Entering autos: discussion split from Glasgow crash thread
I take it back....much simpler.....I can go to sleep now....I learned something!
Pete, if you click "reply" alongside the previous post in question, you get a blank form to make a new post. But then look in the address bar of your browser and you will see some gobbledygook at the end of which is "noquote=1". Change the 1 to a 0 and press enter to reload the page. Now the post in question is quoted and you can insert your text. Best to change the colour of your text so that your additions are obvious.
You Aussie Bikies are always creating trouble!
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Don't follow this advice
PG's statement is utter nonsense and may contribute to an accident.
After recently trialling a large helicopter in auto entry the only thing that will save you is lowering collective. NR decay is critical and aft cyclic did little until collective was lowered. The aft cyclic comment is usually due to cruising above max speed for engines off. A comment about 0 g , that's because the helo is accelerating down and will build NR - feeling 0 g in cockpit means zip unless in a teetering rotor system - then you have bigger problems.
If you have questions talk to training staff or an instructor about your specific type. There are way too many variances between types to generalize. What works in one will cause a severe problem in another.
After recently trialling a large helicopter in auto entry the only thing that will save you is lowering collective. NR decay is critical and aft cyclic did little until collective was lowered. The aft cyclic comment is usually due to cruising above max speed for engines off. A comment about 0 g , that's because the helo is accelerating down and will build NR - feeling 0 g in cockpit means zip unless in a teetering rotor system - then you have bigger problems.
If you have questions talk to training staff or an instructor about your specific type. There are way too many variances between types to generalize. What works in one will cause a severe problem in another.
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In cruise flight,The power stops,add aft cyclic & lower collective as needed,
A +G is good for the rotor system, Aft cyclic loads the system ,It helps get air flow up though the disk, No flow no autorotation, a delay just drags your RPM down & it takes time to get it back. Pete is spot on.
ARMY/NASA tests are public record down loadable,
Heck you can trade speed for altitude and still do a good auto (& with a well timed flare on the bottom end no collective's needed.
)
A +G is good for the rotor system, Aft cyclic loads the system ,It helps get air flow up though the disk, No flow no autorotation, a delay just drags your RPM down & it takes time to get it back. Pete is spot on. ARMY/NASA tests are public record down loadable,Heck you can trade speed for altitude and still do a good auto (& with a well timed flare on the bottom end no collective's needed.
)
Read it and weep.....the 65% Critical Nr Number shows up in an actual flight test.
The caution that the report results should not be applied to other aircraft or conditions reminds us of what has been said.
IAS parameters were limited to 25-80 Knots....and airspeeds outside that range resulted in excessive vibrations.
http://ntrs.nasa.gov/archive/nasa/ca...1969019854.pdf
The caution that the report results should not be applied to other aircraft or conditions reminds us of what has been said.
IAS parameters were limited to 25-80 Knots....and airspeeds outside that range resulted in excessive vibrations.
http://ntrs.nasa.gov/archive/nasa/ca...1969019854.pdf
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Flt tests
The test mentioned was for looking at extended range performance in a light teetering rotor system - not really for this discussion. No argument aft cyclic will increase NR if you have airspeed and if you have lowered collective.
Don't confuse positive G with aerodynamics, all positive G means in an auto is you are slowing by flaring either in pitch or during a descending turn. There is no level flight in an auto. The flare is increasing NR by increasing the angle of attack of the relative airflow to the rotor system.
An Auto by definition means the helo is descending and the relative air flow to the rotor system is from below, angle dependent on airspeed, no requirement for aft cyclic other than to control nose tuck. Just tested it at a variety of airspeeds in a large helicopter.
If you induce aft cyclic at low IAS you just made the situation much worse as you have bled off Airspeed and as indicated by the study where they mention recovering entry auto rpm by lowering collective. Now your in the worse of both worlds, no airspeed and low Nr.
Don't confuse technique to get a smooth entry during routine practise with what will happen when your caught by surprise and NR is already 90%.
To answer PG , NR will recover by doing nothing more than lowering collective aft cyclic is not required to regain NR, it does control nose tuck, done it numerous times, even waiting for the 2 sec count and doing nothing else. In fact it is better in a helo with stabilization not to touch anything except the collective, stabilizes in the auto much quicker., yes you need to re reference the IAS.
please discuss with training staff, this is a complicated discussion and varies by type there is no one answer that fits all and cannot be properly discussed in this forum
Don't confuse positive G with aerodynamics, all positive G means in an auto is you are slowing by flaring either in pitch or during a descending turn. There is no level flight in an auto. The flare is increasing NR by increasing the angle of attack of the relative airflow to the rotor system.
