Question for a Commercial airline pilot, or anyone who knows
Discussion
Hi,
Not a frequent visitor to this part of PH but I think there are a few pilots floating around so hopefully you can answer my stupid question.
Why do pilots bank when they turn and not just use the rudder? OK I get it for takeoff/landing but when you are cruising in the middle of the flight and it seems to the passenger like a small adjustment?
Enlighten me even if it is a bit of a dumb question!!
Not a frequent visitor to this part of PH but I think there are a few pilots floating around so hopefully you can answer my stupid question.
Why do pilots bank when they turn and not just use the rudder? OK I get it for takeoff/landing but when you are cruising in the middle of the flight and it seems to the passenger like a small adjustment?
Enlighten me even if it is a bit of a dumb question!!
To stop the aircraft skidding.
A banked turn is more controllable and more comfortable for those on board.
A skidded turn produces sidewards G forces which passengers may not appreciate (and they might spill their drinks too).
In actual fact, due to the secondary effects of control, initiating a bank (using the ailerons on the wings) will also cause the aircraft to turn into the bank - so little or no rudder need be used for a gentle turn.
A banked turn is more controllable and more comfortable for those on board.
A skidded turn produces sidewards G forces which passengers may not appreciate (and they might spill their drinks too).
In actual fact, due to the secondary effects of control, initiating a bank (using the ailerons on the wings) will also cause the aircraft to turn into the bank - so little or no rudder need be used for a gentle turn.
Eric Mc said:
To stop the aircraft skidding.
A banked turn is more controllable and more comfortable for those on board.
A skidded turn produces sidewards G forces which passengers may not appreciate (and they might spill their drinks too).
In actual fact, due to the secondary effects of control, initiating a bank (using the ailerons on the wings) will also cause the aircraft to turn into the bank - so little or no rudder need be used for a gentle turn.
Not quite true though - the secondary effect of using the ailerons to roll is adverse yaw; the nose swings outside of the turn, which needs to be compensated for with a touch of rudder.A banked turn is more controllable and more comfortable for those on board.
A skidded turn produces sidewards G forces which passengers may not appreciate (and they might spill their drinks too).
In actual fact, due to the secondary effects of control, initiating a bank (using the ailerons on the wings) will also cause the aircraft to turn into the bank - so little or no rudder need be used for a gentle turn.
One can't just 'turn using the rudder'. Whilst you can change the direction the aircraft is pointing (its heading) with the rudder, it will still be travelling in (roughly) the same direction (track), just with the nose pointing in a different direction. Of course what you're doing then is offering up the side of the fuselage to the airflow, creating large amounts of drag, and not actually changing direction.
Big News said:
Not quite true though - the secondary effect of using the ailerons to roll is adverse yaw; the nose swings outside of the turn, which needs to be compensated for with a touch of rudder.
Not strictly true, it depends upon the Lift/Drag Co-Efficient of the wing, the speed of the a/c, and whether or not you have differential ailerons.Adverse yaw occurs typically in Gliders or some 'Puddle Jumpers' and is the result of the down-going aileron causing the wing to rise, because it has increased the lift, but causing increased Induced (ie Lift Dependent) Drag.
Once the a/c has started to roll, then owing to its weathercock stability it will yaw towards the down-going wing. Eventually the nose will drop and a Spiral Dive will occur. In a/c with any reasonable amount of speed the Adverse Yaw will not occur because the a/c moves through that regime too quickly.
Big News said:
One can't just 'turn using the rudder'. Whilst you can change the direction the aircraft is pointing (its heading) with the rudder, it will still be traveling in (roughly) the same direction (track), just with the nose pointing in a different direction. Of course what you're doing then is offering up the side of the fuselage to the airflow, creating large amounts of drag, and not actually changing direction.
Well actually, yes you can (what you are talking about is a cross-controlled skid or slip). If you yaw the a/c then the outside wing will have a higher relative airspeed to the inside wing. Ergo it will produce more lift and the a/c will begin to roll towards the inside wing. Eventually the nose will drop and a Spiral Dive will be the result.If you couldn't turn an a/c with rudder alone, then you wouldn't be able to carry out a 'Stall-Turn'!
Eric basically has it.
OP, think about when you go around a corner fast in a car - Centripetal Force makes it uncomfortable and you end up trying to slide to the outside of the turn owing to Transverse G.
The same thing would initially happen in an a/c (let alone the aerodynamic effects possibly leading to fin-stall and even structural failure).
By banking the a/c and flying a balanced tun, not only is everything more comfortable (because any G applied occurs in the 'Normal' sense), but it is aerodynamically more efficient (less drag).
OP, think about when you go around a corner fast in a car - Centripetal Force makes it uncomfortable and you end up trying to slide to the outside of the turn owing to Transverse G.
The same thing would initially happen in an a/c (let alone the aerodynamic effects possibly leading to fin-stall and even structural failure).
