The Downwind Turn Myth
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- čas přidán 15. 12. 2022
- "Sacred cow hamburger tastes best" says Doug Rozendaal, and in this video we explore the myth of the downwind turn - specifically the (erroneous) thought that an airplane will lose airspeed when turning from a tailwind into a headwind. Why is this incorrect? And why will this old wives' tale not die? Find the answers in this video.
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Please do more videos with Doug Rozendaal. Your videos together are always so insightful and entertaining!
Thank you, Ignacio. We have a few more in the pipeline...
- Martin
I'm a low time pilot, but I've never heard this, or sensed it. Nice job to bust myths though. Keep us all safe!
This is a helpful video. I am an RC fixed wing pilot, not a full scale pilot. I think RC pilots are more likely to get confused about this because they're trying to keep their craft centered over a small plot of land; they can't simply let the aircraft drift with the wind. When they perceive a sudden increase in ground speed on downwind, they inadvertently back off on the throttle on the downwind leg without thinking about the corresponding loss of airspeed.
Someone correct me if I'm wrong, but it helped me to think of it this way: the airplane is part of the wind. It "IS" the wind, in the sense that it is already moving with, and with respect to the wind. On the downwind turn it does not suddenly "encounter wind" (or tailwind) because it already is in the wind: it's part of the wind and is already moving at the same speed relative to those air molecules that it would, whether they are part of a wind or not (still air). Inertia is a factor with flight dynamics in general, but in the case of the downwind turn, with respect to the air molecules around the aircraft, there is no acceleration against those air molecules as you make your way through the turn. (There's a lot of repetition there, but I had to repeat this a lot to myself before I finally got it. :)
There are dangers associated with tailwinds and downwind turns, of course, but they have more to do with low altitude issues, wind shear, obstacle clearance with lower climb angle, things like that. I thought this article did a good job of explaining some of the dangers associated with the downwind turn:
www.australianflying.com.au/news/dragons-of-the-downwind-turn
The key term is "relative wind"....the airplane only FEELS the "wind" that is the airfoil moving THROUGH the air mass. It has no clue what the airmass is doing in terms of direction of movement. There is no "downwind turn"....it's just a turn THROUGH an airmass. Doug is an excellent teacher.
Exactly!
- Martin
I believe the myth is that when you turn downwind, the airplane will lose lift due to the loss of airspeed from the “tailwind”. Of course, Wolfgang Langewieshe dispelled this myth many decades ago by explaining that the airplane is contained in the air that is moving across the ground so that the motion over the ground is a combination of the motion through the air and the movement of the air over the ground. Chapter 6 of “Stick and Rudder” does a great job of explaining this! Highly recommended!!
That's a great book indeed!
- Martin
There's all the reference anyone needs
My favourite book ever! I learnt to flare at the right time thanks to an illustration in that book. My instructor had tried everything to explain, but seeing that picture I just knew where I needed to be in relation to rwy and horizon.
Very down-to-earth, no pun intended, from two gentlemen with a lot of time and experience committing aviation safely and consistently on-purpose. Well-done! ✈️😎👍
Thanks for the kind words!
- Martin
Kind of funny how your tablecloth and your guests shirt match perfectly. Yep I noticed things like that and it's my takeaway from your video. LOL.
This was a really good demonstration of the effect wind has. As always thanks Martin for taking the time to put these videos together for us all.
My pleasure, Kevin.
- Martin
A simple analogy might help: think of a moving walkway such as exist at many large commercial airports. If you walk on the walkway, you walk at the same pace as on the adjacent ground. Of course your “ground speed” increases. If you were to walk the wrong way on the movable walkway, your ground speed decreases. If you were to arrange four moving walkways in a square, then you have almost exactly the same as the pattern with crosswind, downwind, base, and upwind walkways. You can see that there is no need to accelerate at all. You just walk as a uniform pace but your speed over the ground will change instantly.
The walkway is a good analogy, though with four walkways arranged in a square, two of them would have to move sideways to simulate a crosswind.
- Martin
@@martinpauly I did mean that the crosswind walkways would have to be "wide" and you would be walking across them or perpendicular to the axis of motion of the walkway.
I think what perpetuates this myth is the belief that there would to be acceleration as you turn downwind. I think the walkway makes is clear that you do not accelerate your pace at all. All you need for that is one walkway -- and you walk on to it.
BTW, the Coriolis effect is the same thing. Your ground path along veers right (in Northern hemisphere) even though you have a force vector due north.
