The Windward Turn Theory
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OK, fine, the airliner is flying west, so west is the positive direction of our frame of reference. The velocity of the westbound airliner is +500 knots. The man is walking walking in the east direction , so that's -1 knot. a positive 500 knots, plus a negative 1 knot equals positive 499 knots, the man is still moving west at 499 knots. it doesn't become negative because of the direction he is facing.
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You're adopting a frame of reference which changes orientation with the person. The only way you can make sense of any of this is with a constant, non-accelerated frame of reference.
the airliner is flying East at 500 knots. the passenger is walking toward the tail at one knot, he is still moving East at 499 knots. He's not moving west merely because he's facing west.
While I obviously think Brecrow's theory is fallacy, I have to agree with him that the analogy the two if you are using here is just as flawed.
the airliner is flying East at 500 knots. the passenger is walking toward the tail at one knot, he is still moving East at 499 knots. He's not moving west merely because he's facing west.
While I obviously think Brecrow's theory is fallacy, I have to agree with him that the analogy the two if you are using here is just as flawed.
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OK, fine, the airliner is flying west, so west is the positive direction of our frame of reference. The velocity of the westbound airliner is +500 knots. The man is walking walking in the east direction , so that's -1 knot. a positive 500 knots, plus a negative 1 knot equals positive 499 knots, the man is still moving west at 499 knots. it doesn't become negative because of the direction he is facing.
Last edited by Vessbot; 6th Aug 2018 at 15:35.
That's his speed relative to the airframe. When I move backwards relative to the ground, my groundspeed has a minus in front of it.
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Well, yeah, what else are you going to measure ground speed relative to? Again, groundspeed is inherently relative to (in the frame of reference of) the ground.
You can't make any meaningful analysis when the axes of your reference system move whenever a person looks in a different direction.
You can't make any meaningful analysis when the axes of your reference system move whenever a person looks in a different direction.
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Well, yeah, what else are you going to measure ground speed relative to? Again, groundspeed is inherently relative to (in the frame of reference of) the ground.
You can't make any meaningful analysis when the axes of your reference system move whenever a person looks in a different direction.
You can't make any meaningful analysis when the axes of your reference system move whenever a person looks in a different direction.
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Hell we do the same thing about airspeed too, and necessarily so. The positive sign is always applied when air is coming from the direction of the nose, and we take that axis with us wherever we point the nose. If we didn't, then an airplane should fly equally well in a tailslide as in normal flight, and I can tell you from personal experience that it certainly doesn't.
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From a physics standpoint, it is completely meaningless. You are making the identical mistake that Ian was making. In your Scenario A, From the frame of reference of the ground, the airplane went from a velocity +110 knots to a velocity of -90 for a total change in velocity of 200 knots.
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Hell we do the same thing about airspeed too, and necessarily so. The positive sign is always applied when air is coming from the direction of the nose, and we take that axis with us wherever we point the nose. If we didn't, then an airplane should fly equally well in a tailslide as in normal flight, and I can tell you from personal experience that it certainly doesn't.
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From a physics standpoint, it is completely meaningless. You are making the identical mistake that Ian was making. In your Scenario A, From the frame of reference of the ground, the airplane went from a velocity +110 knots to a velocity of -90 for a total change in velocity of 200 knots.
(if there's no wind then the airmass frame and the ground frame are the same, so you should just be able to do a find-and-replace of "ground" with "air" to your post and everything still hold true.)
No, it's perfectly valid, for certain contexts, to rotate the axes as needed.
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Yes, there will be, for the reason explained by the math I posted.
What's the groundspeed before the turn? -499
What's the groundspeed after the turn? 501
The difference is 1000.
I read your post again, and it still rearranges the terms in error. Look at scenario A, and see that obviously everything is right. This is common sense to a private pilot. And then look at how every element translates to scenario B. Have I made any mistakes in the translations?
What's the groundspeed before the turn? -499
What's the groundspeed after the turn? 501
The difference is 1000.
I read your post again, and it still rearranges the terms in error. Look at scenario A, and see that obviously everything is right. This is common sense to a private pilot. And then look at how every element translates to scenario B. Have I made any mistakes in the translations?
I don't really mind where you stick it.
I should add that this is because calculation of groundspeed is a triangle of velocities problem envolving the cosine of the wind-angle. Less than 90 degrees is positive Greater than 90 degrees is negative
(1+500)+(1-500)
=501 +(-499)
=2
Last edited by Brercrow; 6th Aug 2018 at 16:31. Reason: Additional
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Look, it's pretty clear that you simply are unable to grasp the concept of Velocity, how it is different than "speed", why it is imperative that velocity is used in physics and not speed, and why a constant, unchanging frame of reference is necessary to make any kind of a meaningful analysis. I apologize for having wasted your time trying to explain these things and I will stop now.
From a physics standpoint, it is completely meaningless. You are making the identical mistake that Ian was making. In your Scenario A, From the frame of reference of the ground, the airplane went from a velocity +110 knots to a velocity of -90 for a total change in velocity of 200 knots.
Now, a ball can't travel backwards, but people and planes can so + and - is a way of expressing that relative movement.
Acceleration is absolute- if his velocity changed by 1000kts in a fraction of a second, he'd be crushed by the Gs.
We are looking at is groundspeed not his velocity. His groundspeed can be + or -.
What is the ground speed of someone facing sideways?