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I'm not going to cite a bunch of links that everyone could google or even pull from other forums.
When you try to compare planes that were flown in different ways and used different tactics to succeed then there is always going to be a discrepancy. Side by side, both p-51b and p-47d-10 had there advantages. The need for the p-51 was eminent when the escort duties of the 47 would fall short because of fuel consumption. As a result the enemy would just wait beyond the range of the p-47, then attack the bombers. You can make arguments for the superior turn radius of the 51 and the better zoom climbs of the 47, but this fact regarding fuel consumption and flight range is why the p-51 was a favored escort. Lets be real for a second. At high speeds, having a better turn radius is nullified by g force and pilot fatigue. A superior roll rate however, might be more advantageous when avoiding or chasing an enemy. This is how Robert Johnson was able to beat that Spitfire in the mock dogfight. I'm not sure how accurate his statements were, but he says he could roll his 47C three revolutions where the spit9 was rolling one. He could also do a half roll, then roll the opposite direction on a dime, where the Spit also had trouble at higher airspeeds. Was the p-47d a slower plane than the 51...I think later variants equalized the speed performance of both planes, giving the 51 a slight edge over the 47 in level flight. The 47 with a paddle prop and a field mod exceeding 3000 hp had a lot more to say than what would be reported on a flight test. |
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Supposed to be that Johnson was flying next to a Spitfire being ferried to duty and started off with a race then ended
up proving he could get the advantage. He didn't know who was piloting the Spit, they never spoke, it was all off the cuff. A more full account is included in Shaw's Fighter Combat to illustrate a point. When people take a plane out to see what it can do they really find what they can do with it. |
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http://books.google.com/books?...b&as_brr=3#PPA184,M1
bottom of p-184 to 185. My mistake, it was two rolls not three. It does make a point. |
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Oh yah it certainly does! Though there was more than three rolls, those were only the start. He says left, right,
left, right (military mind, leads with the left foot!), "every time he tried to roll with me I flashed away to the opposite side". That was how he built up a lead necessary for the final dive and zoom maneuver to work, with the other off balance and late reacting even before the coup. A masterful ploy! Johnson had some other tricks but I don't have the account I like the best. Asked in an interview what he did when a German was on his tail, he said he pulled straight up, into what I describe as a vertical barrel roll. There was some conversation in the interview on that. He said a smart German would continue on and a stupid one would try and follow. If you can find text of the interview then just why should become clear. Johnson was not your average Jug Pilot by any means! Would you believe that the same account has been used to "prove" that IL2 models gravity wrong since side by side starting with the dive the two planes don't get the same outcome as in the account? No duh, they didn't start side by side in the account! BTW, the book is worth full price. I paid $35 but here it's $26 new and $14 used, plus shipping. The new copy qualifies for free shipping and what shipping costs nowadays, I'd go for that one. When people take a plane out to see what it can do they really find what they can do with it. |
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IIRC, the 47's performance in the oft-posted roll-chart isn't all that glorious - can someone plese elaborate why Johnson possibly felt the Jug's roll-rate to be supreme?
Snap-rolls?  |
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Roll inertia as opposed to roll rate is the reason why Johnson felt the P47 had superior agility. P47, low stiff wing with large aileron surfaces and the weight above the CG centerline in the fuselage lends a destabilizing element which helps to increase agility. It is easier to tip a tall stack of weights than a low squat stack of weights. By their nature, wings have a ton of dampening so it is much harder to get them rolling than to stop them. All the best, Crumpp   Our Museum glorifies no state, but strives to use these aircraft as a memorial for all lost in war. Our freedom can only be truly appreciated when held in contrast to those who sought to destroy it. Our staff is proudly made up of people from many cultures and religions. Click the photos for details of our projects. "Those who do not remember history are destined to repeat it." - Winston Churchill |
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NACA868 is a scientific paper investigating lateral control response (i.e. aileron effectiveness). It shows what happens if you take the aircraft tested, and fly them using the test procedure.
The procedure is not intended to get the maximum possible roll performance out of the aeroplanes tested - it is simply intended to bring out the differences in the performance of their lateral control systems. (Emphasis added) Clearly if you're not performing control research there is no requirement not to help things along with rudder. However, if you depart from the methodology of the report, your results will obviously be different from the results in the report. |
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I don't think people appreciate just how much pilot skill influences aircraft performance. All the best, Crumpp Our Museum glorifies no state, but strives to use these aircraft as a memorial for all lost in war. Our freedom can only be truly appreciated when held in contrast to those who sought to destroy it. Our staff is proudly made up of people from many cultures and religions. Click the photos for details of our projects. "Those who do not remember history are destined to repeat it." - Winston Churchill |
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Nope. Once again you misunderstand basic physics. While it may be easier for you to push over a tall stack of papers in your office you cannot translate this to P-47 roll agility. You see there is something called moment of inertia (I suggest you Google it or look it up in Wikipedia to become more aquainted). The shorter the "stack" is the lower will be the moment of inertia. Angular acceleration is derived from the rolling moment divided by the moment of inertia and hence the the roll acceleration will be larger if the weight is moved inwards, not outwards. So no, The P-47 is not "helped" by the weight above the C.G line. In fact it is the exact opposite. However, you do score on the stiff wing and the large ailerons. Two out of three is not so bad. OK, end of lesson for today! |
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I'm not sure where the p-47 gets it reputation for a good roll rate. It could be in contrast to the 109s relatively stiffer performance at higher airspeeds. Some German models also would've folded under the stresses of high speed maneuvering. Chasing a plane into high speed roll might have meant losing a wing or leaving the flight envelope. At least that was the advantage of the Mustang over the FW190. I cant say for certain if this was the case in a p-47.
