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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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oldbutnotwise    RE:40' engineering   6/23/2005 4:00:06 AM
i have to dissagree, the merlins when you compair the same model were rated at the same power and had the same maintenance schedule, the US forces tended to leave the services longer than RR recomended so the figures are distorted. the alisons were not reliable in thiere later forms and as such were not the engine of choice. there were many changes made to improve it but it was always a unreiable motor, it was developed beyond its limits and it paid for it. the merlin was made from the same steel as the packard and very little of the engine was steel most was alloy.
 
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oldbutnotwise    RE:40' engineering   6/23/2005 4:04:44 AM
PS re power and wieght this is a quote fron an official record of the P82 Production F-82Es were slow in arriving. The problem was the updated Allison V-1710 engine. The Allison was selected because Packard had to pay Rolls-Royce a $6,000 USD royalty for every V-1650 the company produced. During the war, Rolls Royce had been lenient about license fees, but after the end of the conflict Britain's economy was in the dumps and the royalty fee skyrocketed. There was also the fact that General Motors, which owned Allison, had a 40% share in NAA. GM had not been happy with the Mustang's switch to Merlin power during the war, but Allison production for other aircraft such as the P-38 Lightning was strong and GM had not been in a position to protest. With the war over, aircraft production took a dive and GM wanted to sell more Allisons. There were few other reasons to use the Allison engine, since even the two-stage supercharged Allison V-1710 was inferior in power-to-weight ratio to the Merlin
 
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Shooter    RE:40' engineering   6/24/2005 12:03:12 AM
[quote]With the war over, aircraft production took a dive and GM wanted to sell more Allisons. There were few other reasons to use the Allison engine, since even the two-stage supercharged Allison V-1710 was inferior in power-to-weight ratio to the Merlin [/quote] You are right about the fees and politics. But have made just a few mistakes. GM/Allison did not want to build piston engines at all! They refused to do the work to fit the backfire screens that fixed all of the Allison's problems as demonstraited by Schmued, because they wanted to consintrait on jets. You are sadly mistaken about the power to weight ratios of the two engines! The Allison was lighter than the Merlin at every stage of developement. About 15 KILOGRAMS, to be exact! This was the difference in the main block casting, less the increased weight of the Allisons heavier CON-RODs. In addition the LATE MODEL Allisons made more power than Any service Merlin Engine. 2,300HP to 2,080HP! More power and less weight, makes the Allison supirior in this regard and if GM/Allison had been forced to install the screens it would have been an all around better engine. As to the use of steel in airplane and all other engines, the heaviest parts are all steel! The Crankshaft, Conecting Rods, Camshafts, Rocker Arms, Gears, Accessory drives, PTO shafts, Super Charger Impellors and oil pumps are ALL MADE FROM STEEL. TO PROVE THIS POINT FURTHER, THE FIRST THING DONE TO Racing Merlin engines was to replace the RR CON-RODs with Allison units! The Allison Rod was so much stronger than the RR type that the V-1710 had a 3,200RPM red line, while the RR Merlin had both smaller pistons and a lower Red line of 3,000RPM! Both things that promote less stress on the engine. Or to put it another way, the heavier piston put a porportionaly higher load on the Rods and bearings and the load was porportional to the SQUARE of the RPM! Or to put it in EXACT mathematical terms the Allison rod had to be >20.2% stronger than the RR Merlin rod, just to cope with the added stress! It also had a 400 hour TBO, compaired to RR's 150! And no the TBO's were not the same for US and RR made engines! Your own records at the Duxford museum prove this. IIRC! ( It was so long ago, that I might have the wrong place, but I first noted this while visiting a museum in England!) Those record are also available from the US Air Force Museum in Daton Ohio, For a small fee per page photocopied. I can't remember if it is a quarter or dollar per page and this was ~8-10 years ago. just mwrite to the records division and ask for them and give them your CC# or a signed check.
 
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AussieEngineer    RE:cruise speeds   6/24/2005 2:50:00 AM
Are you just assuming this is the case or do actually have something to back it up.
 
