Why can headwind assist planes when taking off and landing? Why does tailwind not help with takeoff?
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Okay so the shape of the wing is what makes the plane go up. The top is curved out. This makes the top longer than the bottom. Because of this the air pushes on the bottom, and gets spread out on the top making less pressure on top. The head wind increases the force pushing on the bottom and so makes take off easier. Tailwind does the reverse
For takeoff, you need a certain velocity of air under your wings. Lets say for simple math that it’s 50km/h. If you have no wind at all, you have to roll your plane on the ground up to 50km/h before the wings will give you lift.
But the important part is it’s not the ground speed that matters – it’s the speed of the air the plane is going through.
So if you have a 20km/h headwind, and get your ground speed up to 30km/h, now the air is moving across your wings at 50km/h and you can fly. If you have a 20km/h tailwind, you’re actually starting at a negative -20km/h air speed. You have to get the plane up to 70km/h on the ground to get your 50km/h of air over the wings.
Airplanes generate lift by the passage of air from the front of a plane across the shaped wings to the back of a plane, which causes lower air pressure above the wing, generating lift.
A headwind pushes air across them faster, decreasing pressure above the wing further and making lift easier. A tailwind does the opposite, which means you need more speed to generate that lift. That’s a problem when taking off, because you need to go faster to generate the lift to get off the ground, but it’s also a problem when landing because it means your approach needs to be faster to land properly. Since runways are typically of finite length and you need to take off/stop before you reach the end of said finite length, headwinds are better.
Crosswinds are the really shitty ones though.
Because the important number when you’re taking off is “air speed” not “ground speed”. Aka, how fast are you going relative to the air. This is because lift comes from the air moving over the wings, and it doesn’t matter if it’s the air moving over a wing or the wing slicing through air. They both mean the same thing for lift.
So if you have a headwind, the wind is adding to the air speed, making it easier to take off. And conversely, a tailwind *subtracts* from the air speed, meaning that the plane has to reach a significantly faster actual speed before it reaches the required air speed.
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
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!
Nice airspeed to minimise stall risk, slower ground speed.
Some old biplanes have so much lift they can land stationary in a stiff breeze.
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.
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 same reason a normal small plane can actually “hover”in one spot or fly backwards, if the wind is strong enough.
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