Robinson R22 Corner [Archive copy]
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The answer is not 104% of design speed, it is 104% of an arbitrary reference. In other words, the number you must remember is 104. We could have made it 269%.
It is funny how people can think that 867 degrees C is a real number, and forget that 0 degrees is 273 degrees above absolute zero, so the degrees are arbitrary.
We paint lines on gages to show the limts, the numbers are actually optional. Would you behave any differently if we labled the top of the green arc 10 and the bottom 5?
It is simply easier to remember 104% than it is 423 rpm, and easier to say.
The Russians actually set 100% at the max rpm in an auto, and cruise at about 82%. Go figure!
It is funny how people can think that 867 degrees C is a real number, and forget that 0 degrees is 273 degrees above absolute zero, so the degrees are arbitrary.
We paint lines on gages to show the limts, the numbers are actually optional. Would you behave any differently if we labled the top of the green arc 10 and the bottom 5?
It is simply easier to remember 104% than it is 423 rpm, and easier to say.
The Russians actually set 100% at the max rpm in an auto, and cruise at about 82%. Go figure!
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Mr S: I don't think our exchange is helping the original poster get a reply. However, you state
"At 10 knots (even backwards) there is very little parasite drag but a large increase in Effective Translational Lift, compared to 0 AS."
EFFECTIVE translational lift doesn't kick-in until about 16 kts. However, plain old TL is present at lower AS but not effective. So our poster (who was hovering, if I can remember back that far) would not have been receiving any noticeable TL in a 10 kt wind.
There is no doubt though that hovering a 22B downwind does take more power - even though the TR is operating in clean air.
YELLOW ARC - agreed. That's the way I have always flown a 22 - keeping the needle out of the yellow. Full carb heat below 18" = noticeable power loss. But above 18" (and particularly at near max power hover) carb icing is unlikely. In the UK we get weather conducive to carb icing about 12 months a year - the real danger zone is not having carb heat pulled on at low(er) power settings. Practise autos and training circuits are high workload times for students - and equally the most obvious times when carb icing is going to occur. And that shows up in the stats.
"At 10 knots (even backwards) there is very little parasite drag but a large increase in Effective Translational Lift, compared to 0 AS."
EFFECTIVE translational lift doesn't kick-in until about 16 kts. However, plain old TL is present at lower AS but not effective. So our poster (who was hovering, if I can remember back that far) would not have been receiving any noticeable TL in a 10 kt wind.
There is no doubt though that hovering a 22B downwind does take more power - even though the TR is operating in clean air.
YELLOW ARC - agreed. That's the way I have always flown a 22 - keeping the needle out of the yellow. Full carb heat below 18" = noticeable power loss. But above 18" (and particularly at near max power hover) carb icing is unlikely. In the UK we get weather conducive to carb icing about 12 months a year - the real danger zone is not having carb heat pulled on at low(er) power settings. Practise autos and training circuits are high workload times for students - and equally the most obvious times when carb icing is going to occur. And that shows up in the stats.
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Hovering in zero wind you have the benefit of ground effect while stationary over the ground.
While taxing downwing at 10kts in 10kts of tail wind you have lost the ground effect due to the ground moving below you although you are in hovering in still air. Could this be more like OGE hovering rather than IGE hovering while still close to the ground and hence different power requirements?
While taxing downwing at 10kts in 10kts of tail wind you have lost the ground effect due to the ground moving below you although you are in hovering in still air. Could this be more like OGE hovering rather than IGE hovering while still close to the ground and hence different power requirements?
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Now we're entering a surreal world: "While taxing downwing at 10kts in 10kts of tail wind you have lost the ground effect due to the ground moving below you although you are in hovering in still air."
Hovering (as per original enquiry) downwind is not the same as a downwind taxi. In the hover, you are flying backwards relative to the air. But your position over the ground doesn't change - that's what you're trying to achieve. The ground effect will still be present up to about 8 ft AGL.
Hovering (as per original enquiry) downwind is not the same as a downwind taxi. In the hover, you are flying backwards relative to the air. But your position over the ground doesn't change - that's what you're trying to achieve. The ground effect will still be present up to about 8 ft AGL.
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most likely an historical evolution
Here's how I bet it works (only Frank could tell us, and he's unlikely to comment on anything with Lu lurking in the wings):
When first designing the R22,Frank took some arbitrary power figure from Lycoming manual and designed/built components to match. This was 100% of derated power 'way back then.
