Height/Velocity Curve: merged threads
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Avoid Area Curve
Hi, while teaching my trainees about the avoid area curve or the deadman's curve as it was known, i got an interesting doubt for which i could not get a satisfactory answer... hope you guys can help...
for a alouette helicopter (single engined) below the knee of the curve, at 100 feet of height the safe speed is 46kts but as you go higher, at 200 ft 46kts is within the unsafe region. How is it that with more height in hand we are still unsafe? during the discussion here... the most popular opinion seemed to be that it has got to do something with the crashworthiness of the aircraft????
any thoughts?
for a alouette helicopter (single engined) below the knee of the curve, at 100 feet of height the safe speed is 46kts but as you go higher, at 200 ft 46kts is within the unsafe region. How is it that with more height in hand we are still unsafe? during the discussion here... the most popular opinion seemed to be that it has got to do something with the crashworthiness of the aircraft????
any thoughts?
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Above the knee, you are assumed to be in the cruise with your hand not necessarily near the collective - therefore an extra second is added to the reaction time.
Phil
Phil
Paco is correct (of course!)
Extracted from AC27-1B CHG 2 : it's well worth reading
Advisory Circular AC27-1B
(4) The knee of the curve separates the takeoff portion from the cruise portion and is defined as the highest speed point on the low speed portion of the HV envelope. Altitudes above this point are considered cruise, or “fly-in,” points, and these test points require a minimum time delay of 1 second between throttle chop and control actuation (reference § 27.143(d)). Altitudes below the knee represent takeoff profile points. For test points in the takeoff portion, takeoff power (or a lower power selected by the
applicant as an operating procedure) and normal pilot reaction time for corrective control actuation will be used.
applicant as an operating procedure) and normal pilot reaction time for corrective control actuation will be used.
Advisory Circular AC27-1B
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Hand away from the collective in the cruise
?!!! In my role as a miltary examiner I would ground such a person instantly and subject them to a rigorous debrief as to the dangers of such appaling airmanship and lack of understanding of rotary PoF - thank the Lord I fly with professionals. Another reason not to leave...
?!!! In my role as a miltary examiner I would ground such a person instantly and subject them to a rigorous debrief as to the dangers of such appaling airmanship and lack of understanding of rotary PoF - thank the Lord I fly with professionals. Another reason not to leave...
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Chopabeefer - do you ever fly single pilot? Have to re-fold a map? Look up a frequency?
There are a ton of things you have to do with your left hand that requires removing it from the collective -
That's the reason for the delay between engine failure simulation and the pilot taking action above the knee.
While the current method of developing the H-V curve isn't perfect, it's a starting point, and how it is developed is something that all helicopter pilots should be aware of, as well as having it demonstrated sometime during their commercial or instructor pilot training.
There are a ton of things you have to do with your left hand that requires removing it from the collective -
That's the reason for the delay between engine failure simulation and the pilot taking action above the knee.
While the current method of developing the H-V curve isn't perfect, it's a starting point, and how it is developed is something that all helicopter pilots should be aware of, as well as having it demonstrated sometime during their commercial or instructor pilot training.
And the winner today is.................................
Hand away from the collective in the cruise
?!!! In my role as a miltary examiner I would ground such a person instantly and subject them to a rigorous debrief as to the dangers of such appaling airmanship and lack of understanding of rotary PoF - thank the Lord I fly with professionals. Another reason not to leave...
?!!! In my role as a miltary examiner I would ground such a person instantly and subject them to a rigorous debrief as to the dangers of such appaling airmanship and lack of understanding of rotary PoF - thank the Lord I fly with professionals. Another reason not to leave...
for the laugh of the day...................
sorry, but couldn't resist.........
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Thanks for the various inputs... but i think my question was not adequately complete... for alouette the knee is just above 200 feet.. so technically the curve at 200 feet is for full power climb conditions and not cruise where the 1 sec delay for engine failure and lowering collective is added to the reaction.
in case of high inertia rotors wont the curve itself change with the knee being lower? considering pilot reactions at both 100 and 200 ft and assuming correct actions have been taken on engine failure, the original question lingers...
leaving controls while on takeoff (considering below knee conditions) or on approach is definitely a no no.. being a mil heli instr myself... i would hand over a warning straightaway... but in cruise conditions with autopilot engaged or frictions tightened... a slight relaxation is allowed... esp single pilot ops where you do need to operate switches...