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Shooter    RE:cruise speeds   6/29/2005 12:27:19 AM
[quote]Are you just assuming this is the case or do actually have something to back it up. [/quote] Yes, I do have several things to back this up. First are the maitanence and service records from the piriod. The AF Museum has the origionals on file. You can get coppies if you are willing to pay. I spent 3 weeks one summer 8-10 years ago there, crawling threw the records and making coppies which I still have. (Stored in my basement someplace.) They do not charge as much if you make them yourself. I was going to write a book, but got tired of it and sidetracked into something else! I even interviewed a famious engine builder who built race engines for the Reno Races. I almost bought a Merlin Crankshaft because it looked so neet and I wanted to show it off to my hot rod friends who would know at a glance that I was building a bigger engine than any of them. Six, 6" throws and 120 ponds of polished steel! I have a "Eclectric or Excentric", I don't know which, colection to say the least. I also recomend the various AEROENGINE books that can be had on the internet cheep. There is a world of info out there, all you have to do is look. I also like "Griffon Engined Racers" and "Round Engine Racers" from the moto book serries. lots of good data there.
 
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AussieEngineer    RE:cruise speeds   6/29/2005 9:23:56 AM
I wasn't refering to engine TBO and so on, but rather cruising speeds.
 
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Shooter    RE:cruise speeds   7/3/2005 10:50:37 PM
[quote]I wasn't refering to engine TBO and so on, but rather cruising speeds. [/quote] Sorry! The cruise speeds of the Spitfire were low because of the very substantial wing aria. It provides a low wing loading but a high cruise drag! Cruse speeds for maximum range were between 210 and 220MPH for every single model of the Spitfire! The minimum cruse speed at the same throttle openings in a Mustang was 260MPH! Or 40MPH more! This differance alone made the range 19% greater! When coupled with the greatly increased gas tankage, the Mustang could go over 100% farther than ANY Spit. When you added Drop tanks and the Spits' increased throttle required to maintain the safe cruising speed, the differance was astrimomical! 950 MILES RADIUS to BERLIN compaired to 450 MILES RANGE on a typical Spitfire fighter sweep. ( That's about a 200 mile radius!)
 
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AussieEngineer    RE:cruise speeds   7/4/2005 5:42:14 AM
Most economical cruise speed for the Mk 21 spitfire was 284 mph. I don't have an exact figure for the Mk XIV but it is fair to say that it would be within plus or minus 10 mph of the Mk 21s. Merlin engine spits cruised much slower, 210 mph for pre mk VII and 220 for mk VII and onward.
 
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Shooter    RE:cruise speeds   7/7/2005 1:39:10 AM
[quote]Most economical cruise speed for the Mk 21 spitfire was 284 mph. I don't have an exact figure for the Mk XIV but it is fair to say that it would be within plus or minus 10 mph of the Mk 21s.[/quote] 1. This plane, the Mk-21 spit was a post war bird. 2. My pilots manual, just aquired over the internet, disputes this claim. This was the "Combat Cruise" speed. The most economical speed was 221MPH. AND it was required to reach the published range. 3. The MkXIV had a carbureted engine in ALL of the versions built durring the war and except for the types with extra tankage and reduced guns/ammo could not reach the plackard range. The big tank/two 20MM guns types were faster cruising than the rest! (224MPH) But they still could not attain the plackard range! 4. The manual states that to reach maximum range, it was required to run the engine "FULL LEAN" This is was very hard on the spark plugs and rest of the engine too. 5. In this condition, full lean, it was just as difficult to change throttle settings as the P-38. Go to full rich mixture, adjust the prop pitch, advance the throttle. 6. The laws of aerodynamics are inviolate! You can't get something for nothing! The more wing area and thus lower wing loading, the slower the cruise speed!
 
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AussieEngineer    RE:cruise speeds   7/7/2005 4:59:02 AM
The Mk21 was in service before the end of the war. That conflicts with what I have, unless what you reading is IAS, which would fit perfectly. That is for the Mk.XIV not the Mk.21. Why would it not reach it's stated range, if that were the case wouldn't they have revised the range down? All the range and endurance data I have used are for aircraft that have either C or E armament and standard fuel loads. Not ones with additional tanks and removed weapons. The wing loading of late model spitfires was very close to that for a mustang. Both had similar wing areas and weights. Engine settings were just part of shifting from a cruise setting to a combat one.
 
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