The Windward Turn Theory
Only half a speed-brake
I cannot comment on your eye-sight, and have no desire to enter that dispute you are having above. It's just physics, especially knowing the "frame of reference" of kinetic energy and vectors. And no, my claim does not justify any of those "create energy out of thin air" theories, which a consider just bags of hot air.
Towards the example you gave above: I only held in a jet-stream once, and while the effects were not as extreme as your hyperbolic choice of words, in a gist you are correct. But that's because the FMS was trying to fly a fixed pattern over the ground. So that should not be relevant here. Or is it?
Towards the example you gave above: I only held in a jet-stream once, and while the effects were not as extreme as your hyperbolic choice of words, in a gist you are correct. But that's because the FMS was trying to fly a fixed pattern over the ground. So that should not be relevant here. Or is it?
It's inertia, INTBH. Those 20k+ pilots must have flown commercially, i.e. heavier planes, where the effect can be seen. Although like you say the craft is moving within a practically uniform parcel of air, Newton's laws still apply. The inertial system is the spheres, so the physics is there.
I have no claim how pronounced or measurable the effect is on those beauties with low wing loading, but our aircraft do show. Level flight, fixed thrust, steady heading with 90° cross-wind: there is a difference in which way you'd turn.
I have no claim how pronounced or measurable the effect is on those beauties with low wing loading, but our aircraft do show. Level flight, fixed thrust, steady heading with 90° cross-wind: there is a difference in which way you'd turn.
The part where people in the pattern get into trouble is by not anticipating the wind and correcting their pattern for it. People spin/stall turning base/final because the picture is different with strong tailwind than calm air and if you don’t start your turn early you will have to increase bank angle, you are faster across the ground so you slow down......
with a tailwind on base, keep your pattern wide, and look at your INDICATED speed.
FlightDetent, I’m sorry, but when it comes to IAS, the frame of reference that matters is the air mass you’re flying in. It doesn’t matter whether you fly fixed holding patterns or shifting orbits, the effect of a constant wind on IAS is the same - nothing (except that to fly a fixed racetrack you’ll sometimes have to tighten or relax the turn to allow for the wind, with a consequent change in induced drag).
If what you believe about wind and inertia were true, it would also change a whole lot about close-in air combat. For the last hundred years, fighter pilots have been doing their utmost to maximise their turn performance and energy state, in an effort to gain every tiny advantage possible. Yet never the slightest thought for the supposed effects of turning in or out of the wind. Perhaps as well as bewaring the Hun in the sun, they should have been worried about the Hun attacking from downwind?
Hans has it right.
If what you believe about wind and inertia were true, it would also change a whole lot about close-in air combat. For the last hundred years, fighter pilots have been doing their utmost to maximise their turn performance and energy state, in an effort to gain every tiny advantage possible. Yet never the slightest thought for the supposed effects of turning in or out of the wind. Perhaps as well as bewaring the Hun in the sun, they should have been worried about the Hun attacking from downwind?
Hans has it right.
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So the downwind turn myth isn’t a myth after all? Oh dear.
I fly the same heavy commercial jets (and previously, things with much higher wing loading again), and contend that the effect can’t be seen, because it doesnt exist.. When you’re flying a holding pattern up in a jetstream, what happens to your IAS - a.) alternating stall and overspeed warnings, or b.) nothing ?
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It's inertia, INTBH. Those 20k+ pilots must have flown commercially, i.e. heavier planes, where the effect can be seen. Although like you say the craft is moving within a practically uniform parcel of air, Newton's laws still apply. The inertial system is the spheres, so the physics is there.
I have no claim how pronounced or measurable the effect is on those beauties with low wing loading, but our aircraft do show. Level flight, fixed thrust, steady heading with 90° cross-wind: there is a difference in which way you'd turn.
I have no claim how pronounced or measurable the effect is on those beauties with low wing loading, but our aircraft do show. Level flight, fixed thrust, steady heading with 90° cross-wind: there is a difference in which way you'd turn.
What is the velocity change from the east heading to the west heading?
Now, same airplane flying East in a 50 kt wind out of the East (direct headwind) at 50 kt GS. The airplane turns to a west heading. Groundspeed is now 150 kts.
What is the velocity change in this example?
Only half a speed-brake
A^2, do you really insist that flying a fixed pattern over the ground, there is no difference between still air and flowing air conditions?
