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Earths Rotation And A/C Speeds  
User currently offlineCerulean From , joined Dec 1969, posts, RR:
Posted (11 years 11 months 2 weeks 13 hours ago) and read 6688 times:

I've always wondered:

What effect does the earths rotation have on aircraft speeds and flight times?

I guess it's that whole "relativity" thing.

Since the earth spins from east to west at about 700 MPH, surely there must be some effect considering that commercial jetliners fly at almost the same speed.

Any information on this subject would be appreciated.

Thank you

-Cerulean


28 replies: All unread, showing first 25:
 
User currently offlineDesertJets From United States of America, joined Feb 2000, 7780 posts, RR: 16
Reply 1, posted (11 years 11 months 2 weeks 13 hours ago) and read 6658 times:

Neglible at best.

Remember the atmosphere itself is pretty well tied to the Earth by gravity. If it wasn't it would have flown off into space a long time ago. Since the atmosphere is bound to the Earth and rotates with it, no plane at altitude would feel much of any effect of Earth's rotation.



Stop drop and roll will not save you in hell. --- seen on a church marque in rural Virginia
User currently offlineAirbus Lover From Malaysia, joined Apr 2000, 3248 posts, RR: 9
Reply 2, posted (11 years 11 months 2 weeks 13 hours ago) and read 6652 times:

Surely that is a good question and I will stay tuned for someone who knows more to explain.. I myself is an ignorant in this field of "Earth science" or whatever u call it

User currently offlineDoug_Or From United States of America, joined Mar 2000, 3414 posts, RR: 3
Reply 3, posted (11 years 11 months 2 weeks 12 hours ago) and read 6590 times:

the way it was explained to me, the earth has friction and space does not. becuase of this, the air moves with the same roattional veloctity as the earth is space (negating wind, the air stays fixed over a set point). That being said, the corriolis force, directly tied to the earth's rotation plays a critical role in high level wind flows, such as the jetsteam.


When in doubt, one B pump off
User currently offlineYbacpa From United States of America, joined Feb 2001, 1108 posts, RR: 1
Reply 4, posted (11 years 11 months 2 weeks 12 hours ago) and read 6580 times:

Directly, the effect is neglibible. However, and I admit I'm not experienced in this field so I'll be brief, the rotation of the earth does affect the weather, which includes wind currents. This is argueably the most significant effect earth rotation has on relative plane speed.




SkyTeam: The alliance for third rate airlines finally getting their act together!
User currently offlineCaetravlr From United States of America, joined Oct 2000, 909 posts, RR: 1
Reply 5, posted (11 years 11 months 2 weeks 12 hours ago) and read 6560 times:

That is a very good question, and I am not sure what holds everything in place, but I am sure that whatever force that keeps the ground from moving three feet when you jump up in the air, is the same one that keeps the aircraft in the same place relative to its point over the earth, and that its movement is based strictly on its own motion. Yes, weather and atmospheric variables play a part, but if the actual rotation of the earth was a factor, then you would only be able to fly in one direction and get anywhere, and then it would be too fast.

I hope that made sense. In my warped mind it does.  Smile Perhaps someone with a little more in depth knowledge of physical laws can explain it to us.  Smile



A woman drove me to drink and I didn't have the decency to thank her. - W.C. Fields
User currently offlineN79969 From , joined Dec 1969, posts, RR:
Reply 6, posted (11 years 11 months 2 weeks 12 hours ago) and read 6560 times:

I asked my parents a similar question when I was 6 or 7. I wanted to know if you could get in a helicopter and hover for a few hours and let the earth rotate under you until the right spot "arrived"?

Anyway, I think DesertJets has the best explanation so far. I am no physicist either but I think gravity holds you at a fixed point on the earth. If you drop somthing out of car, it will fall "back" to the point from which you released (discounting wind resistance and all of that).


