 3.5" drive @10K RPM go at 87 MPH../// assuming 1.5" radius.

 

[abhi@eda]

What exactly are you trying to do? A ceiling fan can only circulate the air which is present at its surroundings. Are you trying to harness wind power with it? :wink:

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On a serious note...you can find the speed at the middle of the blade by halving the blade span with highly approximate results. Rather it would be erroneous also because the middle of any given ceiling fan is curved inwards. And there will be some air pressure considerations too.

No,not trying to harness wind power lol

im just little confused,if the tip speed is 41 miles/hour ,then if i calculate the middle point of the blade with same math,then it will be around 21 Miles/hour and it decreases as radius decreases..

but my question is,the blade is connected to fan,so the blade speed should be same as the rotor speed,so blade tip speed = rotor speed, if blade tip is at 41miles/hour then the motor should be rotating at 41miles/hour...

am i doing something wrong??

 

[D.A.(Tony)Stewart]

rotor only moves at angular velocity.
tip also moves at same angular velocity but converted to a scalar linear velocity.

 

[albbg]

Blades and rotor will have the same angular speed but not the same linear speed. The tip of the blade will run a circumference that is double, with respect to the mid point, in the same time then angular speed is the same but linear speed is double.
Going toward the center, while the angular speed will remain always the same, the linear speed will decrease down to (theoretically) zero in the exact center of the axis of rotation because there the radius (and then the circumference) is zero.

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rotor only moves at angular velocity.
tip also moves at same angular velocity but converted to a scalar linear velocity.

Just a question about english language: I never really understood the difference between the two words "speed" and "velocity". When I've to use "speed" and when "velocity" ?

 

[abhi@eda]

well,then i need to calculate the Angular velocity of the blade where the RPM of the rotor is 300RPM

i got the angular velocity for 300 RMP as 31.42 Radians per second,so the blades are turning at 31.42 Radians per second...

and velocity = ωR
so its 31.42 * Linear velocity where Linear velocity is 41miles/hour

so angular velocity is also 18.35 meter per sec or 41 miles/hour

im confused,how can i calculate the speed of the rotor if it turns at 300RPM which has 0.5842meter blade connected ?

 

[barry]

you're comparing apples and oranges. The angular velocity is constant everywhere on your fanblade, the LINEAR velocity is not. And you don't "need to calculate the angular velocity of the blade", you already stated that it's 300RPM!!

 

[abhi@eda]

you're comparing apples and oranges. The angular velocity is constant everywhere on your fanblade, the LINEAR velocity is not. And you don't "need to calculate the angular velocity of the blade", you already stated that it's 300RPM!!

but i want the angular velocity in Miles/hour,it's in RPM... so if i get the angular velocity in Miles/hour,that will be the true speed of the fan blades,as the linear velocity changes for every point on the blades depending on its radius..

so how can i convert that 300RPM to Miles/hour? is it possible?

 

[barry]

You CAN'T have angular velocity in mph, that's like saying I want to know my weight in inches.

People here keep trying to explain this to you, but you seem to not be listening. I'll try this louder:

THE LINEAR VELOCITY OF THE FAN BLADE DEPENDS WHERE ON THE BLADE YOU ARE MEASURING IT.

 

[albbg]

so how can i convert that 300RPM to Miles/hour? is it possible?

You can convert minutes in hours, but how can you directly convert rotation in miles ? it makes no sense. As the name said, the angular velocity represent the motion of the angle (in degree or radians); you can convert between angle and "rotation" because 1 complete rotation = 360 degrees. For instance, if you want you can convert RPM into degrees/hour.

Linear velocity is, instead, the motion in length, that is meters, miles, etc..

 

[albert22]

You cannot convert angular velocity to linear velocity without knowing the radius in the same way that you cannot convert and angle to a linear distance.
What is 45degrees to a distance? It does not make sense by itself. It is only possible if you consider the full geometry of the problem.

The differences in English between words is:
speed is a scalar (only magnitude of how fast an object moves)
velocity is a vector ( how fast and in which direction moves)

 

[ArNvC]

You can convert minutes in hours, but how can you directly convert rotation in miles ? it makes no sense. As the name said, the angular velocity represent the motion of the angle (in degree or radians); you can convert between angle and "rotation" because 1 complete rotation = 360 degrees. For instance, if you want you can convert RPM into degrees/hour.

Linear velocity is, instead, the motion in length, that is meters, miles, etc..

These posts explain everything...dont confuse yourself

 

[elecbaba]

This is important concept. Earth rotates in24 hours around its own axes. There are different satellites beaming towards a particular area. They have different speed according to their distance. from earth. Concept of lever also apply in the same application.

It can exert maximum force near center and minimum at most distant point where speed is maximum. At the center angular velocity is the same but speed is zero. If you need the speed of rotor where blades are attached. measure its distance from center. For example if it is 4 inches, apply it into the formula and fing speed. See how a manjanik works.

It is explained under the same concept that how you get different speeds at same RPM in different gears in your car

. You can tell what bigger and small pulleys do.

Just a question about english language: I never really understood the difference between the two words "speed" and "velocity". When I've to use "speed" and when "velocity" ?

Speed or Velocity Definitions:

Speed is the rate of motion, or the rate of change of position. It is expressed as distance moved (d) per unit of time(t). Speed is a scalar quantity with dimensions distance/time. Speed is measured in the same physical units of measurement as velocity, but does not contain an element of direction. Speed is thus the magnitude component of velocity. Velocity contains both the magnitude and direction components.

 

[abhi@eda]

thank you all,now i get the idea,the angular velocity on any point on blade is same but the linear velocity changes as the radius increases

for a 300 RPM angular velocity = 300RPM * (2*Pi) =1,884 Radians per minute

so 1,884/60 = 31.42 Radians per second,where 1 radian is 57.32 degrees

whole blade rotates at 31.42 Radians per second..



and now assume if i want to calculate how much air speed the blade experiences as it runs at 300 RPM in a room

the blades creates the airspeed against as it rotates..

so if we take the linear velocity of the blade tip,which is 41 miles/hour,the blade tip really doesn't experience 41miles/hour airspeed ,does it?

as the linear velocity decreases as the point on blade is closer to the center,then the airspeed decreases with it..

or my understanding is wrong?

 

[barry]

You are certainly getting your brain tied in a knot. Airspeed is the speed of an aircraft relative to the air; I don't think it's a term applied to fans. Are you asking what the speed of the blade tip is? Then YES, it's 41 MPH. And if you want to call it "airspeed", then go ahead. If the air is stationary, then the blade tip is moving at 41MPH relative to the air.