Helicopter G limits/manoeuvering speed(R22) + Takeoff w/ Gs
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Helicopter G limits/manoeuvering speed(R22) + Takeoff w/ Gs
Hello,
I found this video on youtube a while ago. The pilot accelerates to around 65 knots and pulls pretty hard for the takeoff.(takeoff at 0:33)
Is that bad for the helicopter/dangerous in terms of G forces? He is clearly outside of the HV diagram, but I would like to know about the Gs.
Also, in the R22 POH, it doesn't talk about G limits at all. There is no maneuvering speed. Does that mean that no matter what speed you are at (below never exceed), you won't exceed any G limits? (basically, NE is below the maneuvering speed)
I am guessing that some other helicopters have maneuvering speeds?
Thank you!!!
I found this video on youtube a while ago. The pilot accelerates to around 65 knots and pulls pretty hard for the takeoff.(takeoff at 0:33)
Is that bad for the helicopter/dangerous in terms of G forces? He is clearly outside of the HV diagram, but I would like to know about the Gs.
Also, in the R22 POH, it doesn't talk about G limits at all. There is no maneuvering speed. Does that mean that no matter what speed you are at (below never exceed), you won't exceed any G limits? (basically, NE is below the maneuvering speed)
I am guessing that some other helicopters have maneuvering speeds?
Thank you!!!
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I'm not a fixed-wing pilot and I'm guessing you are. For me, and from my limited knowledge of such things, I thought manoeuvring speeds were a fixed-wing preserve. My point being, you'll likely break other things on a helicopter long before you get to manoeuvre-induced airframe limits on a rotary bird.
Dan
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There is no maneuvering speed listed for helicopters as it's not possible to generate enough +ve G with the rotor to do any structural damage. Most +ve G that can be generated from the rotor (without doing some pretty amazing tricks) is about 3G, and the structure is designed for much more than that.
I know of no helicopter that lists a maneuvering speed in the flight manual. (and I've flown quite a few).
I know of no helicopter that lists a maneuvering speed in the flight manual. (and I've flown quite a few).
The point of maneuvering speed (Va) in a seized-wing is that, below that speed, a sudden increase in load-factor (for instance, hitting a sharp updraft) will result in the wing stalling, rather than overstressing the wing. The stall, of course, unloads the wing.
As noted above, helicopters don't have such a speed. The R22 does have in the limitations section of the POH a note concerning moderate or above turbulence. You are to fly between 60KIAS and 0.7Vne, but not lower than 57 KIAS.
As noted above, helicopters don't have such a speed. The R22 does have in the limitations section of the POH a note concerning moderate or above turbulence. You are to fly between 60KIAS and 0.7Vne, but not lower than 57 KIAS.
As I recall, the manouevring speed limit on a plank allowed for full-scale deflection of the ailerons (one each way) causing twisting forces on the wing. Above Vmo, only gentle aileron inputs are permitted.
Uptycopters don't have ailerons, the blades are continually on full opposite pitch at high speed, so it probably doesn't matter a rat's patootie.
Uptycopters don't have ailerons, the blades are continually on full opposite pitch at high speed, so it probably doesn't matter a rat's patootie.
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In gliders you are limited to 1/3 control inputs above Va, so are taught to accept g over speed in spin recovery.
Does that 3g rotor limit apply only to centred cyclic? I imagine there would be limits on mast bearings, if not mast itself, for say roll inputs. Not that i'm advocating trying any kind of hard manouvre in a teetering heli!
Does that 3g rotor limit apply only to centred cyclic? I imagine there would be limits on mast bearings, if not mast itself, for say roll inputs. Not that i'm advocating trying any kind of hard manouvre in a teetering heli!
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Shawn cole - Why is it not possible to pull enough Gs for structural damage? I don't understand what keeps the Gs from going high
Graviman - It doesn't seems like a helicopter like an R22 is responsive enough to create a strong side force. Idk it just seems like that. And heli movements are dampened. Anyone heard of damaged bearings from turning
pulling hard is a very extreme case.
