I tried this in our P-47D...it didn't work

[funked]

Toad you might want to put a big disclaimer on that to indicate it is not a typical WW2 setup.  AFAIK all the aircraft in AH had constant speed props with continuously variable pitch.

[Toad]

Can I say "early war setup"? Didn't the early Spits and Hurris have the two-position?

In any event, the point is that changing pitch will alter engine rpm. On our BT, setting the MP at 28" and then easing in a litte prop makes it "manually variable", right? Even though the GI's (who didn't pay for their own engines and gas) probably just used full INCREASE or DECREASE I guess.

But if you say so about the American fighters, I'll believe ya...I don't even own AHT. (But I got a lot of stuff on "how to fly".

 

[SFRT - Frenchy]

I have some diagrams who may help Flakbait and Downtown to understand from my 'constant speed prop' manual but I need a scaner.

[Downtown]

Still reviewing "Americas 100,000" but it only deals with AMERICAN Fighter Aircraft!  I won't speculate on LW, IJN/IJA, VVS, French, or RAF Aircraft.

Americas 100,000 clearly states all U.S. Fighters had Constant Speed Propellors!

Three types.  Hamilton Standard, Curtiss Electric, and Aero???? Something.  The Curtiss seemed to be the most functional but more subject to runaway.

------------------

"Downtown" Lincoln Brown.
    lkbrown1@tir.com    
 http://www.tir.com/~lkbrown1
Wrecking Crews "Drag and Die Guy"
Hals und beinbruch!

[Downtown]

1. Does increasing or decreasing the RPM of the aircraft engine change the RPM of a constant speed propellor?

2. Does varying the cutting angle of a propellor blade change the RPM of a propellor.

3. Did aircraft have the ability to A. Change the RPM of the Propellor, and B. Change the cutting angle of the propellor.

4. Is it possible to set you engine throttle to its highest setting, and change the cutting angle of a popeller?

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"Downtown" Lincoln Brown.
    lkbrown1@tir.com    
 http://www.tir.com/~lkbrown1
Wrecking Crews "Drag and Die Guy"
Hals und beinbruch!

[SFRT - Frenchy]

Downtown, I have some students I need to fly with, as soon as I'm back late afternoon, I will draw something via PSP and post it here to answer all your questions.

"A drawing being worth a thousand words"  

[Minotaur]

 

Originally posted by Downtown:
1. Does increasing or decreasing the RPM of the aircraft engine change the RPM of a constant speed propellor?

2. Does varying the cutting angle of a propellor blade change the RPM of a propellor.

3. Did aircraft have the ability to A. Change the RPM of the Propellor, and B. Change the cutting angle of the propellor.

4. Is it possible to set you engine throttle to its highest setting, and change the cutting angle of a popeller?

Here is the way I understand it.

The engine may be connected directly or via a gearbox to the propellor.  This means that the engine and the propellor may or may not rotate at the same speed.  

But...

At any rate, their speed difference is relative and constant.  It all boils down to this.  An increase in engine RPM will cause a corresponding increase in propellor RPM and vice versa.  There is no shifting of gears, while in flight, of engine to propellor speed ratios.

You can change propellor thrust in two ways.  

• Make a change in the speed of rotation
• Make a change in propellor pitch

These are two functions and controls that happen independently.

The pilot has two methods of control.

• Throttle control --> engine Hp output
• Speed control --> the RPM setpoint of the speed governor

The term "constant speed" is a little misleading.  This is because a plane with a constant speed propellor system can also change engine RPM.  

The idea is so that you can design and use an engine that is most efficient at a certain RPM and couple it to a propellor that is most efficient at a certain RPM.  

The speed control system uses an RPM governor.  This is the speed control.  The RPM or speed governor actually controls propellor pitch, not engine speed.

Normally, this is how it works.  Say that that you increase the throttle.  This would make the engine want to turn faster.  The speed control system senses this increase in RPM, and compensates by increasing the propellor pitch.  Increased propellor pitch raises the Hp requirements of the engine and the engine slows down.  This works the same in reverse for decreasing throttle.

Any attempt to change the engine RPM is compensated by a corresponding change in propellor pitch.  The net result is that the system RPM stays constant.

So in essence here is what you have.  The throttle control effects propellor pitch by using engine Hp output.  The speed control effects propellor pitch by using engine RPM.  The two controls work together and independently.

Back to the original question of changing RPM.  Keep in mind that every engine has ussually two different RPM's where it is most efficient.  One RPM is for the best Hp performance and other RPM is for the best fuel economy.  

The pilot generally wants one or the other, fuel economy or max Hp.  However; the constant speed / engine throttle will always work the same.

Clear as mud?  

[Toad]

The constant speed apparatus just relieve the pilot workload.

The pilot, before the automated functions were designed and implemented, did the work. The new automated stuff lessened the workload so he could do other things. Like fight without worrying about prop pitch and rpm.

It all works the same way though. So basically it's still what Frenchy and Funk and Mino said.

[wells]

A constant speed propeller changes pitch automatically with variations in forward speed to maintain the RPM set for.  I think maybe there's some confusion here about the definition of pitch.  It is a geometric angle, not necessarily the angle of attack of the propeller to the airflow.  The constant speed unit is designed to maintain the optimum angle of attack of the propeller throughout a large speed range.  There is also variable pitch propellers where the pilot controls the pitch directly and must adjust the pitch manually as forward speed changes.  The general rule of thumb is that pitch should not be in coarse with a high throttle setting as engine damage could result.  When throttling back, you pull the throttle back first, then the pitch.  When throttling up, the pitch goes up (fine) first, then the throttle.

[Minotaur]

LOL  

I should also point a couple more things.

Increasing the throttle and/or lowering the speed(RPM) have the same effect.  They both function to increase propellor pitch.  The engine burns less fuel at lower engine RPM and the propellor is more efficient at a  higher pitch.

Dropping RPM and increasing pitch make the plane fly more fuel economical, but keep in mind it is derived experimentaly.  This fuel economy is calculated using a formula that contains speed vs fuel economy by flying the plane at different combonations until the one with optimum fuel economy is found.

Just remember that basically speed = thrust - drag.  If you want to go faster you need more thrust and you will burn more fuel.  

However; every speed has its own best propellor pitch / RPM combonation for best fuel economy.

More mud added!  

------------------
Mino
The Wrecking Crew

"So what do you post here? Poetic love letters?"
Ram

[Renfield]

 

Originally posted by Downtown:
1. Does increasing or decreasing the RPM of the aircraft engine change the RPM of a constant speed propellor?

By definition, yes as they are direct or geared together. But the question is actually flawed - what you do is change the throttle setting - the manifold pressure - not the RPM. When in regulation, changing the MP will not change the RPM, it will change the prop pitch indirectly through the regulator.

 

2. Does varying the cutting angle of a propellor blade change the RPM of a propellor.

Yes. But what you actually do is set MP and RPM and let the regulator manage the pitch of the blades to hold RPM. The governor changes the prop pitch in order to make adjustments to RPM to bring it back to the set value.

 

3. Did aircraft have the ability to A. Change the RPM of the Propellor, and B. Change the cutting angle of the propellor.

Yep. The RPM could be controlled by the throttle(s) when out of regulation (i.e. idle) and by the prop pitch control when in regulation.

 

4. Is it possible to set you engine throttle to its highest setting, and change the cutting angle of a popeller?

Yes. That is what Lindbergh was telling the pilots to do.

Basically you can control the RPM with the throttles when the contant speed regulator control is not regulating. I believe you can always control the RPM with the pitch control because you are changing the load on the engine.