Entering autos: discussion split from Glasgow crash thread
Can't remember if I've mentioned this before, but following the s76 accident in the states where a bird strike retarded both engine control levers to idle, and they failed to enter auto successfully, we embarked on a training programme to cover simultaneous double engine failure. Prior to that, autos were generally done from an already OEI condition whereby the crew were at an enhanced level of arousal.
For me, what came out of seeing many crews perform in the Sim (and knowing it was coming at some point) was a fair degree of certainly that a simultaneous unexpected double engine failure during cruise etc will almost certainly result in a failure to enter auto successfully. It's just human nature and the way we respond whilst at a low state of arousal.
For me, what came out of seeing many crews perform in the Sim (and knowing it was coming at some point) was a fair degree of certainly that a simultaneous unexpected double engine failure during cruise etc will almost certainly result in a failure to enter auto successfully. It's just human nature and the way we respond whilst at a low state of arousal.
Last edited by HeliComparator; 15th Dec 2013 at 12:56.
I can recall being the odd man out in tea room discussions about Bell 212's and choosing safe landing areas along the flight path just as in Single engined Bell 205's. My argument was predicated upon a Drive Shaft Failure.....not a simultaneous Dual Engine failure (although the results are exactly the same).
Having come within a Gnat's Ass of having exactly that kind of failure over the North Sea one ugly Winter night while shuttling in the Ninian field using an S-58T....perhaps I was being a bit sensitive to the topic.
Something as simple as a Rubber covered Torch left in a bad place by an Engineer can morph that 10 to the -9 event into reality.
Yet we have to admit....just how many simultaneous dual engine failures have we experienced over the years?
If I am not mistaken....there have been far more Tail Rotor Failures than dual engine failures.
Having come within a Gnat's Ass of having exactly that kind of failure over the North Sea one ugly Winter night while shuttling in the Ninian field using an S-58T....perhaps I was being a bit sensitive to the topic.
Something as simple as a Rubber covered Torch left in a bad place by an Engineer can morph that 10 to the -9 event into reality.
Yet we have to admit....just how many simultaneous dual engine failures have we experienced over the years?
If I am not mistaken....there have been far more Tail Rotor Failures than dual engine failures.
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Looking at that video of R22 EOLs reminds me of something I have never quite understood. All the EOLs that I have ever done in the training environment in the UK over the last 15 years have been to a grass surface, whereas every US video that I have seen shows them terminating on a hard surface such as tarmac. Is there any reason for this? If you are going down for real and you have the luxury of a choice, should you pick grass or hard?
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Less damaged helicopters on runways - the UK seem to like risking hitting rabbit holes rather than wearing out the bottom of the skids 
Other than that, use whatever is there.
Phil
Other than that, use whatever is there.
Phil
Grassy areas can be too soft....and if you have any forward speed there is a risk of getting into serious trouble.
If you land on a paved surface....unless you arrive to firmly....there is a very good chance things will turn out okay....if not pretty.
In this situation....the hard choice is better than the soft although if crashing....crashing into the softest things around is the better choice.
If you land on a paved surface....unless you arrive to firmly....there is a very good chance things will turn out okay....if not pretty.
In this situation....the hard choice is better than the soft although if crashing....crashing into the softest things around is the better choice.
HC - It's funny that you mention the PHI S-76 "bird strike" crash. My friend Greg was flying an S-76 for PHI at the time. In the sim in Recurrent soon after the reasons for the crash were figured out, the IP gave him the dreaded dual engine failure in cruise. Greg did what was necessary and put the ship down successfully. Reportedly, he was the *first* pilot to do this; every other one before him crashed.
Now, no doubt Greg is a great pilot (probably even better than me), but so were the other S-76 guys "great pilots" too. I think the difference was that Greg really understood how a helicopter flew. He never verbalized this, but I believe that he instinctively hauled back on the cyclic as he lowered the collective. He knew what Pete Gillies is trying to remind us of: that it's not enough to just get the angle of attack of the blades to a minimum value - you have to get the angle of attack of the disk up to a positive value!