So it is ok to pull as hard as you want when flying an R22?
Graviman - It doesn't seems like a helicopter like an R22 is responsive enough to create a strong side force. Idk it just seems like that. And heli movements are dampened. Anyone heard of damaged bearings from turning
pulling hard is a very extreme case.
So it is ok to pull as hard as you want when flying an R22?
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maybe you should quickly PUSH HARD (on cyclic/T bar) while MCP or max take off power and climbing at Vy or Vx.
OR, quickly PULLING HARD (back) on cyclic while somewhere between Vno or Vne.
If you're still alive, answer and comparison with exemplary NTSB reports, on a postcard, please.
Who cares about V speeds in helicopters? Follow the 'avoid' curve/diagram, no abrupt movements, avoid turbulence, avoid unloading disk/creating low G on the bloody flimsy thing. Avoid high RoD, low RPM, too high engine and rotor RPM, keep safe speed when practicing autos. Etc etc.
ifresh, not sure you're aware, but Shawn Coyle wrote pretty thick book about helicopter training/flying and aerodynamics. It's got more stuff than FAA rotorcraft manual.
What keeps us from pulling hard on either control as not desired/recommended? Common sense and some sort of self-preservation left in us.
Sure, frames like Bolkow 105 with rigid rotor system and mil specs durability, they can do some +G maneuvres. None of that in R22 design.
FSXPilot is spot on in a very succint reply.
OR, quickly PULLING HARD (back) on cyclic while somewhere between Vno or Vne.
If you're still alive, answer and comparison with exemplary NTSB reports, on a postcard, please.
Who cares about V speeds in helicopters? Follow the 'avoid' curve/diagram, no abrupt movements, avoid turbulence, avoid unloading disk/creating low G on the bloody flimsy thing. Avoid high RoD, low RPM, too high engine and rotor RPM, keep safe speed when practicing autos. Etc etc.
ifresh, not sure you're aware, but Shawn Coyle wrote pretty thick book about helicopter training/flying and aerodynamics. It's got more stuff than FAA rotorcraft manual.
What keeps us from pulling hard on either control as not desired/recommended? Common sense and some sort of self-preservation left in us.
Sure, frames like Bolkow 105 with rigid rotor system and mil specs durability, they can do some +G maneuvres. None of that in R22 design.
FSXPilot is spot on in a very succint reply.
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Oh I didn't know about shawn. What is the book - I might buy it.
Martin(and everyone): I am not saying(nor do I want to)actually try it and am trying to find out if it is safe. I am simply talking theoretically to build knowledge. As someone with a fixed wing backround who can look at the 172 POH and see limits like 4.4 positive G with a maneuvering speed, I am curious about the limits of helicopters and what they are capable of. If it is true that it is impossible to exceed 3Gs without exceeding Vne for example, that would be really impressive. I am just asking.
Is it wrong to ask?
Id love an little explanation from shawn as to why 3Gs can't be exceeded/why you can't due structural damage due to G forces (or is it in your book at least so I can read there). Thank you very much in advance
Martin(and everyone): I am not saying(nor do I want to)actually try it and am trying to find out if it is safe. I am simply talking theoretically to build knowledge. As someone with a fixed wing backround who can look at the 172 POH and see limits like 4.4 positive G with a maneuvering speed, I am curious about the limits of helicopters and what they are capable of. If it is true that it is impossible to exceed 3Gs without exceeding Vne for example, that would be really impressive. I am just asking.
Is it wrong to ask?
Id love an little explanation from shawn as to why 3Gs can't be exceeded/why you can't due structural damage due to G forces (or is it in your book at least so I can read there). Thank you very much in advance
Design requirement fron FAR's
§ 27.337 Limit maneuvering load factor.