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The "downwind turn danger myth" is as difficult to beat out of believers as the "sky god myth".
Fly a constant bank turn in a moving air mass, no change in power, no change in attitude equals no change in airspeed. However, you will drift over the landscape.
Don't believe me, try it.
Fly a constant bank turn in a moving air mass, no change in power, no change in attitude equals no change in airspeed. However, you will drift over the landscape.
Don't believe me, try it.
Last edited by jack11111; 12th Jul 2018 at 02:59.
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I'm waiting for your answer to my questions above. To wit:
Lets start with basics. Assume a 100 kt airplane flying east in still air with 100 kt groundspeed (obviously). The airplane turns to a west heading. groundspeed is now 100 kt West
What is the velocity change from the east heading to the west heading?
Now, same airplane flying East in a 50 kt wind out of the East (direct headwind) at 50 kt GS. The airplane turns to a west heading. Groundspeed is now 150 kts.
What is the velocity change in this example?
What is the velocity change from the east heading to the west heading?
Now, same airplane flying East in a 50 kt wind out of the East (direct headwind) at 50 kt GS. The airplane turns to a west heading. Groundspeed is now 150 kts.
What is the velocity change in this example?
If the downwind myth were true you would notice some weird effects inside trains and cars and aircraft. Inside a train/car/aircraft the occupants and all inside it are carried along with the train/car/aircraft (much the same as an aircraft travels with the air in a constant wind).
If you were to throw a paper plane that circled inside the carriage when a train was waiting at the platform it might circle nicely. If the myth were true and the train was travelling at speed, the paper plane would now lose or gain airspeed as it turned towards the back or front of the train in its orbits (because it would have 'inertia' relative to the earth that needs to be 'made up' or 'lost' and so the plane would climb and descend as it gained and lost airspeed).
Similarly if you walked about a train's or aircraft's aisle in a circle, you would stumble about as you changed direction as you 'gained' and 'lost' inertia depending on the direction you were walking. Assuming the train or aircraft is travelling at a constant speed and direction, that is not what happens. Even at high speeds, you can comfortably move about the cabin without fighting inertia due to your 'inertia' relative to the earth.
Aircraft fly relative to the air around them, not the earth, same as passengers in constantly moving vehicles measure their practical (ie what it feels like) inertia relative to the vehicle not to the earth.
If you were to throw a paper plane that circled inside the carriage when a train was waiting at the platform it might circle nicely. If the myth were true and the train was travelling at speed, the paper plane would now lose or gain airspeed as it turned towards the back or front of the train in its orbits (because it would have 'inertia' relative to the earth that needs to be 'made up' or 'lost' and so the plane would climb and descend as it gained and lost airspeed).
Similarly if you walked about a train's or aircraft's aisle in a circle, you would stumble about as you changed direction as you 'gained' and 'lost' inertia depending on the direction you were walking. Assuming the train or aircraft is travelling at a constant speed and direction, that is not what happens. Even at high speeds, you can comfortably move about the cabin without fighting inertia due to your 'inertia' relative to the earth.
Aircraft fly relative to the air around them, not the earth, same as passengers in constantly moving vehicles measure their practical (ie what it feels like) inertia relative to the vehicle not to the earth.
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Hi FlightDetent,
I agree, Newton's laws still apply. But you have to be careful to consider what the momentum and energy is relative to.
If the downwind myth were true, then doing a loop in a glider starting into a headwind which matched the flying speed (so ground speed = 0) would be impossible.
What kinetic energy (when ground speed = 0) is being converted into the height gain?
Would you gain more height if you start the loop downwind?
Newton's laws still apply. The inertial system is the spheres, so the physics is there.
If the downwind myth were true, then doing a loop in a glider starting into a headwind which matched the flying speed (so ground speed = 0) would be impossible.
What kinetic energy (when ground speed = 0) is being converted into the height gain?
Would you gain more height if you start the loop downwind?
Further to Jonkster’s post above, I humbly re-submit an earlier post of mine:
“You wake up, not sure where you are. You see that you are in a small, windowless room. Apart from your chair, the room is empty.
On the floor, you find a small model aeroplane with a battery-powered motor driving counter-rotating propellers. A simple instruction sheet tells you that when the motor is switched on and the 'plane is hand-launched, the controls are fixed so that it will fly perfect circles until a timer turns the motor off after 30 seconds.
You launch the model and watch, pleased and impressed, as it flies circles around you.