As the design (pre-certification) evolved, it turned out that more power was (choose one) either a)needed, or b)acceptable in terms of life-limited components. So the usable derated power was boosted a few hp.
The engine RPM needed to boost the power this arbitrary amount was 104% of the original rpm at inital-concept-time.
Subsequently, there was no well-defined inflection point in the design-to-certification evolution when re-defining the new, higher RPM as "100%" would not cause confusion amongst the engineers and onlooking FAA types. God save us from Confusion! (Right, Lu?) So the new higher rpm has forever been known as 104%, damn the torpedoes, full speed ahead.
Just like CCW rotation and the right-seat-command-pilot and the prohibition on flying solo from left side regardless of ballast in the right, it's become a Tradition, and therefore Immutable.
(Is it true that the French are working on refitting imported R22's for CW rotation and left-seat command?)
When first designing the R22,Frank took some arbitrary power figure from Lycoming manual and designed/built components to match. This was 100% of derated power 'way back then.
As the design (pre-certification) evolved, it turned out that more power was (choose one) either a)needed, or b)acceptable in terms of life-limited components. So the usable derated power was boosted a few hp.
The engine RPM needed to boost the power this arbitrary amount was 104% of the original rpm at inital-concept-time.
Subsequently, there was no well-defined inflection point in the design-to-certification evolution when re-defining the new, higher RPM as "100%" would not cause confusion amongst the engineers and onlooking FAA types. God save us from Confusion! (Right, Lu?) So the new higher rpm has forever been known as 104%, damn the torpedoes, full speed ahead.
Just like CCW rotation and the right-seat-command-pilot and the prohibition on flying solo from left side regardless of ballast in the right, it's become a Tradition, and therefore Immutable.
(Is it true that the French are working on refitting imported R22's for CW rotation and left-seat command?)
The Original Whirly
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R22 start-up question.
According to the R22 POH, when you start the engine and put in the clutch, the rotors should start turning within 6 seconds. What would cause them to take a few seconds longer than this...and should I be worrying about it? I've been told it's not a problem, but I'm turning into a deeply suspicious helicopter pilot who worries about...absolutely everything. 
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Whirly,
I came across that about three years ago, when I asked a similar question to one engineer his reply was slow operation of the clutch, I didn't fly that crate again for some weeks and when I did it was much better, It was further explained to me the size of the motor used to engage the clutch was very small and could become tired with many start up's, but then another experienced user said dampness in the system could also cause it, IE heavy dew from early spring or summer mornings. another explanation was oil viscosity on first start up after very cold night if Heli left outside!
Keep looking though, cos its your bottom that will be exposed!
Vfr
PeterR-B
I came across that about three years ago, when I asked a similar question to one engineer his reply was slow operation of the clutch, I didn't fly that crate again for some weeks and when I did it was much better, It was further explained to me the size of the motor used to engage the clutch was very small and could become tired with many start up's, but then another experienced user said dampness in the system could also cause it, IE heavy dew from early spring or summer mornings. another explanation was oil viscosity on first start up after very cold night if Heli left outside!
Keep looking though, cos its your bottom that will be exposed!
Vfr
PeterR-B
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aha, the dreaded 6-second rule surfaces once again
Another of RHC's contributions to folk magic, superstition, rumor, dogma, and confusion!
First off, opinions vary whether the six seconds (some manuals apparently say 5 seconds) is a Minimum or a Maximum. Nextly, is it a ho-hum or critical?
My (former) R22 service center declared my R22 unairworthy on my only incautious flight into their facility when I admitted the rotor was not turning after (gasp!) 8 seconds. Time they were through with me, I had a bill for $5000 (while adjusting the clutch delay, they discovered the bearing was worn, while installing the new clutch motor and bearing they discovered galling on the engine-sheave-layshaft requiring new shaft and fan, etc etc).
Later (having become proficient at adjusting the clutch microswitch myself, in the field, a Criminal Scofflaw wrenching on an Aircraft without mechanic's license) I found that outside air temperature variations changed the clutch-engagement-time between 4 sec and 12 sec, so now I just try to keep the average, ISA, time to about 6 sec.
Why does RHC care? Very clearly, it's intended to guarantee the starter will not be employed to spin the rotor blades, as RHC points out that event might result in bending one or more driveshafts (starter, or clutch shaft to transmission) because the starter is capable of delivering so much torque. Thus it's a minimum time.
