Speed vs Turbulence
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Originally Posted by Goeasy
Slowing down doesn't improve the ride, just prolongs your time in the turbulence
G-V and capt bloggs.... unlike you I'm not stupid enough to go through CB's. I'm referrring to those pilots in clear air who chose to slow up from .82 or 81 to .8 and truly believe they are improving the ride. Totally unprovable, and highly unlikely. Just sheep!
Even in severe turbulence the Airbus QRH only says 'CONSIDER' reducing to Turbulence penetration speed as specified in the table. It isnt even mandatory. Why?
Even in severe turbulence the Airbus QRH only says 'CONSIDER' reducing to Turbulence penetration speed as specified in the table. It isnt even mandatory. Why?
Turbulence speed is not about comfort, the ride down the back; it is required to protect the aircraft structure… and you!
If a manufacturer advises ‘consideration’ then consider… what if. Flying, airmanship, sensible interpretation does not have to be mandated.
G-V see CS 25.341 (and AMC) which discusses turbulence loads; noting that ‘load’ is force, which involves mass and acceleration. Some of the equations might relate to the discussion on a change speed re the effect of turbulence on structure or ride.
Also there are references in certification to ‘extreme’ turbulence, something above severe, but as yet I cannot find a definition which might be suitable for crew use.
If a manufacturer advises ‘consideration’ then consider… what if. Flying, airmanship, sensible interpretation does not have to be mandated.
G-V see CS 25.341 (and AMC) which discusses turbulence loads; noting that ‘load’ is force, which involves mass and acceleration. Some of the equations might relate to the discussion on a change speed re the effect of turbulence on structure or ride.
Also there are references in certification to ‘extreme’ turbulence, something above severe, but as yet I cannot find a definition which might be suitable for crew use.
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Personally, I see no problem slowing a bit to put yourself equally in between the two limits if it makes you feel better. In the B737NG I do notice the ride is better at the published speed for bumps .76/280kts. Perhaps it works better for the wings acting as suspension? Simply that the flex in the wings works better than when slower
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The basic assumption is that the wind turbulence is horizontal. That is where the issues come from.
Consider gusting conditions that have a vertical factor, not simply the resultant wind component.
You have level flight with the associated AoA, and encounter a vertical gust. (be it uplift of downdraft) The effect from vertical winds on AoA can be significant. This is why slowing down appears to lessen the effect.
Given the multitude of angles that a vertical wind can come from, it seems that there really cannot be a definitive direct correlation between speed reduction and the effect on the G force componenet.
Consider that winds are flowing like currents in a stream, winding horizontally and vertically, or ocean waves (kelvin-helmholtz waves are an extreme example) but vertical rolling winds happen on a mesoscale all the time.
So, a few years ago, the FAA had some guidance for small aircraft operators...given that the focus was on G acceleration, you may find some value in these equations.
VA: manuvering airspeed
VB: turbulence penetration speed (max speed where gust will not overstress the ac)
VA and VB are derived as a function of VS, clean stall speed:
VA (gross weight) = 1.95 × VS VB (gross weight) = 1.6 × VS
VA (current weight) = VA (gross weight) × √(current weight ÷ gross weight
(note: VB is slower than VA)
Currently, the FAA and other groups are looking at the circular velocity of the wake vortex, and how to convert this to G force and the associated effect per aircraft type, but that is a long ways off.
Consider gusting conditions that have a vertical factor, not simply the resultant wind component.
You have level flight with the associated AoA, and encounter a vertical gust. (be it uplift of downdraft) The effect from vertical winds on AoA can be significant. This is why slowing down appears to lessen the effect.
Given the multitude of angles that a vertical wind can come from, it seems that there really cannot be a definitive direct correlation between speed reduction and the effect on the G force componenet.
Consider that winds are flowing like currents in a stream, winding horizontally and vertically, or ocean waves (kelvin-helmholtz waves are an extreme example) but vertical rolling winds happen on a mesoscale all the time.
So, a few years ago, the FAA had some guidance for small aircraft operators...given that the focus was on G acceleration, you may find some value in these equations.
