Damping #
5.00 sec
The Speed-to-Fly (S2F) can be damped to smooth the display, with the default set to 5 seconds. Increasing the damping further smooths the display but also delays its response. For example, after leaving a thermal, the indicated speed-to-fly does not immediately increase in response to sink.
The damping value can be adjusted up to a maximum of 10 seconds.
In modern gliders with high wing loading and high cruise speeds (over 150 km/h), reacting to short-lived thermals is often counterproductive. Rapid changes can lead to high load factors due to inertia, reducing overall performance. Some damping is therefore beneficial. It allows the pilot to respond smoothly to sustained climbs or prolonged sink (“blue holes”), rather than reacting to every small fluctuation.
The default value of 5 seconds can be adjusted by the user to suit personal preference and aircraft characteristics.
Blockspeed #
[DISABLE] [ENABLE]
By enabling Block Speed [Enable], the vertical motion of the surrounding air mass (as indicated by the net variometer) is ignored. Only the aircraft load and the MacCready value are used to calculate the optimal speed.
In this mode, the speed displayed by the speed-to-fly command remains constant while circling in a thermal, reflecting the principle that reacting to very short-lived thermals (a few seconds) is generally ineffective due to aircraft inertia.
This was confirmed by numerical simulations at the Technical University of Munich, which showed that the MacCready speed for the upwind case only becomes relevant for thermal durations of approximately 20–30 seconds (about half the period of the phygoid or natural “pump” frequency), or when deliberately pushing the aircraft aggressively.
Some experienced pilots adopt this style and achieve very good average speeds.
S2F Mode #
[Manual]
[AutoSpeed]
[AutoFlap]
[AutoTurn]
[Vario fix]
[Cruise fix]
The S2F “Mode” determines how the instrument switches between circling and speed-to-fly. Several options are available:
Setting [Manual] will control the S2F by the a switch or push button connected to the S2F labeled wires at XCVario cable tree. At any time you may also use a remote stick sending SW commands to XCVario to manually toggle between vario and speed-to-fly, what provides maximum flexibility.
[AutoSpeed] (default): The instrument automatically switches from circling to speed-to-fly at a preset airspeed. The switch-over speed is configured in the “AutoSpeed Thresh.” menu.
[AutoFlap] setting changes the mode depending on your flap position if there is a flap sensor available.
[AutoTurn]: The instrument automatically switches to circling mode when the measured rotation rate exceeds the AutoTurn Rate (in degrees per second). The rotation rate is averaged over 20 seconds and includes a 20% hysteresis—the mode only switches back when the rotation rate drops 20% below the set threshold.
[Vario fix] or [Cruise fix]: The instrument remains in the selected mode and does not switch. In practice, when flying cross-country, these settings are rarely useful. Fixed vario mode may make sense if you prefer a conventional variometer display and do not want to fly according to speed-to-fly.
S2F Switch #
[Disable]
[Switch]
[Switch Invert]
[Push Button]
The hardware type of speed command switch can be configured. The default is [Switch], that may be configured as inverted as well, but a [Push Button] can also be selected, which toggles the mode each time the button is pressed. This is particularly useful, for example, when using a remote stick input device with integrated buttons.
The [Switch Inverted] option reverses the switch logic: the speed command mode is selected when the switch is open rather than when it is closed, useful e.g. if an existing switch is wired or working like that.
Note: The switch can change modes at any time, even if [AutoSpeed] or [AutoTurn] is active, unless the switch type is set to [Disable].
AutoSpeed #
120 km/h
This is the airspeed in AutoSpeed mode at which the variometer switches from circling to speed-to-fly / cruise mode. The default is 120 km/h.
For gliders with higher wing loading or modern high-performance designs, this value can be adjusted higher as appropriate.
AutoFlap Pos. #
1.00 flp
This setting defines the flap position at which the S2F mode should be switched in the “S2F mode”. By default, the flap position is set to +1.00 flp.
Note: This is only visible if your glider has a flap sensor equipped and enabled in the XCVario.
AutoTurn Rate: #
10°
This sets the rotation rate threshold (in degrees per second) at which the device switches to S2F mode in AutoTurn mode.
Lower values cause the device to switch to circling mode earlier, while higher values delay the switch due to averaging over approximately 20 seconds.
For reference, a typical 36-second circle corresponds to a rotation rate of 360° / 36 s = 10°/s, which is the default setting..
Switch Lag: #
5 sec
The Switch Lag setting smooths the automatic activation and deactivation of speed-to-fly mode in AutoSpeed mode. Without it, the system may toggle rapidly when airspeed hovers near the AutoSpeed threshold. The default hysteresis is 5 sec: the instrument switches to speed-to-fly mode 5 seconds delayed. It can be adjusted from 2-20 seconds.
