All Comments
Due to friction and boundary layer considerations, the speed of the wind at the surface can be considerably less than the speed of the wind at altitude. According to research, this gradient of wind speed can vary considerably, with steady state wind speed being attained at as high as 2000 feet agl over rough terrain (hills, urban areas) or as low as several hundred feet (over water and smooth surfaces). (See the work by pioneering wind engineer Alan Davenport at his Boundary Layer Wind Tunnel Laboratory.)
An aircraft departing on downwind can therefore climb into a progressively increasing tailwind. A gradual ascent, with a higher airspeed, will minimize the effect of this change of airspeed on control, and allow a safe margin above stall speed. A steep ascent, near stall speed, can actually lead to an inadvertent departure stall, if the wind gradient is severe enough. (In the extreme, think of a severe wind shear of, say, 50 kts occurring at a very specific altitude. Most light aircraft would inevitably stall as they ascend through the shear, going from an IAS of, say, 80 kts to an IAS of 30 knots, essentially instantaneously.)
With a steady state wind, with no wind velocity gradient variation with altitude, the stall induced by a co-ordinated turn turning crosswind to downwind (or durning any co-ordinated turn) is indeed a myth. However, a steady-state wind, blowing with the same velocity at altitude as it does at the surface, is likewise a myth.
In the final analysis, both Peter Garrison and the NTSB can be correct - Peter with a steady wind at altitude, and the NTSB when in close proximity to the ground, with a wind velocity gradient present. And in the NTSB's defense, most crashes do occur in close proximity to the ground...
Fine, but in the quoted reports, the NTSB is blaming a turn downwind, not a climb into a tailwind. You'd think if the culprit was severe windshear, then the report would say so. I agree with Robert that the way the reports cited above are written, they cannot be correct.
I have never seen wind shear cited as the probable cause during takeoff and climb, but it is entirely possible. I think the inspector is correct, but unfortunately did not make it clear that he was discussing wind shear.
desmdpc - Your explanation provides one example of how a change in wind direction and/or speed can change the relative wind and wing airspeed. We all understand that bad things can happen if the change is great enough to reduce the airspeed below the stall speed, especially in less stable designs. I don't think anyone would disagree with what you say.
Robert - The NTSB case, "The sudden change from a 24-knot left crosswind to a 24-knot tailwind during the pilot’s execution of the right-hand turn . . . most likely induced an aerodynamic stall . . . .” seems like a perfect example of that unarguable fact. I have broken the crest of a forested ridge on more than one mountain takeoff only to see a 10 kt headwind turn into a 15 kt. tailwind. Heavily loaded, I'm still climbing at 80 kts ground-speed but my airspeed drops from 90 kts to 65 kts. Had I been flying an unstable design, a stall/spin might have followed on one of those occasions. My aircraft's design just sinks but there is not doubt that it loses net lift (still wingtip control) and sinks straight down. What am I missing in your explanation? Garrison's case seems like a straw man argument.
Peter Garrison's makes a perfectly valid argument, as a physicist I can vouch for it. Once you are in the air there is no such thing as head or tail wind, at least not from the aircraft point of view. The absurdity of talking about head/tail wind during such a turn reminds of reading thousands of foolish comments on the internet about why aircraft can't take off from a moving conveyor belt (the famous puzzle). If you cross a mountain ridge and there are wind shears (because of altitude or time change) that's a different story but in a perfectly steady wind field the aircraft can't sense any head or tail wind, it is a pure lunacy to argue otherwise.
Every pilot has noticed that quick drop in indicated airspeed while descending into the last fifty feet or so above the ground on approach. Moving from the steady state wind down into the turbulent wind just above the ground, where everything from buildings to trees to big vehicles roils the surface winds. Likewise, on climb out I've often seen the IAS value increase once out of the surface air layer.
Enough wind shear in a short distance can be a challenge for any pilot. If the surface wind and wind at 300 feet changed from upwind to downwind, that's as much as 40 knots of wind shear.
The T-6 appears to have begun turning left at very low level with an increasing bank angle, a recipe for an accelerated stall/spin and an out-of- control crash. Had the T-6 pilot simply climbed to a safe distance —500-1000 AGL — before turning, I doubt this accident would have happened.
The 172's pilot attempted a crosswind landing in conditions well beyond the manufacturer's recommended limit, with a c of g over 2" aft of the rear limit. In that condition the 172's stick force per G decreases, while pitch and roll control becomes increasingly light. Those two factors make it much easier to stall, regardless of the direction the wind is moving at any instant. Then the pilot appears to have lost control after abandoning the landing just 300 feet AGL, probably by not maintaining enough indicated airspeed to prevent a stall that may have been unrecoverable at that low altitude.
In both cases, the pilots appear to have lost control of perfectly running aircraft.
I agree with Goyer, and Garrison, that this downwind turn stuff is nothing but an urban myth, something accident investigators have no business using to explain crashes that appear to be direct results of poor pilotage and inattention to aircraft loading procedures and c of g calculation.
Douglas M
Surrey, British Columbia
He didn't do this near the ground, did he?
Unless you are flying like Michael Goulian , you can not turn a GA airplane 90 degrees quickly enough to change directions, relative to the wind, to have any affect as described in this "down wind turn" scenario.
Sounds like the investigator has never been in a GA aircraft, let alone has any concept of what happens to an airplane in the air after it makes the transition from rolling down the runway to flying in the air.
Or perhaps he has been spending too much time at the airport hangar flying with the Sunday circlers.
The issue with the downwind turn is very real. However, the doubters are going to have to look at things from a different angle.
The turn to downwind at low altitude causes the illusion of increasing airspeed (in fact it is only ground speed that is increasing). It is not uncommon for pilots to "correct" for this perceived airspeed increase by pitching the nose up.
It is this incorrect reaction, be it deliberate or reflex, that can lead to dangerously low airspeeds and departure stall accidents.
A change of the wind direction or speed with position (be it vertical or horizontal) or time is called windshear.
In both of this accidents, it is possible that an increase in tailwind as they climbed out of the ground boundary layer could have been a factor.
That, however, is "climbing into an increasing tailwind", and not turning downwind.
The very real "climbing into an increasing tailwind" that can be found after take-off is equivalent to the "descending into a diminishing headwind" on approach and landing. And as much as you can encounter an increasing tailwind when turning (and climbing) after take-off, you can also encounter a diminishing headwind when turning (and descending) into final, with equal aerodynamic implication, dangers and possible consequences. However, the "headwind turn" lacks the charm of the "downwind turn", and has never reached the myth level.
