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The engines are roaring; the plane speeds down the runway gracefully, pitches up, and takes off. But what is the speed (VTO) of the plane as it takes off?
For smaller, single-engine planes, the takeoff speed can be as low as 60 mph. But for jets, the takeoff speed lies between 150 and 230 mph. Many factors determine takeoff speeds like weight, size, and, most importantly, plane aerodynamics.
Do you know that the biggest airplane in the world is the Antonov An225 Mriya? You would presume it to have the highest takeoff speed, but on the contrary, it has a takeoff speed lower than many other aircraft.
Getting a plane airborne is a complex process. According to airlive.net, a lot of calculations need to be done before the flight. These include calculating the fuel required, understanding the flight path, and also setting minimum and maximum speed limits
How does an Airplane Fly?
Before we dig into takeoff speed, here is a brief reminder of how airplanes fly. Four main forces keep the airplane stable in the sky. They are thrust, drag, lift, and weight. Thrust and drag control horizontal motion, while lift and weight are responsible for vertical motion.
Let us look at horizontal motion first:
- Thrust is the force that moves the plane forward. The only source of thrust on an airplane is, you guessed it, the engine.
- Drag slows the aircraft down. It can be thought of as the air resistance that the plane faces when moving through the atmosphere.
- If thrust is greater than drag, the plane will accelerate. If thrust is less than drag, the plane will slow down. Finally, if thrust is equal to drag, the plane will continue at a constant speed.
- For making the plane go up or down, the following forces are responsible:
- Lift forces the plane upwards. The wings are designed to allow air to collect under them and push the plane upwards.
- The weight pushes the airplane towards the earth. It is important to have an even distribution of weight to keep the plane balanced.
When lift becomes greater than weight, the plane rises. When the lift is less than the weight, the plane starts to descend. Finally, when the lift is equal to the weight, yes, the plane maintains altitude.
What determines Takeoff Speed
Planes have different weights, and thus their takeoff speeds vary. Even two identical planes departing from the same runway in the same conditions can have different takeoff speeds. But for most airplanes, the takeoff speeds are normally consistent, and the variations are very little. The takeoff speed is related to many factors. Let us discuss some of them
One of the most crucial factors that help determine the takeoff speed of an airplane is the weight it is carrying, known by aviators as "Take-Off Weight" or TOW.
In simple terms, Takeoff weight is the total weight of the aircraft and whatever it is carrying. TOW typically includes the following:
- Passengers: The aircraft operators know exactly how many people are on board and can estimate their total weight
- Cargo: There is a reason why your bags are weighed before you get on board an airplane; it helps the crew calculate the exact weight going on to the plane
- Fuel on Board: Yes, even the weight of the fuel is calculated because it can be several tons for larger aircraft
- The Plane Itself: Probably the heaviest thing flying will be the plane itself. Manufacturers often provide plane specifications in great detail. This weight can be picked up from the user manual.
Remember how it is the air that generates lift? As the plane speeds down the runway, it gets more and more air under its wings. If you have a headwind, this means more air is flowing under your wings naturally. Therefore, you will need less speed to generate the right amount of lift and will be able to take off at a slower ground speed.
You might remember from your science class that the air starts to lose its density as the temperature rises. At higher temperatures, you will need more air under your wings to generate the right amount of lift.
Aerodynamics is by far the most important in determining takeoff speed and all other features that a plane has to offer. The wing shape and engines play a vital role in getting the plane airborne. Larger wings will often require less speed to generate more lift.
The Antonov An-225 is a mammoth of a plane. It is so big that it dwarfs almost every other plane around it. Why is it so big, you ask? Because it is designed to carry super heavy loads with a Maximum Takeoff weight of 640,000 kgs, or nearly 1.5 million pounds. Yet this plane can take off at a speed of less than 250 mph; this is possible only because of the impressive aerodynamics of the beast. It houses massive wings with six jet engines mounted on them, each capable of producing 23 tons of thrust.
What Are V Speeds?
In aviation, speed is not only about how fast an airplane is moving. It can be used to understand several operating procedures while flying the aircraft. If you are into planes and aviation, you must have heard about V speeds.
V speeds can be thought of as limit indicators. They let the pilot know which methodologies to adapt as the speed is reached. For example, VSrefers to the stall speed. It informs the pilot that if the plane slows down beyond this speed, it will stall and start to fall from the sky. In addition to VS, three more V speeds are crucial when the plane takes off; let's look at each one briefly.
V1 – Point of No Return
Runways are limited, which means that if an airplane needs to come to a full stop before the runway ends, it needs to be going under a certain speed limit. V1marks the speed after which the pilot has to take off, and trying to cancel the takeoff will cause the plane to run off the end of the runway.
VR – The Rotation Speed
VR is a speed at which the wings generate optimum lift to get the plane in the air. At this speed, the pilot would normally pull back on the controls to pitch the nose upwards, and the plane will start to take off.
For smaller planes, VR can come much before V1, especially if the runway is long. But commercial jets approach VR near or slightly after V1.
V2 – Taking Off with One Engine
V2 is the speed at which the plane can take off with one engine failing for multiengine aircraft. A plane running on one engine and maintaining V2will still reach a safe altitude by the end of the runway.
All these speeds are calculated beforehand, considering the runway length and all other factors we discussed above.
Taking Off Too Early
If the pilot, for some reason, tries to take off the runway before reaching the rotation speed, it can lead to a dangerous tail strike.
As the name implies, a tail strike happens when the aft fuselage, or tail, comes in contact with the ground. This mishap is very dangerous as it can cause severe damage to the plane.
It occurs when the angle of attack is very high relative to the lift being generated. This means that the plane's nose is pitched up to extensive limits, but the plane is failing to take off.
Taking Off Too Late
If the takeoff speed is achieved and the pilot fails to take off, it could lead to very serious consequences. From a tire blowout to a high speed runway excursion, all could prove fatal for the passengers on board. Although aircraft tires are very tough, they have their maximum speed ratings. Pushing them beyond their limits is never a good idea. A blowout during takeoff could result in the plane veering off the runway leading to catastrophe.