work and energy in a turn

[ciurpita]

Sorry to bring this up again, but I believe I have an understanding of the argument made by those that feel there is a difference between a downwind and upwind turn based on the kinetic energy of the plane. I hope this post will be appreciated by those that were so patient in trying to understand the arguments on both sides in previous threads. (Sorry but the previous thread is closed).

The best example is a control line model (tethered to a pole) flown without power in a steady wind. (Please ignore how it obtains its initial speed). Because it is tethered, the plane maintains its ground speed, as it enters the crosswind side of the turn from the downwind side. As it enters the upwind side of the turn, its air speed significantly increases, (though its ground speed is continually decreasing). At the same time there is a corresponding increase in lift. When it again enters the downwind side, its air speed significantly decreases with a corresponding decrease in lift.

This example is similar to a situation many of us has encountered in daily life when we've coasted a car around a turn and have experienced that the car exits the turn with most of the speed it entered the turn with. I believe this has led to the confusion about kinetic energy -- that the speed and energy attained while flying downwind is maintained after a 180 degree turn is completed.

For this tethered example, there is a difference in behavior, between a downwind and upwind turn.

But past arguments have not been about a tethered aircraft, and the kinetic energy is not maintained. So what happens to it?

Any change in energy is due to work (force * distance). however, no matter how great a force, no work is performed if zero distance is traveled. So while there is a tremendous force on the tether in the control-line example, no distance is traveled in the direction of that force, and hence, there is no work performed. The only work performed is due to drag in the direction of travel, which is accounted for by either a decrease in altitude or loss of speed (k.e.).

In the non-tethered non-powered case, however, the aircraft does travel a small distance opposite the direction of lift, and work is performed. The work performed due to the horizontal component of lift first decreases the kinetic energy in the downwind direction, and then causes it to increase in the upwind direction. In windy conditions, the kinetic energy in the down and upwind directions are not the same, and doesn't need to be.

I believe the control-line explanation describes the behavior where there is a difference between down and upwind turns. But this only applies to a tethered aircraft.

I also believe that the changes in kinetic energy are accounted for by the work performed in the turn, and that there is no requirement that the kinetic energy in the downwind and upwind directions needs to be the same.

Those that are still concerned about inertia should consider momentum (mass * velocity).

[HerkS]

Kinetic energy is a vector. That means it must have velocity relative to something. You can't properly express it in the absence of a frame of reference.

In your example there are several frames of reference. Kinetic energy relative to the center of the circle - Relative to the earth - relative to a balloon floating by in the moving air mass - relative to a passing automobile.

You mention momentum -- another vector that requires a frame of reference - and a mass - is it a feather or a bowling ball?

I understand what you are saying, but what is the point? If a pilot in an aircraft tries to fly a circular path while flying level around a specific pint on the earth and the wind is blowing, he has to manage his angle of bank and his power to do so. but it can be done.

In the example you mention, there is no power, so as an old control line pilot I think your aircraft would simply land.

So, once again -- what point are you trying to make?

[JetPlaneFlyer]

I also believe that the changes in kinetic energy are accounted for by the work performed in the turn, and that there is no requirement that the kinetic energy in the downwind and upwind directions needs to be the same.

Ciurpita,
I appreciate your efforts to try to bridge the gap between the two sides of this debate... However i think you are making it more difficult to understand than it need be.

Kinetic energy (KE) of a turning aircraft in a steady state wind is the same throughout the turn providing you use the air mass as your fixed reference point.

If you use any other 'invalid' reference point such as the ground or the moon or the sun or a distant star then things get complicated, and this is where the confusion springs from. If for instance you used the centre of the earth as your 'KE datum point' then even in flat calm conditions a turning aircrafts KE will vary due to it's direction of travel in relation to the rotation of the earth.
No...The best and simplest way to understand the situation is to always use the air mass as your point of reference. The air is the only thing the aircraft 'cares' about anyway. Imagine yourself in a balloon floating along with the wind, forget the earth below, and then it all becomes very easy to understand

Any (non tethered) aircraft in a turn uses extra energy due to the drag from the additional lift it has to generate. This is true regardless of wind state and turn direction and therefore is not directly relevant.

Steve

[Rodney]

Jet Plane Flyer, you gave an excellent discussion, simple and correct.

[ciurpita]

Kinetic energy is a vector.Absolutely, that's why i described the kinteic energy in the downwind and upwind directions.
I understand what you are saying, but what is the point?To better understand how those on one side of the argument were thinking about things.
Kinetic energy (KE) of a turning aircraft in a steady state wind is the same throughout the turn providing you use the air mass as your fixed reference point.Absolutely. using the air mass as the reference frame is the easiest case to understand. As you say, using other reference frames is complicated, but the math and physics should always add up. I believe when you consider work, the distance traveled in the direction of a force while in the turn, it is easier to understand the differences in kinetic energy between the two reference frames.
Jet Plane Flyer, you gave an excellent discussion, simple and correct.Absolutely

[funfly2]

Using the air mass as the only inertial reference point is an oversimplification that results in flawed conclusions.

An aircraft may have more or less kinetic energy related to the air as well as more or less kinetic energy related to the ground, these both energies do affect the aircraft's behaviour.

[JetPlaneFlyer]

Using the air mass as the only inertial reference point is an oversimplification that results in flawed conclusions.

An aircraft may have more or less kinetic energy related to the air as well as more or less kinetic energy related to the ground, these both energies do affect the aircraft's behaviour.
Funfly, we have had this debate ad-nauseam previously, I have no appetite for more..
Suffice to say that your opinions do not reflect the current understanding of physics.. But hey; maybe you are right and all the books and all accepted science is wrong. Everyone is entitled to their opinion.

Steve

[Montag DP]

Using the air mass as the only inertial reference point is an oversimplification that results in flawed conclusions.

An aircraft may have more or less kinetic energy related to the air as well as more or less kinetic energy related to the ground, these both energies do affect the aircraft's behaviour.How does the ground change the airplane's flight behavior, I mean other than by creating wind shear and ground effect? The plane could be flying 100 mph (ground speed) into a 50 mph headwind, and it would behave exactly the same as if it were flying 150 mph (ground speed) in stagnant air.

[Texas Buzzard]

Kinetic energy is a vector. That means it must have velocity relative to something. You can't properly express it in the absence of a frame of reference.

In your example there are several frames of reference. Kinetic energy relative to the center of the circle - Relative to the earth - relative to a balloon floating by in the moving air mass - relative to a passing automobile.

You mention momentum -- another vector that requires a frame of reference - and a mass - is it a feather or a bowling ball?

I understand what you are saying, but what is the point? If a pilot in an aircraft tries to fly a circular path while flying level around a specific pint on the earth and the wind is blowing, he has to manage his angle of bank and his power to do so. but it can be done.

In the example you mention, there is no power, so as an old control line pilot I think your aircraft would simply land.

So, once again -- what point are you trying to make?
.................................................. ...........................................
Both Momentum and Kinetic Energy can only be considered VECTOR Quantities IF their direction of movement or their paths are known. A Vector Quantity must have as variables both DIRECTION and velocity. Velocity is a Vector Quantity AND Velocity has to have Direction ( a known direction). If the direction is not known then it has to be called Speed. And Speed IS NOT a Vector Quantity ; for speed IS A SCALAR Quantity. Scalar quantities have only magnitude and not direction.

I believe what the original poster was referring to was a very long-lived thread that was here about 15 months ago. There were some who beat their chests and proclaimed that the "Downwind Turn Danger" is a Fable or completely false and nonexistent!

I was the first one to introduce the changes in the Kinetic Energy of a Piper Super Cub in a Downwind turn, in which the Border Patrol Pilot was killed by a fatal crash here in Texas. He was circling some illegals in a 25 mph wind and spun in. We think he was concentrating so much on the illegals that he didn't watch his airspeed which naturally would drop when he made a sharp downwind turn!

I posted my calculations that showed that the Piper's Kinetic Energy would decrease as it made the downwind turn. I challenged any poster to discredit my calculations and not one poster did.

Some will say there is no such thing as a Fatal Downwind Turn. Some RC pilots who have not made many low-speed turns while moving downwind will say ,"Oh, the plane doesn't know the wind is blowing!". Do it and watch carefully. But they ignore what we see. Just this past year I made a downwind turn too tightly and fell out of the sky. It will happen if your airspeed is low and you turn too tightly. Can we mention STALL here?

Pilots of RC or full-scale planes who have never made a true tight downwind turn will just sit back and pontificate.

