Japanese Zero vs Spitfire vs FW 190

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Hello Schweik,

Perhaps this graph might make things a bit more clear about what the issues are with a two pitch propeller as compared to a constant speed propeller.

Since I don't happen to know what the propeller parameters were on the two pitch propellers for the Spitfire, I used what I believe to be correct for the later constant speed propellers:
Diameter 9.5 feet
Reduction 1.646:1
Engine RPM is 3000

The Red Line is 30 degrees Pitch
The Blue Line is 45 degrees Pitch
The numbers added below is forward speed in MPH for engine speed of 3000 RPM.

If you look at each flight condition you have:
Take Off (I am guessing about 90 MPH)
The Fine Pitch (30) is better but still not very good as compared to what might be available from an even finer pitch of 20-25 degrees. Coarse Pitch (45) is clearly pretty inefficient.

Climb (I am guessing about 160 MPH)
The Fine Pitch (30) is better but not when compared to what might be available from an even finer pitch of 25 degrees. Coarse Pitch (45) is clearly pretty inefficient.
The solution would be to climb at a higher airspeed and bring the propeller into an area of higher efficiency but of course that also increases drag. It is a nice balancing act.

Maximum Speed (Perhaps 350 MPH)
The Fine Pitch (30) can no longer provide any Thrust. The Coarse Pitch (45) is also not ideal but will at least pull the aircraft.

From this graph, the efficiency of the Fine Pitch (30) propeller drops to Zero at about 330-340 MPH forward speed.
This is because the blades have reached Zero degrees Angle of Attack relative to their airflow. If the aircraft goes any faster, the airflow begins driving the propeller to overspeed.

Hope this makes sense and you can see how all the other angles in between make such a difference in a constant speed propeller.

- Ivan.
 
re Wing Commander Abicair

Full name was Alexander Joseph Abicair

Pre-RAAF service he was an auto and civilian aircraft mechanic.

Served with the RAAF from the mid-1930s (I think) and was a Corporal with No 1 Sqdn RAAF in 1939. At some point between 1939 and 1943 he was promoted to Flying Officer. Promoted to Attack Wing (No 1 Sqdn?) Commander in May 1944. Ended the war as C/O of a Training/Operational Training Wing. Served as C/O of 486 Maintenance Squadron from August 1946 until retirement. As far as I have found he served the entire war in the Australian SW Pacific theater, so probably not associated with the Aboukir filter.

At some point he was awarded the MBE (Member of the Order of the British Empire) for war-time services to the Australian & American air forces.

There is a book about him titled "Abby: Portrait of a Common Man" by Tony Smith (aka Anthony Smith), but I have not been able to find a readily available copy.
 
Shortround6 said:
The French Caudron racer and even the DH 88 used props that automatically shifted to coarse once a certain airspeed was reached.
Click to expand...
In the 1930s there were several attempts to make "fully automatic" variable pitch props that had spring loaded free swiveling blades with no force-type operating mechanism. The idea was that by using spring loading, counterweights, and carefully shaped blades, a balance of centrifugal and aerodynamic forces would adjust the blades constantly to the most efficient pitch angle for the airspeed and engine RPM. Great idea; tricky sumbitch to execute. They worked mostly OK on straight and level planes like transports and distance racers, but couldn't cope with the rapidly changing loads of aerobatics or combat. I saw an acro practice session by an overweight, overpowered death trap of a Stampe biplane with one of those props and I could hear RPM overshoots and wild fluctuations as he wrung it out. He was attempting to duplicate and out match a routine that a Pitts Special with a constant speed prop had just flown, and the soundtrack was jarring and nail-biting. The contest director, no stranger to Stampes and to over eager flying fools, had him DQ'd and grounded.
Now back to WWII.
Cheers,
Wes
 
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You numbercruncher types fall into pitfalls like this when you try to snapshot a fluidly dynamic process like this so you can graphically depict it. By referring to a constant speed parameter while quantifying what are essentially two or several separate "fixed pitch" propellers, you risk leaving the uninitiated or the uncertain with the impression that RPM will somehow remain at 3,000 throughout this. That's fine for theory, as long as it's clear that it's not expected in the real world.
I've been around this bush a thousand times with students, and most of them are dazed, dazzled, and confused by the numerical approach.
Schweik, when a fixed pitch airplane starts to go downhill with no change in throttle setting, the thrust of the propeller is augmented by the "thrust" of gravity, so airspeed increases. Now if throttle is constant and gravity is aiding thrust, the propeller isn't working as hard and it's resistance to the engine's torque is reduced, so now torque exceeds resistance and RPM increases. Same thing in reverse going uphill. Now if you had begun this process cruising at your engine's peak torque RPM and that dropped off in your climb, you have just suffered a drop in your torque and your horsepower, slowing both your airspeed and your climb rate. Wouldn't it be nice if some invisible hand were to give you back your lost RPM, horsepower, airspeed and climb rate by twisting your prop blades to a finer pitch and getting you back up to 3,000 RPM? "Thanks, Guv'nor!"
Cheers,
Wes
 
XBe02Drvr said:
You numbercruncher types fall into pitfalls like this when you try to snapshot a fluidly dynamic process like this so you can graphically depict it.
Click to expand...

