Welcome Guest
HeliTorque
  
User Control Panel

Security Code: : Security Code
Type Security Code Here: :
 
Register Here
Lost Password?

Online Stats:
Visitors: 41
Members: 0
Total: 41

Membership:
New Today: 0
New Yesterday: 0
Registering: 0
Members: 6662
Latest: chrisw

Most Ever Online
Visitors: 447
Members: 10
Total: 457


HeliTorque :: View topic - Gyroscopic Precession
Forum FAQ
Forum FAQ
Search
Search
Memberlist
Memberlist
Usergroups
Usergroups
Profile
Profile
Contact Manager
Contact Manager
Log in
Log in
Log in to check your private messages
Log in to check your private messages
HeliTorque Forum Index » Flight Dynamics

Post new topic   Reply to topic All times are GMT
Gyroscopic Precession Goto page 1, 2, 3, 4  Next
View previous topic :: View next topic  
Author Message
Heliwhore
H Addict
H Addict


Offline
Joined: Mar 29, 2006
Posts: 289
Location: Scotland


australia.gif

PostPosted: Mon Feb 16, 2009 5:05 pm    Post subject: Gyroscopic Precession Reply with quote

OK, blame WG for this one.

Is it possible to have gyroscopic precession in a non-rigid rotor system, I know many instructors teach it, and even Wagtendonk (is that the spelling?) preaches it.

But just because it is a simple and accepted explanation doesn't mean it's right.
_________________
Generally wrapped in rubber, be it in the air or on the water.
Back to top
View user's profile Send private message
WhirlyGirl
Administrator
Administrator


Offline
Joined: Jul 20, 2004
Posts: 3702
Location: Birmingham, UK


uk.gif

PostPosted: Mon Feb 16, 2009 5:13 pm    Post subject: Reply with quote

Dude, we've opened a can of worms... I'm looking forward to the replies though. Laughing

Sarah
_________________
CPL(H) / FI(H) - Cabri G2, R22, S300, R44, B206
Flight Examiner (H), Ground Examiner (H)
Back to top
View user's profile Send private message Visit poster's website Skype Name
Heliwhore
H Addict
H Addict


Offline
Joined: Mar 29, 2006
Posts: 289
Location: Scotland


australia.gif

PostPosted: Mon Feb 16, 2009 5:16 pm    Post subject: Reply with quote

You know Veeany can only resist for so long.
_________________
Generally wrapped in rubber, be it in the air or on the water.
Back to top
View user's profile Send private message
afterburner
H Addict
H Addict


Offline
Joined: Feb 20, 2008
Posts: 1059
Location: New York


usa.gif

PostPosted: Mon Feb 16, 2009 5:38 pm    Post subject: Reply with quote

Ummmm

There are fully-articulated,
There are semi-rigid,
and there are rigid.......

Can you define a non-rigid system for me? That's a new one on me unless I need to add it to my UK/US dictionary. Laughing

As for gyroscopic precession............
Gyroscopic Precession is the resultant action or deflection of a spinning object when a force is applied to this object. Regardless of the rotor system, if it spins and we try to tilt it, GP exists. Can't change physics.

AB
_________________
"A Copter Pilot's Life has it's... ups and downs"
Bell 47-206, Schweizer 300/500, Citation 525
Back to top
View user's profile Send private message
animalsticks
H Addict
H Addict


Offline
Joined: Jul 12, 2008
Posts: 741
Location: solihull


uk.gif

PostPosted: Mon Feb 16, 2009 6:47 pm    Post subject: Reply with quote

my take on it until veeany puts something Laughing

if its anything but a rigid rotor surely the accelerative torque produced by GP can't be translated to the head as the change of path stops at the flapping hinge. is it not people getting confused with phase lag in regards to fully articulated rotorheads.

Now i'm writing this i am thinking that with a teetering hinge you would have the rotation and two opposing forces so in theory...
...ok now i'm confusing myself... Very Happy
_________________
PPL (H)
R22
B206
If it moves i want a go
Back to top
View user's profile Send private message Yahoo Messenger MSN Messenger
veeany
Moderator
Moderator


Offline
Joined: Apr 07, 2005
Posts: 688
Location: England


uk.gif

PostPosted: Mon Feb 16, 2009 7:59 pm    Post subject: Reply with quote

Quote:
There are fully-articulated,
There are semi-rigid,
and there are rigid.......