We don't need basic Physics calculations ( but they prove it) Use the Eyes. :) :cool: :)

[vintage1]

.................................................. ...........................................
Both Momentum and Kinetic Energy can only be considered VECTOR Quantities IF their direction of movement or their paths are known. A Vector Quantity must have as variables both mass and velocity. Velocity is a Vector Quantity AND Velocity has to have Direction ( a known direction). If the direction is not known then it has to be called Speed. And Speed IS NOT a Vector Quantity ; for speed IS A SCALAR Quantity. Scalar quantities have only magnitude and not direction.

I believe what the original poster was referring to was a very long-lived thread that was here about 15 months ago. There were some who beat their chests and proclaimed that the "Downwind Turn Danger" is a Fable or completely false and nonexistent!

I was the first one to introduce the changes in the Kinetic Energy of a Piper Super Cub in a Downwind turn, in which the Border Patrol Pilot was killed by a fatal crash here in Texas. He was circling some illegals in a 25 mph wind and spun in. We think he was concentrating so much on the illegals that he didn't watch his airspeed which naturally would drop when he made a sharp downwind turn!

I posted my calculations that showed that the Piper's Kinetic Energy would decrease as it made the downwind turn. I challenged any poster to discredit my calculations and not one poster did.


On the contrary, all of us did, but you couldn't follow the maths. So didn't believe the logic


Some will say there is no such thing as a Fatal Downwind Turn. Some RC pilots who have not made many low-speed turns while moving downwind will say ,"Oh, the plane doesn't know the wind is blowing!". Do it and watch carefully. But they ignore what we see. Just this past year I made a downwind turn too tightly and fell out of the sky. It will happen if your airspeed is low and you turn too tightly. Can we mention STALL here?

Pilots of RC or full-scale planes who have never made a true tight downwind turn will just sit back and pontificate.

We don't need basic Physics calculations ( but they prove it) Use the Eyes. :) :cool: :)

Shakes head in despair..

[JetPlaneFlyer]

.................................................. ...........................................
I believe what the original poster was referring to was a very long-lived thread that was here about 15 months ago. ..............
I posted my calculations that showed that the Piper's Kinetic Energy would decrease as it made the downwind turn. I challenged any poster to discredit my calculations and not one poster did.

I believe your memory may be failing you Buzzard.. If this is the thread you are referring to: http://www.rcgroups.com/forums/showthread.php?t=814242 I don’t see any calculations posted by yourself, only lots of words. Later in the thread there are some valid calculations posted by others proving the falsehood of your ascertain but that’s all I can find (it is a long thread though so maybe you can track down your own calculations? Or is there another thread?). State your calculation and it will be shot down post haste.

Just this past year I made a downwind turn too tightly and fell out of the sky. It will happen if your airspeed is low and you turn too tightly. Can we mention STALL here?

That's called 'dumb thumb'.... Yes, a model will stall if flown too slowly and/or turned too tightly. The reason for this has nothing whatsoever to do with the turn direction in relation to the prevailing wind, it's simply that you asked the wing to produce more lift than it was capable of at the speed at which it was flying and it stalled...period.

Downwind turns can indeed cause problems but the reason is pilot error caused by trying to fly the model (or full size aircraft) in relation to ground based reference, not physics. Models are especially difficult in this respect because the pilot is stood on the ground and the model is close to the ground. Both aspects making it difficult for the pilot to 'break away' from his ground based frame of reference. The fact that a model has no air speed indication or stall warning devices only go to compound the problem... However I’ll say it again.. 'The dangerous downwind turn' is a (understandable) problem of pilot error, not an issue of flight physics.

I'm leaving gusts and windsheer etc. out of this, they are real and they do affect models but they are not particularly related to turns in any one direction, they can affect a model whichever way it's flying.

[funfly2]

How does the ground change the airplane's flight behavior, I mean other than by creating wind shear and ground effect? The plane could be flying 100 mph (ground speed) into a 50 mph headwind, and it would behave exactly the same as if it were flying 150 mph (ground speed) in stagnant air.The ground [apart from ground effect] doesn't change the aircraft's behaviour in flight, but the aircraft's actual kinetic energy related to the ground affects its behaviour.
We know that a conventional aircraft needs enough airspeed in order for the wings to 'create' lift, this airspeed changes during aircraft's flight due to several factors.

If you throw a stone into the air, it will keep moving through the air for a while because you gave it kinetic energy related to the ground, - it would keep moving even if there were no air - in fact, the air acts as a brake to the stone's movement.
If your aircraft has certain ground speed and you suddenly cut the engine power, the aircraft doesn't suddenly stop moving, but just like the stone, it has also got kinetic energy related to the ground.
Ignoring these facts you'll always come to the wrong conclusions.

[Brandano]

Funfly: ok, you want to muddle up things again by using kinetic energy to prove your point. And then you go on ignoring all the other vectors and forces (the kinetic energy of the air mass, its influence on the lift vector of the plane) because it makes keeping track of all the math too difficult and would disprove your point if you looked at it too carefully. I know another category of people reasoning like this: priests. I am afraid, there is nothing that reason can do against faith, there is no way that a theory will be considered on its merits from someone that isn't ready to doubt his own opposite theory. Btw, the conservation of energy you are referring to is inertia, not the kinetic energy as such.

[funfly2]

Funfly: ok, you want to muddle up things again by using kinetic energy to prove your point. And then you go on ignoring all the other vectors and forces (the kinetic energy of the air mass, its influence on the lift vector of the plane) because it makes keeping track of all the math too difficult and would disprove your point if you looked at it too carefully. I know another category of people reasoning like this: priests. I am afraid, there is nothing that reason can do against faith, there is no way that a theory will be considered on its merits from someone that isn't ready to doubt his own opposite theory. Btw, the conservation of energy you are referring to is inertia, not the kinetic energy as such.I am not a priest and I am not talking about faith, I am talking about facts.
I've brought up the simplest example I could find to show you that this is not only about your air mass oversimplification, yet instead of addressing my factual comments, you start insinuating about me as a person...
That's low!

[Bartleby]

I am not a priest and I am not talking about faith, I am talking about facts.

I suggest everybody take a look at this thread (Bad Science and the Truth (http://www.rcgroups.com/forums/showthread.php?t=839507)) and come to your own conclusions. Excuse the pun, but the discussion has really been going in circles...

Regards

[JetPlaneFlyer]

the discussion has really been going in circles...


Ain't that the truth!

Steve

[funfly2]

I suggest everybody take a look at this thread (Bad Science and the Truth (http://www.rcgroups.com/forums/showthread.php?t=839507)) and come to your own conclusions. Excuse the pun, but the discussion has really been going in circles...

RegardsYes, I guess we all know that one.
The very first post there is an example of how to use more than thousand words to tell us that the writer lacks enough knowledge on this matter...

:)

[JetPlaneFlyer]

Yes, I guess we all know that one.
The very first post there is an example of how to use more than thousand words to tell us that the writer lacks enough knowledge on this matter...
:)
Not the way i read it.... But as i said earlier; everyone is entitled to their opinion.

Steve

[mlbco]

Kinetic energy is not a vector, it is a scalar made up of vector products. KE also depends on the frame of reference you are measuring it in and, most importantly, it may be conserved in one frame of reference and non-conservative in another. Only rigorous math will give the correct answer when analyzed in these 2 different frames. Most people who stumble into the downwind turn argument haven't seen or done the difficult math of energy and work for an aircraft circling in wind as seen by a ground-based observer. Here is an old post of mine that attempts to hilight this without using equations:

http://www.rcgroups.com/forums/showpost.php?p=5711332&postcount=361

Important things to remember are that the lift vector does work on the aircraft when analyzed in the ground based frame of reference. Also, the aircraft and the airmass are oscillating against each other but since the airmass is so big, we normally don't consider this important fact.


Steve

[Brandano]

I never thought that referring to someone as akin to a priest in his method of thought or as sticking to his beliefs only by faith could be considered offensive, most people will find offensive the exact contrary. However, the one major point of difference between belief and science is the acceptance of peer review. Selectively ignoring bits that disprove your own theory is not a proper way to resolve a diatribe.

[funfly2]

Not the way i read it.... But as i said earlier; everyone is entitled to their opinion.

SteveNot surprising that his sermon was so appealing to you.


I'm leaving gusts and windsheer etc. out of this, they are real and they do affect models but they are not particularly related to turns in any one direction, they can affect a model whichever way it's flying.
Hmm, interesting that you're always eager to get gusts and windsheer out of this discussion… you should not.
Because a sudden downwind turn may give exactly the same result as windsheer, since in both cases the plane gets a sudden change of wind direction.

