Edson AB crash, VRS?
There was a thread called “Vuichard Again” a while ago.
A lot of the points here were discussed there and by the same cast of characters….myself included.
Vuichard again
A lot of the points here were discussed there and by the same cast of characters….myself included.
Vuichard again
Sorry it's a long post, but for the benefit of Robbiee and his mates, here is a gathering of Nick Lappos's Urban Myths, plus some notes from the late Shawn Coyle, both these gents being highly qualified test pilots:Helicopter Urban Myths
These Urban Myths pervade our understanding of helicopters and how they operate. Each is fundamentally incorrect, but most are generally held as gospel, because training, lore and reference documents have repeated them long enough that they are simply accepted.
1) Vortex Ring State (VRS) can happen at as little as 300 foot per minute descent, it does not have to be a higher descent rate
2) VRS is more likely at high altitude and high gross weight
3) Hovering with the nose off wind consumes much more power
4) Blade stall is always preceded by vibration
5) Winds affect the power we require when we are in forward flight
6) Downwind takeoffs are absolutely forbidden
7) The Height Velocity curve is a precise guide to the engine failure danger zone
8) Engine failure is the most common accident cause, so full CAT A is the most cost effective safety enhancement we can incorporate into new helicopters.
9) The legal definition of VFR is sufficient to assure flight control and safety using outside references
10) "They" sometimes hide things from us. We should not trust them, the only reliable information we can trust is our own wits.
11) The helicopter is perched on a ball of high pressure air when close to the ground, and "falls off" this ground cushion when it moves forward.
12) Phase lag is cause by gyroscopic precession, and is always exactly 90 degrees
13) LTE is when you run out of power pedal and can be experienced by any single rotor helicopter.
14) NVG are dangerous and should only be used by gifted military pilots.
15) You have to first learn to fly fixed wing before you take helicopter training
16) Torque limits, overspeed limits, temperature limits, hours and airframe limits have huge safety factors built into them by the engineers, so it is OK to bust them every now and then.
Davy07,
The books say so, but they are quite wrong. VRS can only be induced by descending at least as fast as 75% of the downwash velocity of the helicopter and at a forward speed of not more than about 8 knots. For a Robbie this is at least -750fpm rod. For an S76 it is about -1500 fpm.
Why is 300 taught? Because one can start a VRS event by entering a hover with too little power, slip into an overpitching event and in short order, enter VRS. In a helo with scads of OGE hover performance, the 300 fpm is truly a myth, in one without, it is misleading as a VRS cue, but good word as an overpitching warning.
Manfrom Uncle, what you are correctly saying is that going faster uses more power. The wind has nothing to do with it. 80Kts airspeed uses the same power both up and down wind.
For the record, there is no pressure gradient below the rotor, in fact, that lame conventional explanation doesn't even hold water for a millisecond when you realize that ground effect only works on the induced power. How does a "pressure bubble" single out induced power as the only recipient of its wonder?
In fact, pressure bubblers have some difficulty explaining how ground effect works for an airplane at 250 knots, when the "pressure bubble" is about 1/4 mile behind the wing.
Maybe you should get a hold of Shawn Coyle's "Cyclic and Collective":
http://i159.photobucket.com/albums/t...g?t=1195957331
Dear Shawn, Mr. Publisher, dear mods: if this should violate any copyrights and isn't appreciated to be posted, please remove it immediately or have me remove it - I just can't explain it better )
delta 3,
OK, your work is truly great, and I can see the reduction on angle of attack and power. It is truly a desktop universe, and I mean that in a good way.
The problem is that without careful explanation, one could actually think you show how the "pressure bubble" under the rotor is what ground effect is, and that would be untrue. Ground effect is when the ground plane flattens out the flow, causing the rotor to behave as if the blades were much longer. As a result, the tip losses for the blades are sharply reduced, causing a sharp reduction in the induced power requirements. The reason why ground effect does not show very well at 100 knots is that induced power is very low there, but ground effect is still present at 100 knots.
For an airplane, the case is easier to picture. As the wing comes down into ground effect, the tip wash reduces sharply, and the wing behaves as if it were infinitely long. This requires less angle of attack (which had caused a large drag rise prior to entering the ground effect). The induced drag wastes power, so ground effect shows itself as a reduction in angle of attack and a reduction in the power required.
Ground effect is not caused by a pressure rise, nor is the advantage to the aircraft due to any pressure that pushes the aircraft up (or any other such pressure bubble nonsense.)
