The downwind turn myth

Tools said:
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Hafta admit, rule 21 caught me off guard, guess I gotta quit doing that… hmmm.

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Was reading a book about Billy Mitchell. Apparently the early Army pilots wore spurs as part of their uniform. But, the spurs damaged the aircraft so they were banned in the cockpit.
 
FastEddieB said:
I’ve heard of headwind/tailwind affecting engine cooling and trim, as well.
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I had a copilot tell me that the reason the oil temp was higher on the right engine was because the crosswind from the left was blanked out by the fuselage (in cruise flight.)

Same copilot told me that a”classic warm front” comes south out of Canada and builds a solid line of thunderstorms above 50,000 feet.
 
There’s a book called “Contact Flying” by Jim Dulin. A lot of you know-it-alls would benefit from reading it. Learn something. Learn that you really don’t know everything there is to know.

Grow, or stay small.
 
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Velocity173 said:
Doesn’t have to be climbing or descending but sure, you can get wind shear with a change in altitude (inversion layer). As far as the myth you describe, I’ve never heard of this being widespread. If someone believes that, they need to call their CFI and get a refund on their training.
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The myth was more common thirty years ago when I became a pilot.
 
There is never a mention of the large change in potential vs. kinetic energy when turning directly into a headwind OR downwind.

There is horizontal acceleration happening, but not in the airmass.
 
The myth was more common thirty years ago when I became a pilot.
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The myth was more common forty years ago when I first got on the Internet….

Ron Wanttaja
 
IK04 said:
There is never a mention of the large change in potential vs. kinetic energy when turning directly into a headwind OR downwind.
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Kinetic energy is not useful for this analysis, because the answer you get depends on an arbitrary selection of which inertial reference frame you're going to use for the calculation. If you choose the air mass as your reference frame, then you would have to calculate kinetic energy using airspeed, which is not affected by the direction of the turn. If you choose the ground as your reference frame, then you would have to calculate kinetic energy using ground speed, which is affected by the direction of the turn.

There is horizontal acceleration happening, but not in the airmass.
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Not true. Acceleration is a change in the velocity vector, which is a measure of both speed and direction. Consequently, changing direction without changing speed DOES require acceleration.
 
Stewartb said:
There’s a book called “Contact Flying” by Jim Dulin. A lot of you know-it-alls would benefit from reading it. Learn something. Learn that you really don’t know everything there is to know.

Grow, or stay small.
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Other than, “nobody’s as smart as me, because I wrote the book,” what does he say that the know-it-alls here would disagree with?
 
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IK04 said:
There is never a mention of the large change in potential vs. kinetic energy when turning directly into a headwind OR downwind.

There is horizontal acceleration happening, but not in the airmass.
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Interesting. Is there an instrument in the plane, like a sensitive g-meter, that could measure that? Could a pilot feel that via his seat-of-the-pants?

Stipulated that in hypothetical 360° turns at 50kts into a 50kt wind, there is “horizontal acceleration” going on as the plane goes from 100 kts to 0 kts and back again repeatedly. But that’s only relative to the ground, not the airmass the plane is flying in. I still hold that without some reference to the ground, one cannot tell what the wind is doing.

But physics is not my strong suit, so please set me straight if I have something wrong here.
 
The kinetic energy would only matter if you hit the ground. Otherwise, it doesn't exist.
 
Hang 4 said:
The kinetic energy would only matter if you hit the ground. Otherwise, it doesn't exist.
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Exactly. I was just in the process of composing an example.

Approach speed is 50 kts. You know you have a flat nosewheel tire. You approach a runway with a 50 kt direct headwind. As you touch down, you have zero groundspeed or kinetic energy relative to the ground and have zero damage.

Now try it under the same conditions with a tailwind. Ouch!

But none of this came into play until the moment of ground contact. And the downwind turn myth and the other examples given of bad thinking are referring to an aircraft in flight. There, the ground is no longer the frame of reference. Obviously.
 
I have a theory on the myth. It's not about aerodynamics at all. It's about pilot perception at low altitude. An inexperienced pilot makes a turn from a strong headwind to a strong tailwind. The increase in groundspeed leads to a visual sensation of increased speed and even a dive. The pilot pulls back hard on the stick to stop the dive and induces a stall. "It must have been the wind!" gets put out there as the explanation.
 
midlifeflyer said:
I have a theory on the myth. It's not about aerodynamics at all. It's about pilot perception at low altitude. An inexperienced pilot makes a turn from a strong headwind to a strong tailwind. The increase in groundspeed leads to a visual sensation of increased speed and even a dive. The pilot pulls back hard on the stick to stop the dive and induces a stall. "It must have been the wind!" gets put out there as the explanation.
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That’s pretty much it, except that it’s perpetuated by experienced pilots as well.
 
MauleSkinner said:
Because of visual perceptions and Pilot reactions, not simply airspeed change due to turning downwind.
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Not just because of visual perceptions. It’s because of lateral obstructions, close proximity to the ground and the affect of the vertical wind gradient on turn radius. Downwind turns add a big variable in a situation that has very small margin.

