Sometimes it seems unfathomable how something as huge and heavy as a plane can actually lift up into the air.
Surely the laws of gravity would mean that it should stay firmly on the ground, right? Wrong.
A combination of lift and thrust enables aviation to occur, and the speed at which a plane races down the runway directly affects these forces.
The faster a plane thrusts forward down a runway, the more air that is forced under the wings, creating the necessary lift. But exactly how fast does a plane have to go to take-off?
The answer depends on several variables such as the type of aircraft, its size, its weight, and the runway length.
Takeoff is when an aircraft vehicle leaves the ground, becomes airborne, and ascends with the goal of reaching cruising altitude.
For aircraft built or oriented for vertical travel, this is referred to as liftoff, as in “We have lift off”!
For vehicles that take to the sky from a horizontal position, this usually begins with a transition from ground to air at high speed.
For hot air balloons, helicopters, and some specialized fixed-wing aircraft (VTOL aircraft such as the Bell Boeing V22 Osprey), no runway is needed whatsoever.
How Is Aircraft Speed Measured?
The first thing to note is that aircraft takeoff speed is measured in knots (kts) or meters per second (m/sec) rather than in miles per hour. One knot is equal to 1.15 mph. For example, a Boeing 737 takes off at approximately 130 kts which is around 150 mph.
What Forces Enable Takeoff To Occur?
There are four key forces at play when a plane takes flight. These forces are Thrust, Drag, Lift, and Weight.
Whilst Weight and Drag are forces that oppose flight, Thrust and Lift are forces that create flight. For takeoff to occur, the forces of Thrust and Lift must exceed the forces of Weight and Drag.
- Thrust is a force which pushes an aircraft forward in the direction of motion. It is created using a propeller, jet engine, or rocket. Thrust pulls air in and then pushes it out in the opposite direction. One example is a household fan where air particles are sucked in and then pushed out in order to keep you cool.
- Lift is the force that holds an aircraft in the air. Most of the lift used by airplanes is created by the wings. The faster the plane races down the runway, the greater the amount of lift that can occur.
What Factors Affect Takeoff Speed?
To determine the minimum number of knots that a plane must be traveling at in order to take off, you need to consider the following factors:
- Weight of the aircraft – Weight is the force caused by gravity and it directly opposes the force of lift. In almost all cases, the greater the weight of the plane, the faster the speed necessary to achieve takeoff.
- Length of the runway – Larger aircraft with lots of passengers and cargo generally require longer runways than small aircraft with lighter loads. This is because lighter aircraft can travel more quickly. Faster takeoff speeds require shorter runways and vice versa.
- The Aircraft Type – Different types of planes will have different minimum speeds for takeoff. Smaller planes like light sport aircraft typically require lower speeds than larger jets like jumbo jets. Some aircraft are specially designed for short takeoff and landing distances, and these are known as STOL craft.
- Wind conditions – If there is wind blowing against the plane’s direction of travel, this creates drag. Drag reduces the amount of lift that occurs and therefore requires higher takeoff speeds.
- Temperature – High air temperatures affect the physics of how aircraft fly; the lower the air density, the faster an airplane must travel to produce enough lift to take off.
- Air pressure and Altitude – If the air is thin, more speed is required to obtain enough lift for takeoff; therefore, the ground run is longer. An aircraft that requires 745 feet of ground run at sea level requires more than double that at a pressure altitude of 8,000 feet.
- Fuel load – Fuel tanks add weight to an aircraft, especially when they are full. For long haul flights, fuel tanks can increase the weight of the craft considerably. The takeoff speed of a craft with a full fuel tank will need to be faster than that of a plane taking off with only half a tank of fuel.
- Pilot skill level – Pilots who are less skilled may not be able to control their craft at high speeds. As pilots gain experience, they become better at controlling their craft at higher speeds. Beginner pilots will tend to use longer runways and lower takeoff speeds.
- External influences – Weather conditions such as rain, snow, hail, fog, etc., can greatly reduce takeoff speeds.
How Fast Does A Commercial Aircraft Have To Go To Take Off?
Aircraft manufacturers set the minimum speed of a plane required to take off as part of its certification process.
These minimums are based on calculations of what is safe for the pilot, passengers, and crew.
They also consider factors such as the length of the runway available, the weather conditions, and other external factors.
Minimum takeoff speeds for most aircraft are around 80 knots (about 90 miles per hour) or slightly above that.
It takes much longer to reach cruising altitudes because planes have to climb to higher altitudes before they start descending.
What Is The Maximum Takeoff Speed Of A Commercial Aircraft?
Takeoff speeds for the average jetliner is typically something to the tune of 240–285 km/h (130–154 kn; 149–177 mph). Light aircraft, much like the Cessna 150, find lift at around 100 km/h (54 kn; 62 mph).
Ultralights can take off at much lower speeds still.
What Is The Cruise Speed Of A Commercial Plane?
Cruise speeds for commercial airplanes vary by type of plane. Jetliners generally cruise at around 500-600 km/h (310-370 kn; 280-330 mph), while regional jets cruise at 300-400 km/h (186-250 kn; 155-225 mph).
Most smaller passenger planes cruise at around 200-300 km/h (125-185 kn; 120-180 mph).
The minimum takeoff speed is usually specified as part of the aircraft’s certification requirements.
However, this number is subject to change depending on many different factors, including the size of the aircraft, the length of the runway, the weather, and other external factors.