After the flight has ended, you notice that there is actually a window blind in the wall behind you. You open the blind and are amazed to find that you are in fact inside a carriage being pulled by a train along a perfectly straight, smooth track at 60mph.
You consider the fact that the model aircraft was flying in a parcel of air which was moving across the ground at 60mph. To an observer not on the train, it was, in effect, flying in a 60mph wind. This is a speed which is about five times greater than its own flight speed, yet the model did not seem to be affected at all! It did not, for example, exhibit any signs of 'stalling' or losing height when it was turning 'downwind'.
You come to the conclusion that the model was simply unaware of its location and speed relative to the tracks, as were you until you looked out of the window.”
“You wake up, not sure where you are. You see that you are in a small, windowless room. Apart from your chair, the room is empty.
On the floor, you find a small model aeroplane with a battery-powered motor driving counter-rotating propellers. A simple instruction sheet tells you that when the motor is switched on and the 'plane is hand-launched, the controls are fixed so that it will fly perfect circles until a timer turns the motor off after 30 seconds.
You launch the model and watch, pleased and impressed, as it flies circles around you.
After the flight has ended, you notice that there is actually a window blind in the wall behind you. You open the blind and are amazed to find that you are in fact inside a carriage being pulled by a train along a perfectly straight, smooth track at 60mph.
You consider the fact that the model aircraft was flying in a parcel of air which was moving across the ground at 60mph. To an observer not on the train, it was, in effect, flying in a 60mph wind. This is a speed which is about five times greater than its own flight speed, yet the model did not seem to be affected at all! It did not, for example, exhibit any signs of 'stalling' or losing height when it was turning 'downwind'.
You come to the conclusion that the model was simply unaware of its location and speed relative to the tracks, as were you until you looked out of the window.”
Further to Jonkster’s post above, I humbly re-submit an earlier post of mine:
“You wake up, not sure where you are. You see that you are in a small, windowless room. Apart from your chair, the room is empty.
On the floor, you find a small model aeroplane with a battery-powered motor driving counter-rotating propellers. A simple instruction sheet tells you that when the motor is switched on and the 'plane is hand-launched, the controls are fixed so that it will fly perfect circles until a timer turns the motor off after 30 seconds.
You launch the model and watch, pleased and impressed, as it flies circles around you.
After the flight has ended, you notice that there is actually a window blind in the wall behind you. You open the blind and are amazed to find that you are in fact inside a carriage being pulled by a train along a perfectly straight, smooth track at 60mph.
You consider the fact that the model aircraft was flying in a parcel of air which was moving across the ground at 60mph. To an observer not on the train, it was, in effect, flying in a 60mph wind. This is a speed which is about five times greater than its own flight speed, yet the model did not seem to be affected at all! It did not, for example, exhibit any signs of 'stalling' or losing height when it was turning 'downwind'.
You come to the conclusion that the model was simply unaware of its location and speed relative to the tracks, as were you until you looked out of the window.”
“You wake up, not sure where you are. You see that you are in a small, windowless room. Apart from your chair, the room is empty.
On the floor, you find a small model aeroplane with a battery-powered motor driving counter-rotating propellers. A simple instruction sheet tells you that when the motor is switched on and the 'plane is hand-launched, the controls are fixed so that it will fly perfect circles until a timer turns the motor off after 30 seconds.
You launch the model and watch, pleased and impressed, as it flies circles around you.
After the flight has ended, you notice that there is actually a window blind in the wall behind you. You open the blind and are amazed to find that you are in fact inside a carriage being pulled by a train along a perfectly straight, smooth track at 60mph.
You consider the fact that the model aircraft was flying in a parcel of air which was moving across the ground at 60mph. To an observer not on the train, it was, in effect, flying in a 60mph wind. This is a speed which is about five times greater than its own flight speed, yet the model did not seem to be affected at all! It did not, for example, exhibit any signs of 'stalling' or losing height when it was turning 'downwind'.
You come to the conclusion that the model was simply unaware of its location and speed relative to the tracks, as were you until you looked out of the window.”
Avoid imitations
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Further to Jonkster’s post above, I humbly re-submit an earlier post of mine:
“You wake up, not sure where you are. You see that you are in a small, windowless room. Apart from your chair, the room is empty.
