Downwind turn Myth
09-11-2015, 11:25 AM
#1552
Bob, here is a very well written article disproving Mac's explanation. Check it out, a little long but well and simply written http://masterflight.aero/2014/02/11/...downwind-turn/
I know one flight instructor who teaches his students to chant when circling to land, “Airport; airspeed; altitude; airport; airspeed; altitude; airport; airspeed; altitude.” It works; it forces his students to pay attention to airspeed constantly. Always fly the airspeed, not the ground speed.
Lack of altitude airspeed and Ideas plus Gravity will "KILL YA".
09-11-2015, 03:13 PM
#1554
One thing that guys who say that wind has no effect on airspeed keep forgetting is that aircraft have MASS, and anything with MASS has inertia. Inertia is with respect to the earth (i.e., the ground) NOT the air.
Read this: http://macsblog.com/2014/02/turns-wind-and-airspeed/
To quote from it:
"But there are many pilots who simply refuse to believe that turning an airplane in a breeze also changes inertia and thus causes at least momentary change in airspeed."
...
"In a rapid turn an airplane can change the wind from a headwind to a tailwind and inertia demands an adjustment to bring the airspeed back to equilibrium. The adjustment can be a brief loss of airspeed, or an exchange of altitude to regain airspeed when the turn converts headwind into tailwind."
BTW, J Mac McClellan probably has more flying experience than everyone on RCU - he definitely has more experience writing about flying and issues therein...
Now who here thinks that a model Piper Cub flying into the wind with zero ground speed doesn't have a change in inertia when executing a 180 degree turn to downwind?
Again quoting Mac:
"So does it matter if you turn quickly from a headwind to a tailwind? Yes. At least a little. Inertia requires the airplane to accelerate relative to the ground to regain the previous airspeed it had when flying into a headwind. The mass of the airplane, the rate of turn, and the strength of the wind all are factors in how much the turning airplane must accelerate to maintain airspeed in the new wind. For most airplanes the wind caused change of airspeed in a turn will be too small to notice. But it’s there, and if an airplane is operating too near its minimum airspeed the change may be enough to matter."
Bob
Read this: http://macsblog.com/2014/02/turns-wind-and-airspeed/
To quote from it:
"But there are many pilots who simply refuse to believe that turning an airplane in a breeze also changes inertia and thus causes at least momentary change in airspeed."
...
"In a rapid turn an airplane can change the wind from a headwind to a tailwind and inertia demands an adjustment to bring the airspeed back to equilibrium. The adjustment can be a brief loss of airspeed, or an exchange of altitude to regain airspeed when the turn converts headwind into tailwind."
BTW, J Mac McClellan probably has more flying experience than everyone on RCU - he definitely has more experience writing about flying and issues therein...
Now who here thinks that a model Piper Cub flying into the wind with zero ground speed doesn't have a change in inertia when executing a 180 degree turn to downwind?
Again quoting Mac:
"So does it matter if you turn quickly from a headwind to a tailwind? Yes. At least a little. Inertia requires the airplane to accelerate relative to the ground to regain the previous airspeed it had when flying into a headwind. The mass of the airplane, the rate of turn, and the strength of the wind all are factors in how much the turning airplane must accelerate to maintain airspeed in the new wind. For most airplanes the wind caused change of airspeed in a turn will be too small to notice. But it’s there, and if an airplane is operating too near its minimum airspeed the change may be enough to matter."
Bob
09-12-2015, 03:51 AM
#1555
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In fact a certain aerodynamic behavior of especially pylon racers allows this to be done very efficiently. If you turn fast enough airflow separation does not occur, drag does not change much and voila the turn is close to an elastic type or spring bounce.
Ask your "expert" to explain a bouncing ball or change of direction of billiard balls.
As with many terms of reference there are sometimes quite different ways of observing the system. The most difficult one seems to be to discount the relative motion of ground versus moving air. The Airplane knows nothing of the ground. Only when it is flown into it by the downwind turn myth pilots does it know....
09-12-2015, 05:24 AM
#1556
Cant believe this is still going. The "acceleration" required to change "inertia" is simple. Energy conversion. When a turn is made angle of attack is increased, lift is increased resulting in a force vector converting lift into acceleration.
In fact a certain aerodynamic behavior of especially pylon racers allows this to be done very efficiently. If you turn fast enough airflow separation does not occur, drag does not change much and voila the turn is close to an elastic type or spring bounce.
Ask your "expert" to explain a bouncing ball or change of direction of billiard balls.
