Calculated Result
Plotly Graph
Example Data Table
| Case | IAS (kt) | Correction (kt) | Pressure Altitude (ft) | OAT (°C) | Estimated TAS (kt) |
|---|---|---|---|---|---|
| Training Flight | 120 | 2 | 5000 | 10 | 132.58 |
| Cross Country | 145 | 1.5 | 10000 | 0 | 172.00 |
| Low Altitude Check | 95 | 0 | 2000 | 22 | 99.71 |
| High Altitude Cruise | 180 | 3 | 18000 | -10 | 247.47 |
Formula Used
Step 1: If the entered speed is IAS, then CAS = IAS + correction.
Step 2: For this engineering model, EAS ≈ CAS for common subsonic use.
Step 3: Compute static pressure from pressure altitude using the standard atmosphere model.
Step 4: Compute actual density using ρ = p / (R × T).
Step 5: Compute density ratio using σ = ρ / ρ₀.
Step 6: Compute true airspeed using TAS = EAS / √σ.
Step 7: Compute Mach using Mach = TAS / a, where a = √(γRT).
This model is practical for study, planning, and general engineering checks. It is not a substitute for certified aircraft performance data.
How to Use This Calculator
- Enter the measured airspeed value.
- Select whether that value is IAS, CAS, or EAS.
- Enter any calibration correction for indicated speed.
- Enter pressure altitude and choose feet or meters.
- Enter outside air temperature and choose the correct unit.
- Select the preferred output speed unit and decimal precision.
- Optionally set the maximum altitude for the graph.
- Press Calculate True Airspeed to show results above the form.
- Use the CSV or PDF buttons to export the latest calculation.
Engineering Notes
True airspeed is the aircraft speed relative to the surrounding air mass. It usually increases above indicated airspeed when altitude rises and air density falls.
This page uses pressure altitude and outside air temperature to estimate local density. That density then adjusts an equivalent airspeed estimate into true airspeed.
This approach is useful in flight performance studies, propeller analysis, aerodynamic comparisons, and classroom engineering work where quick density based estimates are needed.
FAQs
1. What is true airspeed?
True airspeed is the aircraft’s actual speed through the surrounding air. It differs from indicated airspeed because changing air density affects how the airspeed system reads speed.
2. Why does true airspeed usually rise with altitude?
At higher altitude, air density drops. For the same indicated or equivalent airspeed, a higher true airspeed is needed to produce the same aerodynamic effect.
3. What is the difference between IAS, CAS, EAS, and TAS?
IAS is instrument reading. CAS corrects instrument and position error. EAS also corrects compressibility effects. TAS is the real speed through the air after accounting for local density.
4. Does temperature affect true airspeed?
Yes. Temperature changes air density. Warmer air is less dense, which generally increases true airspeed for the same corrected aerodynamic speed condition.
5. Is this calculator valid for every aircraft and flight regime?
This tool is best for general engineering estimates and subsonic study work. Very high speed, unusual instrumentation, or certified performance planning may require more exact aircraft specific methods.
6. What altitude should I enter?
Enter pressure altitude, not field elevation or indicated altitude. Pressure altitude gives the standard atmosphere reference needed for pressure and density calculations.
7. Why can I enter a calibration correction?
Indicated airspeed can contain instrument or position error. Adding a correction gives calibrated airspeed, which improves the final true airspeed estimate.
8. Is true airspeed the same as ground speed?
No. Ground speed also includes wind effect. True airspeed is speed through the air mass, while ground speed is speed over the ground.