R44 - What happens when you don't pull the mixture after disengaging the clutch?

[Ride]

So I got into a debate about this with my instructor today. Could someone please explain what happens if the clutch is disengaged on rundown and the mixture is left at full rich?

[troll.detector]

Rotor rpm goes down, engine rpm goes up. In fact it can go up a lot. You should not leave it much more than 30 second after disengaging clutch before pulling cut off for that reason.

[WolftalonID]

I agree. In fact, one time I got busy with the radios while going through shut down and did not pay attention to my time after the clutch.....it got real weird real fast. RPMs were screaming up at a fast pace, and belts loose make one hell of a racket. It could have been worse and lost the belts, but I was lucky enough to shut it down fast that day.

[DieselBoy]

.

Edited November 19, 2013 by DieselBoy

[pilot#476398]

If the throttle is at idle just how far does the engine rpm rise?

[rubidug]

I've never been in a 44....

Why cant you just lower the throttle? I assume the governor is off.

Don't you start the engine withe the MR disengaged? If so, what keeps the engine RPM in check then? Why would that be different than shutdown?

[troll.detector]

As for the idea off rolling down to control the engine rpm - The situation happens with throttle control completely at idle. I assume engine rpm will not stay at idle as the belts loosen, because the engine is warm and just recently pushing hard to keep the blades running. Even rolling into detent will not make a difference - as the detent does not lower throttle, it just disables correlator.

 

I like the idea of showing a student how this happens and why 30 sec is on the check list.

[rubidug]

So, how do you start it without the throttle running out of control? Is the clutch engaged on startup?

[pilot#476398]

So, how do you start it without the throttle running out of control? Is the clutch engaged on startup?

 

No On startup you first roll the throttle up a bit, then engage the clutch.

 

I think what they are saying is that if you go longer than 30 sec. on shutdown the engine rpm will climb despite the throttle being at idle? I don't really get it, but its something to try on my next flight!

[rubidug]

But again, with that logic...

You would have to engage the clutch within 30 seconds of starting the engine, or the engine would overspeed?

Why would the engine RPM's be any different on shutdown? Confused

[helipilotm]

But again, with that logic...

You would have to engage the clutch within 30 seconds of starting the engine, or the engine would overspeed?

Why would the engine RPM's be any different on shutdown? Confused

On Robbie's you immediately engage the clutch after the engine is "running". On a warm day or if the engine is warm it's within a few seconds, first start or cold days just a few seconds longer. The reason it's like that is the set the RPM at idle with the clutch engaged and fully tensioned. If they didn't the engine would most likely die when you rolled it to the stop. The drivetrain takes more power to keep turning compared to an unloaded engine with the clutch engaged

[rubidug]

More confused....

So, what happens if you start then engine and don't engage? The engine starts to idle faster and faster? According to the OP, thats what would happen. But according to you, it would quit??? I can see why the OP asked this question!!

 

On the 300, you can idle all day long before you engage. Not sure if it makes any difference, but its fuel injected vs carb. The 300 starts, idles around 1400 and then engage about 1500. It bogs the engine a bit, but never quits (clutch pressure is controlled by pilot, and gradually increased until needles joined). We also have a 3 minute cool down. How is that accomplished on a 44 if you cannot idle disengaged?

[helipilotm]

More confused....

So, what happens if you start then engine and don't engage? The engine starts to idle faster and faster? According to the OP, thats what would happen. But according to you, it would quit??? I can see why the OP asked this question!!

 

On the 300, you can idle all day long before you engage. Not sure if it makes any difference, but its fuel injected vs carb. The 300 starts, idles around 1400 and then engage about 1500. It bogs the engine a bit, but never quits (clutch pressure is controlled by pilot, and gradually increased until needles joined). We also have a 3 minute cool down. How is that accomplished on a 44 if you cannot idle disengaged?

Yes it would idle faster. I said it would quit if they had the idle set to low when u engaged the clutch. The raven II is fuel injected but that has nothing to do with this.

 

On the cool down you cool it down for whatever is recommended ( I can't remember it's been 6 years since I've flown a piston) dissengage the clutch and pull the mixture within 30 seconds.

[pilot#476398]

More confused....

So, what happens if you start then engine and don't engage? The engine starts to idle faster and faster? According to the OP, thats what would happen. But according to you, it would quit??? I can see why the OP asked this question!!

 

On the 300, you can idle all day long before you engage. Not sure if it makes any difference, but its fuel injected vs carb. The 300 starts, idles around 1400 and then engage about 1500. It bogs the engine a bit, but never quits (clutch pressure is controlled by pilot, and gradually increased until needles joined). We also have a 3 minute cool down. How is that accomplished on a 44 if you cannot idle disengaged?

 

I have never had the engine quit, or have the rpm rise on its own if I don't engage the clutch immediately, so I don't get what he's saying about the startup? Here's what we do;

 

ignition switch - start

starter on light - out

set engine rpm - 50 to 60% (our tach is different than yours)

clutch switch - engage

 

On Shutdown its basically;

rpm 60 to 70%

cool down about 3 min.

close throttle

disengage clutch

wait 30 sec.

pull mixture

Edited November 6, 2013 by pilot#476398

[rubidug]

That makes sense to me. Thats basically the same.

[apiaguy]

I'll try...

