Calculating a precise speed at which an aircraft takes off depends on the current weather conditions and each airplane’s specific aerodynamic design characteristics. Key factors that affect airplane takeoff speed (sometimes referred to as its rotation speed) include: direction of airflow, the airplane’s shape (especially its wings), the airplane’s size, and its weight. Infinite combinations of aerodynamic and environmental factors can impact the required speed for any airplane to take off.
This is why every type of airplane has a different takeoff speed. Let’s take a closer look at a few important details that affect how fast airplanes take off.
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What Is Lift?
Lift is an upward force created when air flows over and under an airplane’s wings. During takeoff, if the speed and direction of the airflow around the wings generates enough lift to offset the weight of the airplane, it becomes airborne and takes off. This is why achieving the correct speed is so critical during takeoff. The amount of lift generated is a function of airspeed, and without lift, flight is impossible.
Takeoff Speeds
Takeoff speeds for each airplane vary with the airplane’s size, wing shape and size, the airplane’s weight, and many other factors, including weather conditions. When aircraft manufacturers develop, test, and get regulatory certification for each new type of airplane, an optimum set of specifications is published, including requirements for speed during takeoff. Here are a few examples of takeoff speed specifications for some widely known types of airplanes.
Boeing 747
A typical takeoff or rotation speed of a Boeing 747-400 model—which was the biggest selling of the 747 variants—is around 160 knots. The Boeing 747-8 Intercontinental, the most recent 747 passenger variant, has a typical cruise speed of Mach 0.86 while flying at an altitude of 35,000 feet, according to Boeing.
Beechcraft Super King Air
The Beechcraft Super King Air is a family of popular twin turboprop airplanes—including models 200, 300, and 350—seating up to 11 passengers. In 1996, the manufacturer stopped using the “Super” brand name. A typical minimum rotation or takeoff speed with a full fuel tank and two passengers is around 104 knots. Cruise speed ranges between 228 and 359 knots.
Cessna 172
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Since the first Cessna 172 rolled off the production line in 1956, more than 45,000 have been manufactured, making it the most popular airplane in the world. According to its pilot operating handbook, the Cessna 172’s normal rotation or takeoff speed is about 55 knots indicated airspeed (kias) and its maximum cruise speed is 124 knots.
McDonnell Douglas F-15 Eagle
With a top speed above Mach 2—twice the speed of sound—the McDonnell Douglas F-15 Eagle is the fastest fighter jet in the U.S. Air Force. The F-15 is propelled by two powerful turbofan engines. It has shoulder-mounted wings and twin vertical stabilizers. The minimum rotation or takeoff speed for the F-15 ranges between 120 and 150 knots, depending on the aircraft’s configuration. The cruise speed of an F-15 is 495 knots. Pterodactyl Ascender (Ultralight)
The Pterodactyl Ascender is a family of very small, ultralight, single-engine, single-seat aircraft developed in the 1970s. Outfitted with a Dacron sailcloth wing and a forward canard, the Pterodactyl Ascender’s small two-cylinder engine drives a rear-mounted propeller that pushes the airplane forward. Its minimum takeoff speed is about 20 mph and its cruising speed is around 45 mph.
What Affects Aircraft Takeoff Speed
When trying to determine the ideal speed for a takeoff roll on a runway, there is no magic number that all aircraft must reach to successfully take off. The speed required for an airplane to take off depends on an infinite number of factors, including the current weather during takeoff, the airplane’s weight, the configuration of the airplane, the specific wing design, and the positioning of the flaps and other flight- control surfaces. Let’s take a look at some of the most important factors that affect aircraft rotation or takeoff speed.
Weight
Weight is one of the most critical factors on any aircraft. The heavier an aircraft is, the more lift is required for it to get airborne. Airplanes designed to fly heavy payloads often have wings designed for high-lift, along with powerful engines that can achieve rotation or takeoff speeds sufficient to generate enough airflow across the wings.
Configuration
Airplanes can be outfitted with various optional equipment, depending on the mission. For passenger aircraft, this might be an additional seating capacity. For military aircraft, it might be weapons or defensive systems, or additional fuel tanks. For longer missions, an airplane might be fully loaded with fuel. Changing configurations can add weight to an airplane and sometimes change its aerodynamics. A pilot will consider these variables when choosing the proper speed for takeoff.
Wing Design
Airplane wings are designed to include aerodynamic devices that pilots can manipulate to increase lift during critical phases of flight—such as takeoffs and landings. These devices—including flaps, slots, and slats—can mitigate the effects of additional weight, insufficient airflow, crosswinds, and other factors that may reduce lift. Some airplane wings are specifically designed to generate maximum lift. High-lift wings are generally longer and wider because allowing more airflow over a wing can increase lift. High-lift wings tend to reduce the takeoff speed required to get airborne.
Wind Direction and Density Altitude
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Lift requires proper airflow over and under an airplane’s wings. Optimum airflow is parallel to the direction of the runway so the airplane is pointing into the wind. But sometimes nature has other plans. A slight crosswind might require a slightly higher speed to achieve lift during takeoff. Other weather conditions such as high temperatures could affect the density altitude during your takeoff. Density altitude is defined as pressure altitude corrected for nonstandard temperature variations. Its effects on an airplane are exacerbated during takeoffs and landings at airports located at higher altitudes. For example, a rotation or takeoff speed in Denver, Colorado, on a hot day will have to be higher than on a cold day at a lower altitude airport.
What is STOL (Short Takeoff and Landing)?
STOL (short takeoff and landing) airplanes are designed to take off at very slow speeds on short runways. STOL airplanes are useful for bush pilots who fly in remote areas where improved airports with longer, paved runways are not as common.
STOL airplanes are also suited for taking off and landing in small urban airports with shorter runways surrounded by tall buildings and other obstacles.
These airplanes fly at very slow speeds with the help of large wings that are capable of creating large amounts of lift. The wings often include specially designed flaps and slots.
What Is Assisted Takeoff?
Assisted takeoff is a system that provides an aircraft with speed and momentum during takeoff. Assisted takeoff systems include tow lines attached to powered aircraft—such as those used for glider airplane takeoffs, catapults—-such as those used to assist airplanes taking off from Navy aircraft carriers, and jet- and rocket-assisted takeoff (JATO, RATO) systems.
Assisted takeoff systems are required for airplanes that cannot produce enough takeoff speed to get airborne due to short runway length or—-in the case of gliders—-because they don’t have independent propulsion systems such as engines or electric motors.
Takeoff Speeds Aren’t One Size Fits All
Every type of airplane is different and every airplane has different takeoff speeds under various conditions and scenarios. Airplane takeoff speeds for each type depend on multiple changing factors, including weight, wing configuration, weather, and the altitude of the airport. To learn more about airplane takeoff speeds and all things aviation, subscribe to FLYING Magazine.
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