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Rotor-wing question



 
 
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  #1  
Old September 22nd 05, 07:03 AM
D. Andrews
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Default Rotor-wing question

Hello all,

This is my first time posting here, but I figured maybe you all could
help me out with a question that has been nagging at me for quite a
while. Forgive me if this seems like a stupid question.

Here goes:

Does a helicopter, without lateral movement, have the ability to fly
down, or does it merely stop holding itself up?

I don't know if that makes sense, but I don't know of a better way to
word the question. I would be happy to clarify if necessary, but i
don't know what to add.

Ads
  #2  
Old September 22nd 05, 07:34 AM
Dikkie Dik
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Default

It "stops holding itself up." If you unload the rotor, any air
disturbance can cause so much blade flapping movement that the blade
hits the stops. It could break and come off then. Without stops, the
blade would probably hit a part of the helicopter itself or touch the
ground when standing on the field.
So the rotor is not designed to push you down.

Best regards

D. Andrews wrote:
Hello all,

This is my first time posting here, but I figured maybe you all could
help me out with a question that has been nagging at me for quite a
while. Forgive me if this seems like a stupid question.

Here goes:

Does a helicopter, without lateral movement, have the ability to fly
down, or does it merely stop holding itself up?

I don't know if that makes sense, but I don't know of a better way to
word the question. I would be happy to clarify if necessary, but i
don't know what to add.

  #3  
Old September 22nd 05, 04:53 PM
Simon Robbins
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"The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in
message ...

It stops holding itself up.


But, in an auto-rotation, the mains are still generating lift. Even in a
vertical auto the helicopter is descending slower than it would in a
complete free-fall. So surely it is "flying" down?

Si


  #4  
Old September 23rd 05, 04:25 AM
Stuart & Kathryn Fields
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If I understand the question, the helicopter decreases it's lift by reducing
pitch, which was balancing the weight, and a net force downward is created.
This force is opposed by the drag created by the downward velocity and a
steady state is achieved in essence, still flying, and still in a balanced
condition, but the lift force is now less than the weight. At a certain
downward velocity, you can get a Vortex Ring State created and increase your
downward velocity remarkably.

--
Stuart Fields
Experimental Helo magazine
P. O. Box 1585
Inyokern, CA 93527
(760) 377-4478
(760) 408-9747 general and layout cell
(760) 608-1299 technical and advertising cell

www.vkss.com
www.experimentalhelo.com


"D. Andrews" wrote in message
...
Hello all,

This is my first time posting here, but I figured maybe you all could
help me out with a question that has been nagging at me for quite a
while. Forgive me if this seems like a stupid question.

Here goes:

Does a helicopter, without lateral movement, have the ability to fly
down, or does it merely stop holding itself up?

I don't know if that makes sense, but I don't know of a better way to
word the question. I would be happy to clarify if necessary, but i
don't know what to add.



  #5  
Old September 23rd 05, 01:38 PM
Andrew Crane
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Default


"Dikkie Dik" wrote in message
...
It "stops holding itself up." If you unload the rotor, any air
disturbance can cause so much blade flapping movement that the blade
hits the stops. It could break and come off then. Without stops, the
blade would probably hit a part of the helicopter itself or touch the
ground when standing on the field


You are talking complete crap. If you don't understand the dynamics, please
do not post answers. Hint: watch a r/c helicopter flying upside down.

Unloading the rotor, in isolation to any other factor, is not a problem at
all, even with a teetering head.

It looks like you are thinking of the classic mast-bumping miscalculation
which is brought about by the pilot of a teeter-head trying to correct a
roll, not by the rotor being unloaded. (although the latter of course was a
factor bringing about the need for correction).

Also, unless you are hovering over something really silly, the air
disturbances causing your flapping are subjecting forces equally on both
blades.

I'm not even going to comment on bringing stops into the equation.

Regards
Andrew

--
Inweb Networks 01784494400 www.inweb.co.uk
www.rectel.co.uk -- record your phone calls and retrieve them online without
registering. Just call 08719009000.


  #6  
Old September 25th 05, 01:10 AM
Beav
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Default


"D. Andrews" wrote in message
...
Hello all,

This is my first time posting here, but I figured maybe you all could help
me out with a question that has been nagging at me for quite a while.
Forgive me if this seems like a stupid question.

Here goes:

Does a helicopter, without lateral movement, have the ability to fly down,
or does it merely stop holding itself up?

I don't know if that makes sense, but I don't know of a better way to word
the question. I would be happy to clarify if necessary, but i don't know
what to add.


I'm not sure what the question IS exactly, but let me see if I can try to
understand it.

Does a helicopter "fly" down or merely stop holding itself up?

Well if the pitch of the blades is reduced beyond the point where the blades
provide less lift than required to hold the helicopter in the air (and it's
not travelling in any direction giving translational lift), then the heli
will descend.

This isn't exactly "flying down", it's more "not being held up" as
efficiently as it was. The amount of "hold" varies with the pitch of the
blades and the power from the engine. More of both and the heli rises, less
of both and it descends. Just enough of both and it sits at a given height.
(in simple terms of course)



--
Beav

Reply to "beavis dot original at ntlworld dot com" (with the obvious
changes)


  #7  
Old September 25th 05, 01:11 AM
Beav
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Default


"The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in
message ...
On Thu, 22 Sep 2005 16:53:09 +0100, "Simon Robbins"
wrote:

"The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in
message ...

It stops holding itself up.


But, in an auto-rotation, the mains are still generating lift. Even in a
vertical auto the helicopter is descending slower than it would in a
complete free-fall. So surely it is "flying" down?


I think the OP was inferring the helicopter pushed itself down under
power. In an auto, yes, the mains are generating lift - just not
enough to equal the force of gravity. Enough to slow your descent. I
won't get into the flare portion.


You'd better, or you're buying some new parts :-)


--
Beav

Reply to "beavis dot original at ntlworld dot com" (with the obvious
changes)


  #8  
Old September 28th 05, 06:29 AM
Lionel
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Default


Beav wrote:
"D. Andrews" wrote in message
...
Hello all,

This is my first time posting here, but I figured maybe you all could
help
me out with a question that has been nagging at me for quite a while.
Forgive me if this seems like a stupid question.

Here goes:

Does a helicopter, without lateral movement, have the ability to fly
down,
or does it merely stop holding itself up?

I don't know if that makes sense, but I don't know of a better way to
word
the question. I would be happy to clarify if necessary, but i don't
know
what to add.

First of all there is no such thing as a stupid question! So ask away,
some of spent many years studing and what do we have to show for it?
Just a bunch of stuff filed away in our minds!

Does a helicopter, without lateral movement, have the ability to fly
down,
or does it merely stop holding itself up?

No! it does not fly down, it will hover if the lift is equal to the
weight, thus in a hover the weight is equal to lift, and any change in
lift will change the up or down movement of the airframe. With enough
collective you can continue to rise until the airframes ceiling is
reached.

I have posted an html page for you! I borrowed it from Shirosky to
answer your question, follow the link to:

http://abnops.com/How%20a%20Helicopter%20Works.htm

Also there is a neat helicopter crash video located at

http://abnops.com/links.html


Best Reguards!

Lionel

  #9  
Old October 2nd 05, 11:43 AM
Lionel
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Posts: n/a
Default

say what you might! I have lived through three crashes once due to
enemy fire so I think I have earned to say neat if I want to! If you
dont like well! Tough!

 




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