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The Windward Turn Theory

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The Windward Turn Theory

Old 23rd Jul 2018, 13:13
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Wizofoz: I agree with you however I think you will find that I never claimed lift was proportional to groundspeed! For the windshear analogy to apply the momentum must be related to the groundspeed ie. relative to the earth. Why is it therefore that when operating in the "bubble of air" concept then reference to the earth is discounted? Likewise can you help me understand the often observed phenomenon that I cited.
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Old 23rd Jul 2018, 13:25
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Originally Posted by Meikleour
Wizofoz: I agree with you however I think you will find that I never claimed lift was proportional to groundspeed! For the windshear analogy to apply the momentum must be related to the groundspeed ie. relative to the earth. Why is it therefore that when operating in the "bubble of air" concept then reference to the earth is discounted? Likewise can you help me understand the often observed phenomenon that I cited.

While free flying, the relationship with the ground is purely a navigational one and has nothing to do with the aerodynamics of the plane. Can you really not grasp this?
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Old 23rd Jul 2018, 13:26
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Vessbot:Turning around inside an airliner does not change your momentum with respect to the earth. It is still related to the vector of the aircraft. The only change you could make is to run from nose to tail down the aisle and then you would only reduce it by your running speed times your mass! A tiny reduction compared to the aircraft. This is the same fallacy about being in a runaway lift(elevator) where the occupants are asked to jump upwards just before impact with the bottom to save thenselves! Won't work.

Jet Fan: I think you are being ironic!!
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Old 23rd Jul 2018, 13:38
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Originally Posted by Meikleour
Vessbot:Turning around inside an airliner does not change your momentum with respect to the earth. It is still related to the vector of the aircraft. The only change you could make is to run from nose to tail down the aisle and then you would only reduce it by your running speed times your mass! A tiny reduction compared to the aircraft. This is the same fallacy about being in a runaway lift(elevator) where the occupants are asked to jump upwards just before impact with the bottom to save thenselves! Won't work.

Jet Fan: I think you are being ironic!!
m

the downwind turn myth Is for stupid people to believe in. Turning into a headwind does not translate into an increase in airspeed derived in any way from the headwind. For exactly the same reason, when I turn in the aisle and face the other direction, thus instantly changing my groundspeed to a negative, I feel no change in momentum.

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Old 23rd Jul 2018, 13:48
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Winemaker has it exactly right. If you don't believe him/her, or me, ask a friendly mathematician to construct a position vector from a fixed point on the earth to an aircraft performing a constant rate turn in a steadily moving airmass, and differentiate it twice to determine the acceleration of the aircraft. It is always towards the centre of the circle of the constant turn, a point which itself is moving with uniform speed over the ground. To demonstrate it in flight, choose a windy day and ask an instructor (better still, a test pilot) to fly an accurate rate one 360 degree turn under the hood while you look out of the window. The acceleration will feel fine, bank angle constant and ball in the middle, but at low level your track over the ground will scare you stiff and illustrate why trying to turn near the ground in such conditions using visual references is so dangerous.
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Old 23rd Jul 2018, 14:00
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Originally Posted by D120A
Winemaker has it exactly right. If you don't believe him/her, or me, ask a friendly mathematician to construct a position vector from a fixed point on the earth to an aircraft performing a constant rate turn in a steadily moving airmass, and differentiate it twice to determine the acceleration of the aircraft. It is always towards the centre of the circle of the constant turn, a point which itself is moving with uniform speed over the ground. To demonstrate it in flight, choose a windy day and ask an instructor (better still, a test pilot) to fly an accurate rate one 360 degree turn under the hood while you look out of the window. The acceleration will feel fine, bank angle constant and ball in the middle, but at low level your track over the ground will scare you stiff and illustrate why trying to turn near the ground in such conditions using visual references is so dangerous.
yep,

exactly that
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Old 23rd Jul 2018, 14:50
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Originally Posted by Goldenrivett

Errrr.....by my maths, that is going from 499 kts to 501 kts ground speed i.e 2 kts change in ground speed with respect to both earth and to the aircraft.

