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Aircraft Rudder Chattering

Aircraft Rudder Chattering

Aircraft Rudder Chattering

Hello Everyone
I am currently deployed and i work on the P3C Orion Plane, my question is for the Rudder Hydraulics System, with
hydraulics on and you move the rudder pedals to the left & then to the right the rudder pedals will start to chatter like vibration, and if you go into the access area where the Rudder Hydraulic Booster is, and have someone run thru the system you will hear the chattering in the whole booster area we suspected it to be the rudder input control rod bearings. The bearings pn# is shafer YS-121-c, and the control rod pn# 901575-101. It started with just one A/C and now 5 A/c are starting to do the same thing, there is nothing in our MIMS stating anything accept to run the system thru 6 times to remove air & chattering in the pedals, we have done this numerous times and they all still chatter. We have checked the cable tensions and they check good IAW our MIMS. Thank You.

RE: Aircraft Rudder Chattering

You don't indicate what kind of circuit you are trying to trouble shoot.

Sounds a bit like a Servo circuit that could need the Gain adjusted to slow the response.

Also could be a closed circuit with trapped air.

Not enough information.

Do you have a schematic with pertinent information on the circuit that you could post?

Bud Trinkel CFPE
fluidpower1 @ hotmail.com

RE: Aircraft Rudder Chattering

Neever had direct contact with the P3, but if it's like other aircraft of its generation, the system is likely to be something like:

Engine driven pumps feed a duplicated centralised hydraulic supply with nice big accumulators so supply to the flying control circuits is essentially constant pressure.

Mechanical linkages (rods or cables and bellcranks) from the cockpit to the rear of the aircraft.  These work spool valves to feed double-acting rams which in turn move the control surfaces.  During motion, the spool valve exhausts the other end of the ram to the system reservoir.

Position control is usually achieved by putting the earth end of the ram on the moving surface, the rod onto the airframe, and mounting the spool valve on the side of the ram with the input linkage working parallel to the ram axis.

Hopefully this will give Bud something to get his teeth into.

On the whole, with air (or loose nitrogen) in the system, I'd expect to be hearing hints of trouble in other places too.

Are there any spring cartridges in the linkages?

Looking at it another way - you don't say where you're deployed, but could location be the thing which is suddenly doing something new to several of what ought to be well understood and documented airframes?  Working all the way down the control run, and particularly round the input lever to the Hydraulic Booster, are there any signs of unusual environmental ingress?


RE: Aircraft Rudder Chattering

If the circuit is like zeusfaber says, I would isolate the mechanical from the hydraulic to see which one is causing the problem.

With the mechanical linkage disconnected, manually move the valve spool shifter and see if the chatter is still there.

If the rudder chatters with the linkage disconnected I would get an auxilliary hydraulic unit and connect it to the rudder valve to see if it is the valve or hydraulic supply.

If not then start connecting a section of the control linkage back  to the valve and manually moving the rudder control valve through each reconnected section. If the problem is in the linkage it will show up at some point in the reconnecting scenario when it is tested.

Trouble shooting is often a situation where isolation eliminates piece after piece until the problem area is found.

Bud Trinkel CFPE
fluidpower1 @ hotmail.com

RE: Aircraft Rudder Chattering

Just a note of caution here.  Disconnecting or otherwise disturbing flying controls inevitably sets off a lot of bureacracy

Bud's approach is rigorous and effective, but is very invasive.  Before you start, make sure your operational tempo and command chain will stand the downtime for paperwork, independent inspection, paperwork, post-breakdown functional test, paperwork and subsequent airtest.


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