Sloppy feel in cyclic
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Sloppy feel in cyclic
Hi i am trying to find out what conditions would cause a lynx or other type of helicopter to have a sloppy feel of the cyclic stick?
your ideas would be much appriciated
your ideas would be much appriciated
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The problem is that the question is so wide ranging.
1. The lynx is very different from most helicopters in terms of how the head works, and how movement of the cyclic feels.
2. There are a million failures at all stages of the control runs which will make the cyclic sloppy. (ie loss of all rotor blades will make the cyclic sloppy, but so will a worn bush at various points)
3. Then there are many different trim/autopilot systems ranging from the appalling Gazelle through to decent modern systems, all of which affect the cyclic feel.
1. The lynx is very different from most helicopters in terms of how the head works, and how movement of the cyclic feels.
2. There are a million failures at all stages of the control runs which will make the cyclic sloppy. (ie loss of all rotor blades will make the cyclic sloppy, but so will a worn bush at various points)
3. Then there are many different trim/autopilot systems ranging from the appalling Gazelle through to decent modern systems, all of which affect the cyclic feel.
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i am specifically looking at the lynx. The synerio i was given is that the aircraft was carrying out a max con check and the Nr drooped to 95.5% and that is when the sloppy feel occured and there was also a vibration through the airframe
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Vortex Ring - 'Settling with power'
The signs of a helicopter encountering settling with power are a vibration in the main rotor system followed by an increasing sink rate and a decrease or loss of cyclic authority, depending on the severity of the condition.[2] The failure of a helicopter pilot to recognize and react to the condition can allow high descent rates and impact with terrain, a frequently fatal accident.
This gets my vote, being overhead XMG at 14k without Oxygen does not.
The signs of a helicopter encountering settling with power are a vibration in the main rotor system followed by an increasing sink rate and a decrease or loss of cyclic authority, depending on the severity of the condition.[2] The failure of a helicopter pilot to recognize and react to the condition can allow high descent rates and impact with terrain, a frequently fatal accident.
This gets my vote, being overhead XMG at 14k without Oxygen does not.
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Blade Stall....
...It's been a long time since I worked anything rotary (20 + years), but if I recall sloppy controls and airframe vibration/buffet/rumble generally means a couple of things:
1. Incipient stall - i.e high blade alpha
2. Incipient GB/drivetrain failure
3. Vortex Ring - i.e. high power on the engine, low forward airspeed and descent through the downwash.
1. Incipient stall - i.e high blade alpha
2. Incipient GB/drivetrain failure
3. Vortex Ring - i.e. high power on the engine, low forward airspeed and descent through the downwash.
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I guess thats the punch line before the joke then 
Being type specific could be a red herring, but more likely to narrow down research to single rotor (as opposed to Chinook for example) and it may be that the Lynx semi-rigid rotor head could feature in your answer.
Probably a duff steer, but mention anyway in case you are expected to have some lateral thinking:
Air Test: - ‘over-pitching’ is often misinterpreted as vortex ring. This is where the pilot rapidly increases collective considerably and the engine cannot produce enough power to overcome the large, swift increase in drag on the rotor system. The result is that the rotor system quickly slows down and loses efficiency causing the helicopter instantly to sink. Again, this is not vortex ring. Not sure if this would necesarily induce vibration and loss of cyclic control, but it seems quite resonable to me, anybody else?
Being type specific could be a red herring, but more likely to narrow down research to single rotor (as opposed to Chinook for example) and it may be that the Lynx semi-rigid rotor head could feature in your answer.
Probably a duff steer, but mention anyway in case you are expected to have some lateral thinking:
Air Test: - ‘over-pitching’ is often misinterpreted as vortex ring. This is where the pilot rapidly increases collective considerably and the engine cannot produce enough power to overcome the large, swift increase in drag on the rotor system. The result is that the rotor system quickly slows down and loses efficiency causing the helicopter instantly to sink. Again, this is not vortex ring. Not sure if this would necesarily induce vibration and loss of cyclic control, but it seems quite resonable to me, anybody else?
Last edited by Tiger_mate; 29th Dec 2009 at 20:01.
Ronnie,from what I recall and it`s 38 yrs since I last flew a Lynx,you have 2 hyd. systems,2 generators,and 2 autostabs/autopilots,but await corrections to that. Amax.cont check is usually carried out at a safe height generally at best climbing speed ie appx 60 kts say,with one engine at idle at a time,and power applied until one reaches either a Torque limit/TIT-temp limit/or an Ng limit,before the rotor RPM` droops` significantly. repeat again,then do the other engine. If the RRPM droop significantly,then that engine`s governor needs adjusting,and exercise repeated. I can`t recall the RRPM that the generators drop off-line,possibly 92%, but if the `secondary hydraulic pump is a bit `tired`,or has insufficient fluid,or air in the system,then a collective `demand` may give the autostab/pilot insufficient `power` and make the controls feel `weak/sloppy`,as also there is a reduction in t/rotor performance, requiring a bigger pedal input. There are possibly otherreasons but without a look at the transmission diagrams/hyd /elec systems,this is just a guess..
Tourist; where did you fly a Gaz. with an autopilot ?
