# What are examples of power and thrust

## thrust

Lexicon> letter S> thrust

Definition: the propulsive power generated by a jet engine or rocket engine, for example

Alternative terms: thrust, advance, propulsive force

More general term: force

More specific terms: engine thrust, rocket thrust

English: thrust

Categories: Vehicles, Basic Terms, Engines and Power Plants, Physical Basics

Formula symbol: F.

Unit: Newton (N)

Author: Dr. Rüdiger Paschotta

How to quote; suggest additional literature

Original creation: 02.03.2020; last change: 15.05.2021

URL: https://www.energie-lexikon.info/schub.html

With thrust or Thrust is the term used to describe the propulsive power that a jet engine or rocket engine produces, for example. (The term is hardly used for driving forces of road vehicles.) It is therefore a force, the values ​​of which are to be given with the SI basic unit Newton. Especially in the Anglo-American area, however, outdated units such as the kilopond (kp, weight of one kilogram on the earth's surface) or the lbs (pound-force, Weight of a pound on the surface of the earth).

According to Isaac Newton's law of inertia, thrust is equal to the generated momentum per unit of time.

### Thrust in rocket and jet engines

In a rocket engine, the thrust results from the recoil of the ejected gases. If, in a simplified picture, all of the gas is expelled at the uniform speed, then the thrust is the product of this expulsion speed with the ejected mass per unit of time. For example, an exit speed of 2000 m / s and an output of 1 kg / s results in a thrust of 2000 N = 2 kN (kilonewtons).

In the case of jet engines, the momentum of the drawn air must also be taken into account. It should be noted here that the mass ejected per second is higher than the air mass drawn in per second because of the fuel used - although this difference is not so important for turbofan engines.

### Thrust and propulsion power

The drive power in the sense of the drive energy transferred per unit of time is the product of the aircraft's thrust and speed. This means that, for example, an aircraft engine when stationary (for example with the brakes applied) can produce a high level of thrust, but no drive power; its efficiency is then very low. At the cruising speed, on the other hand, the drive power is considerable:

For example, a thrust of 100 kN at a cruising speed of 850 km / h (= 236 m / s) results in a drive power of approx. 23.6 MW (megawatts). If the engine has a specific fuel consumption of 1.8 · 10−5 kg / s / N, i.e. 1.8 kg kerosene consumed per second, this corresponds to a fuel output of 77.4 MW, calculated on the basis of the calorific value of 43 MJ / kg. The drive efficiency is then 23.6 MW / 77.4 MW = 30.5%. These numbers correspond roughly to those of a typical modern turbofan engine in a commercial aircraft.