Expert: Ray Wilkinson - 6/14/2006

Question
if you had a chance to make a air craft with 2rolls royce mk 602 turbojets,
2pratt and whitney j3tc turbo jets and a air cusioned landing system with a
speed of 2861.25mph what would the mach speed be and/or would it work.


Answer
You can calculate the Mach number by dividing the speed of the aircraft by the local speed of sound. The speed of sound in air varies only according to temperature, and you can look it up for various altitudes (assuming standard atmosphere conditions). At sea level ISA conditions it is 340m/s but falls with altitude as the temperature falls. It's 300m/s at 10,000m for instance. You need to be sure you are using the true speed of the aircraft - there are many variations of what is termed airspeed.

As to whether it would work, it's difficult to say. The Titanic worked well, except in the presence of icebergs, so it depends on how it is designed and how it's used.

I hope this helps.

Regards, Ray