By banking the a/c and flying a balanced tun, not only is everything more comfortable (because any G applied occurs in the 'Normal' sense), but it is aerodynamically more efficient (less drag).
Edited by Ginetta G15 Girl on Monday 26th August 19:54
Ginetta G15 Girl said:
Not strictly true, it depends upon the Lift/Drag Co-Efficient of the wing, the speed of the a/c, and whether or not you have differential ailerons.
Adverse yaw occurs typically in Gliders or some 'Puddle Jumpers' and is the result of the down-going aileron causing the wing to rise, because it has increased the lift, but causing increased Induced (ie Lift Dependent) Drag.
Once the a/c has started to roll, then owing to its weathercock stability it will yaw towards the down-going wing. Eventually the nose will drop and a Spiral Dive will occur. In a/c with any reasonable amount of speed the Adverse Yaw will not occur because the a/c moves through that regime too quickly.
I guess I'm approaching this as a glider pilot, so have a somewhat heightened requirement for bootfulls of rudder!Adverse yaw occurs typically in Gliders or some 'Puddle Jumpers' and is the result of the down-going aileron causing the wing to rise, because it has increased the lift, but causing increased Induced (ie Lift Dependent) Drag.
Once the a/c has started to roll, then owing to its weathercock stability it will yaw towards the down-going wing. Eventually the nose will drop and a Spiral Dive will occur. In a/c with any reasonable amount of speed the Adverse Yaw will not occur because the a/c moves through that regime too quickly.
Ginetta G15 Girl said:
Well actually, yes you can (what you are talking about is a cross-controlled skid or slip). If you yaw the a/c then the outside wing will have a higher relative airspeed to the inside wing. Ergo it will produce more lift and the a/c will begin to roll towards the inside wing. Eventually the nose will drop and a Spiral Dive will be the result.
If you couldn't turn an a/c with rudder alone, then you wouldn't be able to carry out a 'Stall-Turn'!
Okay that's fair enough. I was alluding to the OP's phrasing where he asked why the pilots bank the aircraft instead of just using the rudder. I've done enough spinning and spiral diving to know that you can make the aircraft drop a wing/bank using just the rudder, I was (albeit clumsily) trying to explain that one can't simply steer the aircraft around the sky at a constant attitude with the wings level...!If you couldn't turn an a/c with rudder alone, then you wouldn't be able to carry out a 'Stall-Turn'!
Though equally powered flying may be completely different (I have very little powered experience) and thus I may be talking rubbish!
A car "corners" because of the high tyre friction against the road. The front tyres turn and as a result the body yaws around it's vertical axis. The crucially, the rear tyres are now also at an angle to the direction of momentum, and they to can build a lateral force against the forward motion. As a result, the cars path is forced away from the direction of momentum. If you drive on say sheet ice, which has little friction, you can turn the steering wheels all the way to the lockstops and the car will simply "understeer" and continue in a straight line.
A plane, because it is flying in air, has virtually no "lateral" grip on the air (analogous to the car on ice example). The entire airframe is designed simply to support its mass, using the wings, producing lift in opposition to the mass, in a vertical direction. In order to actually turn, banking the plane into the turn results in the lift vector also point inwards and results in the plane turning with little extra drag.
Simply using the rudder to cause the airframe to yaw around its vertical axis has little effect on the planes heading (the airframe will yaw, but it will effective just slide "sideways" through the air). In this case, it is only the force of the air hitting the fuselage and vertical aerodynamic elements (vertical stabiliser etc) that will eventually result in the heading of the plane slowly changing to that of where the nose is pointing. And, as mentioned above, all this time, the form drag of the airframe is huge, resulting in the need to apply more power (burn more fuel) to maintain a fixed altitude (the airframes lift to drag ratio has fallen). Finally, this slide slip also puts massive forces into the airframe, which generally they are not rated for (unlike in the vertical axis where even an airliner can resist several g before failure)
Of course, some airframes, that have a very "bluff" profile to their fuselage, or huge vertical stabilisers, can be steered effectively on the rudder, but a modern airliner is so well optimised for low drag on cruise they don't respond well to rudder turning.
A plane, because it is flying in air, has virtually no "lateral" grip on the air (analogous to the car on ice example). The entire airframe is designed simply to support its mass, using the wings, producing lift in opposition to the mass, in a vertical direction. In order to actually turn, banking the plane into the turn results in the lift vector also point inwards and results in the plane turning with little extra drag.
