Pilots have a lot of calculations to make before even pushing back from the ramp, and the calculations required for take-off are some of the most critical. So, when it comes to answering why they say “rotate”, it is important to also answer the following question: what is rotation speed?
Pilots say rotate because it is a verbal queue that an airplane has reached its predetermined rotation speed (frequently abbreviated to Vr). This is the speed at which control inputs can be applied to lift the nose off the runway and make the airplane fly away.
So, how is rotation speed calculated and does it change from aircraft to aircraft? Let’s find out!
Table of Contents
What Is Rotation Speed? Is It the Only Significant Part of Takeoff?
There are three critical speeds as an aircraft accelerates during take-off. In sequential order, they are:
V1, which is defined as the speed beyond which takeoff should not be aborted (but the use of full reverse thrust is not mandated). Before V1, takeoff can be aborted.
Vr(rotation speed), which is defined as the speed at which the pilot begins to apply control inputs to cause the aircraft nose to pitch up, after which it will leave the ground. The act of rotating the airplane and pulling the nose up is to achieve lift-off earlier, by increasing the angle of attack of the wing through the air.
V2, which is defined as the takeoff safety speed, at which point the aircraft can safely climb with one engine inoperative, and to be able maintain the speed V2. With one engine inoperative, the airplane must be able to climb at least 35 feet (50 feet for some smaller aircraft) before the end of the runway (screen height), which is a standardized obstacle-clearance height.
Not all airlines have in their standard operating procedures the requirement to call out V2. It must also be said this only applies to multi-engine airplanes!
There are a number of other V speeds that follow, like Vlof (lift-off speed, when the airplane is completely airborne), V3 (flap retraction speed), and V4 (steady initial climb speed), but we will leave those for another day!
What Affects Rotation Speed (and the other V speeds)?
There are a number of factors used to calculate V1, rotation speed, and V2, and we have listed them below!
Takeoff weight: This is self-explanatory. It is the weight of the aircraft at takeoff, which includes all fuel, passengers, baggage, and cargo. It is the single-biggest factor determining rotation speed. The heavier an aircraft, the higher Vr.
Thrust and flap settings: It is not always necessary, nor possible, to use 100% of the available thrust when departing, and it is avoided where possible to limit engine wear. It may also seem counterintuitive to use flaps for takeoff, but a wing generates more lift with the flaps extended
Airplane brakes condition: As brakes wear, their ability to slow down an airplane reduces. That doesn’t mean they are unsafe! It just means they won’t be quite as effective as brakes in brand-new condition.
Runway altitude, length, and surface condition: If a runway has a displaced threshold and is shorter than normal, or is wet, V1 (the speed beyond which takeoff should not be aborted )will be lower because it will take longer to slow down on a wet runway and there is less runway available for slowing down. Additionally, this has been discussed before in our article on why runways aren’t flat
Altitude also has an effect, because the higher an airport, the less dense the air, which negatively affects lift and engine performance.
Environmental conditions: Wind direction and speed don’t affect the speed as such, since it is airspeed and therefore a function of velocity through the air, but a higher wind speed will increase the rate of acceleration. Temperature has a large impact because when it gets hotter, an engine’s performance, and available lift for the wing, decreases.
Can a Pilot Rotate Too Early or Too Late? What Happens?!
It is possible (and it happens on occasion) for a pilot to rotate too early. When this occurs, the airplane has not reached sufficient speed to be able to lift off the ground. The worst outcome when this happens is a tailstrike, when the tail of the airplane makes contact with the runway because its attitude (angle of the aircraft relative to the air or ground) is too nose-up. It doesn’t always result in an accident, but such mistakes can be very costly.
Below is a great video that covers tailstrikes in more depth!
Likewise, it is also possible to rotate late, though the implications are harder to reach simply because as you accelerate, the airplane naturally wants to lift off anyway. What a late rotation can affect is V2, and therefore the airplane’s ability to get above that screen height of 35 feet before the end of the runway. This is where takeoff run available (TORA) and takeoff distance available (TODA) come into play.
Are Rotation Speeds Different For Every Aircraft?
Every airplane will have a different rotation speed, and this varies greatly when taking into consideration the respective takeoff weights for each aircraft type as well.
For example, a single-engine Cessna 172 (with a MTOW approximately 1,100kg) has a rotation speed of approximately 60 knots(K) IAS fully loaded.
A fully-loaded Boeing 747 on the other hand, with a MTOW of about 400,000kg (400 tonnes!) has a Vr of approximately 160K IAS, which is a substantial difference.
Interestingly, even military fighter jets like the F/A18 Super Hornet have a similarly high Vr, ranging from 130K IAS to 165K IAS.
Concluding points
- Pilots say rotate to indicate that the airplane has reached its rotation speed, which is the speed at which the airplane can take off safely without stalling.
- In addition to the rotation speed, there are various critical speeds that pilots take into consideration, such as V1 and V2.
- Rotation before reaching Vr can result in a tailstrike, meaning that the tail of the airplane hits the ground and gets damaged.
- Rotation speeds vary a lot depending on the airplane model.
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