The FAI F9U rules: what a racing model may be.

Which edition

Everything on this page is from the FAI Sporting Code, Section 4 (Aeromodelling), Volume F9 Drone Sports, 2025 edition, effective 1 May 2025, chapter C. The FAI lists a 2026 edition, but its host could not be reached when this site's research was done, so it was not read. Its effective date is reported two ways: 1 January 2026, from a search summary of its cover, and 1 June 2026, from a Prism News trade article also seen only as a search summary. Any article below may have been amended in 2026. The rule book in force at a given event, and the organiser's published event rules, decide.

One more inconsistency in the 2025 text: chapter C is headed "F9U (Official class)" and the change log records the move from provisional status, while article A.1, in the World Cup chapter, still calls F9U provisional.

The model limits at a glance

This site's F9U model checker compares a set of figures against these limits. It is a reading aid only; the event's scrutineers decide.

Article by article

C.1: what the model must and must not do

Every F9U model needs two functions. A fail-safe device stops the motors when triggered, and a pit mode cuts the video transmitter's power when triggered. The rule also bans automation: no pre-programmed manoeuvring devices, no automatic positioning or path correction, and no pre-programmed increases in video power. Recovery modes the competitor activates, such as a "turtle mode" that flips a model back over after a crash, are allowed.

C.1.1: weight and size

Total take-off weight, including batteries, may not exceed 1 kg. Size is set by the motors rather than the frame: all motor axes must fit inside a circle 330 mm across.

C.1.2: power

Only electric motors are allowed. Battery packs may have up to six cells in series, written 6S, and no cell may exceed 4.25 V when fully charged. The rule spells out what that means for two pack sizes, 17 V for 4S and 25.5 V for 6S, and pack voltage is measured before each race. The 2025 change log describes the per-cell limit as a safety measure. Motors may be tilted at most 15 degrees in each direction from the reference plane.

C.1.3: propellers

Propellers may be up to 6 inches (15.2 cm) in diameter, and all-metal propellers are forbidden. The 2025 change log records that an earlier ban on propeller protection devices was removed in the changes effective 1 January 2020, with the FAI stating there was no safety reason to prohibit them; the same changes limited each cell to 4.25 V. The 2019 edition had forbidden any propeller protection device. The 2025 text simply no longer bans them; dropping a ban is not a statement that guards prevent injury.

C.1.4: radio control

Any 2.4 GHz spread-spectrum radio-control system may be used, but frequencies and power must comply with the rules of the host country. Organisers may list other authorised equipment, giving 868 MHz and 915 MHz modules as examples, and those must run at the lower of 100 mW or the host country's limit. The FAI's rule defers to national law here; national radio rules are on radio rules by country.

C.1.5: video and goggles

Video may be analogue or digital, but only in the 5.8 GHz band. The video transmitter's output is capped at 25 mW, on the ground and in the air, centred on designated frequencies with at most 30 MHz bandwidth; a breach can lead to disqualification from the event. Switching on any 5.8 GHz video transmitter at an F9U event without authorisation is strictly prohibited and can bring disqualification from the event whether or not it was intentional.

A competitor's own video receiver and antenna must be mounted directly on the goggles, no more than 160 mm above the goggle antenna connector; personal receiving antennas on masts or stands are prohibited. The organiser's receiving system must handle analogue and digital transmitters and both left-hand and right-hand circular antenna polarisation (LHCP and RHCP). Recording every race is strongly recommended, and the organiser's recording wins in a dispute.

C.1.6: lights

An organiser may require an LED unit so that each model shows a different colour. The rule sets a minimum of 32 RGB LEDs or 280 mm of RGB strip, with colours blue, green, red, yellow, cyan and magenta allocated by the competitors' order in the race. The FAI's 2024 World Drone Racing Championship rules required such a unit at that event.

C.1.7: marking

Each model carries the pilot's three-letter national identification mark followed by their FAI Sporting Licence (or FAI Drone Permission) ID number, readable unaided at arm's length. This is the FAI's sport marking. Countries have their own legal marking and registration rules, set out on each law page.

C.3 and C.4: how many models

A competitor may use at most three models at an event, and each model may be used by only one competitor. Rule C.4 lets the organiser check each registered model's fail-safe and motor cut-off, battery voltage, and radio and video equipment.

Earlier FAI texts

The F9U numbers have been stable across the FAI texts this site's research read. The 2019 edition (effective 1 May 2019) and the FAI's 2024 World Drone Racing Championship Sporting Rules (June 2024) both set the 1 kg weight and 330 mm motor circle, electric motors only and 6-inch propellers. The 2019 edition allowed a 1 percent tolerance for measuring-device inaccuracy on size, weight and battery voltage. The 2024 championship rules expected Raceband frequencies for video at 25 mW and capped radio modules at 100 mW.

Not the same as MultiGP

MultiGP, an organiser, publishes different limits for its own classes; for example, its Open, Whoop and Micro classes allow 4.35 V per cell, against the FAI's 4.25 V. These are two bodies' rules for their own races, not a conflict of fact, and they are never combined on this site. See MultiGP classes.