Simply using the rudder to cause the airframe to yaw around its vertical axis has little effect on the planes heading (the airframe will yaw, but it will effective just slide "sideways" through the air). In this case, it is only the force of the air hitting the fuselage and vertical aerodynamic elements (vertical stabiliser etc) that will eventually result in the heading of the plane slowly changing to that of where the nose is pointing. And, as mentioned above, all this time, the form drag of the airframe is huge, resulting in the need to apply more power (burn more fuel) to maintain a fixed altitude (the airframes lift to drag ratio has fallen). Finally, this slide slip also puts massive forces into the airframe, which generally they are not rated for (unlike in the vertical axis where even an airliner can resist several g before failure)
Of course, some airframes, that have a very "bluff" profile to their fuselage, or huge vertical stabilisers, can be steered effectively on the rudder, but a modern airliner is so well optimised for low drag on cruise they don't respond well to rudder turning.
Edited by anonymous-user on Monday 26th August 20:23
Max_Torque said:
Simply using the rudder to cause the airframe to yaw around its vertical axis has little effect on the planes heading (the airframe will yaw, but it will effective just slide "sideways" through the air). In this case, it is only the force of the air hitting the fuselage and vertical aerodynamic elements (vertical stabiliser etc) that will eventually result in the heading of the plane slowly changing to that of where the nose is pointing.
If the Yawing motion did not turn the a/c then a Stall Turn would not be possible.
However, a Stall Turn is possible!
Indeed if you watch a well executed Stall Turn the pilot is applying opposite aileron to allow the a/c to yaw cleanly - in a poorly executed Stall Turn the lack of opposite aileron means that the a/c rolls and tends to 'fall into' the Stall Turn
Big News said:
I was (albeit clumsily) trying to explain that one can't simply steer the aircraft around the sky at a constant attitude with the wings level...!
You can, it's called using 'Crossed Controls'. It's uncomfortable, inefficient, and puts you close to overstressing (if fast) or spinning/auto-rotating (if slow). However it is the basis of the 'slipping approach' as flown by WWII Fighter Pilots.As Ginetta says, over-use of rudder alone can be disastrous on a large aircraft. The American Airlines A300 that crashed climbing out of New York in 2001 was almost definitely down to excessive rudder application leading to structural failure of the tail fin.
http://en.wikipedia.org/wiki/American_Airlines_Fli...
http://en.wikipedia.org/wiki/American_Airlines_Fli...
Simpo Two said:
I found it most natural (glider) to turn using ailerons and then elevator as required to keep the nose up. But then you get skidding turns so the rudder was used to keep the string (sellotaped to the canopy) straight.
From the above I'd translate 'adverse yaw' as 'understeer'.
demonstration of adverse yaw (caused by aileron and no rudder):From the above I'd translate 'adverse yaw' as 'understeer'.
http://www.youtube.com/watch?v=0fq5l1pL4UQ
I think from the answers above you can see that different types of aircraft require different levels of control input.
Although the overall principles of control are essentially the same, the amount of usage the various controls (rudders, elevators, ailerons etc) get does depend on the size of the aeroplane and the type of flight regime it normally undertakes.
So the control inputs used on an Extra 300 aerobatic plane will be a lot more severe than normally used on an Airbus A380.
Although the overall principles of control are essentially the same, the amount of usage the various controls (rudders, elevators, ailerons etc) get does depend on the size of the aeroplane and the type of flight regime it normally undertakes.
So the control inputs used on an Extra 300 aerobatic plane will be a lot more severe than normally used on an Airbus A380.
Most powerful control surface on a swept wing aircraft is the rudder. Boeing aircraft have a system which I can't remember the name of which, reduces the amount of rudder deflection as the indicated airspeed increases. Full pedal input will not give full rudder deflection as the force generated would most likely result in catastrophic failure of the fuselage.
I use the rudder pedals on taxi, take off roll, engine failure(sim) and decrabbing in the flare. Rest of the time don't touch them.
Fun fact regarding de crabbing, Boeing recommend you don't de crab when the crosswind is above a certain limit. Produces a lot of wobbling heads down the back on touchdown.
I use the rudder pedals on taxi, take off roll, engine failure(sim) and decrabbing in the flare. Rest of the time don't touch them.
Fun fact regarding de crabbing, Boeing recommend you don't de crab when the crosswind is above a certain limit. Produces a lot of wobbling heads down the back on touchdown.
peatmoor said:
So under what circumstances is the rudder used?
Pretty much all the answers to this are above.I only have experience of flying little single engine planes but there are a few circumstances I was taught to use the rudder -
1. Turning - "tread on the ball" - the balance indicator is a little black ball inside the outline of an aircraft and when you start turning the ball moves away from the centreline so you press the corresponding rudder pedal (ie. if the ball moves right you press right rudder) to bring the aircraft back in balance. It just becomes second nature that you apply some rudder input when turning - you don't fly around staring at the indicator.
2. Climbing - "Power Attitude Ball Trim" - increase power, pitch the nose up, check balance and apply rudder if necessary, trim for the climb
3. Descending - "Attitude Power Ball Trim" - pitch the nose down, decrease the power, check balance and apply rudder if necessary, trim for the descent
4. Take off / Landing - rudder helps keep you on the centreline
I'm sure the pro's will be along shortly to correct me / provide further answers
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