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virtualcomposer
11-11-2008, 08:46 AM
I've always wondered this. When a helicopter blade is spinning, is the outer part going faster then the inner? Technically, it's going as fast as the outer since it travels the 360 degrees the exact same time. So then, if that's true, then why is there more motion blur the further out the blade goes? More motion blur in a frame means faster speed right? Is this an anomaly or a physics trick?

KillMe
11-11-2008, 08:53 AM
it is completeing teh same 360 degrees rotation in the same time but the circumferance of the circle beign traveled on the tip of the blade is much greater than the circumference of the cirble at the inner sections down to 0 in the very center

therefor the speed as measured at the tip is greater than the speed further in

the rate of rotation however is teh same

RollerJesus
11-11-2008, 08:53 AM
It covers 360 degrees in the same amount of time, but the outer edge of the rotor travels along a larger circle.

A greater distance in the same amount of time equals a higher speed.

Lightwolf
11-11-2008, 09:17 AM
As a bit of trivia... this is why hard drives are faster on the sectors that are furthest away from the spindle.

Since the density on the platters and the rotational speed is constant, more data passes by the read/write head during the same time.

Cheers,
Mike

virtualcomposer
11-11-2008, 10:40 AM
it's quite an intriguing concept I think.

RollerJesus
11-11-2008, 10:44 AM
All the info you could want (probably)...

http://www.supercoolprops.com/articles/propstips.php

JeffrySG
11-11-2008, 12:24 PM
Also why ice skaters speed up when they bring their hands in towards their body. All the energy needed to make them go fast with their hands out goes with them when they bring them back in towards their body where they have less distance to travel to go in a circle.

Riff_Masteroff
11-11-2008, 05:33 PM
But: If a baseball pitcher throws a ball that is clocked at 90mph with a radar gun, does the pitcher's hand travel at 90mph at the moment of release?

Hopper
11-11-2008, 05:38 PM
But: If a baseball pitcher throws a ball that is clocked at 90mph with a radar gun, does the pitcher's hand travel at 90mph at the moment of release?
Unless there's a wind behind him... yes.

Stooch
11-11-2008, 05:41 PM
But: If a baseball pitcher throws a ball that is clocked at 90mph with a radar gun, does the pitcher's hand travel at 90mph at the moment of release?

of course. probably slightly faster than 90mph since it takes time for the ball to reach the radar detector and slow down. to be more precise, the finger tips are moving along an arc at over 90mph, the shoulder, being the pivot is relatively still.

TripD
11-11-2008, 06:04 PM
No wonder these guys are constantly battling with injuries! I remember watching a Giants game when the pitcher..... who was that guy? anyway, he pitched and immediately fell off the mound in complete anguish. bleh!

Nangleator
11-13-2008, 10:53 AM
I know a bit about this stuff.

(Moderate exception for helicopters. Not entirely sure what makes those magical things fly. I suspect it has something to do with the spinny thing on top.)

A close look at an airplane propeller will show 'wash-out,' which is a twisting along the blade so that near the hub, the angle is severe, and near the tips the angle is shallow. This is so that when the propeller is spinning, the thrust generated is even across the entire disk area. This minimizes flexing of the propeller.

Another thing about propellers is that they can't go too fast, or the tips of the propeller will go faster than the speed of sound. This creates lots of drag and is a very bad thing. Light planes typically have a maximum engine speed of about 2,600 rpm. Helicopters, with much longer rotor blades, must rotate much more slowly.

Quiet1onTheSet
11-13-2008, 11:54 PM
the speed as measured at the tip is greater than the speed further in the rate of rotation however is teh sameYep. Just as has been said, several other ways -- the velocity is greater as you move away from the rotor axis, although the rotational rate is a constant along the length of the blades. :)

krimpr
11-15-2008, 04:43 PM
Yep. Just as has been said, several other ways -- the velocity is greater as you move away from the rotor axis, although the rotational rate is a constant along the length of the blades. :)

and therefore, the tips of the blades age at a slower rate than the hub by an immeasurably small amount while they are in motion due to the speed differential between the two. Bizzare, but true. Ask Albert.

shrox
11-15-2008, 08:07 PM
The tips are traveling faster than the rotor base, this is one reason a SINGLE rotored heli cannot travel supersonically. As the rotor blades spin, as the move forward they are moving very fast in relation to the air so they get good lift, as the blades swing around to travel rearward, they approach stall speed in relation to the and air and lose lift.

