Pitch Attitude in Turns
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if you are trying to maintain a certain path over the ground then you will definatley need these changes in attitude
If not then you won't, but you will be blown down wind.
could also be down to flying with your arm on your leg. turn left move leg in and the arc described by your knee pivoting at your hip pulls back slightly, turn right, move leg out and it moves the cyclic forward...oh but what about pedal input too?
If not then you won't, but you will be blown down wind.
could also be down to flying with your arm on your leg. turn left move leg in and the arc described by your knee pivoting at your hip pulls back slightly, turn right, move leg out and it moves the cyclic forward...oh but what about pedal input too?
I think Jellycopter is talking about an established steady turn, and saying that attitude changes are required to maintain a constant IAS throughout if there's wind blowing, so hand positions and so on shouldn't have an effect.
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This chestnut crops up about once a year, and it is a very hardy nut, indeed. The idea that the aircraft changes trim in its steady turn is simply wrong. I have trimmed several different helos into steady turns of 30 degrees of bank, and let them turn hands off for several turns. No pitch attitude change, nada. No climb no descent, no nothin.
The concept of the downwind turn dies very very hard. The people who see the earth as somehow the stable universal platform see the wind and its effect on the inertial platform of the aircraft. Why are they unable to see the rotation of the earth's surface, which is over 1,000 mph (so if you turn up-rotation, you are going 1,000 mph slower than when you turn down-rotation!!)
How about the 40,000 MPH trip the earth is taking through the universe?
Ppruners, where do the set of blinders stop or start? There is no such thing as a "downwind turn" affecting the aircraft's trim.
The concept of the downwind turn dies very very hard. The people who see the earth as somehow the stable universal platform see the wind and its effect on the inertial platform of the aircraft. Why are they unable to see the rotation of the earth's surface, which is over 1,000 mph (so if you turn up-rotation, you are going 1,000 mph slower than when you turn down-rotation!!)
How about the 40,000 MPH trip the earth is taking through the universe?
Ppruners, where do the set of blinders stop or start? There is no such thing as a "downwind turn" affecting the aircraft's trim.
NL: I should have stated in my observations atleast, but the 'effects of pitch up or down can only be observed with trim switched off, otherwise the SAS/stab will do its job and cancel the attempted break from trimmed flight
Jellycopter never mentions "trim"???
Jellycopter never mentions "trim"???
I think in the november issue of FLYING is a very good article from Peter Garrison. I think it is called "Realy the last article about the downwind turn" or something similar. It explains it all.
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Folks,
My spin on this issue: nil wind or steady wind - absolutely no relevance. Gusts invoke all sorts of rotor effects and are a different story.
If you enter a turn at constant body angle and torque, the tilting of the thrust vector into the turn will reduce the total lift and the aircraft will descend. I suspect that the introduction of cyclic pitch will induce a small element of flapback as well. If you wish to remain level, the total lift must be restored by increasing the thrust vector with collective pitch, which most certainly will induce some flapback. Left unattended, the body angle will increase and the airspeed will decrease. If you wish to maintain airspeed, then a compensatory reduction in body angle is required.
In my experience, different amounts of pitch reduction are required for left or right turns - I always presumed that the difference was a consequence of mast tilt and rigging issues.
Try as I might in some 5000 hours of instructing, I could never detect any effect that could be attributed to the wind whilst flying on instruments.
Stay Alive,
My spin on this issue: nil wind or steady wind - absolutely no relevance. Gusts invoke all sorts of rotor effects and are a different story.
If you enter a turn at constant body angle and torque, the tilting of the thrust vector into the turn will reduce the total lift and the aircraft will descend. I suspect that the introduction of cyclic pitch will induce a small element of flapback as well. If you wish to remain level, the total lift must be restored by increasing the thrust vector with collective pitch, which most certainly will induce some flapback. Left unattended, the body angle will increase and the airspeed will decrease. If you wish to maintain airspeed, then a compensatory reduction in body angle is required.
In my experience, different amounts of pitch reduction are required for left or right turns - I always presumed that the difference was a consequence of mast tilt and rigging issues.
Try as I might in some 5000 hours of instructing, I could never detect any effect that could be attributed to the wind whilst flying on instruments.
Stay Alive,
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4dogs,
I don't think this thread was addressing the natural need for more power (or lower speed) to generate the extra load factor needed in a turn.
You are right, the natural imbalance of the single rotor helo makes the left and right banked turn different. The tail rotor thrust requires a natural right sideslip, and horizontal tail down/upload change the lateral trim significantly. It has been my experience that the left turn needed slightly less bank for a given turn rate, and the right, more bank. Also, the pitch attitude that you trim to is different in each direction, but this varies with the particular helo and its CG, based on how the horizontal tail behaves in the turning flow.
Low speed turns are more affected, since the turn rates are higher, and the radius is smaller, so the turning sideslip is greater.
I don't think this thread was addressing the natural need for more power (or lower speed) to generate the extra load factor needed in a turn.
