A-Star Control question
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A-Star Control question
Weird control system problem. Never experienced anything like it, with nearly 1000 hours in AS-350 series aircraft. Thought I'd throw this into the hat and see if any of you silver haired gents had any info that might help us debug.
First start of the day, the cyclic seems to jam in the middle. It's not the friction plate. It's not totally jammed either. It moves freely for about an inch or so in any direction. After that inch, it's like you hit a wall. If you wait a few minutes, wiggle the stick now and then, the problem goes away. After that it's fine, unless the ship sits over night.
We had postulated that there was a sticking valve in the hydraulic manifold ( because the problem affects all servos ) so that was replaced. The problem remains.
If anyone has experienced anything like this, pls let me know. Right now I'm thinking that maybe the problem is not hydraulic. Because within that one inch of movement, the stick is smooth and light. After the problem goes away, the hydraulic checks both pass.
TIA
HeloBeez
First start of the day, the cyclic seems to jam in the middle. It's not the friction plate. It's not totally jammed either. It moves freely for about an inch or so in any direction. After that inch, it's like you hit a wall. If you wait a few minutes, wiggle the stick now and then, the problem goes away. After that it's fine, unless the ship sits over night.
We had postulated that there was a sticking valve in the hydraulic manifold ( because the problem affects all servos ) so that was replaced. The problem remains.
If anyone has experienced anything like this, pls let me know. Right now I'm thinking that maybe the problem is not hydraulic. Because within that one inch of movement, the stick is smooth and light. After the problem goes away, the hydraulic checks both pass.
TIA
HeloBeez
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No silver hair here but had a similar occurance a couple of years ago.....try the roller bearings on the control tubes under the floor.....they had worn flat surfaces on this particular machine and would randomly jam the cyclic although it was in flight rather than on the ground!!!
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Probably best to talk to your American Eurocopter tech rep, but here's what our wrench turners suggest:
1. Likely mechanical interference under the floor
2. Spray-lubricate the servo input selectors
3. Uniball or swashplate friction tape may be balled-up (check 10 o'clock position on the swashplate guide)
4. Look closely at where the cyclic goes through the floor to the fork
I/C
1. Likely mechanical interference under the floor
2. Spray-lubricate the servo input selectors
3. Uniball or swashplate friction tape may be balled-up (check 10 o'clock position on the swashplate guide)
4. Look closely at where the cyclic goes through the floor to the fork
I/C
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Dis-connect all M/R servo input rods.
Have an assistant hold the rods free,then move the cyclic as you would normally to determine if there is any problem in the mechanical control system. (yes, the cyclic bearings can wear as stated above but not all aircraft have these fitted from memory, it was a mod for early S/n aircraft from the plastic bushing). Check the lower cup half of the cyclic control for interference on the cup casting on the floor, there was a SB for this years ago. Also try the mixing unit (many different types, the newer fitted with self aligning ball bearings)and belcranks. Bit of silicone oil works wonders on the bushings.
If that doesn't sort it check the uni-ball by moving the s/plate by hand(with inputs-PCL's & servos off). These can form a point where the movement can become extremely stiff like the ball is out of round. Also, the teflon tape on the guide but this would not cause the problem you describe.
No. 4 If that ain't it then you are looking at partially seized servo valves or pressure regulation problem.
Are they Dunlop servos or the 'other' type? (which I can't think of right now).
Good luck!
Have an assistant hold the rods free,then move the cyclic as you would normally to determine if there is any problem in the mechanical control system. (yes, the cyclic bearings can wear as stated above but not all aircraft have these fitted from memory, it was a mod for early S/n aircraft from the plastic bushing). Check the lower cup half of the cyclic control for interference on the cup casting on the floor, there was a SB for this years ago. Also try the mixing unit (many different types, the newer fitted with self aligning ball bearings)and belcranks. Bit of silicone oil works wonders on the bushings.
If that doesn't sort it check the uni-ball by moving the s/plate by hand(with inputs-PCL's & servos off). These can form a point where the movement can become extremely stiff like the ball is out of round. Also, the teflon tape on the guide but this would not cause the problem you describe.
No. 4 If that ain't it then you are looking at partially seized servo valves or pressure regulation problem.
Are they Dunlop servos or the 'other' type? (which I can't think of right now).
Good luck!
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We call 'em bugs because they hide...
Well, We've been hunting this one for quite a while, maybe it's fixed, then it comes back... I believe all the servos are Dunlops, not Saams.
The technicians are still focusing on the hydraulics, but have also now dropped the belly pans and inspected, cleaned and lubed the mixing unit, push pull tubes etc. They also changed the drive unit on the hydraulic pump.
We'll see if it comes back...
Thanks for the input gents.
