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HeliTorque :: View topic - Gyros Circuit Breaker - Myth or Fact?
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HeliTorque Forum Index » Instructor Forum

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WhirlyGirl
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PostPosted: Wed Jul 16, 2008 8:49 pm    Post subject: Gyros Circuit Breaker - Myth or Fact? Reply with quote

Just curious...

Many an examiner I've flown with over the years has suggested the Circuit Breaker for the Gyros in the R22 / R44 should remain out during start, claiming that having it in can put unnecessary wear on the instruments.

Recently a couple of PPLs I've flown with have pointed out that their examiners have insisted that they should be in.

Now, what do others think about this? I keep getting conflicting arguments when I fly with people - "instructor 'x' said this", "examiner 'y' said that" and then they ask me who is correct.

The answer I have to give is that I don't know, as with many things that aren't standardised, who do you believe? I thought this might make an interesting discussion...

Sarah
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rjc
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PostPosted: Wed Jul 16, 2008 9:26 pm    Post subject: Reply with quote

Should it not be according to the check list for the aircraft? No-one should argue with that, or do they?

All the R22's I've ever been in have on the checklist gyro in after engine start, and out again after shutdown. Instructor wise have always gone by the checklist, examiner made no comment one way or the other.

Perhaps the extra vibration during startup does them no good?
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PostPosted: Wed Jul 16, 2008 9:36 pm    Post subject: Reply with quote

I've been told by a few engineers that having the Gyro Cb in for start does them no good, it all seems to be to do with preserving the bearings in the Gyros.

a. because the huge voltage drop on start has them slow down then spin up again very quckly.

b. The bearings they are spinning in are delicate and the vibration present when starting a tractor engine (piston) doesn't help their longevity.

I am not an engineer , but when possible I try not to have them in for start.

Also like anything electrical they drain the battery, so if you don't need it why start wth it switched on.

As to whether the checklist should be followed, the offical answer is always, however sometimes knowledge and experience count and SOPs are deviated from with good reason, thats what piloting is all about. Blind adherence to something you don't underdstand can be quite dangerous in some circumstance, but thats a whole other thead on it own.

I am sure there are several counter arguments to this, so lets see what
comes out of the thread !
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PostPosted: Thu Jul 17, 2008 6:00 pm    Post subject: CB in Reply with quote

Hi Veeany,

I am in total agreement with your views over gyros and circuit breakers but would also like an opinion from a instrument manufacturer.

PS, I like the safety website.

blme
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PostPosted: Thu Jul 17, 2008 7:45 pm    Post subject: Reply with quote

I've always read on the checklist & been told by instructors / examiners to pull the gyro CB before start.

But I've always thought it was because the gyro places a heavy load on the battery whilst it is trying to turn the starter motor, not to protect the gyro itself.

RC
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PostPosted: Thu Jul 17, 2008 9:20 pm    Post subject: Reply with quote

I don't fly robbies, but whatever the flight manual says is the gospel. Checklists SHOULD reflect what the RFM says. Although the engineers don't want to put wear and tear on the gyros (because they don't want to fix them), the procedures for the aircraft should be completed as per the RFM (and any supplements provided for optional equipment.

Pretty simple really...things like 'pull this one for start' sneak in...but if there's no support for that procedure in the books, that ain't the way to do it.

MC
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PostPosted: Fri Jul 18, 2008 12:19 am    Post subject: Gyros Reply with quote

Well, this seems to be another mixed bag for sure.

I know that when I fly the 300C, checklist is clear that the gyro cb is pulled until after start. It would be my guess that having them spool up while the helicopter is shaking itself around during the startup would cause excessive vibration and thus reduce gyro bearing life.

Makes sense. But as someone has said, the factory checklist rules!
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PostPosted: Fri Jul 18, 2008 12:34 pm    Post subject: Reply with quote

I've always left it out but I thought that it was due to when you turn the key is there not a big reverse voltage (proper name leaves my mind at the moment - is it 'back emf' perhaps?) that is built up in the battery just as there is in a car when you start it and if this very large voltage were to make its way along to sensitive instruments then they could very well get damaged?