[JetPlaneFlyer]

Kinetic energy is not a vector, it is a scalar made up of vector products. KE also depends on the frame of reference you are measuring it in and, most importantly, it may be conserved in one frame of reference and non-conservative in another. Only rigorous math will give the correct answer when analyzed in these 2 different frames. Most people who stumble into the downwind turn argument haven't seen or done the difficult math of energy and work for an aircraft circling in wind as seen by a ground-based observer. Here is an old post of mine that attempts to hilight this without using equations:

http://www.rcgroups.com/forums/showpost.php?p=5711332&postcount=361

Important things to remember are that the lift vector does work on the aircraft when analyzed in the ground based frame of reference. Also, the aircraft and the airmass are oscillating against each other but since the airmass is so big, we normally don't consider this important fact.


Steve

Steve,
That's a hugely informative post. I have to admit that advanced math was never my strongest suit, so despite knowing intuitivly what answer to expect, the actual analysis of the energy of a circling aircraft from a ground based frame of reference defeats me. So I make it easy and do the analysis using the air as my reference. It's good to see it proved that the answer is (as it must be) the same whatever reference point you use (providing your good enough at math and have the time)

Of course some still wont believe what they dont understand and so will put your post down to 'mathematic trickery' or similar.

Steve

[Bartleby]

The very first post there is an example of how to use more than thousand words to tell us that the writer lacks enough knowledge on this matter...
I do agree that a certain poster tried to obscure a lack of clue with wordiness, but it was not Vintage1.

Hmm, interesting that you're always eager to get gusts and windsheer out of this discussion… you should not.
It is neccessary to isolate a single phenomenon in order to discuss anything meaningful at all. You're throwing in unrelated things simply to obfuscate. I'm just waiting for the buzzwords thermals, wind gradient, and pressure altitude, all of which are unrelated to a turn in STEADY wind. I'm not even mentioning the particulary relevant "Eötvös-Effect (http://www.rcgroups.com/forums/showpost.php?p=9599524&postcount=224)"...

Because a sudden downwind turn may give exactly the same result as windsheer, since in both cases the plane gets a sudden change of wind direction.
You're trying to move the goalposts again: why is the downwind turn supposed to be "sudden"? The argument whether a downwind turn is physically special doesn't benefit from this smokescreen.



See, there are just two cases: either you are flying a circle with reference to the surrounding air, or with reference to the ground. The first case is trivial, constant speed, constant banking angle, you'll never even notice a "downwind turn". All the while your plane is drifting downwinds and circling, plotting a cycloid path, or spirals, over the ground. (see graphics by mlbco)

In the second case, stationary circles, you need to compensate for the drift by flying an opposing cycloid path relative to the air. You're flying spirals into the wind, while the wind is pushing you back to form a circle as seen from the ground. Now you have to constantly adjust banking angle and g-load in order to widen the turn (upwinds) and tighten it (downwinds). Coincidentially, the tightest turn happens on the downwind leg, and that's where distraction meets disaster.

Regards

[bwalt822]

Well, I'll try to help clear things up from an Aero engineer's perspective although I hate getting involved in discussions where people put their feelings ahead of physics and facts.

As many have said before, a plane flying in a steady wind (relative to the ground) does not care what its ground speed is and therefore there is no difference between an upwind or downwind turn that the plane cares about. I have yet to see anyone give a valid reason backed by physics that disproves this. The fact that a rock moves through air when you throw it does not count.

Now, our airplanes do not normally fly in steady winds. They fly in winds that have gusts. Lets say a plane flying 50mph (air and groundspeed) hits a 25 mph headwind gust. Its airspeed will momentarily be 75 mph while its ground speed will still be 50mph. If this gust keeps up then the plane will eventually go to 25mph ground speed and back to 50 mph airspeed.

Now lets say the gust is a tailwind. The plane will momentarily still be flying at 50mph ground speed BUT only 25mph airspeed. If 25mph is less than the stall speed the plane will stall.

Now to apply this to turns. If a gust hits while making a downwind turn (going from against the wind, to with the wind relative to the ground) it will could cause the airspeed to drop and the plane could stall. This combined with the facts that planes slow down in turns and that the plane's high wing may get blown around can cause the misinterpretation that it was the downwind turn and not the gust.

[bwalt822]

in fact, here is the text from an actual book that pretty much sums up what I and others have said, funfly, is this author and is math wrong? And yes, I do understand those equations.

http://books.google.com/books?id=3oc9llQai5YC&pg=PA273&lpg=PA273&dq=difference+between+upwind+and+downwind+turns&source=web&ots=-uXN5SbEdf&sig=JH9ldV3CeoC5zNWoEtyL629EWW0#PPA273,M1

[funfly2]

You're trying to move the goalposts again: why is the downwind turn supposed to be "sudden"? The argument whether a downwind turn is physically special doesn't benefit from this smokescreen.
Why should the downwind turn not supposed to be sudden?!!
You are living in a world where everything is smoth and predictable aren't you?

I said it once and I say it again:
If you are flying at low airspeed near the ground and need to turn, you'd better turn upwind, this if you want to save your butt and/or your plane.

[bwalt822]

Why should the downwind turn not supposed to be sudden?!!
You are living in a world where everything is smoth and predictable aren't you?

I said it once and I say it again:
If you are flying at low airspeed near the ground and need to turn, you'd better turn upwind, this if you want to save your butt and/or your plane.

But you need to turn upwind due to unpredictable gusts, not because there is something physically different between a steady up or downwind turn.

[funfly2]

But you need to turn upwind due to gusts, not because there is something physically different between an up or downwind turn.By suddenly turning downwind you create a situation similar to a sudden tailwind.
How dangerous it may be depends on how strong the wind is and how near the stall speed the aircraft is before the turn.

[Brandano]

No, you do not. The plane moves with the wind and is carried by it. Whether it turns downwind or upwind is irrelevant with regard of how much tailwind it will have. the plane doesn't know about the wind. The amount of inertia that the plane has to counteract to turn from a headwind to a tailwind flight path is the same as that it has to counteract to do the exact opposite task. Plane moves in a 20 knot wind at 100 knot relative to the ground (ias 120 knots, but ignore it for a moment). makes a coordinated turn, keeping the speed constant because the pilot isn't a moron and is applying more throttle to counteract the speed decay (keeps its 120 knots). At the end of its 180 turn it's moving in the opposite direction relative to the wind. IAS is still 120 knots, groundspeed now is 140 knots. In a ground reference it's gained 40 knots of speed, but the plane doesn't know that unless it looks at the ground. Now he does another turn, again keeping the speed constant. It's using the same amount of energy, it needs the same lift and has the same drag. Guess what? It's heading in the same direction as before and just lost 40 knots of ground speed. and yet it kept the IAS at 120 knots all the timeNow, how can two turns that result in the same expenditure of energy result in two very different kinetik energy figures in the ground reference frame? Because you keep on ignoring the energy of that 20 knots wind.
On the ground the plane has to accelerate from 100 to -140 knots, and on the other turn from -140 to 100 knots. The inertia it had to fight in both cases is exactly the same.

[Bartleby]

I said it once and I say it again: ...

Arhhhg, I can't believe I let myself get lured into the oldest bogus argument around. Since you like confusion, let's assume there is a huge treadmill on the ground... :rolleyes:

Brandano (http://www.rcgroups.com/forums/showpost.php?p=10880106&postcount=24) said it best, I believe: "Any thread starting to discuss the "downwind turn" in Modeling Science ought to be automatically locked before religious wars start."

Good luck and don't let those conniving downwind faeries bite you!

[bwalt822]

By suddenly turning downwind you create a situation similar to a sudden tailwind.
How dangerous it may be depends on how strong the wind is and how near the stall speed the aircraft is before the turn.


Can you define a sudden turn and what makes a sudden turn upwind different from one downwind? Wait, it doesn't matter, the only forces acting on a plane are aerodynamic and gravitational. Gravity can be assumed constant so the only forces that matter are aerodynamic forces. Those forces can be modeled with equations. Any equations that I have seen for a plane turning do not involve wind speed relative to the ground and if you can find one in a textbook or other legitimate source you will impress many people here.

Even an extra 300 turning at full elevator deflection doesn't care about wind speed because it is the force of the wings acting against the air that causes the turn.

[bwalt822]

http://www.aerospaceweb.org/question/performance/q0146.shtml

Here is a trustworthy website that derives steady turning equations and wind speed is not mentioned anywhere. These equations are valid for an infinite rate of turn or until the plane stalls, runs out of control authority, or breaks apart.

[HerkS]

By suddenly turning downwind you create a situation similar to a sudden tailwind.
How dangerous it may be depends on how strong the wind is and how near the stall speed the aircraft is before the turn.

This has been debunked so many times that anyone who believes it has clearly made a conscious choice to ignore reality. Kind of like extremist religion. Reality is unimportant -- just a minor problem - an annoyance to be fussed at. Obviously if a plane turned downwind and crashed, to them, the downwind turn caused it. No other explanation is necessary.