You are right, the natural imbalance of the single rotor helo makes the left and right banked turn different. The tail rotor thrust requires a natural right sideslip, and horizontal tail down/upload change the lateral trim significantly. It has been my experience that the left turn needed slightly less bank for a given turn rate, and the right, more bank. Also, the pitch attitude that you trim to is different in each direction, but this varies with the particular helo and its CG, based on how the horizontal tail behaves in the turning flow.
Low speed turns are more affected, since the turn rates are higher, and the radius is smaller, so the turning sideslip is greater.
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Nick,
Actually, I thought it was.
Jellycopter's original post said:
"When a helicopter is flown at a constant angle of bank through a 360 deg turn, the pitch attitude changes in order to maintain IAS constant. This effect is only noticeable when the wind is blowing, it doesn't happen in calm winds."
My analysis was that it had nothing to do with the wind but probably everything to do with the additional power required to maintain level and to maintain IAS constant.
I therefore think, for all of the reasons you state, that we are in heated agreement about why the pitch attitude must change to achieve the stated data point.
Stay Alive,
Actually, I thought it was.
Jellycopter's original post said:
"When a helicopter is flown at a constant angle of bank through a 360 deg turn, the pitch attitude changes in order to maintain IAS constant. This effect is only noticeable when the wind is blowing, it doesn't happen in calm winds."
My analysis was that it had nothing to do with the wind but probably everything to do with the additional power required to maintain level and to maintain IAS constant.
I therefore think, for all of the reasons you state, that we are in heated agreement about why the pitch attitude must change to achieve the stated data point.
Stay Alive,
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No dogs, the ficticious effect he describes is clearly due, in his very question,to the wind and its direction. Of what use would his observation about wind be if the question asked about the obvious, well researched and well understood retrim needed in loadfactor?
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NO, NO, NO, winds aloft do not influence constant-rate turns!
It is worrisome that certificated pilots may get through the system believing that bank angles (absent ground reference maneuvers) must be varied, or do vary, when a wind is blowing.
Let us be very clear (and, therefore, undiplomatic and confrontational) that basic physics dictates that the untethered helicopter is NOT connected to the ground and DOES NOT have the faintest wind influence on bank angle or pitch in turns. Nada. Zip. No way!
IF anybody holds on to the notion that bank or pitch must be varied according to wind, please advise, I shall gin up a reading list for you in the tens of thousands of words refuting this superstition.
Students: if your instructor tries to convince you that a constant-rate turn requires changes in bank or pitch depending on upwind or downwind position in the turn, immediately get a new instructor. The one you have is seriously out of contact with both reality and with the aeronautical literature. Don't let this intellectual virus fester in your own mind!
True, most of the other posters on this thread have indicated the fallacy of pitch/bank variation, BUT BUT BUT you have been far too gentle and oblique. This obnoxious weed in the garden of pilotage must be stamped out firmly and vigorously ASAP lest it poison another generation of young inquiring minds!
And yes, I believe the superstition has also been overdone in the realm of low-altitude downwind turn dangers. Pilots DO get terminated losing ETL and the like turning downwind, but it's because they've not had enough discipline in maintaining IAS in spite of conflicting visual clues (and, of course, unfavorable wind shear!), not because the helicopter "knows" it's getting increasing tailwind.
Free dual instruction for unbelievers (you supply the helicopter).
Dave
Chief Flight Instructor
one of those mutitudinous Florida schools
Let us be very clear (and, therefore, undiplomatic and confrontational) that basic physics dictates that the untethered helicopter is NOT connected to the ground and DOES NOT have the faintest wind influence on bank angle or pitch in turns. Nada. Zip. No way!
IF anybody holds on to the notion that bank or pitch must be varied according to wind, please advise, I shall gin up a reading list for you in the tens of thousands of words refuting this superstition.
Students: if your instructor tries to convince you that a constant-rate turn requires changes in bank or pitch depending on upwind or downwind position in the turn, immediately get a new instructor. The one you have is seriously out of contact with both reality and with the aeronautical literature. Don't let this intellectual virus fester in your own mind!
True, most of the other posters on this thread have indicated the fallacy of pitch/bank variation, BUT BUT BUT you have been far too gentle and oblique. This obnoxious weed in the garden of pilotage must be stamped out firmly and vigorously ASAP lest it poison another generation of young inquiring minds!
And yes, I believe the superstition has also been overdone in the realm of low-altitude downwind turn dangers. Pilots DO get terminated losing ETL and the like turning downwind, but it's because they've not had enough discipline in maintaining IAS in spite of conflicting visual clues (and, of course, unfavorable wind shear!), not because the helicopter "knows" it's getting increasing tailwind.
Free dual instruction for unbelievers (you supply the helicopter).
Dave
Chief Flight Instructor
one of those mutitudinous Florida schools
Thread Starter
Nick L,
I didn't think I'd find myself writing this but; 'Simply not true Nick'. I have observed this effect many, many times. Not only when flying myself but also observing others. Crab labels us 'heretics', and he may well be correct. Nonetheless, it DOES occur! My question that prompted this thread is WHY?