And there are Robinsons

My guess is what HW means by a non-rigid system is something where the blades are free to flap independently. Like a 300, 500, 109 etc.

I'll ask a question thats partially related to the gyros thing which I could probably phrase better if I thought about it. But it shoud get the debate fuelled.

Quote:
Does applying a force to something cause it to move ?
Back to top
View user's profile Send private message Visit poster's website Skype Name
afterburner
H Addict
H Addict


Offline
Joined: Feb 20, 2008
Posts: 1059
Location: New York


usa.gif

PostPosted: Mon Feb 16, 2009 8:57 pm    Post subject: Reply with quote

animalsticks wrote:
my take on it until veeany puts something Laughing

if its anything but a rigid rotor surely the accelerative torque produced by GP can't be translated to the head as the change of path stops at the flapping hinge. ............ok now i'm confusing myself... Very Happy


Yes, you are confusing yourself. If he is referring to the system on the 300/500 etc, then he is referring to a fully articulated rotor system in which the blades are free to flap, lead/lag (or hunt) and feather.

A flapping hinge (horizontal hinge) is part of the rotor system to overcome the effects of Coriolis force.
A lead/lag or drag hinge (vertical hinge) is used to overcome di-symmetry of lift. Neither has anything to do with gyroscopic precession.

If it rotates, it will experience GP. NO way around it.

Veeany,
No necessarily. The rotating body must only "experience" the force being applied. The amount of GP is directly related to the actual deflection of the rotating body from the plan of rotation. It is a matter of Precession therory.

The physics lecture usually runs all day but here it is in a nutshell. (I am renaming it The Veeany Theorim... Laughing )

Precession is due to the fact that the resultant of the angular velocity of rotation and the angular velocity produced by the torque is an angular velocity about a line which makes an angle with the permanent rotation axis, and this angle lies in a plane at right angles to the plane of the couple producing the torque. The permanent axis must turn towards this line, since the body cannot continue to rotate about any line which is not a principal axis of maximum moment of inertia; that is, the permanent axis turns in a direction at right angles to that in which the torque might be expected to turn it. If the rotating body is symmetrical and its motion unconstrained, and if the torque on the spin axis is at right angles to that axis, the axis of precession will be perpendicular to both the spin axis and torque axis. Under these circumstances the period of precession is given by:
T_p = \frac{4\pi^2I_s}{QT_s} In which Is is the moment of inertia, Ts is the period of spin about the spin axis, and Q is the torque.

In general the problem is more complicated than this, however.

Got it all down pat now?
Oh, by the way....I didn't make that up. It's all valid theory.


Very Happy
_________________
"A Copter Pilot's Life has it's... ups and downs"
Bell 47-206, Schweizer 300/500, Citation 525
Back to top
View user's profile Send private message
Ascend_Charlie
H Addict
H Addict


Offline
Joined: Aug 23, 2005
Posts: 266
Location: On a course.... golf course


australia.gif

PostPosted: Mon Feb 16, 2009 10:32 pm    Post subject: Reply with quote

Precession is only a convenient way to explain the phenomenon of phase lag / advance angle.

If GP were TRULY the cause of it, then advance angle would always be 90 degrees.

It ain't. in some machines it is 72 degrees, in others it is 84, in most it is very close to 90, and it is simply the rotational distance it takes for the blade to experience the increase in pitch angle applied by the swash plate, to start moving up as a result of the accelerative force, to have its angle of attack reduced by the increased induced flow, and to peak out at maximum upward deflection before flapping down again on the other side.

But as an approximation to the dumbos in the street, a gyroscope is a good place to start. It ISN'T the cause. Look up Shawn Coyle or Nick Lappos for a more detailed debunking of the GP theory.
Back to top
View user's profile Send private message
veeany
Moderator
Moderator


Offline
Joined: Apr 07, 2005
Posts: 688
Location: England


uk.gif

PostPosted: Mon Feb 16, 2009 10:52 pm    Post subject: Reply with quote

Or Ray Prouty The Article is entitled something like "Is the Rotor A Gyro"

I'll put some of this in detail in the next few days but for now think about these points.

Can the behaviour of a rotor system be described pretty much by how it reacts to the aerodynamic forces acting up it.

If the wind blows on a rotor disc from the front of the aircraft (in the hover or on the ground) which way will the disc flap and why ?

Where is the most lift force generated in this example ? Would the biggest lift force result in the biggest amount of flap or the biggest rate of flap ?