An Auto by definition means the helo is descending and the relative air flow to the rotor system is from below, angle dependent on airspeed, no requirement for aft cyclic other than to control nose tuck. Just tested it at a variety of airspeeds in a large helicopter.
If you induce aft cyclic at low IAS you just made the situation much worse as you have bled off Airspeed and as indicated by the study where they mention recovering entry auto rpm by lowering collective. Now your in the worse of both worlds, no airspeed and low Nr.
Don't confuse technique to get a smooth entry during routine practise with what will happen when your caught by surprise and NR is already 90%.
To answer PG , NR will recover by doing nothing more than lowering collective aft cyclic is not required to regain NR, it does control nose tuck, done it numerous times, even waiting for the 2 sec count and doing nothing else. In fact it is better in a helo with stabilization not to touch anything except the collective, stabilizes in the auto much quicker., yes you need to re reference the IAS.
please discuss with training staff, this is a complicated discussion and varies by type there is no one answer that fits all and cannot be properly discussed in this forum
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Return to target
Yeah you can do a good auto flying a high inertia system with weighted tips, haven't flown that type of system in a long time, my experience with modern systems are that they are low inertia, better get the collective down because with low inertia NR disappears fast and it won't climb far.
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SASless
A brilliant find of a document published in 1969. There are numerous caveats in the document about the test conditions and that the results should not be applied to any other type of helicopter. I particularly note that all tests were carried out with forward airspeed and that the collective was lowered and rotor speed increased in the final stages of the descent to complete the landing.
The purpose of the test appears to have been an attempt to so whether the published manufacturers figures for autorotational glide could be improved upon. The answer was a tentative 'yes'.
The forward speed of the helicopter would have provided some lift and the apparent wind direction through the rotor disc would have been angled, so rotor speeds lower than those normally associated with the onset of rotor stall in a vertical descent could be attained without the helicopter falling from the sky. The vibration and buffeting effects described in the text clearly indicate that the tests were carried out right at the edge of what could be achieved.
Attempts to stretch a glide in any aircraft, fixed or rotary wing, rarely end well. It is however a wonderful tribute to the bravery of the pilot(s) who carried out these tests and proof that there is a bit of latitude in the manufacturers published figures if you have the skills to stretch the limits and the nature of the circumstances absolutely demand you take the risk.
Absolutely fascinating!
A brilliant find of a document published in 1969. There are numerous caveats in the document about the test conditions and that the results should not be applied to any other type of helicopter. I particularly note that all tests were carried out with forward airspeed and that the collective was lowered and rotor speed increased in the final stages of the descent to complete the landing.
The purpose of the test appears to have been an attempt to so whether the published manufacturers figures for autorotational glide could be improved upon. The answer was a tentative 'yes'.
The forward speed of the helicopter would have provided some lift and the apparent wind direction through the rotor disc would have been angled, so rotor speeds lower than those normally associated with the onset of rotor stall in a vertical descent could be attained without the helicopter falling from the sky. The vibration and buffeting effects described in the text clearly indicate that the tests were carried out right at the edge of what could be achieved.
Attempts to stretch a glide in any aircraft, fixed or rotary wing, rarely end well. It is however a wonderful tribute to the bravery of the pilot(s) who carried out these tests and proof that there is a bit of latitude in the manufacturers published figures if you have the skills to stretch the limits and the nature of the circumstances absolutely demand you take the risk.
Absolutely fascinating!
There is a lot of information in that report that bears discussion as it relates to some issues raised in this thread. The test aircraft was the forerunner to the OH-58A.....and Bell 206. The basic concept seemed to be validating Glide Distance can be improved by using a raised collective setting rather than a full down collective setting.
G Loadings was shown in one graph....which had some interesting results.
Some of the comments about effect of controls, the actual bottom limit of NR they used in the test, amount of delay it takes for Torque to drop to Zero following an engine failure, time and height it takes to regain safe Nr to carry out a an EOL, and some other points.
The Test flying was done for a specific purpose but that does not mean the data created cannot be considered for what does tell us.
The fact the aircraft was flown power off at 65% Nr is note worthy as that is 30% below the Handbook Minimum Nr.....well beyond the 5% figure the PG has given as a Critical Point.
As we have been told that a mere 5% below the Normal Power Off Minimum Nr puts us into very dangerous territory. That would not be borne out based upon the test results. The test certainly confirms such a low Rotor RPM does not afford the capability to perform a safe EOL landing.....but that the aircraft flew well at moderate airspeeds with a very low Nr.