The rotorcraft must be designed for—
(a) A limit maneuvering load factor ranging from a positive limit of 3.5 to a negative limit of −1.0; or
(b) Any positive limit maneuvering load factor not less than 2.0 and any negative limit maneuvering load factor of not less than −0.5 for which—
(1) The probability of being exceeded is shown by analysis and flight tests to be extremely remote; and
(2) The selected values are appropriate to each weight condition between the design maximum and design minimum weights.
[Amdt. 27–26, 55 FR 7999, Mar. 6, 1990]
Due to Vne limit and control response it it difficult to exceed even +3 g in your average helicopter. Negative G especially in a twp blade system can result in a much more critical condition and should be avoided like the plague
§ 27.337 Limit maneuvering load factor.
The rotorcraft must be designed for—
(a) A limit maneuvering load factor ranging from a positive limit of 3.5 to a negative limit of −1.0; or
(b) Any positive limit maneuvering load factor not less than 2.0 and any negative limit maneuvering load factor of not less than −0.5 for which—
(1) The probability of being exceeded is shown by analysis and flight tests to be extremely remote; and
(2) The selected values are appropriate to each weight condition between the design maximum and design minimum weights.
[Amdt. 27–26, 55 FR 7999, Mar. 6, 1990]
Due to Vne limit and control response it it difficult to exceed even +3 g in your average helicopter. Negative G especially in a twp blade system can result in a much more critical condition and should be avoided like the plague
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Heliport is right, Shawn is the consummate expert!
Having lurked here for a bit, let me weigh in on this pithy subject:
Unlike an airplane, the G's a helo is pulling are only half the story. That is because every helicopter is really two entirely different systems flying in formation - the fuselage, which behaves like an airplane and which we call the "static structure", and the main rotor, which behaves quite strangely under load, and is called the "rotating system".
In turn:
The Static Structure - The G's that the FAR refers to is the load factor experienced by the fuselage - the engine mounts, the tail cone, the feet of the main transmission, and the G meter on the pilot's panel. When the FAR refers to 3.5 g, they refer to the static structure, since the rotor would long prior give up the ghost as the pilot maneuvered that severely.
Frankly, regarding load factor, the FARs were derived from airplane requirements and so they shadow the way airplane behaves. And airplane's structure experiences load factor across the entire aircraft. The wings produce lift and delivered to the whole structure, until the wing stalls or the structure fails. The most extreme maneuver an airplane can successfully perform occurs at the speed where the maximum load factor at stall matches the structural strength of the wings. We call this maneuvering speed and suggest that the pilot slow below maneuvering speed under severe turbulent conditions. Maneuvering speed protects the airplane from structural harm by assuring that the wing will stall before harmful forces are produced. There is no rotorcraft equivalent to maneuvering speed.
The rotating structure – the rotor of a helicopter produces the load factor but virtually no helicopter can produce the load factor required by FAR since virtually no helicopter has a rotor designed for 3 1/2 Gs, except perhaps a very light H-60 or H-64. A rotor designed for 3.5 g at normal weight would consume far too much power in a hover, and require far too much blade chord, again at a cost of considerable payload. The limits to a rotor during high load factor maneuvers are related to the blade stall and the ensuing pitching moment, and the stresses on the pitch links, swashplate and servos. This topic has been much discussed when we've talked about servo transparency, where the blade forces during high load factor maneuvers result in high stresses on the aircraft's controls.
It is safe to say that most helicopters, under limiting rotating system maneuvering, will produce very high blade and control stresses under surprisingly low static system load factors. Because rotor stall is strongly affected by altitude, airspeed, RPM, and collective pitch, it is very hard to predict precisely what load factor would produce excessive rotor stresses. This is why several manufacturers have attempted to employ servo warning limits systems as a means to directly warn the pilot of excess rotating system stresses during maneuvering. The servo limit lights on some EC models and the cruise guide on some Sikorsky models comes to mind.