Ground effect explained
Misinformed Instructors who propel the pressure bubble myth should be asked to do a quick Yahoo search using "induced drag ground effect" so that they can learn how to tell their students the truth, and not convenient myths. We would be all the better for it. Pressure bubblers, please note:
Induced drag explained:
http://galileo.phys.virginia.edu/cla...ero/node5.html
http://www.grc.nasa.gov/WWW/K-12/airplane/induced.html
Ground effect explained:
404 - File or directory not found.
http://www.pilotfriend.com/training/...g/aft_perf.htm
"Many pilots think that ground effect is caused by air being compressed between the wing and the ground. This is not so. Ground effect is caused by the reduction of induced drag when an airplane is flown at slow speed very near the surface."
The quiz for today, for the bright student:
Define induced drag
define aspect ratio
explain how aspect ratio affects induced drag
explain how proximity to the ground affects aspect ratio
I love this block, we can go round and round it forever!
Some points:
1) I never said that ground effect was a myth, I said that the "pressure bubble" was a myth! Ground effect is very real, and amounts to a typical 15% power savings for most helicopters (where the rotor cannot get closer to the ground that about .3 radius.
2) Those who love the pressure bubble theory are welcome to it, believing myths is not against the law! However, ask yourself why ground effect disappears when you hover over long grass - and don't tell me that grass absorbs pressure! The grass slows the outflow, which is the mechanism that changes the blade angle of attack and reduces the hover power.
3) The pressure bubble theory cannot explain why ground effect only reduces the induced drag of the blades, if that theory is correct, more velocity makes more pressure, and thus saves more power. If the air velocity gets banged against the ground, and pressure builds, then a higher velocity should make even more pressure, and more ground effect, right? No, wrong! Maximum ground effect is about +15% power, regardless of how fast the downwash velocity is. In fact, ground effect is no different for highly loaded rotors, with faster downwash, than it is for low disk loading rotors with gentle downwash.
4) If pressure bubbles push the aircraft up, then high speed airplanes, with the wake hitting the ground hundreds of meters behind the aircraft, should see no ground effect. But they do! That is because the effect is on the wing, where the angle of the flow around the wing is changed by the presence of the ground.
5) Ground effect makes the wings or blades act as if they are longer, and this cuts the tip losses that make the induced drag. They have nothing to do with the pressure under the blade or wing, they have everything to do with the reduction in outflow, and the reduction in the tip vortex pattern due to that outflow.
With my respect for Shawn unabated, I must respectfully disagree with him. There is a meaningful difference between the two cases, light vs heavy. But first we must clarify what we mean by Vortex Ring State (VRS) - and what is meant by a different problem called "Settling with Power (SWP)" or "over pitching" or "insufficient power to Hover OGE"
Most accidents where a hovering helicopter falls and crashes and VRS is blamed are actually cases of SWP or over pitching, where the hover performance is marginal, and insufficient reserve power (power margin) is available to allow moderate climbs and descents while OGE. The aircraft "falls through" the hover, hits hard (usually with just a bent helicopter and bruised ego) and then someone says "It was VRS." Sometimes the mistaken person is an official accident investigator!
In a helicopter at high MGW, with only slight or no margin between the power needed to HOGE and the power available from the engines, "over pitching" is more likely than in a lightly loaded helicopter where lots of power above hover power is available. When lightly loaded, there is much extra power available above the hover power, so the lightly loaded helo is much less likely to experience "over pitching" and thus the lightly loaded helo is much less likely to be mistakenly labeled as a VRS accident.
Now the truth: Since true VRS involves the descent of the helicopter into its own downwash, and since in a light helicopter the downwash velocity is quite a bit less than in that same helicopter when heavy, a lightly loaded helicopter needs much less rate of descent to experience true VRS.
Thus, heavy helicopters require more descent rate to get true VRS, and so are less likely to enter that state, but heavily loaded helicopters have more over pitching power control accidents that are too often labeled "VRS", so the mistaken pilot lore says heavy helicopters are more likely to experience VRS.
For the record, no helicopter can experience true VRS unless it is descending nearly vertically at about 800 to 1000 feet per minute.
Also for the record, most helicopters can experience SWP or overpitching at rates of descent near zero if they have little hover power margin.
Also, heavily loaded helicopters have less propensity to enter VRS because they need more vertical descent rate than lightly loaded helicopters, which need less descent rate to get into VRS.
These Urban Myths pervade our understanding of helicopters and how they operate. Each is fundamentally incorrect, but most are generally held as gospel, because training, lore and reference documents have repeated them long enough that they are simply accepted.
