For Nick Lappos, re: Contention Concerning H/V Diagram
Nick and Paco, is 'heliops' an online publication? I haven't heard of it before and if you are both writing in it I want to read it.
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Originally Posted by Matthew Parsons
If you change from the test conditions (speed, height, density altitude, weight, attitude, etc.) then the chart will no longer be as accurate
Need to be a bit careful where newbies are exposed to normal beer talk chaps.
Is not 'speed' , 'attitude'?
Density altitude, yes does change things, have a look at the rotor rigging graphs in the robinson maintenance manual.
Weight chnages nothing except the time interval, presuming y'all got your auto RPM set up as per the book and not a bit high.
Probably not a good idea to a quote time interval of collective down at any greater than 1 second, that's the rule stick to it.
One very useful rule of thumb for EOL recovery is always try to operate with your collective DOWN as much as possible at all times. Looks after the engine too.
As far as climbing etc, check the airspeed on the graph, how many of you are at 250 feet say and in cruise configuration at 25 knots?
On one of the other threads referred to one dude went into a long discussion about 1929fpm climb being the same as 9.8mpersec - as in gravity - therefore it would take 2 seconds to be established in auto with no power. one to slow down a'goin up and one to speed up a'goin down.
Gee whiz who says you have to be going downhill before you can be in auto?
All that has to happen is the airflow has to be reversed.
saw a super puma on pprune the other day flat out at ground level, so i'll be game and say that I guess all helicopters must be able to do just that. ??
So - what happens when it suddenly goes quiet in that configuration? any one ever teach you don't drop the collective at that point, why you might be a whole lot bettter off giving the collective a bit of a flick UP, so as to get the tail and everything away from the ground for when you want to start a bit of aft cyclic to change the speed,- errr-- attitude to dress yourself up for a zero speed touchdown, of course remembering to start bringing the colllective back down again.
The A/C will have performed - during autorotation - a climb then level flight for a bit then descent profile as the A/S comes back before the final touchdown sequence.
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topendtorque:
Weight does change a lot of things on the HV curve - more than one helicopter has a 'family' of HV curves for different weights and density altitudes.
The intervention time of one second is there to cater for the pilot who doesn't have hands on the collective - and even that is a very short time. All the pilots I know who had real engine failures were quite surprised and said it probably took longer than one second to react. The US military requires a two second intervention time.
You mentioned climbing...
Another one of the things not published in flight manuals for most light helicopters is the takeoff profile. The profile is supposed to keep you out of the HV curve by about 10 feet and 5knots - anyone who is climbing out at 40 knots in a Bell 206 for example is going to be unpleasantly surprised at the results should the engine fail.
Weight does change a lot of things on the HV curve - more than one helicopter has a 'family' of HV curves for different weights and density altitudes.
The intervention time of one second is there to cater for the pilot who doesn't have hands on the collective - and even that is a very short time. All the pilots I know who had real engine failures were quite surprised and said it probably took longer than one second to react. The US military requires a two second intervention time.
You mentioned climbing...
Another one of the things not published in flight manuals for most light helicopters is the takeoff profile. The profile is supposed to keep you out of the HV curve by about 10 feet and 5knots - anyone who is climbing out at 40 knots in a Bell 206 for example is going to be unpleasantly surprised at the results should the engine fail.
Topendtorque, most people in the military will have been taught a low level EOL from high speed - you do not raise the lever! Gentle aft cyclic will zoom climb the aircraft and keep the Nr up (flare effect) but you will need to lower the lever shortly after starting the climb to conserve the Nr. The advantage of the manoeuvre is that it gains you height and therefore time to select a sutiable area for your EOL. Note that you must be gentle nosing over to select your normal auto speed as the slight reduction in G will decay the Nr.
The amount of height gained depends on the entry speed, the rate of cyclic application and the aircrafty type and weight bvut the Gazelle used to gain 2 - 300 feet in this manoeuvre from 120 kts.
The amount of height gained depends on the entry speed, the rate of cyclic application and the aircrafty type and weight bvut the Gazelle used to gain 2 - 300 feet in this manoeuvre from 120 kts.
