How does propeller pitch affect speed again because I got more questions

[GreaterAviation]

So propeller pitch is how far the propeller moves in 1 rotation. Does does the propeller DRAG the plane through the air? Or is pitch the SPEED of the air that the propeller displaces? Also propeller diameter increases thrust but JET ENGINES are just all thrust no pitch so prop diameter should affect speed but by how much?

 

[Merv]

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.

 

[GreaterAviation]

Correct, the pitch, in theory how far the propeller moves on one rotation without any slippage.

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.
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.

When i mean Dragging the plane I mean does the propeller "screw" through the air? I always thought the propeller screwed the plane through the air. Cause the pitch is how far it goes in 1 rotation so i always thought the propeller pulls the plane. Does the propeller like pull the plane with it because the propeller moves its pitch for each rotation. I also got this answer from someone else. "
Pitch of propeller is like changing the angle of attack of a small wing, it will create a greater force, but with higher drag (limiting the rotation speed)"

 

[GreaterAviation]

Correct, the pitch, in theory how far the propeller moves on one rotation without any slippage.

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.
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.

Wait is propeller pitch the speed of the air that the propeller is displacing?

 

[GreaterAviation]

Alright so I talked to some people and this is what I got.
Propeller pitch is the angle of attack of the blades of the propeller, thus creating more thrust/lift. More lift=more drag so the higher pitch the more speed needed to spin it. Diameter DOES affect speed as it increases thrust. Tell me if I'm wrong the source is some random guy on an engineering discord so idk if its reliable but it makes sense.

 

[Merv]

When i mean Dragging the plane I mean does the propeller "screw" through the air?

I'm not sure if this is the question you are asking.
So the very early thinking was that a prop operated like a propeller on a boat and screwed through the air. Look at some of the very early attempts to fly, they built things that looked like giant boat props and put them on an airplane. Like this.

The Wright Bros took a different approach. They thought of a prop like a rotating wing and it turns out they were correct. Props have an airfoil similar to wing.

Pitch of propeller is like changing the angle of attack of a small wing, it will create a greater force, but with higher drag (limiting the rotation speed)"

Yes, a prop is like a rotating wing. Increasing the pitch increases the angle of attack.
When you look at prop sizes, there is a limit to the pitch. You don't see any props with a pitch 25, pitch 8-10 is the limit that I've seen.

Increasing the pitch will increase the drag. Larger diameter or higher RPM also increases the drag. I'm saying by increasing the pitch, diameter or RPM on a prop, it will absorb more energy, it will draw more amps. Finding the "best prop" is a dance between the pitch, diameter & RPM to give you the most thrust at the airspeed you need without drawing more amps that the motor can produce. If you increase one of the 3 you may need to reduce another to prevent overheating the motor.

 

[quorneng]

GreaterAviation
A propeller blade is no more than a wing. It just goes round and round rather than in a straight line. It is nevertheless travelling through air at a positive angle of attack so it creates lift. The blade is fixed to the prop hub. The prop is fixed to the motor which is fixed to the plane so a prop drags the plane forward or a pusher prop pushes but aerodynamic forces are exactly the same.
How hard the prop pulls or pushes (its thrust) depends on the length and width of the blades, the angle of attack to the air and how fast they are going (RPM).

As the plane speeds up the angle of the blade to the air effectively decreases so the thrust starts to fall away. The maximum speed the plane can achieve is when the decreasing thrust of the prop exactly matches the increasing drag of the plane.

A coarser pitch prop looses thrust more slowly as the plane speed up but it needs more power to achieve the same RPM so if the power is limited (as it always is) then the prop diameter can be decreased to compensate but it then produces less thrust to start with so it may be no better off.
Selecting the 'best' prop diameter and pitch is a trade off. If you throw in the aerodynamic efficiency of the prop blade and the various characteristics of electric motors it gets even more involved. Of course the aerodynamics of the plane itself will have a big effect on how the prop performs.

There is no one best solution only 'combinations' that suite particular conditions and preferences.
That's my view on the subject. I hope it helps.

 

[GreaterAviation]

Thanks to everyone who commented here! I think I get it now! Thank you! This was something that was confusing me for a long time.