1) Vortex Ring State (VRS) can happen at as little as 300 foot per minute descent, it does not have to be a higher descent rate
2) VRS is more likely at high altitude and high gross weight
3) Hovering with the nose off wind consumes much more power
4) Blade stall is always preceded by vibration
5) Winds affect the power we require when we are in forward flight
6) Downwind takeoffs are absolutely forbidden
7) The Height Velocity curve is a precise guide to the engine failure danger zone
8) Engine failure is the most common accident cause, so full CAT A is the most cost effective safety enhancement we can incorporate into new helicopters.
9) The legal definition of VFR is sufficient to assure flight control and safety using outside references
10) "They" sometimes hide things from us. We should not trust them, the only reliable information we can trust is our own wits.
11) The helicopter is perched on a ball of high pressure air when close to the ground, and "falls off" this ground cushion when it moves forward.
12) Phase lag is cause by gyroscopic precession, and is always exactly 90 degrees
13) LTE is when you run out of power pedal and can be experienced by any single rotor helicopter.
14) NVG are dangerous and should only be used by gifted military pilots.
15) You have to first learn to fly fixed wing before you take helicopter training
16) Torque limits, overspeed limits, temperature limits, hours and airframe limits have huge safety factors built into them by the engineers, so it is OK to bust them every now and then.
Davy07,
The books say so, but they are quite wrong. VRS can only be induced by descending at least as fast as 75% of the downwash velocity of the helicopter and at a forward speed of not more than about 8 knots. For a Robbie this is at least -750fpm rod. For an S76 it is about -1500 fpm.
Why is 300 taught? Because one can start a VRS event by entering a hover with too little power, slip into an overpitching event and in short order, enter VRS. In a helo with scads of OGE hover performance, the 300 fpm is truly a myth, in one without, it is misleading as a VRS cue, but good word as an overpitching warning.
Manfrom Uncle, what you are correctly saying is that going faster uses more power. The wind has nothing to do with it. 80Kts airspeed uses the same power both up and down wind.
For the record, there is no pressure gradient below the rotor, in fact, that lame conventional explanation doesn't even hold water for a millisecond when you realize that ground effect only works on the induced power. How does a "pressure bubble" single out induced power as the only recipient of its wonder?
In fact, pressure bubblers have some difficulty explaining how ground effect works for an airplane at 250 knots, when the "pressure bubble" is about 1/4 mile behind the wing.
Maybe you should get a hold of Shawn Coyle's "Cyclic and Collective":
http://i159.photobucket.com/albums/t...g?t=1195957331
Dear Shawn, Mr. Publisher, dear mods: if this should violate any copyrights and isn't appreciated to be posted, please remove it immediately or have me remove it - I just can't explain it better )
delta 3,
OK, your work is truly great, and I can see the reduction on angle of attack and power. It is truly a desktop universe, and I mean that in a good way.
The problem is that without careful explanation, one could actually think you show how the "pressure bubble" under the rotor is what ground effect is, and that would be untrue. Ground effect is when the ground plane flattens out the flow, causing the rotor to behave as if the blades were much longer. As a result, the tip losses for the blades are sharply reduced, causing a sharp reduction in the induced power requirements. The reason why ground effect does not show very well at 100 knots is that induced power is very low there, but ground effect is still present at 100 knots.
For an airplane, the case is easier to picture. As the wing comes down into ground effect, the tip wash reduces sharply, and the wing behaves as if it were infinitely long. This requires less angle of attack (which had caused a large drag rise prior to entering the ground effect). The induced drag wastes power, so ground effect shows itself as a reduction in angle of attack and a reduction in the power required.
Ground effect is not caused by a pressure rise, nor is the advantage to the aircraft due to any pressure that pushes the aircraft up (or any other such pressure bubble nonsense.)
Ground effect explained
Misinformed Instructors who propel the pressure bubble myth should be asked to do a quick Yahoo search using "induced drag ground effect" so that they can learn how to tell their students the truth, and not convenient myths. We would be all the better for it. Pressure bubblers, please note:
Induced drag explained:
http://galileo.phys.virginia.edu/cla...ero/node5.html
http://www.grc.nasa.gov/WWW/K-12/airplane/induced.html
Ground effect explained:
404 - File or directory not found.
http://www.pilotfriend.com/training/...g/aft_perf.htm
"Many pilots think that ground effect is caused by air being compressed between the wing and the ground. This is not so. Ground effect is caused by the reduction of induced drag when an airplane is flown at slow speed very near the surface."
