Thrust

Thrust as a force

Thrust is the force that changes the inertia of an object.

Newton

To understand thrust we need to look at Newton’s laws of motion.

1. An object at rest till stay at rest unless an out side force is applied to it.
2. The change in an object’s momentum is proportional to the force applied to it.
3. For every action there is an equal and opposite reaction.

Newton’s second law the Law of Action

Thrust is the force described by Newton’s second law

Force= Mass * Acceleration

Newton’s third law, reciprocal actions

An object accelerated away from another puts force on the both objects.

This can be demonstrated with;

• A balloon letting the air escape from it
• A rocket taking off
• A bullet fired from a gun

The balloon the air in side the balloon has mass it is forced out the back as the balloon contracts. The escaping air forces the balloon in the opposite direction.
The rocket the fuel is accelerated away from the engines the mass of the accelerated plasma forces the engines the opposite direction.
The bullet may shoot out the front of the gun barrel but the gun moves backwards, recoil.

Thrust in flight

There are 4 forces acting on an aerospace vehicle in flight.

1. Thrust
2. Drag
3. Lift
4. Mass

• An aircraft will accelerate as long as the thrust is greater then the drag.
• The aircraft stay the same indicated air speed when thrust and drag are equal.
• The aircraft will slow down when drag is greater then thrust.

Asymmetrical thrust

The engines are mounted on the wings or the body of the ship.
If you apply thrust to one side of the ship and not the other you will start to spin faster and faster.
This concept was demonstrated with the Aeolipile, also known as a Hero's engine,as early as the First Century AD.

• There are earlier demonstrations but Hero is usually credited with the stable display.

Hero built and demonstrated the aeolipile (or aeolipyle, or eolipile) there were no apparent uses of the engine,
But that is the first demonstration of asymmetrical thrust.

Uses for asymmetrical thrust

• Spinning up an orbital object to create artificial gravity.
• Help a ship turn.
• Radical combat maneuvers.

Dangers from asymmetrical thrust

• Loss of control
• Ship damage/destruction
• Death

Ship Control

Modern ships with 2 engines have 2 thrust levers.
Modern Ships with 3 engines typically have 2 levers.

• The center-line engine is assumed to be set to the higher of the outboard engines to help mitigate spinning.