01 / READ THE CHANGE
Total minus static
Impact pressure is sensed total pressure minus sensed static pressure. At appreciable Mach number, it is not simply ½ρV².
THE INSTRUMENT SEES PRESSURE.
Pitot–Static & Airspeed
Separate true speed from pressure-derived indications. Trap a pressure, change the flight condition and reveal the measurement error.
INTERACTIVE CALCULATED DIAGRAMB · LIVE
Diagram · drag background to pan
Drag the turquoise handles, or focus a handle and use arrow keys. The sliders provide the same controls.
Preparing the calculation…
A · no saved reference
02 / READ THE CHANGE
Three different speeds
TAS is motion through the air. EAS represents dynamic pressure at sea-level density. The ideal indicated value is CAS because installation and instrument errors are set to zero.
03 / READ THE CHANGE
A trapped pressure stays trapped
The trapping altitude and speed are separate inputs. A sealed pressure line does not update as the aircraft climbs or accelerates.
THE SAME MODEL, CONNECTED VIEWS
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B · solid turquoise A · dashed amber
Compare A and B
| Quantity | A · saved | B · live | B − A | Unit |
|---|
A remains fixed until saved again. Export includes the model version, settings and plotted data.
Equations, assumptions & sources
Read the balance, then connect each symbol to the model. Open a symbol key for definitions and units. Long equations can be scrolled sideways.
01 · From Mach number to total pressure
This is the isentropic perfect-gas relation used by the subsonic model.
Symbols & units
- Total and static pressure, Pa; γ = 1.4.
- Mach number, dimensionless.
02 · Density connects TAS and EAS
Equivalent airspeed accounts for density when comparing aerodynamic loading.
Symbols & units
- True and equivalent airspeed, m/s.
- Local air density and reference density 1.225 kg/m³.
03 · What the pressure instrument indicates
Blockage can make sensed pressures differ from the surrounding atmosphere. The calculation uses the sensed pressure difference.
Symbols & units
- Sensed impact pressure, Pa. No real CAS is reported for a negative value.
- Reference sound speed √(γR × 288.15 K), m/s; reference pressure 101325 Pa.
- Ideal calibrated airspeed, m/s; instrument and position errors are excluded.
Subsonic isentropic stagnation relation; dry tropospheric ISA pressure, selected temperature offset, no icing growth, leaks, line dynamics or instrument mechanical effects. A negative sensed pressure difference is an invalid indication, not a negative airspeed. Pressure altitude is the ISA inversion of the sensed static pressure.
NASA · isentropic flow ↗FAA · aviation handbook library ↗Physical relations and teaching sources support the stated concepts. Generic coefficients are explicitly illustrative; they are not measured manufacturer data. Numerical verification is separate from experimental validation. Model version: applied-labs-v1.1.