Nick, you also wrote:
QUOTE]I have trimmed several different helos into steady turns of 30 degrees of bank, and let them turn hands off for several turns. No pitch attitude change, nada. No climb no descent, no nothin.[/QUOTE]
I am not speaking of trimming a helicopter into a turn. Infact, trimming into turns, except in specific circumstances, is frowned upon in the UK military with whom I flew helicopters for nearly 20 years.
It is my understanding that 'trimming' sets up a bias within the helicopter's cyclic system to 'hold' the cyclic, and in unaccelerated flight, hold the rotor disc in a given position relative to the airframe. Therefore, assuming a helicopter is trimmed accurately into a turn, one would not expect to see any pitch attitude change. I'd suggest you consider flying the helicopter manually, without trim or auto-stabilisation and, in my experience, you'll see that you need to adjust the pitch attitude to maintain the IAS.
PA42
I didn't mention anything about rate of turn. (However, I do concur that turn rate would vary if IAS was to vary for a given AoB. Alternatively, you could recommend that students consider getting an instructor that has the accuracy and sensitivity of control over their helicopter that they can demonstrate such effects reliably and convincingly, time and time again.
Rotordog,
Thank you for your PM.
J
ficticious effect
Nick, you also wrote:
QUOTE]I have trimmed several different helos into steady turns of 30 degrees of bank, and let them turn hands off for several turns. No pitch attitude change, nada. No climb no descent, no nothin.[/QUOTE]
I am not speaking of trimming a helicopter into a turn. Infact, trimming into turns, except in specific circumstances, is frowned upon in the UK military with whom I flew helicopters for nearly 20 years.
It is my understanding that 'trimming' sets up a bias within the helicopter's cyclic system to 'hold' the cyclic, and in unaccelerated flight, hold the rotor disc in a given position relative to the airframe. Therefore, assuming a helicopter is trimmed accurately into a turn, one would not expect to see any pitch attitude change. I'd suggest you consider flying the helicopter manually, without trim or auto-stabilisation and, in my experience, you'll see that you need to adjust the pitch attitude to maintain the IAS.
PA42
Students: if your instructor tries to convince you that a constant-rate turn requires changes in bank or pitch depending on upwind or downwind position in the turn, immediately get a new instructor.
Rotordog,
Thank you for your PM.
J
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jellycopter,
Given that you and me and most other ppruners can fly, and we can actually fly by hand, the issue under discussion is whether the WIND is the source of the retrim effect. The belief that as you travel up or down wind you need to retrim is ficticious. The need to trim any helicopter, and fly it precisely, is not at issue!
The longitudinal trim of the helicopter is subject the the phugoid mode, where the pitch axis has an oscillation of perhaps 5 seconds. In a turn where you have upset the longtudinal trim of the helo, you have naturally upset this phugoid mode, so you can expect to see the nose work itself up and down in a divergent manner at perhaps 2 to 8 seconds (depoending on many factors, mostly the effectiveness of the horizontal tail). Thus, as you turn, you have to pump the cyclic longitudinally because the nose is slowly bobbing up and down. In windy days you have more turbulence, so the mode might be more active throughout the maneuver.
If I can simply state the main point of this thread (hey its your question, if I have it wrong, correct me!), it is the Assertion:
The wind direction makes the longitudinal axis retrim as the aircraft goes upwind and down wind in forward flight.
I contend that this is not true.
PS, the autopilot CANNOT invisibly fix the aerodynamics of the aircraft, it would show this "retrim" were it a fact. Autopilots are just dumb but precise pilots of their own right, and they cannot change the inherent stability of the aircraft, they can just use the controls to help quell the basic aircraft.
Given that you and me and most other ppruners can fly, and we can actually fly by hand, the issue under discussion is whether the WIND is the source of the retrim effect. The belief that as you travel up or down wind you need to retrim is ficticious. The need to trim any helicopter, and fly it precisely, is not at issue!
The longitudinal trim of the helicopter is subject the the phugoid mode, where the pitch axis has an oscillation of perhaps 5 seconds. In a turn where you have upset the longtudinal trim of the helo, you have naturally upset this phugoid mode, so you can expect to see the nose work itself up and down in a divergent manner at perhaps 2 to 8 seconds (depoending on many factors, mostly the effectiveness of the horizontal tail). Thus, as you turn, you have to pump the cyclic longitudinally because the nose is slowly bobbing up and down. In windy days you have more turbulence, so the mode might be more active throughout the maneuver.
If I can simply state the main point of this thread (hey its your question, if I have it wrong, correct me!), it is the Assertion:
The wind direction makes the longitudinal axis retrim as the aircraft goes upwind and down wind in forward flight.
I contend that this is not true.
PS, the autopilot CANNOT invisibly fix the aerodynamics of the aircraft, it would show this "retrim" were it a fact. Autopilots are just dumb but precise pilots of their own right, and they cannot change the inherent stability of the aircraft, they can just use the controls to help quell the basic aircraft.
Last edited by NickLappos; 9th Jan 2005 at 21:04.