The difference in Nr caused by the movement of the cyclic in either the forward left quadrant or the aft right quadrant gives rise to questions of why that is for us that are aerodynamically challenged.
The Report certainly provides some insight into how the Rotor System reacts in very low Nr autorotative flight regimes. Page 4 and 5....just before the Conclusions Section that is on page 5 hold some very interesting comments. The slow decrease of engine Torque was noted as was the rate of increase in RPM during recovery from the Test RPM of 65% to the Normal RPM limit of 95% along with the associated increase in ROD.
There was also a comment about the results not being representative of any other type and model of aircraft or in conditions other than those noted in the Report.
The one thing it certainly does is remind us there are many ways to fly the same helicopter.....some that are within the Normal Limitations of the aircraft contained within the RFM as approved by the Certifying Authority and other non-approved and non-certified methods.
In keeping with the Nanny State Mentality of some here......the caveat that was not done in Big Bold Bright Type was "Do Not Attempt This At Home Kids!.....as it ain't kosher!".
G Loadings was shown in one graph....which had some interesting results.
Some of the comments about effect of controls, the actual bottom limit of NR they used in the test, amount of delay it takes for Torque to drop to Zero following an engine failure, time and height it takes to regain safe Nr to carry out a an EOL, and some other points.
The Test flying was done for a specific purpose but that does not mean the data created cannot be considered for what does tell us.
The fact the aircraft was flown power off at 65% Nr is note worthy as that is 30% below the Handbook Minimum Nr.....well beyond the 5% figure the PG has given as a Critical Point.
As we have been told that a mere 5% below the Normal Power Off Minimum Nr puts us into very dangerous territory. That would not be borne out based upon the test results. The test certainly confirms such a low Rotor RPM does not afford the capability to perform a safe EOL landing.....but that the aircraft flew well at moderate airspeeds with a very low Nr.
The difference in Nr caused by the movement of the cyclic in either the forward left quadrant or the aft right quadrant gives rise to questions of why that is for us that are aerodynamically challenged.
The Report certainly provides some insight into how the Rotor System reacts in very low Nr autorotative flight regimes. Page 4 and 5....just before the Conclusions Section that is on page 5 hold some very interesting comments. The slow decrease of engine Torque was noted as was the rate of increase in RPM during recovery from the Test RPM of 65% to the Normal RPM limit of 95% along with the associated increase in ROD.
There was also a comment about the results not being representative of any other type and model of aircraft or in conditions other than those noted in the Report.
The one thing it certainly does is remind us there are many ways to fly the same helicopter.....some that are within the Normal Limitations of the aircraft contained within the RFM as approved by the Certifying Authority and other non-approved and non-certified methods.
In keeping with the Nanny State Mentality of some here......the caveat that was not done in Big Bold Bright Type was "Do Not Attempt This At Home Kids!.....as it ain't kosher!".
Last edited by SASless; 18th Dec 2013 at 02:56.
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SASLESS
Agreed there are ways then there are ways.......but not everyone is at the same level in terms of understanding, ability and applicability to type. This is a public forum where very inexperienced pilots may read something and take it as fact, I have never read anywhere on 15 different helicopter types of a 5% NR decay being critical. Have you? Yet a supposedly knowledgable person posted it.....
The initial point of this thread is largely pointless as we are talking fractions of a second, get the collective down and worry about the rest.....but it can be very misleading to a junior pilot who delays reacting because he read..... And yes I have seen that, not just autos, and the aftermath because somebody said......
The initial point of this thread is largely pointless as we are talking fractions of a second, get the collective down and worry about the rest.....but it can be very misleading to a junior pilot who delays reacting because he read..... And yes I have seen that, not just autos, and the aftermath because somebody said......
I, like many experienced UK pilots on this forum, have been following this thread with interest and have refrained from entering the discussion. In the past I’ve had a reluctance to display my experience as it’s no different from many others. But to support the following statement, I am an ex military QHI and civilian TRE/IRE, have been instructing/testing in the military and civilian world for over 30 years (including N.Sea and police aviation) and have therefore engaged in countless auto rotations – as many others here have. I comment here because inexperienced pilots on single engine types who have been following this thread may hesitate a little to assess parameters before reacting to an engine failure.
I agree with Rotor IP and TC. Lower the lever – immediately. Simple. Think about everything else after that action; most times, instinct will drive cyclic inputs, but it won’t help at all if the NR is irrecoverable.
I agree with Rotor IP and TC. Lower the lever – immediately. Simple. Think about everything else after that action; most times, instinct will drive cyclic inputs, but it won’t help at all if the NR is irrecoverable.