On the floor, you find a small model aeroplane with a battery-powered motor driving counter-rotating propellers. A simple instruction sheet tells you that when the motor is switched on and the 'plane is hand-launched, the controls are fixed so that it will fly perfect circles until a timer turns the motor off after 30 seconds.
You launch the model and watch, pleased and impressed, as it flies circles around you.
After the flight has ended, you notice that there is actually a window blind in the wall behind you. You open the blind and are amazed to find that you are in fact inside a carriage being pulled by a train along a perfectly straight, smooth track at 60mph.
You consider the fact that the model aircraft was flying in a parcel of air which was moving across the ground at 60mph. To an observer not on the train, it was, in effect, flying in a 60mph wind. This is a speed which is about five times greater than its own flight speed, yet the model did not seem to be affected at all! It did not, for example, exhibit any signs of 'stalling' or losing height when it was turning 'downwind'.
You come to the conclusion that the model was simply unaware of its location and speed relative to the tracks, as were you until you looked out of the window.”
“You wake up, not sure where you are. You see that you are in a small, windowless room. Apart from your chair, the room is empty.
On the floor, you find a small model aeroplane with a battery-powered motor driving counter-rotating propellers. A simple instruction sheet tells you that when the motor is switched on and the 'plane is hand-launched, the controls are fixed so that it will fly perfect circles until a timer turns the motor off after 30 seconds.
You launch the model and watch, pleased and impressed, as it flies circles around you.
After the flight has ended, you notice that there is actually a window blind in the wall behind you. You open the blind and are amazed to find that you are in fact inside a carriage being pulled by a train along a perfectly straight, smooth track at 60mph.
You consider the fact that the model aircraft was flying in a parcel of air which was moving across the ground at 60mph. To an observer not on the train, it was, in effect, flying in a 60mph wind. This is a speed which is about five times greater than its own flight speed, yet the model did not seem to be affected at all! It did not, for example, exhibit any signs of 'stalling' or losing height when it was turning 'downwind'.
You come to the conclusion that the model was simply unaware of its location and speed relative to the tracks, as were you until you looked out of the window.”
A small, lightweight model aircraft has very low inertia and will easily be blown "downwind" during gusts, but see only relatively small variations in IAS.
A very large aircraft, such as an airliner, will see more variations in IAS but tend to follow the original flight path more closely.
Hence windshear being more of a concern on the approach in a very large aircraft.
The energy "found" during the previous video is being harvested as lift from updraughting airflow and then being converted to airspeed as the aircraft is descended on the "still air" side of the hill.
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Try throwing a ball into the air while driving along in a car. Just after throwing it up have the driver turn sharply. What does the ball do, stay within the cars frame of reference, moving with the air mass? Now try doing the same with a sheet of paper, something with less inertia and more air resistance. Same result?
If you leave a loose article in the cockpit during turbulence does it stay fixed to the aircraft’s plane of reference, moving with the air mass in the cockpit? Why do we think that that an inertial/gravitational frame of reference works differently laterally to vertically?
I think you are all just arguing about the relative balance of inertial to aerodynamic forces. All sort of depends how much inertia you have and how much lift/drag you have.
If you leave a loose article in the cockpit during turbulence does it stay fixed to the aircraft’s plane of reference, moving with the air mass in the cockpit? Why do we think that that an inertial/gravitational frame of reference works differently laterally to vertically?
I think you are all just arguing about the relative balance of inertial to aerodynamic forces. All sort of depends how much inertia you have and how much lift/drag you have.
Try throwing a ball into the air while driving along in a car. Just after throwing it up have the driver turn sharply. What does the ball do, stay within the cars frame of reference, moving with the air mass? Now try doing the same with a sheet of paper, something with less inertia and more air resistance. Same result?
Why do we think that that an inertial/gravitational frame of reference works differently laterally to vertically?
I think you are all just arguing about the relative balance of inertial to aerodynamic forces. All sort of depends how much inertia you have and how much lift/drag you have.
Eckhard’s post was about the most simple and elegant explanation of all this that you’re likely to read, and should’ve put an end to the discussion. Yet here we are.
It will move sideways (relative to the car). Once not in contact with anything in the car, the ball is not accelerated by the car as the car accelerates sideways in the turn and will maintain its straight line motion (relative to the earth) as it is not being accelerated by any force (other than minutely by air resistance).
In your analogy it appears the ball would be the aircraft and car and the "air" contained in the car would be the wind, is that correct?
