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Westland Lynx (Merged threads)

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Westland Lynx (Merged threads)

Old 12th Mar 2001, 03:45
  #41 (permalink)  
Lu Zuckerman
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To: Grey Area

After looking at the diagram I came to the conclusion that not all helicopters have a 90-degree precession angle. It is not that they weren’t designed to have a phase angle of 90-degrees it is that through a combination of design related problems in the dynamics and rotor blade systems the phase angle will vary. I have to believe that or, I will have to download my memory of the Cheyenne helicopter. It too was designed to have a 90-degree phase angle but the rotor system had a tendency to deviate from the 90-degree phase angle. Sometimes it was in excess of 90-degrees and sometimes it was less than 90-degrees. This was caused by a combination of things that included the design of the blades and the stiffness of the blades along with speed and gross weight.

The problem manifested itself in different ways. On some occasions the helicopter would not fly in the direction the cyclic was displaced and on two occasions the rotorblade divergence from the selected flight path was so extensive that the blades hit the fuselage.

It took two years to develop a fix that would eliminate the deviation from the selected flight path. They designed a system that compared the movement of the cyclic stick to the movement of the blades. If there was a deviation between input and response the system would send a signal to the servos via the autopilot and the servos would correct the pilots input to get the desired response at the rotor. This is very similar to the system used on the Lynx at least as it was described to me. The system used on the Cheyenne employed an Electro mechanical feedback loop and it was rife with single point failures that could cause the loss of the aircraft. The program was cancelled and two years later the Apache came on the scene.

Now, with that out of the way please tell me how the control inputs are made to the rotorhead from the fixed servos to the rotating rotorhead on the Lynx if there is no swashplate. Pictures would be appreciated.


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The Cat
 
Old 12th Mar 2001, 14:26
  #42 (permalink)  
Grey Area
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Lu,

Hurrah! That's the point I've been trying to get across for months! As an aside, if you think about it, a delta three rig will also apply an out of phase restoring force.

I'll try and put together a sketch of the Spider system.

I would add that whoever told you that the Lynx ASE actively compensates for phase lag was in error, it is a simple 2 channel ASE with Gyro, compass, radalt/baralt, control position and jack position inputs to the computer.

GA

[This message has been edited by Grey Area (edited 12 March 2001).]
 
Old 12th Mar 2001, 19:51
  #43 (permalink)  
Lu Zuckerman
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To: Grey Area

As I had indicated previously the subject of cross couple came up in a Robinson thread. I mentioned that the Robinson Rotor is rigged with the blades disposed from the lateral and longitudinal axes by 18-degrees during rigging of the flight controls. And as such, with a 90-degree phase angle the blades would in my opinion dip down to the left of the longitudinal centerline if the cyclic were displaced forward from the rigged neutral position. An Army Lynx pilot indicated in his reply to the posting that the Lynx rotorhead is rigged with the blades disposed 15-degrees from the respective axes when rigging of the flight control takes place. He indicated that on the Lynx with the blades rigged in this way and with a 90-degree precession angle the Lynx blades would also dip down and to the left when the cyclic was displaced forward. He indicated that there was an electronic “Black Box” that detected the left roll and compensated for it by modifying the input to the servos. I had also indicated that I might get the terminology mixed up. Obviously I did. Incidentally, your description of the ASE used in the Lynx is very similar to the ASEs that I was familiar with.

I feel that the reason I fought your explanation was because of the description given by the Army Lynx pilot and my unwillingness to accept your description when you used the term cross couple. I understood it as a problem that manifested itself due to the way the helicopter is rigged. I still believe that to be true for the Robinson.

I anxiously await your drawing of the of the Spider arm.

If you have the capability you can send it to me via email.


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The Cat
 
Old 14th Mar 2001, 06:44
  #44 (permalink)  
Lu Zuckerman
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To: Dave Jackson

"The attached site has some wonderful closeup pictures of rotorheads. Three of them are of the Westland Lynx, which this thread is discussing".
http://www.b-domke.de/AviationImages/Rotorhead.html

I logged onto the suggested website and yes the pictures are fantastic. While perusing the site I clicked on the BO-105 PAH rotorhead and found a slight problem. The lower end of the fixed link that connects the longitudinal control lever to the non-rotating swashplate has a cracked uniball bearing. Hopefully it was eventually replaced before anything bad happened. So much for the German Army mechanics.

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The Cat
 
Old 15th Mar 2001, 02:10
  #45 (permalink)  
Dave Jackson
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Lu;

The following web page has a sketch of the Westland Spider System, from one of Prouty's books.

http://www.synchrolite.com/A067.html


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Old 15th Mar 2001, 04:13
  #46 (permalink)  
Flight Safety
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Someone correct me if I'm wrong, but the diagram above does not look like the Lynx rotor head in the following link.

http://www.b-domke.de/AviationImages...head/0789.html

The pitch link rods are below the rotor head, not above it as the spyder diagram shows.

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Safe flying to you...

[This message has been edited by Flight Safety (edited 14 March 2001).]
 
Old 15th Mar 2001, 04:23
  #47 (permalink)  
Lu Zuckerman
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To: Dave Jackson

It seems that this post has been overtaken by events in that Flight Safety posted his while I was composing mine. (The quick Brown Fox…&#8230 .

I checked out the drawing created by Ray Prouty and after a bit I figured out how the system works. However there is a major difference between Proutys’ drawing and the actual Lynx rotorhead. On the pictures shown on http://www.b-domke.de/AviationImages/Rotorhead.html
The Lynx rotor head looks just like any other rotorhead with the pitch links coming from below and connected to what would be assumed to be a swashplate. Obviously if Westland still employs the spider system it does not look like ray Proutys’ drawing. If it is below the transmission like the Enstrom and the Cheyenne the spider must be driven by the transmission.



