Century ll rebuild question

[Mcstealth]

The Century in the Bellanca I am flying was labled "inop."  Gulf Avionics on the field pulled it, and installed a loner from some kind of Piper (has Piper labled on the face plate ). The AP wanders, searching for the heading. It is not usable. 

Two questions. What causes the AP to search for the heading? Is it worth sending the original AP off for overhaul?

Next Avionics question. Same plane. The electric turn Coordinator seems to work fine, both parts of the instrument. The red flag is showing inside the glass. What does that mean? The bubble moves correctly,  as do the wings but something obviously is throwing that flag. 

 

Thanks

David

 

[Jake@BevanAviation]

With any legacy Century system servo start-up voltage is critical for proper tracking.  The higher the start-up voltage gets the worse the performance is, typically poor tracking or oscillation in flight are associated with high start-up voltage.  This can be easily checked in the field with a portable variable dc supply, power on pin C of the servo and ground on D.  Turn the supply up until you hear the motor running and note the voltage,  do this 3 times and take the average.  It needs to be under 2VDC max, the higher the voltage the worse it will perform.  They should also check cable tension and ensure there is no slack.

Another thing to check would be the condition of the AI for the Century system as this is the backbone of the system.  If the gyro is bad it will affect the performance of the system.  On a good AI when the engine is started the AI will do a shake out as the gyro starts to spool.  As the rotor speed increases the gyro the will start to stabilize and level out.  If it does not shake out and is slow to erect you could have stiff gimbal bearings.

Typically a flag in view is indication there is a problem with the associated instrument.  Flags on a TC is normally from slow rotor speed.  Most TC have a pin out placard on the instrument for the connector.  Using a DC supply you can get them to run on the bench to see if they are noisy or if the gyro is even spinning under power.

[Mcstealth]

8 hours ago, Jake@BevanAviation said:

With any legacy Century system servo start-up voltage is critical for proper tracking.  The higher the start-up voltage gets the worse the performance is, typically poor tracking or oscillation in flight are associated with high start-up voltage.  This can be easily checked in the field with a portable variable dc supply, power on pin C of the servo and ground on D.  Turn the supply up until you hear the motor running and note the voltage,  do this 3 times and take the average.  It needs to be under 2VDC max, the higher the voltage the worse it will perform.  They should also check cable tension and ensure there is no slack.

Another thing to check would be the condition of the AI for the Century system as this is the backbone of the system.  If the gyro is bad it will affect the performance of the system.  On a good AI when the engine is started the AI will do a shake out as the gyro starts to spool.  As the rotor speed increases the gyro the will start to stabilize and level out.  If it does not shake out and is slow to erect you could have stiff gimbal bearings.

Typically a flag in view is indication there is a problem with the associated instrument.  Flags on a TC is normally from slow rotor speed.  Most TC have a pin out placard on the instrument for the connector.  Using a DC supply you can get them to run on the bench to see if they are noisy or if the gyro is even spinning under power.

Jake. Wonderfully detailed response. Thank you. 

What I can infer from this is:

#1 if the voltage is wrong now, an overhauled AP could still work poorly? Is there a resistor that keeps that particular voltage low?

#2a bench test of the TC should hilight the path to repair it. 

[N201MKTurbo]

Back in 2005, my CIiB was all over the place. One night, the gremlins snuck into the hangar and disassembled the servo and the servo motor. They said they cleaned all the parts squeaky clean. They turned and polished the commutator to a mirror finish and reassembled it with the finest low volatility, broad temp range instrument grease, and put it all together. They said it would start with 350mv. It sure steers true even today.

[David M20J]

10 hours ago, Jake@BevanAviation said:

With any legacy Century system servo start-up voltage is critical for proper tracking.  The higher the start-up voltage gets the worse the performance is, typically poor tracking or oscillation in flight are associated with high start-up voltage. 

just a dumb pilot here, I have a Century IIB that hunts when ALT hold is on.  could you elaborate more on specifically the start up voltage thing?

or I might just show your post to my A&P and see if he can figure it out

[Jake@BevanAviation]

9 hours ago, Mcstealth said:

Jake. Wonderfully detailed response. Thank you. 

What I can infer from this is:

#1 if the voltage is wrong now, an overhauled AP could still work poorly? Is there a resistor that keeps that particular voltage low?

#2a bench test of the TC should hilight the path to repair it. 

#1 all Century systems use a brushed DC drive motor, over time the carbon brushes will wear and create a carbon dust.  This dust can cause the back bearing to get stiff, when the bearings get stiff it takes more drive voltage from the amplifier to get the motor to run.  A good clean motor with new bearings and brushes is typically around 800mvdc for start up. 

The amplifier provides the drive voltage and the motor moves the control surface in the aircraft.  If the servo is bad, repairing the amplifier or swapping will not resolve a high start-up voltage in the servo.  You can try and run the servo at max drive voltage (12VDC) for a long period of time to try and free up the bearings but this is only a temporary fix.  As long as the brush cap is full of carbon dust the bearings will get stiff again just a matter of time.

#2 If the TC has the pin-out placard on it as most do I would suggest try to run it on a bench.  A good tech should be able to decide if the gyro is spooling under power or if the rotor speed is to slow causing the flag to be in view.

