Rudder Coordination Exercises- what the heck is the rudder for????

[Cripple]

And things get even more interesting once one starts ejecting little ballistic projectiles (aka "bullets") from the front of your aircraft...

 

I've attached several pages from Wing Co. Donaldson's 1943 Notes On Air Gunnery and Air Fighting (as compiled in Fighting In The Air, 1978 ) for info. Short version of this is as follows:

- Bullets go the way the plane is going, not the way the plane's nose is pointed. These are not necessarily the same.

- The way the target's nose is pointing may not be representative of his flight path.

- You must be flying in a coordinated manner in order to shoot straight.

- Your rudder is only "trimmed" at one airspeed (duh!). Climbing or diving to engage the target will change this airspeed, requiring a change of trim to compensate (again, duh!). This should be done instinctively and with the rudder pedals rather than with the trim tabs to allow it to become second nature in combat.

- Never use your rudder alone to nudge your sights on target as you will immediately impart skid/slip/sloppy-flying. Bank and use the rudder to remain in coordinated flight.

- These slips and skids are barely perceptible, and therein lies the danger...

 

(It may also be worth remembering that this is not Star Wars, and these bullets take time to fly to their target. So one is firing where you expect the target to be, rather than where it is when you press the button. If the target or you aren't pointing exactly the way you are flying... Well, you can see the problem. Oh, and that's without even touching on the other wee foibles of ballistics and aerial gunnery.)

[Gooseneck]

Amazing achievement for this man to be a top scoring ace with 2 missing legs.

 

Of course it is. Also his escape from a Luftwaffe hospital, if memory serves. I was being a little sarcy (maybe a lot), in the comment I made, but it's evident that his rudder control wouldn't have been 'toe-sensitive' in turns, which my hotas pedals most definitely are.

 

It'd be great if you real life pilots could somehow give us all a clue as to how sensitive they should be though.

 

I remember Yo-yo saying in his Spit thread, 'be careful what you wish for' as far a stick sensitivity is concerned, but does it really matter when we can ruin all his hard work with the axis tune menu, with deadzones, saturation and curvature?

Edited October 17, 2015 by Dooyar

[bongodriver]

I generally find computer simulation rudder to be a little too sensitive and I'd really like a force feedback rudder one day, in real life it's quite easy to deal with lightness and sensitivity in pitch and roll, but no feedback from the pedals is just odd to me.

 

Yo-Yo made that post and was referencing a report on a MkV, if we end up with a MkIX with a MkV FM then something has gone hideously wrong.

[Gooseneck]

I generally find computer simulation rudder to be a little too sensitive and I'd really like a force feedback rudder one day, in real life it's quite easy to deal with lightness and sensitivity in pitch and roll, but no feedback from the pedals is just odd to me.

 

Thanks Bongo. You betcha. I suppose we can dream of the day.

[Crumpp]

And things get even more interesting once one starts ejecting little ballistic projectiles (aka "bullets") from the front of your aircraft...

 

I've attached several pages from Wing Co. Donaldson's 1943 Notes On Air Gunnery and Air Fighting (as compiled in Fighting In The Air, 1978 ) for info. Short version of this is as follows:

- Bullets go the way the plane is going, not the way the plane's nose is pointed. These are not necessarily the same.

- The way the target's nose is pointing may not be representative of his flight path.

- You must be flying in a coordinated manner in order to shoot straight.

- Your rudder is only "trimmed" at one airspeed (duh!). Climbing or diving to engage the target will change this airspeed, requiring a change of trim to compensate (again, duh!). This should be done instinctively and with the rudder pedals rather than with the trim tabs to allow it to become second nature in combat.

- Never use your rudder alone to nudge your sights on target as you will immediately impart skid/slip/sloppy-flying. Bank and use the rudder to remain in coordinated flight.

- These slips and skids are barely perceptible, and therein lies the danger...

 

(It may also be worth remembering that this is not Star Wars, and these bullets take time to fly to their target. So one is firing where you expect the target to be, rather than where it is when you press the button. If the target or you aren't pointing exactly the way you are flying... Well, you can see the problem. Oh, and that's without even touching on the other wee foibles of ballistics and aerial gunnery.)

