"Stick and Rudder Moments" - redux

Here is a plane taking off while standing still in a high wind. No pilot, no engine running, by by plane.....

 
FastEddieB said:
There's a video online that I'll try to find*.

The instant the tires are clear of the ground, the plane will simply accelerate downwind, unless tethered somehow. If tethered, of course, it can hover, much like a kite.
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I don't follow. If I fly an airplane at 60 knots in a 60 knot headwind, it will hover.
 
I am of the opinion that all those "stick and rudder moments" are fake, in that the pilots who eschew those beliefs ("plane can sense the wind") know the truth, but like to pull our chain. I guess it works. :)
 
RotorDude said:
I am of the opinion that all those "stick and rudder moments" are fake, in that the pilots who eschew those beliefs ("plane can sense the wind") know the truth, but like to pull our chain. I guess it works. :)
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I can only say that they are all genuine, and while it's possible they're trolling, most seemed quite sincere in their beliefs.
 
FastEddieB said:
Of course. Not contested and I've done it.

I thought the "not tied down" part made it clear I was talking about a parked plane. I guess I could have been clearer.
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I guess the problem with a parked plane is that there is no pilot to control it. It doesn't seem to have much to do with wind.
 
FastEddieB said:
I can only say that they are all genuine, and while it's possible they're trolling, most seemed quite sincere in their beliefs.
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Hard to see a subtle wink on the internet. :)
 
dmspilot said:
I guess the problem with a parked plane is that there is no pilot to control it. It doesn't seem to have much to do with wind.
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I remember a video of parked planes - with pilots - encountering sudden gusts.

Let me look.

Here:


Point is, someone opined that a plane, sans pilot, would just levitate and hover in a strong enough wind. It will, but only for a second or two until carried along with the airmass, at which point it will quickly crash/descend due to lack of relative wind.
 
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FastEddieB said:
. But if one holds that the elevator is less effective in a tailwind, I think that's a reach, or at least open to easy misinterpretation.
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Our disagreement then is not one of content but of style, but I just see it a little differently. The false ideas you wish to confront don't materialize from nowhere, so I think it is good to deal with them honestly and preserve the distinction. The diminished control effectiveness is real, although not in the way they may think. Most of the myths you mentioned are harmless misunderstandings, but dealing with a significant tailwind is not. Managing the effects of strong winds in the pattern require an understanding of the effect, not necessarily the cause which is where most people are at and why you get frustrated.

Sometimes people get hung up on a point and are eager to make it at the expense of all others. I've seen it here before and sensed you were headed in that direction, but maybe I misread what you were saying.
 
FastEddieB said:
Shows how subtle effects can be missed.

I still hold that as soon as the last tire leaves the surface, the entire plane will simply move laterally with the air mass, and not "weathervane". It's definitely my experience. Lots of pilots hold that it will, but I think it's because they are so used to crabbing into the wind after takeoff that it seems to happen on its own.

I posted my little experiment before. Here it is again:


I could detect zero tendency for the model to "weathervane"' and that leaf blower was really honkin'!
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Nearly all airplanes will definitely will crab into the wind (done it many times). Here is why...

Taking off on runway 360. Wind is 090 @15. The moment you leave the ground the airplane has 0kts of crosswind speed. (for example 60kts on a 360 heading and 0 kts on a 270 heading) It will take a few seconds for the wind to accelerate the airplane to the 15kt of crosswind (still 60 kts 360 heading but now 15kts on a 270 heading).

During the few seconds where the airplane is being accellerated downwind, by the wind, where the crosswind component is greater than the crosswind movement of the airplane and the airplane is still on the 360 heading, the airplane will want to turn into the wind. This is because the vertical tail creates a larger surface area near the tail of the airplane causing the airplane to want to weather vane. If you had an airplane with equal Moments of surface area ahead and behind the CG it would not want to weather vane. (ie. a vertical sheet of plywood wouldn't weathervane, an arrow will)

Brian
CFIIG/ASEL
 
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Cooter143 said:
Most of the myths you mentioned are harmless misunderstandings, but dealing with a significant tailwind is not...
Sometimes people get hung up on a point and are eager to make it at the expense of all others. I've seen it here before and sensed you were headed in that direction, but maybe I misread what you were saying.
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1) Read through the list, and many of those myths can remain harmless throughout a flying career. But each, under some circumstances, could lead to adverse consequences, be it from misdiagnosing mechanical issues or a basic misunderstanding of how wings fly.