The quiz for today, for the bright student:
Define induced drag
define aspect ratio
explain how aspect ratio affects induced drag
explain how proximity to the ground affects aspect ratio
I love this block, we can go round and round it forever!
Some points:
1) I never said that ground effect was a myth, I said that the "pressure bubble" was a myth! Ground effect is very real, and amounts to a typical 15% power savings for most helicopters (where the rotor cannot get closer to the ground that about .3 radius.
2) Those who love the pressure bubble theory are welcome to it, believing myths is not against the law! However, ask yourself why ground effect disappears when you hover over long grass - and don't tell me that grass absorbs pressure! The grass slows the outflow, which is the mechanism that changes the blade angle of attack and reduces the hover power.
3) The pressure bubble theory cannot explain why ground effect only reduces the induced drag of the blades, if that theory is correct, more velocity makes more pressure, and thus saves more power. If the air velocity gets banged against the ground, and pressure builds, then a higher velocity should make even more pressure, and more ground effect, right? No, wrong! Maximum ground effect is about +15% power, regardless of how fast the downwash velocity is. In fact, ground effect is no different for highly loaded rotors, with faster downwash, than it is for low disk loading rotors with gentle downwash.
4) If pressure bubbles push the aircraft up, then high speed airplanes, with the wake hitting the ground hundreds of meters behind the aircraft, should see no ground effect. But they do! That is because the effect is on the wing, where the angle of the flow around the wing is changed by the presence of the ground.
5) Ground effect makes the wings or blades act as if they are longer, and this cuts the tip losses that make the induced drag. They have nothing to do with the pressure under the blade or wing, they have everything to do with the reduction in outflow, and the reduction in the tip vortex pattern due to that outflow.
With my respect for Shawn unabated, I must respectfully disagree with him. There is a meaningful difference between the two cases, light vs heavy. But first we must clarify what we mean by Vortex Ring State (VRS) - and what is meant by a different problem called "Settling with Power (SWP)" or "over pitching" or "insufficient power to Hover OGE"
Most accidents where a hovering helicopter falls and crashes and VRS is blamed are actually cases of SWP or over pitching, where the hover performance is marginal, and insufficient reserve power (power margin) is available to allow moderate climbs and descents while OGE. The aircraft "falls through" the hover, hits hard (usually with just a bent helicopter and bruised ego) and then someone says "It was VRS." Sometimes the mistaken person is an official accident investigator!
In a helicopter at high MGW, with only slight or no margin between the power needed to HOGE and the power available from the engines, "over pitching" is more likely than in a lightly loaded helicopter where lots of power above hover power is available. When lightly loaded, there is much extra power available above the hover power, so the lightly loaded helo is much less likely to experience "over pitching" and thus the lightly loaded helo is much less likely to be mistakenly labeled as a VRS accident.
Now the truth: Since true VRS involves the descent of the helicopter into its own downwash, and since in a light helicopter the downwash velocity is quite a bit less than in that same helicopter when heavy, a lightly loaded helicopter needs much less rate of descent to experience true VRS.
Thus, heavy helicopters require more descent rate to get true VRS, and so are less likely to enter that state, but heavily loaded helicopters have more over pitching power control accidents that are too often labeled "VRS", so the mistaken pilot lore says heavy helicopters are more likely to experience VRS.
For the record, no helicopter can experience true VRS unless it is descending nearly vertically at about 800 to 1000 feet per minute.
Also for the record, most helicopters can experience SWP or overpitching at rates of descent near zero if they have little hover power margin.
Also, heavily loaded helicopters have less propensity to enter VRS because they need more vertical descent rate than lightly loaded helicopters, which need less descent rate to get into VRS.
By the way, since you guys keep pointing this list out to me, is there any one particular "myth" you all think I'm perpetuating?
Last edited by Robbiee; 21st May 2023 at 17:22.
Robbiee - so when you learned about ground effect, no-one mentioned high pressure air or a bubble under the aircraft? No-one mentioned keeping RoD at slow speed under 300'/min to avoid VRS? No-one explained phase lad by calling it gyroscopic precession?
Sounds like you were trained by Nick and Shawn themselves.......
Sounds like you were trained by Nick and Shawn themselves.......
Originally Posted by [email protected]
Robbiee - so when you learned about ground effect, no-one mentioned high pressure air or a bubble under the aircraft? No-one mentioned keeping RoD at slow speed under 300'/min to avoid VRS? No-one explained phase lad by calling it gyroscopic precession?
Sounds like you were trained by Nick and Shawn themselves.......