 

The basic point of those instructions is uncoordinated flight makes the sights ineffective.

 

If you want to shoot accurately, keep the aircraft coordinated when you pull the trigger.

[Cripple]

The basic point of those instructions is uncoordinated flight makes the sights ineffective.

 

If you want to shoot accurately, keep the aircraft coordinated when you pull the trigger.

 

Yup. :thumbup:

[Bucic]

Umm. The problem with virtual flying, is that the response of the aircraft versus input bears no relation to real life, because it is dependant on your own personal controller setup. A Saitek Cyborg will work and feel differently to a Logitech 3Dpro. With or without twistgrip rudder control.

 

A Thrustmaster Warthog with additional proprietary pedals will work differently to a Logitech G940 Hotas.

 

For instance, my rudder pedals are incredibly sensitive, such that I have to create a 5% deadzone in the 'Axis Tune' menu, followed by an adjustment to the sensitivity curve of 25%. That's with most DCS aircraft. I have no idea whether the rudder response I achieve by this is accurate for any aircraft.

 

The trouble is that we have no way of knowing how our own personal controller/game response relationship matches real life at all, in any computer game or simulation.

 

So how about giving us the benefit of your experience, tell us what controller setup you have, what your deadzone and curvature settings are, and how these relate to your experiences in real life?

 

This would be really helpful.

That alone deserves a separate topic. You see, as with the "roll requires rudder" rule being almost set in stone the same applies to "any curvature or dead zone makes it much harder if not impossible for your brain to process and establish muscle memory reflexes." As with many other issues "being just a preference"...it's not. You only use as much of those as poor your flight controls are. Here's my old topic on the subject:

http://forums.eagle.ru/showthread.php?t=58138&highlight=configuration

 

As for the exercises Crumpp proposes, please consider using a solidly fixed camera to make it easier to watch the motion of the aircraft. For external view I recommend a variant of the F4 view, while for cockpit view I recommend disabling any head bobbing and G force effects. Brain again. In-game you are depraved of the real-life sense allowing you to precisely establish the movement and current position of your head and limbs.

 

And a Spitfire aerobatic (display) routine showing some intense rudder use. ...

Well, it may not be that obvious after all ;)

[ame]

[/ame]
Edited November 19, 2015 by Bucic

[Echo38]

any curvature or dead zone makes it much harder if not impossible for your brain to process and establish muscle memory reflexes." As with many other issues "being just a preference"...it's not. You only use as much of those as poor your flight controls are.

 

This, exactly. It took flying a real airplane for only an hour before I fully understood this, and it was immediately after my first real flight that I removed all curves & deadzones from my stick, ~15 years ago. Since that day, I have never used any settings on my joystick other than direct input. There's no doubt about the effect.

[Crumpp]

it was immediately after my first real flight that I removed all curves & deadzones from my stick,

 

I do not have any special curves. All my controllers are set to default.

 

In-game you are depraved of the real-life sense allowing you to precisely establish the movement and current position of your head and limbs.

 

It seems to work very well just looking out over the nose like I do in a real aircraft in DCS.

 

Now my view is not the default view. In real airplanes, I adjust the seat to see over the nose whether I am flying a large transport category aircraft at work or my Thorp T-18 at home.

 

It gives me a good visual reference for my rudder input and hunching down a little to use the gunsite is not an issue.

[Echo38]

Whenever an aileron is deflected, there is unbalanced lift/drag on the wings and rudder is needed to offset the unwanted yaw. However, as soon as the bank angle is established, the ailerons should be neutralized, which means the rudder input is no longer needed. No aileron, no rudder.

 

This one puzzles me. While, of course, the greatest need for rudder while banking comes from adverse yaw, which only occurs while the ailerons are deflected, I was always under the impression that--while greatly reduced--there was still some need for corrective rudder after the bank was established and the stick neutralized. "To keep the tail from slipping into the turn." Something about the horizontal stabilizer and ... gravity? TBH, I never really understood the reason for the effect, but this is what I always was told, and the effect seems to be present in DCS.