As with many terms of reference there are sometimes quite different ways of observing the system. The most difficult one seems to be to discount the relative motion of ground versus moving air. The Airplane knows nothing of the ground. Only when it is flown into it by the downwind turn myth pilots does it know....
In fact a certain aerodynamic behavior of especially pylon racers allows this to be done very efficiently. If you turn fast enough airflow separation does not occur, drag does not change much and voila the turn is close to an elastic type or spring bounce.
Ask your "expert" to explain a bouncing ball or change of direction of billiard balls.
As with many terms of reference there are sometimes quite different ways of observing the system. The most difficult one seems to be to discount the relative motion of ground versus moving air. The Airplane knows nothing of the ground. Only when it is flown into it by the downwind turn myth pilots does it know....
09-12-2015, 06:22 AM
#1558
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But the change in momentum for a 180 degree turn is exactly the same in a steady wind as in calm air. So wind speed doesn't change the mechanics, unless you are trying to make your turns in the wind look just like your turns with no wind, and nobody is claiming you can't get into trouble trying to do that.
09-12-2015, 06:26 AM
#1559
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You ONLY have to account for it when you contact the ground. cfircav8r just said it best: "Frame of reference is only pertinent when you are interacting with that frame of reference".
09-12-2015, 10:37 AM
#1560
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I can't believe this issue persists for years in RC as well as full scale flying. I have been flying full size for over 40 yrs and RC for almost as long. I have contended with some hellacious winds in the traffic pattern and NEVER fell out of the sky turning downwind because proper AIRSPEED was and is always maintained. There's an old saying...("maintain thy airspeed lest the ground come up and smite thee")
09-12-2015, 02:42 PM
#1561
I can't believe this issue persists for years in RC as well as full scale flying. I have been flying full size for over 40 yrs and RC for almost as long. I have contended with some hellacious winds in the traffic pattern and NEVER fell out of the sky turning downwind because proper AIRSPEED was and is always maintained. There's an old saying...("maintain thy airspeed lest the ground come up and smite thee")
09-12-2015, 07:26 PM
#1565
drac1, you are so confused and out of your depth "mate".
A fixed wing airplane, once airborne, propels itself through the air. The fact that the air mass is moving - or not, does NOT matter to the air-frame.
In other words the air-frame does NOT know there is a crosswind until ground contact is made.
Hence the reason we have to de-crab during the landing flare, or we may chose to side-slip (wing down) on approach. Either way the air-fame is now unhappy as we are flying cross controlled in order to maintain a runway center line in reference to the ground, to which we will make contact with when we land.
And its the same during a crosswind takeoff. The air-frame wants to weathercock into the wind only because we are accelerating down a ground path (runway center line), that isn't into the prevailing wind. Hence the aileron input into the wind and opposite rudder - only required whilst on the ground. Once airborne we neutralist the controls and the air-frame is now balanced (meaning it knows of no such crosswind), and to those on the ground we will be crabbing during the climb (known as drift angle).
A fixed wing airplane, once airborne, propels itself through the air. The fact that the air mass is moving - or not, does NOT matter to the air-frame.
In other words the air-frame does NOT know there is a crosswind until ground contact is made.
Hence the reason we have to de-crab during the landing flare, or we may chose to side-slip (wing down) on approach. Either way the air-fame is now unhappy as we are flying cross controlled in order to maintain a runway center line in reference to the ground, to which we will make contact with when we land.
And its the same during a crosswind takeoff. The air-frame wants to weathercock into the wind only because we are accelerating down a ground path (runway center line), that isn't into the prevailing wind. Hence the aileron input into the wind and opposite rudder - only required whilst on the ground. Once airborne we neutralist the controls and the air-frame is now balanced (meaning it knows of no such crosswind), and to those on the ground we will be crabbing during the climb (known as drift angle).
Last edited by darryltarr; 09-12-2015 at 07:59 PM.
09-12-2015, 08:29 PM
#1566
drac1, you are so confused and out of your depth "mate".
A fixed wing airplane, once airborne, propels itself through the air. The fact that the air mass is moving - or not, does NOT matter to the air-frame.
In other words the air-frame does NOT know there is a crosswind until ground contact is made.
Hence the reason we have to de-crab during the landing flare, or we may chose to side-slip (wing down) on approach. Either way the air-fame is now unhappy as we are flying cross controlled in order to maintain a runway center line in reference to the ground, to which we will make contact with when we land.
