What the Tones Mean¶
This is the complete reference for all OnSpeed audio cues. Print this page and keep it in the cockpit until you've internalized the tone progression.
Tone Regions¶
As you slow down (AOA increases), you progress through five regions:
FAST ─────── L/Dmax ────── ONSPEED ────── SLOW ─────── STALL
(silence) (low pulse) (solid tone) (high pulse) (high buzz)
<50% lift ~50% lift ~60% lift 65-90% lift >90% lift
Complete Reference¶
| # | Region | Tone | Pulse Rate | Fractional Lift | What It Means | Pilot Action |
|---|---|---|---|---|---|---|
| 1 | Fast | None | — | Below ~50% | Above best-glide speed. Positive energy margin. | No action needed. |
| 2 | Approaching | Low (400 Hz) | 1.5 → 8.2 pps | ~50–60% | Between L/DMAX and ONSPEED. Decelerating into the approach range. | Normal deceleration. |
| 3 | ONSPEED | Low (400 Hz) | Solid (0 pps) | ~60% | Balanced effective power. Thrust and drag matched for current weight. | Hold this. |
| 4 | Slow | High (1600 Hz) | 1.5 → 6.2 pps | ~65–90% | Effective power is negative. Unsustainable condition. | Push: add power, reduce AOA, or both. |
| 5 | Stall Warning | High (1600 Hz) | 20 pps | >90% | At the aerodynamic limit. Stall imminent. | Unload: reduce AOA immediately. |
The Push/Pull Decision¶
The tone pattern tells you whether to push or pull:
- Hear high-pitched pulsing? → Push something: throttle forward, nose down, or both
- Hear solid low tone? → Hold: you're balanced
- Hear low-pitched pulsing? → Pull something: throttle back, allow pitch to increase
- Hear rapid buzz? → Unload for control: reduce AOA immediately
This logic works in any flight condition — straight and level, in a turn, climbing, descending.
Pulse Rate Details¶
Within the pulsing regions, the pulse rate changes linearly:
- Region 2 (L/DMAX → ONSPEED): Starts at 1.5 pulses/sec at L/DMAX, increases to 8.2 pulses/sec approaching the ONSPEED band
- Region 4 (below ONSPEED → Stall Warning): Starts at 1.5 pulses/sec just below ONSPEED, increases to 6.2 pulses/sec near the stall warning threshold
The stall warning (Region 5) is a fixed 20 pulses/sec — an unmistakably urgent buzz. Volume also increases in the slow region, and stall warning overrides any audio muting.
Key Performance Conditions¶
Each tone region corresponds to well-defined aerodynamic performance conditions:
Stall Warning (>90% Lift)¶
- Aerodynamic limit — maximum instantaneous turn capability just prior to stall
- No sustainable maneuvering margin
- The wing cannot produce more lift
ONSPEED (~60% Lift)¶
- Balanced effective power at any flight condition (thrust and drag balanced as a function of velocity)
- Maximum sustained turn rate
- VREF (approach reference speed)
- Best angle of climb (VX)
- Maximum endurance
- Optimum low-altitude maneuvering
- Best blend of turn and glide performance, with appropriate energy for landing transition and safe stall margin
The ONSPEED band is approximately ±1° of AOA, resulting in an airspeed band of approximately ±2–3 knots at 1G.
"Slightly Fast" (~50–55% Lift)¶
- Increased stall margin for gusty or turbulent conditions
- Fly here when conditions warrant extra margin
L/DMAX (~50% Lift)¶
- Maximum range (no-wind)
- Maximum range glide (best glide)
- Approximate best rate of climb (VY)
Maneuvering Speed (varies with aircraft G-limit)¶
- The fractional lift associated with VA
- Determined by dividing 100% by the airplane's positive G-limit
- For a normal-category airplane (3.8G limit): ~26% lift
- Below this value, the airplane will stall before reaching the structural limit
Tone Transitions in Practice¶
Here's what you hear during a typical approach in an RV-4 (flaps 0°, ~2300 lbs):
| Speed (KIAS) | Tone | What's Happening |
|---|---|---|
| 120+ | Silence | Downwind — wing at low lift fraction |
| 100 | Silence | Base turn — still above L/DMAX |
| ~87 | First low pulse | At L/DMAX — best glide speed |
| 80–75 | Low pulse, speeding up | Decelerating through the approach range |
| ~72 | Solid low tone | ONSPEED — balanced effective power |
| 68 | High pulse starts | Below ONSPEED — energy deficit |
| 65 | Faster high pulse | Getting slow — correct now |
| ~62 | Rapid buzz | Stall warning — unload immediately |
Your speeds will be different
These speeds are examples for a specific aircraft and weight. After calibration, the tones match your aircraft's characteristics. The beauty of AOA-based tones is that the same AOA thresholds apply regardless of your current weight or G-loading — the tones automatically account for bank angle, weight, and any other factor that changes stall speed.
How Angle of Attack Relates to Speed¶
As airspeed decreases, angle of attack increases — but not linearly. AOA increases more rapidly as you slow down. Approximately half of the wing's lift-producing capability is used in the lower third of the airplane's speed range. This is why maneuvering near approach speeds can quickly become hazardous: angle of attack rises rapidly with even small increases in G.
The tone regions are spaced to reflect this reality. The "slow" region (high-pitched pulsing) covers a smaller speed range but a rapidly changing AOA range, giving the pilot progressively more urgent cueing as margin decreases.
Muted Mode¶
If you press the audio mute button:
- All tones go silent
- The stall warning still sounds (safety override)
- To unmute, press the button again
The stall warning in muted mode only fires if both conditions are met:
- AOA is above the stall warning threshold
- IAS is above the mute-under-IAS setting (default: 25 knots)