Sounds like you were trained by Nick and Shawn themselves.......
ROD being less than 300 fpm with airspeed less than ETL was about not getting into the onset of VRS, not necessarily full blown VRS.
As for gyroscopic precession? No one said the rotor was a gyro, just that it acted similarly to one.
Anyway, none of these read like those "myths" above, and none of them have anything to do with any of my comments on this thread. Which is why I'm puzzled as to why I keep getting referred to them?
Robbiee, you must have learned somewhere other than the Hew Hess Hay - someplace where instructors have over 100 hours more than their students, and where the horsefeathers aren't passed from one under-informed pilot to the next. Well done!
Some people still think that "flapping to equality" is happening in forward flight, and that even though the disk is tilted down at the front, "the advancing blade is still flapping up."
Some people still think that "flapping to equality" is happening in forward flight, and that even though the disk is tilted down at the front, "the advancing blade is still flapping up."
Robbiee, you must have learned somewhere other than the Hew Hess Hay - someplace where instructors have over 100 hours more than their students, and where the horsefeathers aren't passed from one under-informed pilot to the next. Well done!
Some people still think that "flapping to equality" is happening in forward flight, and that even though the disk is tilted down at the front, "the advancing blade is still flapping up."
Some people still think that "flapping to equality" is happening in forward flight, and that even though the disk is tilted down at the front, "the advancing blade is still flapping up."
Still doesn't explain the relevance of this so-called "myths" list to anything I've said about this thread topic, or why I've been referred to it twice?
The disc can't flap to equality when the cyclic position prevents it from doing so. Doesn't mean it isn't trying to.
@helispotter: I very much doubt, that a model helicopter would be appropriate for this kind of test. The problem does not lie in the mass and engine response, but in the dynamics of the main rotor. Building a scaled down model of the rotor with all the correct flexing and flapping isn't as easy as it sounds. The commercially available models lack a lot of components of a real rotor. No flapping- or lead/lag hinges for example. Not even virtual hinges in the blade root. Model helicopters do not need that. And then there is the Reynolds number.
But it has been done to visualise VRS in wind tunnels. But here they want to fly certain manoeuvres and that is difficult in a wind tunnel.
The budget isn't very high. I think for that money it is cheaper to use a real helicopter.
But it has been done to visualise VRS in wind tunnels. But here they want to fly certain manoeuvres and that is difficult in a wind tunnel.
The budget isn't very high. I think for that money it is cheaper to use a real helicopter.
- For evaluating VRS, please note that vortex structures and their development are essentially independent of Reynolds Number, which is not obvious, but happens to be the case. Lots of good experimentation out there covering that topic, go to AIAA ARC (expensive) or NASA NTRS (free).
- For establishing the effects of VRS, the type of rotor head involved is only of relevance to moments transferred to the mast and then to the body suspended from the mast, it doesn't affect the flow through the rotor itself.
- Blade bending and torsion modes don't affect VRS. VRS may excite some high order bending modes, but they would be very low amplitude, there being unsteady inflow conditions to midspan to near full span rotor inflow, which will give more unsteady CL, CD and CM moments, but they are normally unsteady anyway.
- Flapping itself doesn't affect VRS, but VRS will affect flapping, more on rotors withy zero hinge moments, and will affect roll/pitch moments directly on rotors with hinge offset.
- in plane load relief is not particularly affected by VRS, lead-lag is not of great interest in modelling VRS.
- The Lock number is pretty easy to emulate for a series of blades.
Robbiee, you must have learned somewhere other than the Hew Hess Hay - someplace where instructors have over 100 hours more than their students, and where the horsefeathers aren't passed from one under-informed pilot to the next. Well done!
Some people still think that "flapping to equality" is happening in forward flight, and that even though the disk is tilted down at the front, "the advancing blade is still flapping up."
Some people still think that "flapping to equality" is happening in forward flight, and that even though the disk is tilted down at the front, "the advancing blade is still flapping up."
We may be speaking different dialects of English, but here is the equation of motion of flapping in forward flight, [eq:6.130 of reference]
The aerodynamic coefficients are the flap moments due to angle-of-attack changes produced by the blade pitch, twist, inflow, flapping velocity, and flapping displacements, respectively. A flapping velocity produces an angle-of-attack perturbation that changes the blade lift to oppose the motion; hence the blade has aerodynamic damping given by the coefficient MBetadot.
Johnson, Wayne. Rotorcraft Aeromechanics (Cambridge Aerospace Series, 36) . Cambridge University Press.
