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HeliTorque :: View topic - Cockpit Checks R22
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HeliTorque Forum Index » Torque, Chat, and Chill!

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Cockpit Checks R22 Goto page Previous  1, 2
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WhirlyGirl
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PostPosted: Wed Dec 12, 2007 8:00 pm    Post subject: Reply with quote

veeany wrote:
Incidentally I'd be interested if anyone has ever started an R22 Gov On with the throttle open, since the Robinson Procedure Mod and if it saved the engine from overspeeding.


I asked an instructor about this some time ago and they seemed to believe that if the throttle was open above the governor range then it probably wouldn't catch it and stop the overspeed. But I don't know because I've never tried it, and don't intend to either! Yikes!

Sarah
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JeffHall
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PostPosted: Wed Dec 12, 2007 11:57 pm    Post subject: Reply with quote

I can't see how the Robbo governor could possibly prevent an engine overspeed on start-up.

My reasoning is thus:
The governor is a closed loop control that exists to keep the RRPM within a range, we all know nothing happens below 80% and that it ceases to be any use if switched on at greater than 115%.
The governor uses RRPM as the feedback and varies throttle position to give more or less power as required. Obviously the 'system' cannot possibly work without the clutch having been fully engaged as the 'link' between engine power and RRPM isn't present till that point (ie no amount of 'more power Scotty' will translate into RRPM if the belts are slipping).

What I can't understand is why anyone would want to start either an R22 or R44 without the governor being 'on', engine overspeeds will occur regardless of governor position by virtue of the clutch not being engaged - so what difference does it make?

The only way the RRPM can get to the 80% min value is by the engine powering the rotor system (Through the clutch) and by the pilot opening the throttle to get there - any sudden run-away failure at this point would be easily dealt with because the pilot would still be holding the lever and able to close the throttle!

What I do believe is that the governor has an inherent design flaw.
This being the 115% maximum above which it does nothing, this value should have been set at some totally unachievable value such that the system can always take control if the RRPM is above 80%, whilst it wouldn't stop overspeeding the rotor before switching the governor on, it would bring the RRPM back down to a sensible value in this instance.

What would be interesting is to see the FMEA (Failure Modes and Effects Analysis) for the governor system, from what I gather it is all single channel such that a single failure renders it U/S.
What also isn't clear is what would happen if for example the RRPM sensor failed, would the governor wind the throttle down, up or hold position? In my opinion the only safe action would be 'hold'.
If anyone has access to the maintenance manual for either the R22/44 I'd be interested to see the governor section.

Ultimately I would expect Robinson to know the system and its operation better than our CAA, even though it appears the CAA can order POH ammendments for Uk A/C, I fail to understand why they would advise contrary to the manufacturer who holds the A/C type certificate!

Jeff Hall
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veeany
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PostPosted: Thu Dec 13, 2007 7:45 am    Post subject: Reply with quote

Jeff

Once again from memory and I am NOT R22 current, so feel free to shoot me down.

The R22 governor is an engine governor not an RRPM governor. It keeps the ERPM at 104% by monitoring ERPM from a signal generated in the airframe left (engine right) Magneto. [Edited to clear up which one]

It will work between 80% and 115% ERPM to bring the ERPM back to 104%.

The fact that the engine drives the rotors in powered flight is what keeps the RRPM at 104% (ERPM cannot exceed RRPM unless a failure has occured). However it is possible for RRPM to exceed 104% and ERPM to be governed to 104% at which point the governor DOES NOT INFLUENCE RRPM, I had an instructor ask me last week how why is it that with the needles split RRPM >104 % the governor doesn't seem to control RRPM, thats because once the neeedles are split the governor will just keep doing its job and you are in autorotation, a simple check up on the lever will rejoin the needles and you are back with RRPM under control of (being driven by) the engine again.

I can see both sides of the R22 Gov On Off argument, having grown up with it off, reading about a number of overspeed accidents on take off. And then hearing of people scaring themselves silly when the pre engaged governnor runs the ERPM up to 104% at various points in the post engine start sequence.

I am quite lookihg forward to my R22 flying now.

Gary


Last edited by veeany on Thu Dec 13, 2007 8:18 am; edited 1 time in total
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HeliCraig
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PostPosted: Thu Dec 13, 2007 7:53 am    Post subject: Reply with quote

I was trained (last year) to start with the governor off and then put it on before lifting.

However the checklist now says governor on as one of the first items.

Now I am sure that the whole world can't have been doing it wrong for the last 20+ years; but if it is an improvement and reduces the risk of over speeds (in any flight / start up phase) then you can count me in.