Tourist; where did you fly a Gaz. with an autopilot ?
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Not me, but...
Some years ago I was in the back of a Wessex, just about to coast out, when I noticed a ploughed field approaching alarmingly quickly. We made a loverly 3 line groove in the soil. The pilot mentioned a 'floppy cyclic', but not enough time to say 'Mayday', or 'Brace', or something else suitable. Banter aside, he did a good job to cream us on a sloping ground.
Memories fail, (early 80's) but I think it was connected to the Stab, and the yaw, pitch and roll thingies in a cupboard. The Auto Stabilisation Equipment (?) (ASE) pack springs to mind as the source of all things evil to aircrew.
Not much detail, I'm afraid, but that was generally the source of flying control faff's.
Memories fail, (early 80's) but I think it was connected to the Stab, and the yaw, pitch and roll thingies in a cupboard. The Auto Stabilisation Equipment (?) (ASE) pack springs to mind as the source of all things evil to aircrew.
Not much detail, I'm afraid, but that was generally the source of flying control faff's.
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Tiger mate, I agree with your (amended 
) diagnosis.
Bearing in mind that the scenario, as originally presented, involves a hypothetical Max. Contingency engine check, it's possible that the engine failed to produce the rated power, the Nr drooped and the cyclic control became less effective, rather than "sloppy".
The only other condition I can think of is a flying control friction maladjustment or impending failure.
) diagnosis.Bearing in mind that the scenario, as originally presented, involves a hypothetical Max. Contingency engine check, it's possible that the engine failed to produce the rated power, the Nr drooped and the cyclic control became less effective, rather than "sloppy".
The only other condition I can think of is a flying control friction maladjustment or impending failure.
Tourist, I think some civvy Gazelles/usa models were so fitted.
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As stated above, this has nothing to do with vortex ring state.
It has everything to do with the onset of stall on the retreating main rotor blade.
At high forward aircraft speeds (e.g. during max cont check) there is high pitch on the rotors and lift is only being produced by the tip section on the retreating MR blade....due to speed of reverse air flow over that blade.
Reduce the speed of the rotors (i.e. Nr droops) and the reverse flow of air over the retreating blade effectively increases and blade tip starts stalling. At the same time, the other blades are at high pitch with a reduced relative airflow over them. This produces lots of turbulent airflow which causes vibration and the sloppy feel.
Like I said in your max cont thread, this question has set a hyperthetical scenario to get you to think about the condtions and causes.
Ronnie, if you are studying for a foundation degree, maybe you should get a good book on helicopter aerodynamics....where effects such as above are clearly explained.
It has everything to do with the onset of stall on the retreating main rotor blade.
At high forward aircraft speeds (e.g. during max cont check) there is high pitch on the rotors and lift is only being produced by the tip section on the retreating MR blade....due to speed of reverse air flow over that blade.
Reduce the speed of the rotors (i.e. Nr droops) and the reverse flow of air over the retreating blade effectively increases and blade tip starts stalling. At the same time, the other blades are at high pitch with a reduced relative airflow over them. This produces lots of turbulent airflow which causes vibration and the sloppy feel.
Like I said in your max cont thread, this question has set a hyperthetical scenario to get you to think about the condtions and causes.
Ronnie, if you are studying for a foundation degree, maybe you should get a good book on helicopter aerodynamics....where effects such as above are clearly explained.
Sycamore The civilian Gazelle I did my type rating on definatley had an autopilot and as far as I recall was IFR equipped as the instrument panel extended completley across onto the righthand side, I recall this as it made it hard to see out the front coming into a tight confined area so a bit of left pedal and a quick peek out the rh side was in order.I didn't know how to use it myself but it was demonstrated to me by the IP.
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'Sloppy' is a bit imprecise.
The Lynx has an artificial feel system to provide force with displacement, and if memory serves me right, cannot be turned off. So unless something fails in the artificial feel system, the forces on the controls will always be the same. There should be no sloppiness associated with just the controls - if so, it would be there all the time.
The response of the aircraft to control inputs can be less than precise, however. This is probably what should be looked at. This can be caused by a less than well behaved AFCS or less likely, looseness in the mechanical controls. Looseness in the mechanical controls (worn bearings, etc.) would be evident all the time, where something not right in the AFCS can be temporary.
Also if flying at high altitudes, the Lock number effects on the controls can cause unanticipated reaction from a control input - a fore-aft movement will have some roll associated, for example.
More details of when the 'sloppiness' appeared are needed.
The Lynx has an artificial feel system to provide force with displacement, and if memory serves me right, cannot be turned off. So unless something fails in the artificial feel system, the forces on the controls will always be the same. There should be no sloppiness associated with just the controls - if so, it would be there all the time.
The response of the aircraft to control inputs can be less than precise, however. This is probably what should be looked at. This can be caused by a less than well behaved AFCS or less likely, looseness in the mechanical controls. Looseness in the mechanical controls (worn bearings, etc.) would be evident all the time, where something not right in the AFCS can be temporary.
Also if flying at high altitudes, the Lock number effects on the controls can cause unanticipated reaction from a control input - a fore-aft movement will have some roll associated, for example.
More details of when the 'sloppiness' appeared are needed.