Reply #22: Just a couple of comments..... [View All]

[Sweet Pea]

It just happens to be a federal law that planes can't fly that fast below 10,000. The military jets have special areas that are closed to everyone else where they plan their war games and fly at very high speeds.

Very true. The practical limitations on aircraft flying that fast are structural limitations that are unique to the aircraft. Panels start to open up, the hydraulic pressure that keeps things like landing gear doors closed are overcome by the air pressure. The 250 knots below 10,000 feet rule is indeed a hard and fast one enforced by the FAA and that has more to do with noise abatement and sequencing of aircraft in the low altitue structure than anything else. Many, many more things are flying around below 10,000 feet and having someone/something zorching aroung at 400 or 500 knots leaves precious little time for hazard calls and/or aircraft avoidance manuevers.

Other facts: a large jet takes about 3 minutes to respond to the controls. Hard to imagine people taking a few rides in a cessna and then doing simulators to do what was done on 9-11. Now if the WTC had some kind of navigation signal, I can see them doing what they did. That was very sharp flying.

I have no idea where you came up with this tidbit - minutes or even seconds. Modern jetliners have digital fly-by-wire controls. Any control input is instantaneously transmitted to the control surfaces (flaps, ailerons, rudder, spoilers, etc) and then act upon the aircraft flight characteristics immediately. Even the older airliner flight controls are hydraulically boosted and the inputs to flight controls are virtually instantaneous. True, high speed (and by association heavy airflow over the aircraft surfaces) affects the ability of a control surface to defelct into the airflow (Chuck Yeager spoke about this in his autobio, but he also had supersonic air compression deals going on with an experimental aircraft in a flight dynamic that had never been experienced before), but the speeds these airliners were flying would not have proved difficult for control inputs to be made and the aircraft response would have remained immediate.

As for how fast one can fly, the speed of sound varies on temperature. Mach 1 is faster at 30,000 feet than at 1000 feet.

Backwards. The dense air in lower altitudes means the aircraft has to fly faster to achieve mach. Thin air at higher altiudes means the aircraft reaches mach at a lower airspeed.

The speed of sound (or "mach 1") depends on more things than just temperature...air density, humidity, wind speed just to name a few.

"At sea level, the speed of sound is about 761 miles per hour (1,225 kilometers per hour). At 20,000 feet (6,096 meters), the speed of sound is 660 miles per hour (1,062 kilometers per hour)."

http://www.centennialofflight.gov/essay/Dictionary/sound_barrier/DI94.htm