Panman From Trinidad and Tobago, joined Aug 1999, 790 posts, RR: 0
Reply 2, posted (15 years 10 months 2 weeks 4 days 23 hours ago) and read 5135 times:
As far as I am aware the ratio between mph and knots (nautical miles) remains the same. I believe 1 mile is something like 1.18 nautical miles (can't remember - doing this off the top of my head). Unlike Mach No which changes with density and altitude.
Boeing727 From United States of America, joined May 1999, 961 posts, RR: 0
Reply 3, posted (15 years 10 months 2 weeks 4 days 22 hours ago) and read 5125 times:
I usually add about 15% to the value of knots when I tell my passengers how fast we are flying in mph; that is indicated air speed, of course. It is amlost the same ratio as meters to yards, which comes handy when I play golf in Europe.
24291 From , joined Dec 1969, posts, RR:
Reply 8, posted (15 years 10 months 2 weeks 4 days 20 hours ago) and read 5112 times:
I'll try and put this in other terms. One knot means 1 nautical mile per hour. A nautical mile is longer than a statute mile, hence 100 knots is faster than 100 mph. This ratio remains the same as others have said.
I think your confusion lies with indicated airspeed (IAS) vs. ground speed. If you climb at a constant IAS of 250 kts. in calm wind for example, your ground speed will increase as you go higher. This is because as you climb, you pitot tube, which measures ram air pressure and delivers that information to your airspeed indicator, begins to move through less and less air. Its easy to maintain a constant IAS, however, because your airplane will move faster through the thinner air and keep the same volume of air entering the pitot. If you takeoff on a runway that is at 5,000 ft elevation, your airplane will move across the runway at a higher speed than when taking off from a runway at sea level (assuming standard atmospheric conditions), yet you IAS for rotation and takeoff (generally speaking) will always remain the same.
So when you're on an airliner, your airplane may be cruising at 250 kts. IAS, but your pilot may announce a ground speed of something like 600 mph.
It's actually hard to explain but I hope I did a good job.
A330 From Belgium, joined May 1999, 649 posts, RR: 7
Reply 9, posted (15 years 10 months 2 weeks 4 days 16 hours ago) and read 5101 times:
Let me give you the CORRECT definition of a nautical mile:
A NAUTICAL MILE AT ANY PLACE IS THE LENGTH OF AN ARC OF THE MERIDIAN SUBTENDING TO AN ANGLE OF 1' AT THE CENTRE OF CURVATURE OF THE PLACE.
At the pole: 6107.8 FT
At the equator: 6046.4 FT
STANDARD: 6080 Ft or 10852 m
for the mathematic freaks:formulae:
( 6077.1 - 30.7 x cos2*) in feet
* is tèta
6077.1 is the mean value