The reason from that, is that anybody taking as a frame of reference something other than the air itself (for example, someone standing on the ground) can clearly feel the wind in the face turn into a wind in the back as one turns 180°, and then wrongly extrapolate that effect to an airplane that is flying about the AIR itself, where the relative wind speed is always the airspeed and the relative wind direction is always straight headwind +/- slip angle (which is zero in coordinated flight), regardless of what's the speed and direction of the air about the ground (i.e, the wind).
That wrong extrapolation leads to think that one would face an airspeed reduction when turning downwind, which can lead to a stall, but an increase in airspeed when turning headwind, which would never lead to a stall. But both are wrong. The plane doesn't change its airspeed in a turn as a result of its change in direction relative to the wind.
The second report is particularly clear with the mistake: "The sudden change from a 24-knot left crosswind to a 24-knot tailwind during the pilot’s execution of the right-hand turn towards the downwind leg of the landing pattern [...] most likely induced an aerodynamic stall".
The investigator talks about a wind that was always 24 knots, and where supposed change of direction (from crosswind to tailwind) was not the result of a change in the wind itself, but of the aircraft turn. Make no mistake: as viewed from the plane (and sensed by the wings), the wind always comes from the same direction: 100% headwind (as long as it's in coordinated flight).
It's crystal clear that the investigator, in this case, had no intention of talking about a climb into an increasing tailwind, but instead fell in the trap of the mythical and non-existent "downwind turn" stall.
Bbgadzos, it would seem that if the NTSB meant to that the pilot slowed the aircraft due to the illusion of speed (while ignoring attitude and the ASI), then they should have said so. It would have been much more informative. And it would have provided a clear object lesson: fly the wing.
The "myth of the downwind turn" is a myth for the airplane and concerns indicated airspeed (what high flying pilots use to indicate whether they are flying or not.)
The reality of the downwind turn problem concerns ground speed and is of great concern to contact flying pilots at low AGL altitude in maneuvering flight. When spraying a field, we always work crosswind and make repetitive swath runs from the downwind border to the upwind border. Coming out of a swath run, we turn downwind first so that we can make the somewhat greater than 180 degree return to the next swath row fifty feet upwind with an upwind base to final turn. Turning upwind first, with a wind greater than five knots, would not allow a ground track that would keep us in sight of the target (next swath row, runway, whatever) and allow the angle of bank necessary to hit or overfly that target. The greater angle of bank necessary to maintain the required ground track at the greater ground speed of a downwind condition would much more likely cause a mush and eventually a stall.
The same physical problem, increased ground speed requiring a greater angle of bank, occurs on every crosswind landing when we allow intimidation to cause us to make a pattern ending in a downwind base to final turn. There is no regulation preventing good wind management at non-controlled airports. The airplane doesn't care which way you make base to final. It is fine with landing well downwind of the runway following a down wind base to final turn (using the same angle of bank as would be used on the upwind base to final turn.) The problem is that the pilot really wants to land on the runway, so he will bank more in the downwind turn to get there.
There need be no fight about "the myth of the downwind turn." Instrument flight, other than beyond the MAP on a non-aligned approach, involves no downwind turn problem. It is a myth. Contact flight (using no instrument) at low altitude (crop dusting, bush, pipeline patrol, takeoff and landing) requires wind management to control excessive ground speed mitigation of our ability to hit targets and miss obstructions. Not all landing sites (airports, spray strips, bush strips, forced landing fields, etc.) have obstruction and terrain free approaches. It is easier to hit what we want to hit and miss what we want to miss (on the ground) at a slower ground speed. Call it the "reality of the downwind turn."
And yes, it does show up in incidents and accidents. Some us live in a maneuvering flight mode for every hour of every flight. All of us go there when we takeoff and land.
I tell all my crop duster and pipeline patrol students, however, "When he comes out of his aircraft showing teeth rather than a wagging tail, always say, 'you're probably right.' Just keep repeating, "you're probably right" until he shakes his head and walks away." Concerning an aircraft that is high and piloted by one totally unconcerned with the earth below, you are right.
I can remember my instructor talking about relative wind;the only thing that matters after the airplane leaves the ground. He would always add a comment about wind gusts ,especially from the rear , and the deteriorating affect on airspeed.Maybe the assumption could be made that a sudden burst of air from the rear as part of a downwind track could bring on a stall , if everything else remains the same.
I can understand the reasoning that if the plane is moving through the air at a certain speed that a turn downwind should only increase ground speed and not decrease airspeed, especially when the plane is under power. I've had my ticket for 25 years and have flown models for about 40 years and I have observed models losing altitude on an abrupt turn to down wind many times. Also I have seen models that are dead stick and close to stall speed drop from the sky when they turn down wind. Perhaps full scale aircraft in a steep climb experience more prop cavitation on the turn and that contributes to a decrease in thrust that makes the change in relative wind more critical especially with a high wing loading, high pressure altitude, and increased stall speed because of the banked wing.
Sorry, but the crosswind to downwind turn risk is real. Believe the NTSB on this one. Thinking only in terms of airspeed means you're neglecting the inertia of the airplane, which is relative to the ground. While the planes airspeed can change almost instantly by pointing the nose in a different direction, the ground speed changes relatively slowly (how slowly is a function of thrust to weight). Say an airplane is flying a crosswind leg at 70 knots in a 24 knot crosswind. The ground speed will be roughly 70 knots. Now the pilot turns downwind. The airplane will continue a ground track of 70 knots, but the airspeed has dropped to 46 knots at the end of the turn. The airplane will begin to accelerate and will get back to an airspeed of 70 knots, with a ground speed of 94 knots. But it doesn't happen instantly, and this window is where a plane may be more prone to a stall.
chuckyvt, sorry but your comment is absolutely wrong. And that's not an opinion. It's Physics.
Saying that "the inertia of the airplane is relative to the ground" is wrong. The inertia of the airplane is the same in any inertial frame of reference. If the ground can be considered an inertial frame of reference, then any other frame of reference that moves at a constant speed (constant in direction and magnitude) relative to the ground is an inertial frame of reference too. And with a steady wind, no matter what direction and how strong, the air is moving at a constant speed about the ground and hence it is an inertial frame of reference too.
But maybe an example will make that simpler to understand.
Say that you have an airplane flying East (x-axis) at 100 knots and makes a 180° turn to the West. Let's say that the turn takes 10 seconds (just because 10 is a nice number to make calculations, but you can take any other turn rate you like). Let's make an hypothesis that, no matter how much wind in the x-axis (West-East), the airspeed remains constant, and let's see what happens.