HC - just out of interest, since your theory is based on 150 kt double engine failures, how many of those have you had, how many double engine failures have you initiated at 150 kts by pulling back both engines - ie what is your concept of ops based on?
Simulator time perhaps? Calling practice double engine failure in the cruise with both engines running normally?
You are very hardover about this entry to auto technique so where has it grown from?
Simulator time perhaps? Calling practice double engine failure in the cruise with both engines running normally?
You are very hardover about this entry to auto technique so where has it grown from?
Crab as you know I (used to) fly EC225 in oil and gas support. In that role perhaps 95% of the flight time is at MCP doing 145-150 in the cruise, and up to 165 on descent. So taking into account climb time, perhaps 90% at 145+. Obviously the cause of a double engine failure in the cruise is hard to envisage, but since we spend the vast majority of time in the cruise and double engine failure is something we are required to train for, it seems sensible to take the cruise case - and for example I guess the PHI 76 was probably doing 145 when it hit the bird.
Before we had the simulator we used to do this in the aircraft. But we were wimps and simulated auto entry purely by lowering the lever - engine control switches were not retarded due to the risk is using real OEI power. So the "failure" was pilot flying initiated - pretty benign you might think.
Nearly everyone got it right, flaring the aircraft as the lever was lowered to maintain 1g+. But a few (mainly fairly junior IIRC) pilots just lowered the lever rapidly and all hell broke loose with things floating up at sub-zero g including the pilots, then they would react to that and pull the cyclic back a bit, the disc would bite and the Nr would wind up at a phenomenal rate. I recall on my TRE check having a trainee do this and I just caught the Nr with a massive pull as it reached the max transient power off Nr. Scary!
Regarding the bit about Nr continuing to decay at zero g, obviously the nature of our auto entry means I have never seen this, but I think the aerodynamics of it make the consequence clear.
So in summary, from fast cruise rapid entry into autorotation can either be a benign affair if leading with the cyclic, or absolute mayhem if the collective is lowered without any cyclic input.
Thinking back to my days on the AS332L where we did retard the throttles to practice autos, with the entry from say 120kts the effect was less critical, but still noticeable. Entry without aft cyclic was messy rather than mayhem.
Before we had the simulator we used to do this in the aircraft. But we were wimps and simulated auto entry purely by lowering the lever - engine control switches were not retarded due to the risk is using real OEI power. So the "failure" was pilot flying initiated - pretty benign you might think.
Nearly everyone got it right, flaring the aircraft as the lever was lowered to maintain 1g+. But a few (mainly fairly junior IIRC) pilots just lowered the lever rapidly and all hell broke loose with things floating up at sub-zero g including the pilots, then they would react to that and pull the cyclic back a bit, the disc would bite and the Nr would wind up at a phenomenal rate. I recall on my TRE check having a trainee do this and I just caught the Nr with a massive pull as it reached the max transient power off Nr. Scary!
Regarding the bit about Nr continuing to decay at zero g, obviously the nature of our auto entry means I have never seen this, but I think the aerodynamics of it make the consequence clear.
So in summary, from fast cruise rapid entry into autorotation can either be a benign affair if leading with the cyclic, or absolute mayhem if the collective is lowered without any cyclic input.
Thinking back to my days on the AS332L where we did retard the throttles to practice autos, with the entry from say 120kts the effect was less critical, but still noticeable. Entry without aft cyclic was messy rather than mayhem.
Got to be totally honest the theory and mathematics are beyond me but perhaps someone can pick the good points out of this? I think page 44 onwards talks autos....
http://www.scribd.com/doc/81931718/H...ucation-Series
http://www.scribd.com/doc/81931718/H...ucation-Series
Is there any more to be said really? Peter - you have to go away and think hard about conveying your message properly (I don't think you have got it wrong - simply having problems getting it across to us Brits perhaps?).
All those who genuinely believe his mantra need to have a long hard think about what you have been practicing all these years?
[A big thank you to Rotor IP and Prawn2 for backing this up].
Finally and most importantly:
To ALL ab initio's, newbie's wannabee's, observers:
UNDER ALL CIRCUMSTANCES (no exception whatsoever) - LOWER THE COLLECTIVE FIRST IN THE EVENT OF A TOTAL ENGINE(S) FAILURE.
On certain occasions: lower the collective AND simultaneously select appropriate cyclic movement to co-ordinate entry into autorotation.
These 2 statements well serve you well and never do you any harm as you learn to fly any helicopter.
All those who genuinely believe his mantra need to have a long hard think about what you have been practicing all these years?