What momentum is being ignored?
From negative 499 to positive 501, that's a thousand knot increase. The airspeed is 1 knot before and after, unchanged.

And *I* don't think that there is anything ignored about the momentum, but the windward turn theorists do (like the one I quoted in my reply) and I'm challenging then to apply their reasoning to that situation.
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Old 23rd Jul 2018, 14:55
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Originally Posted by Meikleour
Vessbot:Turning around inside an airliner does not change your momentum with respect to the earth. It is still related to the vector of the aircraft. The only change you could make is to run from nose to tail down the aisle and then you would only reduce it by your running speed times your mass! A tiny reduction compared to the aircraft.
Yes, and is this any different (and why?) from turning around inside a uniformly moving airmass?)
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Old 23rd Jul 2018, 15:07
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I always think the easiest way to explain the argument is to use an extreme example.

An aircraft doing 50 KIAS in a constant 5000 KT airmass conducts a rate 1 orbit. What happens to it, compared to the same aircraft conducting the same orbit in nil wind?

Who votes for crash and burn?

The correct answer is: nothing. The aircraft doesn’t know it’s in a 5000 KT airmass. It behaves according to Newtonian physics from the frame of reference of the airmass.
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Old 23rd Jul 2018, 15:39
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Hi Vessbot,
From negative 499 to positive 501, that's a thousand knot increase. The airspeed is 1 knot before and after, unchanged.

And *I* don't think that there is anything ignored about the momentum, but the windward turn theorists do (like the one I quoted in my reply) and I'm challenging then to apply their reasoning to that situation.
I am definitely not a windward turn theorist. My reply was to your confused post #109
How about when you are walking upwind at 1 knot at knots in an airliner, toward the tail, with a groundspeed of negative 499 knots. You turn around to face the nose (downwind) in one second, and keep walking at 1 knot airspeed, but now your groundspeed is 501 knots. You just walked through a one thousand knot self-created windshear in one second, according to your theory, which predicts that there should be some effect.
You haven’t walked through a “”1000 KT self created wind shear”, you have only changed your groundspeed by 2 kts. The fact that you turned around and re-label which is +ve and -ve destroyed your inertial reference frame.
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Old 23rd Jul 2018, 15:58
  #131 (permalink)  
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Originally Posted by Goldenrivett
Hi Vessbot,


I am definitely not a windward turn theorist. My reply was to your confused post #109


You haven’t walked through a “”1000 KT self created wind shear”, you have only changed your groundspeed by 2 kts. The fact that you turned around and re-label which is +ve and -ve destroyed your inertial reference frame.
jesus wept, we know! It’s according to the downwind myth idiots that changes in groundspeed somehow affect airspeed through some mad principal that they can’t explain.
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Old 23rd Jul 2018, 17:28
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Originally Posted by Goldenrivett
Hi Vessbot,


I am definitely not a windward turn theorist. My reply was to your confused post #109


You haven’t walked through a “”1000 KT self created wind shear”, you have only changed your groundspeed by 2 kts. The fact that you turned around and re-label which is +ve and -ve destroyed your inertial reference frame.
This thread is moving fast and I'm at work so I can't get detailed until later, but yes this is exactly a 1000 knot self-created wind shear according to the premises of the windward turn theorists. Check it again.
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Old 24th Jul 2018, 00:39
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Originally Posted by Meikleour
Wizofoz: I agree with you however I think you will find that I never claimed lift was proportional to groundspeed! For the windshear analogy to apply the momentum must be related to the groundspeed ie. relative to the earth. Why is it therefore that when operating in the "bubble of air" concept then reference to the earth is discounted? Likewise can you help me understand the often observed phenomenon that I cited.
No, you do not need to calculate groundspeed to understand winds hear- because the aircraft is not interacting with the ground, so it's momentum relative to it is irrelevant. Windshear happens when the aircraft's momentum relative to the AIR changes.


Say you are turning on a still air day- but on the ground there is a passing truck- you could calculate your momentum relative to IT- it is as relevant a momentum figure as that of the earth, but it doesn't change the dynamics of the situation does it?

