Dynamics - Vibration Control, At Last?
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Dynamics - Vibration Control, At Last?
This thread is for helicopter techno-deviants, and perhaps the very bored.
I claim, with absolutely no modesty (and even less knowledge), that it will be impossible to significantly decrease rotor-induced vibration by physically changing the pitch of the blades. Their moment of inertia about the feathering axis will prohibit oscillatory rotation at all but the lowest of frequencies.
The following is an article from this Saturday's paper, about the work of two 16-year-old students. It conjures up the idea of using electricity to modify the aerodynamic profile of the blade, without changing it's physically profile. This should allow rapid changes in its lift, many times in a single revolution.
Ions & Air Resistance
I claim, with absolutely no modesty (and even less knowledge), that it will be impossible to significantly decrease rotor-induced vibration by physically changing the pitch of the blades. Their moment of inertia about the feathering axis will prohibit oscillatory rotation at all but the lowest of frequencies.
The following is an article from this Saturday's paper, about the work of two 16-year-old students. It conjures up the idea of using electricity to modify the aerodynamic profile of the blade, without changing it's physically profile. This should allow rapid changes in its lift, many times in a single revolution.
Ions & Air Resistance
Last edited by Dave Jackson; 22nd May 2002 at 19:17.
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I must be bored.
This is a difficult concept from an engineering perspective. The only information in the article linked in Dave's post, that communicates what is actually happening in their experiement, is the following comments:
The basic science involved is discussed here:
Plasma physics deals with electrically ionized gases, which can be controlled by either magnetic or electrostatic means. I looked, and there's a huge number of properties associated with plasmas (thus my concern for the engineering difficulties). Some of them include the following, from an online dictionary of plasma physics at the Fusion Energy Educational Website.
Plasma Dictionary
Term: Instability
Definition: A state of a plasma (or any other physical system) in which a small perturbation amplifies itself to a considerable alteration of the state of the system. In plasmas instabilities sometimes leads to disruptions (see entry). Most known instabilities are associated with waves and other natural (linear) modes of plasma oscillation, though some arise only from nonlinear effects. Known classifications of plasma instabilities include: absolute instability, backscatter instability, ballooning instability, bar-forming instability, beam instability, Brillouin instability, cross-field instability, current-driven instability, drift instability, external/free boundary instability, external-kink instability, fishbone instability, flute instability, hydrodynamic instability, ideal MHD instability, interchange instability, internal/fixed boundary instability, internal kink instability, ion ring instability, Kelvin-Helmholtz instability, kink instability, Kruskal-Schwarzchild instability, Langmuir beam instability, Loss cone instability, MHD instability, macroinstability, microinstability, modified two-stream instability, modulational instability, oscillating two-stream instability, parametric instability, pressure driven instability, Raman instability, Rayleigh-Taylor instability, resistive instability, sausage instability, streaming instability, thermal instability, trapped particle instability, two-plasmon instability, two-stream instability, universal instability, and velocity-space instability.
Term: Plasma Wave
Definition: A disturbance of a plasma away from equilibrium, involving oscillations of the plasma's constituent particles and/or the electromagnetic field. Plasma waves can propagate from one point in the plasma to another without net motion of the plasma. Terms used to describe the many kinds of waves in plasmas include: Alfven, Circularly Polarized, Cold Plasma, Drift, Electromagnetic, Electron-Cyclotron, Electron Plasma, Electrostatic, Electrostatic Ion, Electrostatic Ion Cyclotron, Evanescent Extraordinary, Ion-Acoustic, Ion Cyclotron, Ion Plasma, Ion Sound, Langmuir, Left Circularly Polarized, Light, Longitudinal, Lower Hybrid, Magnetohydrodynamic (MHD), Magnetosonic, Negative Energy, Nonlinear, Ordinary, Parallel, Perpendicular, Plane, Radio, Right Circularly Polarized, Shock, Space-Charge, Transverse Travelling, Unmagnetized, Upper-Hybrid, Vlasov, Whistler.
Term: Electrostatic Wave, or Plasma Electrostatic Wave
Definition: One of three categories of plasma waves: electromagnetic, electrostatic, and hydrodynamic (magnetohydrodynamic). Wave motions, i.e. plasma oscillations, are inherent to plasmas due to the ion/electron species, electric/magnetic forces, pressure gradients, and ‘gas-like’ properties that lead to shock waves. Electrostatic waves are longitudinal oscillations appearing in plasma due to a local perturbation of electric neutrality. For a cold, unmagnetized plasma, the frequency of electrostatic waves is at the "plasma frequency".
I think that in their experiement, the lowered air pressure may have come about due to the electrostatic repulsion of the ionized air molecules. For the air flowing over the wings, a charge generator would need to provide a constant electrical output in order to continually ionize the air passing over the wing. That would just be the beginning of the engineering problems.
