Calculating Turbojet Thrust with Exhaust Deflection

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In summary, the idling engines of a landing turbojet can produce reverse thrust by properly deflecting the exhaust, while operating in a normal manner produces forward thrust. At a speed of 150 km/h, an engine consuming air at 50 kg/s and producing an exhaust velocity of 150 m/s would have a forward thrust. However, if the exhaust is deflected 90 degrees without affecting the mass flow, the magnitude and direction of the thrust would depend on the direction of rotation. After the plane has stopped and the exhaust is still deflected at 90 degrees, the magnitude and direction of the thrust would also depend on the direction of rotation, as well as the airflow of 40 kg/s.
  • #1
Freyster98
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Homework Statement



The idling engines of a landing turbojet produce forward thrust when operating in a normal manner, but they can produce reverse thrust if the jet is properly deflected. Suppose that while the aircraft rolls down the runway at 150 km/h, the idling engine consumes air at 50 kg/s and produce an exhaust velocity of 150 m/s.

a. What is the forward thrust of the engine?
b. What are the magnitude and direction (i.e. forward or reverse) if the exhaust is deflected 90∘without affecting the mass flow?
c. What is the magnitude and direction of the thrust (i.e. forward or reverse) after the plane has come to a stop, with 90∘exhaust deflection and airflow of 40kg/s?


Homework Equations





The Attempt at a Solution



Part a was easy, but I'm confused about parts b and c. If the exhaust is deflected 90 degrees, wouldn't the thrust be directed up or down, depending on the direction of the rotation? If so, the "forward or reverse" statement would be irrelevant, right?
 
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  • #2
Sorry guys, I misinterpreted the question. I'd delete this but don't know how.
 
1.

What is a turbojet engine?

A turbojet engine is a type of air-breathing jet engine that uses a gas turbine to generate thrust. It is commonly used in aircraft propulsion systems and works by compressing and heating air, then accelerating it through a nozzle to create thrust.

2.

How is thrust calculated in a turbojet engine?

Thrust in a turbojet engine is calculated using the following equation: T = ṁ(Ve - V0). T represents thrust, ṁ is the mass flow rate of air through the engine, Ve is the exhaust velocity, and V0 is the inlet velocity. This equation is based on Newton's second law of motion, which states that for every action, there is an equal and opposite reaction.

3.

What factors affect the thrust produced by a turbojet engine?

The thrust produced by a turbojet engine is affected by several factors, including engine design, air density, air temperature, and aircraft speed. The design of the engine, such as the number and shape of the compressor and turbine blades, can greatly impact the thrust generated. Air density and temperature affect the mass flow rate of air through the engine, which in turn affects the thrust. Additionally, the speed of the aircraft can also impact the thrust produced.

4.

How does altitude affect turbojet thrust?

Altitude plays a significant role in the performance of a turbojet engine. As the altitude increases, the air density decreases, which means there is less air available for the engine to compress and accelerate, resulting in a decrease in thrust. This decrease in thrust can also affect the aircraft's speed and performance, which is why turbojet engines are not as efficient at high altitudes.

5.

What are some common units of measurement used for turbojet thrust?

The most commonly used unit of measurement for thrust in a turbojet engine is pounds-force (lbf). Other units of measurement that may be used include Newtons (N) and kilogram-force (kgf). In some cases, thrust may also be expressed in terms of specific impulse, which measures the amount of thrust produced per unit of propellant consumed.

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