## Why is a jet engine more efficient at high altitude?

Cool air expands more when heated than warm air. It is the expansion of the air that drives combustion engines. The second reason is the low density of the air. Low density causes low drag and therefore the aircraft flies much faster at high altitude than on low altitude when it is given the same thrust.

## Why does thrust available decrease with airspeed?

Thrust Available Your propellor can generate the most thrust at a slow speed. Why? Because it’s at a high angle of attack. As your airspeed increases, the propellor’s angle of attack decreases, and it can generate less thrust.

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How do airplanes increase thrust?

The most widely recognized method of boosting thrust is the afterburner, also known as tailpipe burning. Fuel is injected into the hot exhaust gas flowing between the turbine and nozzle. The combustion of the gas expands the airflow as it enters the nozzle, which increases thrust.

What increases thrust?

According to the thrust equation, if the mass of airflow increases, thrust will increase. If the density of air increases, mass will increase, and therefore thrust will increase. As an aircraft operates at various altitudes and climates, the ambient air temperature and pressure will vary.

### Does thrust increase with velocity?

The force (thrust) is equal to the exit mass flow rate times the exit velocity minus the free stream mass flow rate times the free stream velocity. As long as the exit velocity is greater than the free stream (entrance) velocity, a high engine airflow will produce high thrust.

### Why do Jets have lower thrust at higher altitudes?

Most jets are operated as max speeds much less than their exhaust gas velocity – about half of V-exhaust I think. Since higher air-speeds are normally used at higher altitudes, thrust generally decreases with an aircraft’s altitude.

What happens to thrust as air pressure increases?

As the air pressure increases, its density increases, causing thrust produced by the engine to increase. Altitude has a double effect on thrust. As the altitude increases, the air becomes colder and denser, up to the beginning of stratosphere.

What is the relationship between thrust and air density?

To summarize: At a constant airspeed (ignoring airspeed measurement nuances) thrust decreases as air density decreases with increasing altitude; at a constant altitude, thrust decreases with increasing airspeed. Note that max thrust is found when stationary, just before take-off, since that’s when incoming air is at its slowest.

#### How does air speed affect thrust in a turbine engine?

Because of ram effect, increasing air speed also increases the pressure of the air & airflow into engine (W a). As turbine powered aircraft begins to move forward for tale off, air is rammed into the inlet duct and mass flow through the engine increases. The faster the aircraft moves the greater the increase in thrust.

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