Hello there,
Per MM, the three servomotors of my aircraft must be “torque checked” (“clutch torque”) every year.
I know some of you disregard that maintenance operation, but, that’s recommended.
My question deals with the tools needed to perform the check: what kind of torque wrench is used for the servomotor of the KAP140 ? And more importantly, where could I buy the tool/set/bench ?
Actually, it would allow me not to send them to a shop, which takes time, is risky and expensive.
I should add that the servomotors reference are:
- KS270-C
- KS271-C
- KS272-C
Thanks !!
The fixture for checking the clutch torque is a strange contraption which has a servo attached to it and you remove the clutch from the aircraft and fix it to this fixture.
The fixture can be bought; it has a Honeywell P/N which should be found in the MMs for the servos.
IMHO this procedure is not needed because you can easily test this clutch on every preflight.
So, after some research through MM, servo testing require:
Slip Clutch Test Stand PN 071-06028-0000
Capstan Gear Adapter PN 071-06021-0003
KM 275 Servo Mount
CA-310 KS-27xC Servo Test Set
Plus few cables (CAB-310), a torque meter (TE12A) and a power supply.
So it may not be on the cheap side !! I would be pleased if someone (@Jesse ?) could estimate this for us.
@Peter
Do you own this equipment ?
No I don’t. It costs thousands.
The clutch slipping adjustment kit is supposed to be owned by every King dealer who is authorised to work on the autopilots.
That servo test set is not necessary if you know electronics. The KS270C/271C/272C servos have self contained tacho feedback and are dead easy to test. They have a -9V to +9V input for max rpm one way to max rpm the other way. I have the MMs for the KFC225 servos (they were not easy to get!). These test sets are for monkeys who know nothing and need to do a pass/fail bench test and issue an 8130-3 if the green light illuminates
What I do have is the KC225 autopilot computer bus extender, which was $1500 and which I bought jointly with another KFC225 owner. That is needed because the KC225 has some trimpots in the side of it. That’s stupid because it has loads of digital config so those pots were not at all necessary.
Peter wrote:
It costs thousands.
This in the end of my Quest
The KS270C/271C/272C servos have self contained tacho feedback and are dead easy to test.
Could you explain that a bit ? So what do you need to test them ? (except letting them where they are )
You need to know electronics, or find a boffin to do it for you. Of course removing and replacing servos is outside pilot privileges 
Also do a search here on e.g.
kfc225 AND servo AND test*
Basically you need a -9V to +9V source, a +24V source, a switch the energise the solenoid inside the servo.
BTW you are not checking the torque of the servo.
The gearing of the servo is of the order of 10,000:1 and that is enough to break something if the output pinion was stalled.
The above gear is to test the torque at which the clutch (which is a part of the servo mounting bracket, and is nothing to do with the servo) slips.
The clutch provides extra safety for cases where a servo has failed and the solenoid operated gear disconnect mechanism (another clutch, but this one never slips) has jammed. Such an event would kill you.
OK, the operation consists in checking the clutch torque.
Then the servo is installed again, and you have to check appropriate rigging.
I have been a bit confused but you will excuse my poor English
More seriously, I am going to dig into the MM to make things clearer.
PS: I don’t want to die too young. Later.
But, why do you have a concern over this?
If you can overpower your servos with the yoke, when doing the standard preflight test (pressing AP and trying to move the yoke in pitch and roll), using the “normal” force, then the clutches are OK.
There is a definition of the required force somewhere. Testing the servo clutches is just a more formal way of doing this.
Very few pilots know about this. I have seen planes where the clutches were seized rock solid and if the autopilot failed and the solenoid mechanism inside the pitch or roll servo had seized too, the pilot would have probably killed himself.
Before the CB-IR I never tested the autopilot function before departure.
Now I found the place in the POH with a clear instruction on how to test it on ground.
This is for a KAP140.