To give a sense for the kinds of forces the rotor blade can place on the controls and servos here is a thought experiment. Imagine that your helicopter was placed in a hangar and the rotor blade was passed through a hole in the concrete wall and that hole was then bricked up tightly around the blade. Now connect a hydraulic mule to the hydraulic system, bring the system to full pressure and start to move the cyclic around. You can imagine the enormous forces the hydraulic cylinders would impart on the swashplate, pitch links, blade horn, and rotor blades while the rotor blade is trapped in the concrete wall. This condition is precisely what occurs in Jack stall, also called servo transparency except it is the blades that produce the force to drive the hydraulic servos backwards against their maximum force capability.
In a nutshell, load factor is not useful to warn pilots of the damaging maneuvers that the helicopter's rotating system can experience, and in fact a G meter might fool a pilot into thinking his maneuvers were acceptable while the rotor was screaming in protest. Meanwhile, it is very doubtful that the rotor would produce the load factors needed to bother the static system.
As pilots who've experienced Jack stall will tell you, under some conditions, it takes little load factor to create these enormous control system stresses, given some airspeed, altitude and gross weight.
Having lurked here for a bit, let me weigh in on this pithy subject:
Unlike an airplane, the G's a helo is pulling are only half the story. That is because every helicopter is really two entirely different systems flying in formation - the fuselage, which behaves like an airplane and which we call the "static structure", and the main rotor, which behaves quite strangely under load, and is called the "rotating system".
In turn:
The Static Structure - The G's that the FAR refers to is the load factor experienced by the fuselage - the engine mounts, the tail cone, the feet of the main transmission, and the G meter on the pilot's panel. When the FAR refers to 3.5 g, they refer to the static structure, since the rotor would long prior give up the ghost as the pilot maneuvered that severely.
Frankly, regarding load factor, the FARs were derived from airplane requirements and so they shadow the way airplane behaves. And airplane's structure experiences load factor across the entire aircraft. The wings produce lift and delivered to the whole structure, until the wing stalls or the structure fails. The most extreme maneuver an airplane can successfully perform occurs at the speed where the maximum load factor at stall matches the structural strength of the wings. We call this maneuvering speed and suggest that the pilot slow below maneuvering speed under severe turbulent conditions. Maneuvering speed protects the airplane from structural harm by assuring that the wing will stall before harmful forces are produced. There is no rotorcraft equivalent to maneuvering speed.
The rotating structure – the rotor of a helicopter produces the load factor but virtually no helicopter can produce the load factor required by FAR since virtually no helicopter has a rotor designed for 3 1/2 Gs, except perhaps a very light H-60 or H-64. A rotor designed for 3.5 g at normal weight would consume far too much power in a hover, and require far too much blade chord, again at a cost of considerable payload. The limits to a rotor during high load factor maneuvers are related to the blade stall and the ensuing pitching moment, and the stresses on the pitch links, swashplate and servos. This topic has been much discussed when we've talked about servo transparency, where the blade forces during high load factor maneuvers result in high stresses on the aircraft's controls.
It is safe to say that most helicopters, under limiting rotating system maneuvering, will produce very high blade and control stresses under surprisingly low static system load factors. Because rotor stall is strongly affected by altitude, airspeed, RPM, and collective pitch, it is very hard to predict precisely what load factor would produce excessive rotor stresses. This is why several manufacturers have attempted to employ servo warning limits systems as a means to directly warn the pilot of excess rotating system stresses during maneuvering. The servo limit lights on some EC models and the cruise guide on some Sikorsky models comes to mind.
To give a sense for the kinds of forces the rotor blade can place on the controls and servos here is a thought experiment. Imagine that your helicopter was placed in a hangar and the rotor blade was passed through a hole in the concrete wall and that hole was then bricked up tightly around the blade. Now connect a hydraulic mule to the hydraulic system, bring the system to full pressure and start to move the cyclic around. You can imagine the enormous forces the hydraulic cylinders would impart on the swashplate, pitch links, blade horn, and rotor blades while the rotor blade is trapped in the concrete wall. This condition is precisely what occurs in Jack stall, also called servo transparency except it is the blades that produce the force to drive the hydraulic servos backwards against their maximum force capability.
