Megan you are confusing cause and effect.
The propeller exerts a rearward force on the air. This force has three effects:
Effect 1. The air exerts an equal and opposite forward force (thrust) on the propeller.
Effect 2. The air is accelerated rearwards.
Effect 3. The rearward acceleration gives the air kinetic energy, which must be provided
by the engine.
The situation when generating lift is similar, just the directions have changed from rearward/forward to downward/upward.
Let’s examine this subject by looking at a few scenarios.
Scenario 1.
We take a helicopter and park it on a concrete pad. The helicopter exerts a downward force (its weight) onto the concrete. The concrete reacts to this by exerting an equal and opposite upward force as predicted by Newton’s Third Law. Because no energy is being transferred from the helicopter to the concrete, the engines do not need to be running and the helicopter can sit there for as long as we want without ever using any fuel.
But a parked helicopter is nothing more than a very expensive shed, so let’s start it up and take it into the hover. The main rotor now exerts a downward force (equal to the helicopter’s weight) onto the air. The air reacts be exerting an equal and opposite upward force (the lift) as predicted by Newton’s Third law. But because the air is unable to resist the downward force, it is accelerated downwards. This acceleration gives the air kinetic energy which must be provided by the engines. The helicopter can only remain in the hover until its fuel supply runs out, because it must provide a constant supply of energy to the air.
The required lift can be generated with or without accelerating anything downwards, but why are the two results so different? Because accelerating the air downwards involves energy being transferred from the helicopter to the air.
Scenario 2.
We want to take a large advertising board and suspend it high above a city. We attach the board to a helium balloon, which is more than able to support the weight of the board, the balloon and its tethering rope. We permit the balloon to float up to the required height then tie the tethering rope to a post. The combined balloon and board exert a downward force on the surrounding air. The air reacts by exerting an equal and opposite upward force on the balloon and board. But the air is not accelerated downwards, so no energy is being lost to the air. The balloon and board can remain in place for as long as we want, without ever using any fuel.
We take the same board and attach it to a helicopter, start the engines and take it into the hover at the required height. The main rotor now exerts a downward force (equal to the helicopter’s weight) onto the air. The air reacts be exerting and equal and opposite upward force as predicted by Newton’s Third law. But because the air is unable to resist the downward force, it is accelerated downwards. This acceleration gives the air kinetic energy which must be provided by the engines. The helicopter can only remain in the hover until its fuel supply runs out because it must provide a constant supply of energy to the air.
Once again the required lift can be generated with or without accelerating air downwards, but the method which does not accelerate anything downwards, is the most efficient.
Scenario 3.
You drive your car along the road at 70 mph. The driving wheels exert a rearward force on the road. The road reacts by exerting an equal an opposite forward force on the wheels. This force pushes the car forward. Because the road surface is rigid enough to resist the rearward force, it is not accelerated rearward. This means that no energy is transferred from the car to the road. This in turn means that all of the energy available at the driving wheels is used to move the car forward.
You modify your car so that the engine does not drive any of the wheels, but instead drives a propeller. The propeller exerts a rearward force on the air. The air reacts by exerting a forward force on the propeller. This forward force pushes the car forward. But the rearward force on the air causes it to accelerate rearwards. This gives kinetic energy to the air. This energy must be provided by the engine, so there is less energy available to do the work of driving the car forward.
The required thrust can be generated with or without accelerating anything rearwards, but the method which does not involve acceleration is the most energy-efficient.
These three scenarios illustrate three facts:
Fact 1. It is not necessary to accelerate anything backwards to create forward thrust.
Fact 2. It is not necessary to accelerate anything downwards to create lift.
Fact 3. Thrust and lift systems which do not accelerate the air are more energy-efficient than those which do.
In designing aircraft to provide the operational flexibility, mobility, speed, manoeuvrability and agility which we need, the propulsion and lift must be provided by interacting with the surrounding air. And because the air is a fluid, these interactions cause it to be accelerated. There are precise mathematical relationships between the accelerations and the thrust or lift generated and these relationships have enabled us to devise powerful equations and analytical tools. But the fact remains that these accelerations are the waste-products of our propulsion and lift systems. They are not the means by which we produce thrust and lift.
To argue otherwise is the equivalent of saying that human being produce waste products in order to obtain the energy needed to life. The truth is that human beings eat in order to obtain the energy needed to live. Human waste products are just an unfortunate consequence of this process.