analyzing the speed of a 767 at 700 feet altitude: I will try to explain the flight of a turbofan jet aircraft in a perfectly ideal environment, and what their problems are. By ideal, I mean in calm air.

My sample plane is flying at 530 MPH at 35,000 feet altitude. Its turbofan is rotating a R rpm and the engine is outputting M mass of compressed heated air to give it the amount of thrust necessary to maintain that speed. The opposing force on the plane, to hold it at that speed, is F.

Now, take the plane down to 700 feet. The opposing force is now XF, but the engines are thrusting out XM mass of compressed heated air. Therefore the speed of the plane remains at 530 MPH. However, even in this ideal situation, there remains problems:

1. Does the planes power plant have enough power to rotate the turbofan at R rpm? What happens to the power plant if it is overloaded significantly? What is its absolute limit? The air density at 700 ft is approximately 3.3 times the air density at 35000 ft. Therefore X equals 3.3, meaning the thrust at 700 feet would have to be 3.3 times as much as at 35000 feet. In other words, the turbofan load would be 3.3 times the load at 35000 ft. If this limit is not reached, then why don't they fly the plane at higher altitudes and faster speeds?
2. Is the airframe sufficiently strong enough to withstand XF force? The opposing force would also be 3.3 times as large.
3. The previous 2 problems would be magnified because of the laws of Physics, namely the 3 laws of thermodynamics, and I paraphrase them in order to simplify:
   1. You can't get something for nothing: If you want to get work out of a machine, you must put energy in.
   2. The best you can do is to break even. You can't get more out of a machine than you put into it. Example: When you cock a spring, you can't get more work out of the spring than you put into it.
   3. You can't even break even. This is due to entropy, the energy lost to internal friction in the machine and in the process of inputting the energy. Therefore the problems mentioned above would be magnified greatly. The strain on the power plant at 700 ft would be much greater that 3.3 because of inherent inefficiencies. This added strain on the power plant would put additional strain on the airframe. Hence, I claim that if a 767 could fly 530 MPH at 700 ft, it could fly 1,000 MPH at 50,000 ft.

Also I would like to know about the plane at the Penatagon and how it could have traveled so fast as such low altitude, I belive it was 20ft off the ground at over 400mph.

And just for a joke could you please tell me how a aluminum plane can meld into a steel and concrete building without twisting breaking or anyhting,,,, OH yeah, and how the nose coming out the other side INTACT!

Kudos, you win the 700ft arguement, to a certain extent!

Take care,
Jeff

My Response to Jeff Hill:

Jeff; I have no further comments on the issue of weither a 767 can fly at 500+mph at 700 ft.

RE:

Also I would like to know about the plane at the Penatagon and how it could have traveled so fast as such low altitude, I belive it was 20ft off the ground at over 400mph.

And just for a joke could you please tell me how a aluminum plane can meld into a steel and concrete building without twisting breaking or anyhting,,,, OH yeah, and how the nose coming out the other side INTACT!

I think these are good questions, and I will respond shortly.

Rodger H