The Unofficial XCSoar Manual
Faq:Maccready
From XCSoar
[edit]
How does MacCready value change Speed (Vmc) and Optimum speed (Vopt) and affect the speed to fly bar? Why is it not changing?
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XCSoar makes the following distinction:
- MacCready speed (Vmc) is the optimal speed to fly in cruise in still air.
- Dolphin speed (Vopt) is the optimal speed to fly in cruise based on the current lift/sink.
Many people prefer to fly at a constant speed between thermals because they dislike dolphining (porpoising), and may find little loss of performance doing so. Indeed, some people think the reduced workload in the cockpit means that this method can be more efficient.
If dolphin speed is required: A speed-to-fly bar does appear on the right side of the screen if XCSoar receives input from a vario providing airspeed information - it is inappropriate to calculate speed to fly corrections if the device doesn't know the airspeed.
