Why can headwind assist planes when taking off and landing? Why does tailwind not help with takeoff?
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For planes it doesn’t matter how fast they are going compared to the ground when it comes to when they can lift off/need to land. They only care about how fast the air is moving over the wings when it comes to flying
Let’s say they need to reach 100mph through the air to lift off. If they have a 20mph headwind they only need to gain 80mph before they can lift off. If they have a 20mph tailwind then they need to gain 120mph to lift off.
On landing they care about how much runway they need to land. If they have a 20mph headwind they only need to bleed off 80mph to land. The same wind in the other direction would have to bleed off 120mph. Imagine stopping at 40mph vs 60 mph.
Sometimes the best way to imagine this is extremes. It is possible (and actually midly frequent) for small planes like Cesnas to fly at 0mph. If the wind is as fast or faster than the flight speed then you can fly in one direction while going nowhere or even backwards!
What creates lift is the amount of airflow over the wings. Think like holding your hand out a car window. The faster the car goes the more lift you can create regardless of wind direction. If the wind I blowing head on it increases the airflow relative to the wings and thus increases lift meaning the aircraft needs less runway to takeoff. The opposite is also true. Tail wind might be ideal once airborne but on takeoff it would actually reduce the airflow under the wings and make it harder to achieve the required lift for takeoff (longer runway).
On landing the same is true but in reverse. You want to be able to approach the runway at the minimum possible speed while still having enough lift to stay airborne. If you were coming in with a tail wind you would need more speed and a longer runway to slow down.
Lift is created by the speed of the air relative to the wing. If I am going 50mph on the runway in still air, I get exactly as much lift as going 25mph on the same runway with a 25mph headwind.
If I have a 25mph tailwind, I would need to go 75mph on the runway to get the same amount of lift.
Planes generate an upwards force using to effects. One is the Bernoulli effect where the faster moving air abow the wing creates a pressure difference which provides an upwards force on the wings. The other effects is air resistance by flying into the air at an angle the air will push the plane up. Its like sticking your hand out from the car window, if its at a 45-ish° angle to the oncoming wind your hand will try to rise.
Now planes when taking off will use a lot of that second effect but they need to get into the air first. Thats where the Bernoulli effect comes in. Now hom much lift comes from that is a function of the velocity of air moving over the wings. Since all kinds of lift comes from the relative air speed for a plane it isn’t the velocity relative to the ground thats important its their air speed. If there is headwind that increases air speed. So the plane has to accelerate less to take off.
Same for landing. The safest landing is a landing preformed with high air speed and low ground speed. You want to have a low velocity relative to the ground so you can stop before you reach the end of the runway. But if the air speed is too low you will stall, an fall. Head wind keeps air speed high to allow the plane to approach much slower.
The way to think about this is that a plane uses fast moving air to stay in the sky but from the perspective of the plane it doesn’t matter whether its the plane moving fast through still air or the wind is blowing fast across the stationary plane. The plane will have lift either way.
The same reason a normal small plane can actually “hover”in one spot or fly backwards, if the wind is strong enough.
The same phenomenon applies to helicopters. Imagine a scenario where a helicopter takes off with a 20 knot tailwind from a runway:
The pilot lifts the helicopter into a 10 foot hover. The aircraft isn’t moving over the ground, but from the perspective of the air mass, it is flying backwards at 20 knots. This speed does reduce the power needed to hover slightly. However, once the aircraft starts the departure/takeoff, it needs to slow down back to 0 knots from the air masses’s perspective. The air mass sees the helicopter going backwards, then as the helicopter starts moving forward, it will eventually be going forward at the same speed as the air mass., which is a zero airspeed hover, which means power required just went up. In addition, the helicopter is now no longer outrunning it’s dirty air and power required will go up due to that as well.
From this point, a more normal takeoff and flyout will commence. But how far down the field or runway is the helo at this point? To get back to the normal no-wind position, the aircraft had to go from flying backwards at 20 knots to a zero airspeed hover. That took some distance.
If you flip the scenario around:
When the helo lifts into a hover, the wind is already pushing the dirty air away from the rotor, and power required is less because the aircraft already has 20 knots of airspeed. As the aircraft starts moving forward, it will require much less room to do a normal climb out profile, because it will hit these speeds much sooner.
The plane’s flight characteristics are affected by its air speed, that is how fast it’s moving through the air, or how fast the air is moving over the plane. The faster the air is moving over the aircraft the more lift the wings generate and the more authority the control surfaces have, which work by deflecting air to change the airplane’s attitude. Since the air is not stationary but it moves independently from the ground due to wind what matters most for an aircraft in flight and not groundspeed, that is how fast it’s moving relative to the ground. Sure you can tell how fast it’s travelling but it’s important to know the airspeed because that determines the flight characteristics of the airplane. It’s important to know since the stall speed, the maximum speed for having the landing gear or flaps extended, the maximum aircraft speed, take off and landing speed and the maneuvering speed, are all dependent on the airspeed and not the ground speed.
So with a headwind, that is the wind blowing from the front of the aircraft, this effectively increases the airspeed, so it’s faster than the groundspeed. This means that with a headwind the airplane needs less distance for its take off run, since the speed of the headwind is effectively added to its air speed. The take off is the most dangerous part of the flight, since the plane is picking up speed on the ground and is at its heaviest so any help it can get to get airborne is very crucial. When landing a headwind is helpful because it does two things, 1) it helps the airplane slow down and 2) it helps it make the approach at a higher air speed, so it’s more stable, but a lower groundspeed, so the touch down happens at a lower than usual speed which makes it smoother and less of a strain on the aircraft’s landing gear. When approaching to land the aircraft has to slow down but it mustn’t stall, a stall is when the air is not going over the plane fast enough to keep it flying stable and it falls down with no control.
[This video](https://www.youtube.com/shorts/7vP13XPMNfc) is a great example of how a strong headwind can help with landing. This is a very lightweight plane so the effect is very exaggerated compared to passenger planes but the principles are the same. Even though the plane is basically stationary relative to the ground, which would normally be well below the stall speed, its air speed is high enough that it can maintain control and safely touch down. There’s videos of similar planes taking off nearly stationary in similar conditions.
Tail winds, that is wind blowing from the rear of the aircraft, have the exact opposite effect, of essentially detracting from the aircraft’s airspeed. So take off runs need to be longer and landings need to be faster. Of course aircraft can still fly with a tailwind because they’re moving forward through the air much faster than any wind can blow from the rear but the tailwind is still there and since aircraft are not designed to be as aerodynamic from the rear, it makes the airflow over the aircraft more turbulent which in turn makes controlling the aircraft harder and the flight less smooth. In most cases however planes don’t take off or land with tail winds because most airports are made, if possible, with the most common weather of the area in mind and offer multiple runways so that even if one runway has a tailwind, another might not. Even if they have to planes can and do take off and land with a tail wind, there’s obviously defined acceptable parameters for each aircraft.
Nice airspeed to minimise stall risk, slower ground speed.
Some old biplanes have so much lift they can land stationary in a stiff breeze.
Airplanes need lift to fly. They get it from the way the air pushes against their wings from the front. It won’t matter how fast the plane is moving if the air is coming from behind them, the wings can’t generate lift backwards. The wings need air pushing against them from the front to generate lift, which is why we push them into the air/wind with propulsion.
Less air colliding with the front of the wings, less lift. No lift, no takeoff. More air colliding with the front of your wings – bingo! Lots of lift!
Others have already explained why. Here’s a video of a plane landing in a strong headwind that will tie it all together for you. https://www.youtube.com/shorts/7vP13XPMNfc
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