VA: manuvering airspeed
VB: turbulence penetration speed (max speed where gust will not overstress the ac)
VA and VB are derived as a function of VS, clean stall speed:
VA (gross weight) = 1.95 × VS VB (gross weight) = 1.6 × VS
VA (current weight) = VA (gross weight) × √(current weight ÷ gross weight
(note: VB is slower than VA)
Currently, the FAA and other groups are looking at the circular velocity of the wake vortex, and how to convert this to G force and the associated effect per aircraft type, but that is a long ways off.
Originally Posted by Goeasy
G-V and capt bloggs.... unlike you I'm not stupid enough to go through CB's.
The fact is going slower through turbulence improves the ride. I reckon it's because L=V².
Bloggs I don't disagree with that point whatsoever. My argument is that the significant speed reduction required to appreciably reduce turbulence effect is not 0.01 or 0.02mach and just isn't available in the confines of coffin corner.
But many pilots seem happy to reduce to or below best l/d speed (green dot on bus) just to 'lighten the load' on the wing. As opposed to trying to maintain mid-point between green dot and red line for max protection from both limits. Call it common sense or airmanship?
Neither is very common now!
But many pilots seem happy to reduce to or below best l/d speed (green dot on bus) just to 'lighten the load' on the wing. As opposed to trying to maintain mid-point between green dot and red line for max protection from both limits. Call it common sense or airmanship?
Neither is very common now!
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Before you come here and start trolling I suggest:
1. Learn how to read
2. Learn how to understand what you are reading and then, may be, you will be able to grasp what this thread is about.
3. Study aviation language / METAR code and, may be, you will learn the difference between Cu and CB
I will try to explain to you what capt bloggs communicated quite clearly:
If you fly thru the same pocket of turbulence (Cu for example) at 320 knots, you will experience much stronger turbulence than doing so at 250 knots.
That is a common fact. Most professional pilots are in agreement about it as you mentioned.
Now the purpose of this thread is to discuss if G-loads decrease linear to the airspeed or not. Nothing else.
It is not about reducing your Mach from 0.82 to 0.80.
At FL250, for example,you can maintain 320 KIAS or slow down to 250 KIAS.
It is clear that you cant contribute anything to this topic so please stop trolling.
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Turbulence speed is not about comfort, the ride down the back; it is required to protect the aircraft structure… and you!
If a manufacturer advises ‘consideration’ then consider… what if. Flying, airmanship, sensible interpretation does not have to be mandated.
G-V see CS 25.341 (and AMC) which discusses turbulence loads; noting that ‘load’ is force, which involves mass and acceleration. Some of the equations might relate to the discussion on a change speed re the effect of turbulence on structure or ride.
Also there are references in certification to ‘extreme’ turbulence, something above severe, but as yet I cannot find a definition which might be suitable for crew use.
If a manufacturer advises ‘consideration’ then consider… what if. Flying, airmanship, sensible interpretation does not have to be mandated.
G-V see CS 25.341 (and AMC) which discusses turbulence loads; noting that ‘load’ is force, which involves mass and acceleration. Some of the equations might relate to the discussion on a change speed re the effect of turbulence on structure or ride.
Also there are references in certification to ‘extreme’ turbulence, something above severe, but as yet I cannot find a definition which might be suitable for crew use.
Couldn't find anything about relationship of G-loads and speed.
G-V, speed - g relationship, is more by inference than exact value.
A very, very simple view of CS 25;-
A value of g is chosen - a structural limit. The aircraft response to the gust model is checked for a range of speeds, reducing until an acceptable compromise if found - the speed at which g is within the structure limit.
A similar assessment is made for low speed margin, with speed increasing, the result of the two being the turbulence speed or range of speeds. As per #28.
Whether this indicates a V^2 or linear relationship with force depends on the equations - a simple view might favour V^2.
The thread question relates to the effect of turbulence, presumably relating to comfort.
Comfort is subjective, an individual assessment. What is rough for a passenger could be a non event for the crew. Similar assessments might depend on aircraft type, or differences in structure and materials. At least one type that I flew had different responses between the cockpit (and rear cabin), and the centre section being least affected (flexing bent-banana mode), and again different modes - sway vs bounce which can affect people differently. And then there is roll …
Irrespective of the degree of comfort, passengers appear to favour a safe arrival, then being able to share their ‘horrific’ experiences, than to suffer physical harm or even not to arrive at all.