 

Anyway, it's quite possible that I'm wrong, but my understanding of the issue was that you needed a lot of rudder when rolling (to counter adverse yaw), and then when returning the stick to neutral, rudder should be brought towards center (because adverse yaw is decreasing along with the stick deflection), but if still in the bank, some slight rudder in that direction should be maintained even after stick is centered (and thus zero adverse yaw). The steeper the bank (up to 90 degrees), the more the rudder needed to maintain coordination.

 

Is this inaccurate, then? Is there no effect--during a constant bank--by which the tail will naturally attempt to fall into the direction of the bank, causing a slight slip, if not corrected for with a small, constant rudder input, proportionate to the degree of bank?

[Crumpp]

It depends on the aircraft and it stability.

 

Most of them remain coordinated. My Thorp T-18 will stay coordinated in left hand turns but because of power effects requires some top rudder to stay coordinated in right hand turns.

[Echo38]

What is the effect, exactly? The horizontal stabilizer provides downforce, right, so--when banked--I would expect that the force vector of that would be away from the direction of the turn, not into it. So what is it that causes the tail of some aircraft to swing into the turn, when not corrected with rudder?

[Bucic]

What is the effect, exactly? The horizontal stabilizer provides downforce, right, so--when banked--I would expect that the force vector of that would be away from the direction of the turn, not into it. So what is it that causes the tail of some aircraft to swing into the turn, when not corrected with rudder?

You shouldn't suddenly switch to global coordinate system. Stick to the one tied to the aircraft you analyze. Then it should be of no problem. The horizontal stabilizer will not meddle with directional stability of the aircraft as you brake down the forces at play.

Edited November 20, 2015 by Bucic

[Echo38]

I don't understand; could you re-phrase?

[Crumpp]

He says, "Eat the elephant ONE bite at a time!" to understand what is going on.

 

You have to examine each axis of the aircraft to determine how it will behave. The vertical stabilizer is not going to pull the aircraft into uncoordinated flight unless it is a poor design or mismatched.

 

My aircraft for example is has a larger engine than the vertical stabilizer was optimized for so the offset for spiral slipstream is not perfectly matched to the engine power. That creates the need for top rudder in shallow banks to the left.

 

I should disassemble it and put a spacer to increase the offset but I have not and probably will not do it. :P

[Captain Orso]

I'm not sure, but I think you guys are confusing Echo38.

 

This is the way I learned it many, many years ago:

 

- To change the heading of an aircraft you change some of the lift-vector (the lift created by the wing moving through the air and holding the aircraft at a stead altitude) toward the direction you wish to turn. This is done by changing the horizontal attitude of the wings with the ailerons in causing the aircraft to go into an attitude know as a bank.

 

- Once the aircraft has reached the desired banking angle, the ailerons can be returned to neutral as the bank will be maintained by the wings.

 

- If nothing else interested you than that the aircraft turns, you have nothing else to think about. The aircraft is now in an attitude with will cause it to turn. However, since some of the lift-vector is now being used to turn the aircraft, the aircraft will start to lose altitude, as there is not enough lift-vector to maintain the original altitude.

 

- Assuming however do you wish to maintain the original altitude, you must exchange another force to compensate for the loss of the lift-vector. This force is forward momentum. To do this, you pull back on the elevator. Now you have compensated the exchange of lift-vector to the turning-vector with the elevator.

 

- Now however using the elevator is going to cause the nose to raise and increase your angle of attack, which will cause your aircraft to climb. But you want to maintain the original altitude. So to prevent the nose from climbing, you use the rudder to hold the nose level.

 

And that's what the rudder is for :joystick:

[Crumpp]

I'm not sure, but I think you guys are confusing Echo38.

 

He is not asking how to use the rudder. He is asking why you do not have to maintain rudder input throughout the turn.