Now, remove flapping to equality and you need a ton of cyclic input to achieve a zero roll moment other than your desired roll command. Helo aerodynamics and the laws of motion, control derivatives etc are fun; there is a lot going on and most of it is non linear, but it has algebraic solutions to give an understanding of what is actually going on. For transition from steady state hover, there is a characteristic cyclic position to achieve a flight path, and that is able to be determined using all of the effects that occur in the process, and right in the middle of that all is the harmonic of flapping motion.
In what context are we telling people that "flapping to equality" (a passable descriptive term of harmonic flapping) doesn't occur in forward flight?
Beta is flapping
Theta is blade pitch
Zeta is lead/lag...
Psi is the azimuth position that is being considered.
And here is the Fourier series of the harmonic motion of a rotor, and that gives the flappy bit above which is occurring in forward flight.
These harmonics don't suddenly stop as the rotor shaft, skids, fuel, engine, and bio mass starts to move forward, they explain the motion that results at all times.
Your comment confuses me, I can only refer to the equations of motion in our universe.
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Originally Posted by [email protected]
The disc can't flap to equality when the cyclic position prevents it from doing so. Doesn't mean it isn't trying to.
I know it is some time since many of us looked at the books, but.... the tip path plane is only partly directed by the cyclic, it is otherwise determined by the flapping resulting from translation of the rotor disk through the air. While flapping alters the TPP, it doesn't add significant rolling moments to the hub (it isn't perfectly isolated though, there are some relatively small consequences). The effect of flapping from the translation is to balance forces, and the cyclic adds an additional force that causes the TPP to alter, and where there is a hinge moment, to develop a roll or pitch moment to the body of the helo, and with zero hinge moment, for the motion of the disk to lead to a moment from the center of the disk to the CG of the helicopter, which then moves the body in lag to the disk.
The cyclic doesn't alter the flapping of the TPP resulting from translation, which is resulting in varying velocity of the advancing and retreating blades. The cyclic is additive to the flapping response, as is shown in the Fourier series that describes the TPP. theta sub 1c is lateral cyclic pitch angle, theta sub1s is longitudinal cyclic pitch angle, and theta subo is the collective pitch angle. beta gives the flapping... zeta is the in plane lead lag, gamma is the lock number (the relationship of aerodynamic to inertial response of the rotor blade).
There is a wealth of really good reading for helicopter drivers out there, stuff that actually tells it as it is, gives the equations of motion, derivatives etc, and which (for my money) is well worth the coin for any helo driver. I do fundamental aerodynamic flight testing in helicopters and jet aircraft, as well as prop planes, and the helicopter is the one that I take the most care over, by far; I respect the courage of young helicopter CFIs that go out and teach engine failure OGE to a zero time student in an R-22, they are braver than I am... knowing the maths is not necessary to fly a helo, but knowing the science (the equations) is worth the effort if you go and play on the periphery of the envelope. The beauty of the helicopter and the reason I love flying them is that they are brutally honest, they show what the pilot is doing instantaneously, more than a Pitts S1 does.
Suggested reading list:
- Principles of Helicopter Aerodynamics J Gordon Leishman.
- Helicopter Aerodynamics Vol 1, Vol 2, Vol 3 Ray Prouty
- Helicopter Performance Stability & control Ray Prouty
- Basic Helicopter Aerodynamics John Seddon & Simon Newman
- Aerodynamics of the Helicopter, Alfred Gessow & Gary C Myers Jr
- Helicopter Theory, Wayne Johnson
- Rotorcraft Aeromechanics Wayne Johnson
- Rotary-wing Aerodynamics W.Z. Stepniewski & C.N. Keys
- Helicopter Flight dynamics Gareth Padfield
- Practical Methods for Aircraft and Rotorcraft Flight Control Design: An Optimization-Based Approach, Mark B Tischler, Tom Berger, Christina M Ivler, M H Mansur, K.K. Cheung, J Y Song
- Cyclic & Collective, Shawn Coyle
- The Art and Science fo Flying Helicopters, Shawn Coyle
- The Little Book of Autorotations, Shawn Coyle
and something written by the FAA.
Shawns work is easy reading and a good operational input. Rays stuff is also relatively easy to get into, and it is worth having in hard back, (I've worn out a couple of copies). Gessow and Myers dates back to 1952, and not much has changed, Ch 7 is worth reading there, and it is consistent with Prouty, Johnson Stepniewski & Keys, and Leishman. (I like Johnsons work, he looks at each state from various analysis and that gives a helpful overview). Gessow and Myers work is available as a PDF, and is still relevant but does use some nomenclature that has fallen from favour in later works, the physics remain the same.
