What is OnSpeed?¶

A Note on the Term "ONSPEED"¶

The term on speed originated in military aviation to describe a flight condition in which the airplane is maintaining the angle of attack associated with the desired approach and landing condition. In this documentation, the convention ONSPEED is used: one word, capitalized, to denote a specific angle-of-attack condition, not an airspeed. ONSPEED represents a narrow band of angle of attack corresponding to the desired aerodynamic state for approach, landing, and certain maneuvering conditions. The airspeed associated with this angle of attack is not fixed — it varies with airplane weight, configuration, and load factor.

Pilots describe deviations from ONSPEED using airspeed-based language: "fast" or "slow" relative to ONSPEED. Although this mixes airspeed and angle-of-attack terminology, the convention is practical — airspeed is simply a surrogate for AOA.

The Problem¶

Unintentional stalls remain a leading cause of fatal accidents in general aviation, resulting in fatality rates nearly 50 percent greater than those associated with non-stall mishaps. Most GA accidents occur during daylight VMC and light winds. A disproportionate number occur during the departure and maneuvering phases of flight — takeoff, initial climb, go-around, and base-to-final turns.

The two fundamental skills required to fly an airplane are controlling angle of attack to generate lift and managing power to generate speed and altitude. Yet angle of attack cannot be seen directly, and there is no cockpit instrument that explicitly displays power required. Pilots receive no direct feedback for the two most critical tasks they must perform.

The airspeed indicator is part of the problem:

Stall speed changes with weight — a lighter airplane stalls at a lower airspeed
Stall speed changes with load factor — a 45° banked turn increases stall speed by ~18%
Stall speed changes with configuration — flaps change the wing's lift characteristics
Airspeed markings apply only at max gross weight and 1G — the rest of the time, the pilot must do mental math

Pilots cannot realistically compute stall speed corrections for changing weight and G-loading during high-workload maneuvering flight.

The Solution: Angle of Attack¶

The wing doesn't care about airspeed. It cares about the angle between the wing chord and the oncoming air — the angle of attack (AOA). A wing always stalls at the same critical angle of attack for a given configuration, regardless of weight, bank angle, or altitude. An airplane can stall at any airspeed and in any attitude, but critical AOA remains the same.

If you know your AOA, you know how hard the wing is working and how close you are to stalling. Always. In every configuration. Angle of attack solves the stall-speed math problem directly — no mental corrections required.

This concept is not new. Orville Wright patented an angle-of-incidence indicator in 1913. Military aviation adopted AOA systems and energy-management training decades ago, substantially reducing loss-of-control mishaps. OnSpeed brings that proven technology to experimental general aviation as open-source hardware and software.

Why Audio? Directive vs. Descriptive Information¶

Conventional flight instruments present descriptive information. The pilot must first perceive the indication visually, then interpret it, then act on it. This "see—interpret—react" loop typically consumes on the order of one second. When pilots become task-saturated or distracted, this loop can break down entirely.

An AOA tone provides directive information. The pilot does not need to look at an instrument or infer meaning from a changing indication — the cue directly calls for action. Pilots can respond roughly twice as fast as with visual interpretation. There is no requirement to notice subtle airspeed decay, buffet onset, or changing attitude.

In the traffic pattern, your eyes should be outside — on the runway, on traffic, on terrain. An audio tone that changes pitch and pulse rate tells you everything you need to know about your energy state without diverting visual attention.

The tone logic is derived from systems originally developed for military carrier operations, and later adopted more broadly. Two aviation communities with extensive experience flying with continuous aural AOA cueing — military fighter aviation and glider operations — have demonstrated the effectiveness of direct auditory feedback for aircraft control.

What the Tones Tell You¶

OnSpeed maps angle of attack to a continuous spectrum of audio cues. As you slow down (AOA increases), the tones progress:

What You Hear	AOA Condition	What It Means	What to Do
Silence	Below L/D_MAX	You're fast — well above best-glide speed	No action needed
Slow pulsing, low tone	L/D_MAX to ONSPEED	Approaching the ONSPEED band	Decelerating normally
Steady tone	ONSPEED	Balanced effective power at any condition	Hold this — you're on speed
Fast pulsing, high tone	Below ONSPEED	Effective power is negative — unsustainable	Push: add power and/or reduce AOA
Rapid buzz	Near stall	Stall imminent — no aerodynamic margin	Immediate AOA reduction

The logic is simple:

Slow tone → Push something (throttle forward, nose down)
Fast tone → Pull something (throttle back, ease back pressure to slow descent rate)
Steady tone → Hold this condition

Because AOA is independent of weight and G-loading, the tones work correctly in turns, at any weight, and at any altitude.

What ONSPEED Represents¶

ONSPEED is not just "approach speed." It corresponds to approximately 60% of the wing's maximum lift capability (fractional lift) and is associated with:

Balanced effective power at any flight condition
Maximum sustained turn rate
Best angle of climb (V_X)
Maximum endurance
V_REF (approach reference speed)
Optimum low-altitude maneuvering

The ONSPEED band is approximately ±1° of AOA — corresponding to an airspeed band of roughly ±2–3 knots at 1G. This is why the system works as both an approach reference and a maneuvering reference.

How It Works¶

The OnSpeed Gen3 controller measures AOA using:

Differential pressure from a probe mounted in your wing or fuselage that senses the air angle
Pitot pressure for indicated airspeed
An IMU (inertial measurement unit) that measures pitch attitude and accelerations
An AHRS algorithm that fuses IMU data into stable pitch/roll estimates

From these inputs, it computes a Derived AOA — the angle between where the fuselage is pointed and where it's actually going. This is calibrated against known speeds to produce accurate AOA-based audio cues for your specific aircraft. Each flap setting gets its own calibration.

Who Is This For?¶

OnSpeed is designed for experimental/amateur-built aircraft. It is not certified for use in type-certificated aircraft. It is a supplemental awareness tool — not a primary flight instrument.

Ideal for:

RV-series homebuilts
Other experimental aircraft with pitot/static systems
Pilots who want stall awareness without a panel-mounted AOA gauge
Aircraft with Dynon, Garmin, or MGL glass panels (for best integration)
Standalone installations on aircraft with only steam gauges