User currently offlineTWFirst From Vatican City, joined Apr 2000, 6346 posts, RR: 52
Reply 7, posted (11 years 11 months 2 weeks 12 hours ago) and read 6545 times:

>>Since the earth spins from east to west at about 700 MPH, surely there must be some effect considering that commercial jetliners fly at almost the same speed.<<


I don't know what planet you're on, but the last time I checked, Earth spins from west to east.



An unexamined life isn't worth living.
User currently offlineCerulean From , joined Dec 1969, posts, RR:
Reply 8, posted (11 years 11 months 2 weeks 11 hours ago) and read 6534 times:

I don't know what planet you're on, but the last time I checked, Earth spins from west to east.

You're absolutely, 100% correct. I stand corrected.

But why the need to hurl the insults?

-Cerulean


User currently offlineJgo From United Kingdom, joined Jul 2001, 68 posts, RR: 0
Reply 9, posted (11 years 11 months 2 weeks 11 hours ago) and read 6526 times:

I think it has something to with inertia (I think that's the one, I'm struggling to remember my higher physics). Basically because when the plane is on the ground, it is already traveling at 700MPH (in whichever direction). The thrust that the engines produce either increase or decrease the speed at which the plane travels with the atmosphere.

If you understand that, you probably deserve a Nobel prize.

- jgo  Smile


User currently offlineSquigee From Canada, joined May 2001, 652 posts, RR: 4
Reply 10, posted (11 years 11 months 2 weeks 10 hours ago) and read 6490 times:

It's funnny this question should come up- I've been asked it by several people the past few months. Here's the answer I give them.

Let's not look at this situation with planetary motion and large scale numbers. Pretend you are on a train, travelling 100 km/hour down a track. The train is moving quite smoothly. To pass the time, you toss a ball between you and your friend. Now, when you toss the ball to your friend, sitting in front of you, the ball might be travelling 30 km/hour. When he throws it back to you, it travels 30 km/hour. The question is, does the fact that the train is travelling at 100 km/hour affect this? Simply, no. Since its "frame of motion" is based on the train and not the ground, it doesn't matter how fast the train is travelling. To the people, the air, and the objects in the train, the ball is moving 30km/hour relative to them.

What throws off a lot of people is the idea of perspective. To the people in the train, the ball is travelling 30km/hour. But to a person standing outside the train, the ball would actually be travelling 130km/hour, or 70km/hour, depending on the direction that the ball is thrown (forwards or backwards).

Let's tie this back to the aircraft. If a plane takes off from a runway, it is travelling 185kts based on ground speed. At this point, we will assume that the air is still and that there is no wind. Just like on the train, everything on the earth is moving at a constant speed. Therefore, we don't percieve motion. So even though the earth, me, and the plane are all travelling at 700mph in planetary terms, to me on the ground, everything is motionless, except the plane travelling at 185kts.

I'll try to give you one more example. When you are driving down the highway, and another car is in the lane next to you, passing you, it looks like it is slowly driving past you. But in reality, you are travelling at 100km/hour, and he is travelling at 110km/hour. To a person on the side of the road, you both zoom by. But to you in the car, he's only going 10 km/hour more than you are! Now imagine the earth spinning at 700mph. The plane is travelling 700+185kts in planetary terms, but to us on the earth, we can only percieve the 185kts.

Now to really bend your mind, consider this. If a train is travelling as fast as a speeding bullet (a bullet train, if you will  Wink/being sarcastic) and someone fires a gun off the back of the train, the bullet's speed and the trains speed would cancel each other out, leaving the bullet to fall to the ground harmlessly.

Hope this clarifies the whole situation!



