Originally Posted by
Pilot DAR
'Careful how you interpret this. Yes, "increase" prop pitch would mean to make it coarser. However, if you read the propeller control "increase" means move toward fine pitch, increase RPM. This is for slowing down quickly, and is somewhat abusive to the engine and prop - particularly geared engines! 'Same poor wording as "full" throttle. Fulling throttling something means cutting off the airflow. "Open" throttle, or "full power" convey properly. I'll say "full power", or "open the throttle", but I never say "full throttle". I'll also say "prop fine pitch" or "increase RPM". There is no flying condition where you'd reduce power, lower flaps, and coarse the prop pitch. If you've closed the throttle, the next thing you'll be doing is opening it again sometime, for which you'll want the prop fine pitch, so we plan ahead.
So, if we infer increased RPM - fine pitch - these are things a pilot would do to slow down quickly, hopefully with a liquid cooled engine they really didn't care too much about. Yes, if you want to change direction more quickly in a turn, reduce the airspeed.
I had carefully researched this term before coming to this conclusion. What you suggest is
not how the higher or lower pitch term is commonly used in "pilot parlance" (and especially not in the even less-specialized terms of a WWII combat report), because the usual reference of pitch is the blade angle, which is higher when rpms are lower: The useage you suggest is counter-intuitive and confusing, referring to the increasing pitch of the blade trajectories if they were screwing through wood like screws, which may be how they are oriented on the lever (engineers being fond of counter-intuitive abstractions), but
not something easy to visualize if by
increasing pitch you mean LOWERING the prop blade angle... I'll just point to some aviation articles I quickly found, where the meaning is
clearly on my side, and
never explained or specified, because in this case the intuitive has obviously won out over something that would be severely confusing:
Quote: "The Mustang is so aerodynamically clean that it glides more efficiently than most general aviation airplanes, but only when the propeller is set to high pitch. Blade pitch affects glide ratio so much that it can be modulated during descent to vary glide performance as necessary during an engine-out approach."
Quote:"
Should you need high RPM (low blade pitch) oil pressure on the back of the plate is reduced slightly. This allows the plate to slide back, pushing the shaft backwards and rotating the beveled cam clockwise. As a result, the blades also rotate clockwise which sets low blade pitch. Because of this plate arrangement the Hamilton can't be feathered; there isn't enough travel room for the plate. In any event of oil pressure loss the prop had no means of control and would usually "run away." The blades would go to high RPM (full low pitch) while producing no thrust and a ton of drag."
I could find many more such quotes, but suffice it to say that the use of a term in a not generalized way, which is also highly counter-intuitive, is, I think,
extremely unlikely...
To this you have to add the circumstances the pilot describes: He is in a low speed turn battle, after slowing to 150-200 mph to intercept,
from 50 ft behind!, a landing aircraft at 150 ft, having climbed 350 ft afterwards to counter a new challenge from above, at 500 ft.... He is now "locked" in a slow speed turn battle with a lighter aircraft, with no real possibility of diving or spiraling down, and so highly pressed from behind that he is forced to stay in the turn as the circle carries him,
repeatedly, into the AAA fire clearly located within the airdrome...
Are you saying in this condition, with flaps down and his engine deliberately reduced in power, after multiple 360s on the deck, that his aim
would be to impose on himself severe drag, after completing multiple complete level circles he did not want to do?
If you are saying he wanted to increase engine rpm, then why would he deliberately lower his throttle? Please do not tell me you think this guy had too much speed, because he was forced to turn i
nto the same AAA multiple times...: There is no way he would choose to approach that airdrome multiple times, unless he was forced to make consecutive full circles near the ground..
. His immediately previous altitude was even lower, and his speed was already low as well.
So my criticism is that you interpretation involves a
highly unlikely use of the term "increasing pitch", and one that cannot fit in any way the situation as it is presented.
What would be your interpretation of what the pilot did, assuming my version of the prop pitch is the correct one?
Originally Posted by
Pilot DAR
If you're flying with that low AoA with any power, the propeller airflow path will hardly be changed from a normal cruise flight AoA. A a single propeller pilot flying a maximum performance rate turn will be flying a higher AoA, closer to a stall AoA - that's where the G comes from.
That is precisely what I wrote my entire previous post about... WWII fighter pilots did not care about maximum unsustained Gs, because for one, as the SETP found out in 1989, these aircraft could barely even reach far above those speeds
in a straight line: The minimum for 6Gs being around 300 mph ias minimum (276 mph spiralling down, and of course much lower in dive pull-outs: 255 to 240)... They could,
horizontally, complete maybe 90° or 180° of turn above 5-6 Gs, briefly, and that was useless in combat, because unless the opponent matched this value exactly, you had no "pepper time". My entire previous post was about how the pre-WWII assumptions of firepower and bisecting trajectories were wrong... Only a few Ace pilots ever managed more than light damage at bisecting angles, given the more usual 1% hit rate...