Another R22 service center IA tried to tell me the six seconds is a maximum time, to ensure that the drivebelts will not suffer undue wear while rubbing on the sheaves before engagement. And that I should never run the engine without engaging the clutch, lest I wear a thin spot in the belts. RHC, presented with this claim, informed me that belt wear was not an issue, the engine could be run with clutch disengaged for short periods (warmup for oil change, perhaps), and that six seconds (five?) is a nominal average only.
So it depends on which expert you talk to. But there seem to be no great quantities of accident reports blaming engage-time discrepancies for fatal accidents, so I suggest you need not worry excessively. Anything between, say, 4 and 10 seconds gets the job done, temperature is a significant factor, and only if the interval steadily increases over several starts would I begin to look for weakened belts stretching. As my belts APPEAR to be 13 years old with 1800 hrs TT, never having been replaced, I would say the belts are Quite Robust. Or the 20-30 A&P's who've worked on the aircraft are derelict in their duties, having made no logbook entries regarding belts.
And a note concerning belt preflight: having, from time to time, dropped wrenches and bolts and the like into the gap between belts and lower sheave, which if undetected before startup would possibly break the belt or seriously score the sheave, I now manually compress the belt around either side of the lower sheave, looking for lumps, before start after maintenance. Cheap insurance!
First off, opinions vary whether the six seconds (some manuals apparently say 5 seconds) is a Minimum or a Maximum. Nextly, is it a ho-hum or critical?
My (former) R22 service center declared my R22 unairworthy on my only incautious flight into their facility when I admitted the rotor was not turning after (gasp!) 8 seconds. Time they were through with me, I had a bill for $5000 (while adjusting the clutch delay, they discovered the bearing was worn, while installing the new clutch motor and bearing they discovered galling on the engine-sheave-layshaft requiring new shaft and fan, etc etc).
Later (having become proficient at adjusting the clutch microswitch myself, in the field, a Criminal Scofflaw wrenching on an Aircraft without mechanic's license) I found that outside air temperature variations changed the clutch-engagement-time between 4 sec and 12 sec, so now I just try to keep the average, ISA, time to about 6 sec.
Why does RHC care? Very clearly, it's intended to guarantee the starter will not be employed to spin the rotor blades, as RHC points out that event might result in bending one or more driveshafts (starter, or clutch shaft to transmission) because the starter is capable of delivering so much torque. Thus it's a minimum time.
Another R22 service center IA tried to tell me the six seconds is a maximum time, to ensure that the drivebelts will not suffer undue wear while rubbing on the sheaves before engagement. And that I should never run the engine without engaging the clutch, lest I wear a thin spot in the belts. RHC, presented with this claim, informed me that belt wear was not an issue, the engine could be run with clutch disengaged for short periods (warmup for oil change, perhaps), and that six seconds (five?) is a nominal average only.
So it depends on which expert you talk to. But there seem to be no great quantities of accident reports blaming engage-time discrepancies for fatal accidents, so I suggest you need not worry excessively. Anything between, say, 4 and 10 seconds gets the job done, temperature is a significant factor, and only if the interval steadily increases over several starts would I begin to look for weakened belts stretching. As my belts APPEAR to be 13 years old with 1800 hrs TT, never having been replaced, I would say the belts are Quite Robust. Or the 20-30 A&P's who've worked on the aircraft are derelict in their duties, having made no logbook entries regarding belts.
And a note concerning belt preflight: having, from time to time, dropped wrenches and bolts and the like into the gap between belts and lower sheave, which if undetected before startup would possibly break the belt or seriously score the sheave, I now manually compress the belt around either side of the lower sheave, looking for lumps, before start after maintenance. Cheap insurance!
I think that you are probably right to be suspicious. The R22 uses a sprag clutch mechanism, thus...
As I understand it (but am more than happy to bow to somebody who understands the type far better), the sprag clutch is effectively a centrifugal mechanism which engages as power comes in, but should automatically disengage if you lose power - so that you can still autorotate after an engine seizure. If you're getting a delays rotor start after clutch engagement, my guess would be that somewhere in that mechanism something is out of tolerance - which could similarly delay disengagement if you had an engine failure (or practice autorotation), with a potentially fatal outcome since you'd not maintain rotor RPM.
Incidentally there have been problems with this clutch mechanism before, there were eleven failures in the late 1990s which were tracked down to faulty manufacture - fortunately this didn't lead to any fatalities. The result was replacement of about 1000 clutches worldwide, and Robinson winning US$7½m from Dana, the clutch manufacturer, in a court case.
