I'm tracking a flight--what does ground speed 390 KTS mean?

[candy]

Just curious!

[Catch22Dem]

1. 390 knots = approx. 450 mph

[candy]

6. Thanks

[DS1]

2. knots

449 of em, give or take

[candy]

8. Thanks

[candy]

11. thanks

[LastDemocratInSC]

3. 390 knots ground speed, may be different from air speed

It means that the aircraft is traveling at 390 knots over the ground. If flying into a headwind the airspeed may be greater - if flying with a tailwind the airspeed may be less.

A knot is 1.17 mph, 1 mph is .622 knot.

[candy]

9. Thanks

[karlrschneider]

19. Back in the early 70s when I got my first flying job, I had a groundspeed

of over 380 Kt in a plane (Cessna 310) that did well to achieve 190 airspeed...from somewhere in Ohio to Virginia, AFAIR...the DME was going berserk. Jetstream was way low that day. :D

[kdmorris]

4. I think KTS is knots

1 KTS = 1.17 MPH

[candy]

10. Thanks

[mhr]

5. 390 Nautical Miles Per Hour = 450 Miles Per Hour

eom

[candy]

13. Thanks

[Silverhair]

7. It means

That you are moving, relative to the earths surface, at 390 nautical miles per hour. A nautical mile is used for aircraft as it is equal to one minute of latitude, which makes for easier calculations.

In ordinary terms, a nautical mile per hour, (called a knot. Never, ever call knots per hour) is 6,080 feet. That is about 1.15151 miles, or about 450 miles per hour.

[A HERETIC I AM]

12. I had always thought a Nautical mile was 2000 yards.......

or 6000 feet, which, if i am not mistaken, is the distance to the horizon when viewed from sea level.

Ever heard this? Or am I laboring under a flawed understanding of the facts?

[Pepperbelly]

15. In the Navy, 2000 yards was a nautical mile.

Exactly.

[Silverhair]

16. Actual figure is 6,076 feet. Link included in text.

http://people.howstuffworks.com/question79.htm

Sorry about the 6,080 figure. I was a bit off on that one too, and I spent 5 years in the US Navy, and was a navigation officer. (Red face from embarrassment)

[Silverhair]

18. Embarrassed from wrong figure, NOT from Naval Service. Proud of that. NT

[billyoc]

20. Navy here too, Merchant Marine after that

different values have been used. The value 1852 meters (6076.1 ft.) has been adopted internationally.

[candy]

14. Thanks

[karlrschneider]

17. It's 448.5 MPH to be exact. 1 Kt (Nautical Mile) is 1.15 Statute miles

Us pilots have to deal with this minutia often. :D
edit: technically, it's one arc minute of the equatorial circumference (which we obviously don't even know precisely) that according to the best guess is actually 1.15756 statute miles...which derives from ancient measurements that relied on the length of the foot of some kings) :eyes:

[Festivito]

21. I my defense , I took a nap today.

1.15 or 1.152 miles per nautical mile.

The diameter of the earth is too oft said to be 8000 miles. Commercial planes often travel five miles up making the diameter 8010 giving that 1.17 figure some people use.

A closer diameter comes from the definition of a meter as one-ten-thousandth the distance of 45 degrees of latitude which extrapolates the worlds circumfrence to an exacting 80,000 km. So,

80,000
/2 /pi diameter in km
*1000 dia in m
*100 dia in cm
/2.54 dia in inches (inexplicably exact)
/12 dia in feet
/5280 dia in miles
7911.54373915808358033503158417414 miles of earth diameter
*pi circumfrence in miles
/360 miles per degree
/60 miles per minute of a degree, i.e. per nautical mile
1.15068739303209994373598923030244
For the fun of it:
*5280
6075.62943520948770292602313599689 feet in a nautical mile...
... despite the 6000 ruling used in the military.

Add 10 miles to the 7911 figure to get the 1.152 in case the plane is measuring its air speed five miles up while you'd use ground distances between cities. But, speed by any other name would not be so fast...

Knots used to measure speed at sea using the number of equidistant knots that would freely drop from the stern of a ship divided by the time they took -- all at sea level back then.

I imagine your friend's plane has arrived by now.

[ladjf]

22. The plane is covering ground at 390 knots. The number is

used by pilots to predict flight time between points on the ground. It factors in the wind component.