Pitch Angle?
Thread Starter
Joined: Aug 2000
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From: Australia
Pitch Angle?
Hi guys/girls,
Just a quick question to those who know the real world numbers...
From flat pitch, to full collective travel, how many degree's do the blades travel?
I have been told a rough figure of nine(9) degrees is normal....
Cheers
Just a quick question to those who know the real world numbers...
From flat pitch, to full collective travel, how many degree's do the blades travel?
I have been told a rough figure of nine(9) degrees is normal....
Cheers
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
Normal full collective for helicopters is about 18 to 21 degrees.
Most helos have about 1 to 2 degrees positive at flat collective (Navy helos can have -2 degrees to stick them to the deck)
Normal forward is 20 degrees, aft is 8 to 10 degrees (swashplate tilt) and lateral cyclic is plus and minus about 8 to 9 degrees (16 to 18 total).
Most helos have about 1 to 2 degrees positive at flat collective (Navy helos can have -2 degrees to stick them to the deck)
Normal forward is 20 degrees, aft is 8 to 10 degrees (swashplate tilt) and lateral cyclic is plus and minus about 8 to 9 degrees (16 to 18 total).
Thread Starter
Joined: Aug 2000
Posts: 121
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From: Australia
Thanks Nick,
If we are at a pitch setting that represents max torque (say a vertical climb) and apply full forward cyclic, what sort of pitch angle would be apparant on the most affected blade (guessing the retreating blade)
The reason I am asking is that I have a rotor head concept that gives me about 30 degrees of pitch angle. I need to know if this is enough for the full flight envelope.
Cheers
If we are at a pitch setting that represents max torque (say a vertical climb) and apply full forward cyclic, what sort of pitch angle would be apparant on the most affected blade (guessing the retreating blade)
The reason I am asking is that I have a rotor head concept that gives me about 30 degrees of pitch angle. I need to know if this is enough for the full flight envelope.
Cheers
Last edited by rotorque; 9th December 2005 at 10:58.
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
That box that I described is for most Sikorsky models, which have pretty high power and thus lots of collective. Generally the rigging diagram is fully additive, so that the description is almost square - full up is 20 degrees, and add then about 18 to 20 for forward cyclic., but the last few degrees are generally cut off Max forward cyclic occurs about 90 degrees earlier in rotation, so the max angle would be on the left side.
Often, these are hard to achieve because of geometry restrictions, so that the extreme corners are cut off. One can argue that at max collective, the most forward cyclic you need (to execute the max pushover while at full aft CG) is much less than 18 degrees. Similarly with left and right cyclic. Real flight data from similar models and similation data is also is used, where the control points that were actually achieved or simulated are plotted to show that they reside inside the proposed rigging box. A glance at the maintenance manual rigging instructions will tell you the real story, and most of this is public data. I don't have that data, unfortunately.
Often, these are hard to achieve because of geometry restrictions, so that the extreme corners are cut off. One can argue that at max collective, the most forward cyclic you need (to execute the max pushover while at full aft CG) is much less than 18 degrees. Similarly with left and right cyclic. Real flight data from similar models and similation data is also is used, where the control points that were actually achieved or simulated are plotted to show that they reside inside the proposed rigging box. A glance at the maintenance manual rigging instructions will tell you the real story, and most of this is public data. I don't have that data, unfortunately.
Thread Starter
Joined: Aug 2000
Posts: 121
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From: Australia
Thanks Nick,
That all makes sense. The only thing I have trouble with is the additive pitch angles that you mentioned.... If I have read correctly, the max pitch experienced for the scenario mentioned would be about 40 degrees... is that right? or can I assume, in practice, that at full collective the swashplate tilt applied for a max pushover will actually reduce the pitch of the 'advancing' blade (right side) and keep the left blade at pretty much the same pitch setting to allow the disc to tilt.
I am pictureing the swashplate from the side pivoting about a point at the very rear.
Appologise for the convoluted description.
Cheers
That all makes sense. The only thing I have trouble with is the additive pitch angles that you mentioned.... If I have read correctly, the max pitch experienced for the scenario mentioned would be about 40 degrees... is that right? or can I assume, in practice, that at full collective the swashplate tilt applied for a max pushover will actually reduce the pitch of the 'advancing' blade (right side) and keep the left blade at pretty much the same pitch setting to allow the disc to tilt.
I am pictureing the swashplate from the side pivoting about a point at the very rear.
Appologise for the convoluted description.
Cheers
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
The best way to describe it is that the corners are cut off (to respect the geometric limits of the blade or its possible fuselage contact) by assuring that the corner will not be used in flight. The logoc is that if you need full forward cyclic and full up, you can't actually be flying.
Usually a clever stop or link is added to the controls system to provide the stop as a combination of the two controls, and this has to be part of the initial design. Often, you take both controls to a rotation bar where their bellcranks both independantly rotate and are side by side. This establishes a common point from which you can run a portion from one crank to the other that makes a mutual stop. That way, when one control is rotated beyond a certain point, it drags the other control along with it, which if properly designed, removes that other control input.
Usually a clever stop or link is added to the controls system to provide the stop as a combination of the two controls, and this has to be part of the initial design. Often, you take both controls to a rotation bar where their bellcranks both independantly rotate and are side by side. This establishes a common point from which you can run a portion from one crank to the other that makes a mutual stop. That way, when one control is rotated beyond a certain point, it drags the other control along with it, which if properly designed, removes that other control input.