I have a design for a supersonic duel rotored helicopter.

Hopper
11-15-2008, 09:38 PM
Hey shrox .. hope your fairing better these days.

*Pete*
11-16-2008, 09:45 PM
I've always wondered this. When a helicopter blade is spinning, is the outer part going faster then the inner? Technically, it's going as fast as the outer since it travels the 360 degrees the exact same time. So then, if that's true, then why is there more motion blur the further out the blade goes? More motion blur in a frame means faster speed right? Is this an anomaly or a physics trick?

the speed on the inner and outer parts are the same when counted as RPM, but not when counted as KMH.

the outer part travels a longer distances during a rotation than the inner part.

if you think of a blade that is infinite at its lenght, rotating it 45 degrees during one hour will give you a speed of movement so small that it is barely noticable 1 metre from the centre.
but at the outer edges of the blade of infinite lenght it would go supersonic, no..even faster than light, faster than any eye could be able to see it.

the speed of rotation is the same, the speed of movement is not

jameswillmott
11-16-2008, 10:07 PM
I have a design for a supersonic duel rotored helicopter.

Does it involve Great Big Rocket Engines? :)

Panikos
11-17-2008, 12:00 AM
As a bit of trivia... this is why hard drives are faster on the sectors that are furthest away from the spindle.

Since the density on the platters and the rotational speed is constant, more data passes by the read/write head during the same time.

Cheers,
Mike

I remember this quiz when I was 1st year student in Computer Studies. At that time Hard Drives were a luxury.

A relative rule says, the information is read the way it was written

toby
11-18-2008, 03:17 PM
and therefore, the tips of the blades age at a slower rate than the hub by an immeasurably small amount while they are in motion due to the speed differential between the two. Bizzare, but true. Ask Albert.
That blew my mind when I learned about it. I'll believe anything now, ghosts, boogeymen, whatever. Someone should strap two identical watches to each end their rotor blades just to demonstrate =)

Nangleator
11-18-2008, 04:50 PM
Heh. That would take rather a long time to show a detectable change.

Long time ago, I memorized Pi to 30 places. Just for giggles, I once calculated the significance of an error in the 30th digit. I believe it was on the order of a millimeter with a circle measured in light years.

virtualcomposer
11-18-2008, 05:05 PM
Heh. That would take rather a long time to show a detectable change.

Long time ago, I memorized Pi to 30 places. Just for giggles, I once calculated the significance of an error in the 30th digit. I believe it was on the order of a millimeter with a circle measured in light years.

that's quite facinating. It does bring a real importance to accuracy. How much of time difference do you thing it would be if you strapped two watches in I e and the other? Since the blade is traveling a nearly a stand still compared to light, is this a measure that is hardly calculatable?

Nangleator
11-18-2008, 05:42 PM
Not incalculable at all, just very, very small. I forget the equation, but it involves a comparison between the target speed and light speed, which is 186,262 miles per second. I remember it being non-linear, so most of the effect occurs very close to light speed. There's probably an exponent involved, or a square root somewhere.

The speed of a rotor tip would be on the order of 207 meters per second. Lightspeed in meters per second is 299,792,458.

Nangleator
11-18-2008, 05:47 PM
Oh, by the way, the GPS system measures your position by detecting the distance between you and a few different satellites. The time difference at light speed in these calculations is tiny. So, very, very accurate clocks are necessary. I think I remember those satellites each have four different atomic clocks on board.

These calculations are so sensitive that they need to take into account the fact that the satellites are traveling at orbital speed. Yes, the clocks up there run slower than they would down here.

toby
11-18-2008, 09:48 PM
It was detectable in an atomic clock that was installed in an airplane in the 50's or something like that, that was the test I saw. So just flying a prop-plane created a measurable result. I'm sure it was tiny.

virtualcomposer
11-18-2008, 10:52 PM
It was detectable in an atomic clock that was installed in an airplane in the 50's or something like that, that was the test I saw. So just flying a prop-plane created a measurable result. I'm sure it was tiny.

tiny but proved a theoretical point. I have another question. When we download updates or software, is it something minute but physical that is transferee over or is it a series of organized code that just tells the Harddrive how to organize 1s & 0s? I think it is the latter but have never been sure.