Beez
The technicians are still focusing on the hydraulics, but have also now dropped the belly pans and inspected, cleaned and lubed the mixing unit, push pull tubes etc. They also changed the drive unit on the hydraulic pump.
We'll see if it comes back...
Thanks for the input gents.
Beez
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HeloBeez
What hydraulic fluid are you using? If it is MIL-H-83282, you might try changing to MIL-H-5606 and see if the problem goes away.I seem to recall that both are approved for the Astar. We hear the occasional story of 83282 causing varnish-like deposits in some servos that results in weird symptoms.
STL
What hydraulic fluid are you using? If it is MIL-H-83282, you might try changing to MIL-H-5606 and see if the problem goes away.I seem to recall that both are approved for the Astar. We hear the occasional story of 83282 causing varnish-like deposits in some servos that results in weird symptoms.
STL
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Recieved the following guidance from our local EC rep (Dave Dunstan). Dave asked me to share this with the community, so grab a cuppa and sit back...
AS350 CYCLIC CONTROL (Binding - Stiffness - Motoring)
1. Servo input linkage (PRIMARY CAUSE)
--->Spray lubricate the Sloppy Link area or input lever linkage.
2. Servo’s (SAMM Servo’s read SL 1446-67-00, Dunlop Servo’s read SL 1064-67-91)
--->Servo’s are the 2nd Primary cause of cyclic binding in one direction but check the preliminary items listed below first. Eliminate the less expensive items.
3. Swashplate guide tape balled-up
--->Look at the forward L.H. quadrant of the swashplate guide with the collective pulled up.
4. Swash plate shimmed too tight
--->Remove shims. The uniball should have 0.012” vertical movement and rotate with hand pressure.
5. Walking beam pivot bolts (located at the bottom of each servo input rod)
--->Caused by stiffness and the pivot bolt nut being over-torqued. Walking beam side play should be min. 0.015”
6. Servo input rods - left and right lateral
--->Realign with the collective up and install the 15 degree upper servo rod end locks. MWC Chapter 67.
7. Cyclic friction cup needs cleaning
--->Lift the cups and clean with alcohol.
8. Dual control coverplate
--->Inspect the underside for rubbing caused by the co-pilot’s cyclic stub.
9. Lateral control rod under the floor
--->Lateral binding only, predominately on older AStars. The rod which goes from the cyclic, left to the center bellcrank. (Spray lubricate the rod end if it is stiff.)
10. Control rod end bearings under the floor (the stamped type)
--->Spray lubricate although this is rare.
11. Hydraulic filter
--->Change, although it would be rare to have a filter so dirty as to create a restriction of the flow.
12. Hydraulic pump inlet filter
--->This inlet finger screen, if dirty, normally causes a restriction which results in a flow / volume problem and causes a Dim Hyd Light or a occasional “Beep” of the horn. Clean this screen periodically.
13. Hydraulic pump
--->Very rare that a pump would not produce the pressure and volume.
14. Mixing unit end bearings
--->Grease with hypo needle (very rare cause).
15. Servo inlet check valve
--->Disassemble and clean (very rare cause).
16. Long. torque tube mount
--->Grease end cap bearings or change (very rare cause).
COLLECTIVE CONTROL BINDING
Note: If the general hydraulic system, fluid, pump inlet screen or the pump is the cause, it should effect the cyclic stick also. Control coupling between the collective and the cyclic is caused by the Dunlop servos sloppy link which needs spray lubrication, or the MGB deck bellcrank pivot bolts being too tight.
1. Collective Friction
--->Check.
2. Anticipator spring
--->Check the spring is not extending with the collective up. The pilot sometimes states he has reached the upper stop when he feels the spring extend. This becomes a Governor rigging problem or a binding Gov. cable problem.
3. Governor cable:
--->Cable binding internally -> change the cable (very common).
--->Cable may have tie wraps securing it to the engine -> It should be free floating under the engine.
4. Swashplate guide or tape
--->Lift the collective and check the left front quadrant of the swashplate guide for balled up tape.
5. Co-pilots collective cover plate
--->The co-pilot's collective stub is rubbing the cover plate.
6. Snap-on connector of the Gov. cable at the FCU connection
--->Remove and grease.
7. Scissors (MRH) binding
--->Check for the proper side play and the pivot bolts for lubrication. Scissors' pivots points should be disassembled and greased each 500 hours and if necessary spray-lubricated at 100 hours to keep them free.
8. Mixing-unit torque tube end cap bearings
--->Inject grease (normally shows in forward flight as the rotor loads build-up and goes away at a lower airspeed).