[A big thank you to Rotor IP and Prawn2 for backing this up].
Finally and most importantly:
To ALL ab initio's, newbie's wannabee's, observers:
UNDER ALL CIRCUMSTANCES (no exception whatsoever) - LOWER THE COLLECTIVE FIRST IN THE EVENT OF A TOTAL ENGINE(S) FAILURE.
On certain occasions: lower the collective AND simultaneously select appropriate cyclic movement to co-ordinate entry into autorotation.
These 2 statements well serve you well and never do you any harm as you learn to fly any helicopter.
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UNDER ALL CIRCUMSTANCES (no exception whatsoever) - LOWER THE COLLECTIVE FIRST IN THE EVENT OF A TOTAL ENGINE(S) FAILURE.
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Peter, I have been a strong supporter of your CYCLIC-AFT policy for all normal operations (excluding hovers and extreme low level where specific techniques need to be taught and practised that are paradoxical).
However, your statement that lowering the collective will not stop the Nr decaying must surely not be true if the Nr, at the point the lever hits the floorplate, is at least in the green and probably in the "Safe" margin proved during certification (thanks TPs).
There is always a little hiatus until the ROD develops and the airflow reverses through the disc. This differs according to type but does not last long if the lever is lowered fully with NR in the green range.
I think the flare (cyclic aft) removes the hiatus by more rapidly reversing the airflow through the disc and therefore will help any situation where the NR is too low and certainly nuetralises decay faster than waiting for the hiatus to end. For this reason I support the cyclic aft policy for normal cruise flight BUT surely, the lever must be fully lowered as fast as possible.
If your statement was true I beleive there would be no condition of stable Nr in autorotation.
DB
However, your statement that lowering the collective will not stop the Nr decaying must surely not be true if the Nr, at the point the lever hits the floorplate, is at least in the green and probably in the "Safe" margin proved during certification (thanks TPs).
There is always a little hiatus until the ROD develops and the airflow reverses through the disc. This differs according to type but does not last long if the lever is lowered fully with NR in the green range.
I think the flare (cyclic aft) removes the hiatus by more rapidly reversing the airflow through the disc and therefore will help any situation where the NR is too low and certainly nuetralises decay faster than waiting for the hiatus to end. For this reason I support the cyclic aft policy for normal cruise flight BUT surely, the lever must be fully lowered as fast as possible.
If your statement was true I beleive there would be no condition of stable Nr in autorotation.
DB
Chop: I think your aim in life is to be a tw*t for a s long and as often as possible. That is why I put the second paragraph in - just for prats like you, but even you couldn't get that far with the reading of it before posting could you.
Please stick to RC drones and find a drone web site to plague but you really are making a complete and utter d*ck of yourself lately (even more than usual).
Happy Christmas CJ.
Please stick to RC drones and find a drone web site to plague but you really are making a complete and utter d*ck of yourself lately (even more than usual).
Happy Christmas CJ.
HC - yes, I have had students slam the lever at the floor to enter auto and it does make the nose drop and generate less that 1g - as I said earlier, a co-ordinated entry is nearly always the best solution, as you advocate.
However, I cannot agree with Peter's aft cyclic assertion - flare effect is temporary, min pitch is a far more permanent solution where Nr is concerned.
In certain circumstances, flare effect can be used to gain height from a high speed entry to auto - the Gazelle would climb 2 - 300' from 120kts and you could hold the lever above min pitch during that zoom climb.
However, people were often lulled into a false sense of security by it as it was usually initiated verbally - when the same exercise was flown and initiated by hacking the throttle, the amount of climb was reduced and the lever had to be lowered further to prevent decay - and that was without the 1 -2 second reaction time that would occur in the real case.
So I come back to - lower the lever first, and always (except low hover) and do with the cyclic what you want or need to in order to recover the lost Nr.
No big secret - it's been taught that way for years
However, I cannot agree with Peter's aft cyclic assertion - flare effect is temporary, min pitch is a far more permanent solution where Nr is concerned.
In certain circumstances, flare effect can be used to gain height from a high speed entry to auto - the Gazelle would climb 2 - 300' from 120kts and you could hold the lever above min pitch during that zoom climb.
However, people were often lulled into a false sense of security by it as it was usually initiated verbally - when the same exercise was flown and initiated by hacking the throttle, the amount of climb was reduced and the lever had to be lowered further to prevent decay - and that was without the 1 -2 second reaction time that would occur in the real case.
So I come back to - lower the lever first, and always (except low hover) and do with the cyclic what you want or need to in order to recover the lost Nr.
No big secret - it's been taught that way for years