01 / READ THE CHANGE
Control the outflow
With a prescribed supply, the controller changes outflow area to follow an illustrative cabin-altitude schedule. Relief paths act separately.
STORE MASS. STORE ENERGY.
Cabin Pressurisation & Thermal Control
Set the climb, change the supply and open a leak. Trace cabin pressure and temperature as a controller changes the outflow area.
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
Pressure depends on temperature too
The gas follows pV = mRT. A pressure change can come from stored mass, temperature, or both.
03 / READ THE CHANGE
Close both balances
The cabin stores mass and internal energy. Incoming enthalpy, outgoing enthalpy and wall heat transfer determine its thermal response.
THE SAME MODEL, CONNECTED VIEWS
Follow the calculation
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 · Store or release cabin air
Pressure responds to stored mass, not just to the instantaneous inlet flow.
Symbols & units
- Air mass stored in the fixed cabin volume, kg.
- Aggregate mass-flow rates, kg/s. Incoming streams include any ambient backflow represented by the model.
02 · Balance stored energy
Incoming streams carry enthalpy. The air already inside the cabin stores internal energy.
Symbols & units
- Constant-volume and constant-pressure specific heat, J/(kg K).
- Absolute temperatures, K. Each incoming stream j has its own temperature.
- Overall cabin-to-ambient thermal conductance, W/K; this model uses 25 W/K.
03 · Convert the stored state to pressure
Both mass and temperature influence cabin pressure.
Symbols & units
- Cabin absolute pressure, Pa; fixed volume, m³.
- Specific gas constant for air, 287.05 J/(kg K).
Rigid 60 m³ well-mixed cabin, initial sea-level pressure and 293.15 K. Aircraft climbs linearly for 900 s then levels; cabin target is min(0.25 × aircraft altitude, 2400 m). Synthetic outflow controller, 55 kPa relief onset and vacuum relief. Compressible orifice coefficient 0.7, wall UA = 25 W/K. Finite relief flow can permit pressure overshoot. No physiological limits, ECS pack cycle or aircraft-specific operating schedule.
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.