These are great videos. Doug is an amazing expositor.
I had a on-going debate for months in the letters page of the AOPA UK magazine. They guy wouldn't give up, mis-quoting theories of planetary movement and worse, to defend his point that the downwind turn was dangerous. I asked the editor why he allowed such misinformation - because some readers were thanking this writer for "explaining" this. The Editor said "all views are represented on our pages". And there is the problem...
Right... which also reminds me I am glad I am not an editor who has to defend what gets published and what doesn't.
- Martin
I’m glad he said the wind “carried” us and not “pushed” us, because that is a better description of what happens with airborne objects. Airborne literally means carried by the air.
I learned to fly in Oklahoma where it was normal to train on windy days. I remember very early in training turning downwind and getting the sensation of rapid acceleration. I also remember learning turns around a point on a windy day. You really have to adjust bank angle significantly to keep your reference point in place.
Good observation, David. The sensation of acceleration is real, as is the increase in ground speed. But it changes nothing aerodynamically.
- Martin
This is pretty standard and I have had this argument with other pilots. The thought experiment is simple: if you are flying into a 100kt wind and you are doing 100kt, and thus 0 ground speed, do you fall out of the sky? It's amazing how many pilots get confused about this.
Yes!
Nice choice of subjects! I have finally resorted to telling students (and sometimes fairly high-time certificated pilots) that there is NO WIND when you are airborne. The planet simply spins faster or slower or in a different direction. The aircraft behaves normally. It's a hard concept for some to grasp. Another way of presenting the concept is to ask if a fish knows if it is in the ocean or a deep, wide, fast moving river. Nope. Good job.
Thanks. "There is no wind" - I think that's a valid way to look at it, though I wonder if it's easy for everyone to grasp the concept. I like the fish analogy.
Regards,
Martin
Try doing steep turn practice with winds up there at 30 knots. Keep same attitude. See you climbing headwind, and descending tailwind. Don do them at full power, do them at about Vglide speed or bit faster only, like turning final with a base leg tailwind on it. You will descend on tailwind section too. Some pull in fear and stall there.
Thanks for making this video! I don't know how many times I have had to argue this with people and they still don't get it. Now I can just send them this :)
It comes up a lot in RC airplane flying as well - where the ground speed acceleration close to the ground is especially visible and people think they can get away with pulling it around a turn faster which leads to a "tip stall" (whatever that is)
Thanks, Curt. I can see how the sensation is magnified in RC flying, where airspeed is typically slower and the difference in ground speed going upwind vs. downwind is a larger percentage of the airspeed.
- Martin
Yep, more of an RC thing where airspeed of the aircraft is somewhat judged by its groundspeed relative to the pilot on the ground via visual cues. If the RC pilot flies the airplane in such a manner that the speed looks the same as a day with no wind he will be entering the turn slower and then demanding a steeper turn rate since the wind is trying to carry the plane away from the pilot. Enough of a not good combination to have created a deeply seated myth.
The thumbnail made me think you were going to do a video on how downwind to final is usually a wild adventure in attempting to make a proper base leg. - but this is good too, and provides real insight into why that is tough sometimes. Also didn't dawn on me that Doug is based at KMCW til now, that's awesome!
Some people might understand if you demonstrate with the addition of vectors. I particularly like the idea that the aeroplane is flying through a parcel of air; the wind is the parcel of air moving. You are still travelling at 60 knots through the parcel no matter what the parcel is doing. 😊
this myth is actually mntioned over and over againin kay vids on youtube, when people show their pattern work/ training! thanks for the info...watching your explanations is like honing one's roughly casted knowledge to something sound...
Everything that was said is spot on. My only word of caution is that the wind down low is seldom constant, so beware of low airspeeds in turns, downwind or otherwise. A sudden change in wind velocities can play havoc!
You are right about the effect of changing wind, but then I think your statement "beware of low airspeeds in turns" can be further generalized to "beware of low airspeeds", because wind gusts don't just happen in turns.
Regards,
Martin
@@martinpauly Agreed. Just a little higher wing loading in a turn plus people get distracted in a turn, especially base to final!
Very good explanation and the flight demo really brought home the subject. Thanks for sharing.
Thank you, Ken - glad you found it helpful.
- Martin
I’ve nearly given up on trying to slay these sacred cows. Whether in aviation or motorcycling, these myths such as the downwind turn and countersteering only working above a certain speed, are just impossible to remove from some people’s minds.
