r22 clutch

[baobab72]

Dear all
premitting that i am not an heli pilot but that i am very intrigued by them, surfing the net i came across an article about the r22.
Now it is my understanding that power is transferred from the engine to the main rotor system via two dual V belts running on an upper sheave and on a lower sheave driven by an electric gear motor controlled by the CLUTCH switch.
For start up, to prevent the starter from having to overcome the load of the main rotor, the upper sheave is lowered towards the lower one loosing the belts while as the engine spools up as the CLUTCH switch is flipped to the ENG position, the gear motor drives the upper sheave up and away from the lower one, towards the in-flight position, tightening the belts and bringing the load of the main rotor system onto the engine, as reflected by an increase of RRPM’s.
Thereafter the gear motor is controlled by a pressure sensing switch in such a manner to keep the belts in tension at all times as they warm up and stretch.
At engine shutdown the top sheave is lowered again towards the lower sheave loosing the belts and releasing the engine from the load of the main rotor system.
My questions are:
when must the clutch be engaged? is there a minimum ERPM and what do you check once you engage it - RRPM, engine and rotor needles matching-?
What is the function of the CLUTCH warning light? does it ever illuminate in flite?
Which means do you have to monitor the clutch?
How is related to the rotor brake?
When do you disengage the clutch?
If you have to add anything to the clutch topic, please do so.

Many thanks

Baobab

[Practice Auto 3,2,1]

To answer your Q's in order Bao:

when must the clutch be engaged? is there a minimum ERPM and what do you check once you engage it - RRPM, engine and rotor needles matching-?

Soon as the engine is started and you get oil pressure, clutch switch to engage.

What is the function of the CLUTCH warning light? does it ever illuminate in flite?

To tell the pilot that the clutch actuator motor is operating. It does from time to time illuminate in flight but only when the belts are being re-tensioned. If the light comes on and stays on for more than a set time (7 seconds I think, but I don't have a PoH in front of me) then you have to pull the CLUTCH CB, land and get it checked out.

Which means do you have to monitor the clutch?

The light. As above its on whenever the clutch actuator motor is running, either up or down. It can be heard running down POST shutdown its its not too noisy outside.

How is related to the rotor brake?

No connection at all*. The rotorbrake is a simple mechanism attached to the main rotor gearbox that is operated by pulling a chain above and behind the pilot after shutdown. The RB is two arms with 'brake pad' type material that when pulled contact the MRGB output yoke, which then slows down the M/R.

*They have one small connection. If the clutch switch is in the ENGAGE position and/or the rotorbrake is ON, then the starter in inhibited and you wont be able to start the engine

When do you disengage the clutch?

30 seconds after pulling the mixture to stop the engine. If you have new belts fitted to the A/C then there is a procedure to not disengage the clutch in order to stretch said new belts. But thats a bit of irrelevant info for you.

Hope that helps.

[baobab72]

Many thanks for your prompt answer!
So let me see if i have gotten it right: during start up as you crank the engine and as the oil pressure increases you engage the clutch, how do you know that the clutch has engaged? - RRPM? the CLUTCH light will goes out, does the 7 second time limit still apply?
which effect will it have a clutch failure or in other words if you have to disconnect the clutch by pulling the CB, what will happen to the rrpm's? will the rotor wind down?

Many thanks

Baobab

[Practice Auto 3,2,1]

Not quite, start the engine. Once its running you move the switch to ENGAGE. Clutch light will illuminate and you know the clutch actuator motor is running. Blades will (should) start to turn within six seconds. The clutch light will go out once the belt tension has been reached (the motor stops running and the light goes out) after approx 50-60 seconds.

The 7 second limit is only in flight. If the light comes on and stays on then the actuator is either engaging or disengaging. Neither are favourable. If it engages too far the belts will stretch and could potentially break or if it disengages too much you will loose the drive between the engine and the drive system. You pull the Clutch CB to remove power to the system and stop the motor going either up or down. Pulling the CB will have no effect on ERPM or RRPM but as per the PoH you need to land and get the system inspected and the defect rectified.

[T bar]

If the clutch light illuminates for more than 7-8 seconds in flight, land immediately and then shut down. I have been told after this you can switch the clutch fuse behind the cowl door with the replacement and then you can give a good ground run. If satisfied then you can proceed with the flight.


T bar

[Flyin'ematlast]

Baobab

Practice Auto is correct except that you disengage the clutch 30 seconds BEFORE you pull the mixture to stop the engine when shutting down.:uhoh: This is to unload the clutch (slacken the belts) before the engine stops.