This conversation is turning into an apples and oranges situation.

The level flight constant airspeed downwind turn is obviously safe. The is also no impact on airspeed. What does change is ground track.

In the low level world we often have to fly a very specific ground track to avoid hitting things. There is also almost always a vertical component to the turns exposing us to shears.

two completely different conversations.

Pilots with experience low level caution new pilots about downwind turns because it’s vital to account for the winds affect on ground track when planning the turn. If it’s not considered then it’s very easy to setup a scenario where the ground track is actually not achievable. While it’s easy to call this a “perception” problem it’s also a “I don’t want to hit the cellphone tower problem.”
 
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Kinetic energy (= mass * velocity squared) depends on latitude because your actual speed varies with latitude. If, for example you are flying at 100 knots eastward over Kennedy Space Center (at 28.59 degrees), your velocity would be 100 + cos(28.59°) × 904.1 knots = 893.84 knots (904.1 is the tangential velocity of the earth at the equator). If you wanted to fly westward, you would be going backwards at 693.84 knots. This is why so many aircraft are lost in the Bermuda triangle.
 
Dan Thomas said:
… Gravity only works in the vertical. It cannot affect you laterally…
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Not exactly true… to wit:

5A34D25C-609E-407F-B819-D4D128F95978.png

See definition #2.

Hehe, in case you’re wondering how I found something so arcane, I happened to coin this term. Never knew it had been inserted into the urban dictionary until now! It’s named after my good friend Keith Rucker. Glory days!
 
Tarheelpilot said:
This conversation is turning into an apples and oranges situation.
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Unfortunately this conversation almost always turns into apples and oranges. Also unfortunately, apples is a knowledge building block that needs to be understood before oranges can be applied properly.
 
Tarheelpilot said:
Not just because of visual perceptions. It’s because of lateral obstructions, close proximity to the ground and the affect of the vertical wind gradient on turn radius. Downwind turns add a big variable in a situation that has very small margin.

This conversation is turning into an apples and oranges situation.

The level flight constant airspeed downwind turn is obviously safe. The is also no impact on airspeed. What does change is ground track.

In the low level world we often have to fly a very specific ground track to avoid hitting things. There is also almost always a vertical component to the turns exposing us to shears.

two completely different conversations.

Pilots with experience low level caution new pilots about downwind turns because it’s vital to account for the winds affect on ground track when planning the turn. If it’s not considered then it’s very easy to setup a scenario where the ground track is actually not achievable. While it’s easy to call this a “perception” problem it’s also a “I don’t want to hit the cellphone tower problem.”
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Maybe, but I don't see it used as a "caution," as in "be aware that you may have a visual illusion at low altitude when turning from upwind to downwind in strong winds." It's more often used as if it's an aerodynamic danger zone.
 
Are you saying we need to get to the core of the matter before peeling superficial layers?
 
Tools said:
Are you saying we need to get to the core of the matter before peeling superficial layers?
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I’m not sure that’s what I’m saying, but it sounds erudite enough that people might think I’m more photosynthesis than I actually am. ;)
 
Capt. Geoffrey Thorpe said:
Kinetic energy (= mass * velocity squared) depends on latitude because your actual speed varies with latitude. If, for example you are flying at 100 knots eastward over Kennedy Space Center (at 28.59 degrees), your velocity would be 100 + cos(28.59°) × 904.1 knots = 893.84 knots (904.1 is the tangential velocity of the earth at the equator). If you wanted to fly westward, you would be going backwards at 693.84 knots. This is why so many aircraft are lost in the Bermuda triangle.
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That analysis is based on an inertial reference frame located at the center of the Earth. It would be just as valid to base the analysis on an inertial reference frame located at the center of the Sun, or at the center of the galaxy. Each of those would give wildly different results.

Here is a more accurate definition of kinetic energy [emphasis added]:

"In physics, kinetic energy is the energy an object has due to its motion. It is defined as the work required to accelerate a body of a given mass from rest to a certain velocity. Once the mass reaches the velocity, its kinetic energy remains unchanged unless its speed changes. However, velocity and thus kinetic energy depend on the frame of reference. In other words, an object’s kinetic energy is not invariant."​

https://sciencenotes.org/what-is-kinetic-energy-kinetic-energy-examples/
 
midlifeflyer said:
Maybe, but I don't see it used as a "caution," as in "be aware that you may have a visual illusion at low altitude when turning from upwind to downwind in strong winds." It's more often used as if it's an aerodynamic danger zone.
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Well that’s the neat thing about anecdotal evidence, it’s generally meaningless.

I’ve only seen the “downwind turn” discussion in the context of a caution in an appropriate setting based on accurate knowledge of what is happening. As opposed to your experience where it’s always someone talking out of their ass.

I only replied to this thread to highlight the fact that every time someone says something about downwind turns they are not necessarily talking out of their ass.
 
Would this summary be correct in a steady wind (i.e., barring things like gusts, wind shear, updrafts, and downdrafts)?

When performed as a ground-reference maneuver, the direction of turn relative to the wind can affect the risk of a stall, depending on how the pilot handles the controls.