It's ironic that this video just posted after I finished watching the multi engine ground school video that you and Doug did. It was the third time I had watched it. Doug is a great teacher and has a great way of making things easy to understand! Keep the great videos coming! I really look forward to them and enjoy the content.
Glad to hear, Kevin.
- Martin
The airplane has no way of knowing which way the ground is blowing.
people don,t understand that they fly in the air...they are always fixed on the ground with their conceptions instead of seeing that mass of air, that moving sea of gas in whixh they basically swim! 🤷♀️thanks for showing...good as always! 👍
"Seeing that mass of air" - that's a helpful way to think about it.
- Martin
Totally awesome video!
Great informative video. Thank you
My pleasure, Kevin.
- Martin
Doug got his shirt and tablecloth as a matching set!
Just joking around, great video as always.
I agree completely with your slaughter-fest. Great job! It seems like the difference between airspeed and groundspeed is just a hard concept for some people to understand. I always just thought of it like a boat in a river, and I never had an issue.
Thanks, Marty. And the boat in a river is a good analogy; I might use that in the future.
- Martin
All this makes good sense. However, the danger I see is that wind is not always constant. If you suddenly lose the wind, or it changes direction suddenly, you cannot suddenly accelerate to make up the difference. It takes a finite amount of time to get back up to speed. Isn't that what windshear is all about?
You are correct - however, the (rather persistent) myth is that airspeed changed happen in a turn even if the wind IS constant. That’s what we tried to address here.
Pretty cool to see Clear Lake. I fly up there occasionally to visit family. Always a fun trip to MCW from SQI.
Mason City is a great airport!
- Martin
Thanks for simplifying this confusing point in the video.
Glad it was helpful!
- Martin
The interesting thing though, you DO accelerate the entire delta V. If you are going 50knts in one direction and turn to be flying at 50knts 180* the other way. You have accelerated the aircraft by 100 knots total deltaV. Just that its not coupled to your airspeed as long you maintain the added power for the level turn.
Thinking about the slip caused by wind when doing rotation flying is something paraglider pilots do a lot. Not just their own position relative to the ground, but the thermals position and how it's "leaning" with the wind.
The net is. If you fly a perfect circle your circular track on the ground will travel at the wind speed.
You are absolutely correct. And it's of course the horizontal component of lift during the turn which provides the force for this acceleration; the math works out weather you use the air or the ground as a reference system.
- Martin
No, you do not accelerate the entire delta V. Acceleration is still only coming from forces and no strong forces act on the plane. It's rather the result of observing the speed from the ground which is the vector addition of the wind speed and the plane speed.
@@martinrenschler4046 Thats not what physics says.
@@1over137 It's exactly what physics say. A body does not change its speed unless forces act on it. Once in the air and being accelerated by a constant wind, no extra forces act on the plane compared to flying on a no-wind day. The plane's reference system is now the wind. It does not know the wind itself is moving. Just you as the observer on ground see a big difference between the plane moving with or against the wind relative to ground.
@@martinrenschler4046 The fact the plane is producing over a ton of upward "lift" has completely slipped your attention.
I think this belief in loss of airspeed turning downwind comes from turning downwind in gusty conditions when the airspeed can fluctuate as you travel through the turn. People see some rapid changes in airspeed and it makes them nervous given the low altitude/airspeed combination.
Agreed. Airplane flies in the airmass. Velocity is relative and we can't perceive it, but we can feel accelerations.
Seen another famous CZcamsr "real" pilot make this same mistake recently. By suggesting that after take off, turning into the wind can help you climb. All that will do is lower your ground speed for the climb. It won't create more lift.
That's another loaded topic - and by the way, you don't need more lift to climb, as I explain in another video:
czcams.com/video/S59_BaQv1vU/video.html
Climbing into a headwind can result in a good rate of climb if the amount of headwind increases with altitude, which - let's face it - is quite often the case after we take off. During our climb, the change in wind speed does cause a change in airspeed (due to the inertia of the airplane), and the airplane will convert that into more altitude gain as it seeks balance (read: as it seeks the trimmed airspeed). But that's a change in wind speed, which is different than the "downwind turn" situation from this new video.
Regards,
Martin
So turning downwind decreases airspeed? But not a realized quick altitude loss?
@@MrCobb-rq8iv No. Turning downwind has no effect on airspeed, all else (incl. wind) being equal.
Your example from your earlier response was a different situation, where wind changes with altitude as the airplane climbs.
