Double "Ponie"

[earl1937]

Colonel Sharp's statements raise some huge red flags.  He said the P-82 rolled around the pilot, the other aircraft arcing.  The P-82 would have rolled around its longitudinal axis (the center-line of the plane).  Then he states that the allison engine could pull 145 in/mg with 145 octane gas, but that they were limited to 75 in/mg. 

So basically one erroneous statement and one bogus statement. 

Good points Dave~ another one of his mistakes was the direction of rotation of props, they did not turn in as he claims, because when they tried that, it created so much drag, it could not get airborne. The left engine had a "gear" box in it in the final fix, to turn that prop to the left and the right engine to the right!
As far as climb speed, I once made the statement, 5,000 feet per minute, but I am not sure, but with 40% fuel and no ords, the top number on the ROC indicator was 4 and I saw it pegged several times. Even with 2 250 lb practice bombs and 10 rockets, 1 tree of 5 on left wing and 1 tree of 5 on right wing, it would still do between 2500 and 3,000 feet per minute. Of course you have to take density altitude into consideration as that has a drastic effect on climb performance. In winter time, it would climb like a rocket, but in summer, not so good.

[Old Crow]

Colonel Sharp's statements raise some huge red flags.  He said the P-82 rolled around the pilot, the other aircraft arcing.  The P-82 would have rolled around its longitudinal axis (the center-line of the plane).  Then he states that the allison engine could pull 145 in/mg with 145 octane gas, but that they were limited to 75 in/mg.  

So basically one erroneous statement and one bogus statement.  

The important thing to take from Colonel Sharp's account is that he said the other airplane on the other side SEEMED to roll around him in an arc, not that it actually did. We all know as I'm sure he does that airplanes roll around their longitudinal axis. I think he was trying to stress the rolling prowess of the P-82 with its 17 to 1 boost ratio in the ailerons and the pilot rolling on a point and snapping the pilot's head etc. I take the statement to be akin to a plane "turning on a dime" which we all know to be impossible as well. As far as the engine limitations go, all aircraft engines "could" pull a certain amount of power but all were certainly limited to some degree. The fact that he says it was a 475+ mph airplane is impressive to me. The 75-in. pulled is still more than the 60-in. quoted in a previous post and that would make a big difference in performance, all things being equal.

Good points Dave~ another one of his mistakes was the direction of rotation of props, they did not turn in as he claims, because when they tried that, it created so much drag, it could not get airborne. The left engine had a "gear" box in it in the final fix, to turn that prop to the left and the right engine to the right!

At this very moment, they are working on restoring a P-82 back to flying condition and they describe the powerplant as follows: "Two Packard-built Rolls Royce V-1650-23-25 Merlins; 1,860 hp each, counter rotating.  After first flight, props turned inboard.  Left engine - right-hand rotation.  Right engine - left-hand rotation." Here is the website if you want to check it out: http://xp-82twinmustangproject.blogspot.com/p/facts-at-glance.html  I find it hard to believe they have the engine rotation wrong. Also, any picture I have seen of the P-82 and the pitch direction of the propellers show inward rotation being the only possible way to have the plane move forward. I'm fairly certain they turned inward, not outward. I'll have to agree with Colonel Sharp on this one.

[Widewing]

Actually they didn't.  The problem was solved by the same guy working on propeller mach flow problems.

I am not sure how much design work you do but in my design days we call it a design error.

It's a design error if there was data showing that high Mach behavior would be unsatisfactory. There was no such data when the P-38 was designed (1938), and aircraft design teams really didn't have a good grasp of localized transonic behavior until the late 1940s.

I can't think of a single WWII fighter that didn't experience Mach tuck when dived well beyond critical Mach. The P-38 experienced it at a lower air speed due to the outer wing profile selected (inner wing had a higher critical Mach than the outer).

Later P-47s incorporated dive recovery flaps. So did the F7F and F8F. In the P-38L, deploying the recovery flaps resulted in a 3g hands-off pull-out.

[earl1937]

The important thing to take from Colonel Sharp's account is that he said the other airplane on the other side SEEMED to roll around him in an arc, not that it actually did. We all know as I'm sure he does that airplanes roll around their longitudinal axis. I think he was trying to stress the rolling prowess of the P-82 with its 17 to 1 boost ratio in the ailerons and the pilot rolling on a point and snapping the pilot's head etc. I take the statement to be akin to a plane "turning on a dime" which we all know to be impossible as well. As far as the engine limitations go, all aircraft engines "could" pull a certain amount of power but all were certainly limited to some degree. The fact that he says it was a 475+ mph airplane is impressive to me. The 75-in. pulled is still more than the 60-in. quoted in a previous post and that would make a big difference in performance, all things being equal.
At this very moment, they are working on restoring a P-82 back to flying condition and they describe the powerplant as follows: "Two Packard-built Rolls Royce V-1650-23-25 Merlins; 1,860 hp each, counter rotating.  After first flight, props turned inboard.  Left engine - right-hand rotation.  Right engine - left-hand rotation." Here is the website if you want to check it out: http://xp-82twinmustangproject.blogspot.com/p/facts-at-glance.html  I find it hard to believe they have the engine rotation wrong. Also, any picture I have seen of the P-82 and the pitch direction of the propellers show inward rotation being the only possible way to have the plane move forward. I'm fairly certain they turned inward, not outward. I'll have to agree with Colonel Sharp on this one.

  You are right I guess, I am relying on a 80 year old mind, about something that occurred 57 years ago. I tried to research that a little and all I could come up with was some info on wiki as follows:The XP-82 was to be powered by two Packard-built Rolls-Royce V-1650 Merlin engines. Initially, the left engine was a V-1650-23 with a gear reduction box to allow the left propeller to turn opposite to the right propeller, which was driven by the more conventional V-1650-25. In this arrangement both propellers would turn upward as they approached the center wing, which in theory would have allowed better single-engine control. This proved not to be the case when the aircraft refused to become airborne during its first flight attempt. After a month of work North American engineers finally discovered that rotating the propellers to meet in the center on their upward turn created sufficient drag to cancel out all lift from the center wing section, one quarter of the aircraft's total wing surface area. The engines and propellers were then exchanged, with their rotation meeting on the downward turn,
It sounds as though the right was turning right and left was turning left, according to this, but not sure of their info creditability. I just do remember that when you reduced power to 12 inches, (zero thust) on the left engine, you had your hands full and a lot of right rudder to keep it straight, but with the right reduced, and the left doing the work, it wasn't much problem to keep it straight. Again, I am relying on an old mind and I could have those backwards.

[drgondog]

I can't think of a single WWII fighter that didn't experience Mach tuck when dived well beyond critical Mach. The P-38 experienced it at a lower air speed due to the outer wing profile selected (inner wing had a higher critical Mach than the outer).

The P-51 with the NAA/NACA 45-100 seemed to have far less adverse CMac due to the Max T/C at 45% rather than 25%+- for virtually every other fighter.  The primary issue was the Yaw build up in the dive that took a boosted rudder tab, then reverse boost to 'incent' the pilot to get out of the dive. I don't know about the P-63 experience..