There seems to be a bit of confusion.
Sprag Clutch:
The sprag clutch is a friction device, not centrifugal. Look at the diagram. If you turn the shaft one way, the 'sprags' catch and friction locks the shaft and the pulley. Turn the shaft the other way and the sprags release their grip. Simple really.
Clutch System Checks
Here are the rules:
1. Check blades turning within 5 seconds. (POH)
2. Check clutch light out within 100 seconds. (Maintenance manual) How many of you check this? You should.
3. If clutch light comes on in flight for more than 7 seconds, pull the circuit breaker, and land as soon as possible. Be prepared for autorotation. (POH)
Examine the discrepencies.
1. Blades start turning with starter motor: Some more stress on the starter motor. Not a major problem. Some more stress on belts. Minor problem. Slight strain on engine. Negligable. So really not a massive problem.
2. Blades NOT turning within 5 seconds: Yes, this is a worry*.
Causes and Implications:
Belts are too loose or stretching = too much upper pulley travel in order to tension the belts. This causes stress on the flex couplings and might not leave enough play for inflight retensioning. = Loose belts in flight.
Clutch system meeting resistance = possible impending mechanical malfunction of clutch motor.
Upper Limit Microswitch failure = belts will be overtightned to the point of snapping.
Belts stretching due to wear = impending failure
3. Clutch light not out before 100 seconds: Causes and Implications much the same as '2' above.
4. Clutch light on in flight for more than 7 seconds: See '2' above.
So as you can see the clutch system must be understood in order to make a judgement on any deviations from POH and Mx Manual guidelines.
*The weather does affect the belts and it is impossible for mechanics to set these perfectly. The next day they would be different.
So long as your aircraft is close to the recommended numbers you should be alright. 5 seconds is a 'safe average'. However, you should be very careful to note trends. These will tell you that something is going wrong. e.g. 5 seconds one day and 8 the next, 9 the day after.
Hope this helps:
cl12pv2s
P.S. Here are is a tester for H269 (Schweizer 300) and R22 pilots.
Question: If the clutch light comes on in flight, R22 says to pull clutch circuit breaker. H269 POH says nothing of the sort. Why?
When I ask students about this light in H269, people always tell me they would pull the breaker. This suggests poor understanding of the differences between the two systems.