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Subject: How to fix the design defects of the Spitfire airplane of WW-II.
Shooter    5/26/2005 5:12:16 PM
Given 20-20 hind sight, It is easy to see where R.M. went wrong with the Spitfire! The following list of items is my idea of how they should have done it, IF THEY HAD READ ANY OF THE COMMON TEXTS instead of designing a newer SPAD for the last war! 1. Start with the late Seafire or even better the Martin Baker MB-5! they have contra props and wide track gear. The MB-5 also has a much higher LOS out of the pit forward. This is also one of the Spits larger problems. 2. Change the shape/planform of the wing and eppinage from eliptical to trapiziodal. The eliptical surfaces caused the construction time and cost of the Spitfire to be more than double that of the Mustang and almost as much as the P-38. 3. Reduce the wing cord and thus area by 35-40%! This reduction in surface aria will increase the cruising speed substantialy! This is probably the single biggest defect in the design. The change in aspect ratio will also help fuel ecconomy! 4. To compensate for the increased landing and take off speeds install triple slotted fowler flaps with a long hinge extension. This gives a huge increase in wing area and changes the camber for supirior "DOG FIGHT" ability, should you ever need it! ( because the pilot really screwed up!) At full extension and deflection, they would reduce the landing speed by 11~13MPH? (Slip Stick calcs!) 5. Remove the wing mounted radiators and install a body duct like the P-51 or MB-5! This one change would add ~35MPH to the plane? 6. use the single stage griphon engine and install a "Turbo-charger" like the P-38 and Most American Bombers had. This would increase power and save weight, both significant contributers to performance. 7. Remove the guns from the wings! This would lower the polar moment of rotation and give the plane snappier rates of roll! It also makes room for "wet wings" with much more fuel. A chronic Spit problem. It also fixes the Spit's gunnery problem of designed in dispersion! 8. Install the Gun(s) in the nose! Either fireing threw the prop boss/hub or on either side 180 degrees either side of the prop CL. This fixes the afore mentioned dispersion problem. One bigger gun between the cilinder banks or upto four 20MMs beside the engine or both, depending on what your mission needs were! 9. Make a new gun based on the American 28MM or 1.1" Naval AA ammo! This shell was particuarly destructive, had a very high MV and BC and was all ready in service. A re-engineered copy of the existing gun to reduce weight and increase RoF is a faily simple task. Pay the Americans for it if British spring technology is not up to the task! it also frees up much needed production capasity for other things. 10. Design a new drawn steel "Mine" shell for the above gun! Spend the money to load it with RDX instead of the TNT used for the first 4/5s of the war. 11. Pay North American or Lockheed to design it for you, since the Supermarine staff was to tied up fixing the origional spitfire design to get it done any time soon. Did I miss anything?
 
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larryjcr    RE:Extra fuel spitfire   12/16/2005 11:14:04 AM
As I mentioned before, the fuel mods to the PR Spits were mostly not applicable to fighters. Those you list involve removal of all armament and most if not all armor.
 
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larryjcr    RE:Mach Limits   12/16/2005 11:15:32 AM
Appearantly using airspeed indicators. At high subsonic Ms these instuments are not accurate due to shock effects forming withing the pilot tube.
 
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MustangFlyer    RE:Mach Limits   12/16/2005 4:25:56 PM
I agree, which is why they used a range of instruments and over several months of testing. The information was combined from all the instruments, including the trailing pitot comb. There was a 0.94 recorded once (by another spitfire, 1952 - details in wikipedia) but it was discounted because of that reason. I'd reasonably suspect that the forward pitot was non-standard. Anyone able to get to the UKs public record Office to chase this up, it's facinating. Also there must have been comparable NACA tests as well. This link http://www.spitfireperformance.com/sd2011.jpg shows a typical dive profile and results (in this case) up to 0.85. is worth a look , its got great stuff, on Mustangs & Tempests as well. Quoted from wikipedia. "From: Spitfire - A Test Pilot’s Story - Arrow Books (I must get that book. ) "That any operational aircraft off the production line, cannons sprouting from its wings and warts and all, could readily be controlled at this speed when the early jet aircraft such as Meteors, Vampires, P-80s, etc could not, was certainly extraordinary" —Jeffrey Quill", Test Pilot (he tested every Spitfire Mk). Source: http://en.wikipedia.org/wiki/Supermarine_Spitfire
 
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larryjcr    RE:Mach Limits   12/16/2005 5:18:30 PM
NACA did a lot of similar tests, and ultimately the result was the Machmeter, because it was never possible to get accurate readings from airspeed indicators which worked on air pressure. They got away from trying to measure IAS at all, measuring Mach by its own effects.
 
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larryjcr    RE:Mach Limits   12/16/2005 5:22:54 PM
I would be vary interested in the mechanics of pitch control for any WW2 a/c. As the Spitfire (like any a/c of the day) had a fixed horizontal stabilizer, buffeting and 'tuck' were unavoidable once compressibility took hold and the airflow from the wind trailing edge changed angle. As I mentioned in an earlier post, the 'all flying' hoizonal stabilator was the answer, becuase it could tip to meet the new flow properly.
 
