"Stick and Rudder Moments"

[FastEddieB]

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”.

 

 

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.

 

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 it 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.

 

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) There was the suggestion to use an iPad app’s speed readout as an aid when landing.

 

9) "When the autopilot is turned on, the only time it asks for trim is elevator, and only when it wants the nose held down in a strong headwind."

 

 

 

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".

 

Note: I also posted this to SportPilotTalk.com, since not everyone there frequents this site. I may also post it to PilotsofAmerica.

[Anticept]

I laughed at these physics problems. I've had to, on more than one occasion, try to explain that the ground means nothing to the aircraft flight characteristics, it's all about movement of air molecules.

 

The fun one is an airplane on a conveyor belt affecting take off time. While frictional forces in the wheel bearings will affect the takeoff time, it's so minor that it might as well not be a factor.

[mocfly]

I think the turn from base to final is more likely to lead to a stall spin accident as you are lower and slower than the turn from downwind to base.

I am reminded of the points my primary instructor drilled into my head when working in the pattern. Ball, needle, airspeed using the DG to rollout onto final. He used to really get annoyed when I would be in the turn and start looking for the runway. When I am able to video my landings I pay close attention to my turns in the pattern to see how coordinated they are and have caught myself raising the nose.

[Top Cat]

When I was a CFI with a student in the pattern we usually always turned crosswind to base over a sports facility. As a guide we'd use that to help the student plan their pattern. As they got better we'd tell them that any changes to position (we're past it, we're inside it etc) coupled with an eye on the wind and any changes to its direction and speed would indicate they needed to modify their pattern to compensate.

  Coupled with this, a review of stalls and the dreaded stall/spin on base to final.

 

 One day, the student, getting anxious as the PPL check ride loomed, was getting frustrated in the pattern, overshooting final and increasing bank angle to get aligned, seeking perfection for the examiner.

 

 I decided to go back to the practice area. We did slow flight, stalls and focussed on keeping coordinated and ball centered. His frustrations increased. 

I got us climbed back to 3000 feet, which turned out to be a wise decision.

  We started slow flight and stalls in a turn again and he got so frustrated that he wasn't coordinated that he jammed the rudder in hard in anger and suddenly as we stalled  we flipped right into a spin. He wouldn't let go of the controls and despite my tugging his panic kept a firm grip. 

As we went through 1500 feet I gently eased him off and quietly tried to get him to let go. He did and I corrected the spin, retracted the flaps and was amazed as the windshield filled with a local radio station 1000 below. Breaking news!

 

  He was really upset and defeated so we talked about this as a great teachable moment. Was that a spin he asked? Yes I said and how much altitude did we lose? How quick did we descend? He remarked how now he could see what I meant about shooting through final, farther down the pattern and so lower than normal. Pulling back on the stick  so as not to get any lower as he increased bank to get back on centerline then using opposite rudder to straighten out and not paying attention to airspeed. Cross controlled, low airspeed and low altitude over the golf course near the sports facility. He remarked how he could have spun in really quickly by doing what we'd done today in the practice area.

 

  He recovered quickly and became really positive about the whole thing. He became a huge better pilot and passed his PPL with flying colors.

 

I learned a lot too.  I taught it, but this was the first time we did it. It was instructive and sobering too.

[Ed Cesnalis]

Pitch or power?  The right answer is in the fine print.

 

http://www.flywba.com/id38.html

 

“When power is available and variable, pitch controls altitude and power controls airspeed.”

[Anticept]

My CFI would have fired this student.  Anger in the cockpit is a recipe for a fatality.

We would be really really close to doing that too, depending on how the student acts. If it's a first offense and they show regret after that (not just from the spin) and apologetic about getting mad, then they learned from it. If they act like an ass about it from then on, they are kicked out.

[Top Cat]

My CFI would have fired this student.  Anger in the cockpit is a recipe for a fatality.  Especially the kind of anger leading to freezing on the control in a spin.

 

   If you read what I wrote again you'll see that this student, like many of us trying hard to be successful, got frustrated with himself , yes a little angry, and his performance reflected this. Remember…he's a 'student' pilot being taught to reach PPL standards.

 

  "Firing him' would have been totally the wrong thing to do. As a CFI these things happen during instruction. Instead, I got him turned around so that he learned from this, from the mistakes he was making and how he was handling it.