Imagine actually thinking that turning downwind at 1,600' will make one's elevator less effective. Would not one then move the controls more to compensate for that imagined effect?

2) I agree that the list can be read with a rolling of the eyes. I mean, really??? Yet those anecdotes on the list are from personal encounters, or from posts to mostly five aviation forums. Yet each provides the opportunity for a concise explanation to lead to an "AHA!" moment for the one holding the misconception.

For instance, the fellow that swore that his engine temps are higher with a tailwind than a headwind, even given the same power setting. Yes, it's easy to mock. Yet, as you say, these ideas don't materialize from nowhere, and are commonly expressed enough to be concerned about. And with patient explanation and analogy, sometimes learning does take place. Yay!

Yet, frustratingly, some seem immune to edification once they "dig in". I think the CT owner will still crow about his 2-axis autopilot keeping the ball in the center, for instance, or that he runs out of nose down trim more often in a headwind. At that point, one can only hope that others may learn from the debate, in spite of the originator clinging at all costs to his or her misconception.
 
brcase said:
Nearly all airplanes will definitely will crab into the wind (done it many times). Here is why...

Brian
CFIIG/ASEL
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Brian,

This is one where I changed my opinion.

Over 40 years I became quite convinced that as soon as the wheels left the ground, the plane simply drifted downwind with no yaw, and that any yaw into the wind was pilot initiated. Lengthy discussion on COPA gradually brought me around, though I still hold the effect is very small and very transient.

Here's a series of crosswind launches into what, to scale, would be a hurricane force crosswind:


In nearly every case, the nose does twitch slightly right, into the hurricane.

So, physics wins again, though I still hold the effect is quite small in practice.
 
I like the weather ones...

after descending into the tops at 4000 ft with reported moderate icing, getting to 2500 feet approximately 20 miles from the FAF, and starting to collect ice like crazy, I suggested climbing back on top. The captain stated that "there's freezing rain on the surface, that means it's warmer aloft." Guess what...it wasn't warmer where we were. We had so much ice on the airplane when we landed that I doubt the gear would have retracted properly in the event of a missed approach.

flying eastbound along the U.S./Canadian border, my copilot pointed to a wedge-shaped cloud formation at the top of the line of severe thunderstorms to our left, and commented that it was a "classic warm front". Upon further query, he stated that yes, a "classic warm front" comes south out of Canada and produces 60,000-ft thunderstorms.
 
Quote from initial post:

"One thought exercise is to imagine that you’re flying a plane capable of 50k slow flight in a 50k wind. Start directly into the wind with a zero groundspeed. Then start doing 360’s. With each 360 your groundspeed goes from zero to 100k and back to zero. Imagine how that will feel as you speed up to 100k only to slow back down to zero. How will that feel? How will that sound? You surely will be able to tell when you’re upwind and when you’re downwind, right? The answer is so nonintuitive that you might not believe it, but its true. Try it some time under the hood and the answer will be clear - though not what you might think."

I think ground track is a cycloid and feeling is no different than it would be with no wind. Everything outboard of the longitudinal center line of the plane actually moving backwards with regard to the ground track when pointed directly into the headwind (like a point on the flange of a train wheel when at the point of contact of the wheel with the rail).
 
Graueradler said:
Now it works. Amount of weather vane effect depends on offset between CG and center of lateral effort while the plane is being accelerated sideways up to crosswind speed.
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The thought experiment that helped convince me was a bowling ball with a few feet of PVC ending in a vertical fin. Pop it into the air in a wind. Would it not, at least initially, be expected to rotate around its CG to point into the wind?

I just had/have trouble seeing that effect in real life, but I stipulate it must be there. I think the small yaw into the wind was so overshadowed by the overall downwind drift of the plane that I just didn't notice it.

As far as a crosswind "automatically" yawing you into a wind correction angle on a crosswind takeoff, I still hold that a pilot should expect very little help in that regard. Experienced pilots will rotate with enough aileron into the wind as to make the establishing of a wind correction angle appear almost automatic, however.
 
Stick and Rudder.
One of my favorite books, ever. I think I first read it when I was 12 years old.
 
Shepherd said:
Stick and Rudder.
One of my favorite books, ever. I think I first read it when I was 12 years old.
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When I first got serious about lessons, I called a couple of CFIs. One, an older guy, told me to read that book first, then start lessons. I later found out he had a stroke not long after we talked, and I've read that book a couple more times since.
 