There are tactics that i've read about, that prove to be effective in the game. As for dive performance, i can only say that the p-47 would accelerate in a dive faster than the game allows, thus effecting its zoom climb performance. It still has the best zoom climb in the game, barring jets and the other "obscure" planes. |
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Certainly not. |
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The fact the weight is above the CG line does very much cause lateral instability. I am certain you will argue this point to death because you think I said the the heavier weight of the P47. Since you do not understand the concept of keel effect you will try and focus the discussion on your misinterpretation in an attempt to make it my mistake.
It is called the keel effect. It is also where an internet education will fail you because it is not spoonfed to you. It is one of those concepts you learn in a classroom. It is spelled out in a few textbooks though. Vertical wing position dictates whether it is a stabilizing element or a destabilizing element. That is why low wing aircraft require more dihedral for the same level of stability when compared to a high wing aircraft. The P47 having weight and a large area centerline above the AC would help make it more responsive laterally.
http://en.wikipedia.org/wiki/Keel_effect In a low wing aircraft, the weight is high acting as destabilizing force. The opposite of a high wing:
http://www.allstar.fiu.edu/aero/axes33.htm
All the best, Crumpp Our Museum glorifies no state, but strives to use these aircraft as a memorial for all lost in war. Our freedom can only be truly appreciated when held in contrast to those who sought to destroy it. Our staff is proudly made up of people from many cultures and religions. Click the photos for details of our projects. "Those who do not remember history are destined to repeat it." - Winston Churchill |
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Sorry bud, Crumpp is right here. I think you're a little out of your league on this one. ---------------- Flying online as nate85 "I can buy a scalpel, that doesn't make me a surgeon." - M_Gunz |
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I have yet to see a single person on this board go through the PUBLISHED paper and actually refute the content with facts. No, there are a lot of posters are very good at taking making snide cheapshots, but when it comes to backing up their opinions, just a little short on content. But that's par for the course. |
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Did you edit the title of the thread to take out "Doctorate Thesis", Buzzsaw? Our Museum glorifies no state, but strives to use these aircraft as a memorial for all lost in war. Our freedom can only be truly appreciated when held in contrast to those who sought to destroy it. Our staff is proudly made up of people from many cultures and religions. Click the photos for details of our projects. "Those who do not remember history are destined to repeat it." - Winston Churchill |
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Yes I did. After acknowledging my mistake earlier, no point in continuing to provide an incorrect title for the thread. Now perhaps that we've gotten past the semantics of titles, maybe you could provide some actual concrete criticisms of the content of the Paper? |
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No,I'm not because I know how useless it is to argue with you and I can't spare the time right now. The only thing I want to add: The vast majority of WW2 figther are all low wing so the "keel" or high wing/low wing argument is not valid. Your argument that having weight high is a good thing is just plain wrong. A P-47 with a LOWER fuselage will have a higher roll acceleration than one with a HIGHER fuselage given the same weight. Moving the weight higher up will when it overcomes the dihederal effect lead to instability and increase the pilots work load to maintain the roll angle which is not the same as agility. Get it? People can read what I wrote and what you wrote on the subject of agility and they can form their own opionion. |
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http://findarticles.com/p/arti..._2/?tag=content;col1 Since the design goal of any fighter is a low static margin I would have to say it does not make any sense to argue that having a large static margin improves roll rate. In fact it is stupid.
All the best, Crumpp Our Museum glorifies no state, but strives to use these aircraft as a memorial for all lost in war. Our freedom can only be truly appreciated when held in contrast to those who sought to destroy it. Our staff is proudly made up of people from many cultures and religions. Click the photos for details of our projects. "Those who do not remember history are destined to repeat it." - Winston Churchill |
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You have that backwards. With a high fuselage, as soon as you roll even a fraction of a degree to either side, more and more of the weight above the centerline starts to create a "toppling moment" in the same direction as the roll. This toppling moment adds to the rolling moment caused by the ailerons and increases the angular acceleration of the roll. This is simple physics. I can draw you a diagram to help explain it if it will help you understand. It's no trouble, let me know.
You're crossing your concepts. Instability is conducive to agility. If something is unstable, it is very easy to change it's orientation/direction/etc. For an agile aircraft, you want to be able to change your attitude and direction easily and quickly. ---------------- Flying online as nate85 "I can buy a scalpel, that doesn't make me a surgeon." - M_Gunz |
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