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have been reading these posts (on the other thread) with amusement.
On the other side any talk about an aircraft in a curve is complete theory. The weight of a plane is not a constant, unless the oil and fuel tanks of the plane are dirctly on its centre of gravity and centre of lift then its performance is not a constant. The lift of a planes wings are a general value, a plane in a turn has two wings doing two speeds form one extremity to the other and the airflow is not completely straight.
have been reading these posts (on the other thread) with amusement.
On one side when a post mentions "thrust in a curve" the poster has moved above Isaac Newton in laws of motion.
On the other side any talk about an aircraft in a curve is complete theory. The weight of a plane is not a constant, unless the oil and fuel tanks of the plane are dirctly on its centre of gravity and centre of lift then its performance is not a constant. The lift of a planes wings are a general value, a plane in a turn has two wings doing two speeds form one extremity to the other and the airflow is not completely straight.
So it defines the horizontal repercussions (distortion/breakup), but what about the vertical post 505mph? Mach tuck? I was under the impression that many ww2 fighter airplanes easily exceeded 550-575mph before recovery was not possible (again altitude dependent).
From one of my sources - "The lowest air speed at which a fighter can pull structural or aerodynamic limiting" Which tells me either I'm going to stall or break the plane (or both) when I hit this number. Spot on Bill!
I noticed that the two graphs are slightly different. The one on from the flight manual shows indicated airspeed and the other one shows equivalent airspeed. I would guess the one from the flight manual would have some altitude definition although I don't see one.
Dave - I pulled from two different sources - one from TF-51D Manual and the other 'generic' - but I liked the generic simply because it helped explain what happens when you exceed Limit load and head toward Ultimate (and kiss your ass goodye) load.
There was no point I was making in showing one with IAS in mph and the other in EAS. I reality the 'IAS" as near as I can tell is TAS in reality for SL.. when i did the Vmax calc for a 51D@8000 pounds at SL I got ~250mph at 8g for the corner speed. I suspect the difference is what NAA used for CLmax versus mine based on level flight stall while reducing velocity at 1Kt/sec. If NAA had less than 1.72 that would explain the slight difference between their graph and my calc
EDIT - I tried CLmax=1.6 and it yielded 259 mph at 8G @8000 pounds on the deck... which seems very close to the manual chart..
I didn't think you were trying to make some point. I was curious and just pondering the difference between IAS and EAS in the chart. No pilot uses EAS for anything. It is primarily a design tool to estimate vehicle performance. Calibrated airspeed, equivalent airspeed, and true airspeed, and, if no wind, ground speed, are all equal at SL standard day. Indicated airspeed will vary slightly due to installation and position error.
ww2 fighter airplanes easily exceeded 550-575mph before recovery was not possible (again altitude dependent)
The stick force of the P-51 was actually heavier according to some tests between the FG-1 (8lbs), P-47(12lbs) and P-51(20lbs).There was a 1G 'mach tuck' per se in the 51 which resulted in heavy stick forces, but much less than P-47/P-38/F4U, and never resulted in the strong negative pitching moment near Mcr that other WWII fighters encountered.
I would add, how many aircraft could exceed those speeds if not from a steep dive from high altitude?
a shallow dive?
In most test dive charts, it's revealed that most fighters had to be dove from 35-40K feet and 550-575 TAS was probably a more realistic top speed than the presumed 600+ mph touted in previously published assessments.
maybe the late Spitfire from used in the mid 50s, but nothing from WW2.
505 mph (TAS) was the placard for the P-51. greater speeds were obtained in very risky terminal dives up to measured .83-.85 Mach and every aircraft was 'bent' to a degree.
The stick force of the P-51 was actually heavier according to some tests between the FG-1 (8lbs), P-47(12lbs) and P-51(20lbs).