In the first case, let's consider that there is no wind.
The airplane starts with an airspeed of 100 kts East and ends with an airspeed of 100 kts West.
The change in airspeed in the West-East axis is 200 knots, which in 10 seconds means 20 knots per second (average) in this axis.
Since there is no wind, the ground speed also starts at 100 knots East and ends at 100 knots West. Again a change of 20 knots per second.
Second case, lets consider that the plane is initially flying with a tailwind of 20 knots and turns into the wind.
The airplane again starts and end with an airspeed of 100 knots but in opposite directions in the West-East axis, so that's again a change of 200 knots in 10 seconds, or 20 knots per second.
The ground speed, on the other hand, starts at 120kts East (100kts of airspeed + 20 kts of wind) and ends at 80kts West (100kts of airspeed - 20kts of wind) . Again a change of 200 kts in 10 seconds.
Finally, let's consider that it's initially flying with a headwind of 90 kts and turns downwind.
Again the airplane starts with an airspeed of 100 knots East and ends with an airspeed of 100 knots West for a total change of 200 kts in 10 seconds.
The ground speed, on the other hand, changes from 100-80=20kts East to 100+80=180kts West, again for a total change of 200knots in 10 seconds in that axis.
So as you see, assuming that the airspeed doesn't change leads to conclude that the change in airspeed and ground speed are the same, and that this holds true regardless of the wind. That the change in air and ground speeds is the same in the same amount of time, means that the acceleration about the air and about the ground are the same, showing that the inertia is equally present in both frames of reference.
Because these are all reversible conditions, the implication also works in the other way: assuming that the inertia is the same in both cases leads to conclude that the change in airspeed is the same than the change in groundspeed, regardless of the wind. And because we know that the change in airspeed is twice the airspeed when there is no wind (the magnitude does n0t change but the direction is the opposite), then with any wind you must find exactly that same change in the airspeed and groundspeed.
Now, no matter from what end we start, we start from an assumption: either that the airspeed doesn't change in the turn, or that the inertia is the same in both frames of reference. Can we rely on those assumptions?
Yes.
As you probably know, the second Newton's law of motion states that F = m x a.
To begin with, the mass of the airplane is the same in any frame of reference (even in non-inertial ones).
But, what is the force that makes the speed change 200 kts in 10 seconds, in all of the examples above?
It's the lateral component of the lift (the lift is tilted when the airplane banks and there is a lateral component of the lift).
The rate of turn is given by the airplane's airspeed and the bank angle. Since in all of the examples above the airspeed was the same and the turn took the same time (hence the same rate of turn), then the bank angle must have been the same.
Since the bank angle was the same, and the lift was the same in all cases (because the vertical component of the lift had to cancel the airplane's weight which was the same in all cases), hence the lateral component of the lift was the same in all cases.
Now, because the lateral component of the lift was the same and the mass of the ariplane was the same in all the cases, then the acceleration HAD to be the same in all the cases. And this holds true for the acceleration about the air and about the ground.
Not only is that consistent with the hypothesis of the inertia being the same in both frames of references (about the air or about the ground), but also (and not surprisingly, because one implies the other and vice-versa) with the result of the same change in speed of 200kts in 10 seconds, be it about the air or about the ground, and with any wind (as long as it is constant).
The amazing part of this article is the number of people and possibly 'licensed' pilots who are trying to argue the validity of this myth. To those who claim this is a valid concern, answer me this. I filled an empty 16 ounce glass with 8 ounces of ice then top off the glass with water. When the ice that is floating above the rim of the glass melts, how much water will overflow the glass ?
If that question stumps you, maybe this will be easier. What is heavier, a pound of lead or a pound of feathers ?
Enquiring minds want to know.
There is a good discussion of this topic in the forum section on this site. http://www.flyingmag.com/forums/technical/turning-upwind-down-wind-and-a...
And holy cow chuckyvt really needs to review some basic theory on this topic. I sure hope it is a joke.....
Mark in Idaho: a pound of lead weighs more than a pound of feathers if the masses are the same. the feathers weight less due to their buoyancy resulting from the volume of air it displaces- for the same reason a pound of feathers would float in water while a pound of lead would obviously sink. This of course does not include the effect of the solar torque force or time dilation due to density differences.....:)
The Palm, Prop Cavitation? This is air, not water. Air does not boil at low pressures. And losing altitude in a turn is a result of pilot error alone and nothing at ALL to do with wind direction. (Wind shear is another topic altogether) Ground speed picks up in a turn to downwind, so an inexperienced pilot may look out the window and notice a faster than normal GS and pull up, reducing airspeed. But that is it. There is no inertial change, no IAS change, no AOA drop, nothing. A turn is a turn is a turn, as long as it is coordinated. In this case, the NTSB report is flat out wrong.
Some of those accidents sound more like poor piloting technique to me.
Quoting from 'Win Your Wings' copyright 1941, authored by Colonel Roscoe Turner and Jean DuBuque, page 230. "Reverting to my earlier interposition, regarding airspeed relative to groundspeed, it will be observed, during downwind turns close to the ground, that when the plane is approximately crosswind, it seems to suspend momentarily without speed and as the turn is completed to the downwind course, the ship seems to gain speed with a rush, resulting in misapprehension of the actual airspeed on part of the novice pilot. Bear in mind that these seeming actions are purely optical illusions caused by watching the ground even though the pilot may not be directing his full attention toward it. Only the speed relative to the ground is affected, whereas the airspeed remains constant. For example, assume you are flying "on instruments," that is, without visual reference to any ground object. How do you know which way is upwind, downwind, sidewind, or what have you? The airspeed, naturally, will not vary during a normal turn because the plane moves, when free of the ground, in relation to the air masses and not the earth (emphasis is the authors).
The authors continue; “Don’t misunderstand me, as I am not advocating use of the downwind turn, but I am endeavoring to clarify for you the principals involved, and to belittle the prevalent fallacy regarding this maneuver” (emphasis my own).
