Left Fuel Tank Issue

[Ian]

Kinda like when you take your hands and feet off of the controls the plane begins to fly real nice?

I flew Cessnas and Pipers for a good many hours and quickly learned that the rudder pedals were just for resting your feet on - LOL

[gbigs]

If you don't have a yaw dampener, your airplane is flying in coordination by happenstance.  You cannot fly in coordination at all times without rudder control, either human or automated.  It's, you know...physics.

 

Do you have the Dynon autopilot?  Well, get into a CT that has one, you will see the effect. 

 

It centers the ball everytime.  In fact, it's fun to see how well it does it.  Level flight, turning between waypoints ball centered.  There is a TRK-ALT mode that lets you fly the plane with the joystick knob.  Heck, you can even alter altitude by simply changing the ALT bug.   And while the plane ascends or descends, the ball just gets stuck in the middle somehow.  Maybe Dynon's world of physicists is different than yours Morden?

[gbigs]

If the autopilot gets it right then it rather implies that the human being flying doesn't quite understand what the rudder pedals are for and how to achieve coordinated flight doesn't it?

 

I love the autopilot.  It flies better than you, me or anyone else.  If you don't have one, get one.  It makes any cross country a joy.  The hardest part of using the Dynon autopilot is finding a way to keep my feet off the rudder peddles.  But I manage it somehow.

[Ian]

:rolleyes: :rolleyes:

Words fail me!

[FlyingMonkey]

Do you have the Dynon autopilot?  Well, get into a CT that has one, you will see the effect. 

 

It centers the ball everytime.  In fact, it's fun to see how well it does it.  Level flight, turning between waypoints ball centered.  There is a TRK-ALT mode that lets you fly the plane with the knob-toggle.  Heck, you can even alter altitude by simply changing the ALT bug.   And while the plane ascends or descends, the ball just gets stuck in the middle somehow.  Maybe Dynon's world of physicists is different than yours Morden?

 

This is not a function of the model of autopilot you have.  No airplane can be flown in coordination at all times without access to the rudder as a control, any more than you could hand fly the airplane in coordination without using rudder.  Flying in coordination is a function of yaw control....what makes the ball go out is yaw, it cannot be brought back into the center without using rudder, e.g. yaw control.  Your AP has no yaw control, as it has no control of the rudder.  Therefore, it will not fly in coordination under the AP in all flight conditions.    

 

Don't get me wrong, I *totally* believe the AP flies the airplane better than you do...  I'm just saying it can't be doing it coordinated through turns, power changes, etc unless it has a servo controlling the rudder.

 

If you are in high speed cruise with the AP on, and you pull power to idle, the ball WILL swing out to the left.  Likewise, if you are at very low power setting in cruise and then you firewall it, the ball WILL swing out to the right.  If not, the ball display in your glass panel is inoperative.  Eventually the ball will settle back down, after aerodynamics catch up to engine torque changes.  But for some period of time, the airplane will fly out of coordination, because neither you nor the AP are controlling the rudder.

 

Dynon gear really does work on physics too, not hopes and wishes.    

[Ed Cesnalis]

I love the autopilot.  It flies better than you, me or anyone else.  If you don't have one, get one.  It makes any cross country a joy.  The hardest part of using the Dynon autopilot is finding a way to keep my feet off the rudder peddles.  But I manage it somehow.

 

I use the pedals when the AP flies.  I can quiet the yawing in turbulence and coordinate the turn if needed.

[gbigs]

This is not a function of the model of autopilot you have.  No airplane can be flown in coordination at all times without access to the rudder as a control, any more than you could hand fly the airplane in coordination without using rudder.  Flying in coordination is a function of yaw control....what makes the ball go out is yaw, it cannot be brought back into the center without using rudder, e.g. yaw control.  Your AP has no yaw control, as it has no control of the rudder.  Therefore, it will not fly in coordination under the AP in all flight conditions.    

 

Don't get me wrong, I *totally* believe the AP flies the airplane better than you do...  I'm just saying it can't be doing it coordinated through turns, power changes, etc unless it has a servo controlling the rudder.

