I was sitting in The Chair as the dentist poked and scraped my freshly cleaned teeth. He was commenting about his upcoming Southwest Airlines flight to Phoenix…
Dr. S: Ken, my flight from Louisville to Phoenix is scheduled for 4 hours and 10 minutes…
Ken: uhh huh.
Dr. S: …and the return flight is 3 hours, 20 minutes.
Ken: uhh huh.
Dr. S: Is there really that much difference between flying east and west?!?
Ken: uhh huh. Wahhn you hlying eassh you hahh a hailwinn.
Dr. S: Well, that’s what I thought but I didn’t realize it was that much!
Ken: Uhh huh.
Clean teeth and free from the Cavity Creeps. But what about my dentist’s question? His westbound flight takes nearly an hour longer than his flight back home. Why is there so much difference in the flight time? He knew that winds had something to do with it. But an hour difference for a relatively short flight?!
To understand the effects of wind on an airplane, it helps to think about a motor boat on a river. In the animations below, the river is flowing left to right at 10 knots (about 12 mph). Both boats are traveling through the water at 15 knots. Both motors have the exact same throttle setting.
The first boat is traveling the same direction as the water (downstream). The boat enjoys a nice increase in speed because its speed through the water is added to the speed of the river current:
Boat speed + river current speed = speed relative to the ground. 15kts + 10kts = 25kts.
In the next animation, the boat is traveling upstream and again moving through the water at 15 knots. Since the water current is flowing towards the boat, it takes it longer to travel the same distance along the river bank. We’ll have to change our formula and subtract the water speed:
Boat speed – river current speed = speed relative to the ground. 15kts – 10kts = 5kts
The boat heading downstream cruises along at 25 knots while the upstream boat crawls at 5 knots. Quite a difference!
Airplanes fly in moving bodies of fluid, too!
Like boats, airplanes also move through a large body of fluid… air! If our aircraft’s speed through the air is 450 knots and the air mass is moving at 160 knots in the same direction (a tailwind), our speed across the ground will be a smoking fast 610 knots (700 mph).
The downside is when we fly the opposite direction; the wind works against us. Now we subtract the headwind from our airplane’s speed: 450 knots – 160 knots = 290 knots across the ground. 610 knots vs. 290 knots – yuck!. Depending on the distance of travel, the time difference between a westbound and eastbound flight can be anywhere from a several minutes to a few hours!
Airplanes flying backwards?
Conventional airplanes can’t actually fly backwards, but they can move across the ground backwards. I did this demonstration with my students when I was a flight instructor in the dark ages. It’s really cool.
If you fly a small airplane into a 50 knot headwind then slow the plane down until its airspeed is about 45 knots, something interesting happens.
Aircraft speed – wind speed = ground speed 45kts – 50kts = -5kts
That’s a negative 5 knots of ground speed! The headwind is faster than the airplane’s speed through the air. The airplane still flies just fine (it doesn’t care that there’s a strong headwind, it only cares about the speed of the air flowing over the wings), but when you look down at the ground, you will be moving backwards. EEEK!
Here’s a video demonstrating this. These guys achieve several seconds of zero ground speed and a little bit of negative ground speed. Backwards Flying!
Flight Planning and Wind
When pilots and dispatchers plan flights, we take a very close look at the high altitude winds. The weather chart below shows the location of “jet streams” (the green lines) in North America and the Atlantic. Jet streams are narrow bands of strong winds. During winter in the northern hemisphere, they can reach as high as 200 knots. If I’m crossing the Atlantic ocean eastbound to Europe, I want to fly close to the jet stream so I get a nice push to save time and fuel. Flying the other direction, I want to stay away from these strong winds.
Wind Speed vs. Altitude
Wind speeds and direction can change quite a bit as we change altitude. Airline dispatchers look at the winds aloft forecasts for several different altitudes to find the best combination of routing and altitude for each flight.
The following images are taken from windy.com (a great website for exploring winds at different altitudes). It’s easy to see the difference between the wind speeds and patterns at 16,000 feet and 34,000 feet.
Breaking the Sound Barrier?
On February 9, 2020, a British Airways 747 broke the record for fastest sub-sonic flight from New York to London. The flight was a remarkable 4 hours 56 minutes, breaking the previous record by 17 minutes.
Check out the aircraft ground track. The wind barbs in the center of the Atlantic indicate winds around 200 knots (230 mph). The aircraft had quite a push. [Learn more about wind barbs and winds aloft]
The flight reached a top speed of 825 mph across the ground. The speed of sound at cruise altitude was 674 mph (the speed of sound changes with temperature). So, did the aircraft break the sound barrier? It was certainly moving across the ground faster than the speed of sound…
BA flight 112 was flying at its normal cruise speed of around Mach .88 (88% of the speed of sound). The airflow over the wings was sub-sonic, so no shock wave, and no sonic boom. The aircraft did not break the sound barrier. The airplane flew happily within its normal operating envelope.
As demonstrated earlier, airplanes fly within a body of fluid. If it had been a boat, the 747 was cruising at the normal speed on a river that was flowing at over 230 mph toward London.
More About Winds
Fascinated by winds and air mass movement? Learn more about Winds and Temperature Aloft Forecasts!
