Ticket #1943 (new enhancement)
|Reported by:||davidswelt||Owned by:|
I suggest to include a warning mechanism that alerts the pilot if the airspeed drops below a predefined or glider-model derived value.
Rationale: True stall horns and angle-of-attack instruments require hardware, but in order to prevent stalls during the approach phase - specifically the typical stall/spin accident during the turn to final - I assume that a speed monitor will go a long way, and is simple if not trivial to implement, if ASI data is available.
UI: Provide a radio control for airspeed warning (off, manual, auto), an input field specifying the minimum safe airspeed for approaches.
Implementation: Hard-code a minimum height (AGL) for the system's activation. Activate the system below this height, but only if aircraft has been in motion above the minimum speed several seconds (catch winch launch failures and other early releases). If ASI reported by external device drops below the minimum speed, warn immediately. Play sound or, if possible, pre-recorded "speed!" verbal announcement.
Auto mode: calculate Vref=1.3xVso, based on ballast, bugs (?), and glider data (is the polar indicative), plus a wind component (assuming we're landing into wind).
Caveats: ASI information may be unreliable during slips. This requires reliable ASI input, 3D GPS fix, and terrain data. Pilots might choose a higher or lower Vref based on gust factors, terrain properties and so on, but this is intended to serve as a backup warning system rather than an approach speed calculator.