Finally, I'd suggest reading the memo below.
G
As I understand it (but am more than happy to bow to somebody who understands the type far better), the sprag clutch is effectively a centrifugal mechanism which engages as power comes in, but should automatically disengage if you lose power - so that you can still autorotate after an engine seizure. If you're getting a delays rotor start after clutch engagement, my guess would be that somewhere in that mechanism something is out of tolerance - which could similarly delay disengagement if you had an engine failure (or practice autorotation), with a potentially fatal outcome since you'd not maintain rotor RPM.
Incidentally there have been problems with this clutch mechanism before, there were eleven failures in the late 1990s which were tracked down to faulty manufacture - fortunately this didn't lead to any fatalities. The result was replacement of about 1000 clutches worldwide, and Robinson winning US$7½m from Dana, the clutch manufacturer, in a court case.
Finally, I'd suggest reading the memo below.
G
The Original Whirly
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First off, opinions vary whether the six seconds (some manuals apparently say 5 seconds) is a Minimum or a Maximum.
Just to get this clear - you're saying that the "engage" and "disengage" mechanisms on the clutch are separate and a (apparent) fault in the engaging mechanism, as evidenced by a delay in rotor start in no way indicates the clutch's ability to disengage in the event of torque loss? I'm more than happy to accept that this may be the case - just asking.
Just as an aside, on a fixed wing aeroplane about 2 years ago that I was maintaining I had a horrendous starting problem - basically it would start when completely cold or very hot, but if the engine had run anything from about 5 minutes to 12 hours previously it wouldn't start at-all. I had to take expert advice and found that the clutch mechanism (actually a torsional shock absorber, it had no controls but was designed to jump in overload) in the propeller drive was at certain oil viscosities setting up a torsional oscillation in antiphase to the starting cycle. I learned about engineering from that !
G
Just as an aside, on a fixed wing aeroplane about 2 years ago that I was maintaining I had a horrendous starting problem - basically it would start when completely cold or very hot, but if the engine had run anything from about 5 minutes to 12 hours previously it wouldn't start at-all. I had to take expert advice and found that the clutch mechanism (actually a torsional shock absorber, it had no controls but was designed to jump in overload) in the propeller drive was at certain oil viscosities setting up a torsional oscillation in antiphase to the starting cycle. I learned about engineering from that !
G
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The sprag clutch (freewheel) and the clutch used to engage/disengage the rotors from the engine during startup/shutdown are 2 entirely different entities...
Edit:
you beat me to it!
Edit:
you beat me to it!
Thanks, that's what I'd missed. So, assuming that all Robinson's Sprag clutch problems are solved (or at-least unrelated), this is almost certainly about the mechanisation of the manual clutch mechanism.
G
G
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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.
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.
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The clutch light in the Schweizer 300 tells you one of two things: either the actuator motor is operating, or the actuator is not fully drawn in. The actual belt tension is maintained by a compressed spring which is drawn to a fixed compression by the actuator. Since the Schweizer clutch actuator in always fully withdrawn after rotor engagement, if the light comes on in flight, it could be: a) a false indication, b) an uncommanded continuous extension of the actuator, c) a partial extension which has stopped. In any of those cases, pulling the breaker will kill the power to the actuator motor, "freezing" the extension rod. However, since you don't know how much tension is still on the compressed spring and drive belts, you will want to seek a suitable landing spot ASAP, and watch the needles!
The R22/44 series measures belt tension continuously, and operates the tension/engagement motor to maintain it. If the light comes on for extended periods, it indicates "one of many possible problems" (as they put it in the safety course). You could have lost a belt, and the tensioner is now adding (excessive) tension to the other belt. It could also be loosening the belts. If the light flickers continuously, you could have a bad driveshaft bearing, and of course it could be a false indication. Again, pulling the breaker will freeze the actuator, and again you want to find a good spot to land ASAP!
BTW, the sprag "clutch", as mentioned earlier, is not part of the engagement system, nor is it centrifugal (if it were, it wouldn't work when you rotated the driveshaft by hand).