- Martin
Another example - Angle of climb will increase in your scenario. Just not rate. Imagine taking off and climbing (at 70knots) into a 70 knot headwind. In this perfect weather example, you will be climbing perfectly stationary above your liftoff point at zero ground speed but the ANGLE of
Climb is 90 degrees while
you’ll see a normal RATE of
Climb on the vsi as you ascend like an elevator. (Which is why some people get fooled into believing you have increased rate of climb performance.). Once you’ve leveled off, make a 180 degree turn from there and you will not see a decrease in indicated (or true) airspeed or altitude. The turn will look like a corkscrew on ForeFlight. In short, THE WING DOESNT CARE ABOUT YOUR GROUNDSPEED.
The airplane doesn’t know the ground exists…. Also there is no “wind” per se once aloft, only a moving air mass that the plane is flying in. The plane does not know the air mass is moving.
How would it work in a helicopter? A helicopter could be turned using rudder only to turn so that its inertia causes it to contines to fly into the wind but backwards. It would have a negative airspeed until it slowed, stopped and accelerated in the opposite direction.
Great video Martin!
Thank you, Richard.
- Martin
An airship documentary mentioned that the USS Macon would turn into the wind to take aboard the Sparrow Hawk fighters it housed. This would be sound procedure if it were an aircraft carrier landing the fighters, but of no consequence for an airship and aircraft flying in the same airmass. Same faulty perception!
You guys do a great job but you got this one slightly wrong. If the wind quickly changed direction your airspeed would change. I.e. wind shear
The reason the airspeed stays constant in the turn is the time it takes for the airplane to turn allows the wind to accelerate the the airplane.
The airplane does speed up or slow down as recorded on the ground speed
The truism I heard was "If the wind is perpendicular to the runway, choose the runway that will make your crosswind turn INTO THE WIND." Please explain why airliners have crashed on final when flying thru a microburst and a 40 mph headwind suddenly becomes a 40 mph tailwind. Conservation of momentum means the groundspeed "wants to remain constant," and the indicated airspeed can suddenly drop by 80 mph as large mass cannot change speed across the terrain quickly.
A 40 Kt headwind to a 40 kt tailwind is windshear. That is a different animal and then the sea of air that the airplane was flying in has changed, so the airplane has to change as well.
This is very simple illustration called illusions created by drift. As long as you keep your flight coordinated you will have no issues!
I've noticed a tendency for my RC airplane to stall when I turn upwind actually
However, watch closely between 6:30 and 7:12
Does it not dip from almost 70 to almost 60 for a few seconds? Specifically at 6:48 on your vid.
How is this even an argument...I've never even heard of it...there is a tiny bit of inertia that must be overcome as it accelerates to its new speed relative to space, but it is minuscule to the point of being irrelevant...
Merry Christmas Martin and Doug from Sydney.
Fantastic tutorial: "my nickel on the grass." If you've got some money to purchase a higher horsepower engine and propeller, and maintain airspeed.
Or....
Study meteorological conditions and select a favourable wind direction to fly in?
🌟
🌲
Thank you, John, and Merry Christmas to you as well!
- Martin
Thanks so much been arguing with people about this years. Nice i have a video
In my humble opinion the concept is simple to understand this way: Imagine the airmass around you as a volume moving alltogether at wind speed/vector and forget GS for a moment. Then put your imaginary airplane in that moving airmass: every change in heading will affect your attitude, (maybe) not your TAS, no matter if you accelerate or decelerate...
QED Martin! :)
Based on what you are explaining here. Why are we told to keep extra speed on gusty days on final?
To attempt to keep from slowing to below target airspeed during a windshear event.
@@ericsd55 yeah I hear you… and I guess it means I don’t understand this video. I agree with what you are saying but they just went in circles with varying wind directions showing the ias staying constant.
@@Shaneepe1 it was a steady wind. Extra speed is for wind gusts, not for steady winds.
@@B25Flyer gotcha thanks!
Hi Shane. A gusty day is different from what we showed in the video. In the video we assume the wind is steady. Gusts by definition mean the wind changes - over time, over altitude (e.g. wind shear), etc. A change in wind will change airspeed momentarily until the trimmed airspeed is reestablished. To apply that to your example of the final in the pattern, if you are at your normal (no gust) approach speed and fly into a 20 knot headwind, a wind gust could reduce that headwind from 20 knots to, say, 10 knots, very suddenly. Inertia means that your airspeed is then reduced by 10 knots, which brings you under the approach speed and closer to stall speed. The plane will pitch down to seek the trimmed airspeed, but close to the ground you'll want a little speed buffer so as to not get close to stall speed.