9. Servo input rods to the servo’s are misaligned with the collective pulled up.
--->Install the upper servo rod end bearing new 15 degree lock per MWC Chapter 67
10. MGB deck bellcrank
--->The lateral bell cranks are just under the MGB deck and the longitudinal is on the top front left of the MGB deck. These bell cranks must have 0.010” to 0.020” side play and the pivot bolts must be clean and not over torqued. This is very important.
11. Mixing unit torque tube Teflon bushings
--->Rare cause.
12. Collective torque tube Teflon bushings at the base of the collective
--->Rare cause.
13. Stamped control rod end bearings
--->Rare cause.
TAIL ROTOR CONTROL BINDING
Note: Control problems caused by the hydraulic pump or the pump inlet screen should effect all the controls.
1. Tail rotor control cable binding inside its sheath (average life is 2000 hours).
--->The pilot will have to push hard to break thru the binding.
2. Tail rotor control cable 14 mm jam nuts have come loose
--->Located in the upper rear baggage compartment and under the R.H. front floor.
3. Tail rotor control tube binding on the tail boom mounts
--->The heat shrink may be rolling up where the tube passes thru the hangar mounts.
4. Tail rotor spider binding on the TRGB chrome shaft
--->Due to the split bushings installed with too much adhesive. Max pull of the spider on the shaft is 30 lb of force.
5. Tail rotor bellcrank expandable bolt
--->Lubricate and look for minimum 0.015” vertical movement of the bellcrank. Look closely at the bellcrank and TRGB ears to see if the bushing in the bellcrank or in the two ears has came loose and is limiting the bellcrank vertical movement.
6. Tail rotor pedal pivot point in the cockpit.
--->Rare cause.
7. Tail rotor servo or the servo input linkage
8. Yaw compensator (AS350 B2/B3)
--->It is rare for the yaw compensator to be the cause, although there is sometimes a misunderstanding of the compensator and it gets changed prematurely (can be expensive). When in doubt ask the Eurocopter Pilot section, as they teach the system and have a very good understanding of it. A yaw compensator document is available (send your email address).
I/C
AS350 CYCLIC CONTROL (Binding - Stiffness - Motoring)
1. Servo input linkage (PRIMARY CAUSE)
--->Spray lubricate the Sloppy Link area or input lever linkage.
2. Servo’s (SAMM Servo’s read SL 1446-67-00, Dunlop Servo’s read SL 1064-67-91)
--->Servo’s are the 2nd Primary cause of cyclic binding in one direction but check the preliminary items listed below first. Eliminate the less expensive items.
3. Swashplate guide tape balled-up
--->Look at the forward L.H. quadrant of the swashplate guide with the collective pulled up.
4. Swash plate shimmed too tight
--->Remove shims. The uniball should have 0.012” vertical movement and rotate with hand pressure.
5. Walking beam pivot bolts (located at the bottom of each servo input rod)
--->Caused by stiffness and the pivot bolt nut being over-torqued. Walking beam side play should be min. 0.015”
6. Servo input rods - left and right lateral
--->Realign with the collective up and install the 15 degree upper servo rod end locks. MWC Chapter 67.
7. Cyclic friction cup needs cleaning
--->Lift the cups and clean with alcohol.
8. Dual control coverplate
--->Inspect the underside for rubbing caused by the co-pilot’s cyclic stub.
9. Lateral control rod under the floor
--->Lateral binding only, predominately on older AStars. The rod which goes from the cyclic, left to the center bellcrank. (Spray lubricate the rod end if it is stiff.)
10. Control rod end bearings under the floor (the stamped type)
--->Spray lubricate although this is rare.
11. Hydraulic filter
--->Change, although it would be rare to have a filter so dirty as to create a restriction of the flow.
12. Hydraulic pump inlet filter
--->This inlet finger screen, if dirty, normally causes a restriction which results in a flow / volume problem and causes a Dim Hyd Light or a occasional “Beep” of the horn. Clean this screen periodically.
13. Hydraulic pump
--->Very rare that a pump would not produce the pressure and volume.
14. Mixing unit end bearings
--->Grease with hypo needle (very rare cause).
15. Servo inlet check valve
--->Disassemble and clean (very rare cause).
16. Long. torque tube mount
--->Grease end cap bearings or change (very rare cause).
COLLECTIVE CONTROL BINDING
Note: If the general hydraulic system, fluid, pump inlet screen or the pump is the cause, it should effect the cyclic stick also. Control coupling between the collective and the cyclic is caused by the Dunlop servos sloppy link which needs spray lubrication, or the MGB deck bellcrank pivot bolts being too tight.
1. Collective Friction
--->Check.
2. Anticipator spring
--->Check the spring is not extending with the collective up. The pilot sometimes states he has reached the upper stop when he feels the spring extend. This becomes a Governor rigging problem or a binding Gov. cable problem.
