Turning and Sideslip???
Thread Starter
Join Date: Apr 2004
Location: Australia
Posts: 42
Likes: 0
Received 0 Likes
on
0 Posts
Turning and Sideslip???
When the aeroplane is turning, it will sideslip due to the horizontal force component caused by the tilted lift vector.
I read a good statement on this sideslip effect on a website and it stated:
As the lift always acts at 90º to the wing, and weight always acts straight down, the resultant imbalance of forces causes the aircraft to sideslip to the left.
So does the sideslip effect occur at all time when in turning flight or only initially when the aeroplane is rolled into the turn??
Thanks all..............
Big Kev
I read a good statement on this sideslip effect on a website and it stated:
As the lift always acts at 90º to the wing, and weight always acts straight down, the resultant imbalance of forces causes the aircraft to sideslip to the left.
So does the sideslip effect occur at all time when in turning flight or only initially when the aeroplane is rolled into the turn??
Thanks all..............
Big Kev
Join Date: Jan 2001
Location: He's on the limb to nowhere
Posts: 1,981
Likes: 0
Received 0 Likes
on
0 Posts
Is that from the model airplane site talking about secondary effects of a single control? What's the rudder used for? A good site for discussion of aerodynamics is by Denker
So does the sideslip effect occur at all time when in turning flight or only initially when the aeroplane is rolled into the turn??
As I'm sure you're aware, it's perfectly possible to fly most modern aeroplanes around a turn without rudder. While the horizontal component of lift provides the force needed to change the direction of motion of the centre of gravity of the aircraft, a yawing moment is required to change the heading of the aircraft in a corresponding way. Without rudder, that yawing moment comes from the effect of sideslip.
Guest
Posts: n/a
Big Kev,
I've not really considered this side-effect of turns before. So as there is no confusion, I am asumming perfect ailerons and so there is no need for rudder to produce a balanced turn.
Because, as you say, the weight is straight down but the upforce component is reduced because of the angle of the lift vector then the aircraft will simply descend vertically, but the aircraft is at an angle so hence the understandable use of the term "sideslip" in this case. Therefore, there is the need to increase the lift vector by such an amount that the upforce component again matches the weight to prevent the sink. This is accomplished by increasing the angle of attack of the wing through the use of the up elevator control.
To answer your question, sideslip in a perfectly executed level turn, where the pilot correctly compensates for reduced upforce with up elevator, would be non-existent. In reality...
In a climbing or descending turn then there must be a small amount of sideslip. In practical terms it is nugatory.
The angle of bank could be so great that it is not possible to compensate with up elevator. That is another matter.
I've not really considered this side-effect of turns before. So as there is no confusion, I am asumming perfect ailerons and so there is no need for rudder to produce a balanced turn.
Because, as you say, the weight is straight down but the upforce component is reduced because of the angle of the lift vector then the aircraft will simply descend vertically, but the aircraft is at an angle so hence the understandable use of the term "sideslip" in this case. Therefore, there is the need to increase the lift vector by such an amount that the upforce component again matches the weight to prevent the sink. This is accomplished by increasing the angle of attack of the wing through the use of the up elevator control.
To answer your question, sideslip in a perfectly executed level turn, where the pilot correctly compensates for reduced upforce with up elevator, would be non-existent. In reality...
In a climbing or descending turn then there must be a small amount of sideslip. In practical terms it is nugatory.
The angle of bank could be so great that it is not possible to compensate with up elevator. That is another matter.
Guest
Posts: n/a
perfect ailerons
In older aircraft, with my definition of "perfect ailerons", it's the pilot's feet moving the rudder that makes the aircraft turn, not the ailerons.
Join Date: Mar 2002
Location: Euroland
Posts: 2,814
Likes: 0
Received 0 Likes
on
0 Posts
With the lift vector banked into the turn, the combination of lift and weight will create a force towards the centre of the turn (slip).
Since the aircraft is travelling in a circle, there is centrifugal force acting opposite to the slip and in a perfectlt executed turn the two will cancel each other.