Why waste time trying to explain reality to someone who is unwilling to make the effort to understand it; and just insists upon repeating the same quaint and incorrect explanation over and over. Good information and excellent references have been provided over and over and just been completely ignored.

The best thing to do with this argument -- when it comes up -- just totally ignore it. Let the ones that keep bringing it up spend their efforts annoying each other.

If someone insists that the world operates withing the limits of their own mis-understanding, I don't think reality will have any effect on their thinking at all. They just come back to the same error over and over, and never bother to try to understand any view but their own.

I say let 'em.

[bwalt822]

Thats a good point and Ive done all that I will do, at least these pointless arguments keep me up to date on my aero theory. I suppose next he will tell us that the top surface of an airfoil doesn't matter because lift is provided by the air being deflected on the bottom surface.

[Montag DP]

If you throw a stone into the air, it will keep moving through the air for a while because you gave it kinetic energy related to the ground, - it would keep moving even if there were no air - in fact, the air acts as a brake to the stone's movement.
If your aircraft has certain ground speed and you suddenly cut the engine power, the aircraft doesn't suddenly stop moving, but just like the stone, it has also got kinetic energy related to the ground.
Ignoring these facts you'll always come to the wrong conclusions.Obviously you have to worry about the ground. If you hit it, it will hurt. However, the ground doesn't change how the plane actually behaves in the air (except for wind shear and ground effect, as I mentioned), which is what we're discussing.

[funfly2]

Can you define a sudden turn and what makes a sudden turn upwind different from one downwind? Wait, it doesn't matter, the only forces acting on a plane are aerodynamic and gravitational. Gravity can be assumed constant so the only forces that matter are aerodynamic forces. Those forces can be modeled with equations. Any equations that I have seen for a plane turning do not involve wind speed relative to the ground and if you can find one in a textbook or other legitimate source you will impress many people here.

Even an extra 300 turning at full elevator deflection doesn't care about wind speed because it is the force of the wings acting against the air that causes the turn.The pilot in the video below also thought that his plane was just flying in "a sea of air" no matter the wind direction…

If he only had done the very same manoeuvre upwind [instead of downwind] the plane would not stall and they might be still alive today...

http://i58.photobucket.com/albums/g264/bumpa2/th_planecrash.jpg (http://s58.photobucket.com/albums/g264/bumpa2/?action=view&current=planecrash.flv)


And just like some "experts" here, the pilot in the video below also assumed that his glider was moving in a "steady state" carried by "a sea of air" and therefore kept turning it downwind instead of upwind.
Obviously he also got stuck in some inertial frame of reference...

http://youtube.com/watch?v=_xCct8cDtyk

[Brandano]

you mean "if he had watched his IAS".. bah, who cares. You don't want to listen, I hope never to fly as your passenger.

[JetPlaneFlyer]

If he only had done the very same manoeuvre upwind [instead of downwind] the plane would not stall the way it did and they might be still alive today...

Lets see.. Engine fails in low speed climb-out. The pilot decides in the heat of the moment (possibly with no clear landing area ahead of him) to attempt a turn. Very clearly with insufficient flying speed or altitude he tragically stalls and spins in...
What makes you think it would have been any different if the flight direction had been reversed? How does this video 'prove' anything other than it's dangerous to attempt turns if you don’t have necessary airspeed or height?
The 'safe' thing to do would have been not to attempt any turn but to simply push the stick forward and land straight ahead.. 'if' there was anywhere to land. Do you really believe that it's 'safe' to perform an 'upwind' turn under similar conditions to those shown in the video :eek:

Did you check the earlier mathematical proof that there was no change in energy for a circling aircraft from a ground based reference? Or have you simply chosen to ignore it?

Steve

[funfly2]

Lets see.. Engine fails in low speed climb-out. The pilot decides in the heat of the moment (possibly with no clear landing area ahead of him) to attempt a turn. Very clearly with insufficient flying speed or altitude he tragically stalls and spins in...
What makes you think it would have been any different if the flight direction had been reversed? How does this video 'prove' anything other than it's dangerous to attempt turns if you don’t have necessary airspeed or height?
The 'safe' thing to do would have been not to attempt any turn but to simply push the stick forward and land straight ahead.. 'if' there was anywhere to land. Do you really believe that it's 'safe' to perform an 'upwind' turn under similar conditions to those shown in the video :eek:

Did you check the earlier mathematical proof that there was no change in energy for a circling aircraft from a ground based reference? Or have you simply chosen to ignore it?

Steve
What I've said and repeat is:
If the pilot only had done the very same manoeuvre upwind [instead of downwind] the plane would not stall.
This regardless of the actual circumstances and the reason why the pilot took that chance/risk.

[Brandano]

Btw, just to show that I tend to do my research, here's the investigation report by the designated Australian investigation body:
http://www.atsb.gov.au/publications/investigation_reports/1994/AAIR/pdf/ASOR199401106.PDF

here are a couple of excerpts if you don't want to download the PDF:
The time between the first engine splutter and the aircraft commencing a left turn was 3.5 seconds. The time between that first splutter and ground impact was 5.8 seconds. If VH-UNA was climbing at 50 kts, the rate of loss of airspeed after an engine power interruption is estimated to be 5 kts per second. The aircraft has a stall speed of approximately 40 kts. Therefore the pilot would have had just two seconds to apply corrective action before the aircraft stalled. There is evidence that the aircraft had on at least one occasion attained only 45 kts, which would allow even less time to react to an unexpected emergency situation.

and:
4. Immediate, appropriate control inputs were not applied and control was consequently lost at a height insufficient to effect a recovery.

and finally, in the recommendations:
The Bureau of Air Safety Investigation recommends that the Civil Aviation Authority review all approvals granted for high drag installations fitted to aircraft to ensure that the particular aircraft has been proven to have a satisfactory performance. This should meet, as a minimum, the manufacturer's climb speed, and take regard of common emergency conditions that could arise.

[edit]: oh yes, I forgot: The weather was fine with a light breeze from the north-west. Weather was not considered to be a factor in the accident.

[bwalt822]

The pilot in the video below also thought that his plane was just flying in "a sea of air" no matter the wind direction…

If he only had done the very same manoeuvre upwind [instead of downwind] the plane would not stall and they might be still alive today...

http://i58.photobucket.com/albums/g264/bumpa2/th_planecrash.jpg (http://s58.photobucket.com/albums/g264/bumpa2/?action=view&current=planecrash.flv)


And just like some "experts" here, the pilot in the video below also assumed that his glider was moving in a "steady state" carried by "a sea of air" and therefore kept turning it downwind instead of upwind.
Obviously he also got stuck in some inertial frame of reference...

http://youtube.com/watch?v=_xCct8cDtyk


Where in the stunt plane video are winds mentioned? You have no idea which way the winds were blowing and therefore cant make any statement about how wind would have effected it. T_R_O_L_L

[funfly2]

Where in the stunt plane video are winds mentioned? You have no idea which way the winds were blowing and therefore cant make any statement about how wind would have effected it. T_R_O_L_LIf you bothered looking at the smoke after the crash you'd noticed the actual wind direction.
So, stop calling me troll, I'm not your father.

[bwalt822]

Looks like he was taking off dead into the wind which would mean that a left vs right turn would make no difference unless you want to imply that planes can make right turns better than left?

[funfly2]

Looks like he was taking off dead into the wind which would mean that a left vs right turn would make no difference unless you want to imply that planes can make right turns better than left?
You don't understand what I'm trying to convey.
Just forget the actual circumstances and just imagine the very same manoeuvre upwind [instead of downwind] and the plane would not stall.

[bwalt822]

he was going upwind and therfore making a crosswind turn when the plane actually stalled, there was no other type of turn he could have made right after takeoff.

I hope you're not suggesting that planes takeoff with the wind so they have more energy relative to the ground when they finally leave the ground.

[Brandano]

Lookie: downwind turn, low altitude, and no engine. Starting from close to stall speed too! http://www.youtube.com/watch?v=hAwSTg4jeLM

[funfly2]

he was going upwind and therfore making a crosswind turn.
Yes, we all know that...
But imagine he was flying downwind (having the same airspeed) and making the same manoeuvre upwind, in this case the plane would not stall.
This is just a hypothetical situation to show you the difference between turning downwind and upwind.

[bwalt822]

Im imagining him making the turn but going from with the wind to against it. I see the plane stalling still because his airspeed was the same.

[funfly2]

Im imagining him making the turn but going from with the wind to against it. I see the plane stalling still because his airspeed was the same.Imagine he had the same airspeed before turning (at that time the plane was not stalled). Then turns upwind and would not stall.