Furthermore, I don't know this but I suspect that the other crews (the ones who crashed) merely lowered the lever and let the RRPM drop to an unrecoverable value. That, or they never got the thing in a stabilized auto until it was too late.
We should be thanking Pete instead of vilifying him. Engine failures don't always happen way up high, with plenty of time and altitude to sort things out.
Now, no doubt Greg is a great pilot (probably even better than me), but so were the other S-76 guys "great pilots" too. I think the difference was that Greg really understood how a helicopter flew. He never verbalized this, but I believe that he instinctively hauled back on the cyclic as he lowered the collective. He knew what Pete Gillies is trying to remind us of: that it's not enough to just get the angle of attack of the blades to a minimum value - you have to get the angle of attack of the disk up to a positive value!
Furthermore, I don't know this but I suspect that the other crews (the ones who crashed) merely lowered the lever and let the RRPM drop to an unrecoverable value. That, or they never got the thing in a stabilized auto until it was too late.
We should be thanking Pete instead of vilifying him. Engine failures don't always happen way up high, with plenty of time and altitude to sort things out.
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This is a great thread, as it makes us think. Why I weighed in is very simple: Today especially there exists a certain kind of distrust of some of the fundamentals of our existence, think born out of the intellectual freedom the web excites (a very good and powerful thing!)
This thinking that goes something like this:
"Those idiots who make XXX (insert a term like: vaccines, evolution textbooks, public laws, medical procedures, missions to the moon, reports on assassinations, flight manual procedures, investigations of 911 acts. ......) are all YYY (insert a term like: too stupid, on the take, drunk with power, ......) and I know because ZZZ (insert term like: I saw a youtube video, my cousin's Aunt's brother told me, a great web site proves otherwise, Glenn Beck told me,....).
The thing that makes me laugh is that within 100 meters of my desk are world class experts who have spent 20 years of so studying, designing, building and testing helicopter stuff. They (like their peers in France, Russia, Texas, Philadelphia, and Yeovil) have become very expert in ways that operators cannot fathom, any more than they can appreciate what a night rig approach is like.
When I read of a person who basically says "that page in the operating limits section of the flight manual is just bull****, do it this way and you will be so happy you will pee your pants!" I react.
Ppruners, do what you will, but while you do, please respect the flight manual, and those who wrote it. Trust them, they know so much more than you can fathom about the machine, because it is their job. That is not an arrogant statement, it is a simple fact. It take nothing away from your expertise, it is a simple statement of how we are a team, and that we rely on each other to stay safe and productive.
This thinking that goes something like this:
"Those idiots who make XXX (insert a term like: vaccines, evolution textbooks, public laws, medical procedures, missions to the moon, reports on assassinations, flight manual procedures, investigations of 911 acts. ......) are all YYY (insert a term like: too stupid, on the take, drunk with power, ......) and I know because ZZZ (insert term like: I saw a youtube video, my cousin's Aunt's brother told me, a great web site proves otherwise, Glenn Beck told me,....).
The thing that makes me laugh is that within 100 meters of my desk are world class experts who have spent 20 years of so studying, designing, building and testing helicopter stuff. They (like their peers in France, Russia, Texas, Philadelphia, and Yeovil) have become very expert in ways that operators cannot fathom, any more than they can appreciate what a night rig approach is like.
When I read of a person who basically says "that page in the operating limits section of the flight manual is just bull****, do it this way and you will be so happy you will pee your pants!" I react.
Ppruners, do what you will, but while you do, please respect the flight manual, and those who wrote it. Trust them, they know so much more than you can fathom about the machine, because it is their job. That is not an arrogant statement, it is a simple fact. It take nothing away from your expertise, it is a simple statement of how we are a team, and that we rely on each other to stay safe and productive.
And of course for real, the guys probably had to contend with a face full of bird feathers and guts, and a good peppering with broken plastic - something that is fairly hard to replicate in the Sim!