Quote :
Avoid Area Curve
Hi, while teaching my trainees about the avoid area curve or the deadman's curve as it was known, i got an interesting doubt for which i could not get a satisfactory answer... hope you guys can help...
for a alouette helicopter (single engined) below the knee of the curve, at 100 feet of height the safe speed is 46kts but as you go higher, at 200 ft 46kts is within the unsafe region. How is it that with more height in hand we are still unsafe? during the discussion here... the most popular opinion seemed to be that it has got to do something with the crashworthiness of the aircraft????
any thoughts?
in case of high inertia rotors wont the curve itself change with the knee being lower? considering pilot reactions at both 100 and 200 ft and assuming correct actions have been taken on engine failure, the original question lingers...
leaving controls while on takeoff (considering below knee conditions) or on approach is definitely a no no.. being a mil heli instr myself... i would hand over a warning straightaway... but in cruise conditions with autopilot engaged or frictions tightened... a slight relaxation is allowed... esp single pilot ops where you do need to operate switches...
Quote :
Avoid Area Curve
Hi, while teaching my trainees about the avoid area curve or the deadman's curve as it was known, i got an interesting doubt for which i could not get a satisfactory answer... hope you guys can help...
for a alouette helicopter (single engined) below the knee of the curve, at 100 feet of height the safe speed is 46kts but as you go higher, at 200 ft 46kts is within the unsafe region. How is it that with more height in hand we are still unsafe? during the discussion here... the most popular opinion seemed to be that it has got to do something with the crashworthiness of the aircraft????
any thoughts?
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The difference between 46kts & 100' versus 46kts & 200' is likely due to increased difficulty in managing rotor speed at the higher height. However, without flying those profiles in that type, I can only speculate.
Matthew.
Matthew.
so technically the curve at 200 feet is for full power climb conditions
It's also the most compelling reason its shouldn't be in the limitations section of a Part-29 RFM
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@212 man,
it is given in several articles fairly clearly that till the knee, the hepter is considered to be in a full power climb while above the knee it is in level flight. of this i have definitely have no doubt. your post yesterday quoting paco also refers to the same.
a further study on the topic also brings out that reason seems to be due to management of rotor inertia.. something similar to what mathew has said in his post
it is given in several articles fairly clearly that till the knee, the hepter is considered to be in a full power climb while above the knee it is in level flight. of this i have definitely have no doubt. your post yesterday quoting paco also refers to the same.
a further study on the topic also brings out that reason seems to be due to management of rotor inertia.. something similar to what mathew has said in his post
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The published HV curve is an attempt to put some repeatable (between types) data on paper for all pilots.
It's not perfect, but with the same rules applied to everyone, many things become clear.
From my experience, the portion from the low hover to the knee is one of the more difficult to test- there is the requirement to attempt to simultaneously get takeoff power, the necessary height and then the necessary airspeed all at the same time. The height and power are pretty easy, but the airspeed system doesn't work well at the airspeeds being tested. For one type, we looked at GPS ground speed and compared it to indicated airspeed (in zero wind conditions), and found that there was at least a 10 knot error with the airspeed lagging well behind the actual speed.
But throughout that region, it was evident that the reaction of immediately lowering collective when the engine failure was initiated and also starting a flare was key. Going from nose down and accelerating to nose up and flaring was very natural.
The same airspeed for entry from above the knee is a different story - 40 knots in most helicopters from level flight at 200' means that you don't have enough energy to flare, nor enough height to get more airspeed. So that's the reason why there might be a difference between 'below the knee' and 'above the knee'.
It's not perfect, but with the same rules applied to everyone, many things become clear.
From my experience, the portion from the low hover to the knee is one of the more difficult to test- there is the requirement to attempt to simultaneously get takeoff power, the necessary height and then the necessary airspeed all at the same time. The height and power are pretty easy, but the airspeed system doesn't work well at the airspeeds being tested. For one type, we looked at GPS ground speed and compared it to indicated airspeed (in zero wind conditions), and found that there was at least a 10 knot error with the airspeed lagging well behind the actual speed.
But throughout that region, it was evident that the reaction of immediately lowering collective when the engine failure was initiated and also starting a flare was key. Going from nose down and accelerating to nose up and flaring was very natural.
The same airspeed for entry from above the knee is a different story - 40 knots in most helicopters from level flight at 200' means that you don't have enough energy to flare, nor enough height to get more airspeed. So that's the reason why there might be a difference between 'below the knee' and 'above the knee'.
it is given in several articles fairly clearly that till the knee, the hepter is considered to be in a full power climb while above the knee it is in level flight. of this i have definitely have no doubt. your post yesterday quoting paco also refers to the same.
Hand away from the collective in the cruise?!!! In my role as a miltary examiner I would ground such a person instantly and subject them to a rigorous debrief as to the dangers of such appaling airmanship and lack of understanding of rotary PoF - thank the Lord I fly with professionals
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Interestingly enough, the Mil standard calls for a 2 second delay, rather than the 1 second civil standard, which implies there are considered to be good reasons why you may have your hand away from the lever
I wonder if it takes into consideration the fastest avoidance profile for suddenly seen projectiles heading toward yon helicopter.
Oh yeah, she's right mate, eh - maaiit! waaait two - then duck.
I'd reckon one of the dudes in the back would have said pilot by the juglar before he counted to two.
just my 2 cents.