[funfly2]

Lookie: downwind turn, low altitude, and no engine. Starting from close to stall speed too! http://www.youtube.com/watch?v=hAwSTg4jeLMI know that planes can fly downwind (it happens all the time) provided they have got enough airspeed before the turn.
Anyhow, the glider on your video lands upwind after 360 deg turn...

[Brandano]

yep. And the one crashing in your crashes upwind after stalling and entering a spin. Check the windsock in the foreground
[edit]: i meant upwind

[bwalt822]

Can you show me a pilot training course that goes over how to handle downwind turns then? It surely must be in a manual somewhere right? There must be a calculated Vndt (Velocity for no downwind turn) table for various windspeeds for every type of aircraft, can you find it for us for any airplane?

[bwalt822]

Wait wait, now I see. Its like when you drive a jet ski in a river, if you turn to hard going downstream to upstream you may flip over because you are traveling too fast relative to the shore, oh wait...

We better get onto the jetski forums fast to warn them.

[funfly2]

Can you show me a pilot training course that goes over how to handle downwind turns then? It surely must be in a manual somewhere right? There must be a calculated Vndt (Velocity for no downwind turn) for every type of aircraft, can you find it for us for any airplane?I guess the very existence of a windsock and communication between control tower and pilots may help preventing such accidents.
And last but not the least the awareness of the danger and the knowledge that planes are not always flying in a "steady state" carried by "a sea of air"...

[JetPlaneFlyer]

Imagine he had the same airspeed before turning (at that time the plane was not stalled). Then turns upwind and would not stall.
Funfly,
Which way he turns makes no difference.. Wind speed does not add or subtract to the aircrafts airspeed as it turns.
The two aircraft in your videos simply stalled because of inadequate airspeed and/or too tight a turn, due to a combination of difficult circumstances and pilot error. The direction of the turn in relation to wind was irrelevant, as born out by the actual air crash investigation report... Or are you saying the investigators were wrong too?

[Brandano]

Tower only tells you what's the active runway, if there's any significant crosswind or windshear, and then lets it to you. The pilot is GOD, as far as flying the plane is concerned. Usually tells you to bugger off the runway as soon as you touched down too.
[edit] I am trying to find out the accident report on the 2nd video, but it's probably in German and I am not really able to search it properly. The accident was on a Sunday afternoon near Magdeburg, the pilot apparently walked away with minor cuts and bruises, but I can't see the registration numbers. Looking at the accident chances are the glider was recovered too. Apparently it was a tow break at 80 meters altitude. Should have een plenty enough to make a lazy teardrop and land downwind, but looks like the pilot panicked and tried to pull too many G's at low altitude.

[JetPlaneFlyer]

It surely must be in a manual somewhere right? There must be a calculated Vndt (Velocity for no downwind turn) table for various windspeeds for every type of aircraft, can you find it for us for any airplane?

That's a good one :D :D :D :D

[bwalt822]

That's a good one :D :D :D :D

Yeah and just think about all of the boaters out there that dont know about this phenomenon and are making dangerous turns on rivers.

Do you think even kayakers or canoe paddlers need to know? I guess birds can tell what the windspeed is also otherwise they must collect their dead when they fall out of the sky.

[funfly2]

Funfly,
Which way he turns makes no difference.. Wind speed does not add or subtract to the aircrafts airspeed as it turns.
The two aircraft in your videos simply stalled because of inadequate airspeed and/or too tight a turn, due to a combination of difficult circumstances and pilot error. The direction of the turn in relation to wind was irrelevant, as born out by the actual air crash investigation report... Or are you saying the investigators were wrong too?I didn't say anything that contradicts the crash investigation report. Stop putting words in my mouth.

If you throw a stone into the air, you know that the stone will start moving through the air because you gave it kinetic energy related to the ground. It was not because of the air, and besides the stone has no wings...
Just like the stone, any plane moving through the air has also kinetic energy related to the ground which does affect its behaviour.

[JetPlaneFlyer]

I didn't say anything that contradicts the crash investigation report. Stop putting words in my mouth.
You specifically stated that the wind in relation to the turn direction caused, or contributed to, the crash (it was not me that put these words in your mouth).. The report stated weather (including wind) was not a contributing factor.

If you throw a stone into the air, you know that the stone will start moving through the air because you gave it kinetic energy related to the ground. It was not because of the air, and besides the stone has no wings...
Just like the stone, any plane moving through the air has also kinetic energy related to the ground which does affect its behaviour.
The stone does not move because it has kinetic energy 'related to the ground'. The stone would in fact continue to move even if the ground magically 'disapeared'.
The stone continues to move because as described by Newton’s first law of motion.. A body persists its state of rest or of uniform motion unless acted upon by an external unbalanced force.
In other words the stone started to move because you applied a force to it and will continue to move until an external force stops it. That external force could come from the ground but only once the stone lands on it. up until the stone contacts the ground its motion is unaffected by it (other than gravity obviously)


Steve

[Brandano]

lifted right off wikipedia: (http://en.wikipedia.org/wiki/Kinetic_energy)
Kinetic energy of rigid bodies

In classical mechanics, the kinetic energy of a "point object" (a body so small that its size can be ignored), or a non-rotating rigid body, is given by the equation

E_k = \begin{matrix} \frac{1}{2} \end{matrix} mv^2

where m is the mass and v is the speed of the body. In SI units (used for most modern scientific work), mass is measured in kilograms, speed in metres per second, and the resulting kinetic energy is in joules.

For example, one would calculate the kinetic energy of an 80 kg mass traveling at 18 meters per second (40 mph) as

E_k = \begin{matrix} \frac{1}{2} \end{matrix} \cdot 80 \cdot 18^2 = 12,960 \ \mathrm{joules}.

Note that the kinetic energy increases with the square of the speed. This means, for example, that an object traveling twice as fast will have four times as much kinetic energy. As a result of this, a car traveling twice as fast requires four times as much distance to stop (assuming a constant braking force. See mechanical work).

The kinetic energy of an object is related to its momentum by the equation:

E_k = \frac{p^2}{2m}

where p is momentum.

For the translational kinetic energy[clarification needed] of a body with constant mass m, whose center of mass is moving in a straight line with speed v, as seen above is equal to

E_t = \begin{matrix} \frac{1}{2} \end{matrix} mv^2

where:

m is mass of the body
v is speed of the center of mass of the body.

Thus[clarification needed] kinetic energy is a relative measure and no object can be said to have a unique kinetic energy. A rocket engine could be seen to transfer its energy to the rocket ship or to the exhaust stream depending upon the chosen frame of reference. But the total energy of the system, i.e. kinetic energy, fuel chemical energy, heat energy etc, will be conserved regardless of the choice of measurement frame.
Naturally, this is still relating to newtonian phisics. Once you get into general relativity you find some oddities like the fact that the speed of light is the absolute maximum attainable whatever the frame of reference is,which in turn brings to the conclusion of space contracting and time dilating for an object close to light speed (so that it will still experience light going at the same speed in its own local frame of reference), but this probably isn't the case for planes flying well below the speed of sound, let alone light. Oh, yes, a point at the equator will possibly experience little difference in time speed at diferent times of day, since at noon will travel against the earth rotation and at midnight it will travel along the earth rotation (or is it the opposite? can't remember). The earth wizzes by at a fair lick, so flying east or west at different times of day should make some major difference even in still air. Not to mention the speed at which the entire solar system is travelling towards the star Vega in the Hercules constellation, roughly 220 km/s. But no worries, it will take roughly 1400 years to travel just one light year at that speed, and in the meantime vega will have moved away at the same speed.

[bwalt822]

what happens when you throw a stone from a plane? A black hole I suppose.

We need to start figuring out the change in entropy of the universe for a downwind vs an upwind turn. Maybe the downwind turn has a greater delta s.

Funfly, out of curiosity, what is your educational or experiential backround on this subject?

[JetPlaneFlyer]

What about if you threw the stone forward out of your spacecraft that was travelling a stones throw speed below lightspeed?.. Would time for the fly sitting on the stone stand still in relation to the observer in the spacecraft?.. Would the stones mass increase to infinity?

What about if you then attempted a downwind turn?

[bwalt822]

As long as the spaceship or the rock didnt go slower than Vndt then it should be fine

[HerkS]

The Down-Wind Turn
By Herk Stokely
01-Jun-1996
I recently saw a brief item, in a model flying newsgroup,
which instructed novice flyers on the basics of flying in wind.
Among the excellent items of good advice was a technical
explanation of the problem of turning downwind. It is so good to
see again that there are people who understand this difficult
phenomenon properly. Educating new pilots about this insidious
and dangerous condition is a very important activity.