Someday, we'll look back at this, laugh nervously, and then change the subject.
User currently offlineCapt.Picard From , joined Dec 1969, posts, RR:
Reply 11, posted (11 years 11 months 2 weeks 10 hours ago) and read 6480 times:

Squigee, my brain hurts.....  Laugh out loud

I'm with you, but I still find it difficult to accept the "frame of motion" phenomenon. It still amazes me that we don't all go spinning off the face of this earth. Or is that due to gravity pulling us to the centre?! *Ouch....* says the artist...  Big grin


User currently offlineBackfire From Germany, joined Oct 2006, 0 posts, RR: 0
Reply 12, posted (11 years 11 months 2 weeks 10 hours ago) and read 6463 times:

In short, it's inertia.

If you stand on the roof of a speeding train then it's pretty obvious that you're travelling forwards at a high rate of knots. If you jump up and down, you're not doing anything to stop that forward motion. So you'll land in the same place on the roof.

It's all down to Newton's first law. A body will maintain its velocity unless acted upon by a force. Since your aeroplane is spinning at the same speed as the Earth while it's on the ground, it will continue to spin with the Earth when it takes off.


User currently offlineEA CO AS From United States of America, joined Nov 2001, 13612 posts, RR: 62
Reply 13, posted (11 years 11 months 2 weeks 10 hours ago) and read 6448 times:
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If you liked this thread, you'll REALLY enjoy this older one:

"If A 747 Were To Have 100,000 Pigeons In It..."

http://www.airliners.net/discussions/general_aviation/read.main/730650/

Informative, and hysterical!  Big grin



"In this present crisis, government is not the solution to our problem - government IS the problem." - Ronald Reagan
User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6461 posts, RR: 54
Reply 14, posted (11 years 11 months 2 weeks 9 hours ago) and read 6427 times:

The surface of the earth spins around its axis at 1036 mph at the Equator and at zero mph at the North and South Poles. And 700 mph "somewhere" in between those places.

It has roughly the same effect on an aircraft as the fact that the earth spins around the sun at some 67,100 mph. And whatever speed the sun rotates around the home galaxy center.

Anyway, going straight and level, then going east the aircraft will be a little lighter than going west, simply because in relation to space the greater speed will create more centrifugal forces. Anyway, at speeds below Mach 10 the effect will be negligible.

A low orbit earth satellite travels at roughly 17,500 mph at which speed centrifugal forces incidentally cancels out gravity - or rather "bends" the trajectory at the same curve as the surface of the earth.

When a satellite is launched near Equator on an eastward trajectory, then it gets a speed of 1036 mph for free, so it needs only an acceleration of 16,500 mph - 18,500 mph if launched westwards.

For fuel saving reasons you never see a westwards traveling satellite on the night sky. But you may see one traveling north or south, simply because the task of the satellite demands that it can observe the earth at or near the poles.

If launched westwards the Space Shuttle would not be able to carry any payload at all.

But going at speeds below several thousand mph it all means ounces on a Jumbojet instead of tons.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlinePW100 From Netherlands, joined Jan 2002, 2485 posts, RR: 12
Reply 15, posted (11 years 11 months 2 weeks 8 hours ago) and read 6383 times:

Cerulean
Excellent question!
I have thought about it for quite some time. So for you guys that have time to spare and willing to study the effect of earth rotation to aircraft, here’s my 101 synopsis:

Basically there are two effects of earth's rotation to aircraft speed, one direct effect and one indirect effect.