And its the same during a crosswind takeoff. The air-frame wants to weathercock into the wind only because we are accelerating down a ground path (runway center line), that isn't into the prevailing wind. Hence the aileron input into the wind and opposite rudder - only required whilst on the ground. Once airborne we neutralist the controls and the air-frame is now balanced (meaning it knows of no such crosswind), and to those on the ground we will be crabbing during the climb (known as drift angle).
A fixed wing airplane, once airborne, propels itself through the air. The fact that the air mass is moving - or not, does NOT matter to the air-frame.
In other words the air-frame does NOT know there is a crosswind until ground contact is made.
Hence the reason we have to de-crab during the landing flare, or we may chose to side-slip (wing down) on approach. Either way the air-fame is now unhappy as we are flying cross controlled in order to maintain a runway center line in reference to the ground, to which we will make contact with when we land.
And its the same during a crosswind takeoff. The air-frame wants to weathercock into the wind only because we are accelerating down a ground path (runway center line), that isn't into the prevailing wind. Hence the aileron input into the wind and opposite rudder - only required whilst on the ground. Once airborne we neutralist the controls and the air-frame is now balanced (meaning it knows of no such crosswind), and to those on the ground we will be crabbing during the climb (known as drift angle).
If wind doesn't make any difference, you could land any direction with no problems.
09-12-2015, 08:35 PM
#1567
As I teach many this may help some. Its known as "The Triangle of Velocities", and is used for Navigational Purposes.
Vector ONE = Heading (HDG) and True Air Speed (TAS)
Vector TWO = Track (TRK) and Ground Speed (GS)
Vector THREE = Wind Direction and Speed
The methodology is this: One plus Three equals Two (1 + 3 = 2)
In other words the air-frame only recognizes Indicated Air Speed (TAS for plotting), and the Wind (or moving air mass), blows you onto your TRK and GS.
Regardless of how strong (or from which direction) the moving air mass is, it has no bearing on the air-frame or Air Speed.
Vector ONE = Heading (HDG) and True Air Speed (TAS)
Vector TWO = Track (TRK) and Ground Speed (GS)
Vector THREE = Wind Direction and Speed
The methodology is this: One plus Three equals Two (1 + 3 = 2)
In other words the air-frame only recognizes Indicated Air Speed (TAS for plotting), and the Wind (or moving air mass), blows you onto your TRK and GS.
Regardless of how strong (or from which direction) the moving air mass is, it has no bearing on the air-frame or Air Speed.
Last edited by darryltarr; 09-12-2015 at 11:03 PM.
09-12-2015, 08:50 PM
#1568
NO, Not Correct and once again you are confused. We choose to takeoff and land into the wind as this optimizes performance as runways length is finite.
If the wind was down the runway at 50 knots, and my takeoff speed was 50 knots, all I would have to do is line up on the runway, apply full throttle, and pull the stick back. I would then get airborne with zero ground speed (very efficient takeoff distance). Do you think the wing (air-frame) knew or cared about ground speed, it doesn't know.
And the same could be said for a takeoff with a 50 knot tailwind. I would have to accelerate to 50 knots ground speed before the wings feel a zero wind component, and then accelerate another 50 knots to get airborne. My airspeed would be 50 knots (the wings are happy), but I have now used an indefinite amount of runway and possible exceeded my tire limit speed.
Last edited by darryltarr; 09-12-2015 at 09:39 PM.
09-12-2015, 11:56 PM
#1569
NO, Not Correct and once again you are confused. We choose to takeoff and land into the wind as this optimizes performance as runways length is finite.
If the wind was down the runway at 50 knots, and my takeoff speed was 50 knots, all I would have to do is line up on the runway, apply full throttle, and pull the stick back. I would then get airborne with zero ground speed (very efficient takeoff distance). Do you think the wing (air-frame) knew or cared about ground speed, it doesn't know.
And the same could be said for a takeoff with a 50 knot tailwind. I would have to accelerate to 50 knots ground speed before the wings feel a zero wind component, and then accelerate another 50 knots to get airborne. My airspeed would be 50 knots (the wings are happy), but I have now used an indefinite amount of runway and possible exceeded my tire limit speed.
If the wind was down the runway at 50 knots, and my takeoff speed was 50 knots, all I would have to do is line up on the runway, apply full throttle, and pull the stick back. I would then get airborne with zero ground speed (very efficient takeoff distance). Do you think the wing (air-frame) knew or cared about ground speed, it doesn't know.
