The takeoff optimization principle has the objective of attaining the highest possible performance limited takeoff weight while fulfilling airworthiness requirements.
| V1/Vr Range |
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| V2/Vs Range |
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V1/Vr Ratio Influence
- Increase in V1/Vr ratio decreases the take of distance required and hence increase the MTOW for engine failure case. (Ref: Balanced Field Length & Unbalanced Field)
- Although V1 speed has no effect on climb gradient but higher V1 value decreases TODR (Takeoff Distance Required). Therefore start of takeoff flight path is obtained at a shorter distance and require lower gradient to clear the obstacles. Increase in V1/Vr increase the MTOW limited by obstacle and has no effect on MTOW limited by first segment, second segment and final segment. (also check Takeoff Segments | Climb Gradient Requirements | Obstacle Clearance Requirements)
- V1 max is limited by Vmbe(maximum brake energy speed). As the aircraft weight increases Vmbe decreases.
All these factors are considered to calculate optimum V1/Vr Ratio.
V2/Vs Ratio Influence
| Runway Limitations | Climb and Obstacle Limitations | Brake Energy & Tire Speed Limitations |
As explained in above two reason any increase in V2/Vs leads to decrease in runway limited MTOW. |
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Conclusion
- For every V2/Vs value it is possible to find out optimum MTOW and associated V1/Vr ratio
- This procedure is followed for entire range of V2/Vs.
- At the end highest of all optimum MTOWs and associated optimum V1/Vr is retained.
This takeoff speed optimization process indicates that at MTOW, takeoff can only be done with single set of takeoff speeds V1, Vr and V2. Use of any speed other than this set of value will result in MTOW reduction.
