russ_watters said:
"Sorry, but I'm just not seeing how the issue you are describing is functionally different from P-factor, and also would like to point out that a 3.2 g turn is 70 degrees angle of bank, so the plane is pitching into the turn more than it is yawing. "
Well, pitching is precisely my main concern... The effect I describe is nearly the
exact opposite of the P-factor, which claims the thrust is increased on the outside turn portion of the disc (this because, on the outside, the blades are angled [by the AoA] to move forward, while, on the inside turn portion, the blades are moving backwards).
This may well happen in pitch, in theory (the yawing is, of course very real, and explains the preference to one side of some types), but the effect is, in pitch, completely obliterated by the increase of inner disc thrust due to the curvature of the air.
The P effect in my view only really exists in yaw: Just like a wheel turning it pushes the nose to one side... But this is from the lateral drag of turning the blades, and this is separate from their longitunal load.
The fact the P effect is assumed to be also dominant in pitch is a reflection of the inability of wind tunnels to replicate curving air... Naturally, they would consider as dominant something that works
without air curvature...
Slanted air at an angle, and
curving air, are simply not the same...
If the P-factor was dominant in pitch, that is, other than yaw to the turning direction, the propeller would
assist a 70 degree bank turn, so
more power would
increase the sustained turn rate... This is exactly the
opposite to what was widely observable to WWII pilots... They would try to increase the low speed sustained turn rate by maintaining the lowest power possible, in multiple consecutive 360s, at slow speeds and at ground level. Karhila: "If the opponent lowered power, I would lower it even more [reducing speed, but reducing the radius even more].
160 mph seemed to be the optimal sustained turn speed."
160 mph is far lower than the minimum sustained speed radius of turn, at full power, for the 1500 hp (and 406 mph capable!) Me-109G, which is likely around 220 mph, perhaps higher at WEP. This means power, up to a point, is definitely
adverse to the sustained low speed turn
rate, contrary to what is currently assumed...: Apparently a higher sustained turn rate exists as low as 55 mph above landing speed...
russ_watters said:
"Some analysis:
Google tells me the P-51 has an 11' diameter propeller and a minimum turn radius of 531' at 270mph and an 18.5 degree stall aoa. So the difference between inside and outside of the turn for the propeller tip is 2% of the turn radius. At 270mph, that's 5.4mph. "
I think that is for 7 Gs... The minimum speed to reach 6 G was found by the SETP (in 1989) to be 276 mph, in a slight downward spiral. It seems from their wording that,
without a downward spiral, the minimum for 6 Gs was closer to 300 mph...
They do not explicitly say the figure was higher without diving, but it is implied by the phrase "Corner Speed (6G) on all 4 types was found to be
very close to their maximum
level speed at METO." This METO speed at 10 000 ft. was 320 mph for the P-51...
The reason the P-51 flight manual claims a minimum 255 mph (flaps up), for 6 Gs
horizontally , could be that all the manual G values were achieved with dive pull-outs, which unloaded the prop... (21 mph higher than 255, in a nose-down spiral, is
the best the SETP could do, so they were
unable to match flight manual figures)
This is not really central to my thesis, but you definitely sense the real puzzlement of the SETP towards the poor ability of these WWII aircrafts to reach high Gs at "useable" middle range speeds... This is because, in reality, you have to go really fast for the prop to become less loaded enough to allow even touching 6 Gs...
This is why anyone who has read a ot of WWII combat accounts knows values like 6 Gs are really of little relevance to actual fighting...: 3.2 or 3.4 Gs sustained is where the real meat of the matter lies. The P-51 was rather an exception to this, being exceptionably able to reach high Gs (6-7) at moderately high speeds (350-400 mph), hence the use of G-suits, but even then, the SETP in 1989, being used to jet testing, found the P-51 unimpressive...: "
An interceptor type aircraft of limited turning ability": Because, in the mind of a jet pilot, turning really boils down to quite high Gs... Even the high G-gifted P-51 found jet jockeys near impossible to please...
With jets, Gs beyond 4-5 are far more easily achievable, and far more sustainable for far longer, because they are not impeded by increasing prop asymmetry as the turn tightens, and speed decays, while power is kept up.
russ_watters said:
"So that's why I don't think this is something much talked about. Note that the speed differential between the inside and outside wings is of course many times larger and therefore is considered/discussed much."
If the bank angle is 70 degrees, I don't see how the wing speed turn difference is all that much larger than the span of the prop disc width...
Pilots could increase the bank angle further by riding the turn on deflected ailerons... Even for sustained turns, turning can become largely a pitch issue, with fairly moderate wingtip speed difference, while still with a full prop diameter, nearly perpendicular to the trajectory...
russ_watters said:
"That's said, I think I do get the difference you are referring to: the P-factor causes a pitching plane to yaw, so it or a similar effect would cause a yawing plane to pitch."
Yet the whole point of my theory is that the prop
resists pitching...
The assumption that P has authority in pitch is likely caused by something else: By the changes in the CL position, when the CL is subjected to high prop loads, and this from a long nose leverage: If the CL moves forward, it can "hide" the prop's real pitch-averse behaviour, but at a gigantic cost in extra needed lift, given the minuscule leverage available to the displaced Center of Lift, all of eight to ten feet behind the prop...
Where does the CL get this huge extra lift is where the current error resides, but measuring wing bending, while actually turning horizontally at full prop load (which was obviously never done on low wing WWII prop types), would immediately reveal this extra wing load (imposed by the prop resisting pitching)...
As to the difference of 5.4 mph in prop tip speed, it will tell us little about the actual cost of tilting the prop, if we don't know how much the wings are actually suffering through bending: It is possibly only the extra (over assumed math value) bending measured in the wings that will tell us exactly how much the prop is actually fighting them...
WoA