I read that (1989 Experimental Test Pilot Report) and it flies in the face of many opposites POV as well as my own (limited) experience so I wonder. The America's 100,000 by Dean said exactly the opposite among a group of 20+ test pilots convening at Patuxent River in October 1944 and they ranked all of the primary US Fighters. My own experience (never in a terminal dive but in the .7 + M range did not yield high stick forces or a pronounced tuck, but the bird did yaw to the right - controllable with rudder but rudder pedals stiff. I have read excerpts of the 1989 Experimental Test Pilot Report and have serious doubts about the conclusions. One of my biggest issues is only one pilot flew all a/c at reduced loads and reduced engine powerplant. We are back to anecdotal discussions and I prefer 20+ anecdotes to one.
That has more to do with the context of the stick force described.
A P-47 in compressibility would obviously have more issues, though other than descriptions of the stick having the feeling of being set in cement, their were also the tests where it was not an issue of force, but an issue of response, because the pilot could pull full deflection but there was a disruption of the airflow over the elevators.
The P-47 also had a pronounced tuck near compressibility - distinctly like the P-38. I did not not have the same sense in my time in a 51 but I did not push to ultimate Mcrit, although I was in the Drag rise region >.65M. I found the control forces very responsive up to 300-350kts TAS.
It has been argued that the heavy stick force was worked into the design of the P-51 to keep pilots from over stressing the aircraft, and in some ways the heavier stick force allowed pilots to better gauge aircraft limitations.
A reverse rudder boost was introduced to make it difficult for the pilot to put too much input (stiffer rudder pedal response) during the yaw in dive... basically all -20 late production and retrofit into all D's, Aileron response on the other hand was improved from the original XP-51 with sealed and balanced ailerons in the P-51B forward. Ailerons were stiffer >300Kts but not so stiff as to make the airplane unresponsive.
Read all the test pilot reports from WWII to gain a better sense of their reactions to the Mustang controllability
The P-51 was initially quite flawed when it came to mach tuck vs control force, where the P-47 was generally considered better suited for similar types of dives, being more structurally sound for the uncoordinated effects of mach tuck. It was eventually learned that a primary cause for the tuck was the pilots tendency to throttle back in the dive, increasing the drag therefore increasing the tuck.
That would be incorrect relative to the 51. What sources led you to conclude that? First the laminar flow wing for all its failures to achive true laminar flow, did display superior response in drag rise through Mcrit. Second, the Mustang did not 'tuck' relative to P-38 and P-47 probably due to the delayed onset of Mcrit and the location of separtation on the airfoil.
The Mustang and the P-47 and the P-38 were all initially designed to 8G limit/12 G Ultimate - no difference. The P-47 was restricted to .75 Mach as the P-51 and thye P-38 was limited to .68M
They did manage to better engineer the later P-51Ds to manage the tuck and trim effects encountered in a dive.
The two design changes to improve dive pullout response were a.) changing fabric covered elevators to metel ailerons and b.) decreasing the horizontal stabilizer incidence from 2 degrees to 1/2 degree - both reduced the required stick forces to recover, but the incidence change required more nose down trim input in lower speeds.
In the dive, there is a nose up tendency, which the pilot would normally counter with trim.Not with a 51 - if you input nose down trim during the dive, you would experience even greater loads on the elevator/Stab during pullout. The training emphasizes stick and rudder control and leave trim alone.
If the pilot encountered tuck he would let out trim to hold the angle of dive, but in the absence of tuck the nose would want to pop back up suddenly. (That is exactly why you don't input 'up' trim in a dive The retooling of the elevator throw involved easing the stick force so the pilot was less reliant on trim and could simply use a moderate amount of stick forward to hold the dive.
In reading up on compressibility dives of the P-51 and P-47.That would be incorrect relative to the 51. What sources led you to conclude that?
In the context of my description, mach tuck requires the pilot to counter the increased nosed down force of the aircraft. He does this with stick, or with trim. In mach tuck, he has to pull up to hold the angle of dive.Nose up (pitch forces) would normally be a result of CM changes due to a near complete loss of airflow over the wing
Bill - do you know what causes a "mach tuck"? It is caused when the shock wave forms and moves aft, changing the aerodynamic center of the wing.
As to 'varying wing thickness' - true but for both the Mustang and Jug (and virtually all WWII and beyond fighters) ALL varied 'wing thickness' spanwise but maintained the ratio of thickness to chord spanwise by virtue of wing taper out to wing tip area.