These authors seem to think a downwind turn can be a cause for an accident as does the NTSB, but for reasons of human factors not physics. Turner and DuBuque finish the discourse this way on page 231;
“ Since the optical illusion, resulting from indirect observation of the ground, after the completion of the downwind turn, has a definite bearing on the reactions of the in-expert pilot or poorly trained pilot, let me admonish you to refrain from believing your has increased and from attempting to force the plane into a steeper climb” (emphasis is the authors).
this is a corrected repost;
Quoting from 'Win Your Wings' copyright 1941, authored by Colonel Roscoe Turner and Jean DuBuque, page 230. "Reverting to my earlier interposition, regarding airspeed relative to groundspeed, it will be observed, during downwind turns close to the ground, that when the plane is approximately crosswind, it seems to suspend momentarily without speed and as the turn is completed to the downwind course, the ship seems to gain speed with a rush, resulting in misapprehension of the actual airspeed on part of the novice pilot. Bear in mind that these seeming actions are purely optical illusions caused by watching the ground even though the pilot may not be directing his full attention toward it. Only the speed relative to the ground is affected, whereas the airspeed remains constant. For example, assume you are flying "on instruments," that is, without visual reference to any ground object. How do you know which way is upwind, downwind, sidewind, or what have you? The airspeed, naturally, will not vary during a normal turn because the plane moves, when free of the ground, in relation to the air masses and not the earth (emphasis is the authors).
The authors continue; “Don’t misunderstand me, as I am not advocating use of the downwind turn, but I am endeavoring to clarify for you the principals involved, and to belittle the prevalent fallacy regarding this maneuver” (emphasis my own).
These authors seem to think a downwind turn can be a cause for an accident as does the NTSB, but for reasons of human factors not physics. Turner and DuBuque finish the discourse this way on page 231;
“ Since the optical illusion, resulting from indirect observation of the ground, after the completion of the downwind turn, has a definite bearing on the reactions of the in-expert pilot or poorly trained pilot, let me admonish you to refrain from believing your airspeed has increased and from attempting to force the plane into a steeper climb” (emphasis is the authors).
I hold Peter Garrison in high esteem, just short of godhood. He's the columnist I most look forward to reading every month in Flying. Nonetheless, I've always thought there was one aspect of the "downwind turn" that he is not taking into account: inertia. This is best seen with a powered model airplane turning circles in a breeze of even moderate speed. I had one such model years ago, which I flew in an open field with my son as chaser, retrieving the plane when the batteries ran down and the plane came down in some random location, oftentimes a several hundred yards away. Note that this was not an R/C airplane, just one that could be set to fly in circles.
Now here's the relevant part. As the plane would track around the circle and turn into the wind, it would climb aggressively for a short time then begin to level out. As the turn continued and the plane turned "downwind," it would lose altitude, sometimes precipitously. This was not just a one-time event, nor a phugoid oscillation, but predictable, and behavior I came to expect every flight. The stronger the breeze the more noticeable the climb/descend or stall behavior could be. The obvious explanation is that when the plane turned into the wind its speed relative to the surrounding airflow increased because of its inertia (or momentum, if you prefer that term). The plane, even as light as it was, could not decelerate instantly to maintain the same airspeed it had before turning into the wind; relative airspeed would increase, and the plane would climb. The reverse is true when turning quickly so that the wind comes aft fairly abruptly: the speed of the airplane relative to the airflow decreases fairly rapidly, and the inertia of the plane works against it accelerating instantly to maintain the airspeed it had a moment earlier in level flight, so the airplane descends or even stalls.
Yes, the airplane is traveling in a fluid medium, and in a steady state the airplane doesn't know or care how fast the air in which it is traveling is also moving over the ground. But hypothetically, if the wind was to instantly reverse direction, the speed of the airplane relative to the airflow would change by the same amount, and it would take time for the airplane to accelerate its inertia, so to speak, to restore the airspeed it had before the sudden airflow reversal. At slow airspeeds, this hypothetical situation would result in a stall until the airplane could accelerate its mass to the previous airspeed.
This is nothing more than classic wind shear. We all know that accidents are frequently attributed to sudden wind shear, e.g. a microburst, such that an airplane low and slow can be hit from behind by a sudden tailwind and is unable to accelerate quickly enough to prevent a stall and impact with the ground. So why is it not possible that the same phenomenon exists when a plane turns "downwind?" No, the situation would not be as dramatic as that induced by a microburst, but it would still be there. An abrupt, aggressive turn on climbout such that the airplane rapidly turns away from the prevailing wind is going to reduce airspeed to some degree for a short time. If climbing at Vx (already slow) and banking steeply, the stall speed could be lowered enough that the "downwind turn" could possibly precipitate an undesirable loss of altitude, maybe even a stall. Don't believe me? Go fly a model aircraft, even an R/C model, and try to fly level circles in a stiff breeze WITHOUT adjusting pitch as it circles.
From Gabriel: "Saying that "the inertia of the airplane is relative to the ground" is wrong. The inertia of the airplane is the same in any inertial frame of reference."
You are absolutely correct, any inertial frame of reference works. However since a traffic pattern is relative to the airport, reference to ground is important if the pilot wants to fly a correct pattern. When you turn into a 24 knot cross wind in an airplane moving at 70 knots airspeed, you will need to crab into the wind a few degrees to maintain a correct crosswind ground track relative to the airport. (Your ground speed will be 47 knots with a wind correction angle of -8 per the E6B simulator I just found online) Then when you turn downwind your groundspeed will still be roughly 47 knots with a tailwind of 24 knots for an airspeed of 23 knots. The airplane will accelerate back to an airspeed of 70 knots over a period of time but is at risk of stalling until it does so. Also, I do appreciate your well thought out response, instead of calling my previous post a joke, etc.
Fly a U-Control plane which always fly in a circle no matter the wind and you will experience a lot of down elevator when going into the wind,and a lot of up elevator when it goes downwind. The effect is less if the wing has a symetrical airfoil since then it is not as speed sensitive.
Try this experiment. Fly around under the hood with a safety pilot in a steady wind and see if you can tell when you are upwind/crosswind/downwind. I will bet any amount of money that with just a 6-pack of instruments and your "feel" you can not tell the difference.
When you are driving a boat in circles on a large moving river, can you feel the "acceleration" when going from upstream to downstream? Nope. There is no acceleration. Relative to the bank there is, but that is not a "felt" acceleration, just a perceived one. Your only frame of reference is the water, just as the air is while flying. (Substitute submarine for boat if you are about to argue that a boat is on top of the water and not in it....)
Inertia is not relevant to this discussion at all. The inertia of the aircraft through the air is CONSTANT as long as the TAS is constant, no matter what.
Would you hit the ground harder going downwind that upwind if you crashed? Yes, and that is a different, but interesting discussion in itself:)
Goyer and Garrison should be ashamed of spewing nonsense like this. Since they don't believe windshear is a problem, tell them to call the FAA to turn off the wind shear alerts. Oh, and don't bother adding extra speed on approach during gusty conditions since increasing tailwind (decreasing headwind) does not matter to them.
