Hot answers tagged

16

Flutter happens when the eigenfrequencies of two oscillations move close together so their motions can reinforce themselves mutually. When that happens, then the amplitude will increase with each oscillation, up to a point where the amplitude is big enough to break things. That is how bridges are destroyed: Ever more energy is accumulated in the structure, a ...


14

Short answer: By not flying faster than the 104 did and adhering to the lessons learned. Flutter first started to cause crashes in WW I when improved engine power and aerodynamics made a substantial rise in flight speed possible. Every time technological advance allowed higher speeds, flutter became an issue which was then solved both by trial and error ...


13

Imbalanced or loose (and, in extreme cases, structurally weak) control surfaces can cause flutter, a type of harmonic motion. Flutter is a very dangerous condition; if it is not stopped, it can cause structural failure and potentially lead to a fatal accident. V-tail Bonanzas had a series of such accidents related to flutter of the butterfly ruddervator tail....


10

The XF-104 is a prototype aircraft, which lead to the F-104 starfighter. Usually, during the development of an aircraft, flutter testing is carried out and corrective actions are taken. The Wikipedia article you liked has a point: Production aircraft would also feature a redesigned fin structure using stainless steel spars to eliminate the flutter problem....


6

Flutter is an aero-elastic problem, a complicated sort of spring-mass-damper issue. Complicated because spring, mass, damping and the applied force are linearly distributed over the wing span. Basically, the problem is as follows: The wing root is fixed to the aircraft fuselage, the wing tip is not fixed and can twist. The air streaming over the wing ...


6

This is flutter. The ways to counteract the flutter, as found here (section Flutter Fixes), are: Move the center of gravity of the wing closer to the center of twist. Raise the frequency of the flutter by making the wing stiffer and lighter (better energy dissipation). Tune shape and other characteristics with the help of computer simulations or wind tunnel....


5

Flutter happens when the frequency of two modes coincide. These modes must be of different nature, so their frequencies can move in different directions. Typical examples are elastic modes (with eigenfrequencies independent of speed) and aerodynamic modes (with eigenfrequencies proportional to speed). When flight speed increases, the aerodynamic mode becomes ...


4

To better understand what flutter is, see the structure as a mass-spring system like a spring pendulum that has a damper attached to it. The aerodynamic forces both make the spring stiffer and dampen the movement. Crucially, they will act with a delay to the motion of the spring pendulum. Since we are dealing with oscillatory phenomena here, this delay ...


4

Flutter is an energy storage and release phenomenon. Surface moves, applies a load to the fixed surface it's attached to, fixed surface bends under the load, stores some of the energy like a spring, then releases it in moving back to its original position, and some of this released energy is transferred to the moving surface attached to it, which is also ...


4

YouTube is really your best bet - is there any reason you wouldn't be able to use one of the many NASA videos? If you need a release for legal reasons NASA is famously liberal about granting rights to their research/educational videos - just contact then and you'll almost certainly get an official "Sure, you can use it!"


4

The discipline that deals with flutter and other air-structure interactions is called "aeroelasticity". Aeroelasticity analyses the dynamic modes of the structure taking into account the coupled effects of the air (that causes pressure change) and the effects of the deformed structure geometry on the flow. Flutter is a nightmare for flight and is not ...


3

Not necessarily if the aircraft flies slowly so forces stay small. But it is better to have balanced control surfaces. Now imagine that you fly through a vertical gust and the aircraft pitches up, then down. Since it rotates around its center of gravity, the tail will make the largest excursions from a straight line. Now imagine the elevator has no mass ...


3

Flutter requires 3 factors to come together: flexibility of the structure that a control surface is attached to; the natural frequency of said structure; and an undamped moving mass attached to the structure with an internal CofG offset from the hinge point of the mass such that inertia helps magnify motion of the mass. If you have an ultralight with a ...


3

It's an aeroelastical phenomenon driven by pitching moment, torsion stiffness, and inertia of the wing. It's a classical spring-mass-damper problem: increased aerodynamic pitching moment causes torsion on the wing structure, which causes more pitching moment until the local airfoil AoA is such that the air flow separates. Torsion is counteracted by the wing ...


2

This 1986 USAF experiment might help. The purpose of this test was to demonstrate in flight for the first time the feasibility of powering a primary flight control surface with an electromechanical actuator (EMA) in place of the standard hydromechanical actuation system. An advanced development model model EMA drove the left aileron on a specially ...


2

Flutter is essentially an aerodynamic and structural interaction that has gone unstable. At certain speeds and flight conditions, the aero forces interact with the structural dynamics of the aircraft. This aero and structural dynamic instability can be seen in other places other than aircraft as well, the most famous that comes to mind is the one with the ...


1

You might want to try reviewing MIL-A-8870C AIRPLANE STRENGTH AND RIGIDITY VIBRATION, FLUTTER, AND DIVERGENCE. The CRJs were certified to this standard. Available here: http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-A/MIL-A-8870C_6746/ Just click the Download File button.


1

the forward structural section of the engine nacelle which supported the reduction gearbox for the propeller drive and connected the gearbox mounts to the rest of the engine supports were designed in such a way that if the plane made a hard landing, those structures would be weakened enough to allow the establishment of undamped whirl-mode flutter/resonance. ...


1

Flutter is a natural frequency resonance phenomenon. Something is oscillating, and its oscillation, at some point, starts to match the natural frequency of the structure it's attached to, and a mutual input/feedback cycle starts that stores and returns the energy in such a way that it magnifies the initial input and away you go. The outer wing was the ...


1

Flutter and vortex induced vibrations (VIV) are both dynamic instabilities arising from the interaction of unsteady aerodynamic, inertial and elastic forces. They both extract energy from the air stream to persist. Instead of perceiving the interaction as aerodynamic forces causing structural motion or structural motion generating aerodynamic forces, it is ...


1

This is a very interesting question, with a very complicated answer! The problem of Aero-Elasticity is not easy or simple to solve. The reason is, that the equations (or better the system of equations) which describe it are not simple (in this case the non-linearity of the aerodynamic forces create most of the analytical problems). Flutter can be assessed ...


Only top voted, non community-wiki answers of a minimum length are eligible