3. Governor cable:
--->Cable binding internally -> change the cable (very common).
--->Cable may have tie wraps securing it to the engine -> It should be free floating under the engine.
4. Swashplate guide or tape
--->Lift the collective and check the left front quadrant of the swashplate guide for balled up tape.
5. Co-pilots collective cover plate
--->The co-pilot's collective stub is rubbing the cover plate.
6. Snap-on connector of the Gov. cable at the FCU connection
--->Remove and grease.
7. Scissors (MRH) binding
--->Check for the proper side play and the pivot bolts for lubrication. Scissors' pivots points should be disassembled and greased each 500 hours and if necessary spray-lubricated at 100 hours to keep them free.
8. Mixing-unit torque tube end cap bearings
--->Inject grease (normally shows in forward flight as the rotor loads build-up and goes away at a lower airspeed).
9. Servo input rods to the servo’s are misaligned with the collective pulled up.
--->Install the upper servo rod end bearing new 15 degree lock per MWC Chapter 67
10. MGB deck bellcrank
--->The lateral bell cranks are just under the MGB deck and the longitudinal is on the top front left of the MGB deck. These bell cranks must have 0.010” to 0.020” side play and the pivot bolts must be clean and not over torqued. This is very important.
11. Mixing unit torque tube Teflon bushings
--->Rare cause.
12. Collective torque tube Teflon bushings at the base of the collective
--->Rare cause.
13. Stamped control rod end bearings
--->Rare cause.
TAIL ROTOR CONTROL BINDING
Note: Control problems caused by the hydraulic pump or the pump inlet screen should effect all the controls.
1. Tail rotor control cable binding inside its sheath (average life is 2000 hours).
--->The pilot will have to push hard to break thru the binding.
2. Tail rotor control cable 14 mm jam nuts have come loose
--->Located in the upper rear baggage compartment and under the R.H. front floor.
3. Tail rotor control tube binding on the tail boom mounts
--->The heat shrink may be rolling up where the tube passes thru the hangar mounts.
4. Tail rotor spider binding on the TRGB chrome shaft
--->Due to the split bushings installed with too much adhesive. Max pull of the spider on the shaft is 30 lb of force.
5. Tail rotor bellcrank expandable bolt
--->Lubricate and look for minimum 0.015” vertical movement of the bellcrank. Look closely at the bellcrank and TRGB ears to see if the bushing in the bellcrank or in the two ears has came loose and is limiting the bellcrank vertical movement.
6. Tail rotor pedal pivot point in the cockpit.
--->Rare cause.
7. Tail rotor servo or the servo input linkage
8. Yaw compensator (AS350 B2/B3)
--->It is rare for the yaw compensator to be the cause, although there is sometimes a misunderstanding of the compensator and it gets changed prematurely (can be expensive). When in doubt ask the Eurocopter Pilot section, as they teach the system and have a very good understanding of it. A yaw compensator document is available (send your email address).
I/C
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I haven't had much to do with these machines, but do they have an accumulator of some sort in the hydraulic system like some other EC types? If so it could just be that it is in need of a recharge of Nitrogen or that it may be faulty.
Just my tuppence worth.
Just my tuppence worth.
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Collective Binding
Ian - thanks for that post. I have printed it out for our mechanic. We are having a collective "binding" where the collective feels like it springs back when you pull it up to a high setting. Usually around 97% Ng. Anything above that, the collective wants to come down and settle around 96.5%. Have you heard of that before? Our mechanic has tore it down a few times and spoke with EC reps and various other techs in our company with no good solution.
It looks like, from your list of possible problems, that that the issue may be related to #2 or #8? .
It does seem like airspeed has an effect on the "force" of the collective wanting to spring back down at higher settings. Thank you.
2. Anticipator spring
--->Check the spring is not extending with the collective up. The pilot sometimes states he has reached the upper stop when he feels the spring extend. This becomes a Governor rigging problem or a binding Gov. cable problem.
8. Mixing-unit torque tube end cap bearings
--->Inject grease (normally shows in forward flight as the rotor loads build-up and goes away at a lower airspeed).
It looks like, from your list of possible problems, that that the issue may be related to #2 or #8? .
It does seem like airspeed has an effect on the "force" of the collective wanting to spring back down at higher settings. Thank you.
2. Anticipator spring
--->Check the spring is not extending with the collective up. The pilot sometimes states he has reached the upper stop when he feels the spring extend. This becomes a Governor rigging problem or a binding Gov. cable problem.
8. Mixing-unit torque tube end cap bearings
--->Inject grease (normally shows in forward flight as the rotor loads build-up and goes away at a lower airspeed).