Last edited by fdr; 22nd May 2023 at 07:31.
A lovely dismissive series of post there FDR without actually adding anything to the thread other than a level of maths that most pilots really don't care about.
Test pilots don't usually talk in pilot language, they usually lecture in engineer degree maths-speak, but Nick and Shawn were different in that respect - maybe you could try that.
Should I tell a pilot who is trying to fly us into the ground to remember his Fourier transformations and flapping harmonics or just get him to pull back on the cyclic?
Test pilots don't usually talk in pilot language, they usually lecture in engineer degree maths-speak, but Nick and Shawn were different in that respect - maybe you could try that.
Should I tell a pilot who is trying to fly us into the ground to remember his Fourier transformations and flapping harmonics or just get him to pull back on the cyclic?
Originally Posted by [email protected]
AC - most of those links don't work any more unfortunately.
I was lucky to find Nick Lappos and Shawn Coyle on these pages 25 years ago and have tried to pass on their wisdom where possible ever since.
I was lucky to find Nick Lappos and Shawn Coyle on these pages 25 years ago and have tried to pass on their wisdom where possible ever since.
Originally Posted by [email protected]
A lovely dismissive series of post there FDR without actually adding anything to the thread other than a level of maths that most pilots really don't care about.
Test pilots don't usually talk in pilot language, they usually lecture in engineer degree maths-speak, but Nick and Shawn were different in that respect - maybe you could try that.
Should I tell a pilot who is trying to fly us into the ground to remember his Fourier transformations and flapping harmonics or just get him to pull back on the cyclic?
Test pilots don't usually talk in pilot language, they usually lecture in engineer degree maths-speak, but Nick and Shawn were different in that respect - maybe you could try that.
Should I tell a pilot who is trying to fly us into the ground to remember his Fourier transformations and flapping harmonics or just get him to pull back on the cyclic?
If something is being added that has a potential to impact the operation of some young driver, it should be supportable if represented as fact, otherwise it adds to the mass of uncontrolled anecdotal wisdom. You have more than enough operational experience to add to the knowledge base, people read your commentary, are you sure you are happy with the accuracy of your recent post:
The disc can't flap to equality when the cyclic position prevents it from doing so. Doesn't mean it isn't trying to.
P.S.: I did a bit of proof reading of Shawn's work, so I do agree in your view in that area. Shawn was a kindly and capable guy to go fly with or spend time with. His passing in June 2021 was another loss to the industry.
Last edited by fdr; 22nd May 2023 at 07:30. Reason: PS
I suppose colored pencils are akin to wax crayons and are basic visual aids for those not fully weaned from their use in the explanation of complex problems that require the understanding of higher forms of math in order to achieve more precise understanding of the principles governing helicopter aerodynamics.
Did the many exams inflicted upon our British fellows fail somehow to elicit a more detailed grasp of those principles than might be garnered from the results of delving into for's reading list?
I am of the thought the colored pencil brigade may have imposed unintended limits upon the desired outcome even allowing for the basic assumption their transfer of knowledge was satisfactory for practical purposes despite failing to arise to the level one might obtain elsewhere and by different methods and different instructors.
One thing for sure is those believers in the pencils do not care to be challenged or alas contradicted.
One thing I learned very early in my flying career was I can always learn something from others no matter who they are or how much experience they have.....even if the teaching point is only to never to do it the way they did.
The reading list offered by fdr points us to some very useful information although I am not sure the FAA would on my list of favorites.
I always found it useful to re-read the wonderful small Sikorsky Blue Booklet on Helicopter Aerodynamics as it was written in language that was easily understood.
Did the many exams inflicted upon our British fellows fail somehow to elicit a more detailed grasp of those principles than might be garnered from the results of delving into for's reading list?
I am of the thought the colored pencil brigade may have imposed unintended limits upon the desired outcome even allowing for the basic assumption their transfer of knowledge was satisfactory for practical purposes despite failing to arise to the level one might obtain elsewhere and by different methods and different instructors.
One thing for sure is those believers in the pencils do not care to be challenged or alas contradicted.
One thing I learned very early in my flying career was I can always learn something from others no matter who they are or how much experience they have.....even if the teaching point is only to never to do it the way they did.
The reading list offered by fdr points us to some very useful information although I am not sure the FAA would on my list of favorites.
I always found it useful to re-read the wonderful small Sikorsky Blue Booklet on Helicopter Aerodynamics as it was written in language that was easily understood.
