How fast can a 747 go?

[AngryAmish]

I was flying recently and they would put the speed, altitude etc of the plane on the screen. At certain points the ground speed they put up on the screen was 700 mph +. It seemed a bit fast to me. So I looked up the speed of sound on wikipedia and they say the speed of sound at altitude is about 660 mph.

What gives aviation buffs? Is this a ground speed v. flight speed thing? Does the fact that we were in the jet stream at the time (I think)make any difference?

[Rabrrrrrr]

1. The Jet Stream can add a lot of mph to one's speed

so your plane was probably doing 600, plus 100 or so for the jet stream. And, since the speed of sound is the speed of sound in air, and since the air is thus moving at 100 mph (or whatever, approximately), you still aren't above the sound barrier, because you are only going 600 mph in relation to the air around the plane.

Though I do hope that some expert will chime in, and let us know what they mean about plane speed in the air - I've always wondered if they mean in relation to the ground, or actual speed through the air without any relation to the ground. And is the air speed different than land speed, in the way that nautical speed is different than land speed.

Someone, answer the OP question, and this one!

[billyskank]

5. Rabrrrrrr is quite correct

The speed they tell you in the plane is the ground speed. Depending on whether you have a headwind or a tailwind will affect your ground speed by +-100mph or more. It's your air speed that determines whether you're breaking the sound barrier, and 747s do not fly supersonic. In fact, with Concorde out of service, no civil aircraft do so any more.

[AngryAmish]

6. I think it was 740 mph at one point

We had a 140 mph tail wind, I think. If so that means the plane was really going about 600 mph which is within the specs, I think.

Thanks for the info.

[GCP]

2. You're confusing knots with mph

The speed of sound is around 660 knots per hour.
1 knot = 1 nautical mile per hour = 6076 feet per hour
1 mph =1 mile per hour = 5280 feet per hour
Therefore the speed of sound is 761 mph.

http://www.lerc.nasa.gov/WWW/K-12/WindTunnel/Activities/knots_vs_mph.html

[baldguy]

3. The speed of sound also varies

Depending on air temp & pressure.

[anarch]

4. according to the technical specs, about .92 mach

I think that does depend on altitude, but cruising speed is usually anywhere from 500-600mph. It's definitely a sub-sonic aircraft, but as for the rest of it, :shrug:

[DS1]

7. Probably just a little past Mach 1

In a nosedive.

Then you run out of altitude and smash into the ground.

[Rabrrrrrr]

8. Nah, all you have to do is pull the air brake lever

[pokerfan]

9. You were flying east, weren't you?

[AngryAmish]

10. Yes

[ChoralScholar]

11. That's what I was thinking

Flying against the rotation of the earth will increase ground speed.

However, the earth rotates (roughly) from west to east. So the OP would have to be flying West for artificially inflated ground speed numbers.

[pokerfan]

12. Coriolis Force is responsible for the prevailing winds

which tend to be from west to east for most locations in the United States.

[The Velveteen Ocelot]

14. The rotation of the earth has no effect on an airplane's groundspeed.

http://www.newton.dep.anl.gov/askasci/phy00/phy00385.htm

However, the prevailing winds in the northern hemisphere are generally west to east. At a high altitude an aircraft can encounter the jetstream, where the winds can be very high. This, not the rotation of the earth, will affect the groundspeed (not the true airspeed) of the aircraft.

[Oeditpus Rex]

13. Air Force One is a 'special' 747

If it's trying to hide * after terrists blow up stuff, it can go as slowly as 2 mph.

If it's taking him to DC in the dead of night to interfere with a right-to-life case, it can do about a brazillion.

Talented aircraft, that.

[Rabrrrrrr]

16. LOL! And if it's heading to Iraq on an emergency Thanksgiving

Hillary-troop-greeting-preempting mission, it can do instantaneous.

[Parche]

15. 747

was it a 747-200 or 747-400?

sounds like a real heavy tail wind

[AngryAmish]

17. 747-400