As a former Navy pilot I have spent thousands of hours
flying in the dangerous low altitude environment, at sea, where
the winds are strong and a single mistake can be fatal! Those of
us who have experienced this kind of flying agree that the "down-
wind turn" is a very real danger. If I was to make such a turn
in my Navy aircraft while flying low and slow; say at 100 knots
while flying into a 40 knot headwind, I had to "accelerate from a
ground speed of 60 knots (upwind) to 140 knots (down-wind) in a
matter of seconds. An inattentive pilot could lose it right
there and spin in with his whole crew.

I'm really writing however, to tell you about a related, but
less well known, and even more subtle danger to flight which we
Navy pilots call the "Calm Day Carrier Deck Effect".

The sea is a restless and unstable reference system at best,
but to those of us who fly from carriers, the ship itself (our
home base) is our single most important point of reference.
Flying around the ship on the occasional calm day at sea, we have
observed that even though there is no wind, the ship by its
movement is creating a wind (over the deck) which can be 30 knots
or more. Flying in the landing pattern at 100 knots we're moving
parallel to the ship at a deck speed of 70 knots; then turning
down-ship to land, we rapidly accelerate to 130 knots deck speed,
producing exactly the same effect as if a wind were blowing. The
discovery of this effect has helped to explain many mysterious
accidents. Further, a wind makes this situation even more
dramatic. For instance - 30 knots ship speed into a 30 knot wind
gives a combined wind over the deck of 60 knots. Now we must
accelerate from 40 knots deck speed upwind to 160 knots downwind:
an unimaginably dangerous maneuver.

Originally we thought that on a calm day this effect was
limited to flights conducted within sight of the ship. Careful
radar tracking of aircraft performing a down-ship turn at great
distances has shown exactly the same accelerations as when it was
done right over the ship. Sit back and imagine the complexity of
this situation when there are several ships and each steaming on
a different course. If I'm not incredibly skillful, I could make
a down-ship turn (off one ship) and an up-ship turn (off another)
at exactly the same time - literally ripping the plane in half.
Needless to say it's important to train new pilots in this
critical matter.

Now that we have laid to rest the question of the down-wind-
turn, we're going to devote our energies to even more subtle and
dangerous phenomenon that lurk in waiting for the unwary pilot.
The first we'll tackle is the tidal-gravity-gradient-effect, or
the deadly "down-Moon-turn!

[Brandano]

Hmm, when you think about it it's amazing how much astrophisics do NOT affect the flight of airplanes. Take the planet earth, for example. It's circumference at the equator is 40,075.02 km. Let's say 40,075 to be conservative, and a point on the equator will travel this distance in 24 hours (let's ignore leap seconds too) so a point on the earth equator at sea level travels at 40075/24 = 1669.8 km/h. That's well above the speed of sound, so in theory people near the equator and at close latitudes shouldn't be able to speak, as the roaring wind will travel away for them too fast for their words to be carried over it. Naturally, the atmosphere had a lot of time to catch up, so this doesn't happen, but the earth rotation still affects the winds somewhat due to conservation of energy. Masses of air moving north or south from the equator will speed up like a skater contracting his arms, and masses moving towards the equator will slow down for the opposite reason. Then there's th speed at wich the earth moves around the sun (average, it's a slightly elliptical path, so it varies a bit during the year). This is about 107,218 km/h, still below the speed of light, but several Mach numbers above anything man has ever built. This doesn't seem to affect the earth much, but is close enough to lightspeed that we can judge the speed of other stars by redshift and blueshift in different times of the year. I hope nobody gets seasick at thinking how fast we are moving while trying to stand still.

[Brandano]

What about if you threw the stone forward out of your spacecraft that was travelling a stones throw speed below lightspeed?.. Would time for the fly sitting on the stone stand still in relation to the observer in the spacecraft?.. Would the stones mass increase to infinity?

What about if you then attempted a downwind turn?
It's not as silly a question as you would think, actually. To you, in the spaceship, the stone would travel away at the normal speed. However, to an external observer, it would travel at near lightspeed, so it would seem incredibly slow compared to the rest of the craft (that in the meantime has squeezed to almost a point). the space that you percieve as normal has become much shorter on the outside, the time you sense as flowing normally is moving incredibly slowly. Inside the ship you don't see this, you don't have any frame of reference to see this with. Actually, what you probably would see is the outside world growing incredibly larger, the things in front of you becoming bluer and those behind you becoming redder. the thing is, in the ship the rock would appear to behave normally, but in the time it travelled the length of the ship, the ship would have travelled an amazing distance, and a lot of time will have passed.

[bwalt822]

HerkS, that is a satirical article that you wrote right? Im pretty sure it is due to the mention of the down moon turn but just wanted to make sure.

[Brandano]

Herk, on a more serious note, since you seem to have experience in this: since the landing deck of your average carrier is angled with regard to the datum of the ship, I'd expect the landing deck to move sideways during your landing pattern, is that so? Does the carrier adjust its navigation with relation to the wind to compensate, or do the pilots have to deal with this on their own?

[bwalt822]

Hmm i never thought about that, What would be easier to land, with the carrier compensating for the slight angle of the landing strip i.e. no actual crosswind or for the pilot or for the pilot to sideslip himself?

[Brandano]

Well, in flight sim games you estimate where the deck is going to be on touchdown and aim there. However, simulations are not reality. For one thing ina sim you can't crane your neck, actually seeing the deck while holding the proper glide path is a task in and of itself.Also, better to have a few too many knots and risk a bolter than landing a couple of feet shotr of the deck with your engines spooled down. Some planes even require the engine to be spooled up to get the blown flaps working (the F4 Phantom, the Crusader, i think the A7 too since it was a derivative) and the Fouga Magister had such a slow spool up time that it was preferred to land with the engine revved up and the airbrakes open. Faster to close the airbrakes than to spool up the engine from idle.

[HerkS]

Herk, on a more serious note, since you seem to have experience in this: since the landing deck of your average carrier is angled with regard to the datum of the ship, I'd expect the landing deck to move sideways during your landing pattern, is that so? Does the carrier adjust its navigation with relation to the wind to compensate, or do the pilots have to deal with this on their own?

The ship angles off the wind to compensate, so that the relative wind is down the deck. However if there is not enough wind, the pilot does have to deal with a bit of crosswind.

[HerkS]

HerkS, that is a satirical article that you wrote right? Im pretty sure it is due to the mention of the down moon turn but just wanted to make sure.

What I wrote is a ridiculous satire. And, I have found that it usually has very little effect on the "true believers." The physics of the situation are just beyond their comprehension.

The error most people make when they visualize a downwind turn is that they forget that velocity and acceleration are vector quantities. That means they have BOTH direction, and magnitude. In terms of math and physics the direction part means that in this simplest of all cases, there has to be a direction reference system that ends up giving them a + or - value.

I'll give you an example of both the mistaken and the correct way of looking at this.

If a plane is flying at 15 mph into a 5 mph wind - it has a ground speed of 10 mph. If it then makes a turn and begins to fly downwind its ground speed changes to 20 mph. Since the plane has inertia it has to accelerate to the new ground speed, and this can cause it to lose flying speed. Although there is an element of this analysis that is correct, it is misleading because it infers that the situation is different because the wind is blowing.

If it was stated more correctly the analysis would show that the plane accelerated from (plus) 10 mph to (minus) 20 mph ground speed. This is a total acceleration (in the minus direction) of 30 mph - the magnitude of the difference between +10 and -20. This is a true acceleration and the laws of physics require that a force be applied to the model to make this acceleration happen. The force comes from the sideways component of the lift force generated by the banked wing of the plane.

What's correct about the misleading analysis is that the plane has to
generate extra lift to be able to make the turn and take up level flight in another direction. It's also correct that this affects the performance of the plane while it's turning.

What's incorrect (as I said) is that the impression is given that the
situation is different because of the wind. In fact, the acceleration is exactly the same when there is no wind. In this case the plane accelerates from plus 15 mph to minus 15 mph for a total acceleration in the minus direction of 30 mph. The acceleration is the same, the amount of inertia to be overcome is the same and the wind has nothing to do with it. In fact you could observe the turn from a passing aircraft - or from the moon, and the acceleration wouldn't be affected by the apparent speed of the reference
point.

Important things affect the flight of a plane on a windy day - particularly boundary layer shears and turbulence at low altitude. The problem with this old down-wind turn business is that the endless discussion of it, kind of covers up a clearer understanding to the things that are really affecting the plane.

Some people get tired of going over it repeatedly while some others insist on retaining an incomprehension of the physics involved. Their faulty perception is more powerful than the science involved. -- Herk Stokely

[bwalt822]

Well you and I and most of the rest of the world understand this but some people just cant accept that they are wrong and that we are missing some key detail.