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MustangFlyer    RE:Mach Limits   12/16/2005 7:18:37 PM
Though the wings were critical the total aerodynamic package was important. Any asymetric effects (which affected late model Me 109s) could eaily cause yaw changes that overstressed the airframe. The size shape and relationship of elevators to the wings also would affect control capability. A good wing with poor elevators would not be very nice at 500+mph! Response of control surfaces to high (not even transonic) speeds were also important. If the controls stiffened up at high speed anyway then moving into the transonic region would have been very hairy. The Spit had very light elevator controls and small control could be maintained, enough to pull out of a dive. I think I said before that Closterman actually used his elevator trim control to pull out of his chase. I can speak from personal experience how hard it was to control at high speeds, in the Mustang in a 400mph (trimmed for level flight) I was using both hands and all my strength to hold it. I got this from http://home.att.net/~historyzone/Seversky-Republic4.html "Testing showed that the Thunderbolt could be flown out of a terminal velocity dive as it descended into warmer air at lower altitudes. This is because as the plane continues down, the relative speed of sound goes up. Eventually, the aircraft’s Mach number will drop (although its actual airspeed does not) and the shock wave will dissipate, allowing the pilot to regain control again. Pilots were instructed to pull off the throttle, and avoid using too much up elevator trim. Too much trim, or too much back pressure on the stick could over-stress the airframe when the fighter began to respond to control inputs. Pilots who had flown the P-47 into compressibility came away with bruises to verify their adventure. The Thunderbolt’s ailerons would flutter as it exceeded its critical Mach limits, causing the stick to move violently from side to side; pummeling the inside of the pilot’s thighs black and blue." From a pilots combat point of view the Spit and Mustang were probabaly preferable, The Spit could go to the limt and if you were (very) careful you could get out of it, the Mustang apparnetly started to porpise, warning a pilot that they were at the limit, giving them a chance to back off. Very hairy in a Me109, P47 or P38 (in the latter 2 you would be praying that the dive brakes had been serviced properly). Must have had an effect on pilot confidence, by late in the war the performance levels were so high that having the confidence to push your plane to the limit could often be a deciding factor. I suspect the Tempest was also very good, pilot accounts seem to show no lack of confidence in fighting at the 500+ mph region at any height, though I haven't read of any formal mach tests (yet).
 
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larryjcr    RE:Mach Limits   12/17/2005 4:33:55 AM
Your sites were very interesting. The dive profile is internally consistant, but that still leaves the question of how the Spitfire got a dispensation from the laws of physics that effected all other a/c of the period. Lightness of the controls in compressibility shouldn't have any effect on recovery. Generating higher AoA while Mach shock still effected the wings would only make things worse. The dive recovery flaps WERE NOT dive brakes. They had very little speed reduction effect. That wasn't the purpose. They increased the air pressure under the wing, providing a 'lift' effect to counteract the loss of lift caused by Mach shock on the upper surface. At that point, some upward AoA could take effect, if you could get it fighting the 'tuck'. The 'tuck' resulted from upward deflection of the airstream striking the horizontal tail surface from below. This also caused serious tail buffeting. I'm aware of the 'diving into denser air' solution. It was how most P38s and P47s got out before the recovery flaps. The structural failures were, as your post mentions, the result of overstressing due to excessive upward elevator. Probably the very positive pitch control of the P38 was a problem here. Remember, what got us started on this whole subject was the claim that tails fell off of P38s in dives because of structural weakness.
 
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AussieEngineer    RE:Mach Limits   12/17/2005 6:53:53 AM
The spitfire wing must have simply had a higher critical mach number. It still entered compressibility, just at higher speeds than it's contemporaries. I'm sure the lightness of it's controls would have made little difference once it actually reached compressibility speeds.
 
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larryjcr    RE:Mach Limits   12/17/2005 11:36:10 PM
It still seems hard to believe that the Mcr for the Spit could be higher than that of other a/c of the same era, including early jets by something like one tenth of M. An Mcr of .85 would be very respectable for any transonic or supersonic a/c. It would be superior to the P80, and the people who designed that had been hip deep in Mach studies for more than two years and probably knew more about it than anyone (except maybe the Germans) at the time.
 
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MustangFlyer    RE:Mach Limits   12/18/2005 12:39:19 AM
I agree, quite remarkable. According to the aerodynamcist Sir Morien Morgan the RAF had nothing that could out dive it until the F-86 Sabre. As he said Mitchell's decision on the wing in 1935 was "bold and inspired". It was a very close run thing, a little thinner and it would have been too weak. So it was right at the technological limits for the time and took a while to master manufacturing. Got it sorted out though (just in time), after all they made 22,000 of them! Interesting reading about the design process, they came to the elipitical wing for the same reasons that Hawker later did creating the Tempest, needed room for guns (6 in the orginal RAF spec and then changed to 8, very late in the design process). The earlier wing design was straight, after a very early gull wing design that was rejected by the RAF.
 
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