You got us. We're very ashamed of saying that thing we didn't say.
Now, if you believe that wind shear and the downwind turn are the same thing . . . then you need to read a bit more carefully. Sorry again for saying that gravity didn't exist. (or was it air?)
Let's just keep it simple kids. Go on out on a nice post cold front day with a nice north westerly flow in progress . Say 25 kts at 6000. Establish yourself In steady flight on a North west heading. Roll into a turn either way maintaing altitude and a constant bank. Once the airspeed stabilizes with constant pitch power and bank do you notice any airspeed gains or losses corresponding to particular headings ? Of course not.
Think about it.If we did, every time we changed course we would see a corresponding airspeed change while in cruse. And the greater the wind speed aloft the greater the airspeed changes would be. Up in the jet stream at flight levels where wind velocities can approach 180 kts the effect would have to be tremendous. Fortunately this effect does not exist.
Now if you want to talk about how sudden CHANGES in WIND velocity due to altitude gradients or gust fronts effect aircraft performance that's a different matter. But then as others have pointed out that would be " wind shear".
Not loss of performance due to turning in a particular direction.
Just my observations after 53 years and 27000 something hours of trying to keep the blue. " on top".
I do understand that wih a constant wind speed an airplane and its passengers wolud not differentiate if its downwind or crosswind except for the groundspeed. We've all learn this basic physics in school. I'd be more interested in learning why those airplanes crashed, and most importantly what do we as pilots have to do to avoid being on those NTSB (wrong or not) reports. I have my own theory - as I see all of us on the giving an opinion have, but would like to learn Flying's perspective. Mr Goyer do you care to enlight us? Thanks a lot
There are a number of plausible theories here, but in general, density altitude, out-of-CG condition, low-level turbulence, and sloppy flying are always good bets when it comes to accidents such as these. I will not speculate on these. I will say, however, that neither had anything to do with downwind turns.
Peter Garrison speakes heresy to suggest that the TSA is smarter than the NTSB. I'm surprised he's not on the no-fly list.
The NTSB is simply a group of guys doing their jobs. Some do it better than others. This particular gentleman just misunderstands the physics of this subject and is letting intuition get the best of him. I saw this many times with my primary students. Turning to downwind while doing ground reference maneuvers they visually notice an increase in ground speed, and incorrectly correlate that with IAS. They assume that if their speed is increasing and power output is constant, the only reason for the increase in speed is a descent. Subconsciously they pull up in attempt to arrest the supposed descent which will in fact decrease airspeed, putting the aircraft in a slower than normal condition. There is no inertial change, no acceleration or deceleration, only a reaction to an observed increase in ground speed. There are many analogies to stress this point, but in the end the physics prevail. The only time stall becomes an issue is with wind shear or mountain wave. My day job plane flies at 370 and close to called the coffin corner. When we encounter mountain wave while maintaining altitude, the descending side of the wave can cause a precarious decrease in airspeed and has caused a number of high altitude stalls in the past. Other than that, steady wind has NO effect on IAS or inertia.
Guys who still speak of the "inertial" effects of the downwind turn.
Do we agree that a steady wind is a mass of air moving at constant speed about the ground?
Do we agree that the mass of air inside the fuselage of an A380 at cruise is moving about the ground at the same constant speed than the A380's groundspeed itself? (say some 500 kts)
Do we agree than, given the two statements above, the air inside the fuselage of the A380 at cruise is effectively a 500kts steady wind?
Now please explain me why if I launch a single-digit-knots paper plane to make a circular flight (could be a turn or a loop) inside an A380 at cruise, the plane neither vaporzies nor is smashed against the rear bulkead when it's subject to such an acceleration that suffers a change in it's airspeed of some 1000 kts within a few seconds?
Answer: because it doesn't change. Or try this on your next flight while at crusie: walk a circular pattern in the aisle or galley. Do you find any problem holding a constant speed about the airplane's floor, that is the same than against the air inside the plane (that is, your airspeed), despite the fact that the plane and that air are moving at 500 kts about the ground?
Once again:
The A380 is parked on the ground. When the 5 kts paper plane makes a 180 from moving forward to moving to the back of the plane, it's airpseed vector changes from 5 kts forward to 5 kts rearward. A change of 10 kts. The ground speed changes from 5 kts forward to 5 kts rearward. Again a change of 10 kts.
The A380 is cruising at 500 kts. When the 5 kts paper plane makes a 180 from moving forward to moving to the back of the plane, it's airpseed vector changes from 5 kts forward to 5 kts rearward. A change of 10 kts. The ground speed changes from 505 kts forward to 495 kts rearward. Again a change of 10 kts.
That is enough to rest may case. But for those who want to go more advanced. People who decide to go on must be aware that, while I tried to make it as simple as I could (a chalk and blackboard would have helped), what follows is not very simple and can be a tough read involving some concepts of dynamics in circular motion.
The change in the airspeed VECTOR is always the same: 10 kts in the longitudinal axis. The change in the groundspeed VECTOR is always the same: 10 kts in the longitudinal axis. The change in the airspeed MAGNITUDE is always the same: zero. The change in the ground speed MAGNITUDE is NOT always the same, but it doesn't need to be: The acceleration is the change in the speed VECTOR, not in the speed MAGNITUDE. THE ACCELERATION IS ALWAYS THE SAME AND THE CHANGE IN SPEED IS ALWAYS THE SAME (be it airspeed or groundspeed, be it with no wind or whatever steady wind).
The reason why the MAGNITUDE of the airspeed vector doesn't change is because the acceleration is provided by a force, and that force is the lateral component of the lift when the airplane banks, which, by definition of LIFT, is always perpendicular to the airspeed vector (lift is the component of the total aerodynamic force that is perpendicular to the airspeed vector, the other component, parallel to the airspeed vector, is, you guessed, drag). And when the force and acceleration are perpendicular to to the speed vector, it has the ability to change only its direction, not it's magnitude. (Disclaimer, if more power is not added to keep the airspeed constant, the airspeed will diminish because of the increased induced drag caused by the increase of lift needed to sustain the increase in load factor that happens in a turn, but that's another story: Whatever you make to keep the airspeed constant with no wind also works to keep the airspeed constant when turning in any steady wind, and with any I mean any wind direction and any wind speed).