To answer your follow-up questions when starting the R22 the POH says you:
- Check that the strater on light is out (ie: starter not jammed on)
- Set engine RPM to 50 - 60%
- engage the clutch
- Check for blades turning within 5 seconds
- Switch alternator on (and check the ammeter moves)
- Check that the oil pressure is at least 25psi within 30 seconds
- Switch on avionics & don headsets
- Wait for the clutch light to go out.

The checklist goes on of course.

The clutch light can take some time to go out (the belts reach correct tension) and you do not increase the ERPM beyond 60% until the light goes out. You see a rapid rise in the RRPM needle to "join" the ERPM needle on the tachometer. this tells you that the clutch is engaging correctly. The light extinguishing confirms that the clutch is fully engaged.:ok:

The proceedure for pulling the clutch CB if the clutch light engages for more than "7 or 8 seconds" in flight is simply that the light tells you that the clutch motor is running, not why or in which direction. There could be a fault causing the clutch to disengage (leading to loss of drive but not in 8 seconds) or causing the clutch to further engage which could over-tension the belts leading them to fail. In either case pulling the CB will stop the motor and you then reduce power and land immediately for safety then get the cause identified.

If you pull the CB after 7 to 8 seconds the RRPM should not drop and you should be able to perform a normal landing, albeit being ready for any power loss.

I hope this helps you understand what is a simple, cheap, effective and reliable system.

Cheers

Ian.

[Practice Auto 3,2,1]

Oops, Ian is very much correct about disengaging before mixture pulling :ok:

[ascj]

Boabab you have more knowledge of robbie clutch systems than most junior pilots i have come across!

[baobab72]

thanks a lot to everybody

the explanations that you provided were very concise and helpful.

another question that maybe doesn t have anything to do with the technical side of the r22. What will i be able to do in let say 5 hours at the controls of an R22 considering that i fly fixed wing aircrafts for leaving?

baobab

[JaredYng]

After about 5 hours, you'll be able to think "I'll never be able to hover"!

Seriously though, not much after 5 hours. It's going to take a bit more to hover all on your own and even then it won't be pretty. Don't expect much from your fixed experience in terms of actually flying a helicopter. About all it will help you with is scanning, radios, situational awareness and possibly some control but not much.

[rotorfan]

You can have a lot of fun and learn much in 5 hours, but not likely hover. If you do start your training, you must have the discipline to not push the cyclic forward quickly, like you would do to prevent a stall in a FW. I was a FW pilot for 18 years before learning rotary, and I was paired with a fresh 200-hour instructor that knew nothing of airplane flight. I could have gotten us in trouble, or killed us, by going into a low-G situation. Fortunately, I had done much reading on helicopters, so I was aware of this possibility, even though my instructor was not.:eek: Be aware that your airplane instincts can take over in an emergency, and don't let it happen.

[Daysleeper]

If the clutch light illuminates for more than 7-8 seconds in flight, land immediately and then shut down. I have been told after this you can switch the clutch fuse behind the cowl door with the replacement and then you can give a good ground run. If satisfied then you can proceed with the flight.

What? :confused: That sounds foolish, the motor is running beyond the limit time for reasons unknown. Why would why would changing the fuse make any difference?

Besides...are you a licensed engineer? If not then you are limited to... land, shut down, put in tech log and call maintenance while strolling over to the pub.

[Aucky]

could anyone offer a definite answer to this.
With the clutch in the 'engage' position in flight and light coming on in flight for 're-tensioning' as it's often generally referred to, is the clutch only able to tighten the belts or is the clutch able to move in either direction as required to maintain tension? (I appreciate that usually it would be a tensioning of the belts due to expansion with heat, but the clutch light often comes one with both a large increase in power AND lowering the power).

[Figure Of Merit]

With the clutch in the engage position.....is the clutch only able to tighten the belts or is the clutch able to move in either direction as required to maintain tension?

The former.

Why would why would changing the fuse make any difference?

The fuse is rated substantially less than the circuit breaker that protects the clutch circuit. The fuse will blow before the CB pops. That way a motor problem will blow the fuse but the warning light will stay on. If one just relied on the circuit breaker (and no fuse were in the circuit) then an overload problem would trip the CB thereby preventing the correct level of tension in the belts and simultaneously extinguishing the warning light - not a good thing. If the fuse blows it might have just been because the fuse has got old and tired or a short duration transient caused the fuse to blow. In these circumstances changing the fuse will get you back in the air again. That's why a spare fuse is provided. It's happened to me once, I discussed by phone with the duty engineer. Changing the fuse on his advice got me back to base (and ultimately to the pub).

[500e]

All ways wondered why they had both.
Was to idle to ask or think it through, a poor idea anyhow LED and resistor or relay & normal bulb would sort it without fuse, still as I have no wish to fly a 22 will get my coat.:E