When performed at a specified attitude and power setting, the direction of turn relative to the wind cannot affect the risk of a stall.​
 
Palmpilot said:
Would this summary be correct in a steady wind (i.e., barring things like gusts, wind shear, updrafts, and downdrafts)?

When performed as a ground-reference maneuver, the direction of turn relative to the wind can affect the risk of a stall, depending on how the pilot handles the controls based on visual perception or not properly accounting for increased turn radius requirements.

When performed at a specified attitude and power setting, the direction of turn relative to the wind cannot affect the risk of a stall.​
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I would add what I added ;) and maybe change “stall” to a more generic “aerodynamic upset.”
 
Palmpilot said:
That analysis is based on an inertial reference frame located at the center of the Earth. It would be just as valid to base the analysis on an inertial reference frame located at the center of the Sun, or at the center of the galaxy. Each of those would give wildly different results.

Here is a more accurate definition of kinetic energy [emphasis added]:

"In physics, kinetic energy is the energy an object has due to its motion. It is defined as the work required to accelerate a body of a given mass from rest to a certain velocity. Once the mass reaches the velocity, its kinetic energy remains unchanged unless its speed changes. However, velocity and thus kinetic energy depend on the frame of reference. In other words, an object’s kinetic energy is not invariant."​

https://sciencenotes.org/what-is-kinetic-energy-kinetic-energy-examples/
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This is similar to the old arguments about the gyroscope and with what is its rigidity referenced to. It is rigid in space, of course, which is why we see our mechanical heading indicators display apparent precession as the earth turns. But so many think it's the earth.
Foucalt's Pendulum works like a gyroscope. Inertia in space. https://www.smithsonianmag.com/smit...aults-pendulum-prove-earth-rotates-180968024/
 
Bottom line is that Doug and Martin chose so do a video about the downwind turn myth, and limited their discussion to the myth. They could have published a doctoral thesis on downwind turns, and somebody would still say they missed the fact that an AOA with a blue donut indicates a different color than an AOA with a green donut.

But does anyone really believe that a pilot with extensive experience in low altitude flying, often under the direct observation of the FAA both for waivers and operationally, with pretty rigid boundaries, doesn’t understand the whole picture?
 
MauleSkinner said:
But does anyone really believe that a pilot with extensive experience in low altitude flying, often under the direct observation of the FAA both for waivers and operationally, with pretty rigid boundaries, doesn’t understand the whole picture?
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No. But what percentage of PPLs would those pilots be?

Never underestimate ignorance. It's everywhere, even in flying. The stupid numbers of carb ice accidents prove it.
 
Dan Thomas said:
No. But what percentage of PPLs would those pilots be?

Never underestimate ignorance. It's everywhere, even in flying. The stupid numbers of carb ice accidents prove it.
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So have the ignorant pilots watch the video until they understand the content. Then give them the additional info in bite-size chunks that can be understood.

“memorize Aerodynamics for Naval Aviators before your first lesson” isn’t going to be effective for the vast majority, either.
 
Dan Thomas said:
No. But what percentage of PPLs would those pilots be?

Never underestimate ignorance. It's everywhere, even in flying. The stupid numbers of carb ice accidents prove it.
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I don’t think I’ve ever met anyone who actually believed in the downwind turn IAS myth. If you did a poll on POA that percentage would be small…at least I would hope so.
 
Velocity173 said:
I don’t think I’ve ever met anyone who actually believed in the downwind turn IAS myth. If you did a poll on POA that percentage would be small…at least I would hope so.
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I have met several. I won’t guess at percentages, but there is a significant population IMO.
 
I'm not even near the smartest guy in the room and I thought this was just common sense ...
 
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Palmpilot said:
Kinetic energy is not useful for this analysis, because the answer you get depends on an arbitrary selection of which inertial reference frame you're going to use for the calculation. If you choose the air mass as your reference frame, then you would have to calculate kinetic energy using airspeed, which is not affected by the direction of the turn. If you choose the ground as your reference frame, then you would have to calculate kinetic energy using ground speed, which is affected by the direction of the turn.
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I was referencing potential energy (mass). What other frame of reference is there besides the earth and ground speed?

Palmpilot said:
Consequently, changing direction without changing speed DOES require acceleration.
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Isn't that what I said?
 
Hang 4 said:
The kinetic energy would only matter if you hit the ground. Otherwise, it doesn't exist.
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If two objects of equal mass (airplanes) were traveling in opposite directions at the same airspeed, one with zero groundspeed and the other with 40 knots groundspeed and they collided head on, would the resultant impact favor the object with the greater release of kinetic energy (mass * velocity squared)?
 
IK04 said:
If two objects of equal mass (airplanes) were traveling in opposite directions at the same airspeed, one with zero groundspeed and the other with 40 knots groundspeed and they collided head on, would the resultant impact favor the object with the greater release of kinetic energy (mass * velocity squared)?
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The pointier one would probably do better than the blunt one. ;)
 
IK04 said:
I was referencing potential energy (mass). What other frame of reference is there besides the earth and ground speed?



Isn't that what I said?
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It's possible that I misunderstood your post.
 
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