Oh, Doubting Thomas... I was not there to witness it, but I would never doubt my friend Greg's truthfulness or sincerity in telling me about the sim session. And if it's true that he was the first S-76 sim pilot to survive the dual engine-failure scenario then I, as an experienced helicopter pilot have to make a couple of educated guesses. That's exactly that they are, and that's exactly how I qualified them.
While I've never flown the S-76, I do know how quickly the RRPM decays in other helicopters if you do nothing but lower the collective after an engine failure at cruise. It takes aft cyclic to bring the RPM back, and sometimes a lot of it. If you're starting from 500 feet that doesn't leave you much room or time. While you're working to get everything under control and get into a stabilized auto, you're losing altitude and your choice of landing spots is getting smaller and smaller.
So I won't go as far as to swear on a stack of Bibles in a courtroom as to why my buddy was the first pilot to pull it off and the other presumably good, competent pilots crashed, but it doesn't take a scientist of rocketry to figure it out. All I'm saying is that those of us who actually know how to fly a helicopter flies...as opposed to, say, you... we understand what Pete Gillies was trying to convey to us.
And HC, it's true, the guys who actually crashed the real one had a lot of things working against them. That other pilots in the relatively sanitary conditions of a simulator also crashed is telling...at least to me...and probably to them as well.
While I've never flown the S-76, I do know how quickly the RRPM decays in other helicopters if you do nothing but lower the collective after an engine failure at cruise. It takes aft cyclic to bring the RPM back, and sometimes a lot of it. If you're starting from 500 feet that doesn't leave you much room or time. While you're working to get everything under control and get into a stabilized auto, you're losing altitude and your choice of landing spots is getting smaller and smaller.
So I won't go as far as to swear on a stack of Bibles in a courtroom as to why my buddy was the first pilot to pull it off and the other presumably good, competent pilots crashed, but it doesn't take a scientist of rocketry to figure it out. All I'm saying is that those of us who actually know how to fly a helicopter flies...as opposed to, say, you... we understand what Pete Gillies was trying to convey to us.
And HC, it's true, the guys who actually crashed the real one had a lot of things working against them. That other pilots in the relatively sanitary conditions of a simulator also crashed is telling...at least to me...and probably to them as well.
... Ppruners, do what you will, but while you do, please respect the flight manual, and those who wrote it. Trust them, they know so much more than you can fathom about the machine, because it is their job. That is not an arrogant statement, it is a simple fact. It take nothing away from your expertise, it is a simple statement of how we are a team, and that we rely on each other to stay safe and productive.
The ones I have seen do not properly allow for variations in mass and density altitude, which affect the outcome in reality. On the (twin) type with which I am most familiar, the HV curve is a single line oblivious to any of the above variables. Fortunately, although the graph is in the limitations section, no-where does it say that you shouldn't operate within the blue zone. Which is just as well because every offshore takeoff puts us into it!
Perhaps one answer to having the HV better respected, is to improve the HV diagram.
Last edited by HeliComparator; 16th Dec 2013 at 10:14. Reason: To remove "wind" from my list of complaints about HV diagrams, and because it is a blue zone, not a red zone
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HV diagram
Presumably the HV diagram is based on demonstration - what a competent pilot should achieve at MAUW and no wind.
There must also be a purely theoretical diagram based solely on modelling or calculations. How different is it?
There must also be a purely theoretical diagram based solely on modelling or calculations. How different is it?
Last edited by Ornis; 15th Dec 2013 at 18:31.
Nick,
Did Sikorsky ever run models of the HV's to accommodate head winds of say....20-30 Knots and if so....what effect does Wind have on the shape (Limits) of the HV Curve?
I can recall doing numerous constant airspeed Auto's at Redhill in the Bell 206....holding 25-30 Knots/Miles Per Hour IAS and doing a slight Decel at the bottom and using up all the Collective during the landing. It quite a pleasant ride.