7 hours ago, David M20J said:

just a dumb pilot here, I have a Century IIB that hunts when ALT hold is on.  could you elaborate more on specifically the start up voltage thing?

or I might just show your post to my A&P and see if he can figure it out

Pin out of Century 1,2,3, and 4 system servos are as follows.

A= Solenoid power

B= Solenoid ground

C= Motor drive

D= Motor drive

All you need to check motor start-up voltage is a variable DC power supply.  Applying power to C and ground on D will cause the motor to drive.  You start at 0VDC and slowly turn the voltage up till you hear the motor start to run.  Note the voltage and repeat the test 3 times in total and take the average.  This average voltage should be under 2VDC max.  If you are above 2VDC the motor needs to be cleaned and possibly new bearings and brushes.

The Century II system is roll only, a Century III system is roll, pitch and would have alt hold.  If you do have the IIB my guess is you have a additional box from a different manufacture that does alt hold, possibly S-Tec 30 alt or 60 PSS.  S-Tec systems use brushed DC motors from Globe just like Century and are susceptible to start-up issues as well.  They also rely on the pressure transducer to control alt hold functions and the old blue plastic ones are known for issues.

Interconnect prints for some of the legacy systems are available for free on Century's website (https://www.centuryflight.com/).  See Technical help / Drawings and Schematics.

[Mcstealth]

2 hours ago, Jake@BevanAviation said:

#1 all Century systems use a brushed DC drive motor, over time the carbon brushes will wear and create a carbon dust.  This dust can cause the back bearing to get stiff, when the bearings get stiff it takes more drive voltage from the amplifier to get the motor to run.  A good clean motor with new bearings and brushes is typically around 800mvdc for start up. 

The amplifier provides the drive voltage and the motor moves the control surface in the aircraft.  If the servo is bad, repairing the amplifier or swapping will not resolve a high start-up voltage in the servo.  You can try and run the servo at max drive voltage (12VDC) for a long period of time to try and free up the bearings but this is only a temporary fix.  As long as the brush cap is full of carbon dust the bearings will get stiff again just a matter of time.

#2 If the TC has the pin-out placard on it as most do I would suggest try to run it on a bench.  A good tech should be able to decide if the gyro is spooling under power or if the rotor speed is to slow causing the flag to be in view.

Pin out of Century 1,2,3, and 4 system servos are as follows.

A= Solenoid power

B= Solenoid ground

C= Motor drive

D= Motor drive

All you need to check motor start-up voltage is a variable DC power supply.  Applying power to C and ground on D will cause the motor to drive.  You start at 0VDC and slowly turn the voltage up till you hear the motor start to run.  Note the voltage and repeat the test 3 times in total and take the average.  This average voltage should be under 2VDC max.  If you are above 2VDC the motor needs to be cleaned and possibly new bearings and brushes.

The Century II system is roll only, a Century III system is roll, pitch and would have alt hold.  If you do have the IIB my guess is you have a additional box from a different manufacture that does alt hold, possibly S-Tec 30 alt or 60 PSS.  S-Tec systems use brushed DC motors from Globe just like Century and are susceptible to start-up issues as well.  They also rely on the pressure transducer to control alt hold functions and the old blue plastic ones are known for issues.

Interconnect prints for some of the legacy systems are available for free on Century's website (https://www.centuryflight.com/).  See Technical help / Drawings and Schematics.

Wow. Where do send my payment? 

 

[David M20J]

11 hours ago, Jake@BevanAviation said:

#1 all Century systems use a brushed DC drive motor, over time the carbon brushes will wear and create a carbon dust.  This dust can cause the back bearing to get stiff, when the bearings get stiff it takes more drive voltage from the amplifier to get the motor to run.  A good clean motor with new bearings and brushes is typically around 800mvdc for start up. 

The amplifier provides the drive voltage and the motor moves the control surface in the aircraft.  If the servo is bad, repairing the amplifier or swapping will not resolve a high start-up voltage in the servo.  You can try and run the servo at max drive voltage (12VDC) for a long period of time to try and free up the bearings but this is only a temporary fix.  As long as the brush cap is full of carbon dust the bearings will get stiff again just a matter of time.

#2 If the TC has the pin-out placard on it as most do I would suggest try to run it on a bench.  A good tech should be able to decide if the gyro is spooling under power or if the rotor speed is to slow causing the flag to be in view.

Pin out of Century 1,2,3, and 4 system servos are as follows.

A= Solenoid power

B= Solenoid ground

C= Motor drive

D= Motor drive

All you need to check motor start-up voltage is a variable DC power supply.  Applying power to C and ground on D will cause the motor to drive.  You start at 0VDC and slowly turn the voltage up till you hear the motor start to run.  Note the voltage and repeat the test 3 times in total and take the average.  This average voltage should be under 2VDC max.  If you are above 2VDC the motor needs to be cleaned and possibly new bearings and brushes.

The Century II system is roll only, a Century III system is roll, pitch and would have alt hold.  If you do have the IIB my guess is you have a additional box from a different manufacture that does alt hold, possibly S-Tec 30 alt or 60 PSS.  S-Tec systems use brushed DC motors from Globe just like Century and are susceptible to start-up issues as well.  They also rely on the pressure transducer to control alt hold functions and the old blue plastic ones are known for issues.

Interconnect prints for some of the legacy systems are available for free on Century's website (https://www.centuryflight.com/).  See Technical help / Drawings and Schematics.

Thank you very much, and yeah you were right its a IIB with a S-TEC 60