Now, why does the MAGNITUDE of the groundspeed vector changes when there is a steady wind and the plane turns? The easy answer is that it has to, because the groundspeed vector is the vectorial sum of the airspeed vector and the windspeed vector. And when you sum two vectors and one of them changes only it's direction, the resultant vector necessarily changes it's magnitude (believe me, or draw some arrows and check it, or go study some vectorial algebra). Hoeve,r that doesn't help understand WHY it changes, just to accept that it does.
So going more to the roots, the reason why the magnitude of the groundspeed vector changes when there is a steady wind and you turn, you need to imagine an airplane turning viewed from above.
And I'm sorry, Robert, but Maddogdriver went too far with the over-simplification when he said "Nope. There is no acceleration. Relative to the bank there is, but that is not a "felt" acceleration, just a perceived one. Your only frame of reference is the water, just as the air is while flying."
No frame of reference is "special". Anything that you explain using one frame of reference, you must be able to explain using any other one. One could be more practical, intuitive, or simplify the calculations. But that's all. And in this case in particular, the acceleration vector (the only one, let's leave the qualificators like "felt" and "perceived" at a side) is the same in any and all inertial frames of reference, and the water or the air moving at constant speed about the ground are as inertial as the ground itself, so any acceleration about the air or water is also there about the ground.
Let's start with no wind. The plane is flying East and it banks. The lateral component of the force aims North and, since that's perpendicular to the airspeed vector, it has the ability to change only the direction but not the magnitude of the speed vector. When the plane has turned 90° it's heading North, now the lateral component of the lift aims West. Again perpendicular to the speed vector, again changing only the direction of such speed vector but not its magnitude. And that applies to both the airspeed and groundspeed because, with no wind, they are the same. And the trajectory of the plane about the air (thing that it was leaving a trail of poofs of smoke) or about the ground (say that it was dropping paint on the ground) are exactly the same: perfect circles that superimpose perfectly one over the other.
Now let's say that there is a wind from West to East. Again the airplane banks and the lateral component of the force aims North, which is perpendicular to both the airspeed and groundspeed vectors, and hence has the ability to change only their direction but not their magnitude. But that's about to change for the groundspeed vector. As soon as the plane starts to turn.
Let's take a snapshot at the point when the plane has turned 90° and is heading North.
The lateral component of the lift now aims to the West and, since the airplane is heading North, again it's perpendicular to the speed vector and has the ability to change only the direction but not the magnitude of said speed vector. But what speed vector?
When the airplane is heading North, the AIRSPEED vector is heading North. However, the airplane is now in a crosswind (from West to East, remember), and hence the airplane is drifting right. It's ground trajectory, it's ground track if you will, is not due North, but deviated somehow to the East. How much will depend on the magnitude of the airspeed and of the windspeed. But it's ground track, and hence the direction of the groundspeed vector, is not North but diagonal somewhere between North and East. However, the lift vector cares very little about what frame of reference we are using, and will still aim West in any of them (because it has to be perpendicular to the airspeed vector, remember?, and the direction of the airspeed vector is, again, due North). So figure this, and here is the KEY:
The force that is providing the acceleration needed to turn, and hence the acceleration itself, is aiming West, and the groundspeed vector is aiming somewhere diagonal between North and East. The acceleration is NOT perpendicular to the gorundspeed vector. It has a component that is perpendicular (that will make the groundspeed vector change its direction) but also a component that is parallel to the groundspeed vector (that will make it change its magnitude). Not only that, but since the acceleration aims West and the groundspeed vector aims somehow east, the acceleration is REDUCING the magnitude of the groundspeed vector.
Make no mistake: The acceleration vector is THE SAME in ANY inertial frame of reference. It is how you descompose that acceleration in a component perpendicular to the speed vector and another parallel to the speed vector what changes with the frame of reference: about the air (airspeed vector) or about the ground (groundspeed vector).
So, in summary, you were flying East with pure tailwind, turn left, now you are passing North and notice (by calculation, not that you feel anyhting special) that the acceleration doesn't change the magnitude of the airspeed vector but it is changing (reducing) the magnitude of the groundspeed vector. No wonder that by when you reach West (completing a 180° turn and changing from pure tailwind to pure headwind) the airspeed will not have changed and the groundspeed will have reduced (exactly by 2 x windspeed, by the way).
Mr Goyer thank you for your response. While the NTSB report on the Cessna 172 crash is poorly stated, I do think that turning into the downwind with gusts did play a role on this accident. The key words being turning, downwind and gusts. The pilot was atempting a goaround after having bounced several times at the runway with strong cross winds, at 5000 ft msl on a C172 with 4 pass on board. The climb performance of that airplane at that altitude is reduced by 30% in fpm according to the poh. It is fair to say that he probably did not have excess power or speed during the manouver. As we all know on a turn he would have needed something like 5 to 10 extra nots to avoid a stall depending on the bank angle. Now comes the downwind part. A gust on crosswind probably rocks the wings but has noeffect on lift. He might have get away with it with low speed during initial climb, but when turning into downwnd, that same gust means a suddent decrease in airspeed. If he had low airspeed to begin with, higher stall speed due to the turn/bank, those downwind gusts could have put the plane on a stall/spin at low altitude. Of course we can skip all this theory and just atrribute it to sloppy flying...
P.S. You are right. The NTSB investigators should know better then that.
You're right, Gabriel, he did go too far. There's no element of the "downwind turn" myth that could possibly come into play.
Lowflying, I don't agree with this:
"Now comes the downwind part. A gust on crosswind probably rocks the wings but has noeffect on lift. He might have get away with it with low speed during initial climb, but when turning into downwnd, that same gust means a suddent decrease in airspeed."
A gust typically doesn't care what's the average wind direction.
A gust can be "positive" (increases the wind speed) or "negative" (decreases the wind speed).
To say it in other words, if there is a wind of 15 gusting to 25, it's as likely that means that the average wind is 15 and the "gust delta" is 10. But the Delta can be in any direction. Typically, in those conditions, a sudden gust of 25 kts (15+10) is as likely as a sudden gust of 5 kts (15-10). Not only that, but the gust can be in any other direction relative to the average wind.
For example, if you are flying with a head wind of 15 gusting to 25, be ready to gain or loose 10 knots at any time, but also be ready to get a lateral gust of 10 knots at any time. Conversely, if you are flying with a crosswind of 15 gusting to 25, be ready to have a lateral gust, but also be ready to gain or loose 10 knots at any time. That's why, for approach, the "gust factor" (or better, delta) is fully added to the approach speed no matter the direction of the wind.
