So propeller pitch is how far the propeller moves in 1 rotation.
Correct, the pitch, in theory how far the propeller moves on one rotation without any slippage.
Does does the propeller DRAG the plane through the air? Or is pitch the SPEED of the air that the propeller displaces?
I'm not sure of the difference you are describing.
Let's take 2 setups, both props are rotating at 12,000 rpm. One prop is a 12x4 & the other an 8x8. Both props cause the motor to draw 35 amps. The 12x4 will have more thrust on the test stand, but the plane has a top speed of say 30 mph. The 8x8 will have less thrust on the test stand but the plane will have a much higher top speed.
Think of a transmission, in low gear you have a lot of lugging power but limited top speed. In high gear you have less lugging power but higher top speed.
Also propeller diameter increases thrust but JET ENGINES are just all thrust no pitch so prop diameter should affect speed but by how much?
I must disagree, jet engines have a pitch. Jet engines operate at much higher rpms, 100,00+.
The thrust of the prop must overcome the drag of a plane. As airspeed increased the planes drag increases and the thrust a prop produces goes down. When these two are equal, the plane has reached top speed. If you want a higher speed, you can reduce drag or increase thrust at the airspeed. To increase thrust, you can increase diameter, increase rpms or increase pitch.
The bottom line, is takes the same amount of energy to move a large amount of air slowly as it does to move a small amount of air fast. If on a test stand the air from a 12x4 prop is moving 35 mph, the top speed of a plane will be say 30 mph. If on a test stand the air from a 8x8 prop is moving 70 mph. the top speed of a plane will be say 60 mph.
Any motor will have a limit on the power it can produce. You can decide at what air speed do you want to express this power.