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There are many disagreements, often between knowledgeable experts, in the interpretation of performance charts. It happens at times that experts have different opinions but each is correct because of their individual experiences. Each test pilot who responds to certification questions does so from their individual experience. The Limiting Height – Speed Envelope (H-V or ‘Dead man’s Curve) has generated more than its fair share of controversy over the years.
My H-V testing experience has been in the testing of helicopters for US Military and FAA certification on land and sea. Most of my comments will be based on the FAA certification basis for single engine helicopters below six thousand pounds.
Certification regulations change over time and the methods and procedures to show compliance with these regulations also change. CAR6, FAR 27 or FAR 29 is the various regulations that have been the certification basis of most US manufactured helicopter s. Each individual regulation has been amended so to speak of the individual requirements of one regulation you must be specific as to time. Strange as it may seem there are different and acceptable methods of testing to show compliance with the regulations as long is it meets provides for an equivilent level of safety. Each manufacturer has individual methods of showing compliance. Sikorsky is different than Bell which is different than Hughes which was different than Robinson or McDonnell Douglas or Hiller or Boeing and every other company in the business.
The FAA published an advisory circular 27-1 to assist certification applicants by providing a history of the certification process and to provide at least one acceptable method to demonstrate compliance with Part 27 and to some extent the other parts.
The above is written so that it is understood that my experience is different than that of Nick or Shawn or other test pilots, and what follows will reflect that bias.
Nick writes:
“1) The H-V Curve is only precise at the one tested condition of weight, altitude, wind and temperature, it can be very very inaccurate if you are at a much lower weight, higher wind or much lower altitude/temp.”
I respond:
My experience is that there is a build up process during Limiting Height – Speed Envelope testing. Tests are conducted and test data generated at several different combinations of weight, altitude, wind and temperature and that data is accurate. The Limiting Height –Speed Envelope information presented in the Performance Section of the Rotorcraft Flight Manual is that required by regulation. The guidance is that the flight manual should list any procedures which may apply to specific points (e.g., high speed points) and test conditions, such as runway surface, wave height for amphibious tests, marginal areas of controllability or landing gear response, etc. The HV curve should be presented in the RFM using actual altitude above ground level and indicated airspeed. Manufacturers may include data for other tested conditions but it will be in the unapproved section of the flight manual if not validated by the FAA. The curve is not ‘inaccurate’ at other weight, winds, altitude, temperatures, landing surfaces or any other specific condition not tested; it is just not applicable to those conditions and can be used to predict performance.
Nick writes:
“2) Is based upon programmed delays in lowering the collective. If you are quick as a bunny, your personal H-V ciurve would be much smaller, if you are slower, you cannot trust the H-V curve because it is too small for you.”
I respond:
Item 2 is the reason I have chosen to post on this matter. The FAA has two primary methods of entry for H-V testing. A one second delay or normal pilot reaction time are the ‘programmed delays’ allowed by the FAA and which technique is used depends on the point tested. The technique applies to collective and the interpretation concerning allowable movement of the other controls such as cyclic and pedals, as well as the definition of normal pilot reaction time are the subject of considerable debate. Of one thing I have no doubt. A test pilot, who has completed a buildup program, is concentrating on only one task, and who initiates a simulated engine failure will be faster than a pilot who is task saturated, not practiced, and unaware of an engine failure event. No matter how fast a ‘normal pilot’ - the bunny pilot - he or she will not be faster than the test pilot who established the point on the curve. When I hear someone say that a good, experienced pilot can somehow beat the curve my blood boils. Do not count on it! As one example of the reason I am so confident in this opinion consider that scientific testing in controlled circumstances has concluded that recognition and response times can be as much as 4.4 to 5.7 seconds; contrast that with the 1 second (at most) delay in testing.
Nick writes:
3) If you are descending, the H-V curve is wrong, the real one would be very much smaller.”
I respond:
The H-V curve is not wrong. It is accurate for the stated conditions. The tested data presented in the H-V curve does not represent a specific condition of descent. You may consider the values presented for hover or climb or level flight to be conservative compared to descending flight, but not ‘wrong’.
Nick writes:
“4) If you are climbing, the H-V curve would be very much bigger.”