 

If you are in high speed cruise with the AP on, and you pull power to idle, the ball WILL swing out to the left.  Likewise, if you are at very low power setting in cruise and then you firewall it, the ball WILL swing out to the right.  If not, the ball display in your glass panel is inoperative.  Eventually the ball will settle back down, after aerodynamics catch up to engine torque changes.  But for some period of time, the airplane will fly out of coordination, because neither you nor the AP are controlling the rudder.

 

Dynon gear really does work on physics too, not hopes and wishes.    

 

Like I said, I am experiencing the EXACT outcome I have described. 

 

The autopilot in the Dynon Skyview in the Flight Design CTLSi maintains center-ball during cruise flight, ascending, descending and in turns when the winds are below 25kts.  Above that, turbulence can overcome the servos and cause them to slip and manual control is necessary again.

 

Here is a good overview of all the functions the Autopilot provides:  http://www.dynonavionics.com/docs/SkyView_AutopilotServos.html

[Tom Baker]

Like I said, I am experiencing the EXACT outcome I have described. 

 

The autopilot in the Dynon Skyview in the Flight Design CTLSi maintains center-ball during cruise flight, ascending, descending and in turns when the winds are below 25kts.  Above that, turbulence can overcome the servos and cause them to slip and manual control is necessary again.

 

Here is a good overview of all the functions the Autopilot provides:  http://www.dynonavionics.com/docs/SkyView_AutopilotServos.html

Some of us have been doing this a little bit longer than you have. We know how the autopilot works and how it effects the control system. For instance if using the autopilot while flying in a crosswind the airplane will keep trying to turn into the wind to maintain its track. The next time you are using the autopilot look at the wingtips to see if they are level to the horizon, if you have a crosswind they won't be level.

[FastEddieB]

Tom, either you are expressing yourself poorly are you have that quite wrong. Once that wind correction angle is established the wings will in fact be quite level.

 

Again, the airplane will be flying straight and level in an air mass which is itself moving.

[Ed Cesnalis]

Agreed Eddie as long as the rudder is trimmed.  You can trim the rudder for a wing low cruise i.e. CT fuel management mode.

[Tom Baker]

Tom, either you are expressing yourself poorly are you have that quite wrong. Once that wind correction angle is established the wings will in fact be quite level.

Again, the airplane will be flying straight and level in an air mass which is itself moving.

In theory I Agree with you, but what I observe in real life has been quite different. I don't have a bunch of time in other airplanes with autopilots, but all of the CT's I have flown with autopilot shown this behavior.

[FlyingMonkey]

In theory I Agree with you, but what I observe in real life has been quite different. I don't have a bunch of time in other airplanes with autopilots, but all of the CT's I have flown with autopilot shown this behavior.

 

It could be that once the AP is able to maintain the heading and/or altitude desired, it will happily do so with one wing down if that is where it first establishes an equilibrium it can maintain.  

 

After all, all the AP cares about is that the assigned heading and/or altitude is maintained.  It doesn't give a whit about wings being level.

[Ed Cesnalis]

In theory I Agree with you, but what I observe in real life has been quite different. I don't have a bunch of time in other airplanes with autopilots, but all of the CT's I have flown with autopilot shown this behavior.

 

Tom, if you are in cruise with the AP flying and a wing is low just use the rudder trim to level the wings.  Coordinated flight has less drag and is more efficient.

[FredG]

My 2-axis TT autopilot will establish a stable crab into the wind with wings level to maintain a ground track  during flight with crosswind (essentially, it will establish and fly the wind correction angle).  For a given power level, the ball may need to be adjusted once with rudder trim to be in the center.  In steady state flight with the autopilot, regardless of wind correction angle, when the ball is in the center, the wings are level.

 

In my plane, if the autopilot flies the plane with a low wing, the ball will be out of center and the rudder needs trimming.  Don't know anything about other planes.  

[Ed Cesnalis]

To have your plane fly like Fred's first use the rudder trim to cruise wings level, then after that works get your ball adjusted.  For many that means moving the whole binnacle back where it belongs.

[FredG]

Consistent with what CT said, my panel had to be adjusted so that the Dynon was level (ball in center) after the wings were leveled on the ground.  

[gbigs]

As I noted before.  My rudder and aileron trim are PERMANENTLY left at neutral.  The only trim i set by hand is elevator, an electric toggle.  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.  