Add some head wind.....and it made for a very short ground slide.....and an almost vertical descent due to the wind effect.
Did Sikorsky ever run models of the HV's to accommodate head winds of say....20-30 Knots and if so....what effect does Wind have on the shape (Limits) of the HV Curve?
I can recall doing numerous constant airspeed Auto's at Redhill in the Bell 206....holding 25-30 Knots/Miles Per Hour IAS and doing a slight Decel at the bottom and using up all the Collective during the landing. It quite a pleasant ride.
Add some head wind.....and it made for a very short ground slide.....and an almost vertical descent due to the wind effect.
Don't know Mate.....kept my eyes closed the whole way down!
When the other guy did that last gulp of air thing filling his lungs to scream....I pulled Pitch to the up stop and held on for the impact.
Actually the video does not completely compare to the maneuver we were doing.....as we did a noticeable deceleration but no where as deep or held as long as in a normal ordinary Autorotation in that there was very little airspeed to trade for RPM or need to slow. It did require some ground slide if the wind was slack....and none if there was some decent wind.
Practice Autorotations in a Jet Ranger are pretty tame.....as compared to the Hughes 500 Series or the BK-117. The Hughes and BK are far more fun and sporty.
When the other guy did that last gulp of air thing filling his lungs to scream....I pulled Pitch to the up stop and held on for the impact.
Actually the video does not completely compare to the maneuver we were doing.....as we did a noticeable deceleration but no where as deep or held as long as in a normal ordinary Autorotation in that there was very little airspeed to trade for RPM or need to slow. It did require some ground slide if the wind was slack....and none if there was some decent wind.
Practice Autorotations in a Jet Ranger are pretty tame.....as compared to the Hughes 500 Series or the BK-117. The Hughes and BK are far more fun and sporty.
Unrecoverable Nr and H-V
Unrecoverable Nr first.
Peter Gillies wrote:
Then, in a second post, reiterated:
By virtue of several affirmations in this thread, it seems that Peter Gillies has wide experience in the operational side of this business, thus I conclude that this is a case of his being misinformed (by someone equally misinformed).
Truth is, that, though the test standards for US military and civil qualification are somewhat different in the area of transition to power off flight and the testing required to substantiate the H-V plots, one thing is true, and that is, during the course of flight testing any of the machines I have been involved with, this area of testing has always resulted in Nr excursions below the low end of the published green arc ( into the low 80% range ), and I am sure that the test pilot group at the other manufacturers will attest similarly. Thus one's flight is not " over " as Mr. Gillies suggests.
The aero guys at SA in answer to an internal query on an accident investigation some decades ago, did some simulation and opined that there is an Nr number, where at least from the lift vector and angle of attack calculations, the Nr can reach a point where the decay is unrecoverable, and hence ( and this was assumed at full low collective ) you need to put the throttle(s) forward or use your chute. Number was in the 60% range. So there is some margin between where the qualification test crews operate and the point at which the situation turns really dangerous. With an Nr decay rate of 10%/second, though, one does not have all day.
Since either the FAA or the cognizant military test organization gets copies or witnesses all of this testing, the actual Nr behavior is anything but a " deep dark secret ".
As to the H-V subject, I think Nick has said it all. Hard to comment on other manufacturers/models H-V diagrams, but I and Nick have more than a passing relationship with the UH-60, SH-60, all S-76 models and the S-92 models, and for those, I will pass on that the H-V tests were flown to the required structural limits of the machine by pilots who had experience doing that stuff. If one wants to ignore their validity, as at least one poster suggests, have at it, but do have an adequate supply of band-aids on hand.
Thanks,
John Dixson
Peter Gillies wrote:
Very few helicopter pilots realize that if, with a total engine failure, the rotor rpm is allowed to fall more than about 5% below low green, the flight is over. OVER. There is no recovery possible regardless of what actions the pilot may take or how high the helicopter is above ground. This fact is not mentioned in the sales literature for helicopters nor in the approved rotorcraft flight manuals. It is not mentioned in any of our FAA publications having to do with how helicopters fly and how to fly them. It is treated as a deep dark secret, unfortunately.
