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HomeAircraftHelicopterHelicopter Main Discussion › Question about head speed
01-02-2011 10:58 AM  7 years agoPost 21
Mr. Miyagi

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Detroit, Michigan

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Last I heard head speed is measured in RPM, revolutions per min. It does not matter if its at the root or 100' out
if I am wrong I will admit that I am, but I don't think I am. I will get to the bottom of this and get back with facts.

You're not a "pilot" if you fly an RC helicopter. Sorry to crush your dreams #HardTruth

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01-02-2011 02:04 PM  7 years agoPost 22
Heli 770

rrProfessor

USA.

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Commandant_Lassard
You looking for RPM. or Blade tip Speed?

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01-02-2011 03:12 PM  7 years agoPost 23
ShuRugal

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Killeen, TX

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There are two kinds of optical tachometers used in this hobby. The first kind has a simple photodiode, and it measures "blinks" per minute. The second has a high-speed shutter, and it works by operating the shutter at varying speed until the shutter speed aligns with the rotor speed, producing a static image of the spinning rotors.

The kind you are asking about is the first. It works by holding it near enough to the blades for the photodiode to pick up on the change in light as the blade passes by it. This type of tach does not care what the velocity of the blade is as it moves by, it only counts how many times per minute it sees a blade. The very basic type displays this raw number, and you divide by the number of blades on your bird to get RPM. Other versions of this tach have a switch to tell it how many blades on your model, and it does the match automatically and displays RPM.

In both types of tachometer, linear speed is never being measured: they both directly measure how many times per minute the head is rotating.

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01-02-2011 03:29 PM  7 years agoPost 24
McKrackin

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Lucasville,Ohio

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Quote
if I am wrong I will admit that I am, but I don't think I am.
You are definitely wrong.lol...

When the bolt in the root has made one revolution around the main shaft,so has the tip of the blade.

Even the RPM on the side of the main shaft itself is turning the same RPM as the blade tips.

I'd like to see how someone sets up a heli that makes the blades turn more RPM's than the shaft.lol...

If the blades were 100 miles long and the tips were traveling super sonic,they would still be turning the same RPM as the root.

I literally never use the word literally right.

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01-02-2011 03:39 PM  7 years agoPost 25
ShuRugal

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Killeen, TX

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way to go mcrackin, that's exactly what he said.

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01-02-2011 03:46 PM  7 years agoPost 26
McKrackin

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Lucasville,Ohio

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way to go mcrackin, that's exactly what he said.
Who said?
Did I miss something?

I literally never use the word literally right.

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01-02-2011 04:14 PM  7 years agoPost 27
GyroFreak

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Orlando Florida ...28N 81W

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Or when the blade breaks away from the blade holder, blade rpm goes pretty much to near zero while main shaft continues to turn at X rpm. .
This is a case of RPM turning into linear velocity. Some of us have painfully experienced this strange law of physics.

I think about the hereafter. I go somewhere to get something, then wonder what I'm here after ?

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01-02-2011 05:31 PM  7 years agoPost 28
ShuRugal

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Killeen, TX

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did i miss somethng?
excerpt from the text you quoted.
...revolutions per min. It does not matter if its at the root or 100' out
excerpt from your "rebuttal"
If the blades were 100 miles long and the tips were traveling super sonic,they would still be turning the same RPM as the root.
nowhere in the text you quoted did he say that the RPM of the shaft is different from the RPM of the blades... He said that RPM is the same at center of rotation or 100 feet out.

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01-02-2011 05:35 PM  7 years agoPost 29
McKrackin

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Lucasville,Ohio

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excerpt from your "rebuttal"
Read a little closer then.
I wasn't rebutting that statement.I agree with it.

Mr Miyagi said he doesn't agree with that but may be wrong.
I simply said that he is in fact wrong.

I see how it may have been misread so I edited it for clarity.
Read Miyagis first post on this page.

I literally never use the word literally right.

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01-02-2011 06:00 PM  7 years agoPost 30
AirWolfRC

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42½ N, 83½ W

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This should not be a problem for Mr Miyagi . . . the real one anyway
When people generally measure head speed, are they measuring from the blade root or the blade tip? Because the tips would be spinning considerably faster according to physics.
Spinning ? ? When something is spinning, it is going around in circles and the speed of something going around in circles is measured in Revolutions Per Minute. This measurement is not to be confused with a linear velocity like tip speed.

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01-02-2011 06:04 PM  7 years agoPost 31
Michaelm0268

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Louisiana

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The iPhone has an app called heli tach that is pretty accurate.

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01-02-2011 06:13 PM  7 years agoPost 32
AirWolfRC

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42½ N, 83½ W

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Does that app work on electric helis ?
Is it looking for exhaust sound to get speed ?

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01-02-2011 06:16 PM  7 years agoPost 33
Michaelm0268

rrApprentice

Louisiana

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Yes you point it at the head of the helicopter and it calculates it for 2-3 bucks you can't beat it.

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01-02-2011 06:19 PM  7 years agoPost 34
McKrackin

rrProfessor

Lucasville,Ohio

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Does that app work on electric helis ?
Is it looking for exhaust sound to get speed ?
It's optical.
Works with the camera.
At least the one I saw did.

I literally never use the word literally right.

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01-02-2011 06:20 PM  7 years agoPost 35
Michaelm0268

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Louisiana

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Yea works with the camera.

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01-02-2011 06:24 PM  7 years agoPost 36
AirWolfRC

rrProfessor

42½ N, 83½ W

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That sounds like an interesting bit of programming.

What's the range on that ?

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01-02-2011 08:20 PM  7 years agoPost 37
ShuRugal

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Killeen, TX

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Read a little closer then.
You are definitely wrong.
i don't see any two ways to read that phrase.

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01-02-2011 08:26 PM  7 years agoPost 38
Michaelm0268

rrApprentice

Louisiana

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I was wondering the range as well I personally don't know

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01-02-2011 08:36 PM  7 years agoPost 39
McKrackin

rrProfessor

Lucasville,Ohio

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i don't see any two ways to read that phrase.
It's aimed at Miyagi.
HE is the one that says the tip of the blades turn at a higher RPM than the root.

YOU are just determined to make me out as being wrong.
Have you read the thread or do you just troll along behind me?

I literally never use the word literally right.

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01-02-2011 10:13 PM  7 years agoPost 40
ShuRugal

rrKey Veteran

Killeen, TX

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ah, so, what you said was not aimed at the text you were quoting?

and to answer your question, yes, i have read the thread. I now must pose the same question back onto you, because my first post was a rather exhaustive answer to myagi's questions.

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