How does reducing speed in turbulence improve the ride?
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Originally Posted by DERG
I don't see the logic in the above answers. In fact they are based on false premises.
How come you people think you can make up the rules of physics as you go along? Everytime I visit this type of thread I am always surprised at what you believe or have been taught.
How come you people think you can make up the rules of physics as you go along? Everytime I visit this type of thread I am always surprised at what you believe or have been taught.
Let me suggest a different attitude. Having worked with CliveL professionally for well nigh 15 years now, I have learned, when I don't quite grasp something he is saying about aerodynamics, to think about it hard, maybe even hit the books, until I do understand. It works every time!
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No malice in that statement. Since I found this site I often find bloomers like this. I came to the conclusion that the machines you use are so automated that you forget the basics.
Is it not perfectly obvious that if you slow the velocity the effects of the turbulance will be less? And that the heavier the mass of the 'plane the less the effect.
This is interesting
AvioConsult - Aircraft Expert and Consultant - Home Page
Don't take this personal...show me another airframe that is stronger than the 787....per metric tonne. Maybe the B748..?
So many variables here though..don't you agree.?
P.S. I see our colleague "forget" was off line when I posted this, if turns up on this thread please be aware of the current situation between me and him .. not good. Regards
Is it not perfectly obvious that if you slow the velocity the effects of the turbulance will be less? And that the heavier the mass of the 'plane the less the effect.
This is interesting
AvioConsult - Aircraft Expert and Consultant - Home Page
Don't take this personal...show me another airframe that is stronger than the 787....per metric tonne. Maybe the B748..?
So many variables here though..don't you agree.?
P.S. I see our colleague "forget" was off line when I posted this, if turns up on this thread please be aware of the current situation between me and him .. not good. Regards
Last edited by DERG; 26th Feb 2011 at 08:14.
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DERG
Sorry DERG, but it your premises that are completely and utterly false.
As for the principles of physics, I don't make them up but at least I understand them so far as aircraft design is concerned, which is not always true in this thread! When I visit the thread I am in turn surprised as to how people with very little real knowledge can pontificate.
Buffeting has very little to do with mathematics, and if you had the remotest idea of aerodynamics you would know that the criterion on which a design should be judged is not Mach Number but the lift one can develop at a given Mach Number before the wing starts to buffet.
It is an anonymous forum which precludes biographical details, but in the light of your last remark I will just say that I was in overall charge of, inter alia, calculating the design loads for the A320, A330 and A340 aircraft, so yes, I have thought about the stress on the airframe when in turbulence - which incidentally does not result in serious events every week.
PS: Thank for your support PBL!
I don't see the logic in the above answers. In fact they are based on false premises.
How come you people think you can make up the rules of physics as you go along? Everytime I visit this type of thread I am always surprised at what you believe or have been taught.
If Boeing says the 'plane can do XYZ it will do XYZ : thats why they are late. Better late than have events like the A388 has suffered.
As far as the worry about buffeting goes maybe Boeing uses better math than Airbus does....
I am not saying that Boeing and Airbus know EVERYTHING about the products the make something like the 0,85 value does tell us about the airframe.
Every week there are quite serious events with people being thrown around in turbulence. Do you ever think about the stress on the airframe when these events happen?
How come you people think you can make up the rules of physics as you go along? Everytime I visit this type of thread I am always surprised at what you believe or have been taught.
If Boeing says the 'plane can do XYZ it will do XYZ : thats why they are late. Better late than have events like the A388 has suffered.
As far as the worry about buffeting goes maybe Boeing uses better math than Airbus does....
I am not saying that Boeing and Airbus know EVERYTHING about the products the make something like the 0,85 value does tell us about the airframe.
Every week there are quite serious events with people being thrown around in turbulence. Do you ever think about the stress on the airframe when these events happen?
As for the principles of physics, I don't make them up but at least I understand them so far as aircraft design is concerned, which is not always true in this thread! When I visit the thread I am in turn surprised as to how people with very little real knowledge can pontificate.
Buffeting has very little to do with mathematics, and if you had the remotest idea of aerodynamics you would know that the criterion on which a design should be judged is not Mach Number but the lift one can develop at a given Mach Number before the wing starts to buffet.
It is an anonymous forum which precludes biographical details, but in the light of your last remark I will just say that I was in overall charge of, inter alia, calculating the design loads for the A320, A330 and A340 aircraft, so yes, I have thought about the stress on the airframe when in turbulence - which incidentally does not result in serious events every week.