Easy. As I said in my earlier post, allowing the rotor rpm to drop below the critical point with no engine power to bring it back into the operating range will cause this to happen every time. No exceptions. And as I said before, there is no recovery from this situation. None.
Truth is, that, though the test standards for US military and civil qualification are somewhat different in the area of transition to power off flight and the testing required to substantiate the H-V plots, one thing is true, and that is, during the course of flight testing any of the machines I have been involved with, this area of testing has always resulted in Nr excursions below the low end of the published green arc ( into the low 80% range ), and I am sure that the test pilot group at the other manufacturers will attest similarly. Thus one's flight is not " over " as Mr. Gillies suggests.
The aero guys at SA in answer to an internal query on an accident investigation some decades ago, did some simulation and opined that there is an Nr number, where at least from the lift vector and angle of attack calculations, the Nr can reach a point where the decay is unrecoverable, and hence ( and this was assumed at full low collective ) you need to put the throttle(s) forward or use your chute. Number was in the 60% range. So there is some margin between where the qualification test crews operate and the point at which the situation turns really dangerous. With an Nr decay rate of 10%/second, though, one does not have all day.
Since either the FAA or the cognizant military test organization gets copies or witnesses all of this testing, the actual Nr behavior is anything but a " deep dark secret ".
As to the H-V subject, I think Nick has said it all. Hard to comment on other manufacturers/models H-V diagrams, but I and Nick have more than a passing relationship with the UH-60, SH-60, all S-76 models and the S-92 models, and for those, I will pass on that the H-V tests were flown to the required structural limits of the machine by pilots who had experience doing that stuff. If one wants to ignore their validity, as at least one poster suggests, have at it, but do have an adequate supply of band-aids on hand.
Thanks,
John Dixson
Does a rigid head, vs a fully articulated head, make any difference? I am thinking of the differing coning angles at least towards the root, between the two technologies at low rpm. I have it in mind that a high coning angle reduces the increased angle of attack caused by high rate of descent.
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Hello, John. The information about there being a point of no return came to me from Bell Helicopter years ago. Where is this point? The manufacturers won't tell you and don't want you to try and find it for obvious reasons. Just "keep it in the green." My research says that our FAA requires that the rotor rpm be recoverable within 5% below the lower red line. Some rotor systems may be recoverable below that point. I don't know, and I'm not about to experiment with the engine off line. In our light turbines, the idling engine normally keeps the rotor rpm within the green with the collective full down, so the only way to experiment would be to force the engine to idle more slowly or to flame it out (dumb).
The real world many of us fly in every day is often light years away from the finely tuned world of the test pilot. I admire all of you that possess this fine, sharply tuned knowledge, skill and understanding of rotor dynamics and flying on the edge. My comments, thoughts and suggestions to this forum are meant for all the rest of us who simply fly the aircraft and hope we never have to deal with engine failures and the like.
Pete Gillies
The real world many of us fly in every day is often light years away from the finely tuned world of the test pilot. I admire all of you that possess this fine, sharply tuned knowledge, skill and understanding of rotor dynamics and flying on the edge. My comments, thoughts and suggestions to this forum are meant for all the rest of us who simply fly the aircraft and hope we never have to deal with engine failures and the like.
Pete Gillies
The aero guys at SA in answer to an internal query on an accident investigation some decades ago, did some simulation and opined that there is an Nr number, where at least from the lift vector and angle of attack calculations, the Nr can reach a point where the decay is unrecoverable, and hence ( and this was assumed at full low collective ) you need to put the throttle(s) forward or use your chute. Number was in the 60% range. So there is some margin between where the qualification test crews operate and the point at which the situation turns really dangerous. With an Nr decay rate of 10%/second, though, one does not have all day.
However (and needless to say) one's objective must be to do all possible to maintain Nr within the green.