Entering autos: discussion split from Glasgow crash thread
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FH1101 - re energy & SASless - re calm.
There's lots of energy in a rotor, but not too much.
The kinetic energy of a rotor in a small helicopter is in MJ.
Generally (in J) ~ 0.005 x rotor mass (in kg) x disk area (in m-squared) x rpm-squared; for Glasgow, 200kg, 75m^2 and 200rpm gives ~3MJ.
However, it's powered by a MW or so, so if you turn off the engines from a high power setting and do nothing else, the energy stored is only matched to a few seconds of power.
Other relevant quantities are the energy from forward speed
(in J) ~ 2 x total-mass (in kg) x speed-squared (in kts); for Glasgow, 2500kg and 100kts gives ~5MJ.
And potential energy from height
(in J) ~ 3 x total-mass (in kg) x height (in feet); for Glasgow, 2500kg and 700ft gives ~5MJ.
Each of these energies is comparable, and so all need to be taken into account.
When cruising along, there's a good fraction of a MW going into beating the air too.
While I'm sure you should "Keep Calm", sometimes you'll need to "Act Quickly" as well.
The kinetic energy of a rotor in a small helicopter is in MJ.
Generally (in J) ~ 0.005 x rotor mass (in kg) x disk area (in m-squared) x rpm-squared; for Glasgow, 200kg, 75m^2 and 200rpm gives ~3MJ.
However, it's powered by a MW or so, so if you turn off the engines from a high power setting and do nothing else, the energy stored is only matched to a few seconds of power.
Other relevant quantities are the energy from forward speed
(in J) ~ 2 x total-mass (in kg) x speed-squared (in kts); for Glasgow, 2500kg and 100kts gives ~5MJ.
And potential energy from height
(in J) ~ 3 x total-mass (in kg) x height (in feet); for Glasgow, 2500kg and 700ft gives ~5MJ.
Each of these energies is comparable, and so all need to be taken into account.
When cruising along, there's a good fraction of a MW going into beating the air too.
While I'm sure you should "Keep Calm", sometimes you'll need to "Act Quickly" as well.
Well sure, Awblain, we all understand that the energy stored in the unpowered rotor is not limitless. But here's the thing: If you're zooming along at 115 to 120 knots in your 407 or 350 or 119 or whatever, you're well above the speed for a stabilized autorotation. So you need to decelerate to that speed.
There are those who squawk like parrots, "RAWK, MAINTAIN RPM, MAINTAIN RPM! RAWK!!" But they're missing the point. Sure, RPM is important, I get that, I'm not an idiot and neither is Pete Gillies. But that's not all there is to it, right? There is a whole other half to the equation of entering an autorotation.
The "Maintain RPM" squawkers apparently would prefer to decelerate from cruise to best-auto speed while descending for a power-off landing. I, on the other hand, would prefer to do that decelerating in a level (or nearly so) cruise. If I can use the stored energy to buy a couple of those "...few seconds" that you talk about, then all the better! If only the "Mosby" pilot had had those "few seconds" more than the five seconds he ended up with.
I think it's truly laughable - and by that I mean the sheer arrogance of some of the pilots on this board who apparently all think they're better than me. And maybe they are, I don't know. Maybe everybody here is a better pilot than both me and the "Mosby" pilot.
I don't think I'm better than anyone. In fact, I know that overall I'm a pretty "average" helicopter pilot despite having a logbook with just as many hours as some of the more pompous credential-wavers on this forum. I read accident reports and go, "Dang, that could've been me!" I'm 58. I don't have lightning-sharp reflexes and powers of perception (if I ever did). I know that in any given emergency it might very well take me "...a few seconds" (but hopefully no more than two or three) to figure out what's going on and react properly to it.
We talk about a "normal pilot reaction time" of one second...one second? One-thousand-one. There, that was one second. Did you process the engine failure and react to it in time? Probably not. But you know what? Even two seconds is not a whole lot of time either.
I usually fly at a higher altitude than many of my friends...pilots who tell me that they, "...just prefer to fly low," who seem inordinately concerned (bordering on paranoid?) about some catastrophic failure that will require them to be on the ground right-goddam-now!
So when I fly I like to give myself time. You can squawk about rotor rpm all you want, but you're not looking at the complete picture.
There are those who squawk like parrots, "RAWK, MAINTAIN RPM, MAINTAIN RPM! RAWK!!" But they're missing the point. Sure, RPM is important, I get that, I'm not an idiot and neither is Pete Gillies. But that's not all there is to it, right? There is a whole other half to the equation of entering an autorotation.
