Constant Speed Propellers, thinking out loud

[mgh]

The previously linked FAA's Pilot's Handbook of Aeronautical Knowledge gives a better description than those in this thread.

[Brett_Henderson]

It's resistance in the same sense that a small spatula going through cookie dough has more resistance when it is perpindicular to the line of travel than when it's turned parallel to the line of travel. A coarse pitch, all else remaining equal, takes more power to reach a certain RPM than it takes for the same RPM with a fine pitch, thus resistance.

We're quibbling over semantics, here, so that's my last word on the subject, Brett.

It would be semantics.. if all we're talking about are RPMs (if that's was your intent, we agree), ... From the big picture though, it's not resistance... more power = more work accomplished.. Consider the airplane trimmed for level flight... where power is increased and it climbs, as airspeed remains constant. The wings aren't "resisting" the engine's effect on airpseed, they're just translating the increased power into a climb.

[lnuss]

RPM regulation was what I was discussing, re resistance. But if we're nitpicking, the single engine aircraft (with rare exceptions) don't maintain speed when power is increased or decreased, due to the slipstream over the elevator. Thus adding power, if you do nothing else, slows the airplane, in addition to making it climb, as power decreasing increases the airspeed. On aircraft without propwash over the horizontal tail surfaces it's different.

[mgh]

It would be semantics.. if all we're talking about are RPMs (if that's was your intent, we agree), ... From the big picture though, it's not resistance... more power = more work accomplished.. Consider the airplane trimmed for level flight... where power is increased and it climbs, as airspeed remains constant. The wings aren't "resisting" the engine's effect on airpseed, they're just translating the increased power into a climb.

Of course it’s resistance. A propeller resists being turned. The resistance is in the form of a torque (turning moment. Also for a propeller turning at a constant rpm, this propeller torque is equal to the torque developed by the engine.

On opening the throttle the first thing that happens is that the torque developed by the engine increases and so becomes greater than the torque needed to turn the propeller. As a result the rpm of the engine/propeller increases. The constant speed governor detects this increase and increases the pitch of the propeller blades, increasing the torque required to turn it until the rpm returns to the initial value with the propeller and engines torques equal.

Moving the propeller lever towards a higher speed commands a higher speed from the constant speed governor. The governor then begins to reduce the pitch of the propeller blades, making the propeller torque less than the torque developed by the engine. As a result the rpm of the propeller/engine combination increases until the rpm reaches the commanded value with the propeller and engines torques equal.

[Brett_Henderson]

RPM regulation was what I was discussing, re resistance. But if we're nitpicking, the single engine aircraft (with rare exceptions) don't maintain speed when power is increased or decreased, due to the slipstream over the elevator. Thus adding power, if you do nothing else, slows the airplane, in addition to making it climb, as power decreasing increases the airspeed. On aircraft without propwash over the horizontal tail surfaces it's different.

Fair point, RE: nitpicking.. and that would be an important addition to a discussion, and anything BUT nitpicking, about; stick-n-rudder fundamentals ie. pichting for airspeed, and powering for vertical speed, and what really happens; aircraft specific. (especially on an approach).

I was just using the analogy to better describe what a CSP actually does.. and I've no doubt you understand the comparison.

[Brett_Henderson]

Of course it’s resistance. A propeller resists being turned. The resistance is in the form of a torque (turning moment. Also for a propeller turning at a constant rpm, this propeller torque is equal to the torque developed by the engine.

On opening the throttle the first thing that happens is that the torque developed by the engine increases and so becomes greater than the torque needed to turn the propeller. As a result the rpm of the engine/propeller increases. The constant speed governor detects this increase and increases the pitch of the propeller blades, increasing the torque required to turn it until the rpm returns to the initial value with the propeller and engines torques equal.

Moving the propeller lever towards a higher speed commands a higher speed from the constant speed governor. The governor then begins to reduce the pitch of the propeller blades, making the propeller torque less than the torque developed by the engine. As a result the rpm of the propeller/engine combination increases until the rpm reaches the commanded value with the propeller and engines torques equal.

We agree about resistance, as it applies to RPM..

[mgh]

We agree about resistance, as it applies to RPM..

And how does/doesn't it apply to other things?

[Brett_Henderson]

And how does/doesn't it apply to other things?

The additional power (torque) is not resisited or restricted.. it gets translated into more thrust..

[mgh]

The additional power (torque) is not resisited or restricted.. it gets translated into more thrust..

If the propellor did not resist the additional torque the rpm would increase indefinitely - or until something broke. That's basic physics.

Also if a propeller is put into the feathered position (blades at about 90 deg pitch) on a stationary aircraft and the engine torque increased slightly then the propeller rpm would increase until propeller torque equalled the engine's torque without generating any significant thrust.

[Brett_Henderson]

If the propellor did not resist the additional torque the rpm would increase indefinitely - or until something broke. That's basic physics.

We already agree about that.. in strict terms of RPM. Would you disagree with me if I said that after a power increase, more work is being done per revolution ?

OR.. let me try it this way.. We'll use HP..

Can we agree that HP is a function of Torque and RPM ?

An increase in either torque or RPM =more HP ?

So as torque increases, but RPM remains constant (for reasons, we agree), HP increases (as in, it has not been restricted) resulting in more thust.. ?

Also if a propeller is put into the feathered position (blades at about 90 deg pitch) on a stationary aircraft and the engine torque increased slightly then the propeller rpm would increase until propeller torque equalled the engine's torque without generating any significant thrust.

Agreed.. but that has nothing to due with CSP function, inside of its operational range.