aircraft stability and controls?

Question

1. Explain the terms static and dynamic stability associated with an airplane. Is the
stability part of the airplane design and operation? Does the pilot apply control in
this respect? Please illustrate.

Answer 1

Don't know what the subejct of this question is for, and not sure what you are trying to ask without the background information. Base on the names in question, I would venture that static stability is the parts of the aircraft operation that would require miminal oversight once the aircraft is airborne or any other conditions in which the aircraft can be counted as stable.

Dynamic stability implies that the operations of the aircraft that would require constant supervisions no matter the condition the aircraft is in. The operation B-2 bomber is a good example of dynamic stability control. Because of its unique airframe, it would require constant tinkering to keep the plane in flight. However, this is done by microcomputers all over the plane. Pilots simply can't keep track of all the modifications needed to keep plane flying.

This brings to the last part of your question. What does the pilot do? It depends. Like B2 bomber, the pilot is really not involved in the dynamic stability of the airplane. If the onboard computer reports a problem, he might have to deal with it, but it would not be much different from controls for static stability, which I consider to be mostly landing and takeoff of the aircraft.

As for illustration, well, Yahoo! Answer is not exactly picture friendly, and I really don't know what kind of picture to draw. Plus I am not sure if I am answering the question. Hope this helps.


XR

Answer 2

"static stability is usually stated in terms of the neutral point."

the neutral point has to do with the CG (center of gravity) of the airframe.

Basically, static stability has to due with the airframes ability to fly at a constant speed and constant angle of attack as long as the controls are not moved.

"Dynamic stability is typically expressed in terms of the damping and frequency of a natural mode."

Basically, dynamic stability has to due with airframes ability to recover from "small" disturbances. That is changes in the atmosphere, passenger movement etc. It is typically desired to have these "impulses" diminish quickly rather than continue to cause the airframe to oscillate.

Stability is a HUGE part of aircraft design (arguably the most important part). The airplane might look very "cool" or be very large or small to fulfill some need, BUT if it is unstable it will not fly.

For the stealth fighter and bomber for example, engineers first made the basic airframe "invisible" to radar. THEN they had to figure out a way to get it fly. The solution was to have computers with sensors monitor the stability of the plane and continuously make tiny corrections to the flight control surfaces (without the pilots knowledge) in order to keep the plane in the air.

So, depending upon the airplane and the disturbance the pilot may or may not be a part of the "control system". In general however the pilot IS part of the control system.

Answer 3

Your question blends two concepts:

1. Aircraft stability and control which is the study of vehicle handling characteristics in pitch, roll and yaw, and the tendency of the vehicle to track its intended course in the presence of disturbances. Aircraft stability and control, in this context, generally considers only the rigid body dynamics of the vehicle. Longitudinal and lateral aircraft instability is evident when the vehicle exhibits long period or short period oscillations after an input to the flight control system, typically after a pilot moves the controls. The factors that influence aircraft stability are cg location, and the size and location of wing and empennage surfaces and control surfaces. Aircraft designers must balance mission requirements with safe handling and pilot workload to ensure that aircraft operation is stable throughout the mission and the flight envelope. Stability (or vehicle damping) can be improved through passive aerodynamic design measures, computerized stability augmentation systems or full authority redundant fly-by-wire systems, such as is used in the B2 bomber mentioned above.

2. Static and dynamic aeroelastic stability of aircraft structures, which is the study of how aircraft wing (or helicopter main/tail rotor blade) design can be exploited to prevent catastrophic structural failure at certain flight conditions.

Static stability, similar to buckling of a column, refers to the tendency of a wing (or rotor blade) to twist and fail in torsion and bending. Static instability, otherwise known as divergence, is generally associated with wings/rotor blades that are swept forward by design, or achieve a swept forward condition during operation.

Dynamic aeroelastic instability of aircraft structures refers to the tendency of a wing/rotor blade to exhibit vibratory bending and torsion at high aircraft speed. The amplitude of such motion grows rapidly with time/velocity until the structural limits of the wing/rotor blade are exceeded and catastrophic failure occurs. Dynamic instability, otherwise known as flutter, occurs when there is insufficient aerodynamic, structural and inertial damping in the combined aeroelastic system.

Not limited to aircraft, aeroelastic flutter instability was the root cause in the collapse of the Tacoma Narrows Bridge in 1940