I respond:
This depends on the phase of flight where the climb occurs. In the take-off corridor the data reflects climb. A climbing OGE hover would however require a larger H-V curve. It is not the climb or climb rate that is the significant variable but the power used (main rotor blade pitch) because that increases rotor decay. There is also the type of engine failure that occurs. As an example a test pilot who retards throttle or power lever on a FADEC equipped engine will see a programmed rate of engine decay that would be much slower than that experienced in an actual engine failure. That equates to less time for the pilot response.
Nick writes:
5) If you have 5 knots of steady wind, the H-V curve would be very very much smaller. With 20 knots of wind, there is practically no H-V curve.
I respond:
This should be self evident by the curve itself and general pilot knowledge of aerodynamics. The reverse is true of tail winds and cross winds which is why the conditions on which the curve is predicated must be understood by the professional pilot. I have longed believed that CAT A performance should be predicated on 17 knots of down wind (hover controllability) because so few pilots understand what a tail wind can do to single engine fly away capability.
I do not disagree that the Limiting Height – Speed Envelope is a performance chart that should be used as a guide from which to make predictions based on specific conditions but; it is a useful guide nonetheless.
There are many who have long advocated a change to the certification basis for engine out performance and the Limiting Height – Speed Envelope such as more realistic pilot reaction times or additional performance testing such as a take-off power climb at VY, and actual engine out testing (Hiller did it once).
My H-V testing experience has been in the testing of helicopters for US Military and FAA certification on land and sea. Most of my comments will be based on the FAA certification basis for single engine helicopters below six thousand pounds.
Certification regulations change over time and the methods and procedures to show compliance with these regulations also change. CAR6, FAR 27 or FAR 29 is the various regulations that have been the certification basis of most US manufactured helicopter s. Each individual regulation has been amended so to speak of the individual requirements of one regulation you must be specific as to time. Strange as it may seem there are different and acceptable methods of testing to show compliance with the regulations as long is it meets provides for an equivilent level of safety. Each manufacturer has individual methods of showing compliance. Sikorsky is different than Bell which is different than Hughes which was different than Robinson or McDonnell Douglas or Hiller or Boeing and every other company in the business.
The FAA published an advisory circular 27-1 to assist certification applicants by providing a history of the certification process and to provide at least one acceptable method to demonstrate compliance with Part 27 and to some extent the other parts.
The above is written so that it is understood that my experience is different than that of Nick or Shawn or other test pilots, and what follows will reflect that bias.
Nick writes:
“1) The H-V Curve is only precise at the one tested condition of weight, altitude, wind and temperature, it can be very very inaccurate if you are at a much lower weight, higher wind or much lower altitude/temp.”
I respond:
My experience is that there is a build up process during Limiting Height – Speed Envelope testing. Tests are conducted and test data generated at several different combinations of weight, altitude, wind and temperature and that data is accurate. The Limiting Height –Speed Envelope information presented in the Performance Section of the Rotorcraft Flight Manual is that required by regulation. The guidance is that the flight manual should list any procedures which may apply to specific points (e.g., high speed points) and test conditions, such as runway surface, wave height for amphibious tests, marginal areas of controllability or landing gear response, etc. The HV curve should be presented in the RFM using actual altitude above ground level and indicated airspeed. Manufacturers may include data for other tested conditions but it will be in the unapproved section of the flight manual if not validated by the FAA. The curve is not ‘inaccurate’ at other weight, winds, altitude, temperatures, landing surfaces or any other specific condition not tested; it is just not applicable to those conditions and can be used to predict performance.
Nick writes:
“2) Is based upon programmed delays in lowering the collective. If you are quick as a bunny, your personal H-V ciurve would be much smaller, if you are slower, you cannot trust the H-V curve because it is too small for you.”
