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1

It's happened. For instance,UA Flight 826 in 1997 had a passenger die after she hit the ceiling. Peak negative g of 0.824.


1

Yes, airplanes can experience strong vertical acceleration simply by flying across the boundary between an updraft and a downdraft. Example: flying from an updraft of 5m/s to a downdraft of 5m/s, in one second, gives a downward acceleration of about 1g. It can easily be more. Such turbulence is quite common. Planes are built strongly to handle it. The ...


0

This is not unlike the question "can you theoretically balance a perfect pencil on its tip". The answer is always "no". No, because the initial conditions cannot be perfectly obtained; and the equations of motion are such that a small perturbation from the initial condition will grow. You cannot generate perfectly laminar flow on a molecular scale, ...


1

The simplest answer to your question would be: Yes, put the flag out on a day when there is no wind. If you want to be able to distinguish which country it represents, tilt it so that its pole is horizontal. But I guess that this is not the situation that you have in mind. I imagine that you are asking if it is possible that wind will be strong enough to ...


0

The Reynolds number gives a ratio between forces of inertial origin and those of viscous origin. For a given geometry of the problem, increasing the Reynolds number will lead to turbulent flow from a certain threshold. However, this threshold is strongly dependent on the geometry: this is actually common knowledge, a better design (more "aerodynamic" we say ...


4

Use the Reynolds number equation: $Re={vL \over \nu}$ where $\nu\approx 1.5\times10^{-5}m^2/s$ is the kinematic viscosity for air. If you enter this into the equation, you end up with $Re\approx 67000{v\over{m/s}}{L\over m}$ i.e. for a race car traveling at 40m/s and with a length of 4m it comes out to be around 10 million, which is certainly ...


1

The characteristic length is the dimension that defines the length scale of a physical system. This implies that for any system, which my contain several length scales, there may only be one characteristic length scale. This is also generalizable to the other characteristic scales such as time, speed, etc. As you may have read in my other answer, generally ...


-1

Regarding lift more blades means more flying wing area which is a good thing up to the point where the following blades create too much turbulence. (2) blades is symmetrical balanced and efficient. Why would (4) blades not be , if not twice as good, at least significantly better and worth the cost to build a more complicated swashplate for collective ...



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