The 5k excess as a SFH'er pays for a lot of flying!
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PostPosted: Thu Dec 13, 2007 8:07 am    Post subject: Reply with quote

Now I'm really confused!
From a control theory point of view, why would you want to control ERPM in a closed loop when the obvious target is to control RRPM?

I was aware that engine speed came from one of the magnetos but I thought that would be just to feed the tacho on the panel - now I think about it, that would be why the governor can go nuts if the magneto fails...

I think next time I'm flying I'm going to study the POH in some detail and try and quiz the tech's.

Is this controlling ERPM common to all heli's or is it a uniquely Robbo thing? I can't help thinking that turbines would control on RRPM because turbines are relatively slow to react.

Interesting topic though - has got me thinking!

Jeff
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PostPosted: Thu Dec 13, 2007 8:36 am    Post subject: Reply with quote

Jeff

I think the reason ERPM is used, is that if you look at my post above about the magnetos being the signal source. When ERPM < RRPM you are either in autorotation or the inertia in the rotor system is keeping it spinning with an ever reducing RPM, until the needles rejoin and the ERPM = RRPM reducing the ERPM will just compund the situation and split the needles further. [Edited to be pedantic about ERPM < RRPM]

It is an important concept and one which I think some of the lower houred instructors have never had pointed out to them, so how can they be expected to teach it [not a dig].

The freewheel unit (sprag clutch) effectively opens the control loop between engine and rotor, for want of a better way to put it ,forgive me for using terminology from your world in mine, but its the best way I can think of to explain it.

We can't get rid of the freewheel , its quite handy sometimes Laughing , so we need to make the best attempt at controlling the RRPM with ERPM without actually being in a position to do so in all flight conditions.

I never flew them, but the older Robinson governor did monitor RRPM and had a link to the collective as well.

Older Turbines (specifically the Allisons) are governed but in a completely different way, the governor does not monitor electronically the RPM but using a combination of mechanical RPM inputs, fuel and air pressures. The pilot sets his datum condition (equivalent to the 104%ERPM in the robinson) say 100% in a 206, using a control in the cockpit usually a lever mounted RPM up/down switch, and the governor will maintain that datum RPM by metering fuel to the engine. Once set it requires no electrical input at all.

The newer turbines have a plethora of monitored variables and a computer to modulate fuel flow and control engine power output, thats essentially what FADEC does.

Gary
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James T Lowe
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PostPosted: Thu Dec 13, 2007 3:29 pm    Post subject: Governor On or Off Reply with quote

JeffHall wrote:
What I can't understand is why anyone would want to start either an R22 or R44 without the governor being 'on', engine overspeeds will occur regardless of governor position by virtue of the clutch not being engaged - so what difference does it make?


When I learnt, all those years ago... (wow, over 6 years now!) the POH and laminated checklist included a check to ensure the govenor was Off prior to starting, turning on prior to flight, and turning it off on shutdown.

A couple of years ago (2005), Robinson changed that, in response to engine overspeeds on startup. We discussed that here, last year (2006).

James T Lowe wrote:
it was changed last year from governor off to governor on. I think it also applies to the R44. You should note that the governor now isn't switched off during the cooldown, so it should always be left on. (Must say, through training before the directive, it's habitual to remove the governor at the end of a flight!)

I believe that it was introduced to help to prevent overspeeds, although I'm personally not convinced that it will - for a start, the governor is ineffective over 115%! The item on the checklist that prevents overspeeds would be "Thottle Closed". Wink

I always learnt the governor off method, so the change is something which is slightly odd to me! Cool

To a degree, it will depend on where you fly, if you use a checklist from Robinson, ignoring a slightly different checklist that has been provided by your 'school/SFH/heli-owner/etc.' and you have a problem, where do you stand? "Sorry, didn't use your checklist - used this one instead..." I'll generally use the one supplied with the machine, which for all the ones I've flown at Costock recently, show governor on at startup.


So Jeff, why I would want to start without, would be to do with how I was trained in the first place. BUT, as I said last year, for my SFH, I would follow the checklist provided with the machine - if that's start governor on, then so be it!
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PostPosted: Fri Apr 11, 2008 7:42 pm    Post subject: Reply with quote

Just some information for you all. The Robinson POH had previously contained a CAA supplement overriding the FAA checklist, and stating that it should be off at startup. Since all the school checklists I have come across recently said "on", I decided to bring the governor on / off issue with Dick Bendy, who suggested he would bring it up at the next instructor / examiner meeting at the CAA.

Apparently EASA have brought in a rule saying that if one JAR state things the FAA checklist is ok, the UK CAA can't override it. Well, the meeting apparently provoked some differences of opinion, but the result was that Fred Cross stated that you must follow the Flight Manual, as written by the FAA - start with it ON.

Hope this clears it up once an for all... (until the rules change again!!) Laughing Laughing

Sarah
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