And the same could be said for a takeoff with a 50 knot tailwind. I would have to accelerate to 50 knots ground speed before the wings feel a zero wind component, and then accelerate another 50 knots to get airborne. My airspeed would be 50 knots (the wings are happy), but I have now used an indefinite amount of runway and possible exceeded my tire limit speed.
What I am saying is that wind makes a difference and your example agrees with that.
09-13-2015, 03:28 AM
#1570
Now you're just being argumentative. When you make a turn, the only reason you need to worry about wind is if you need to maintain a specific ground track/speed. Then, yes it is now possible to put your plane into an untenable position, especially if you don't understand how the wind is, and isn't, affecting your plane.
From the pages here.
False: don't present too much of the wing into the wind as it will push you down and make it impossible to get the nose pitched back into the wind.
Truth: don't bank too steep as you may overload the wing and stall,especially at lower landing speeds, and don't use more rudder to tighten the turn without over loading the wing as this will ensure any stall will be a spin.
False: you need extra power for turns in wind especially during landings.
Truth: you need to plan your turns and adjust the timing of your turns to compensate for a different ground speed and track.
Arguing semantics doesn't help people understand wind, and understanding wind will give you better tools to prevent accidents and understand them to avoid them in the future. There are limits to the amount of bank and power to compensate for wind but there are no limits to proper planning, so if you continue to believe that it is about overcoming that erroneous momentum problem, you will eventually exceed your envelope. If you understand it is merely a navigation issue you should never run out of good planning.
From the pages here.
False: don't present too much of the wing into the wind as it will push you down and make it impossible to get the nose pitched back into the wind.
Truth: don't bank too steep as you may overload the wing and stall,especially at lower landing speeds, and don't use more rudder to tighten the turn without over loading the wing as this will ensure any stall will be a spin.
False: you need extra power for turns in wind especially during landings.
Truth: you need to plan your turns and adjust the timing of your turns to compensate for a different ground speed and track.
Arguing semantics doesn't help people understand wind, and understanding wind will give you better tools to prevent accidents and understand them to avoid them in the future. There are limits to the amount of bank and power to compensate for wind but there are no limits to proper planning, so if you continue to believe that it is about overcoming that erroneous momentum problem, you will eventually exceed your envelope. If you understand it is merely a navigation issue you should never run out of good planning.
09-13-2015, 06:21 AM
#1571
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Truth: you need to plan your turns and adjust the timing of your turns to compensate for a different ground speed and track.
That is what you are doing to overcome that "erroneous momentum problem"
That is what you are doing to overcome that "erroneous momentum problem"
09-13-2015, 02:53 PM
#1573
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"Erroneous momentum problem", in physics there is no erroneous momentum problem. The energy is in the fluids density and the planes collisions with that fluid. Gravity is center of mass to center of mass.
Throw a ball in the water near a rocky shore and watch the wave action smash the ball against the rocks or a pier pilling.
The ball's momentum is changing constantly, as is a planes. When the water smashes the ball into the rocks it has nothing to do with a downstream turn, it is the power of the fluid that smashes it.
The power of the fluid is a little harder to see when it is invisible (air is invisible).
But, it is not the planes turn, which changes the momentum slightly it is by the added drag of manuvering slowing it's relative speed.
It is the fluid that the plane is captive in where the power lies. With all physics it is the case that the energy is conserved. There is no loss that is not easily seen as a gain elsewhere. Nor gain that is not seen as a loss elsewhere.
14 pounds per square inch pressure @ STP is enough at speed to fly a 1,000,000 lb 747 at take off speed in that invisible fluid.
Downwind turn is a myth! Attitude plus power equals performance.
Throw a ball in the water near a rocky shore and watch the wave action smash the ball against the rocks or a pier pilling.
The ball's momentum is changing constantly, as is a planes. When the water smashes the ball into the rocks it has nothing to do with a downstream turn, it is the power of the fluid that smashes it.
The power of the fluid is a little harder to see when it is invisible (air is invisible).
But, it is not the planes turn, which changes the momentum slightly it is by the added drag of manuvering slowing it's relative speed.
It is the fluid that the plane is captive in where the power lies. With all physics it is the case that the energy is conserved. There is no loss that is not easily seen as a gain elsewhere. Nor gain that is not seen as a loss elsewhere.
14 pounds per square inch pressure @ STP is enough at speed to fly a 1,000,000 lb 747 at take off speed in that invisible fluid.
Downwind turn is a myth! Attitude plus power equals performance.
Last edited by kmeyers; 09-13-2015 at 02:57 PM.