Amazing text my friend!
Thanks for reading, Bruno!
Can not comprehend. If a plane is doing 100 knots and has a 50 knot tailwind, isn’t the plane Outrunning the wind by 50 knots?
Is it the lack of air resistance In Front of the plane that is changing it performance?
Forget about the term “wind.” Airplanes fly within a large air mass – Just like boats float on a large mass of water.
Imagine being in a small boat sitting in the middle of a river with no engine running. The river is flowing at 10 knots. If you look at the shoreline, you can tell you are moving 10 knots as the boat moves along with the water current. The boat, however, is sitting perfectly still with reference to the water. If you place your hand in the water, it isn’t moving – you will feel no resistance, no water pushing against your hand. If you have a speedometer that measures water speed, it will read 0 knots.
Now, point the boat in the direction of the current and start the engine. Adjust the power to provide 5 knots of speed. The speedometer will read 5 knots. If you put your hand in the water, you will feel the water moving past your hand at 5 knots. The boat is most definitely moving through the water at 5 knots, but the body of water the boat is sitting in is moving at 10 knots. If you look at the shore, you will see that your speed in reference to the shore is now 15 knots.
The boat has no idea that the body of water it sits in is moving. The same applies to aircraft.
Another way to think about it: Walking around inside a moving train. Your body doesn’t know it’s moving at 60 miles an hour. If you walk forward at 2 miles per hour, your speed relative to the tracks is now 62 mph. Walk toward the rear of the train and your speed relative to the tracks is 58 mph.
I hope that helps!
Really well explained. When I don’t understand the complicated technical jargon on Wikipedia I look for sites like yours. I’m currently reading about the recent Dubai Emirates accident and this helped me understand head & tailwinds in the accident report. Could you write about indicated airspeed and true airspeed? Thank again for the wonderful easy to understand information.
Thank you for the kind words! I’ll add the airspeed idea to my list.
Thanks for reading!
Thanks a lot for explaining all this. This is like ground school for dummies and I truly appreciate it. If you’re not already, you should really think about becoming an instructor ?
Thank you for the kind words. I appreciate the feedback. I was an instructor for several years and really enjoyed it!
Thanks for reading!
For a math paper, I was actually comparing flights from New York to Los Angeles to flights from Los Angeles to New York, and there was a 5 hour difference between the two! (8 hours vs 3 hours) I was so surprised I jumped out of my chair! Until I realized that there exist time zones.
Funny! Glad you figured it out! 🙂
What is better for passenger comfort: headwind or tailwind?
Assuming winds are steady, their direction has no impact on how smooth a flight is. A headwind simply means it will take an airplane longer to fly from point A to point B. Opposite for a tailwind.
Super web site. I’m not working in whatever close to airplanes but I’m “savvy” about that stuff. Everything is well explained, especially the topic on stoping an airliner on the runway.
However, I still wonder how you can control an airplane when touching down with strong sidewind. I’ve seen many clips showing planes slaloming at landing… do you use brakes to stabilize the plane with the front wheels still in the air ? Or the tail stabilizer ??
Also, I will fly on a 787 for the first time soon (YUL-CMN). I heard about compensation systhems to neutralize turbulences induce movement. It is said to be the quitest airliner around for passengers. Can you talk about this plane ?
When making a crosswind landing, we use a couple of different techniques. If the aircraft is in a crab at touchdown (nose pointing slightly off to the side) we use the rudder to straighten the nose. Inertia of the aircraft also helps to straighten the nose before the nose gear touches down. Brakes are not used until the aircraft is completely on the ground and spoilers are extended.
I have flown as a passenger on the 787 and agree it’s a wonderful aircraft. I really don’t know much about the advanced systems on it. Enjoy your flight!
I just found this blog, I hope I’m not too late for the party, I enjoy your writing and your topic of course, aviation is awesome. I want to become a pilot myself but not commercial, my dream is to become a private pilot (instrument rated) and one day own my own airplane—hopefully a Cirrus SR22T, beautiful specimen. I have a question for you and given your expertise as a pilot I hope you can answer.
I’m currently soloing in the pattern—not right now that would be highly irresponsible writing this down while flying, but I’m at that stage of my training—and I can only fly during the weekends and a lot of my flights get cancelled due to weather—specially crosswinds. So, sometimes I have several weeks in a row without flying and that is very harmful to my training in such an early stage. I sometimes have to redo lessons because I do not perform as expected after such long times without practicing. My question is, do you have any recommendation to deal with uncontrollable factors such as weather during training? How can I deal with this problem?
Thank you very much for all your wisdom. Cheers,
Every pilot experiences this when they begin training. Sometimes the weather and/or the aircraft don’t want to cooperate. Definitely do some “chair flying” at home when you can’t do the real thing. Chair Flying means to go through your procedures in your head and even pretend to manipulate and touch the controls. It helps!
Good luck with your training,
Thanks for the reply Ken. I am definitely going to do more chair flying during the week because winter is giving me a really hard time.
I really enjoyed your article…no affiliations…just random interest…you explain everything perfectly.
Thanks for reading! Glad you enjoyed it.