The minimum V2 speed is defined by regulations (Part 25.107): 

V2min = 1.2 VS (A300/A310) V2min = 1.13 VS1g (Fly-By-Wire aircraft) . (V2/VS)min = 1.2 or 1.13 

The stall speed depends on weight. So, the minimum V2 speed is not a fixed value, whereas the minimum V2/VS ratio is known for a given aircraft type. 

Moreover, a too high V2 speed requires long takeoff distances and leads to the reduction of climb performance (Figure J4). As it doesn’t present any advantage, the V2/VS ratio is limited to a maximum value (V2/VS maxi), which depends on aircraft type: 

Figure J4 : 2nd Segment Climb Gradient versus V2/VS ratio 

V2max = 1.35 VS (A300/A310)

V2max = 1.35 VS1g (A320 family) 

V2max = 1.40 VS1g (A330) 

. (V2/VS)max = 1.35 or 1.4 or 1.5 

V2max = 1.50 VS1g (A340)

The V2/VS ratio is used in the optimization process, since its range is well-identified: 

(V2/VS)min ≤ V2/VS ≤ (V2/VS)Max 

Any V2/VS increase (resp. decrease) should be considered to have the sameeffect on takeoff performance as a V2 increase (resp. decrease). 

2.3.2. V1/VR Ratio Influence 

The purpose of this paragraph is to study the influence of V1/VR ratio variations on takeoff performance, while the V2/VS ratio remains constant. For that purpose, it is assumed that the following parameters are fixed: 

2.3.2.1. Runway Limitations 

2.3.2.2.   Climb and Obstacle Limitations 

The V1 speed (decision speed on ground) has no influence on climb gradients (first, second and final takeoff segments). 

On the contrary, the obstacle-limited weight is improved with a higher V1, as the takeoff distance is reduced. Therefore, the start of the takeoff flight path is obtained at a shorter distance, requiring a lower gradient to clear the obstacles. 

Any V1/VR increase leads to (Figure J6): 

An increase in MTOW limited by: 

Obstacles 

Not influencing the MTOW limited by the: 

First segment 

Second segment 

Final takeoff segment 

2.3.2.3. Brake Energy and Tire Speed Limitations 

A maximum V1 speed, limited by brake energy (VMBE), exists for each TOW. To achieve a higher V1 speed, it is necessary to reduce TOW. 

On the contrary, the decision speed doesn’t influence the tire speed limit. 

2.3.2.4. All limitations 

The following Figure (J8) shows that the highest of the maximum takeoff weights can be achieved at a given optimum V1/VR ratio. This optimum point corresponds to the intersection between two limitation curves. 

Fixed V2/VS ratio 

The result of this optimization process is, for a given V2/VS ratio, an optimumMTOW and an associated optimum V1/VR ratio. 

2.3.3. V2/VS Ratio Influence 

The purpose of this paragraph is to study the influence of V2/VS ratio variations on takeoff performance, for a given V1/VR ratio. 

2.3.3.1. Runway Limitations 

As a general rule, for a given V1/VR ratio, any increase in the V2/VS ratio  leads to an increase in the one-engine-out and the all-engine takeoff distances. Indeed, it is necessary to acquire more energy on the runway, in order to achieve a higher V2 speed at 35 feet. As a result, the acceleration phase is longer. 

On the contrary, V2 speed has no direct impact on the ASD. But a higher V2 speed results in a higher VR speed and, therefore, for a given V1/VR ratio, in a higher V1 speed. Hence, the effect on ASD. 

2.3.3.2.  Climb and Obstacle Limitations 

As shown in Figure J4, any V2/VS increase results in better climb gradients (1st and 2nd segment) and, therefore, in better climb limited MTOWs (1st segment, 2nd segment, obstacle). 

On the other hand, as the final takeoff segment is flown at green dot speed, it is not influenced by V2 speed variations. 

Any V2/VS increase leads to (Figure J10): 

An increase in MTOW limited by the: 

First segment 

Second segment 

Obstacles 

Not influencing the MTOW limited by the: 

Final takeoff segment 

2.3.3.3. Brake Energy and Tire Speed Limitations 

V2 speed does not directly impact brake energy limitation. Nevertheless, any V2 increase results in a VR increase and, therefore, in a V1 increase, at a fixed V1/VR ratio. Hence, the effect on brake energy limited weight. 

The lift-off speed, VLOF, is limited by the tire speed (Vtire). As a result, V2 is limited to a maximum value. Any V2/VS increase is then equivalent to a VS reduction, since V2 is assumed to be fixed, and thus the tire speed limited takeoff weight is reduced.