Finally, still in other words, if you are flying in winds of 15 gusting to 25, be ready to loose 10 knots of airspeed regardless the direction of the average wind and the direction of the flight.
All this means that, if the gusting wind was a factor, then it is as likely as he got a sudden increase in downind after turning downwind as that he got a sudden reduction in headwind after turning into the wind (had he done so),
Hence:
The gust could have been factor.
The turn can be a factor for the reasons that you explained (increase in stall speed).
Climbing into an increasing downwind could have been a factor (wind gradient / windshear).
The wrong pilot's reaction to the visual illusion of increasing speed when turning downwind could have been a factor.
The loose of airspeed because of the downwind turn itself CANNOT be a factor, gusts or not.
This investigator did not "state it poorly", as you've said. He was plain wrong. (This little dot after the "wrong" is a full stop, period, basta, hasta la vista baby)
"I do think that turning into the downwind with gusts did play a role on this accident. The key words being turning, downwind and gusts. The pilot was atempting a goaround after having bounced several times at the runway with strong cross winds"
I will point out that if the pilot was departing with a strong crosswind, then he was flying the downwind in a strong (opposite) crosswind. Just because it's called the downwind, doesn't mean necessarily that it is in fact down wind, in a strict sense.
I also note that there is awful lot of talk here about airspeeds, gains and loss, fast and slow, etc etc etc. Airspeed, airspeed, airspeed. Everyone seems to be too focused on airspeed.
An airplane will stall at any airspeed.
These accidents/stalls likely happened because the wing exceeded the flying angle of attack. Frankly, it does not matter, in the final sense, whether you speed up or slow down in the turn to the downwind. What matters is what is happening with your angle of attack – and that is most certainly affected by changes in wind velocity and direction, particularly at the low/approach speeds.
Maintain a flying angle of attack, stay aloft. Exceed it at your own peril, so close to the ground.
Delta V:
Amen! With one comment:
When you receive a sudden and significant reduction of airspeed (as a result of a gust, wind gradient, or other type of wind shear), the angle of attack will not instantly change but remain initially the same. The plane, however, will start to sink (because, at a slower airspeed and same AoA, the lift is now lower) and the sink motion will increase the AoA. However, being the airplane longitudinally stable, the plane will begin to lower the nose (because the AoA also increases on the tail) and the AoA will start reducing again (starting the famous phugoid motion), likelly before the it reaches the critical AoA (that is before the airplane stalls). However, at this point the plane is sinking, the nose is pitching down, and you are low. Here is where most pilots will institively pull up, effectively and actively increasing the AoA. That's not bad in itself: Crashing without stalling, while not as bad as a stall spin accident, is bad quite bad already. So you want to arrest that descent, and the way to do it is to pull up (especially if you already had full power, like in these accidents). The problem here is how much: As much as you like, as long as there is no sign of approach to stall (stall warning, buffet, etc). As soon as the first sign of stall appears the AoA MUST be IMMEDIATELLY reduced at least as necessary to make all sign of stall stop. If a pull up around the onset of the signs of approach to stall doesn't work, then pulling further up and stalling will certainly not work either. At this point, the only rational (but very hard to self-enforce) decision is to keep the AoA below stall and crash in control.
But in the end you are right. It's very difficult that a sudden loss of airspeed makes the airplane stall "by itself" (stick free). It's the subsequent pull-up what makes the plane stall.
I tried an experiment in MS Flight Simulator that helps explain what's happening in a downwind turn. I set the sim up with a 100 knot steady wind and myself in a Cessna 172 at 3,000 feet over Seattle. I then made a series constant bank 360 degree turns for about 20 minutes.
The result? My airspeed never changed but my ground speed sure did. After the flight I checked my ground track. My turns all looked the same: I basically corkscrewed away from Seattle farther and farther out over the water as the wind took me for a ride.
I also tried this experiment at a reduced power setting and 80 knots. Despite the 100-knot wind, I never stalled - though I might have flown backward a few times.
The airspeed is the addition (or substraction if you prefer) of the absolute speed (the referential could be the stars, but ground speed is a good approximation as earth is moving very steadily) and the air mass (where you are flying) speed. If the absolute speed is changing rapidly and this is the case when you are changing your ground speed by turning downwind there must be an acceleration, this is Newton's law. As there is inertia, your absolute speed does not change instantaneously and your airspeed diminishes when turning downwind until thrust and drag find a new balance and stabilize. The effect depends of the windspeed and the rate of turn and is very very visible with an airliner reaching a turning point in a jetstream. The exemples of Mr Garrisson are stupid because in an A380 when you are turning backward your absolute speed does not change more than at the surface of earth. But when turning downwind from upwind in a 25 knots wind your absolute speed is changing 50 knots. What is important is how long it takes you and what is the speed change. Yes a rapid turn downwind in a strong wind is dangerous.
Over many years and several thousand hours, I've had 3 unintentional stalls. Two were at low altitude on final and the third was in cruise at 5000 feet. Three different planes were involved. I have related these before.
The first was as a student with instructor in a 150. We were carrying half the gust factor as recommended, but we hit a non typical gust. The bottom fell out and I punched the throttle. I have very quick reflexes, but when the throttle hit the panel I discovered the instructor and I were holding hands<:-))
With the addition of power the 150 was almost immediately flying again.
The second was in a Cherokee 180 after several hundred hours. This too was on final from a gust that was way more than typical or forecast. The ASI dropped off scale and I was on the express elevator down. All I could do was firewall it and hope that what nature had taken away, nature would give back.
The wind did pick back up, byt the old Cherokee was in ground effect, only a couple of feet off the ground, just short of the end of 06 when it finally started flying again.
The third was in the old Debonair, headed for Bo specific training pyut on by te ABS in conjunction with the Air Safety Foundation at Port Columbus in Ohio.
It was a beautiful sun shiny spring day with a clear blue sky. Light winds and no forecast turbulence except some light stuff at my destination. I was moving at about 190 MPH (old airplane) at 5000 feet, fat, happy, warm, sleepy, and complacent when I hit a very hard bump. A couple of seconds later I hit another one and instinctively pulled the throttle back. A couple seconds later I hit a really hard bump and found myself looking straight ahead “at the ground”! I eased the nose back up and maintained Va for a couple of minute, expecting to find another set of three bumps. I went back to cruise after those bumps didn't materialize.
These were all due to wind shear albeit the last, most likely from something BIG having passed through the area shortly before I did.