I just found it really ironic that the following book was mentioned in a company wide email today, i'm going to have to keep posting this link when I come across those like funfly.

http://www.rburton.com/work1.htm

[HerkS]

Well you and I and most of the rest of the world understand this but some people just cant accept that they are wrong and that we are missing some key detail.

I just found it really ironic that the following book was mentioned in a company wide email today, i'm going to have to keep posting this link when I come across those like funfly.

http://www.rburton.com/work1.htm

Yep - that's a good one. It's called "Confirmation Bias" A really good illustration of it is "Morton's Demon." http://www.answersincreation.org/mortond.htm

You can do a google search on "confirmation bias" and pick up a pretty good idea of the background information available.

[vintage1]

Excellent links, guys..

Philosophically speaking, it can be proved that there are no facts. There are just memories of observations based on assumptions. These are three steps removed from Wittgensteins 'whatever is the case'.

Each stage, the interpretation of sensation into perception, the classification of perception into objects in a space-time-material theater, and the recording of those as events, let alone the recalling of them as past experience, is subject to interpretations and filtering and discarding and compression.

And the view that results, is completely dependent on the thing that is considered to be the 'most true' in that process.

E.g.Creationism is based on the stated assumption that the Bible and what is in it is more real than our perception of the world, and the data contained therein.

Whereas Science is based on the implicit assumption that our perceptions are true renditions of the world-as-it-is and perceiving the world does not change it materially, and that our memories are by and large accurate, and, if written down, even more so.

Sadly, in the limit, none of these are absolutely true :D

I don't object to Creationism, but I do object to Intelligent Design. Which attempts to use the logic and reasoning of science, whilst avoiding the basis on which proper science is founded.

Its precisely the same thing here. You can talk about 'control reversal when the model is coming towards you ' or the 'downwind turn' and they have validity in an egocentric and naive view of model flying.

But when someone trots out basic Newtonian physics to 'explain' them, having no idea how to translate between frames of reference, and indeed no understanding of what that means, I do get a little upset. It is not permissible to use a system based on one assumption, when analysing data produced by another.

The proponents all suffer from a simple deficiency. Just as they are unable to imagine the point of view of the nonexistent pilot flying IN the model plane, they are likewise incapable of placing themselves in any point of view that is not uniquely their own.

This monstrous egocentricity makes them utterly incapable of changing their perspective to accommodate anyone else's, and makes them completely right, in every respect, all the time. Since no other viewpoint is admitted other an the one they currently occupy, how could they ever be wrong, with respect to it?

For them, the primary Truth is that their own experience is more correct than the sum of everybody else's: that their analysis is flawless, and everyone else's is flawed.

The really sad fact is that they feel the need to convince others. To me that indicates that at a deep fundamental subconscious level, they are extremely insecure.

It behooves one to understand that any discussion with such people, is played from their perspective: which is essentially to bolster their egocentricity, not to understand anyone else's point of view. Their inability to understand anyone else's explanation, is translated into 'no one has proved I am wrong'.

By all means engage in dickering with such personalities, but never expect to change them. My late and sadly fairly unlamented mother, was one such, and a lifetime of argument never changed her conviction of her absolute correctness in every respect about things of which she knew precisely nothing, and her final descent into dementia uncovered the real basis of her personality: In that any contact with other peoples' intelligences was seen not as a free interchange of potentially useful ideas about the world, but as a savage battle for survival of her views pitched headlong against the views of all those who would 'prove her wrong' - usually from malicious motivations.

In short the world consisted of people battling to achieve some kind of intellectual one-upmanship, in which pursuit of the truth never mattered: what was important was the ability to convince and control and manipulate by any means available the thought processes of others. Because the alternative was to be swamped in a sea of inconsequentiality, and to become as truly unimportant as she really was. Unthinkable. :(

She would much rather believe that people were actively and maliciously trying to 'do her down' than the reality, that ultimately no one gave a damn about her, apart from feeling rather sorry for her.

So you might say I am an expert in these matters. :rolleyes:

Gentlemen: there is an 'ignore list'.

Don't waste your lives arguing. Use it.

I once worked for a couple of guys, one of who went out of his way to manipulate,and put down everybody who worked for him. One day I asked his partner ..

"Tony, why does Richard behave in a way that is guaranteed to make people dislike him?'"

There was a long pause.

"Oi rackon it's becuz, with Dick, he don't know what to do bout people: If they all hate him, at least he knows exactly where he stands!".

Later on, I watched while the pair of them defrauded their creditors, and bankrupted the company after paying themselves large bonuses. You wouldn't do that to people you LIKE, so it all made a twisted kind of sense.
Subsequently, not having been recompensed with several months wages, I sold some equipment that had been given to me to repair 'so you can get your money back, trust me'.

Tony was furious. "where d'you learn a trick like that?"

I gave him a considered pause. Fair is always fair..

"From you, Tony."

A friend of his was witness to the conversation.."He's got you there Tony" was all he said :D

Later, someone gave me a book. Which explained it all. I recommend it to anyone starting out in business. It's called 'Winning through Intimidation" by Robert J Ringer.

My erstwhile employers were described in exact detail. What is delicately termed 'sociopathology' by psychologists, is what drives the business world.

And since the sociopaths seem to have ruined it for us, its worth another read...learn how to spot these guys..

[funfly2]

You specifically stated that the wind in relation to the turn direction caused, or contributed to, the crash (it was not me that put these words in your mouth).. The report stated weather (including wind) was not a contributing factor. You put words in my mouth because I didn't say that the wind was the cause of the accident, I said that the pilot tried to land by turning downwind. And as I did say before:
If you are flying at low airspeed near the ground and need to turn, you'd better turn upwind, this if you want to save your butt and/or your plane.
Following is part of that report:

4. Immediate, appropriate control inputs were not applied and control was consequently lost at a height insufficient to effect a recovery.



The stone does not move because it has kinetic energy 'related to the ground'. The stone would in fact continue to move even if the ground magically 'disapeared'.Right, the stone would continue to move even if the ground magically disapeared.
But, I am also right when I say that the stone has got kinetic energy related to the ground, in fact it may also have got kinetic energy related to the air depending on wind's direction and strength related to the stone's movement.



The stone continues to move because as described by Newton’s first law of motion.. A body persists its state of rest or of uniform motion unless acted upon by an external unbalanced force.
Exactly, and the very same law applies to any aircraft that has got some ground speed.

[bwalt822]

Maybe those inappropriate control inputs were trying to turn period. The most appropriate control inputs to me and most other pilots would have been to push the stick forward to gain speed and land straight ahead.

How can you possibly interpret that because they mention inappropriate control inputs that the pilot should have turned upwind instead of downwind?

You should stop bending facts to attempt to support your incorrect view and look at them to try to disprove yourself.

I think we need to come up with Funfly's 3 laws of motion:

1: Objects can be influenced by their reference plane and not solely by the physical environment in which they operate.
2: Objects in motion stay in motion...Period.
3: For every action there is an equal and oposite reaction...but only in zero wind conditions.

[funfly2]

Maybe those inappropriate control inputs were trying to turn period. The most appropriate control inputs to me and most other pilots would have been to push the stick forward to gain speed and land straight ahead.

How can you possibly interpret that because they mention inappropriate control inputs that the pilot should have turned upwind instead of downwind?

You should stop bending facts to attempt to support your incorrect view and look at them to try to disprove yourself.It's obvious to everybody that the pilot in such circumstances could not turn other than downwind and he would better (if possible) try to land straight ahead.

It seems you simply can't understand what my point is.
I told you that it was an hypotetical scenario to imagine the plane flying downwind at the same airspeed (as it had flying upwind) and then turn upwind with the same turn radius.
With this hypotetical scenario the plane would not stall.

As for the rest of your ramblings you are not worth my time.

[JetPlaneFlyer]

Funfly,

I think it's best we quit this now before things start to digenerate as these dicussions often do.. It's clear you are 100% convinced that your view is right and everyone else is somehow 'missing the point'. It's equally clear that regardless of what arguments, texts from reputable sources, mathematical proofs or shear weight of opinion is stacked up against you nothing will put a dent in your conviction.
Sometimes all that can be done is agree to differ and I believe that this is one of those times (again).

Steve

[funfly2]

Funfly,

I think it's best we quit this now before things start to digenerate as these dicussions often do.. It's clear you are 100% convinced that your view is right and everyone else is somehow 'missing the point'. It's equally clear that regardless of what arguments, texts from reputable sources, mathematical proofs or shear weight of opinion is stacked up against you nothing will put a dent in your conviction.
Sometimes all that can be done is agree to differ and I believe that this is one of those times (again).

