Dutch roll sequence
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Dutch roll sequence
Aircraft yaws, outer wing travels faster, more lift, then rolls. After roll, aircraft sideslips and the dihedral effect will cause the inner wing to develop more lift, so it rolls the opposite way and causes as a secondary effect, a yaw develops, then it rolls again......
Please correct me?
Please correct me?
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Dutch roll--oscillatory stability :when an aeroplane is yawned it rolls (with a swept wing there is a marked rolling tendency with yaw).
The fin and rudder then oppose the yaw,slow it down and stop it,and return the aircraft towards straight flight.
Design of the fin and rudder will determine if this roll is stable or unstable,resulting in divergent motion.
To correct a dutch roll motion you should apply one firm ,not big,correction to the aileron controlling the upcoming wing.(in and out,don't keep it).Then again,if necessary. It is not advised to use rudder to correct dutch roll,the roll is much visible than the yaw,so easier to correct.
And I guess you were correct,maybe an aditional efect on the swept upcoming wing by the yaw motion,not only that it travels faster,but also modifies the angle to the airflow,resulting lift..
brgds...
The fin and rudder then oppose the yaw,slow it down and stop it,and return the aircraft towards straight flight.
Design of the fin and rudder will determine if this roll is stable or unstable,resulting in divergent motion.
To correct a dutch roll motion you should apply one firm ,not big,correction to the aileron controlling the upcoming wing.(in and out,don't keep it).Then again,if necessary. It is not advised to use rudder to correct dutch roll,the roll is much visible than the yaw,so easier to correct.
And I guess you were correct,maybe an aditional efect on the swept upcoming wing by the yaw motion,not only that it travels faster,but also modifies the angle to the airflow,resulting lift..
brgds...
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Roll stability
Letīs look at the sequence starting from roll.
1) Airplane rolls. When not stalled, it has roll stability - one wing dropping has higher angle of attack, more lift - that stops the fall of the wing. But does not yet reverse it - a rapidly rising wing would lose angle of attack and therefore lift.
2) With airplane banked, part of the lift works sidewards - the plane starts yawing in the turn
3) Yawing means the outer, upper wing has higher airspeed than the inner and lower wing. Not sure about how the angles of attack compare... anyway, this may mean more lift on the upper wing, causing overbanking tendency, which would mean spiral instability and drive the plane into a graveyard spiral.
Now, what exactly will the fin and wing dihedral do to stop the spiral dive and return the plane - perhaps into a Dutch roll?
1) Airplane rolls. When not stalled, it has roll stability - one wing dropping has higher angle of attack, more lift - that stops the fall of the wing. But does not yet reverse it - a rapidly rising wing would lose angle of attack and therefore lift.
2) With airplane banked, part of the lift works sidewards - the plane starts yawing in the turn
3) Yawing means the outer, upper wing has higher airspeed than the inner and lower wing. Not sure about how the angles of attack compare... anyway, this may mean more lift on the upper wing, causing overbanking tendency, which would mean spiral instability and drive the plane into a graveyard spiral.
Now, what exactly will the fin and wing dihedral do to stop the spiral dive and return the plane - perhaps into a Dutch roll?
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From http://www.centennialofflight.gov/es...ty_II/TH27.htm
Dutch roll is a motion exhibiting characteristics of both directional divergence and spiral divergence. The lateral stability is strong, whereas the directional stability is weak. If a sideslip disturbance occurs, as the airplane yaws in one direction, the airplane rolls away in a countermotion. The airplane wags its tail from side to side.
You can also read: http://en.wikipedia.org/wiki/Dutch_roll
It is short and sweet.
For the true aerodynamic explanation, go here: http://www.av8n.com/how/htm/equilib.html
Dutch roll is a motion exhibiting characteristics of both directional divergence and spiral divergence. The lateral stability is strong, whereas the directional stability is weak. If a sideslip disturbance occurs, as the airplane yaws in one direction, the airplane rolls away in a countermotion. The airplane wags its tail from side to side.
You can also read: http://en.wikipedia.org/wiki/Dutch_roll
It is short and sweet.
For the true aerodynamic explanation, go here: http://www.av8n.com/how/htm/equilib.html
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All airplanes roll coincident with yaw, because as you stated the outer wing is accelerated, gains lift, and the innerwing slowed down, losing lift. With a swept wing this is worse because the effective aspect ratio changes and the outer wing becomes less swept and the inner wing more swept, further degading oscillatory stability. the solution is a big tail fin, but this can really degrade your spiral qualities (under banking, neutral or over banking qualities) because the large fin wants to continuosly "coordinate" the steepening turn and therefore send you into a spiral dive, past a 25-30 deg bank angle. However, some aircraft with large fins have both decent spiral qualities and no dutch roll... but only Boeing knows how they've accomplished that with those particular beast 
. Generally, dutch roll is worse at high speed and high altitudes though not always (US Air Boeing 737 accident after yaw damper failure and a few more), however LONG TERM spiral stability is ususally improved at high altitude, high Mach number flight ironically because of the degraded tail effectiveness; these two stabilities are a tradeoff of one another... and both can lead to a nasty dive into the terra firma.
. Generally, dutch roll is worse at high speed and high altitudes though not always (US Air Boeing 737 accident after yaw damper failure and a few more), however LONG TERM spiral stability is ususally improved at high altitude, high Mach number flight ironically because of the degraded tail effectiveness; these two stabilities are a tradeoff of one another... and both can lead to a nasty dive into the terra firma.
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I have anyother version of this
the aircraft is yawed intentionally or unintentionally then it rolls. what causes it to roll the other way next? simply because the fin will experience a side force ( vector on the same side as the first roll's inner wing ) then tends to right the aircraft then it all starts all over again.
the aircraft is yawed intentionally or unintentionally then it rolls. what causes it to roll the other way next? simply because the fin will experience a side force ( vector on the same side as the first roll's inner wing ) then tends to right the aircraft then it all starts all over again.