FDR - the problem with people with your level of education and depth of knowledge is that you often see what is meant to be a simple statement as an affront to accuracy because it isn't supported by pages of proof.
If I had wanted to offer a cogent argument to ACs post with supporting evidence and referencing, I would have done so - but I didn't - this, as you know, has been (another) thread about VRS and SWP following yet another avoidable accident and the more off-topic the thread goes, the less value it is to those young drivers.
I have taught those young drivers for nearly 40 years in a variety of roles and never once have I been asked for mathematical proof for what I have demonstrated or explained because for 99.9% of the time it is irrelevant.
If my operational and instructional experience and credentials aren't enough for you then I apologise - I have never claimed to be an aerodynamicist nor a maths or engineering guru - I am just a fairly well trained and tested pilot and instructor who seems to have got the message across reasonably well in the past.
If you want to explain the subtleties of flapping here then please do so in language clear and unambiguous to me and those young drivers but it might be worth a new thread.
I am always very happy to be educated - I have read a number of those sources you quote and regularly refer to my Prouty and Gessow and Myers .
If I had wanted to offer a cogent argument to ACs post with supporting evidence and referencing, I would have done so - but I didn't - this, as you know, has been (another) thread about VRS and SWP following yet another avoidable accident and the more off-topic the thread goes, the less value it is to those young drivers.
I have taught those young drivers for nearly 40 years in a variety of roles and never once have I been asked for mathematical proof for what I have demonstrated or explained because for 99.9% of the time it is irrelevant.
If my operational and instructional experience and credentials aren't enough for you then I apologise - I have never claimed to be an aerodynamicist nor a maths or engineering guru - I am just a fairly well trained and tested pilot and instructor who seems to have got the message across reasonably well in the past.
If you want to explain the subtleties of flapping here then please do so in language clear and unambiguous to me and those young drivers but it might be worth a new thread.
I am always very happy to be educated - I have read a number of those sources you quote and regularly refer to my Prouty and Gessow and Myers .
You never can resist a dig Sasless..........sad.
In what context are we telling people that "flapping to equality" (a passable descriptive term of harmonic flapping) doesn't occur in forward flight?
My comment was that a lot of people think that the advancing blade is flapping up in forward flight and the retreating blade is flapping down , when in fact they are doing the exact opposite.
Regarding Shawn, I had a delightful lunch with him in LA back in 2003, and got a signed copy of his book as well. I found quite a few things that could have been clarified better, and lots of spelling and grammatical errors, and I sent him a list of the suggested amendments. But when the next edition came out, the same errors were there - perhaps he didn't like the critique, or maybe the 2nd edition was already in the hands of the printers, will never know. But a lovely guy.
AC think the problem is a lot to do with the exact English and exactly whatever one is talking about. Case in point the blade does flap down if one is in forward flight, but most will think about accelerating the helicopter then the disc is trying to flap back and hence the push forward on the cylic. I have found over the years a picture paints a thousand complicated words, as long as the driver knows what happens when he does x or y , it doesnt really matter the why's and where fore's
Well, since we're on this ride,...
If Dissymmetry of Lift is being eliminated through flapping (as my textbook tells me) then why does the R22 have a right trim knob which (I am told) is to alleviate the right cyclic pressure needed to counter, Dissymmetry of Lift?
If Dissymmetry of Lift is being eliminated through flapping (as my textbook tells me) then why does the R22 have a right trim knob which (I am told) is to alleviate the right cyclic pressure needed to counter, Dissymmetry of Lift?
The Vertical Flight Society has a library of about 15,000 articles among which are many dealing with research studies re helicopter aerodynamics.
It would be interesting to see how many professional helicopter pilots are members of the VFS or other similar organizations that offer continuing education on topics relating to our profession.
One thing we should consider is the difference between the theoretical and the practical and find a consensus where that line should. be drawn when assessing what a licensed helicopter pilot should know.
As in other professions, actually in order to be considered a profession there should be a requirement for continuing education for its members.
Is there such a thing for helicopter pilots.....not training or testing....but education?
It would be interesting to see how many professional helicopter pilots are members of the VFS or other similar organizations that offer continuing education on topics relating to our profession.
One thing we should consider is the difference between the theoretical and the practical and find a consensus where that line should. be drawn when assessing what a licensed helicopter pilot should know.
As in other professions, actually in order to be considered a profession there should be a requirement for continuing education for its members.
Is there such a thing for helicopter pilots.....not training or testing....but education?