 

The Skyview autopilot must be unusually good since I have never in over 14 months of using it seen the ball go out except in a strong gust, and then the servos slip and I have to take control.   

 

When flying through Bravo where my altitude needs to be held constant i set the autopilot in TRK-ALT mode so i can alter heading when requested without having to take back manual control.  The aircraft always makes full coordinated banked turns with ball centered. No other adjustments need to be made.

[Ed Cesnalis]

Things that make a 2-axis AP fly coordinated.

1. A long coupled airplane that exhibits less adverse yaw, especially at low bank angles, than a short coupled design.  (A CT is generally short coupled with ample adverse yaw.)
2. AP settings like gain settings that limit bank angles and do more gradual turns that have less need for rudder correction.

If you and your AP use abrupt control inputs you are going to need rudder to correct, if you use limited inputs you might get a result more like hamburger describes.

[FastEddieB]

I've been on the road with Karen in Florida but others have covered the subject pretty well.

 

To reiterate, I thought the implication in Tom's original post was that by flying wing low, the autopilot was constantly turning into the wind to prevent drift. That's what I was objectiing to.

 

With the wing down and the heading not changing, the plane is definitely not turning, nor correcting for the "wind" in way. It's simply flying along in a slip, due to something being slightly out of rig or trim.

 

If a CT or any other plane is doing that, something is wrong. If anyone recalls, it was one of the scenarios I listed in my "Stick and Rudder Moments" thread, where the Cirrus demo pilot opined the right wing in the demo was low due to a right crosswind.

 

Anyway, I did not mean to jump on anyone. My antenna are just for things like that, and they're certainly not uncommon!

[gbigs]

Things that make a 2-axis AP fly coordinated.

1. A long coupled airplane that exhibits less adverse yaw, especially at low bank angles, than a short coupled design.  (A CT is generally short coupled with ample adverse yaw.)
2. AP settings like gain settings that limit bank angles and do more gradual turns that have less need for rudder correction.

If you and your AP use abrupt control inputs you are going to need rudder to correct, if you use limited inputs you might get a result more like hamburger describes.

 

 

CT, the word 'abrupt' is subjective.

 

What I do when i fly with TRK-ALT is turn the joy-stick-knob about three degrees per second (standard rate turn).  I don't spin the knob.   I have not tried to spin it fast enough to cause the autopilot grief.  If I have to turn more than about 20 degrees after an ATC directive then I take it off the autopilot and make the turn, and put it back on gain.  I am more concerned with servo slip, than rudder input.

 

The bank angle is set to 30 degrees max at present - the default.  It makes these turns ball centered without additional inputs also.

 

Pulling on the stick or pushing on a rudder while the autopilot is operating is frowned upon in any case and not necessary.  I assume because it is possible to break a shear pin or otherwise degrade or destroy a servo.

[FastEddieB]

That's another one I'll add to my "Stick and Rudder Moments" list

[Tom Baker]

Tom, if you are in cruise with the AP flying and a wing is low just use the rudder trim to level the wings.  Coordinated flight has less drag and is more efficient.

 

Every CT I have flown except one with autopilot on required rudder trim be adjusted for the wings to be level. The ball was always out of center. The one exception had weak rudder centering springs and you could place it a yawed position and it would stay there.

 

Edited to add: trimmed wings level ball center with out the autopilot does not feel like it is un-coordinated, and generally I can feel when an airplane is slipping or skidding.

[FlyingMonkey]

This whole conversation reminds me of a story, about a mother watching her son in the local marching band as they went by in the town parade. Beaming with pride, the mother remarked:

 

"It's appalling that *every* one of the band members is out of step, except my son!"

[Ian]

Why would your autopilot want nose down trim in a strong headwind?  That makes no sense.

Nothing new there then!

[Ed Cesnalis]

Every CT I have flown except one with autopilot on required rudder trim be adjusted for the wings to be level. The ball was always out of center. The one exception had weak rudder centering springs and you could place it a yawed position and it would stay there.

 

Edited to add: trimmed wings level ball center with out the autopilot does not feel like it is un-coordinated, and generally I can feel when an airplane is slipping or skidding.

 

Wings level in AP cruise is coordinated, ball centered indicates coordinated cruise as well but the ball can be wrong.