 

  For what it's worth, he was a great student, apart from that one day. He passed his PPL and went on to join the USAF and  was very successful there and as happy as a clam! I'm very proud of how he turned out.

[FredG]

Stick and Rudder is a fine read.  

[Top Cat]

One thing I don't get about 'stick and rudder' flying…..is that sometimes I fly by the seat of my pants.

[FastEddieB]

9) "When the autopilot is turned on, the only time it asks for trim is elevator, and only when it wants the nose held down in a strong headwind."

[Ed Cesnalis]

9) "When the autopilot is turned on, the only time it asks for trim is elevator, and only when it wants the nose held down in a strong headwind."

 

Strong headwind = reduced ground speed.  Plane flies in the relative wind and drifts along with the air mass.  The plane in cruise is not aware of a steady state strong headwind.

 

Setting the AP for a 500fpm descent without a throttle reduction when in cruise would call for nose down trim.

 

The AP probably never asks for flaperon trim because it sees it as a course correction even if it is a 'heavy wing' from lack of trimming.

[gbigs]

Wind is a force.  A change in that force in a 'steady stream' does indeed affect control surfaces of the aircraft.  Flying in turbulence is a good example.  The FD will buck like a horse or roll like a boat when hit from varying angles by gusts (turbulent air). 

 

The autopilot is setup to fly the plane in a coordinated state along a heading and course either manually set by TRK-ALT or by the flight plan defined in the Garmin using HSI-ALT.   The autopilot issues a yellow/audible warning to change the elevator trim up or down allegedly to make sure when the pilot retakes manual control, the plane will not jerk suddenly up or down based on the trim the autopilot is maintaining to achieve level and coordinated flight.  The autopilot does not issue any warning for rudder or aileron trim.

 

I may not be describing this well enough.  But flying the Dynon Skyview autopilot one time is a big eye opener and an oh wow moment how perfectly it keeps that ball centered. And maintains the altitude indicated in the altitude bug. 

[gbigs]

   If you read what I wrote again you'll see that this student, like many of us trying hard to be successful, got frustrated with himself , yes a little angry, and his performance reflected this. Remember…he's a 'student' pilot being taught to reach PPL standards.

 

  "Firing him' would have been totally the wrong thing to do. As a CFI these things happen during instruction. Instead, I got him turned around so that he learned from this, from the mistakes he was making and how he was handling it.

 

  For what it's worth, he was a great student, apart from that one day. He passed his PPL and went on to join the USAF and  was very successful there and as happy as a clam! I'm very proud of how he turned out.

 

I am happy to hear he settled down and went on to success.

[Tom Baker]

Wind is a force.  A change in that force in a 'steady stream' does indeed affect control surfaces of the aircraft.  Flying in turbulence is a good example.  The FD will buck like a horse or roll like a boat when hit from varying angles by gusts (turbulent air). 

 

The autopilot is setup to fly the plane in a coordinated state along a heading and course either manually set by TRK-ALT or by the flight plan defined in the Garmin using HSI-ALT.   The autopilot issues a yellow/audible warning to change the elevator trim up or down allegedly to make sure when the pilot retakes manual control, the plane will not jerk suddenly up or down based on the trim the autopilot is maintaining to achieve level and coordinated flight.  The autopilot does not issue any warning for rudder or aileron trim.

 

I may not be describing this well enough.  But flying the Dynon Skyview autopilot one time is a big eye opener and an oh wow moment how perfectly it keeps that ball centered. And maintains the altitude indicated in the altitude bug. 

 

The autopilot does nothing to keep the ball centered. Having the airplane trimmed before you turn on the autopilot will help to keep the ball centered. If you want proof of this go flying and trim the rudder until the ball is not centered and turn on the autopilot and see what happens. After this experiment go fly with your CFI and have him re-trim the airplane for you.

[Doug G.]

Sigh...

[FastEddieB]

Flight instructors love imparting knowledge and nothing is better than seeing a student or another pilot have that "AHA!" moment when something finally clicks.

 

So along those lines...

 

1) Is wind a force? Well, duh:

 

A 3kt wind has enough force to barely spin an anemometer.

 

A 50kt wind has enough force to potentially blow you off your feet.

 

A 100kt wind has enough force blow off a roof or worse!

 

But what do the anemometer, your body and the roof have in common?