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The Cat
 
Old 15th Mar 2001, 09:38
  #48 (permalink)  
Dave Jackson
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Red face

Interesting.


Perhaps the mast has a large diameter and the four spider legs protrude out of the mast, below the rotor plane, through four holes. Just a guess.


The following is quoted from J. Gordon Leishman, and might be of some interest:-
"Raul Hafner introduced the "spider" cyclic-pitch control system to autogiros. This provided a means of increasing collective pitch and also tilting the rotor disk without tilting the rotor shaft with a control stick as in de la Cierva's direct control system. Hafner used this design in his third autogiro, the AR-3, which flew in 1935."

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Project: UniCopter.com

[This message has been edited by Dave Jackson (edited 15 March 2001).]
 
Old 15th Mar 2001, 17:06
  #49 (permalink)  
Grey Area
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Correctly guessed. The central shaft of the spider runs up through the main gearbox and rotor shaft, the arms protrude through the shaft. If you look carefully at the pictures you might see the rubber "boot" that covers the spider arm as it passes through the shaft.
 
Old 15th Mar 2001, 20:31
  #50 (permalink)  
Flight Safety
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Grey Area, I noticed those. It looks like there are 4 rubber boots protruding down from the shaft. Although you can't see it, it appears the boots might terminate at the bottom of the pitch link rods.
 
Old 15th Mar 2001, 22:01
  #51 (permalink)  
Lu Zuckerman
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To: Grey Area

Now that we are all reading from the same sheet of paper I have several questions.

1) The attachment ears on the rotating ball joint connect with the longitudinal and lateral inputs. At what angle do these two attach points intersect?

2) Are the longitudinal and lateral inputs aligned with the respective axes of the helicopter? That is, is the longitudinal input aligned with the longitudinal axis and is the lateral input aligned with the lateral axis of the helicopter?

3) What is the maximum deviation of the rotating ball joint from its’ point of neutrality in any given direction when cyclic input is made?

4) From the Prouty diagram the rotating ball joint seem comparatively small. How big is it?

5) Is the rotating ball joint a high maintenance item? It would seem that if it fails you would lose all control of the helicopter. This has happened on Aerospatial helicopters when the swashplate bearings locked up with disastrous results.

6) The Prouty diagram shows the inputs to the rotating ball joints as control rods. Do the servos connect directly to the rotating ball joint or, are they rods as shown in the diagram?

7) In the picture of the Lynx rotorheads it seems that the pitch horns lead the blade by what appears to be 45-degrees. Is this correct?

Once I have the answers I will return with more questions. This should take up a lot of your spare time.


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The Cat
 
Old 3rd Oct 2001, 00:31
  #52 (permalink)  
 
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Unhappy Future Lynx

Anyone seen the Lynx IPT roadshow yet?

I hear that it is something of a Westlands sales pitch. Apparently the Lynx IPT favours FLynx in preference to any other options - now there is a surprise! All the recent criticism must have thickened a few skins, so they just don't care about any accusation of bias.

Also an interesting interpretation of the user requirement to carry 8 troops with kit - if they won't fit; you just take 2 aircraft!

Make sure you get a seat when the circus comes to town so that you can ask some meaningful questions - like what will be the AUM, and how do they justify their claim of 7 maint hours per flying hour.

If it is a foregone conclusion that we get FLynx for political reasons then at least be honest about it.

Never believe everything a salesman tells you.
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Old 3rd Oct 2001, 04:37
  #53 (permalink)  
 
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FLynx?

Is this Lynx LUH?

Explique moi, s'il vous plait?
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Old 3rd Oct 2001, 23:06
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Lightbulb

Sorry, that wasn't very clear was it. I am referring to the Battlefield Light Utility Helicopter (BLUH)which will replace Lynx from about 2006 onwards.
It could be made by Sikorski, Agusta Bell or ... Westlands.
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Old 5th Oct 2001, 00:05
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Robin Hood you must of sat in the same presentation as i did, best laugh i've had all year, they should start charging entrance fees to see it!

The concept of carring 8 troops with all their kit around the battlefield is great, using 2 aircraft to do the job isn't, in fact its what we do now.

I can't beleave in the year 2025 that future air Corps pilots will be flying with an aircraft that is no more capable than one built in 1989.

Don't miss the Lynx IPT roadshow, it will either make you very annoyed or put a smile on your face for the weekend.
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Old 6th Oct 2001, 02:45
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We shall be interested to see responses to this thread as the feeling is a re-spray is the order of the day.
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Old 6th Oct 2001, 21:49
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and I bet you still can't get a stretcher into it. I mean don't get me wrong, the lynx is a great aircraft, but it just isn't what we need fo a battlefield helo.

Why can't those westlands murderers (you know who you are) just build blackhawk on licence? It worked with the apache, so what's the problem?
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Old 6th Oct 2001, 22:40
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Cool

Christopher - You could always get a stretcher into a Lynx, 2 in fact if you use the correct fit - You've just got to take the time to saw the carry handles off first..
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Old 8th Oct 2001, 21:18
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Talking

Don't fret you Army types because no doubt it'll be RAF just like the AH64!!
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Old 8th Oct 2001, 21:54
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Exclamation

Correct me if I'm wrong, Windy. But the last time I saw a WAH, it had ARMY written on the tail.

Judging by your reply on the floppy thread it appears you have an inferiority complex with Lynx pilots. It's understandable, your only human. The SAM can prescribe you something, a home pregnancy test kit.

What use would an Apache have with an old Wessex loadie any way?
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