PS: Thank for your support PBL!
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Well most of those 'planes appear to be in one piece so far...so yes you must have at least a grasp of loadings. Thanks for the advice.
"When I visit the thread I am in turn surprised as to how people with very little real knowledge can pontificate."
Still do not understand how the mass does not play a role...
Well actually the press are reporting quite a lot of injury accidents every week or so....people thrown about etc. No bits dropping off. Not sure about those B737NGs though with rough shod manufacture issues.
"Buffeting has very little to do with mathematics" This is IDEAL territory for the Bayesians...hopefully you can guide them.
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Just an additional note: you would be surprised how the original documents in German on some of these concepts vary from the accepted translations here in the UK...thats why Lufthansa sometimes rips stuff out..can't blame them either.
"When I visit the thread I am in turn surprised as to how people with very little real knowledge can pontificate."
Still do not understand how the mass does not play a role...
Well actually the press are reporting quite a lot of injury accidents every week or so....people thrown about etc. No bits dropping off. Not sure about those B737NGs though with rough shod manufacture issues.
"Buffeting has very little to do with mathematics" This is IDEAL territory for the Bayesians...hopefully you can guide them.
Rock
OnJust an additional note: you would be surprised how the original documents in German on some of these concepts vary from the accepted translations here in the UK...thats why Lufthansa sometimes rips stuff out..can't blame them either.
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No malice in that statement. Since I found this site I often find bloomers like this. I came to the conclusion that the machines you use are so automated that you forget the basics.
Is it not perfectly obvious that if you slow the velocity the effects of the turbulance will be less? And that the heavier the mass of the 'plane the less the effect.
Don't take this personal...show me another airframe that is stronger than the 787....per metric tonne. Maybe the B748..?
So many variables here though..don't you agree.?
Is it not perfectly obvious that if you slow the velocity the effects of the turbulance will be less? And that the heavier the mass of the 'plane the less the effect.
Don't take this personal...show me another airframe that is stronger than the 787....per metric tonne. Maybe the B748..?
So many variables here though..don't you agree.?
But I am not using any machine!If you read my original post (#6 in this thread) you will find a statement that makes it obvious that low velocity and high mass reduce the effects of turbulence.
I really don't know what you mean by 'stronger per metric tonne'. It is a meaningless concept.
Apart from the fact that nobody outside Boeing knows how strong the 787 will be, all aircraft are designed to the same rules which govern the loads the airframe must withstand. If anybody designs a structure that can withstand considerably more than the requirements then the aircraft will be too heavy (unless they deliberately build in some margin for growth).
I would just add that the critical case for turbulence loads is usually around FL200 for several reasons:
The design gusts are much lower at cruise altitudes
Aircraft generally cruise as high as they can for performance reasons. This means that they fly at a fairly high lift coefficient and are limited in the amount of 'g' they can develop there. I would say the maximum 'g' before running out of lift would be about 2.0 (at cruise AUW, where the aircraft must be designed for 2.5g at MTOW)
All of which is consistent with my remarks that just citing a turbulence penetration Mach Number says nothing about the aircraft strength
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Yes .. seeking a measure of ability to withstand turbulance per metric tonne total mass. Basically how good you got the strength/mass ratio...how good a designer you are.
But listen no matter..can see this is not straight forward
Thanks for the reply.
PS. I am big fan of the A34s. Very nice aeroplane. Good job!
But listen no matter..can see this is not straight forward
Thanks for the reply.
PS. I am big fan of the A34s. Very nice aeroplane. Good job!
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Yes .. seeking a measure of ability to withstand turbulance per metric tonne total mass. Basically how good you got the strength/mass ratio...how good a designer you are.
To complicate life a little more, the bottom skins are designed by fatigue or damage tolerance considerations, so the metric tonnes of wing weight are set by how good you are at designing for these as much or more than by pure static strength.
And I will say that traditionally Boeing have been very good at it
IMO strength would have nothing to do with it given we're talking about high altitudes. Mach limits are Buffet limits.
And regarding entering tubulence with higher speed: I'm not sure your esteemed SLF will really appreciate that feature being bounced around more severely.
To put it more bluntly: This feature might not be a feature, it might be a bug.