When you start the 44 (or the 300). The engine (at idle while cold) will run a bit rough and at a lower rpm than when it has been running and is warm. Depending on how precise the idle and idle mixture is set when you disengage the clutch (300 too) after the drag of the rotors falls off the engine will pick up a few hundred RPM compared to it's idle speed (even in the 300... idle speed is supposed to be 1300-1400 with no load on the engine) I have seen engines easily go to 1600 and possibly a bit more which compared to a loaded engine at idle of about 800-1200 (the 6 cyl. of the 44 would easily idle at a lower rpm than the 4 cyl 300) I'm not a robinson guy but i'm sure the maintenance manual dictates what the rpm is supposed to be....

Point is operating with the belt drive disengaged is discouraged in any helicopter... things are unsupported (in the 300 the lower pulley coupling shaft can chatter and damage itself) and the belts are slipping..... get on with it...

[Mikemv]

"Point is operating with the belt drive disengaged is discouraged in any helicopter... things are unsupported (in the 300 the lower pulley coupling shaft can chatter and damage itself) and the belts are slipping..... get on with it..." Great point from a knowledgable A&P/IA.

 

I would not demo this RPM increase to every student without authorization from the maintenance dept/school. Follow the POH/RFM procedures and as a CFI do not decide what you will do beyond that without approval!

[pilot#476398]

If this issue is so important why have I never heard of it before? I've been to the Safety Course 4 times, and have over 220 hours with various CFIs (a couple of whom were also A&Ps)! Yet no one ever mentioned it?

 

Seems to me that not letting the engine run for more than 30 sec. after disengaging the clutch because it might damage some parts would be a good "NOTE" under Shutdown Procedures in the Normal Procedures section of the Flight Manual?

[Mikemv]

If this issue is so important why have I never heard of it before? I've been to the Safety Course 4 times, and have over 220 hours with various CFIs (a couple of whom were also A&Ps)! Yet no one ever mentioned it?

 

Seems to me that not letting the engine run for more than 30 sec. after disengaging the clutch because it might damage some parts would be a good "NOTE" under Shutdown Procedures in the Normal Procedures section of the Flight Manual?

Follow all of the items on an OEM checklist and parts/equipment will not be damaged needlessly. That is why the OEMs produce a checklist. They do not go thru the entire checklist mentioning what happens line item by line item if not followed.

 

Get CFIs deciding they will demonstrate things beyond the recommended procedures and things may get damaged.

 

Repeatedly demonstrating things beyond the checklist will bring on the damage sooner or more severely.

 

Do CFIs follow the check list during run-up or demonstrate repeatedly what happens if you do not?

 

P47, this is not directed towards you, I just used your quote to initially answer your question.

 

I would bet that you follow the checklist!

[ridethisbike]

The governor on the robbies can be slow to react.

 

Start up on a cold day and the RPM will rise as the engine warms up

When shutting down, the reduction in required power is seen as a rise in RPM

 

If that RPM is allowed to go above 80% the governor will take over and bring it to operating RPM. When the engine is unloaded, there is potential for the slow reacting governor to NOT catch the RPM before it overspeeds the engine.

 

 

 

I wouldn't mess with it. Don't show it to a student on your own accord. If you really want to see, get maintenance to show you or someone higher up the food chain than you to demonstrate it. If you want to show a student, video tape it and show them in the safety of the office.

[WolftalonID]

Ride you got it spot on. We should be disengaging the govenor during shut down as a precation, however, I have more than once found it left on which means, if the shut down check list is not performed as its written, govenor run away is a huge potential. Along with that, loose belts can do alot of damage if they break.

[pilot#476398]

Ride you got it spot on. We should be disengaging the govenor during shut down as a precation, however, I have more than once found it left on which means, if the shut down check list is not performed as its written, govenor run away is a huge potential. Along with that, loose belts can do alot of damage if they break.

 

We used to turn it off, but I think too many pilots were forgetting to turn it on and overspeeding on takeoff, so now they want you to leave it on all the time!

[lelebebbel]

The engine in a Raven II will idle at around 70% +/- RPM when hot with clutch disengaged. You can easily see this if you restart an engine shortly after shut down, it will sit happily near 70% in those few seconds it takes for the belts to gain traction as the clutch is engaging. The same would be true if you didn't cut off the mixture on shutdown. No overspeed, no governor kicking in (depending on the idle setting - in any case the pilot should be holding the throttle, so the governor can't do a thing), nothing explodes or melts - at least not immediately.

 

 

Obviously the time running with the clutch fully disengaged must be minimised to prevent burning or derailing the belts. That's why the manual also says "engage clutch immediately" and "Blades should be moving within 5s after clutch engagement" on start... and on shutdown, "mixture off after 30s"

 

(I suppose the 30s delay on shutdown is to reduce belt tension before the belts stop turning, while at the same time the needles should still be joined at the 30s mark)

 

 

Allowable idle RPM range with clutch engaged is 53-57% on the Raven, and 58-62% on the Raven 2

Edited November 7, 2013 by lelebebbel

[Goldy]

Seems to me that not letting the engine run for more than 30 sec. after disengaging the clutch because it might damage some parts would be a good "NOTE" under Shutdown Procedures in the Normal Procedures section of the Flight Manual?

First they do tell you to shutdown after 30 seconds.....so why would they have to tell you to not leave the engine running for longer? Follow the procedures and move on.

 

Kinda like saying if the engine quits lower collective. I guess they could say that another way as well......like. If the engine quits and you don't lower collective you will die.

[d10]

 

We used to turn it off, but I think too many pilots were forgetting to turn it on and overspeeding on takeoff, so now they want you to leave it on all the time!

 

Following the checklist is a good way to prevent that. Rolling on the throttle carefully until the governor takes over is also a good practice. Failing to control your helicopter and blaming a system that wasn't on because you failed to follow the checklist is just bad for so many reasons.