I think it would take a great deal of work to both verify their experiment, and to also quantify the exact behavior of ionized air passing over a wing. Just look at the entries in the plamsa dictionary to get an idea of just how many physical properties plasmas have.
This is a difficult concept from an engineering perspective. The only information in the article linked in Dave's post, that communicates what is actually happening in their experiement, is the following comments:
The two Toronto students took the "Best of Fair" prize in Saskatoon after demonstrating how to limit "boundary layer acceleration" - overcoming some of the slowing effects of air resistance by generating an electrical field. "If you pass an electrical field over the surface going through the air, it creates ions that lower the air pressure," explained Glen Stone, a spokesman for the Youth Science Foundation. "It has tremendous application."
Mr. Ismail said they began looking at a project for Sci-Tech Ontario involving "plasma physics," but then changed to "fluid mechanics." They combined the two to come up with their idea for reducing drag.
Plasma Dictionary
Term: Instability
Definition: A state of a plasma (or any other physical system) in which a small perturbation amplifies itself to a considerable alteration of the state of the system. In plasmas instabilities sometimes leads to disruptions (see entry). Most known instabilities are associated with waves and other natural (linear) modes of plasma oscillation, though some arise only from nonlinear effects. Known classifications of plasma instabilities include: absolute instability, backscatter instability, ballooning instability, bar-forming instability, beam instability, Brillouin instability, cross-field instability, current-driven instability, drift instability, external/free boundary instability, external-kink instability, fishbone instability, flute instability, hydrodynamic instability, ideal MHD instability, interchange instability, internal/fixed boundary instability, internal kink instability, ion ring instability, Kelvin-Helmholtz instability, kink instability, Kruskal-Schwarzchild instability, Langmuir beam instability, Loss cone instability, MHD instability, macroinstability, microinstability, modified two-stream instability, modulational instability, oscillating two-stream instability, parametric instability, pressure driven instability, Raman instability, Rayleigh-Taylor instability, resistive instability, sausage instability, streaming instability, thermal instability, trapped particle instability, two-plasmon instability, two-stream instability, universal instability, and velocity-space instability.
Term: Plasma Wave
Definition: A disturbance of a plasma away from equilibrium, involving oscillations of the plasma's constituent particles and/or the electromagnetic field. Plasma waves can propagate from one point in the plasma to another without net motion of the plasma. Terms used to describe the many kinds of waves in plasmas include: Alfven, Circularly Polarized, Cold Plasma, Drift, Electromagnetic, Electron-Cyclotron, Electron Plasma, Electrostatic, Electrostatic Ion, Electrostatic Ion Cyclotron, Evanescent Extraordinary, Ion-Acoustic, Ion Cyclotron, Ion Plasma, Ion Sound, Langmuir, Left Circularly Polarized, Light, Longitudinal, Lower Hybrid, Magnetohydrodynamic (MHD), Magnetosonic, Negative Energy, Nonlinear, Ordinary, Parallel, Perpendicular, Plane, Radio, Right Circularly Polarized, Shock, Space-Charge, Transverse Travelling, Unmagnetized, Upper-Hybrid, Vlasov, Whistler.
Term: Electrostatic Wave, or Plasma Electrostatic Wave
Definition: One of three categories of plasma waves: electromagnetic, electrostatic, and hydrodynamic (magnetohydrodynamic). Wave motions, i.e. plasma oscillations, are inherent to plasmas due to the ion/electron species, electric/magnetic forces, pressure gradients, and ‘gas-like’ properties that lead to shock waves. Electrostatic waves are longitudinal oscillations appearing in plasma due to a local perturbation of electric neutrality. For a cold, unmagnetized plasma, the frequency of electrostatic waves is at the "plasma frequency".
I think that in their experiement, the lowered air pressure may have come about due to the electrostatic repulsion of the ionized air molecules. For the air flowing over the wings, a charge generator would need to provide a constant electrical output in order to continually ionize the air passing over the wing. That would just be the beginning of the engineering problems.
I think it would take a great deal of work to both verify their experiment, and to also quantify the exact behavior of ionized air passing over a wing. Just look at the entries in the plamsa dictionary to get an idea of just how many physical properties plasmas have.
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I must be bored as well.
Many of todays helicopter rotor blades have electrical charges induced in them, also known as static electricity. I've not noticed the torque indications become 30% lower during these periods. But I'll look out for it now.
What happens when it rains?
Many of todays helicopter rotor blades have electrical charges induced in them, also known as static electricity. I've not noticed the torque indications become 30% lower during these periods. But I'll look out for it now.
What happens when it rains?
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Flight Safety, ~ Thanks for the information. Roberto Celi agrees with you and the difficulty in implementing the idea.
400 Hertz, ~ Thanks for the static.
Oh well,
back to reality.
400 Hertz, ~ Thanks for the static.
Oh well,
back to reality.