 

They're all directly or indirectly in contact with the ground. The perceived "force" is simply the resistance to the movement of an airmass over the ground at 3, 50 or 100 kts working on objects on the ground. But a plane in flight feels none of this force. Throw the anemometer in the air and it will move with the air mass and will quickly read zero. Presto-Chango - the wind force disappears. Totally. Completely. Except for...

 

2) Often in discussions like this about the effect of the wind, we are talking about hypothetical steady state winds. Really the movements of air masses. Most statements should and usually are at some point preceded by "Disregarding gusts and shear...", as they should be. But then, all too often, you get, "Well, what about gusts? Or shear???"

 

For instance, from post #12: "A change in that force in a 'steady stream' does indeed affect control surfaces of the aircraft.  Flying in turbulence is a good example.  The FD will buck like a horse or roll like a boat when hit from varying angles by gusts (turbulent air)."

 

Well, again, duh. But this is totally unrelated to whether a plane should fly wing down in a crosswind, or will need more nose down trim in a headwind.

 

 

Anyway, still fishing for that "AHA!" moment when suddenly everything becomes clear. But even if its never reached for one particular pilot, I hope the discussion has benefitted at least one person reading this thread. If so, my work is done!

[FastEddieB]

Finally, pilots should understand that if an autopilot is not hooked up to the rudder, there is no combination of pitch and/or roll it can command that can keep the ball centered. None. Can't happen. Basic aerodynamics.

 

If at cruise speed the ball does stay in the center under command of the autopilot, its good design unrelated to the autopilot. A plane can be designed so that NO rudder is required for a coordinated turn at one particular speed. Normal cruise is a good place for that to happen.

 

Frise type ailerons are but one way. There are others which are easy to research.

 

Maybe someone knows if the CT uses some particular aileron "magic" to reduce the need for rudder at cruise?

[gbigs]

The autopilot does nothing to keep the ball centered. Having the airplane trimmed before you turn on the autopilot will help to keep the ball centered. If you want proof of this go flying and trim the rudder until the ball is not centered and turn on the autopilot and see what happens. After this experiment go fly with your CFI and have him re-trim the airplane for you.

 

The autopilot in the FD CTLSi centers the ball.  The plane is not trimmed before it's activated.  The rudder and aileron trim wheels are left in neutral at all times.  The elevator trim is randomly set before setting the autopilot.  The Dynon Skyview autopilot immediately begins to fly the plane in a coordinated fashion when it's activated regardless of where the elevator trim is at the time it's turned on.

 

I report this from experience using the device almost daily.   Maybe others who own a CTLSi with Dynon Skyview and the Dynon autopilot can offer what their experience is, anyone?

 

I don't have a CFI.  I am a license private pilot.

[FastEddieB]

The autopilot in the FD CTLSi centers the ball.

 

It really does not.

 

Unless it connects to the rudder.

 

Does it? If it does, I stand corrected, and you have some sort of yaw damper, which would be cool!

 

But please reconsider my last post. The ball may stay in the center, but that has nothing to do with the autopilot.

[Znurtdog]

I have to chime in and say that the CTLSi (or LS or SW) does NOT have an autopilot that affects rudder or coordination. I have flown probably 10 CTLS' and a few months ago delivered a brand new Jubilee CTLSi from east coast to west with Dynon Skyview. I assure you, if you are getting coordinated flight it has nothing to do with the autopilot. As is suggested in another post, next time you're coordinated and a/p is on, pull back the throttle and watch the ball. It will go to the left. I promise. 

 

Edit to add.. The autopilot is specifically called "2-axis". That's pitch and roll (aileron) only. 

[FastEddieB]

Thanks.

 

That confirms my assumption.

[Doug G.]

Thanks for the educational info, although I would guess almost all of us knew it.

[FastEddieB]

Thought experiment...

 

Which needs more nose down trim: a CT flying into a 50kt headwind, or one flying with a 50kt tailwind?

 

Which would be louder in the cockpit?

 

Which would run cooler?

 

If the answers to any of those are not obvious, I would again recommend a read - or reread - of Stick and Rudder.

[DoctorJohn]

With a 2 axis autopilot flying the airplane, the only reason it would be in coordinated flight is the rudder trim is set properly for the current flight regime.  It has nothing to do with the autopilot.  There is nothing special about the CTLSi or the autopilot.  This technology has been around for decades.

[ctfarmer]

50kt headwind for the first and second questions.

Need more information for the third but likely a 50kt tailwind.

 

Obvious really. I always tend to fly a lower airspeed when i have a good tail wind for fuel economy.