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Feb
2
comment If the Earth is curved, why don't planes need to adjust attitude to stay parallel to the ground?
@Dargscisyhp: So you should know what I mean, having had your hands on the controls yourself. Aircraft power is not on/off, if it more/less. Aircraft are always gliding. Whether they glide down or glide up is just a matter of whether the thrust is less than the drag or more. If you want the plane to maintain constant height above the earth, that's one power setting. If you want it to follow a "straight line" and ascend, that takes a higher power setting. If you want to descend to the airport, you decrease the power, to idle if necessary.
Feb
2
comment If the Earth is curved, why don't planes need to adjust attitude to stay parallel to the ground?
@DavidHammen: Yeah, sure. Good planes, properly loaded, damp that out. (I'm talking about common aircraft. Aerobatics and fighters are a different story.)
Feb
2
answered If the Earth is curved, why don't planes need to adjust attitude to stay parallel to the ground?
Jan
29
revised How do the Americas Cup Yachts sails work?
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Jan
28
comment How do the Americas Cup Yachts sails work?
@Carl: Glider speed record.
Jan
28
comment How do the Americas Cup Yachts sails work?
@Carl: The key is that 'other fluid'. Aircraft are built to resist sideways motion through the air, so you might call that a 'keel'. But as you say, they can't extract power from the wind. I take that back - if they are flying in an area of wind shear, they can. Some radio-controlled gliders have reached crazy speeds by doing vertical loops on the lee side of a hill.
Jan
28
comment How do the Americas Cup Yachts sails work?
@Carl: Well, they sort of do, actually.
Jan
28
comment How do the Americas Cup Yachts sails work?
++ for DWFTTW :) The car can go directly downwind, but the sails (the rotary wings) are going at an angle. In fact, I think it can also go upwind faster than the wind.
Jan
28
revised How do the Americas Cup Yachts sails work?
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Jan
28
revised How do the Americas Cup Yachts sails work?
added 2 characters in body
Jan
28
answered How do the Americas Cup Yachts sails work?
Jan
26
comment Aircraft Thrust to weight ratio contradiction with energy conservation
You don't need a giant airplane to understand this. Make a paper airplane and throw it. Once you let go, it has zero forward thrust. Even so, it glides and maintains its speed, though it loses altitude gradually. Once an airplane has been accelerated to flying speed, all the engine thrust (minus drag) does is determine the angle of ascent or descent.
Jan
26
comment Aircraft Thrust to weight ratio contradiction with energy conservation
Lift is proportional to velocity squared. It is also proportional to angle of attack, for small angles.
Jan
24
comment Why are four-legged chairs so common?
There are 1-legged chairs.
Jan
24
comment How much energy would it take to take down a 747 using vibrations?
Look up aeroelastic flutter. This is a problem that aircraft engineers take seriously, and they have various methods to minimize it, such as putting weights in the control surfaces.
Jan
23
awarded  aircraft
Jan
22
revised How to sensor Jerk=$d^3{\bf r}/dt^3$, or higher derivatives (4th, 5th, 6th order) when applied in the equation of motion of a ballistic missile?
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Jan
22
comment How to sensor Jerk=$d^3{\bf r}/dt^3$, or higher derivatives (4th, 5th, 6th order) when applied in the equation of motion of a ballistic missile?
@DukeofSam: It's difficult to take derivatives of physical signals because the noise is amplified. The reason accelerometers are so useful is that you can integrate them, once to get velocity, and twice to get position. They do need to be calibrated to offset constant error, and they do drift, as gyroscopes do, so they occasionally need correction. But there's no good way to take numerical derivatives without heavy smoothing.
Jan
22
revised How to sensor Jerk=$d^3{\bf r}/dt^3$, or higher derivatives (4th, 5th, 6th order) when applied in the equation of motion of a ballistic missile?
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Jan
22
answered How to sensor Jerk=$d^3{\bf r}/dt^3$, or higher derivatives (4th, 5th, 6th order) when applied in the equation of motion of a ballistic missile?