I'm still shocked at the expensive price of $8.95 as quoted in the Whole Earth Catalog.
 
Where is this smooth air of which you speak?

Rogers and Hammerstein opened a catchy old tune with a description of the winds here in OOOOOOOklahoma.;)

In regard to the yawing effect on a crosswind takeoff, if it happens to be a crosswind from right to left, could having a significant amount of right rudder input to correct for torque/p-factor intensify the perceived weathervaning immediately upon takeoff?
 
FastEddieB said:
In another thread a pilot opined that wind made a difference in cooling in a Seneca. I searched every which way and cannot find my original post on "Stick and Rudder Moments". So, I thought I would amend it (example #5) with the current example and re-post it:


As background, Stick and Rudder is a book written by Wolfgang Langewiesche in 1944. Though a little dated, it still makes good on what the subtitle promises: “An Explanation of the Art of Flying”.

51L%2BZAJhzYL.jpg



Much time is spent in the book describing what makes flying so different and challenging compared to ground based activities.

We spend most of our lives anchored to the ground in one way or another. In fact, to say someone is “well grounded” or that he or she “has their feet on the ground”, is generally considered a compliment.

But all that time spent on the surface may make it difficult to shift gears when the wheels of a plane leave the ground. It takes a while to adjust and to understand, and even experienced pilots can slip up from time to time.

It has to do with frames of reference. One is the ground. We think of it as stationary, but standing on the surface of the planet you may be moving up to about 1,000 mph, depending on your latitude. But if you know how to juggle, you don’t have to factor in the speed at which you’re moving - relative to the surface you’re stationary, and that’s all that matters. Similarly, if you’re juggling on a moving train - since your frame of reference is now the train, no allowance for its movement need be made.

The essence is that, once in the air, the plane has zero reference to the ground as far as flight characteristics go. Your frame of reference now becomes the air mass in which you are moving. The implication is that a steady wind has no effect on the plane, other than its path over the ground. The plane is simply flying in an air mass which is itself moving. Disregarding gusts and shear, once a plane is in the air, like a free balloon, there is no wind.

I wish to clarify what I mean when I call something a “Stick and Rudder Moment”. A pilot will do or say something where a lightbulb goes off in my head and I suspect they may not be adequately making the transition from ground-based to flight-based thinking. The upside is that it can often become a "teachable moment".


Here are some examples I’ve come across, and I’m sure you guys can come up with many more.

1) The “Dreaded Downwind Turn”.

This is the grandaddy of "Stick and Rudder Moments". Many pilots believe that the turn from crosswind to downwind is especially dangerous. Why? The plane may stall as it is picking up a tailwind during the turn, putting it closer to the stall.

Such is not the case. If planes do tend to stall there, it is due to the illusion of increased speed leading them to slow down too much or not realize speed is decaying. There is no “wind” pushing against the rear of the plane, causing it to stall.

2) A fellow on the Cirrus Owner’s site observed that a quartering tailwind seemed to push his plane ahead by more than the wind velocity. For example, he’d be flying along with a TAS of 190k and a quartering tailwind of 10k and find his groundspeed being greater than the combination of 190+10. He figured it was like a sailboat “tacking”, and that some sort of trigonometry was letting the quartering tailwind “squeeze” his plane forward faster than the wind velocity.

The thread (“Winds?”) went on for hundreds of posts with other pilots and instructors trying every imaginable explanation and analogy to show him the error of his reasoning. I don’t know if we ever did, and the same theme was continued in another thread by the same fellow. But it was a fun, if somewhat aggravating ride.

3) Flying a demo Cirrus northbound in FL, I noticed on autopilot it was flying slightly right wing down. I mentioned it to the demo pilot, who opined that it was probably just the autopilot correcting for the right crosswind.

4) A pilot posted that when he approached in a crab with a crosswind from a certain direction, he could feel it in his prop.

5) I’ve heard it said cowl flaps are especially useful when flying downwind, when cooling would otherwise be compromised by the tailwind. More recently, a forum poster here thought winds affected cooling in a Seneca, possibly due to cowling shape. Then he doubled down with: "On my 206 I've notice a 5-10 degree change in CHT based on a strong wind. I am not a fluid dynamics expert, so I have no idea exactly why. Perhaps a slight pressure change in the cowl as I mentioned, or slight turbulence in the relative wind, IDK."