KHTL is an excellent place to experience changes in wind speed and direction close to the ground. With a Northerly wind it spills over the trees to the north of the runwat. Brush and a slight rise to the S of thr runway will cause the wind to roll up and reverse. When on final for 27 you have a wind from the North. If you don't land right at the end of the runway you hit turbulence and an abrupt wind shift to the South followed by another abrupt shift to the North when about 50 feet off the runway. For the unsuspecting this can make for a very exciting landing, particularly with gusts from all directions. I've been 90 degreed a number of times up there.
Great place to take those who think they have cross winds mastered,
I've mentioned win shear, wind speed variations and directional changes close to the ground. All good reasons to cause problems, but unlike the “down wind turn” they really do cause a change in the relative air speed.
I find it troubling that FAA personnel would refer to “the down wind turn” or lack the writing skills to make their intent clear if it was otherwise.
Sylvestre, that is all 100% incorrect. Sorry bud, your intuition is sound, but the reality of the situation is much different. Turning downwind in a steady wind does not change your airspeed, not matter the rate of turn, as long as the turn is coordinated (and thrust is added to counter the increased drag from the higher AOA inherent in any level turn). Neither the speed of the wind nor the speed of the aircraft has any relevance to this topic.
I am sure you are asking where the energy came from that increases your inertia relative to the earth when you turn downwind, as you would obviously hit harder with a higher ground speed if you crashed. The answer is the initial speed of the air mass. When you are holding on the runway before takeoff with a 30kt headwind, your plane must resist the 30kt force pushing it backwards. This can be done with brakes, weight (inertia) or thrust, but when you accelerate to take off with a rotation speed of 70kts lets say, you only really accelerate 40kts over the ground. Your inertia relative to the air is 70kts, but only 40kts relative to earth. The extra 30kts is being provided by the moving air mass. When you turn downwind, the air mass's inertia moves to the positive side of the equation and ground speed increases, but because both the air mass and the aircraft are moving at a constant rate, there is no net acceleration.
Same for putting a boat in a moving river. To keep it stationary relative to the shore so you can get in, a force must be applied in a direction opposite the direction of the moving water mass. You now have some inertia relative to the water, but zero relative to the earth. Let go of the shore, and you will feel an acceleration as the inertia relative to the water drops to O and increases relative to everything else in the universe, most relevantly the shore.
I grappled with the counter-intuitiveness of this at one point too, but after some thought experimenting the physics became clear. And trust me.....I'm no rocket surgeon. I mean brain scientist.
Sylvestre, accelerating your aircraft in the [also moving] mass of air within which you are flying requires energy. You can buy that energy with either fuel, or altitude (or both). No other forms of payment are accepted.
Those who still believe in the downwind turn should themselves these questions:
Why is it that these "downwind turn-related" accidents always seem to involve aircraft manueuvring at very low altitude? Have you even heard of anyone stalling, spinning and crashing/burning/dying due to a change of direction from into the wind to crosswind to downwind at, say, 1000 feet or more? Me neither. We routinely takeoff into headwinds sometimes quite strong, then within a minute we turn crosswind, then downwind when flying circuits (Canadian version of flying the pattern), so why aren't there a spate of these type of crashes every month? Who doesn't think low flying will sooner or later get you, when you get complacent, mentally lazy or distracted? At 300AGl, as little as five to fifteen seconds of distraction or inaction could cause a crash.l
As many others have pointed out above, at low altitudes changes in groundspeed might easily be mispercieved sufficiently to cause them to pitch upward and stall. That's why the manufacturer of that plane put attitude indicators and airspeed indicators and altimeters and VSIs right in front of you!!! They're there so you can confirm by instrument what your eyes are already telling you. VFR does n0t mean you never check your gauges.
The only pilots I know of who routinely fly low are aerial sprayers and helicopter pilots. The rest of us should climb to at least 500 feet AGL before turning crosswind or downwind, unless a specific IFR procedure calls for an earlier turn. For example, a SID at JFK either did, or still does require for a turn off runway heading just 400 feet AGL. Airline pilots do that a hundred thousand times a year, so where are the airliner downwind turn accidents?
Finally, being more disciplined and circumspect and learning to fly the numbers would prevent a lot of low-level accidents: : a specific power setting (about 75%), plus a certain attitude ( five to 15 degrees up on your attitude indicator) will create a positive rate of climb every time, regardless of changes in wind direction as you climb.
Sometimes I think the skill level of the GA pilot population needs to be raised at least a few notches. Too many pilots are dying or maiming themselves and others in preventable accidents where they should know better. Either we collectively improve our safety record, or the regulator will attempt to do it for us through additional laws and further expense.
Or we could all take up golf. That' safe, isn't it? Not!!!!
Douglas M
Surrey, BC
When turning upwind to downwind, with for example 25 knots of wind, you are gaining 50 knots of ground or absolute speed but it takes time to do so. Specially if you have a propeller that is giving you a power and not only thrust, any loss of airspeed diminishes the drag, except at very low speed, and the loss of airspeed increases the thrust of the propeller ( that is why planes with propeller are more stable in speed) and the aircraft should accelerate by himself. So on most occasions you would not even notice the loss of airspeed. But if you have a strong wind and a rapid change of direction you will notice it, specially with a heavy jet. The effect is the same that the one caused by a windshear, the important thing is the rate of the change, not the change himself. Once in my career I had to make a 180 degrees turn with 100 knots of wind from upwind to downwind: with climb power and maintaining the same altitude we were unable to accelerate to the flap retraction speed and had to diminish the turning rate and even stop the turn for a while. We needed 200 knots of absolute speed gain during this turn and it was not as natural as Mr Garrisson expect it (but two knots of speed change is easy inside an A380 or a train when going backwards to the toilets, as easy than at home). Hopefully strong wind are most of time associated with low level turbulence and this is a good reason to avoid steep turns at low altitude.
iused2fly- valid point. The low altitude flying involved is a very good indicator of the real issue here. You would think that a jet holding at a fix at 35,000ft in the jet stream with winds of 120kts+ that there would be a lot of stalls going on. A ground speed change of 240kts from upwind to downwind is pretty severe, and if there really was a deceleration in the turn, it would be violent.
A more dedicated me would love to calculate the supposed acceleration experienced by a 180 degree turn in 30 seconds with a 240kt ground speed acceleration during that turn.
Also, a 60 degree bank is 2 g's. Period. No matter what. If you are really accelerating when turning down wind, theoretically a 60 degree bank would result in more that 2 g's, which does not happen. Ever. That fact alone should settle this argument.