The "Maintain RPM" squawkers apparently would prefer to decelerate from cruise to best-auto speed while descending for a power-off landing. I, on the other hand, would prefer to do that decelerating in a level (or nearly so) cruise. If I can use the stored energy to buy a couple of those "...few seconds" that you talk about, then all the better! If only the "Mosby" pilot had had those "few seconds" more than the five seconds he ended up with.
I think it's truly laughable - and by that I mean the sheer arrogance of some of the pilots on this board who apparently all think they're better than me. And maybe they are, I don't know. Maybe everybody here is a better pilot than both me and the "Mosby" pilot.
I don't think I'm better than anyone. In fact, I know that overall I'm a pretty "average" helicopter pilot despite having a logbook with just as many hours as some of the more pompous credential-wavers on this forum. I read accident reports and go, "Dang, that could've been me!" I'm 58. I don't have lightning-sharp reflexes and powers of perception (if I ever did). I know that in any given emergency it might very well take me "...a few seconds" (but hopefully no more than two or three) to figure out what's going on and react properly to it.
We talk about a "normal pilot reaction time" of one second...one second? One-thousand-one. There, that was one second. Did you process the engine failure and react to it in time? Probably not. But you know what? Even two seconds is not a whole lot of time either.
I usually fly at a higher altitude than many of my friends...pilots who tell me that they, "...just prefer to fly low," who seem inordinately concerned (bordering on paranoid?) about some catastrophic failure that will require them to be on the ground right-goddam-now!
So when I fly I like to give myself time. You can squawk about rotor rpm all you want, but you're not looking at the complete picture.
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FH1100
I'm not suggesting you're wrong to say "the rotor has lots of energy", but I think it is helpful to quantify how much energy it has, and to bring these issues of trading and juggling energy to the fore.
That the energies in rotor speed, forward speed and typical height are comparable emphasizes the importance of managing that energy. I get the impression from the extended discussion that there are incorrect assumptions being made that the rotor energy is either dominant or negligible.
This is much more relevant than for fixed-wing flying where there is a much-simpler single height-speed conversion that always applies. The trade in helicopter energy is both three way and potentially rapid - the total energy is quite low by the standards of a fixed-wing aircraft of the same price.
That the energies in rotor speed, forward speed and typical height are comparable emphasizes the importance of managing that energy. I get the impression from the extended discussion that there are incorrect assumptions being made that the rotor energy is either dominant or negligible.
This is much more relevant than for fixed-wing flying where there is a much-simpler single height-speed conversion that always applies. The trade in helicopter energy is both three way and potentially rapid - the total energy is quite low by the standards of a fixed-wing aircraft of the same price.
Last edited by awblain; 20th Dec 2013 at 15:39.
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There seem to be a number of posters here who read, then analyze, and somehow come up with hidden meanings from within the text. What a load of tosh! A prime example, the word "simultaneously", dictionary meaning: Happening,existing or done at the same time. What is so difficult about that that some people have to then go and say because the word cyclic comes before collective then there must be a subliminal message. The meaning is the same whether cyclic or collective is written first.
SAS go to the top of the class.
SAS go to the top of the class.
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I am just wondering if we should really move the pedals first before we move the cyclic and collective.......
So:
1. Pedals to correct yaw
2. Mayday
3. Collective
4. Cyclic
Will that work?
DB
So:
1. Pedals to correct yaw
2. Mayday
3. Collective
4. Cyclic
Will that work?
DB
Moving all three Controls at the same time works too, DB.
Trimming the Aircraft reduces Yaw, Drag, and helps center the Cyclic, as well as point the aircraft nose in the direction it is traveling which would help the Crew see what is actually in front of them and perhaps make the other control movements more efficient and useful .....don't you think?
Why this constant focus upon moving a single control unilaterally.....are some of you unable to mentally figure out how to do that....or only able for some physical reason to move one extremity at a time?
Doesn't the wonderful 225 AFCS/Autopilot do all this when Captain George is put in charge of things?
If the Autopilot can....and does.....why do Humans have such problems with doing it?
Trimming the Aircraft reduces Yaw, Drag, and helps center the Cyclic, as well as point the aircraft nose in the direction it is traveling which would help the Crew see what is actually in front of them and perhaps make the other control movements more efficient and useful .....don't you think?
Why this constant focus upon moving a single control unilaterally.....are some of you unable to mentally figure out how to do that....or only able for some physical reason to move one extremity at a time?
Doesn't the wonderful 225 AFCS/Autopilot do all this when Captain George is put in charge of things?
If the Autopilot can....and does.....why do Humans have such problems with doing it?
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Simultaneous
Your wife is going shopping. You give her a list of things to buy at the same time. So what do you put at the top of the list?
The instruction "Do A, B, C, ... simultaneously" contains two elements. The first is the action and the second is the timing. Logically they are independent and it does not imply all actions are equally important, just that they're to be done at the same time.
