Speed Of 747 At Takeoff

Airliner Takeoff Speeds

- question from name withheld

Past "boilerplate commercial airline plane," I assume y'all are referring to large passenger jetliners such equally Boeing and Airbus products. The takeoff speed of such aircraft varies quite a bit, depending on the takeoff weight and the employ of high-elevator devices like flaps (2) and slats. All the same, a skilful average speed range is about 160 mph (260 km/h) to 180 mph (290 km/h). Some typical takeoff speeds for a diversity of airliners are provided below.

Aircraft	Takeoff Weight	Takeoff Speed
Boeing 737	100,000 lb 45,360 kg	150 mph 250 km/h 130 kts
Boeing 757	240,000 lb 108,860 kg	160 mph 260 km/h 140 kts
Airbus A320	155,000 lb lxx,305 kg	170 mph 275 km/h 150 kts
Airbus A340	571,000 lb 259,000 kg	180 mph 290 km/h 155 kts
Boeing 747	800,000 lb 362,870 kg	180 mph 290 km/h 155 kts
Concorde	400,000 lb 181,435 kg	225 mph 360 km/h 195 kts

Only you might be wondering merely how these speeds are determined. Commercial airliners are certified under the Federal Aviation Administration (FAA) Federal Aviation Regulation (FAR) Role 25 which specifies takeoff velocity requirements that must exist observed by transport aircraft. The progression of takeoff speeds dictated by these regulations is illustrated in the post-obit figure.

Takeoff velocities for a multiengine aicraft

This diagram starts with the airplane at residuum, indicated by V=0. The first critical speed encountered during the takeoff run is the stall speed, V_{due south}. The stall speed is an of import quantity throughout aerodynamics as information technology dictates the slowest speed at which an aircraft can travel and generate but enough lift to remain or get airborne. This velocity is heavily dependent upon the configuration of the airplane, primarily the state of flaps, slats and other lift-control devices. Determining the stall speed is relatively straightforward using our handy bang-up friend, the lift equation:

In this case, we know that nosotros demand enough elevator (Fifty) to counteract the takeoff weight (W), we know the reference expanse, and nosotros know the density at the takeoff altitude. The lift coefficient that concerns u.s. here is the maximum lift coefficient in the takeoff configuration (typically flaps down at five� or 10�) represented by C _{50 _max} . This last value is by far the most difficult to estimate, but some typical values are 2 to 2.5 for a traditional airliner layout and 1.6 to one.8 for a supersonic design. Knowing these values, we tin now solve for the stall speed using the following equation.

Even though the aeroplane is capable of taking off every bit soon as the stall speed is reached, it is a very unstable condition. Fifty-fifty the slightest change in the orientation of the aeroplane or the condition of its command surfaces will cause the fly to lose lift (i.east. the wing stalls, hence the proper name "stall" speed) and the aircraft volition drop back onto the rails.

Due to the danger of trying to takeoff at stall speed, a number of additional speed requirements have been implemented for safety reasons. The first of these relates to multi-engined shipping, which covers all commercial airliners. Should an engine fail during the takeoff run, there is commonly a yawing moment since the engine(s) on one side of the plane produce more thrust than those on the other side. A yawing moment, which causes the nose to turn side-to-side, is countered by a deflection of the rudder, which produces a yaw moment in the opposite management. The 2 moments will then cancel each other out and keep the airplane headed straight down the runway. Beneath a certain speed, at that place simply is non plenty aerodynamic force generated past the rudder to produce the correcting yaw. This velocity is called the minimum command speed, V_mc.

The adjacent critical speed, which must be at to the lowest degree as fast as 5_mc, is likewise related to the failure of an engine during the takeoff run. If the engine fails fairly far downwardly the runway, the plane might accept enough speed to proceed the takeoff safely. Conversely, if the engine fails early on in the takeoff, there ought to be enough track left to abort the takeoff and come to a end. But what if the engine fails somewhere in between? To provide the pilot with some definite criteria on which to brand a decision, the FAR Part 25 specifies a critical engine-failure speed, 5_ane. Below this speed, the pilot should abort and bring the plane to a end if an engine fails. If the engine fails subsequently the aircraft has exceeded V_one, he should continue the takeoff using the remaining engines. The critical engine speed therefore defines the point on the runway at which the distance needed to stop is exactly the aforementioned as the that required to reach takeoff speed. The resulting total takeoff distance is correspondingly known as the balanced field length.

Definition of critical engine-failure speed and balanced field length

The adjacent velocity of interest to us is that at which the aircraft can begin to rotate its olfactory organ into the air, conveniently chosen the rotation speed, 5_r. While V_r must be at least v% greater than V_mc, information technology demand not exist any greater than 5_one.

Next comes the minimum unstick speed, Five_mu, which defines the point at which the aircraft could take off if the maximum possible rotation angle were reached. This maximum angle would occur if the tail of the plane were to actually scrape the ground.

Since such a takeoff would be damaging to the airplane and most unnerving to passengers, the aircraft really lifts off at a slightly greater velocity chosen the liftoff speed, V_lof. Liftoff speed must be at least 10% greater than Five_mu when all engines are operating and 5% greater when one engine has failed.

Now that our happy picayune aeroplane has finally become airborne, it accelerates into takeoff climb speed, V₂, which must be reached at an altitude high plenty to clear a given obstacle. For FAR 25 shipping, the obstacle clearance height is 35 ft (ten.7 chiliad). The takeoff climb speed must be at least twenty% greater than stall speed, V_s, and 10% greater than V_mc.

These speeds are summarized below.

Speed	Description	FAR 25 Requirement
5_s	stall speed in takeoff configuration	-
V_mc	minimum control speed with one engine inoperative (OEI)	-
5₁	OEI determination speed	= or > V_mc
Five_r	rotation speed	five% > V_mc
V_mu	minimum unstick speed for rubber flight	= or > V_south
V_lof	liftoff speed	10% > V_mu 5% > V_mu (OEI)
V₂	takeoff climb speed at 35 ft	20% > 5_s 10% > 5_mc