Glossary
One sentence per term, and a link when the site treats it properly. Organized by system, not alphabet — neighbouring terms explain each other.
The aircraft & flying
| Term | Meaning |
|---|---|
| FPV | First-Person View — flying via a live camera feed in goggles, not by watching the aircraft |
| Acro mode | The FC holds the rotation rate you command; centered sticks hold attitude, not level (Module 0) |
| Angle / horizon mode | Self-leveling modes — a second control loop wrapped around acro (Module 4) |
| Arming | The deliberate switch action that allows motors to spin — the aircraft's most important safety interlock |
| AUW | All-up weight: ready to fly, battery included; every performance number is meaningless without it |
| TWR | Thrust-to-weight ratio; freestyle wants 8–12 (Module 2) |
| Punch-out | A full-throttle vertical climb — the maneuver that stress-tests pack, ESC and video all at once |
| Propwash | Turbulence from your own props re-entering them on descents; the classic wobble (Module 9) |
| Whoop | A tiny ducted-prop quad, usually flown indoors — the recommended first aircraft (Tiny whoop build) |
| BNF / PNP / RTF | Bind-and-fly / plug-and-play (add your RX) / ready-to-fly — how much building you're skipping |
| Maiden | An aircraft's first flight — gated by the pre-maiden checklist |
| Turtle mode | Flip-over-after-crash: spins props in reverse to right an upside-down quad — for healthy quads only |
| Failsafe | What the FC does when the control link drops; configure and bench-test it before flight one (Receiver) |
| VLOS | Visual line of sight — goggles don't count, which is why the EU wants a spotter (Module 13) |
The radio link
| Term | Meaning |
|---|---|
| Radio / transmitter | The handset — the one purchase that outlives every drone |
| EdgeTX | The open-source operating system running on nearly every modern radio |
| ELRS (ExpressLRS) | The open-source control link that took over the hobby: cheap, tiny, enormous range |
| Bind phrase | ELRS's identity string — same phrase on TX and RX means bound, forever (ELRS binding) |
| Packet rate | Control updates per second; fewer packets = more range, more latency (Receiver) |
| RSSI | Raw received signal strength, in dBm — "how loud" |
| LQ | Link quality — the percentage of packets arriving; falling LQ with good RSSI means interference, not distance |
| Telemetry | Data flowing back from the quad over the control link: link quality, voltage, GPS |
| Model match | Ties a receiver to one radio model, so the wrong quad can't arm |
| Diversity | Two antennas, the better signal wins moment to moment — on receivers and on goggles |
| dBm / dB | Absolute RF power / a ratio; every 3 dB is a factor of two (Module 1) |
| Link budget | The accounting of TX power, antenna gains and path loss against sensitivity — it decides your range (Module 1) |
| EIRP | Effective radiated power including antenna gain — the number the law actually limits (Module 13) |
The video system
| Term | Meaning |
|---|---|
| VTX | Video transmitter — analog 5.8 GHz or a digital air unit (VTX) |
| OSD | On-screen display: telemetry drawn over your video — fly the voltage, not the clock |
| DVR | The goggles' recording — how you diagnose video problems and find downed quads (Goggles) |
| Analog vs digital | Analog degrades gracefully into snow; digital is sharp until its cliff (Goggles) |
| Pit mode | VTX at near-zero power so you can work on the bench without jamming other pilots |
| Patch / omni | Directional / all-round antennas; the classic goggle pair is one of each (VTX Antenna) |
| RHCP / LHCP | Right/left-hand circular polarization — mixing them costs ~20 dB, so don't |
Power
| Term | Meaning |
|---|---|
| LiPo / Li-Ion | The two cell chemistries: punch versus endurance (Battery) |
| S count | Cells in series — 6S ≈ 22.2 V nominal, the freestyle default |
| C-rating | Claimed max discharge multiple — marketing; measure internal resistance instead |
| Internal resistance (IR) | The honest pack-health number; it only rises — retire at ~2× new (Module 6) |
| Sag | Voltage drop under load, — the OSD dip on punch-out |
| Storage voltage | ~3.8 V/cell — where packs live between sessions (Charger) |
| Balance charging | Holding every cell at the same voltage while charging — non-negotiable |
| Smoke stopper | A current limiter for first power-up: turns a short into a dim bulb instead of a fire (Module 10) |
| BEC | The regulator making clean 5 V / 9 V from pack voltage — brownout it and things reboot mid-air |
| Low-ESR capacitor | The ≥ 470 µF can across the ESC pads absorbing switching spikes — cheapest reliability money in FPV (Module 6) |
Firmware & configuration
| Term | Meaning |
|---|---|
| FC | Flight controller — the computer running the control loop thousands of times a second |
| 4-in-1 ESC | All four motor drivers on one board under the FC — together they're "the stack" |
| Betaflight / INAV / ArduPilot / PX4 | The open-source flight firmwares: freestyle / GPS-cruising / autonomy (Module 0) |
| Target | The firmware build for your exact board — flash the right one (Flashing firmware) |
| DFU mode | The bootloader state a board flashes in; "bricked" usually means a DFU driver problem |
CLI / diff all | The text interface under the GUI; diff all is your whole configuration as text — back it up (Betaflight basics) |
| DShot | The digital motor protocol; bidirectional DShot lets ESCs report RPM back |
| RPM filter | Notch filters parked on each motor's actual frequency via that RPM telemetry — enable before tuning anything (Module 9) |
| Blackbox | High-rate flight logging — turns "it feels weird" into a spectrogram (Module 9) |
| UART | A serial port on the FC; you'll budget them like money (Flight Controller) |
| SmartAudio / Tramp | Protocols letting the FC control the VTX over a UART |
Building & tuning
| Term | Meaning |
|---|---|
| Stack | FC + ESC mounted together; 30.5 × 30.5 mm is the 5″ pattern |
| 2207, 1855 KV | Motor naming: 22 mm stator diameter × 7 mm height; KV ≈ RPM per volt, unloaded (Module 5) |
| 5.1 × 4.66 × 3 | Prop naming: diameter × pitch × blades, in inches — the geometry is exact, thrust claims aren't (Propellers) |
| CW / CCW props | Props come in both rotations; on backwards they push down (Flips on takeoff) |
| Soft-mount / grommets | Rubber isolation between frame vibration and the gyro — a mass-spring system with real math (Module 10) |
| PID | The rate controller: P stiffness, D damping, I wind-hold (Module 4) |
| Feedforward | Control from where the stick is going, not just the error — stick-connectedness without ring |
| Rates | The curve from stick position to rotation speed — feel, not tune |
| Notch / lowpass | The two filter shapes: a scalpel at one frequency vs a blunt roll-off with phase cost (Module 9) |
| Desync | An ESC losing sync with its motor — a stutter under load with a whole decision tree |
| Cold joint | A solder joint that looks dull and grips weakly — the site's arch-villain (Module 10) |
| Ground loop | Multiple ground paths turning into video noise (Video noise) |
Regulation (EU framing)
| Term | Meaning |
|---|---|
| Open category / A1–A3 | The EU's risk classes; self-built ≥ 250 g lands in A3 (Module 13) |
| C-class mark | Factory certification label; self-built aircraft have none — the decisive fork |
| Operator registration | Your number, on the airframe, required ≥ 250 g or with a camera |
| The 250 g line | The single most consequential number in drone design — below it, a different regulatory world |
| Geo-zones | Airspace where flying is restricted — checked per flight, in the current app |
Missing a term?
If a page assumed a word you had to look up elsewhere, that's a bug in this handbook — report it and it gets added here.