Unless otherwise stated, the first in a list assumes greater importance. It's the way we think. Ask people in an election whose names start with "A". They get far more random votes. Why? Because they're first.
The fact is, the advice "Move A and B simultaneously" is not exactly the same as "Move B and A simultaneously". The outcome may be the same but the emphasis is not.
The instruction "Do A, B, C, ... simultaneously" contains two elements. The first is the action and the second is the timing. Logically they are independent and it does not imply all actions are equally important, just that they're to be done at the same time.
Unless otherwise stated, the first in a list assumes greater importance. It's the way we think. Ask people in an election whose names start with "A". They get far more random votes. Why? Because they're first.
The fact is, the advice "Move A and B simultaneously" is not exactly the same as "Move B and A simultaneously". The outcome may be the same but the emphasis is not.
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SAS - I expected a Bite but not from you......I was joking Bud.
Ornis - my wife tells me to "Shut up and tell me the answer" is that simultaneous as well.
DB
Ornis - my wife tells me to "Shut up and tell me the answer" is that simultaneous as well.
DB
Small flaw in your logic sport.....as we have an Alphabet that is based upon order....when you use the Letters A...B....C....D....you inject order into the sequence.
Nice try......but still wrong.
Grammar Rules set forth the concept that the use of the conjunction "and" is used to connect two equal sentence segments.
"Equal" connotes "the same"....."as one".....and not in a"ranked" order.
As the way we communicate is by language.....we have to use the established rules (Grammar) that sets forth the construction and meaning of what we speak.
You want to discuss "Probability" or "Statistics".....that will be done using proper Engilsh Grammar as the foundation of the arguments.....don't you agree.
The only we can have commonality of definition is to have settled rules on language otherwise we have anarchy which would prevent effective communication.
Nice try......but still wrong.
Grammar Rules set forth the concept that the use of the conjunction "and" is used to connect two equal sentence segments.
"Equal" connotes "the same"....."as one".....and not in a"ranked" order.
As the way we communicate is by language.....we have to use the established rules (Grammar) that sets forth the construction and meaning of what we speak.
You want to discuss "Probability" or "Statistics".....that will be done using proper Engilsh Grammar as the foundation of the arguments.....don't you agree.
The only we can have commonality of definition is to have settled rules on language otherwise we have anarchy which would prevent effective communication.
For no other reason than First is First and only by sheer physical location in the Sentence.....and if worded just the opposite.....again First would still be First purely by its position in the sentence......thus each equally could be in front of the other and its being there has absolutely no significance re importance or rank.
If there was a way to have both "First" simultaneously then there would be no chance for some to continue with their word twisting.....but that is not possible due to English Grammar.
In this case.....the Law is the Law and there is exactly one interpretation.
Exactly - Definition and More from the Free Merriam-Webster Dictionary
If there was a way to have both "First" simultaneously then there would be no chance for some to continue with their word twisting.....but that is not possible due to English Grammar.
In this case.....the Law is the Law and there is exactly one interpretation.
Exactly - Definition and More from the Free Merriam-Webster Dictionary
Anyway, someone mentioned the yaw pedals and it is interesting to contemplate what should be done with them. Many helicopters have collective /yaw coupling so that the pedals are pretty much in the same position at cruise power as they are at flat pitch (EC225 excepted) so why the need to move the pedals when the engines fail? Well it's just to cover the period when the lever is still up - so the collective /yaw coupling is applying a fair bit of pitch to the tail rotor - but the engine torque has disappeared. So a dab of pedal is required simultaneous with starting to lower the collective, to kill the yaw. After that, on many helicopters the pedals go back to the neutral position, just a little bit in the anti-power direction. The initial yaw - occurring during the pilot reaction time - will typically cause the nose to dip (I am talking about in cruise flight, where me and my colleagues spend most of their time) so another good reason to apply some aft cyclic as an autonomous action, rather than in response to a perceived attitude change - the latter taking longer to process of course.
Because the 225 autopilot is your GOD and you should bow down and worship it. Obviously.
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The initial yaw - occurring during the pilot reaction time - will typically cause the nose to dip (I am talking about in cruise flight, where me and my colleagues spend most of their time) so another good reason to apply some aft cyclic as an autonomous action, rather than in response to a perceived attitude change - the latter taking longer to process of course.
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A fellow poster clued me in on a very significant AAIB accident report that has a lot to say about pilot reaction time to a double engine failure. I am impressed by the thoroughness of the typical AAIB investigation. Check out Report 4/83 on the AAIB website. A Westland Wessex 60, G-ASWT, 13 Aug 81. It's a long read but well worth it. Check out paragraph 1.16.2 regarding pilot reaction time, and paragraph 2.3.2 regarding rotor speed decay. And throughout this detailed investigation there was no mention whatsoever of applying any aft cyclic at all following the failure of the two engines.