The R22/44 series measures belt tension continuously, and operates the tension/engagement motor to maintain it. If the light comes on for extended periods, it indicates "one of many possible problems" (as they put it in the safety course). You could have lost a belt, and the tensioner is now adding (excessive) tension to the other belt. It could also be loosening the belts. If the light flickers continuously, you could have a bad driveshaft bearing, and of course it could be a false indication. Again, pulling the breaker will freeze the actuator, and again you want to find a good spot to land ASAP!
BTW, the sprag "clutch", as mentioned earlier, is not part of the engagement system, nor is it centrifugal (if it were, it wouldn't work when you rotated the driveshaft by hand).
Passion Flying Hobby Science Sponsor Work
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Clutch
For R22 and R44
The clutch is operated by an electric system that starts tightening the belt as soon as you throw the switch until a micro switch tells it to stop.
If it takes too long then the micro switch is not calibrated well.
Wether 6 sec is long or not depends a lot on the situation:
- The prime concern is not to wear the drive belt by putting friction on one spot by a lose turning wheel. This should be not too much of a problem if occasional.
- The belt normally displays a negative temperature coefficient : if warmer the belt actually gets shorter and vice versa (normally things stretch when getting warmer). This is a good behaviour because the stress on the belts would be worse if they are warm. But normally a warm system will engage faster.
- In cold conditions, first start of the day, it is actually OK to wait a few sec to throw the switches, because stalling the engine (especially R44 Raven I) and restarting again puts more stress on everything then waiting 3 secs more in the first cold start.
- In warm conditions long waits are not so good, but in this case normally the clutch should engage faster (see above). Si if long delays in this case, recalibrating is definitely necessary.
Hope that helps.
Delta3
The clutch is operated by an electric system that starts tightening the belt as soon as you throw the switch until a micro switch tells it to stop.
If it takes too long then the micro switch is not calibrated well.
Wether 6 sec is long or not depends a lot on the situation:
- The prime concern is not to wear the drive belt by putting friction on one spot by a lose turning wheel. This should be not too much of a problem if occasional.
- The belt normally displays a negative temperature coefficient : if warmer the belt actually gets shorter and vice versa (normally things stretch when getting warmer). This is a good behaviour because the stress on the belts would be worse if they are warm. But normally a warm system will engage faster.
- In cold conditions, first start of the day, it is actually OK to wait a few sec to throw the switches, because stalling the engine (especially R44 Raven I) and restarting again puts more stress on everything then waiting 3 secs more in the first cold start.
- In warm conditions long waits are not so good, but in this case normally the clutch should engage faster (see above). Si if long delays in this case, recalibrating is definitely necessary.
Hope that helps.
Delta3
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I also wonder about the age and hours of pa42's belts. I'm not calling you a liar but up until a few years ago when I stopped working on them, they had a life of 500 hrs.
As for the engage time, about 8 seconds give or take a few is what we used and all this told you was whether or not belt tension was adequate.
What happens when you engage the clutch is the belts are stretched because the top sheave is pushed away from the bottom sheave until a PRE DETERMINED tension is reached inside the clutch actuator worm drive assembly. Adjusting the micro switch only changes the amount of time/distance the upper sheave will travel downwards, ie toward the bottom sheave to loosen the belt tension. This then affects the distance to be travelled and the time to get the rotors spinning on the next clutch engagement.
Hope that helps. You can also get a very good idea of belt tension by using the following rule of thumb.
Find the u shaped part on the frame where the belts run past that seems to serve no other purpose than to keep the belts from wobbling. It is just below the top sheave but I can't remember which side. Just under that, using you middle finger, push directly in on the belt. Disengaged, you should be able to push your middle finger in so that the second knuckle sits under the u shaped belt guide.
As for the engage time, about 8 seconds give or take a few is what we used and all this told you was whether or not belt tension was adequate.
What happens when you engage the clutch is the belts are stretched because the top sheave is pushed away from the bottom sheave until a PRE DETERMINED tension is reached inside the clutch actuator worm drive assembly. Adjusting the micro switch only changes the amount of time/distance the upper sheave will travel downwards, ie toward the bottom sheave to loosen the belt tension. This then affects the distance to be travelled and the time to get the rotors spinning on the next clutch engagement.
Hope that helps. You can also get a very good idea of belt tension by using the following rule of thumb.
Find the u shaped part on the frame where the belts run past that seems to serve no other purpose than to keep the belts from wobbling. It is just below the top sheave but I can't remember which side. Just under that, using you middle finger, push directly in on the belt. Disengaged, you should be able to push your middle finger in so that the second knuckle sits under the u shaped belt guide.