If so, in that analogy, by turning the car rapidly, you are causing a sudden change in the direction of the "wind", not a change in direction of the "aircraft".
Of course if the wind direction or magnitude changes rapidly there will be IAS changes and that is seen when flying in turbulence or with windshear.
Perhaps we need to define the myth we are arguing against or the phenomena we are arguing for.
If we are talking about turbulence, varying wind speeds, windshear situations etc then of course, IAS will vary as we encounter changing wind velocities.
If the wind is steady and we perform a constant rate turn in a wind, the myth I will argue against, is that the airspeed will vary as the aircraft changes direction from flying the into wind direction to the downwind direction. In a constant wind, it won't.
I spent many hours in my early flying years low to the ground circling around stock in many different wind conditions from dead still to steady flow to strong and gusty days with lots of thermals. Always I found the aircraft flew relative to the air, any variations in airspeed were due to turbulent flow and didn't limit themselves to any particular part of the orbit.
Early on I had to learn to resist the very strong urge to over bank or over rudder the aircraft in strong steady winds due to the illusion the aircraft was skidding or slipping when orbiting low level in a wind. There be dragons.
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That’s no longer the same discussion. We’re talking about the behaviour of aircraft in a constant airmass. Using car analogies is fine, but once you start swerving around in the car, it’s no longer analogous to a constant airmass.
We don’t.
Er, really?
Eckhard’s post was about the most simple and elegant explanation of all this that you’re likely to read, and should’ve put an end to the discussion. Yet here we are.
Eckhard's post doesn't really explain the basic physics because the train isn't accelerating.
Try doing the same as the train slows, accelerates or goes round a corner. is the aircraft now fixed to the moving air mass?
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Jonkster,
I'm not trying to argue for or against any myths or theories, just trying to get the basic physics straight.
An aircraft going downwind at 120kts airspeed, into a 60 kt headwind with 180 kts groundspeed tailwind has a lot more kinetic energy and inertia than one going at 120 kts airspeed into a 60 kt headwind with only 60 kts groundspeed. Compare the braking distances if you try and land off those conditions. The question is so what? When turning downwind that extra kinetic energy has to come from somewhere and over the course of a downwind turn the aerodynamic forces provide that acceleration without drama.
However, someone above suggested trying a loop in a glider into a strong headwind starting with zero knots groundspeed. Try that and let us know how you get on?
I'm not trying to argue for or against any myths or theories, just trying to get the basic physics straight.
An aircraft going downwind at 120kts airspeed, into a 60 kt headwind with 180 kts groundspeed tailwind has a lot more kinetic energy and inertia than one going at 120 kts airspeed into a 60 kt headwind with only 60 kts groundspeed. Compare the braking distances if you try and land off those conditions. The question is so what? When turning downwind that extra kinetic energy has to come from somewhere and over the course of a downwind turn the aerodynamic forces provide that acceleration without drama.
However, someone above suggested trying a loop in a glider into a strong headwind starting with zero knots groundspeed. Try that and let us know how you get on?
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Neither is the wind. The Downwind theory myth is that an airplane in a steady, un-accelerated wind, (no gust, no turbulence, no wind shear) turning downwind will lose airspeed. A railroad train traveling at a constant velocity on a straight track is perfectly analogous to a steady, gust-less, shear-less wind.
Last edited by A Squared; 15th Jul 2018 at 02:31.
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Jonkster,
I'm not trying to argue for or against any myths or theories, just trying to get the basic physics straight.
An aircraft going downwind at 120kts airspeed, into a 60 kt headwind with 180 kts groundspeed tailwind has a lot more kinetic energy and inertia than one going at 120 kts airspeed into a 60 kt headwind with only 60 kts groundspeed.
I'm not trying to argue for or against any myths or theories, just trying to get the basic physics straight.
An aircraft going downwind at 120kts airspeed, into a 60 kt headwind with 180 kts groundspeed tailwind has a lot more kinetic energy and inertia than one going at 120 kts airspeed into a 60 kt headwind with only 60 kts groundspeed.
100 kt airplane, 50 knot wind out of the east. Airplane flies east into wind with 50 knot groundspeed, then turns 180 degrees and flies west with a 150 knot groundspeed.
What is the velocity change from upwind to downwind.
Same airplane, no wind. Flies East at 100 kt, turns 180 degrees flies west at 100 knots
What is the velocity change from eastbound to westbound?