Could it be that the gyroscopic properties of a spinning rotor system are overwhelmed by the aerodynamic ones which work in a similar sense ?

Could it also be that some member(s) of the forum believe that Wikipedia should be quoted without question ? Laughing
Back to top
View user's profile Send private message Visit poster's website Skype Name
animalsticks
H Addict
H Addict


Offline
Joined: Jul 12, 2008
Posts: 741
Location: solihull


uk.gif

PostPosted: Mon Feb 16, 2009 11:04 pm    Post subject: Reply with quote

i just posted saying "that's what i read on wikipedia" then saw veeanys post... back pedal back pedal!!! Laughing
_________________
PPL (H)
R22
B206
If it moves i want a go
Back to top
View user's profile Send private message Yahoo Messenger MSN Messenger
Heliwhore
H Addict
H Addict


Offline
Joined: Mar 29, 2006
Posts: 289
Location: Scotland


australia.gif

PostPosted: Mon Feb 16, 2009 11:07 pm    Post subject: Reply with quote

Nice one AC.

A non-rigid rotor system?, teetering head system perchance? Especialy one with coning hinges as well? Things as floppy as a month old carrot. The only rigidity there would be in the lead lag, and even that is there whilst one blade leads, the other lags.

Another question, is rigidity not one of the fundamental requirements of a gyroscope?
_________________
Generally wrapped in rubber, be it in the air or on the water.
Back to top
View user's profile Send private message
SFA
Starting to 'Torque
Starting to 'Torque


Offline
Joined: Aug 23, 2006
Posts: 25
Location: Hall Green


ireland.gif

PostPosted: Mon Feb 16, 2009 11:07 pm    Post subject: Reply with quote

veeany wrote:


If the wind blows on a rotor disc from the front of the aircraft (in the hover or on the ground) which way will the disc flap and why ?

Where is the most lift force generated in this example ? Would the biggest lift force result in the biggest amount of flap or the biggest rate of flap ?


At constant RRPM would "amount" and "rate" not be directly proportional?
Back to top
View user's profile Send private message
animalsticks
H Addict
H Addict


Offline
Joined: Jul 12, 2008
Posts: 741
Location: solihull


uk.gif

PostPosted: Mon Feb 16, 2009 11:11 pm    Post subject: Reply with quote

Heliwhore wrote:
Nice one AC.

is rigidity not one of the fundamental requirements of a gyroscope?



Yes Very Happy
_________________
PPL (H)
R22
B206
If it moves i want a go
Back to top
View user's profile Send private message Yahoo Messenger MSN Messenger
afterburner
H Addict
H Addict


Offline
Joined: Feb 20, 2008
Posts: 1059
Location: New York


usa.gif

PostPosted: Mon Feb 16, 2009 11:42 pm    Post subject: Reply with quote

Ascend_Charlie wrote:
But as an approximation to the dumbos in the street, a gyroscope is a good place to start. It ISN'T the cause. Look up Shawn Coyle or Nick Lappos for a more detailed debunking of the GP theory.


I don't believe that you are trying to sell us on "debunking" the GP theory which has been part of helicopter development since the first copter flew!

I have read some of Coyle's and Lappos' works and look upon them more as fiction than fact.

Besides, I do not look upon myself as a "dumbo in the street" but rather knowledgeable, reasonable, and open minded (most of the time).

However, as far as this goes, I'll stay with the present GP theory, and so will my students.

No offense meant, and none taken.

AB

ADDED:
Read my post on the Precession Theorem which clearly shows GP is the proper explanation for the aerodynamic phenomenon.


Laughing
_________________
"A Copter Pilot's Life has it's... ups and downs"
Bell 47-206, Schweizer 300/500, Citation 525
Back to top
View user's profile Send private message
veeany
Moderator
Moderator


Offline
Joined: Apr 07, 2005
Posts: 688
Location: England


uk.gif

PostPosted: Mon Feb 16, 2009 11:50 pm    Post subject: Reply with quote

I believe the rigidity relating to gyroscopes refers the gyroscopes desire for its spin axis to remain rigid in space ( aligned where it is already) and not whether its a rigid disc.
Back to top
View user's profile Send private message Visit poster's website Skype Name
Display posts from previous:   
Post new topic   Reply to topic    HeliTorque Forum Index » Flight Dynamics All times are GMT

 
Goto page 1, 2, 3, 4  Next
Page 1 of 4

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Sponsors


Billund Air Center

Visit HeliTorque!