StevePity that you rest your case now when it seems we've agreed on some points…
:)

[eflightray]

Instead of throwing a stone, try throwing a chuck glider.

Or is that going to mean we now have to explain why a glider only seems to stall greater when turning into wind, or power models always 'climb' when turning into wind.

Wow, climbing when turning into wind, that means you could slow down and ..........

Sorry. :D

[Brandano]

planes climb at the same amount of feet per minute whether flying with the wind or against it. It's just to the ground observer that the flight path appear steeper, but the rate of climb is the same.

[bwalt822]

planes climb at the same amount of feet per minute whether flying with the wind or against it. It's just to the ground observer that the flight path appear steeper, but the rate of climb is the same.


but what if you are climbing while going over a mountain and someone is observing you while driving a car up the same mountain. You will have to watch out for the windshear that the car creates because its elevation is increasing too and we all know that the observer affects the plane based on funfly's first law of motion. God forbid that car then tries to turn around, then we might have a discontinuity in the space time continuum.

[bwalt822]

maybe someone should just make a video of themselves doing some down and upwind turns in flightsim with the stall warning buzzing for the whole turn both ways.

[Brandano]

I did a nice hammerhead turn in a real plane when I was a kid (and it was a mil plane to boot... ok, small low wing 4 places prop plane used for glider tows, leisure and travel, but still military issue), but can't really tell what direction the wind was at the time. I had my eyes stuck on the sideslip and IAS indicators for most of the time. I remember clearly the stall warning buzzer going off, and the pilot in charge (I was in the right seat) dismissing it...

[bwalt822]

was it an upwind or downwind hammerhead, it must have been upwind.

[Brandano]

Hmm, can't really remember what direction it was initiated from. I remember that the re was a slight sidewind, exactly 90 degrees from the left of runway, and that the pattern was left-handed. This means that it would be an upwind turn at takeoff and a downwind turn at landing. However it was really a calm day, a bit overcast with a light drizzle. I had some trouble on my takeoff because the plane was bumping a bit about... the pilot's fault really. The guy told me to follow the plane ahead of me, and I kept right in its wake :)
The plane was one of these... it might have been the exact one, because the flight group shield does match http://www.flugzeuginfo.net/acimages/s208m_riccardobraccini.jpg

[HerkS]

It seems you simply can't understand what my point is.
I told you that it was an hypotetical scenario to imagine the plane flying downwind at the same airspeed (as it had flying upwind) and then turn upwind with the same turn radius.
With this hypotetical scenario the plane would not stall.

As for the rest of your ramblings you are not worth my time.

Your point is perfectly understood, it's just completely wrong.

I won't go into what or might not be worth your time. Obviously you aren't interested in wasting your time understanding anything in the way of factual information. Your statement - that the facts aren't worth your time indicates exactly why your incomprehension remains fully intact.

If you had any interest in understanding this (which I doubt ) ignore the practical issues and try flying your control line model from the basket of a balloon floating with the wind. If your mind is capable of visualizing that you might just get a hint of enlightenment.

[bwalt822]

he was referring to funfly's three laws of motion that i am trying to derive wasting his time i think

[nauga]

maybe someone should just make a video of themselves doing some down and upwind turns in flightsim with the stall warning buzzing for the whole turn both ways.Shoot, you can do it in a full-scale if you've got the inclination and a steady arm. You can also prove the point in a full-scale by doing steady turns 'under the hood' (i.e. a view-restricting device that's intended to keep you from getting outside references). At any speed and g as long as the turn is stabilized (constant AOA, power, g, altitude and bank angle) the airspeed will not change regardless of the wind as long as it's constant. Put another way, challenge someone to do stabilized turns under the hood and determine wind speed and/or direction. So long as there is no external reference (including moving maps, etc), you *cannot* determine a steady wind from airspeed changes.
The problem comes when you try to maintain some ground reference...but those airspeed changes are pilot-induced.

Nauga,
who has done hard turns in the jetstream

[Montag DP]

maybe someone should just make a video of themselves doing some down and upwind turns in flightsim with the stall warning buzzing for the whole turn both ways.If you use X-Plane you could even turn on a tracer behind the plane so you could see the cycloids over the ground after you complete the circles.

[Roj]

Well you and I and most of the rest of the world understand this but some people just cant accept that they are wrong and that we are missing some key detail.

I just found it really ironic that the following book was mentioned in a company wide email today, i'm going to have to keep posting this link when I come across those like funfly.

http://www.rburton.com/work1.htm

Thankyou, best link I've seen in a while.
Having endured more than my fair share of meaningless circular debates with the personality in question, here is what i would surmise is His most basic law of motion (and the basis of His entire constellation of misconceptions):

Any object that lies still on the ground, by my feet, has NO kinetic energy. No ifs or buts. None of this "relative to" fancy stuff. Who needs vectors? Still = still = zero moementum = zero velocity = no motion = zero kinetic energy = unflyable.
Amen.

[Roj]

Yes, we all know that...
But imagine he was flying downwind (having the same airspeed) and making the same manoeuvre upwind, in this case the plane would not stall.
This is just a hypothetical situation to show you the difference between turning downwind and upwind.

Hey here's a simple & fun experiment you can all do yourselves:

You know those "travellators" (long flat moving platforms - like a treadmill, found in airports for passengers)?

- Stand on one and start walking in circles , while the travellator is moving.

- At some given moments you are walking against the flow of the travellator, and at others you are walking with the flow of the travellator. Agreed?

Then, following His principles:

- While you walk against the direction of the travellator you have less kinetic energy than when you walk with the direction of the travellator.

So it must be harder to turn in one direction than the other. Right?

[vintage1]

here is what i would surmise is His most basic law of motion (and the basis of His entire constellation of misconceptions):

Any object that lies still on the ground, by my feet, has NO kinetic energy. No ifs or buts. None of this "relative to" fancy stuff. Who needs vectors? Still = still = zero moementum = zero velocity = no motion = zero kinetic energy = unflyable.
Amen.

And the earth is the center of the Universe,and God is in his place Up There Somewhere.


What's a Medievalist doing flying toy planes anyway?

[funfly2]

And the earth is the center of the Universe,and God is in his place Up There Somewhere.


What's a Medievalist doing flying toy planes anyway?It sucks how much time and effort you've spent here on mockery and derogatory comments rather than using arguments to make your point.
You'll not prove you're right just because you ridicule somebody else.

The same old argument that "if you are flying in circles with the same radius, the airspeed will not change as long as the wind is constant"… simply doesn't apply because I am not talking about flying in circles with the same radius in a steady state.

And eventually you all have to use the ground as reference unless you always land on the clouds...

Here's another one:
http://s58.photobucket.com/albums/g264/bumpa2/?action=view&current=plane_crash.flv

[Brandano]

Ok, from the description it appears to be windshear or gusty wind, not steady wind. Anyway, the plane is a DHC-5 Buffalo, the crash was at an airshow, so it ought to be relatively easy to find. Time for me to start digging...
[EDIT:] I suspect it might be this one: C-GCTC, crashed at Farnborough in 1984
http://www.airliners.net/photo/De-Havilland-Canada/De-Havilland-Canada/0953522/M/
It was a prototype for a civilian version, but he project was discontinued.
Still searching for the accident report...

[JetPlaneFlyer]

The same old argument that "if you are flying in circles with the same radius, the airspeed will not change as long as the wind is constant"… simply doesn't apply because I am not talking about flying in circles with the same radius in a steady state.


Funfly, then what are you talking about?.. The discussion so far has been about turning in steady wind conditions. Do you now agree that in a steady wind turn direction does not impact on airspeed?

As for the video.. The aircraft was actually turning INTO wind for it's landing approach (an 'upwind' turn).. So how this could be used to show the supposed danger of a downwind turn is beyond me :rolleyes:

And yes, groundspeed is obviously relevant at the moment of take off and landing, no one claims otherwise. The discussion is about turning in wind, not landing.

Steve

[Brandano]

Found it, assuming it's the same plane:
http://aviation-safety.net/database/record.php?id=19840904-0
from the page:
PROBABLE CAUSE: "An error of judgement by the aircraft commander. Unfavourable weather conditions, a transitory handling problem whilst flying outside the tested flight regime and the pressure on the commander to complete his flying sequence, where probably contributing factors."

[vintage1]

The actual report makes fascinating reading.

It appears he slammed the props into reverse to steepen the descent, and ended up possibly with the tail being blanked by the lack of propwash..got himself all crossed up and missed the best point to put power on again and get control back..

All to demonstrate just how short a landing he could make. Well it was pretty short. As it happened..;)