The G levels that mattered in WWII combat where the maximum sustained speed Gs, so around 3 Gs: Because this was sustainable, this was where the real damage was done.
As to what AoA angle turning at 3Gs represent, I assumed around 7°, since 6Gs is 14°, not including the wing camber: If that is wrong I would be glad to be enlightened.
Originally Posted by
Pilot DAR
In such case, the torque of the prop will have more effect on the handling of the plane than a change of airflow over or under the wing. This effect is increased right up to the stall, where the plane will roll with torque if the power is up. The tendency of one wing to stall before the other (and at least induce a roll, if not a spin) will be much more subject to uneven AoA of each wing, and imbalanced aerodynamic forces, than airflow over or under the wing. I'm not saying it's not a factor, it's just not a major factor.
If the wing effect is 6% of the thrust, leading to a 9% prop imbalance, would you agree that this is around 300 lbs of nose-down trim trim at the end of a 10 foot nose?
Since this effect would be purely vertical, is it inconceivable the wing's lift would take up the slack, and you would be completely unaware that they are doing so?
Here is some calculations I made as to what these -imperceptible- 300 lbs of prop imbalance would do: a 120 inches long nose would need to be countered by a forward movement of the CL, in front of the CG. How far in front of the CG can the CL move? I have no way to know... It could be a foot, it could be one inch....
If the figure is one inch, then it is costing the wings 36 000 lbs of lift to conceal, to the pilot, that the prop is pulling down... If that is indeed what they are doing, how would you know the difference? Only by measuring/comparing raw turning performance, where energy outcomes are affected by the intensity of conflicting internal forces (since the wings have to bear the internal conflict)...
All of a sudden, the notion of a 45 lbs/square foot FW-190A out-turning, at slow sustained speeds, a 30 lbs/square foot Spitfire, is not so outlandish...:
Johnny Johnson (top Spitfire ace of WWII) "My duel with the Focke-Wulf": (At about 1000 ft. above seal level) "With wide-open throttles I held the Spitfire V in the tightest of vertical turns [Period slang for vertical bank]: The Mk V was also known as better turning than the Mk IX and all later models]. I was greying out. Where was this German, who should, according to my reckoning, be filling my gunsight? I could not see him, and little wonder, for he was gaining on me: In another couple of turns he would have me in his sights. I asked the Spitfire for all she had in the turn, but the enemy pilot hung behind like a leech. It could only be a question of time..."
Originally Posted by
Pilot DAR
The only plane I've flown that comes near being a WW2 fighter would be the Harvard.
Note that at the top of a loop, with lots of power, a bunch of AoA, and not a lot of airspeed, I have the ailerons wings level, 'not overcoming propeller airflow change effects.
How would you know, if 300 lbs of force is cancelled out by an extra 30 000 lbs from the wings? It bears repeating: These forces are cancelling each other out, whatever is the value that they have. To know their value you would have to
measure how much you wings are bending in actual turning flight: The reality is that they might bend a lot more than is assumed, since bending in flight measurements were never done for these types.
There is two ways to detect the effect I am talking about
: 1-Measuring prop blade load uniformity (during each rotation) in a level turn 2-Measuring wing bending in a level turn.
It really is quite simple, but so far I have never seen data that suggests this was ever done for the 1000+ hp low-wing types we are talking about (at least not in sustained level turns, where the prop is at its highest load, so of course
not dive pull-outs): That data, if it existed, would instantly prove my theory wrong...
Originally Posted by
Pilot DAR
Okay... but I don't think the outcome of WW2 will be affected. Interesting thinking point, and perhaps a peripheral aerodynamic characteristic, but not very relevant to airplanes in use today.
Oh please...
.
Originally Posted by
Pilot DAR
Okay, if you have a piloting game which models the forces affecting airplane handling so accurately that this factor could affect things, well done!
If the wing lever is 1 inch, and the nose lever is 120 inches at 300 lbs, then the forces involved on the wing are 36 000 lbs,
on top of what is curerently assumed: 30 000 lbs at 3 G for a P-51, plus 36 000, so possibly 66 000 lbs. Obviously that is too high, but yes, they do have the structural margin to take it, since the effect tapers down at high speeds (It obviously has to, since the prop load goes down at higher speeds.). Mustang wings easily take 70 000 lbs, and their maximum rating is around 120 000 lbs (or 12 Gs).
And since these are all forces whose total sum is zero, this is perfectly within accepted physics. Because as a pilot you are at the balance point of much larger forces, there is no way you can tell just how large these forces actually are. You can just gauge the residual energy outcomes in side by side fly-offs... And in the case of the FW-190A, it does breach and greatly exceed a 20 000+ lbs of wing load difference, because of a lower leverage ratio being less taxing to its smaller wings (the only way this observable gap could be overcome, in my reckoning).
Gaston