The direct effect is quite small and is caused through inertia. Moving on or around a planet will cause a natural tendency to reduce gravity. If the speed is sufficiently high, the object will even escape from the planet's gravity. Escape speed from earths gravity is Space Shuttle speed, about 40000 km/hr, or about 11 km/second. In other words, if an aircraft would fly at 40000 km/hr, no wing-lift would be required, since it could escape from earth's gravity by inertia alone! Please note that earth's rotation does not affect this speed in absolute terms.
However the earths surface is rotating, at equator the rotational speed is something like 1500 km/hr. So a stationary aircraft at the equator would already have a 1500/40000 [= 1/27] part of the speed required to escape from earths gravity.
Consider a 747 @ 360000 kg, flying over the equator @ 900 km/hr ground speed [airspeed is not important here, inertia doesn’t care about the speed of the air around an object!]. Now flying @ 900 km/hr with earth's rotation would increase the absolute rotation speed to 1500 + 900 = 2400 km/hr. 2400/40000 [= 1/17], meaning that 1/17th of the Jumbo’s lift requirement is being met through inertia! For a 747 @ 360000 kg @ 900 km/hr, this represents 21600 kg! Therefore the wings need only generate 338400 kg of lift.
If the aircraft was flying against earth rotation, the net rotational speed of the aircraft would be 1500 - 900 = 600 km/h. Now 600/40000 [= 1/67] part of the 360000 kg would be generated through inertia [= 5400 kg]. So there is a difference of 21600 - 5400 = 16200 kg in lift requirement for the 360000 kg Jumbo @ cruise [!] if it's flying with or against earths rotation over the equator!
It must be noted that this difference in lift requirement is translated in fuel economy, and not in cruising speed! The difference also reduces if the aircraft is further away from the equator.

The second effect is indirect, and is caused by coriolis. The earth's rotation has a very-very significant effect on high-altitude winds. The jetstream over the North Atlantic is a prime example.
The equator is warmer than the poles. Warm air around the equator will rise, since warm air is lighter than cool air. Rising air at the equator will flow off toward the north and the south. So the rising air at the equator will cause air to flow north in the northern hemisphere, from the equator towards the north pole. At the equator, this air has a rotational speed of 1500 km/hr [no east – west movement relative to earth’s surface], as has the earth’s surface at the equator. Now suppose this air flows off and reaches 45 degrees latitude. At 45 degrees, the earth surface rotational speed is approx. 1000 km/hr [at the pole it's 0!], but air flowing from the equator still has 1500 km/hr rotational speed. Since the earth is rotating from west to east, the air flowing from the equator towards the poles, will have excess speed in relation to the earths surface. This causes the air to translate the excess speed into a strong west to east component --> jetstream at high altitudes! Due to the damping affect of the atmosphere, and the friction between earth surface and the atmosphere, the jetstream air speed is smoothened. However under certain conditions, it can reach speeds of upto 300 km/hr!

Since most of the aircraft weight is being aerodynamically compensated [rather than through inertia], aircraft speed relative to surrounding air is much more important that aircraft speed relative to earths surface. @ 900 km/hr air speed, a 300 km/hr jetstream will results in a 1200 km/hr ground speed or 600 km/hr ground speed… Therefore prevailing winds will generally cause the east bound part of an Atlantic crossing to be 1 – 2 hrs shorter in terms of flight time compared to an west bound crossing.

Now I need to get some rest and clear my mind…..

PW100



Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
User currently offlineTWFirst From Vatican City, joined Apr 2000, 6346 posts, RR: 52
Reply 16, posted (11 years 11 months 2 weeks 8 hours ago) and read 6366 times:

What I'm curious about is:

If you go to either pole, and lay a broomstick (or pipe or any such similar object) on the ground (or ice, as it may be) with one end directly on the point of the axis, and then hover over the spot for a period of time in a helicopter, would you observe the object rotating, much like the hands on a clock?



An unexamined life isn't worth living.
User currently offlineArrow From Canada, joined Jun 2002, 2676 posts, RR: 2
Reply 17, posted (11 years 11 months 2 weeks 8 hours ago) and read 6359 times:
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Another interesting facet of this is the effect of the planes's speed relative to the earth's positioning against the sun. Presumably, if the plane is travelling west at 700 mph, the sun will never set ... or rise.

That's why Concorde lands in New York before it takes off from Paris/London. And why you lose a day when you fly from North America to Asia or Australia -- only to pick it up on the way back.



