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Summary

EASA Open Category A2 requires drone operators to maintain a maximum horizontal speed of 4.8 m/s in reduced-distance mode near people. In Betaflight, this speed ceiling is enforced by enabling throttle limiting on a dedicated rate profile (Profile 2 — Cinematic) and calibrating the throttle limit percentage against measured GPS ground speed. The limit is per-profile and switchable from the transmitter, preserving full-speed capability in Profile 1 for open-area operations. Calibration requires a GPS-equipped flight controller or a separate GPS module and one straight-line test flight.

Concept

What A2 reduced-distance mode requires

EASA Open Category A2 drone operators who have passed the A2 certificate of competency may fly within 30 m of uninvolved people (reduced from the default 150 m separation) if — and only if — the drone is operating at low speed. "Low speed" is defined as ≤ 4.8 m/s horizontal ground speed. There is no firmware certification requirement for this: the operator is responsible for maintaining the speed limit, and may do so by any means including firmware throttle limiting.

Throttle limiting in Betaflight does not guarantee ≤ 4.8 m/s in all conditions — wind assistance, dive angles, and gyroscope-induced motor differences can push speed slightly above the limit. The limit is an operational tool, not a hard safety ceiling. The operator remains responsible for maintaining safe speed.

Betaflight throttle limiting

Betaflight's throttle_limit_type = SCALE reduces the effective throttle range from 0–100% to 0–N%, where N is the configured limit percentage. At full stick, the motors receive only N% of their maximum PWM signal. throttle_limit_percent sets N.

The limit is profile-specific. By convention, libdrone uses: - Profile 1 (Chase): no throttle limit — full speed for open-area FPV - Profile 2 (Cinematic): throttle limit calibrated to ≤ 4.8 m/s

Profile switching is mapped to a transmitter switch. The pilot activates Profile 2 before entering A2 reduced-distance operations and confirms the speed limit is active.

Calibration procedure

The correct throttle_limit_percent value depends on the specific build's AUW, motor KV, prop size, and battery voltage. It cannot be calculated from first principles without a detailed motor model. The practical calibration method is:

  1. Set an initial estimate (start at 40%).
  2. Fly a straight line at full throttle in Profile 2 in calm conditions.
  3. Read peak GPS ground speed from the OSD or GCS log.
  4. If peak speed > 4.8 m/s, reduce throttle_limit_percent by 5 points and repeat.
  5. If peak speed < 4.0 m/s, the limit is more conservative than necessary — increase by 3 points if desired.
  6. Target: peak speed 4.2–4.5 m/s (margin below the 4.8 limit to account for wind assistance).

Reference

Betaflight CLI commands (Profile 2): ```bash

Switch to profile 2

profile 2

Enable throttle limiting

set throttle_limit_type = SCALE set throttle_limit_percent = 40 # Starting estimate; calibrate

Save and reboot

save ```

OSD GPS speed display: Enable gps_speed in the OSD element list to see real-time ground speed during the calibration flight.

Transmitter profile switch mapping (TX16S): In EdgeTX, assign a 3-position switch to SF (Betaflight rate profile): - Position 0: Profile 1 (Chase, no limit) - Position 1: Profile 2 (Cinematic, throttle limited) - Position 2: Profile 3 (reserved)

Confirm profile activation in Betaflight OSD: the active profile number is displayed if the OSD pid_profile_name element is enabled.

Procedure

Full A2 throttle compliance calibration

  1. Ensure GPS is functional and OSD GPS speed element is enabled.
  2. Enter Profile 2 in Betaflight CLI. Set throttle_limit_type = SCALE, throttle_limit_percent = 40. Save.
  3. Fly a straight-line pass at full throttle in calm conditions (< 2 m/s wind). Read OSD peak GPS speed.
  4. Adjust throttle_limit_percent per the rules above (±5% per iteration).
  5. Confirm final peak speed ≤ 4.5 m/s on three separate passes.
  6. Document the calibrated value in the build log with the battery cell count and prop size — if either changes, recalibrate.

Rationale

A separate rate profile for A2 compliance was chosen over a dedicated flight mode or arming condition because it requires no flight controller modification — it is a pure Betaflight parameter change compatible with any Betaflight version. The profile switch on the transmitter gives the pilot direct, immediate, reversible control over the speed limit. Alternative approaches (GPS-based speed limiting in firmware) require features not available in standard Betaflight releases and add software complexity without improving the operational outcome.

Connections

requires: - easa-open-category - betaflight-profiles - betaflight-setup related: - regulatory-overview - gnss-gps - flight-modes - remote-id-compliance leads_to: - betaflight-profiles - first-flight