 

 

This is the way I learned it many, many years ago:

 

- To change the heading of an aircraft you change some of the lift-vector (the lift created by the wing moving through the air and holding the aircraft at a stead altitude) toward the direction you wish to turn. This is done by changing the horizontal attitude of the wings with the ailerons in causing the aircraft to go into an attitude know as a ba

 

I absolutely sure you were taught that in a tricycle gear airplane. It is pretty much wrong.

 

:smilewink:

 

You lead the ailerons with just enough rudder input to keep the nose aligned on the longitudinal axis as you establish the turn.

 

That is all there is to it. That is the only way to make a coordinated turn in an airplane.

 

In a coordinated turn, the airplane’s nose should appear to stay in one place as the airplane rolls into or out of a bank.

 

http://www.jetairgroup.com/2013/03/19/how-to-make-coordinated-turns/

 

Just like the tracks I posted, the and just like Rod Machado relates.

 

So, when we bank the airplane by lowering the outside aileron and raising the inside one, we've asked for more lift on the outside wing and less on the inside wing. This is another way of saying we've increased drag on the outside wing and decreased it on the inside one. So, what happens when there is more drag on the outside wing than on the inside one? That extra drag pulls the outside wing back, so the nose yaws to the outside of the turn. Enter the rudder to save the day. A little rudder is applied in the direction of the turn, along with the ailerons, to offset that yaw and keep the nose turning.

 

A rule not to be violated: Whenever an aileron is deflected, there is unbalanced lift/drag on the wings and rudder is needed to offset the unwanted yaw. However, as soon as the bank angle is established, the ailerons should be neutralized, which means the rudder input is no longer needed. No aileron, no rudder. Period.

 

http://flighttraining.aopa.org/magazine/2005/December/200512_Features_Choose_to_fly_right.html

 

The rudder always leads the ailerons just a fraction of a second beforehand to stop that yaw created by asymmetrical lift experienced in the roll.

 

The way to see if you did it right is by looking at the nose and NOT the inclinometer.

 

http://www.aircraftspruce.com/menus/in/inclinometer.html

[jvanhoog]

Great thread, thanks.

[Anatoli-Kagari9]

And in gliders, which are particularly prone to adverse yaw effects, we many times use almost full rudder to initiate a turn and capture a tight thermal, and only then input required aileron for coordination, most of the time, during the turn, using cross controls to stay coordinated :-)

[Bucic]

I don't understand; could you re-phrase?

What is the effect, exactly? The horizontal stabilizer provides downforce, right, so--when banked--I would expect that the force vector of that would be away from the direction of the turn, not into it. So what is it that causes the tail of some aircraft to swing into the turn, when not corrected with rudder?

You switched from local coordinate system to the global c.s. Simply put you analyze forces acting on the (an?) A/C in the standard coordinates tied to it, with lateral axis along the wings, long. axis along the fuselage etc. When the aircraft banks you don't discard the convention. And so, when banked the horizontal stabilizer continues do provide down force without contributing to the lateral sum of forces. The school is to establish the balance/imbalance of forces in that coordinate system and then deduct the impact of the imbalanced forces on the trajectory and angular accelerations. It may sound like stuck-up rule but I can hardly imagine a case this would complicate things rather then simplify.

 

So, in the local coordinate system:

in an established balanced turn with ailerons neutral there is no significant difference between straight and level flight and your turn as far as investigating what may cause a sideslip. And I don't see anything but propeller slipstream that could cause a sideslip.

Correct me if I'm wrong, anyone.

[Bucic]

.

Could you please tell me what does 'top rudder' mean?

Also, why do you blame tricycles? Sure it's not the nose wheel which makes the difference in yaw behavior in flight. :)

[Echo38]

And so, when banked the horizontal stabilizer continues do provide down force without contributing to the lateral sum of forces. The school is to establish the balance/imbalance of forces in that coordinate system and then deduct the impact of the imbalanced forces on the trajectory and angular accelerations. It may sound like stuck-up rule but I can hardly imagine a case this would complicate things rather then simplify.

 

So, in the local coordinate system:

in an established balanced turn with ailerons neutral there is no significant difference between straight and level flight and your turn as far as investigating what may cause a sideslip.