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And don´t forget that all that theory (v², wing loading and that stuff) is just valid for a rigid body, which an aircraft is not. The same applies to wing loading, it is not the overall wing loading but it also depends on where you do have the mass. High weight due to full wing tanks and low weight due to most of the mass being the payload in the fuselage makes quite a difference. Soft structure allows for "evading" the vertical airspeed hence reducing the effective AoA hence "smoothing out" the gust. That might be the perfect reason why the 787 can fly faster through the same gust, just because the soft wing will dampen it a little more amd hence reduce the peak load on the structure (and the passenger).
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My argument is that so many pilots reduce by .01-.02mac which I dont think improves the ride at all. Just prolongs it.
However to reduce by 10-20% might improve the ride, but aint possible at most cruise altitudes.
Am I right? Happy to be corrected if 5-10kt reduction at mach .8ish is significant turbulence-wise. It never feels different to me!
However to reduce by 10-20% might improve the ride, but aint possible at most cruise altitudes.
Am I right? Happy to be corrected if 5-10kt reduction at mach .8ish is significant turbulence-wise. It never feels different to me!
Last edited by outofsynch; 25th Jun 2013 at 07:31. Reason: speeeeeeeelin
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Another reason might have to do with preventing speed excursions. Flying at high speed (ie high cost index in a headwind), you'll be pretty near MMo. With rather large speed fluctuations and a slow-responding (as per design) autothrottle system, it reduces your workload to reduce speed slightly.
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Aircraft of earlier generations tended to have nearly rigid wings. Now they are designed to be more flexible. " To give a smoother ride..." so we were then told.
Someone published a video of the wingtips of an aircraft in "moderate turbulence" on this thread a year or two ago.
{ As a SLF I try to watch the wing-tips lift, on the opposite side to where I am sitting on the aircraft, as they start to do their job on T/O. This was something I had been unable to see as a pilot. And our wings, then, were supposed to be (very nearly) rigid, anyway!)
Perhaps the " smoother ride " story may have been at least partially true !
Someone published a video of the wingtips of an aircraft in "moderate turbulence" on this thread a year or two ago.
{ As a SLF I try to watch the wing-tips lift, on the opposite side to where I am sitting on the aircraft, as they start to do their job on T/O. This was something I had been unable to see as a pilot. And our wings, then, were supposed to be (very nearly) rigid, anyway!)
Perhaps the " smoother ride " story may have been at least partially true !
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On the 777, I noticed that a lot of guys wind down the speed when there is light to moderate turbulence. They claim that by reducing the speed, the ride will be smoother
The only aircraft I've flown have a stated "turbulence penetration speed" published. This is a speed decided by the manufacturer that maximises buffet margins (high and low) in the event of extreme IAS excursions - in other words is specified for structural and control reasons. It surely has nothing whatsoever to do with comfort/ smooth ride.
I frequently fly with FOs who, as soon as a bump is felt, wind the speed back to turbulence speed "because we're in turbulence". My impression is they do this in the belief that it is required for pax comfort rather than being limited to structural limitations in extreme turbulence as opposed to light chop. This technique is so widespread I'd say it is almost universal in my company so there are clearly misunderstandings in the practical use of Turb speed.
"But we're required to use turbulence speed in turbulence" is the usual response - usually accompanied by a "everyone knows that, what the &%$£'s the matter with you?" look. (It is an airline noted for pavlovian training methods)
Last edited by Agaricus bisporus; 25th Jun 2013 at 12:50.
E=0.5 x mv² so if you go a little slower, you will reduce the kinetic energy effects from the turbulence.
In our company, and I assume in most others, we go to turbulence speed which is halfway between VLS and MMO to give us the maximum speed excursion protection between those two limits.
But as mentioned, the seatbelt switch seems to stop most turbulence.........
In our company, and I assume in most others, we go to turbulence speed which is halfway between VLS and MMO to give us the maximum speed excursion protection between those two limits.
But as mentioned, the seatbelt switch seems to stop most turbulence.........
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How does reducing speed in turbulence improve the ride?
Relative to the air mass you are moving at 800 kph. Reducing to 795 kph does not improve the ride. I guess people do it to fly between the red bands which has never been recommend by Boeing. Who honestly cares if the airplane overspeeds for a second or two? Just fly it like the cooking book tells you to.
Reducing to 795 kph does not improve the ride.
I guess people do it to fly between the red bands which has never been recommend by Boeing.
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@president
If you report an overspeed, then someone is forced to care. There are overspeed checks to be done on the ground, often leading to delays and $$$ 
Who honestly cares if the airplane overspeeds for a second or two?