As to the increased rate of descent you cite, did it come with an increase in airspeed also? I have often observed older FMCs get caught out but changes in wind and do some radical stuff to maintain programed path.
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Old 24th Jul 2018, 00:44
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Originally Posted by Brercrow
This is explained as follows: The aircraft turns due to a horizontal component of the lift force. Lift force is the equal and opposite effect of momentum given to the air. In a turn, part of that momentum is horizontal. As the aircraft turns from downwind to crosswind it loses momentum as it loses groundspeed. This acceleration is caused by the aero-forces acting on the aircraft modified by the angle of drift. The air gains horizontal momentum and part of that is in the same direction as the wind. So aircraft loses momentum and wind gains momentum.
At the same time, due to inertia, the airspeed is affected by the reducing tailwind component and there is a slight tendency for airspeed to increase. (Same as an increasing headwind)
If the aircraft is descending in IAS hold and constant thrust, the effect is that the auto pilot will hold the airspeed and the rate of descent will decrease slightly but only during the turn.
When the aircraft rolls out on the crosswind heading, the thrust is insufficient to maintain the reduced rate of descent and the IAS hold pitches the nose down to maintain the airspeed. The rate of descent increases rapidly but settles back once equilibrium is restored at the original rate of descent.
In case anyone was wondering, pretty sure this is the author of the website. Same ridiculous toss.
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Old 24th Jul 2018, 01:33
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Here's a typical flight example of the windward turn that should suffer an airspeed loss according to the windward turn theorists:

Vehicle making the turn: Cessna 172
Wind (uniform airmass over the ground): 10 knots, East to West
Initial heading: East
Initial airspeed: 100 knots
Initial groundspeed: 90 knots (airspeed minus headwind, 100-10)
Groundspeed after 180 degree turn: 110 knots (airspeed plus tailwind, 100+10)
Groundspeed change, aka "self created wind shear:" +20 knots (final groundspeed minus initial groundspeed, 110-90)

And my equivalent example:

Vehicle making the turn: Human body inside an airliner
Wind (uniform airmass inside the airliner): 500 knots, East to West
Initial heading: East
Initial airspeed: 1 knot
Initial groundspeed: negative 499 knots (airspeed minus headwind, 1-500)
Groundspeed after 180 degree turn: 501 knots (airspeed plus tailwind, 1+500)
Groundspeed change, aka "self created wind shear:" +1000 knots (final groundspeed minus initial groundspeed, 501 minus negative 499)

The windward turn theorists say that in the first example there is a tendancy to lose airspeed due to the headwind loss/tailwind gain, but in most situations it's minor enough not to notice since the turn is so slow comapared to the shear amount (20 knots over 1 minute) that the momentum is gradually changed to stay caught up with the airspeed.

If this logic is true, it implies that there could be an example, if we tweak the numbers enough, where the momentum doesn't have a chance to gradually change, and the result would be a noticable airspeed loss. So how about it, if 20 knots over a minute is not enough, how about 1000 knots over a second? Has anyone ever noticed any effects of this while walking up and down the isle of an airliner? Maybe it's still not enough for the effect to rise above the noise floor. Do we have to tweak the numbers further to make the airmass be the inside of a Concorde? Or an Apollo command module on translunar coast?

Of course not, this is bogus and Newtonian relativity holds true, i.e., if you close the window shades all physics occur as if it's sitting still. Or moving uniformly in any direction at any speed.
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Old 26th Jul 2018, 02:25
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Well things went dead quickly... surely I couldn't have had the last word, could I?
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Old 26th Jul 2018, 03:20
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Originally Posted by Vessbot
Well things went dead quickly... surely I couldn't have had the last word, could I?

No, THIS is the last word......
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Old 26th Jul 2018, 05:06
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Originally Posted by Wizofoz
No, THIS is the last word......
Are you sure?
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Old 27th Jul 2018, 13:14
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Originally Posted by A Squared
Are you sure?
Yes, that was definitely the last post.
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Old 27th Jul 2018, 14:58
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Originally Posted by Wizofoz
Yes, that was definitely the last post.
I'm not so certain.
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