If my premise is true, this line of inquiry has major historical significance, to say nothing of of the future conception of innumerable simulation games...
If there is a significant undetected imbalance in prop thrust -on the vertical to fuselage plane-, this has enormous implications on our basic understanding of how these particular aircrafts functioned at the most basic level...: If unknown vertical variations are true, we go from prop power being largely neutral to sustained turns to adverse to sustained turns (especially if assuming nearly 80° of bank in many cases)... This would explain the constant WWII obsession with reducing power in slow speed sustained turns, at the lowest limit, even after many consecutive 360s at very low speeds. And no one ever using "Emergency Power" in turning combat, only when wanting to go straight (innumerable interviews to that effect)...
In fact, the entire notion of "speed is life" would be entirely turned on its head, since WWII gun firepower was usually not effective enough to tolerate high bisecting angles (in non-expert hands at least, which is why it is mostly aces who pronounced dogfighting "dead" at the time), and this explains the increasing obsession with slow speed turn-fighting right up to 1945, especially in Europe, where opponents had matching top speeds, and thus could "rope in" each other into a "locked" decelerating turning contest. This is entirely contrary to the usual narrative of dogfighting becoming obsolete as power increased, at least during the gun/prop era...: In fact, the presumed "obsolescence" of dogfighting was widely assumed as early as the monoplane era was established (1930s), causing the entire worldwide late-1930s obsession with the failed concept of the twin engined "heavy" day fighter, real-life firepower turning out to be insufficient, at high bisecting angles, in the hands of most pilots...
If the prop is turn averse by a significant amount, on the vertical-to-fuselage plane, the implication is phenomenal: It means a faster sustained speed turn rate, from minimal speed, will be achieved by reducing power.
This is how I interpret the quote I posted above (there are innumerable other hints going the same way, with nothing to the contrary, in thousands of combat accounts I have read on this topic). I use it here only because it is so exemplary, and combines with the use of coarse prop pitch at low speeds.
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Hanseman (505 sq.) combat report, 24 May 1944 (Merlin P-51)
"Dogfight at 500 ft. (with a second higher aircraft,afterclimbingfrom130 ft., having closed to 50 ft. on a wheel down 109G that was landing)"--"At first he began turning inside me. Then he stopped cutting me offas I cut throttle, dropped 20 degrees of flaps and increased prop pitch.Every time I got close to the edge of the airdrome they opened fire with light AA guns."(Meaning several successive 360 turns near the same airdrome)--"GraduallyI worked the Me-109G away from the fieldand commenced to turn inside of him as I reduced throttle settings."
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So this is my interpretation: Assuming the Angle of Attack (of about 6-7°) lowering the wing does force a vertical dogleg (longer trajectory) in the lower prop half's air, then this air "shifting" above the wing would force an acceleration of that air: Acceleration of that air would have several major effects, even if the overall loss of thrust is only 6%.
1-A 6% loss of outer turn disc half thrust would cause an increase of 3% on the inner turn disc half load, through asymmetry of load: I assume half of the loss of thrust would get expressed as a deceleration, since the upper to fuselage disc half is unaffected by air acceleration, but the whole aircraft is decelerated by the 6% loss, half of which would affect the upper disc half by adding a load.
2-So we are now at a 9% disc imbalance, to which we may add 1% from the turn curvature: A 10 foot prop over a 1000 feet turn radius is roughly a 1% imbalance. So -6% outside and + 4% inside: 10% of total imbalance. At high load, a figure I read was a 3000 lbs of overall prop load, so we could have 300 lbs of adverse pitch load at the end of a ten foot nose...
3-A very important point is that such a load should feel to the pilot as a heavy nose-down trim, yet it obviously doesn't at all... (In some WWII types there is even a nose-up pitch in low speed turns only): Something is obliterating that effect in pitch, yet the effect is still there, since the turn rate is increasing with less power...
4-The important thing is the acclelerated air: In the pilot account above, he finds it advantageous to use a coarser pitch, despite being at a very low speed: This use of a coarse prop pitch indicates the presence of accelerated air inside the prop disc, in a way that is adverse to the turn (so outside the turn): A coarser blade pitch would mitigate the accelerated air unloading the outside turn/lower prop half. A coarser pitch would, in effect, "reload" the "unloaded" outer half.
5-He also reduces power: This would simultaneously unload the now overloaded inner turn/upper disc half.
The overall description is clearly that of prop power being adverse to sustained turns at minimum speed, after several consecutive 360s, so it is not a sitution where he has too much speed at all...
I will go into other points later.
Gaston
Last edited by Gaston444; 11th Mar 2020 at 23:09.