Never let the facts get in the way of a good story.
User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 18, posted (11 years 11 months 2 weeks 8 hours ago) and read 6351 times:

TWFirst; no, you won't, because as all the above posts explained, your helicopter is already rotating along with the earth. Now if you did it at night, and flew the helicopter to hold the stars steady, then the object and the earth would move, since you would not be rotating in relation to the universe.

User currently offlineTWFirst From Vatican City, joined Apr 2000, 6346 posts, RR: 52
Reply 19, posted (11 years 11 months 2 weeks 8 hours ago) and read 6347 times:

>>...and flew the helicopter to hold the stars steady<<

Yes, this is what I was meaning to imply in my earlier post. I understand that otherwise the helicopter would be rotating counterclockwise with the earth (if you were on the north pole, clockwise on the south).

But perhaps you wouldn't have to do it at night fixed on the stars. Perhaps you could do it fixed on the closest star: the sun.



An unexamined life isn't worth living.
User currently offlineKcle From United States of America, joined Feb 2001, 686 posts, RR: 0
Reply 20, posted (11 years 11 months 2 weeks 8 hours ago) and read 6339 times:

Ok, but what about this (And this has happened a lot to me):

You are in a train, plane, or bus, and the lav's are well behind you, so when you need to use them you have a small voyage to the rear part of the mode of transportation. Now this mode of transportation is going straight and on level ground (or flight) and is at a steady cruise.

As you get up to walk to the back of this mode of transportation, you notice that your normal size step seems doubled and you are walking at your normal rate of speed but you are walking twice as fast as you usually do.

When you are done and return to your seat (you were not in the lav. long enough for the outside forces to change), you find that your regular walking pace is cut in half as you find it a bit harder to get back to your seat.

What causes this?


User currently offlineJhooper From United States of America, joined Dec 2001, 6204 posts, RR: 12
Reply 21, posted (11 years 11 months 2 weeks 8 hours ago) and read 6333 times:

The Space Shuttle is launched eastbound for this reason.


Last year 1,944 New Yorkers saw something and said something.
User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 22, posted (11 years 11 months 2 weeks 8 hours ago) and read 6337 times:

kcle; that should only happen if you are going uphill, or if the vehicle is accelerating. Otherwise, I don`t think it should happen.

User currently offlineArrow From Canada, joined Jun 2002, 2676 posts, RR: 2
Reply 23, posted (11 years 11 months 2 weeks 6 hours ago) and read 6289 times:
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kcle:

I think that's because when you are walking backwards, you are decelerating relative to the ground over which you are traveling. When you walk forward, you are accelerating, and you have to overcome inertia.

Did I screw that up? Any physicists out there?



Never let the facts get in the way of a good story.
User currently offlineTWFirst From Vatican City, joined Apr 2000, 6346 posts, RR: 52
Reply 24, posted (11 years 11 months 2 weeks 6 hours ago) and read 6286 times:

Well, I think there's an even simpler explanation. When you are walking back to the lavatory, you are unintentionally walking twice as fast because you have to pee really bad.

When you return to your seat, it's a bit harder to get back because you are now paying more attention to all those people whose elbows you bumped on the way down the aisle to the lav, but didn't notice because you were hurrying since you had to pee so bad. Navigating around all those elbows and legs in the narrow aisle of a 737 as you make your way back to your seat takes more time.



An unexamined life isn't worth living.
25 Timz : If the 747 is flying eastward along the equator, with total speed 2400 km/hr, then centrifugal force is Weight of the plane times speed (in m/sec) squ
26 UBBA Pilot : I somewhat agree with AVT007, however, if you are in most Boeing aircraft (the 757/767 and 737 that I know of for sure) during cruise, the aircraft is
27 VirginFlyer : Ok, something which I don't think has been mentioned yet (if it has, apologies, I must have missed it) is conservation of angular momentum. It isn't e
28 VirginFlyer : Just as an addendum to my post, just in case any of you were wondering whether I had overlooked conservation of linear momentum, you will of course fi
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