If you try turn using rudder alone (wings level), you create the centrifugal force but have not created any slip force to cancel it out. Result - aircraft skids put of the turn.
Use excessive bank compared to yaw and the slip force is greather than the centrifugal force and the aircraft slips into the turn.
Regards,
DFC
Since the aircraft is travelling in a circle, there is centrifugal force acting opposite to the slip and in a perfectlt executed turn the two will cancel each other.
If you try turn using rudder alone (wings level), you create the centrifugal force but have not created any slip force to cancel it out. Result - aircraft skids put of the turn.
Use excessive bank compared to yaw and the slip force is greather than the centrifugal force and the aircraft slips into the turn.
Regards,
DFC
Join Date: Nov 2005
Location: UK
Posts: 65
Likes: 0
Received 0 Likes
on
0 Posts
My take on it:
As the aircraft banks, the lift vector, staying perpendicular to the wings, is tilted. This resolves into two components. A vertical component, counteracting the weight of the aircraft, and a horizontal component, giving a centripetal force that pushes the aircraft sideways into a turn. Since the vertical component is initially smaller than the weight, it must be increased by use of elevator to keep the aircraft level. As the plane rolls into the bank, two sources of yaw develop. The first is to yaw into the turn, caused by the flow of air on the fin tending to want to weathercock the aircraft. The second is the adverse aileron yaw, caused by the lowered aileron on the raised wing slowing that wing down more than the lower wing, thus causing the plane to yaw away from the turn. Adverse aileron yaw is usually greatest, so rudder must be applied to cancel it out. Thus, in a balanced turn, there is no slip force in either direction, since centripetal and centrifugal forces are balanced. In an unbalanced turn, then under-rudder allows a slip force which skids the plane out, and over-rudder causes a slip force which yaws the plane into the turn. These forces are present throughout the turn - not just in the initial roll - so rudder must be applied throughout to remain in balance.
Does that sound right?
As the aircraft banks, the lift vector, staying perpendicular to the wings, is tilted. This resolves into two components. A vertical component, counteracting the weight of the aircraft, and a horizontal component, giving a centripetal force that pushes the aircraft sideways into a turn. Since the vertical component is initially smaller than the weight, it must be increased by use of elevator to keep the aircraft level. As the plane rolls into the bank, two sources of yaw develop. The first is to yaw into the turn, caused by the flow of air on the fin tending to want to weathercock the aircraft. The second is the adverse aileron yaw, caused by the lowered aileron on the raised wing slowing that wing down more than the lower wing, thus causing the plane to yaw away from the turn. Adverse aileron yaw is usually greatest, so rudder must be applied to cancel it out. Thus, in a balanced turn, there is no slip force in either direction, since centripetal and centrifugal forces are balanced. In an unbalanced turn, then under-rudder allows a slip force which skids the plane out, and over-rudder causes a slip force which yaws the plane into the turn. These forces are present throughout the turn - not just in the initial roll - so rudder must be applied throughout to remain in balance.
Does that sound right?
Guest
Posts: n/a
so rudder must be applied throughout to remain in balance.
Well specifically I disagree with the statement more than the reality. Shaggy Sheep said it all really. Just to add that the only reason the ball isn't centred is because you have aileron induced drag on the up wing, so therefore you use rudder when you use aileron. Some types generate significant drag so to prevent over/under bank in the turn you may need a little aileron and subsequently rudder too. My practical experience of 152s, Arrows, etc is that aileron drag is realitively insignificant and bank corrections in the turn don't cause any significant imbalance (none that my virtual clogs can accurately cancel anyway) so no need to use the feet in the turn. Come to think of it, I don't recall older designs like the Super Cub nor the Vagabond being problematic in that regard either.I don't think the answer to the original question had anything to do with adverse yaw though.
Originally Posted by High Wing Drifter
Just to add that the only reason the ball isn't centred is because you have aileron induced drag on the up wing, so therefore you use rudder when you use aileron.