09-13-2015, 03:43 PM
#1574
I'll type this slow so you can understand, you land into the wind to shorten the ground roll. PERIOD.
09-13-2015, 06:24 PM
#1575
One thing that guys who say that wind has no effect on airspeed keep forgetting is that aircraft have MASS, and anything with MASS has inertia. Inertia is with respect to the earth (i.e., the ground) NOT the air.
Read this: http://macsblog.com/2014/02/turns-wind-and-airspeed/
To quote from it:
"But there are many pilots who simply refuse to believe that turning an airplane in a breeze also changes inertia and thus causes at least momentary change in airspeed."
...
"In a rapid turn an airplane can change the wind from a headwind to a tailwind and inertia demands an adjustment to bring the airspeed back to equilibrium. The adjustment can be a brief loss of airspeed, or an exchange of altitude to regain airspeed when the turn converts headwind into tailwind."
BTW, J Mac McClellan probably has more flying experience than everyone on RCU - he definitely has more experience writing about flying and issues therein...
Now who here thinks that a model Piper Cub flying into the wind with zero ground speed doesn't have a change in inertia when executing a 180 degree turn to downwind?
Again quoting Mac:
"So does it matter if you turn quickly from a headwind to a tailwind? Yes. At least a little. Inertia requires the airplane to accelerate relative to the ground to regain the previous airspeed it had when flying into a headwind. The mass of the airplane, the rate of turn, and the strength of the wind all are factors in how much the turning airplane must accelerate to maintain airspeed in the new wind. For most airplanes the wind caused change of airspeed in a turn will be too small to notice. But it’s there, and if an airplane is operating too near its minimum airspeed the change may be enough to matter."
Bob
Read this: http://macsblog.com/2014/02/turns-wind-and-airspeed/
To quote from it:
"But there are many pilots who simply refuse to believe that turning an airplane in a breeze also changes inertia and thus causes at least momentary change in airspeed."
...
"In a rapid turn an airplane can change the wind from a headwind to a tailwind and inertia demands an adjustment to bring the airspeed back to equilibrium. The adjustment can be a brief loss of airspeed, or an exchange of altitude to regain airspeed when the turn converts headwind into tailwind."
BTW, J Mac McClellan probably has more flying experience than everyone on RCU - he definitely has more experience writing about flying and issues therein...
Now who here thinks that a model Piper Cub flying into the wind with zero ground speed doesn't have a change in inertia when executing a 180 degree turn to downwind?
Again quoting Mac:
"So does it matter if you turn quickly from a headwind to a tailwind? Yes. At least a little. Inertia requires the airplane to accelerate relative to the ground to regain the previous airspeed it had when flying into a headwind. The mass of the airplane, the rate of turn, and the strength of the wind all are factors in how much the turning airplane must accelerate to maintain airspeed in the new wind. For most airplanes the wind caused change of airspeed in a turn will be too small to notice. But it’s there, and if an airplane is operating too near its minimum airspeed the change may be enough to matter."
Bob
I have great respect for you, your modelling skills, (BVM F100F) and your general knowledge of aviation both model and full size. However, in this instance, you, and Mr McClellen are wrong. (or perhaps as we say in Australia ”having a lend of us”).
Jack is correct..
The Inertia of an object has nothing to do with the planet earth.. The definition of inertia; “is a bodies tendency to resist acceleration The tendency of a body at rest to remain at rest or of a body in motion to stay in motion in a straight line unless acted on by an outside force.
This article explains it nicely.
http://www.flyingmag.com/pilots-plac...d-turns-really
My Experiment. (as if we need another one!!)
- Take a constant state wind condition. (Pick your own wind strength, 25 knots will do).
- Add an air plane, in flight. C 172 will do.
- Put said airplane into a rate two turn (6 deg per second).
- Set throttle to maintain this turn at constant bank angle, constant air speed, and constant height.
- Freeze the controls, and throttle, so the turn continues indefinitely, maintaining height and speed in the moving mass of air.
- Continue this turn indefinitely.
The plane is now in a stable condition, completing a360 deg turn once every 60 seconds. (albeit drifting in the direction the wind is blowing.)
As the plane completes each lap, you will not see the plane “zoom” as it turns towards the wind direction. You will not see the plane “sag” as it turns away from the wind direction. There is no momentary "sag" in airspeed as the plane turns away from the wind direction, while it’s inertia catches up.. And there is no excess of inertia causing a "zoom" as it turns toward the wind direction.
With controls locked, the plane will happily circle at constant airspeed/height all day, until fuel runs out!!
Roger