In a nutshell, load factor is not useful to warn pilots of the damaging maneuvers that the helicopter's rotating system can experience, and in fact a G meter might fool a pilot into thinking his maneuvers were acceptable while the rotor was screaming in protest. Meanwhile, it is very doubtful that the rotor would produce the load factors needed to bother the static system.
As pilots who've experienced Jack stall will tell you, under some conditions, it takes little load factor to create these enormous control system stresses, given some airspeed, altitude and gross weight.
Last edited by NickLappos; 8th Apr 2011 at 07:27.
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ifresh21 - Don't get me wrong. I never said you're aspiring test pilot in R22. There WERE plenty guys in the past who taught us how to get killed in some helicopters through NTSB reports, serving us to avoid these.
Well, some of his/her past posts earlier on talk about C172 stuff. He/she obviously did some fixed wing flying in the past.
Considering ifresh21 user posted some stuff about own R22 lesson with some overspeed issues, I'm safe to say he/she just likes flying and interest in rotary aerodynamics has reason behind it.
I'm fixed wing PPL, glider pilot and can fly rotary - nearly PPL (with more to come this year, finally). Does that make me more into fixed wing than helicopters?
Back to Shawn Coyle's book.
Well, I prefer having good deal, value for money. Probably the best bet is Amazon marketplace with brand new or used books with considerable discounts. I didn't pay RRP for C&C.
heliport: ifresh21 is a fixed-wing student pilot.
Considering ifresh21 user posted some stuff about own R22 lesson with some overspeed issues, I'm safe to say he/she just likes flying and interest in rotary aerodynamics has reason behind it.
I'm fixed wing PPL, glider pilot and can fly rotary - nearly PPL (with more to come this year, finally). Does that make me more into fixed wing than helicopters?
Back to Shawn Coyle's book.
Well, I prefer having good deal, value for money. Probably the best bet is Amazon marketplace with brand new or used books with considerable discounts. I didn't pay RRP for C&C.
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Thanks for the super detailed response Nick.
So if I understand correctly, you are saying that something else would break before 3Gs is achieved? You also talked about rotor stall. Is it possible to stall the rotor if you remain inside the RPM limits in a helicopter like the R22? Or is it that you would run out of power(within MAP limits) to maintain RPM with before reaching a high G load?
But if the FARs say that the helicopter has to be able to withstand a certain number of Gs, why would that not count for the entire helicopter? That means that the helicopter would not be able to handle the Gs required by FARs - right?(cause the rotor system would break or jack stall etc.)
The R22 doesn't use hydraulics, so is there some sort of equivalent problem since jack stall is impossible?
Is it that the rotor can't physically produce the load factor to bother static system because of rotor stall?
Im pretty confused about this
What about helicopter that can do a loop like the apache ah64
how many Gs would that be
So if I understand correctly, you are saying that something else would break before 3Gs is achieved? You also talked about rotor stall. Is it possible to stall the rotor if you remain inside the RPM limits in a helicopter like the R22? Or is it that you would run out of power(within MAP limits) to maintain RPM with before reaching a high G load?
But if the FARs say that the helicopter has to be able to withstand a certain number of Gs, why would that not count for the entire helicopter? That means that the helicopter would not be able to handle the Gs required by FARs - right?(cause the rotor system would break or jack stall etc.)
The R22 doesn't use hydraulics, so is there some sort of equivalent problem since jack stall is impossible?
Is it that the rotor can't physically produce the load factor to bother static system because of rotor stall?
Im pretty confused about this
What about helicopter that can do a loop like the apache ah64
how many Gs would that be