A very, very simple view of CS 25;-
A value of g is chosen - a structural limit. The aircraft response to the gust model is checked for a range of speeds, reducing until an acceptable compromise if found - the speed at which g is within the structure limit.
A similar assessment is made for low speed margin, with speed increasing, the result of the two being the turbulence speed or range of speeds. As per #28.
Whether this indicates a V^2 or linear relationship with force depends on the equations - a simple view might favour V^2.
The thread question relates to the effect of turbulence, presumably relating to comfort.
Comfort is subjective, an individual assessment. What is rough for a passenger could be a non event for the crew. Similar assessments might depend on aircraft type, or differences in structure and materials. At least one type that I flew had different responses between the cockpit (and rear cabin), and the centre section being least affected (flexing bent-banana mode), and again different modes - sway vs bounce which can affect people differently. And then there is roll …
Irrespective of the degree of comfort, passengers appear to favour a safe arrival, then being able to share their ‘horrific’ experiences, than to suffer physical harm or even not to arrive at all.
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Thread creep again...but,I think many of us,up there,like to see our fellow pilot opening the speed window,and reducing speed,when the going gets slightly more than rough.
For instance,when going for the suckers gap,that so often closes up,it gives us the feeling that our fellow pilot is thinking in the right direction.
When I sit in the tops(if I can't avoid them), and my colleague does nothing with the speed window,as the Mach increases to .87 or .88, I find myself having less than respectable thoughts.
As many have pointed out here,the above scenario will,99.9% of the time,not result in severe turbulence....but,that is not how we operate,is it!
We hope for the best,and plan for the worst...
For instance,when going for the suckers gap,that so often closes up,it gives us the feeling that our fellow pilot is thinking in the right direction.
When I sit in the tops(if I can't avoid them), and my colleague does nothing with the speed window,as the Mach increases to .87 or .88, I find myself having less than respectable thoughts.
As many have pointed out here,the above scenario will,99.9% of the time,not result in severe turbulence....but,that is not how we operate,is it!
We hope for the best,and plan for the worst...
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Thankfully I'm past it all,which is probably just as well but I'd hope that an ex-national man would do a bit more that have 'less than respectable thoughts' I'd kick ass and tell him to slow the ----er down!
CRM anyone?
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330 def. rides bumps better at .80 than at the wing design cruise mach of .82 and I always do this with respect to the margin available for pax comfort, the Athr also seems to cope better.
I never found that slowing down made much difference on the 320.
I never found that slowing down made much difference on the 320.
NOT TROLLING AT ALL...
In fact its always quite a good discussion topic. What I find curious about some claims here, is how can anyone say convincingly... oh by reducing speed from X to X made the ride better? By nature turbulence isn't constant, so speed reduction may have been followed by less turbulent air. Couldn't it?
What if you reduced speed then turbulence coincidentally increased?
That is all I was trying to emphasise, that we have no idea if a reduction of 5-10 knots actually improved the ride, without turning back through the same turbulent area, and comparing G-loads. I'm quite happy to accept that a reduction of speed by 20-30 knots or more will likely lighten the loads, but this just isn't feasible at the cruise altitudes of most airliners these days.
In my book, staying as close to mid-point between two red lines may be the safest option, in anything stronger-than-light turbulence.
What if you reduced speed then turbulence coincidentally increased?
That is all I was trying to emphasise, that we have no idea if a reduction of 5-10 knots actually improved the ride, without turning back through the same turbulent area, and comparing G-loads. I'm quite happy to accept that a reduction of speed by 20-30 knots or more will likely lighten the loads, but this just isn't feasible at the cruise altitudes of most airliners these days.
In my book, staying as close to mid-point between two red lines may be the safest option, in anything stronger-than-light turbulence.
Last edited by goeasy; 22nd Sep 2017 at 08:26. Reason: spelling
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Fly turb penetration speed. If you don't have one published look at the manoeuvre capability graph and fly the speed that coincides with the peak of the curve for your altitude. This gives you the most manoeuvre margin and probably matches the turb penetration speed you forgot!!