So how quickly did pilots react to the double engine failures: The minimum reaction time was 1.5 seconds. The maximum was 7 seconds. The mean was 3 seconds. THREE SECONDS before the flight controls were moved.
Pete
Pete
So how quickly did pilots react to the double engine failures: The minimum reaction time was 1.5 seconds. The maximum was 7 seconds. The mean was 3 seconds. THREE SECONDS before the flight controls were moved.
Pete
Pete
Pete, before you go on about leading with the cyclic, I suggest you ponder on how a lot of models of helicopters
have control mixing that make compensatory movements in other control channels when one moves a single channel. Each helicopter model will have its own unique mix and balance based on its overall design.
The difference between the lateral coupler in an SH-2 and the far more complicated control mixing in the SH-60 mixing unit is an example I am familiar with. I am not up to speed enough on FBW suites to understand how that control mixing is done.
With some aircraft, you may have a control mixing combination that, when you lower the collective is already compensating with a pitch command independent of cyclic input, and that coupling may be up, may be down. You really have to know which aircraft you are flying, which once again makes me leary of your one size fits all approach.
Interesting thing about reaction times. As true in FW as RW, but maybe more dire in RW due to our peculiarities.
Factors will include: training, recency of experience, quality of experience, do you really know your aircraft, and of course and the "startle factor."
I think we agree that we have a crap load more variables in autorotational entry than the current energy state of the aircraft and the rotor system. Nice of you to cherry pick a crash, how many non crashes did you investigate?
Don't get me wrong, Pete. I appreciate your efforts.
My skepticism regards the oversimplification you are pounding away at.
Control Nr.
How do you do that?
Depends on your flight condition and energy state.
Your complaint of oversimplification in re the collective (as though people only fly with one hand ... do they? **** me, that's scary!) can be applied to your oversimplification in re the cyclic.
I like the emphasis on simultaneous.
Why?
It's how I was trained.
It's how helicopters are (generally) flown.
FH110:
Please don't make **** up. What you did there is called a strawman, which weakens your attempts at argument.
But one of your points I'd like to heartily concur with:
When you aren't otherwise constrained, fly at an altitude and airspeed that gives you TIME to deal with that problem ... cannot agree more!
Well said.
have control mixing that make compensatory movements in other control channels when one moves a single channel. Each helicopter model will have its own unique mix and balance based on its overall design.
The difference between the lateral coupler in an SH-2 and the far more complicated control mixing in the SH-60 mixing unit is an example I am familiar with. I am not up to speed enough on FBW suites to understand how that control mixing is done.
With some aircraft, you may have a control mixing combination that, when you lower the collective is already compensating with a pitch command independent of cyclic input, and that coupling may be up, may be down. You really have to know which aircraft you are flying, which once again makes me leary of your one size fits all approach.
Interesting thing about reaction times. As true in FW as RW, but maybe more dire in RW due to our peculiarities.
Factors will include: training, recency of experience, quality of experience, do you really know your aircraft, and of course and the "startle factor."
I think we agree that we have a crap load more variables in autorotational entry than the current energy state of the aircraft and the rotor system. Nice of you to cherry pick a crash, how many non crashes did you investigate?
Don't get me wrong, Pete. I appreciate your efforts.
My skepticism regards the oversimplification you are pounding away at.
Control Nr.
How do you do that?
Depends on your flight condition and energy state.
Your complaint of oversimplification in re the collective (as though people only fly with one hand ... do they? **** me, that's scary!) can be applied to your oversimplification in re the cyclic.
I like the emphasis on simultaneous.
Why?
It's how I was trained.
It's how helicopters are (generally) flown.
FH110:
The "Maintain RPM" squawkers apparently would prefer to decelerate from cruise to best-auto speed while descending for a power-off landing
But one of your points I'd like to heartily concur with:
When you aren't otherwise constrained, fly at an altitude and airspeed that gives you TIME to deal with that problem ... cannot agree more!
Well said.
It's not a strawman, Lone. If you bottom the pitch FIRST, then you WILL start a descent at whatever speed the helicopter was going at the point of engine failure. Guaranteed. Anyone want argue that?
Thought not.
Okay, once the descent is started, THEN the pilot who bottomed the pitch must now decelerate back to best-auto...unless the plan is to come screaming down at cruise speed which, doesn't sound like a good idea to me.
So, Lonewolf, tell me again how my statement is wrong?
Thought not.
Okay, once the descent is started, THEN the pilot who bottomed the pitch must now decelerate back to best-auto...unless the plan is to come screaming down at cruise speed which, doesn't sound like a good idea to me.
So, Lonewolf, tell me again how my statement is wrong?