That's just what I thought though from my knowledge of batteries. I always follow the check-list for that particular helicopter though every time. If I do that and it all goes wallop then at least it wasn't my fault and I would think that I am covered pretty well then Wink

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PostPosted: Fri Jul 18, 2008 3:11 pm    Post subject: Gyro Reply with quote

Mark,

I think you are referring to the surge current that flows momentarily through the lines. Most electrical equiment will pull a bit more than it needs until it reaches its' steady state current draw. Howver, since gyros are mainly vacuum operated, I doubt the electrical factor comes into play, It very well might be part of the overall wear and tear in general. That is why we have our radios and such turned off during start, to limit the current draw and prevent "burnouts".

I think that we all will agree......do whatever the POH says. Keep in mind that many operators tailor their checklist. I always review the manufacturer's checlist to see if any major changes have been made, and question any item that is not in accord with the manufacturer.

That way, as you said, if anyrthing goes "pop", you followed the POH.

Safe flying.
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PostPosted: Sat Jul 19, 2008 7:03 pm    Post subject: Reply with quote

Just checked my R22 POH. It doesn't say anything about the Gyro CB; it just says "Circuit Breakers .......... In" before engine start.

So I checked the laminated checklist that my flying school issue. It's exactly the same. Yet every time I've ever flown an R22 I've pulled the Gyro CB having been shown so by my original instructor, and no check flight has ever queried it!

RC
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PostPosted: Mon Jul 21, 2008 8:13 pm    Post subject: Reply with quote

This is a conflicting matter of which I have been asked about millions of times over the years.

In theory CB's shouldn't be used as switches, but...

I personally pull the CB before shut-down, pop it back in after start. The BATT gets thrown on and off dozens of times a day as aircraft get fuelled, pre-flighted etc. Voltage changes during start also have a similar effect as mention previously. This all just adds to wear, that can be avoided.

Treating the caging mechanism like a pinball machine also knackers them, be gentle please, they're not cheap to replace!

HH
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PostPosted: Mon Jul 21, 2008 8:31 pm    Post subject: Reply with quote

Well, this is turning out to be an interesting topic! I can see the logic in not causing unnecessary wear and tear on an expensive and sensitive piece of equipment, so if the engineers are encouraging this perhaps the flying school / operator checklists should be amended.

Besides, according to the POH "electrical systems description" and instrument panel diagrams (section 7), the AH and DI are not even mentioned, in fact their positions on the instrument panel are listed "optional instruments". Surely when the POH checklist says "circuit breakers in", it is referring to those which are "standard fit" and are actually detailed in the POH, rather than the optional extras.

Keep the replies coming...

Sarah
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PostPosted: Sat Feb 20, 2010 12:13 pm    Post subject: Reply with quote

Since the Gyro instruments are not a standard fit to the R22 any POH bought from a school or Robinson will be generic and not make specific mention of them. Whether or not there has been anything added to a machine specific POH where gyros have been fitted I've never really looked.

Most R44's I've flown and taught in and some R22's have a master avionics switch which is put on after start which includes the gyros as well as the radios GPS etc. This is a mod I believe put in over here when the machine arrives but it does suggest the gyros go on with the avionics part of the checklist not pre start. This makes sense in terms of protecting the instruments.
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PostPosted: Sat Feb 20, 2010 2:50 pm    Post subject: Reply with quote

Yea, i don't remeber having seen one... although i don't look down there that often!

Problem is with a master is you would have to have it in for engine start calls Smile
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PostPosted: Fri Sep 17, 2010 5:26 pm    Post subject: Checklists Reply with quote

Just scanning through old posts and came across this one. The CBs out prior to start has always been a point I have pushed for......for the reasons stated above "unecessary wear" "battery drain on cold mornings" etc etc but the topic has brought up a query for fellow 22/44 drivers out there in the uk. Do you follow the 'official' laminated robbo checklist supplied as standard or have you come up with your own?

I had a discussion with a fellow instructor regarding the unsuitability of the robbo 'list due to the omissions of several of the UK requirements in the supplement sections ie alt switch off, check ammeter & light, alt switch back on plus open door, remove headset, listen for unusual sounds etc. He disagreed.

Personally I find the official 'list very scattered and it seems to be designed around getting airborne asap, not great for a new pilot who needs to take their time and find a pattern so as not to miss things out.

Responses on the back of a fag packet please!

PEF Very Happy
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