6) Someone suggested in a strong enough wind, a plane that was not tied down could eventually just hover.

7) Many have expressed that banking the airplane may cause fuel to flow unevenly from wing tanks. When queried, they were not referring to uncoordinated flight.

8) And, of course, there was the suggestion to use an iPad app’s speed readout as an aid when landing.



One thought exercise is to imagine that you’re flying a plane capable of 50k slow flight in a 50k wind. Start directly into the wind with a zero groundspeed. Then start doing 360’s. With each 360 your groundspeed goes from zero to 100k and back to zero. Imagine how that will feel as you speed up to 100k only to slow back down to zero. How will that feel? How will that sound? You surely will be able to tell when you’re upwind and when you’re downwind, right? The answer is so nonintuitive that you might not believe it, but its true. Try it some time under the hood and the answer will be clear - though not what you might think.

Anyway, let me open the floor to discussions of any of the above, or feel free to add your own “Stick and Rudder Moments".
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The book was considered top shelf when it appeared and for many years after. His son is also a gifted author and well regarded.
 
I happened on it just before I started dying lessons, not long ago. Read it through and it has just tons of interesting and good information. He also is a great writer, he managed to entertain, explain, simplify and most of the drawings are pretty nice too.

I know for sure it helped me when I was studying flight aerodynamics. Some of his concepts stayed with me after the first read.
 
FastEddieB said:
It has to do with frames of reference. One is the ground. We think of it as stationary, but standing on the surface of the planet you may be moving up to about 1,000 mph, depending on your latitude.
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At the equator, you'll be moving around the rotational axis at a bit less than 1000 MPH. But the earth is orbiting the sun, which is orbiting in the Milky Way Galaxy, which is flying outward from the center of the universe at enormous speed. We're all doing way more than 1000 MPH through space, and it's relative to space that inertia is effective.
 
Dan Thomas said:
At the equator, you'll be moving around the rotational axis at a bit less than 1000 MPH. But the earth is orbiting the sun, which is orbiting in the Milky Way Galaxy, which is flying outward from the center of the universe at enormous speed. We're all doing way more than 1000 MPH through space, and it's relative to space that inertia is effective.
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Is that like saying it's turtles all the way up?
 
Cooter143 said:
To be more precise, it would be relative to other matter not space.
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No, not really. Accelerated matter does not determine an inertial reference frame. People used to assume stars determined the rest frame of the universe. Now we have the microwave background, and know that stars and galaxies are not at rest.

But it won't make much difference in an airplane.
 
MAKG1 said:
No, not really. Accelerated matter does not determine an inertial reference frame. People used to assume stars determined the rest frame of the universe. Now we have the microwave background, and know that stars and galaxies are not at rest.

But it won't make much difference in an airplane.
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Not a physicist here, but you mentioned things that meet the definition of matter, with the exception maybe of microwave radiation. Inertial reference is meaningless without reference to some form of matter, right? No training in those things, so set me straight if I'm way off. Does microwave radiation apply force to any object?
 
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Cooter143 said:
Not a physicist here, but you mentioned things that meet the definition of matter. Inertial reference is meaningless without reference to some form of matter. No training in those things, so set me straight if I'm way off.
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Matter is not necessary to determine an inertial reference frame, and the microwave background is an example.

In the context of an airplane, we define inertial reference in terms of gyroscopes. Those do not require outside matter to work, and if you throw baseballs past them, they don't notice.
 
MAKG1 said:
Matter is not necessary to determine an inertial reference frame, and the microwave background is an example.

In the context of an airplane, we define inertial reference in terms of gyroscopes. Those do not require outside matter to work, and if you throw baseballs past them, they don't notice.
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EDIT:
Ok, to the post I responded to he said that inertia is relative to space. My point is that speed and inertia aren't measured in relation to space but to other objects, singular or plural. Does that need to be corrected or not? How can anything exert force with no mass? Mass against space is not restrained or altered, isn't that the fundamental?
 
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Cooter143 said:
Ok, to the post I responded to he said that speed is relative to space. My point is that speed and inertia aren't measured in relation to space but to other objects, singular or plural. Does that need to be corrected or not?
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Yes, it needs correction. The microwave background is not an object, and you can measure velocity and acceleration relative to it. Space itself determines inertia, even if it has nothing in it. You can still determine if you are accelerating even in an empty universe and even if you can't look outside. That's Einsteins elevator thought experiment.
 
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