Regards,
Martin
But what about a plane on a treadmill? Can it still take off?
Where’s the confusion? The answer is people are confusing ground speed with airspeed. We fly in a block or air, nothing changes.
I agree that the myth is false, BUT....I was surprised and dismayed that the phrase "ground reference maneuver" was not used even once in this video. This flying exercise is what "ground reference maneuvers" IS. The flight path on Foreflight tells the story, but you just left it hanging. You can clearly see that turning to downwind, while it has no effect on your airspeed, definitely makes your turn wider (and vice versa), and that's probably a component of the myth, and the whole point of the "Turns Around a Point" exercise is to recognize this and fly a path counter to it, so your path along the ground is a circle. I'm convinced that not recognizing/knowing/believing that the downwind turn will be wider is what killed Cory Lidle. Imagine what your turn would look like, flying along a narrow river in a crosswind, with tall buildings on both sides. If they'd recognized it, moved over to the other side of the river and did a right 180, they'd probably have been alright.
Here's an Army training video for Bird Dog pilots that goes over this better than anything I've seen. It might help some pilots understand better. It did me. czcams.com/video/aDbMHtglTOA/video.html
Thank you for pointing me at that US Army video. I agree, it's very nice.
- Martin
@@martinpauly I didn't mean to sound so critical; it just seemed like, at the time of the Cory Lidle crash, almost nothing was said about this phenomenon, and the need to understand ground reference maneuvers, and it reminds me that my own primary training was also lacking. I didn't understand all this until I watched the Bird Dog video.
I also still don't understand how you can hit a building in a turn in a low wing airplane. They have to have seen it coming for several seconds.
The animation early on is why people get confused. You drew the turn as a semicircle, but it's not. The point at which the 180 turn is complete will NOT be level with where the turn commenced because the wind, or medium in which you are turning is moving steadily in one direction. But, as was said, if you taxied at 20 knots into a 20 knot wind your airspeed would be 40 knots and if you then turned 180 degrees and taxied downwind at 20 knots the airspeed would indeed indicate 0. Another way to look at it would be to make a 180 degree turn while swimming in an infinity pool. (By that I mean a pool with the water flowing so you can swim continuously without getting anywhere.)
If you look closely at that animation, you'll see that the 180 degrees turn is NOT a semicircle - it is skewed to the left, because as you said after 180 degrees we wont be abeam the point at which we started the turn.
- Martin
What’s the wives tale?
The old wives' tale is that the airplane loses airspeed when turning downwind (because the wind is now from behind, no longer flowing over the wings as fast as it did before the turn). Some people believe that brings the plane closer to a stall.
- Martin
Heads up display showing airspeed solves it…Time to spend some$$$
I am confused, what is the myth?
The myth is that you somehow increase your risk of stalling when turning from upwind to downwind. It represents a fundamental misunderstanding of basic flight principles.
As @loreendjones said, many pilots believe the plane loses airspeed when turning downwind (because the wind is now from behind, no longer flowing over the wings as fast as it did before the turn). They believe that brings the plane closer to a stall.
- Martin
I would equate this topic like "flat earthers".
I see where you are going with that... though to be honest, I think they are on two very different levels. I can understand why someone might fall for the downwind turn myth. I have no understanding whatsoever why someone can be fully convinced that the earth is flat.
- Martin
If we assume that the Earth is stationary and we're flying into a 20 mph headwind at an indicated airspeed of 100 mph, our ground speed is 80 mph. If we make a 180° turn, there's no way we'd have a 120 mph ground speed unless the airplane gains 40 mph relative to the Earth. If you hit something at 120 mph, it's going to hurt a bit worse than if you hit it at 80 mph. So, where did the extra 40 mph and energy come from? It came from the wind accelerating the plane. And, I guarantee you that it didn't go from 80 to 120 instantly. So, the quicker you make that turn, the less time there will be for the plane to gain that 40 mph.
In both cases there is the same 200 mph overall momentum change. The wind doesn't do anything. The ground can not impart a force on the airplane. There's no reason to make the turn any quicker or slower.
Now try the aircraft on a conveyer belt.
That thing turns on a dime! Aviation equivalent of doing doughnuts.
Still don't understand the point of this video
P r o m o S M