 

The vector of Earth's gravity has changed, and is now pulling on the aircraft from the low side, rather than from directly below. This means that it is no longer aligned with the downforce vector of the horizontal stabilizer.

 

However, this indicates to me that a skid would be caused*, rather than the slip which I was (years ago) told to expect (and which slip appears to occur in DCS, as well as most sim/games). Which just makes me even further confused. On one hand, several things (e.g. some real-life sources, tests within DCS) indicate that there should be (e.g. in aircraft designed prior to modern balancing methods) some slip during an established bank with ailerons & rudder neutralized. On the second hand, Crumpp & others state that there should not be such a slip (at least on "normally"-balanced aircraft). Finally, at the third end, my own (doubtless flawed) examination of the vectors indicate that there should be a skid, rather than a slip, during said established bank with ailerons & rudder neutralized.

 

So, what am I missing? I think I've noted that gravity was not being accounted for in your explanation, but while I am in mine, it appears to do the opposite of what I've always believed to be the effect. Hence my confusion. The three different explanations involved have, for the necessary position of the rudder to maintain coordination in a steady bank, two at opposite positions, and one in the middle.

 

* Clarification: to take an extreme example to demonstrate the effect, if the aircraft is banked 90 degrees, then gravity is no longer providing any downward (local coordinate) force upon the tail, but rather 1G of side-force. As such, the net total of combined downforce on the tail (stabilizer downforce + gravity's downforce) has been reduced, and so the tail should rise upward (still local coordinate, so into the turn, reducing the turn rate). But the gravity vector is pulling from the side, which should cause the tail to drop into the direction of the turn (and thus the nose to skid away from the direction of the turn). This is the opposite effect from the one which my real-life sources and within-sim tests indicate should happen. And Crumpp says that neither of those two effects should normally occur.

 

So what am I missing? Maybe someone should draw some vector diagrams ... I'm having great difficulties with this. Adverse yaw is easy (aileron deflection = adverse yaw, no aileron deflection = no adverse yaw, regardless of anything else), but the rest of it is tricky, because of things like gravity and local-vs.-global, and turn-vs.-climb.

Edited November 21, 2015 by Echo38

[Crumpp]

Could you please tell me what does 'top rudder' mean?

Also, why do you blame tricycles? Sure it's not the nose wheel which makes the difference in yaw behavior in flight. :)

 

Top rudder means you have to add some opposite rudder in the turn once it is established to maintain coordinated flight.

 

When I turn to the right in my aircraft, it requires a little left rudder to maintain coordinated flight once the turn is established.

 

You still lead the turn itself with right rudder to remain coordinated and as the turn is established add a little "top rudder" because you are stepping on the blue side and not the green side!

 

The nose gear in a tricycle gear aircraft has a stabilizing effect on the aircraft. It acts very similar to a vertical stabilizer. It is the reason so many modern pilots have lost the "rudder" in their stick and rudder skills.

 

 

Maybe someone should draw some vector diagrams

 

 

I think this picture might help.

 

Edited November 21, 2015 by Crumpp
Clarity...it looked like I was explaining force vectors to Bucic.

[Crumpp]

Normal Turn is a coordinated turn, btw.

[Crumpp]

However, this indicates to me that a skid would be caused*, rather than the slip which I was (years ago) told to expect (and which slip appears to occur in DCS, as well as most sim/games). Which just makes me even further confused. On one hand, several things (e.g. some real-life sources, tests within DCS) indicate that there should be (e.g. in aircraft designed prior to modern balancing methods) some slip during an established bank with ailerons & rudder neutralized. On the second hand, Crumpp & others state that there should not be such a slip (at least on "normally"-balanced aircraft). Finally, at the third end, my own (doubtless flawed) examination of the vectors indicate that there should be a skid, rather than a slip, during said established bank with ailerons & rudder neutralized.

 

Keep in mind the method of turn entry determines the turn properties.

 

If you establish a turn in a skid or slip, it will stay a skidding or slipping turn for a while.