I respond:
Item 2 is the reason I have chosen to post on this matter. The FAA has two primary methods of entry for H-V testing. A one second delay or normal pilot reaction time are the ‘programmed delays’ allowed by the FAA and which technique is used depends on the point tested. The technique applies to collective and the interpretation concerning allowable movement of the other controls such as cyclic and pedals, as well as the definition of normal pilot reaction time are the subject of considerable debate. Of one thing I have no doubt. A test pilot, who has completed a buildup program, is concentrating on only one task, and who initiates a simulated engine failure will be faster than a pilot who is task saturated, not practiced, and unaware of an engine failure event. No matter how fast a ‘normal pilot’ - the bunny pilot - he or she will not be faster than the test pilot who established the point on the curve. When I hear someone say that a good, experienced pilot can somehow beat the curve my blood boils. Do not count on it! As one example of the reason I am so confident in this opinion consider that scientific testing in controlled circumstances has concluded that recognition and response times can be as much as 4.4 to 5.7 seconds; contrast that with the 1 second (at most) delay in testing.
Nick writes:
3) If you are descending, the H-V curve is wrong, the real one would be very much smaller.”
I respond:
The H-V curve is not wrong. It is accurate for the stated conditions. The tested data presented in the H-V curve does not represent a specific condition of descent. You may consider the values presented for hover or climb or level flight to be conservative compared to descending flight, but not ‘wrong’.
Nick writes:
“4) If you are climbing, the H-V curve would be very much bigger.”
I respond:
This depends on the phase of flight where the climb occurs. In the take-off corridor the data reflects climb. A climbing OGE hover would however require a larger H-V curve. It is not the climb or climb rate that is the significant variable but the power used (main rotor blade pitch) because that increases rotor decay. There is also the type of engine failure that occurs. As an example a test pilot who retards throttle or power lever on a FADEC equipped engine will see a programmed rate of engine decay that would be much slower than that experienced in an actual engine failure. That equates to less time for the pilot response.
Nick writes:
5) If you have 5 knots of steady wind, the H-V curve would be very very much smaller. With 20 knots of wind, there is practically no H-V curve.
I respond:
This should be self evident by the curve itself and general pilot knowledge of aerodynamics. The reverse is true of tail winds and cross winds which is why the conditions on which the curve is predicated must be understood by the professional pilot. I have longed believed that CAT A performance should be predicated on 17 knots of down wind (hover controllability) because so few pilots understand what a tail wind can do to single engine fly away capability.
I do not disagree that the Limiting Height – Speed Envelope is a performance chart that should be used as a guide from which to make predictions based on specific conditions but; it is a useful guide nonetheless.
There are many who have long advocated a change to the certification basis for engine out performance and the Limiting Height – Speed Envelope such as more realistic pilot reaction times or additional performance testing such as a take-off power climb at VY, and actual engine out testing (Hiller did it once).
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Certainly a subject about which we could all learn (when you going to write that book Nick?) as its always a topic of conversation in crewrooms and you are left wondering as to the "real" story. Enlightened by some expert commentry here. Recall a high houred Cat A twin captain saying the graph represented the aircrafts ability to fly away after an engine failure. Certainly not what it said on the graph (S-76).
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Rick:
A very thorough post.
I think what Nick was meaning about 'quick as a bunny' was those who, in training, can safely execute an engine failure from inside the published curve. What they don't realize is the other conditions relevant.
I've been accosted by experienced instructors on this subject.
A very thorough post.
I think what Nick was meaning about 'quick as a bunny' was those who, in training, can safely execute an engine failure from inside the published curve. What they don't realize is the other conditions relevant.
I've been accosted by experienced instructors on this subject.
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Thankyou Rich an’ all, yes very good posts. It would be superflous to go into serious detail of particular procedures. It must be remembered that there is only one power source during autorotation – gravity – from that premise NEVER practice judgemental techniques or procedures for the real thing with the needles joined.
At that point – disregard your sight picture and FLY away. This is because with the needles joined you are transmitting power to the drive train and changing your flight path and - stuffing up your sight picture judgement.
I think it is great that the previous posts have got a good broad canvas approach out on the board so that it can be seen that there are more ways to kill a cat than choke it with butter.
The old dog instructor that set me up for operational check and endorsement training used the analogy of autorotations being like playing a fighting fish on a light line, he runs with power, let him, he goes limp, reel him in, etc.
The underlying message of all posts is that when you finish ab-initio stage, be cool until you can hunt around and find an–old dog- to help you straight on issues that worry you. His pointers will be good, so will others have good points.
It is still a worry to suggest that those who enjoy the privileges of a rotary license may have reaction times way beyond one second. I would have to say that it is an extreme worry to me that those that even enjoy the privileges of a motor car or motorbike license would be of like – inept - disposition.