To make a point mass go round a turn, all you have to do is apply a force at right angles to its direction of motion. But an aeroplane isn't a point mass. It has a nose and a tail, and it has not only to change its direction of motion like the point mass, but also its heading.
A conventional aeroplane with a fin applies yaw damping, i.e. it applies a yawing moment in the opposite direction to any yaw rate. Thus if you want a constant yaw rate, you must apply an into-turn yawing moment yourself. You can either do this with rudder, or you can allow the aircraft to slip out of the turn, which provides an into-turn yawing moment.
Thus there is a small residual requirement for rudder, even without aileron input.
Guest
Posts: n/a
Re: Turning and Sideslip???
Bookworm,
Possibly strange thinking on my part due to liberal largess with regard to brandy butter and new year's champers but I'm not sure about the use of the word "yaw". To me yaw is movement about the a/c local vert axis, not the world's.
My take on it is thus (assuming an aeroplane free of adverse yaw): When you bank the nose drops (however slightly) due to weathercocking (as SpekeToMe put it) and loss of lift, that is the only yaw I can perceive and is induced naturally by the design of the aeroplane without any need for the slightest touch of the rudder. Naturally this is countered by increasing the the horiz stab downforce (add power and/or up elevator) which holds the nose up, reduces the yaw and induces the turn.
I really can't see where the rudder enters the equation within the context of an adverse yaw free turn.
No. Something has to make the aircraft yaw...Thus if you want a constant yaw rate, you must apply an into-turn yawing moment yourself.
My take on it is thus (assuming an aeroplane free of adverse yaw): When you bank the nose drops (however slightly) due to weathercocking (as SpekeToMe put it) and loss of lift, that is the only yaw I can perceive and is induced naturally by the design of the aeroplane without any need for the slightest touch of the rudder. Naturally this is countered by increasing the the horiz stab downforce (add power and/or up elevator) which holds the nose up, reduces the yaw and induces the turn.
I really can't see where the rudder enters the equation within the context of an adverse yaw free turn.
Re: Turning and Sideslip???
Possibly strange thinking on my part due to liberal largess with regard to brandy butter and new year's champers but I'm not sure about the use of the word "yaw". To me yaw is movement about the a/c local vert axis, not the world's.
The aircraft is rotating about its "local vert axis" (as well as rotating a little about its axis running wingtip to wingtip). You seem to be suggesting that the nose of the aeroplane does not rotate relative to the nose of the aeroplane, which is doubtless true but not very helpful from a mechanical point of view.
To do the mechanics, you have to look at the angular velocity relative to an inertial frame. Once you have identified that angular velocity, it may be helpful to consider its components in the directions of the axes of the aircraft, and apply all that complicated stuff Euler talked about. But the angular velocity is the same (pseudo-)vector in any inertial frame, and in particular for aerodynamic effects, the frame of the air.
In other words, it is yawing.
Guest
Posts: n/a
Re: Turning and Sideslip???
Bookworm,
*hic*
Shorry, I didn't ekshplain myshelf prop, prop, properly. Gawd it's so difficult to explain every nuance without scripting a tome.
Did I write that 
No argument about the existance of yaw, just that it has nothing to do with rudder input.
Cheers!
*hic*
Shorry, I didn't ekshplain myshelf prop, prop, properly. Gawd it's so difficult to explain every nuance without scripting a tome.
You seem to be suggesting that the nose of the aeroplane does not rotate relative to the nose of the aeroplane
No argument about the existance of yaw, just that it has nothing to do with rudder input.Cheers!
Re: Turning and Sideslip???
Originally Posted by High Wing Drifter
Did I write that No argument about the existance of yaw, just that it has nothing to do with rudder input.
No argument about the existance of yaw, just that it has nothing to do with rudder input.The key is that if there's yaw, there has to be a yawing moment driving the yaw. That can come from rudder, or it can come from sideslip -- you need one or the other.