NumberCruncher Types? Hey! I resemble that remark!

Seriously though: Thanks for pointing out the flaws in the example. I do see what you are describing and have "experienced" it while flying Albatros and Fokker types from the Great War in the simulators.

As you point out, the RPM would constantly be changing which means that the Advance Ratio would also be changing and the efficiency graphs would be stretched or squeezed proportionately.
As for determining how quickly RPM would change, one would have to be able to calculate the Propeller Power Coefficient using air density and instantaneous engine output.....

Computers can approximate it pretty well. God does it perfectly every time.

- Ivan.
 
Shortround6 said:
ROFLMAO
They got a prop shaft brake, the dead or malfunctioning engine was put into coarse pitch and a brake was applied to keep the prop from turning.
Click to expand...

And a prop shaft brake turns the propeller into a very effective air brake which causes the aircraft to yaw badly which in turn increases drag resulting in an even greater degradation in ability of the aircraft to maintain height and the pilot to maintain control
 
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And a windmilling prop at ANY pitch setting fighting 12 or 14 cylinders of engine compression gives you ten times MORE drag, so a shaft brake is better than nothing, but a sorry excuse for lack of a feathering propeller. In the days of multi engine planes with fixed pitch or unfeatherable props, ANY engine failure resulted in a barely controlled "drift down" maneuver with "three churnin', one draggin', and both pilots standin' on the rudder pedals". The drag from the windmilling prop and asymmetric flight was more than the remaining engine(s) could handle, even at full throttle, and maintain altitude and a safe airspeed.
My instructor drove that home to me by getting us out over the Gulf of Mexico and pulling the Apache's right engine back to idle, then shutting off the fuel to kill the engine and wouldn't let me feather it. It was all I could do to keep the speed above Vyse, the sink rate under 300 feet per minute, and the airplane from turning right, even at full throttle on the left engine. If I flew faster, I sank faster; if I flew slower, I would start to lose directional control and have to sacrifice some altitude to get my speed back. We flew all the way back to base in drift down mode, where my tormentor let me restart the right engine, but insisted it stay at idle, where he surreptitiously pulled the circuit breaker on the standby hydraulic pump, forcing me to hand pump the landing gear down while wedged in my seat, left leg muscles cramping from the rudder pressure, and the plane yawing left and right as I fought to keep it straight. I swear the man had a death wish. But I learned a lot!
The landing wasn't very pretty.
Cheers,
Wes
 
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Was that a military or civilian instructor? Was he doing it to make you better or just being a jerk?
 
Some of the overpowered American transports of the 30s

had feathering propellers as early as 1936. The lockheed 10 with 450hp Wasp Junior engines was supposed to have a single engine ceiling of 4,000ft. With 550hp Wasps the single engine ceiling was supposed to be 9,000ft.
The British going sub hunting with Avro Ansons with wooden fixed pitch props and claiming twin engine "safety" needs a lot of explaining.
 
Cosmotabis said:
At the beginning of the war there was one fighter that was markedly superior to the Zero
That was the P-38 Lighting.
Click to expand...

In April 45 the USAAF tested an almost new A6M5, with known defects, against defect free P-38, P-47 and P-51.

Findings include


The above airframe discrepancies are not identified but there is this engine defect which would have affected performance






You stated opinion but not the facts.

Even in 1945, when the Japanese aircraft industry was on its knees, the A6M was still markedly superior to the P-38 in a number of areas
 
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pinsog said:
Was that a military or civilian instructor? Was he doing it to make you better or just being a jerk?
Click to expand...
He was a retired career Marine pilot working as a civilian DOD employee and instructing on the side, a "triple dipper" and a no-nonsense aviator. He knew how to drive you right up to the edge, then calmly talk you back. Left you with lessons you wouldn't soon forget.
Cheers,
Wes
 
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"Superior" is such an infinitely elastic word. If you try hard enough you can find some parameter in which to call just about any fighter superior to just about any other. Not to belabor the obvious, but in any comparison of a particular parameter, what matters is how was it able to contribute to success in combat given the other variables of tactics, doctrine, pilot skill, etc.
The pre-introduction P38 was clearly superior to the Zero in several important performance parameters, and as MiTasol pointed out, inferior in a couple others, right up to the end of the war. So were most other contemporary allied fighters. Freshly minted P38 pilots had an advantage over their predecessors in the "know thine enemy" department and had the doctrine and tactics to maximise their advantages. The P39 and P40 pilots had to learn the hard way that the "turn and burn" tactics they were taught were not the way to survive the Zero. Somehow it seems in hindsight that it took longer for this lesson to penetrate the USAAF training system than the USN's.
Cheers,
Wes
 
MiTasol said:
You stated opinion but not the facts.

Even in 1945, when the Japanese aircraft industry was on its knees, the A6M was still markedly superior to the P-38 in a number of areas
Click to expand...


You missed the part that said at low speed, what 1945 fighter pilot flying a Spit XIV P47D P51D capable of doing over 400mph would get into a turning fight with a Zero under 200mph?.
 
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