If the military, which has been oft quoted as training for a two second delay, ever trained students in a Robinson then they would soon promulgate a more mature point of view. Just spend five seconds talking with (ex military) Tim Tucker about how difficult it was for him to adhere to the mandatory one second delay for Robinson certification.
For me anyone who is at all slower than one second doesn’t even get a second chance.
I would have much preferred to hear about sharp military pilots being trained to an even sharper degree than their civil cousins, without putting too fine a point on it, please do not take offence.
For those that fly around single engine with their hand off the collective, change your career, your first emergency WILL be your last. At low level your collective is your PRIMARY control and your LIFE, look after it.
Depending on the pilot or his job I often spend quite a bit of time at low level, real low level, doing EOL’s with differing procedures, involving both collective (coriolis effect) and cyclic (flare and coriolis effect). Remember, when you have a sudden and TOTAL power loss, like - not a pansy turbine fadec run down, then the A/C bloody well sinks.
If you are an idiot and fly at six inches above the ground for no reason you will crash if you rely on the cyclic. Get someone who knows to show you why. No disrespect to Rich’s or others post. In the meantime fly a bit higher.
All operational check and training requires the check pilot to use his experience to blend as much as possible their calculated assessment of just what may be needed to suit the particular pilots’ job profile and temperament.
A super important point is that not one person who has been checked by an ‘old dog’ need think themselves smart in any way just because ‘old dog’ checked them out, quite the reverse in fact.
At that point – disregard your sight picture and FLY away. This is because with the needles joined you are transmitting power to the drive train and changing your flight path and - stuffing up your sight picture judgement.
I think it is great that the previous posts have got a good broad canvas approach out on the board so that it can be seen that there are more ways to kill a cat than choke it with butter.
The old dog instructor that set me up for operational check and endorsement training used the analogy of autorotations being like playing a fighting fish on a light line, he runs with power, let him, he goes limp, reel him in, etc.
The underlying message of all posts is that when you finish ab-initio stage, be cool until you can hunt around and find an–old dog- to help you straight on issues that worry you. His pointers will be good, so will others have good points.
It is still a worry to suggest that those who enjoy the privileges of a rotary license may have reaction times way beyond one second. I would have to say that it is an extreme worry to me that those that even enjoy the privileges of a motor car or motorbike license would be of like – inept - disposition.
If the military, which has been oft quoted as training for a two second delay, ever trained students in a Robinson then they would soon promulgate a more mature point of view. Just spend five seconds talking with (ex military) Tim Tucker about how difficult it was for him to adhere to the mandatory one second delay for Robinson certification.
For me anyone who is at all slower than one second doesn’t even get a second chance.
I would have much preferred to hear about sharp military pilots being trained to an even sharper degree than their civil cousins, without putting too fine a point on it, please do not take offence.
For those that fly around single engine with their hand off the collective, change your career, your first emergency WILL be your last. At low level your collective is your PRIMARY control and your LIFE, look after it.
Depending on the pilot or his job I often spend quite a bit of time at low level, real low level, doing EOL’s with differing procedures, involving both collective (coriolis effect) and cyclic (flare and coriolis effect). Remember, when you have a sudden and TOTAL power loss, like - not a pansy turbine fadec run down, then the A/C bloody well sinks.
If you are an idiot and fly at six inches above the ground for no reason you will crash if you rely on the cyclic. Get someone who knows to show you why. No disrespect to Rich’s or others post. In the meantime fly a bit higher.
All operational check and training requires the check pilot to use his experience to blend as much as possible their calculated assessment of just what may be needed to suit the particular pilots’ job profile and temperament.
A super important point is that not one person who has been checked by an ‘old dog’ need think themselves smart in any way just because ‘old dog’ checked them out, quite the reverse in fact.
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Hey Paco,
will look for your article, hope all is well with you.
Another 5 hours or so today and only 4 and a half of them were in the curve...just got to hope that CWP stays dark.
Banjo
will look for your article, hope all is well with you.
Another 5 hours or so today and only 4 and a half of them were in the curve...just got to hope that CWP stays dark.
Banjo
