What is directional stability

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How to say directional stability in sign language? Numerology Chaldean Numerology The numerical value of directional stability in Chaldean Numerology is: 2 Pythagorean Numerology The numerical value of directional stability in Pythagorean Numerology is: 2.

Select another language:. Please enter your email address: Subscribe. Discuss these directional stability definitions with the community: 0 Comments. Notify me of new comments via email. Directional-Lateral Coupling Dutch Roll aka Free Directional Oscillations Roll and Yaw are not separate forces, they act together If the plane yaws, it will invariably roll as well When the plane yaws, one wing speeds up while the other slows down The yaw will cause greater lift on one wing more than the other This causes a rolling moment which in turn causes a sideslip to be set up whereby the process starts all over again.

Adverse Yaw These two forces oppose the turn entry and cause adverse yaw. Aileron drag is another common cause of adverse yaw. Frise ailerons and differential aileron travel are common ways of offsetting the effects of aileron drag. Using spoilers to turn solves this problem.

Coupled Effects Bad Things There are 3 types of motion associated with the coupling of yaw and roll: —Spiral divergence —Directional divergence —Dutch roll Bad things Coupled Effects 1. Spiral Divergence happens when directional stability is greater than lateral stability. What happens is there is little sideslip when the aircraft is displaced and next to no dihedral effect. The plane enters an ever tightening spiral. Normally the pilot would correct this, however, in some situations, IFR it could prove to be trouble Bad things 2.

Directional divergence results from negative directional stability The plane develops a sideslip after being disturbed which causes a further yaw or roll The plane will eventually end up yawing sideways to the relative wind.

Bad things 3. So, elevators provide lateral rotation to achieve longitudinal stability, and vice versa for ailerons. It differs slightly for the vertical axis, as if your plane is both longitudinally and laterally stable, it's also "vertically stable", however the plane is longitudinally and laterally stable, but completely out of control, in a "flat spin".

Stability in the vertical axis therefore is secondary to "directional stability", which keeps the longitudinal axis pointing in a particular direction along the geometric plane formed by the lateral and longitudinal axes. In this case the rudder both controls yaw and provides directional stability. In addition to control surfaces, weight and especially the aircraft's center of gravity is important in stability. Ideally, most small planes are most stable in level flight when the CG of the aircraft is exactly on the centerline of the aircraft between the tip of the nose and the tip of the tail and slightly forward of the aircraft's center of lift which depends on the wing's angle of attack but is usually close to the thickest point in the wing's cross-section.

In this configuration, while the aircraft is travelling forward normally, downwash from the wings flow over the top of the horizontal stabilizer, keeping the nose level. In a stall, the slight nose-heavy configuration along with the stabilizers in the rear will cause the nose to point downward gently, restoring normal airflow and allowing the pilot to recover.

If the CG is too far forward, the pilot will need to apply upward pitch or trim to keep the nose level.

This will reduce the amount of travel he will have available to pitch up, and in a stall, the plane will nose down sharply and the elevator may provide insufficient force for the pilot to pull out of the dive. If the CG is too far aft, the plane will want to nose up constantly, and the pilot will have to apply downward elevator or trim. In a stall, a plane with an aft CG won't nose down, preventing the pilot being able to restore normal airflow over the wings. This is especially dangerous in an uncoordinated stall aka a spin; the aft center of gravity in combination with the forward thrust of the engine will "stabilize" the plane in the spin and make it impossible to recover.

If the CG is off the aircraft's centerline, the plane will tend to roll towards its heavier side. This is compensated for with ailerons or aileron trim, and for most everyday flight it's the easiest to compensate for, but it can cause unfamiliar roll behavior and a tendency to spiral down, which the pilot must be aware of and correct for. Lateral stability is roll stability: the tendency of the aircraft to reduce its rolling and return to an upright position unless continually maintained in position by e.

This is usually only partial. Longitudinal stability is pitch stability: the tendency of the aircraft to reduce its pitching and return to a level position relative to the direction it's traveling, at least unless countered by e. Directional stability also known as vertical stability is yaw stability: the tendency of the aircraft to reduce its yawing and return to a straight position relative to the direction it's traveling, at least unless countered by e.