I wanted to showcase the difference between TAS (True Air Speed) compared to IAS (Indicated Air Speed)

P-51D

Stall Speed at 9611lb (4360kg) loaded weight - 110.7mph (178km/h) at Sea Level

(No flaps, level flight)

That's Wing Lift Coefficient of 1.31 CL_Max which is standard for a laminar flow wing.

With this info I can calculate the stall speed at different altitudes by changing the air density to match different altitudes.

This is the TAS it needs so it doesn't stall at altitudes with different air density.

IAS = TAS at Sea Level, however TAS has to increase to maintain same IAS stall speed due to decreasing amount of air as altitude increases.

ALTITUDE / SPEED / AIR DENSITY

Sea Level - 178km/h - 1.225kg/m3

1000m - 187km/h - 1.112kg/m3

2000m - 196km/h - 1.007kg/m3

3000m - 207km/h - 0.9093kg/m3

4000m - 218km/h - 0.8194kg/m3

5000m - 230km/h - 0.7364kg/m3

6000m - 242km/h - 0.6601kg/m3

7000m - 256km/h - 0.5900kg/m3

8000m - 272km/h - 0.5258kg/m3

9000m - 288km/h - 0.4671kg/m3

10,000m - 306km/h - 0.4135kg/m3

This is why stall speed is measured in IAS.

P-51D has 178km/h IAS stall speed but it needs to at least travel at 306km/h at 10,000m to maintain 178km/h IAS and avoid stalling. As a result of higher stall speed in TAS for all planes, as you get higher the more sluggish planes turn. Their radius of turn increases drastically and also their power output is also reduced at higher altitudes making the power to weight ratio worse and worsening the sustained turn capability.

FUN FACT:

To get into Space and leave gravitational pull of earth you need to go beyond 100,000m altitude.

If P-51D was to reach 80,000m altitude, it would have to travel at 45,800km/h TAS (Mach 37.1) to maintain 178km/h IAS in order to not stall.

This is why even jets like SR-71 Blackbird have service ceiling of 26,000m altitude.

Conclusion:

TAS = How fast you travel from point A to point B. Basically how much distance you move in set amount of time.

IAS = The airflow over your wings. You need to go faster to maintain same airflow due to decreasing amount of air as you go higher in altitude. All the TAS speeds at different altitudes = 178km/h IAS

———

Another Fact:

Every plane has a structural limit and there is a maximum limit at every altitude where the plane will fall apart at certain TAS due to the extremely high IAS.

The newer next generation jets which are suppose to reach Mach 6 will still be limited to same speed at low altitudes to earlier jets, the difference is the capability of going even higher which allows the jet to achieve greater TAS before reaching structural IAS limit of an airframe. Jet technology today is at its Apex level right now that increasing max speed is the same as saying - Increasing Service Ceiling. It's a matter of creating engines which can still operate at altitudes with ridiculously low air density which would increase service ceiling.

P-51D

Stall Speed at 9611lb (4360kg) loaded weight - 110.7mph (178km/h) at Sea Level

(No flaps, level flight)

That's Wing Lift Coefficient of 1.31 CL_Max which is standard for a laminar flow wing.

With this info I can calculate the stall speed at different altitudes by changing the air density to match different altitudes.

This is the TAS it needs so it doesn't stall at altitudes with different air density.

IAS = TAS at Sea Level, however TAS has to increase to maintain same IAS stall speed due to decreasing amount of air as altitude increases.

ALTITUDE / SPEED / AIR DENSITY

Sea Level - 178km/h - 1.225kg/m3

1000m - 187km/h - 1.112kg/m3

2000m - 196km/h - 1.007kg/m3

3000m - 207km/h - 0.9093kg/m3

4000m - 218km/h - 0.8194kg/m3

5000m - 230km/h - 0.7364kg/m3

6000m - 242km/h - 0.6601kg/m3

7000m - 256km/h - 0.5900kg/m3

8000m - 272km/h - 0.5258kg/m3

9000m - 288km/h - 0.4671kg/m3

10,000m - 306km/h - 0.4135kg/m3

This is why stall speed is measured in IAS.

P-51D has 178km/h IAS stall speed but it needs to at least travel at 306km/h at 10,000m to maintain 178km/h IAS and avoid stalling. As a result of higher stall speed in TAS for all planes, as you get higher the more sluggish planes turn. Their radius of turn increases drastically and also their power output is also reduced at higher altitudes making the power to weight ratio worse and worsening the sustained turn capability.

FUN FACT:

To get into Space and leave gravitational pull of earth you need to go beyond 100,000m altitude.

If P-51D was to reach 80,000m altitude, it would have to travel at 45,800km/h TAS (Mach 37.1) to maintain 178km/h IAS in order to not stall.

This is why even jets like SR-71 Blackbird have service ceiling of 26,000m altitude.

Conclusion:

TAS = How fast you travel from point A to point B. Basically how much distance you move in set amount of time.

IAS = The airflow over your wings. You need to go faster to maintain same airflow due to decreasing amount of air as you go higher in altitude. All the TAS speeds at different altitudes = 178km/h IAS

———

Another Fact:

Every plane has a structural limit and there is a maximum limit at every altitude where the plane will fall apart at certain TAS due to the extremely high IAS.

The newer next generation jets which are suppose to reach Mach 6 will still be limited to same speed at low altitudes to earlier jets, the difference is the capability of going even higher which allows the jet to achieve greater TAS before reaching structural IAS limit of an airframe. Jet technology today is at its Apex level right now that increasing max speed is the same as saying - Increasing Service Ceiling. It's a matter of creating engines which can still operate at altitudes with ridiculously low air density which would increase service ceiling.

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