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FM/DM threads Everything about FM/DM in CoD

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  #1  
Old 05-06-2011, 05:27 PM
TomcatViP TomcatViP is offline
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Did I say that I luve yo ? (quoting AB ) i am so glad to read you.

let's go a step behond if you don't mind :
The elliptical theory is a misunderstanding of a Math tools applied to aero. It does not hve a real bckgrd unless with biased assumptions.

The fact is (as stated by Vip above) that thickness ratio and the wonderful Merlin made the spit what it was as a real performer. And the all genie of R. Mitchell was to build the Spit as a weapon platform that any average pilot could use and perform where German's Nazi kept arguing with their elitist theory (the UberMensh bulls***etc...). The result was that the 109 was harder to perform than the Spit or the Hurri....

As a side note lets say that it is sad that the elliptical wing was made as a brand mark for vick-Sup. IMHO it leads to the rapid demise of the Supermarine design bureau as soon as the war ended (mid 50's).

It is also funny to see how history can repeat itself nowadays in Eu

But this is way out of topic

~S!
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Old 05-06-2011, 08:42 PM
Sternjaeger II Sternjaeger II is offline
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Viper, you know that I respect you because of your factual approach, and yes, there are a lot of misconceptions about the Spit wing design, but according to a gentleman in the UK who owns and regularly flies his Spit MkIX, his Hurri IIb and P-51D, the maneuverability of the Spit is unparalleled, simply because its wing behaves and performs better, albeit being more prone to torque along its span and flex ("the whole plane feeling is of extreme agility and flimsiness, it was obviously an aeroplane that has been based on a sport design and not conceived for war").

As for wing sturdiness, I have walked to the wingtip of a Mustang without the plane making a single movement, but you wouldn't be able to do the same on a Spitfire. A cannon strike on the single spar Spit wing is more likely to do more damage and above all weaken the structure enough to cause a fracture than on a robust Mustang double spar.

Let's not forget that a Mustang is almost twice the weight of a Spitfire!
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Old 05-06-2011, 10:16 PM
41Sqn_Stormcrow
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Walking to the wingtip without making move the plane (Mustang) is barely an indicator of the wing strength. I'd say it didn't move because the landing gear is set so much more apart from each other in a P51 than in a Spit that made the difference here.

One thing is fact which in turn is exploited today on purpose for modern fighter design but which also extends to other domains:

The less stable a device is the more prone is it to change its state. This principle can be exploited in a beneficial way. If you make something instable it is more easier to move around. For instance designs like the Eurofighter is instable and only kept on course because of computer software. This inherent instability allows to be more manoeuverable than a stable plane because anythings stable will tend to maintain its current status and is highly unwilling to assume another state (that is another attitude or flight direction).

So if the Spit is as manoeuverable it is likely on the edge of stability and thus somewhat nerveous.
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Old 05-06-2011, 10:24 PM
617Squadron 617Squadron is offline
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^^^
This.

A lot of the veteran Spitfire pilot interviews have them talking about "strapping a Spitfire on and becoming part of the machine", however, they all comment that it wasn't an easy aircraft to fly for the inexperienced and it took a lot of hours to become fully proficient at throwing it around the sky.

More than a few Spitfires were written off or damaged as a result of poor landings by inexperienced pilots, usually wingtip stalls during or nose-ups after landing.

Let's not get into a peeing up the wall contest as to how much we each know about WW2 aircraft, eh? I'm beginning to think that I need a check shirt, a top pocket full of pens and glasses two inches thick to come on here....
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Old 05-08-2011, 06:09 PM
Sternjaeger II Sternjaeger II is offline
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Quote:
Originally Posted by 41Sqn_Stormcrow View Post
Walking to the wingtip without making move the plane (Mustang) is barely an indicator of the wing strength. I'd say it didn't move because the landing gear is set so much more apart from each other in a P51 than in a Spit that made the difference here.
If you ever get a chance get to the wingtip of a Spit, rock its wing and see what happens, then do the same on a Mustang (if you can grab the tip that is, it's SO thick!). The whole impression you get from being around a Spitfire that it was designed with (mostly wrong) performance in mind, not with sturdiness as main concern.

Quote:
One thing is fact which in turn is exploited today on purpose for modern fighter design but which also extends to other domains:

The less stable a device is the more prone is it to change its state. This principle can be exploited in a beneficial way. If you make something instable it is more easier to move around. For instance designs like the Eurofighter is instable and only kept on course because of computer software. This inherent instability allows to be more manoeuverable than a stable plane because anythings stable will tend to maintain its current status and is highly unwilling to assume another state (that is another attitude or flight direction).

So if the Spit is as manoeuverable it is likely on the edge of stability and thus somewhat nerveous.
that is true with designs which are designed to behave as such. The Spit wing was designed in a time when transonic and supersonic envelopes hadn't been fully explored yet, and its flexibility could prove fatal if stressed under sustained heavy G loads.

Some years ago I had the chance to speak to a gentleman who fought first with Macchi 202 and then with Bf109s for the Regia Aeronautica. He met Spitfires over Northern Africa and he said that in two separate occasions saw two Spits diving to chase Macchis only to lose controls under what seemed to be compressibility issues of the tail surfaces.
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Old 05-09-2011, 06:39 PM
TomcatViP TomcatViP is offline
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Compressibility is not really affecting the tail surface (even if it does). In fact most comments on this phenomena are describing the formation of shocks waves on the wing surface that affect the pitching moment. The pitching moment is so great that the tail surface can't compensate for it... Hence the horrific impression to pull the stick without effect. The immediate solution is to lower the Mach number.

yeah yeah ... I know I am "marking" the wall myself here too but ... this thread is full of info for anyone (e.g : a reminder is a valid info)... Let's step fowrd pass that ugly wall

Note :
1. the Stuka's pilot impression is really good add.
2. Closterman's feelings abt the Spit as one of the top scoring ace of the ETO shld be taken into account more seriously. And even if it does not affect the Spitfire MkI it's an important point of view regarding the Spitfire capabilities vs vs the assumptions made here that tends to extrapolate perfs out from charts of latter variants.
3.the pitching moment is negative on most airfoil section

Last edited by TomcatViP; 05-09-2011 at 07:28 PM.
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  #7  
Old 05-10-2011, 11:20 AM
Sternjaeger II Sternjaeger II is offline
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Quote:
Originally Posted by TomcatViP View Post
Compressibility is not really affecting the tail surface (even if it does).
LOL I love you man

Quote:
In fact most comments on this phenomena are describing the formation of shocks waves on the wing surface that affect the pitching moment. The pitching moment is so great that the tail surface can't compensate for it... Hence the horrific impression to pull the stick without effect. The immediate solution is to lower the Mach number.

yeah yeah ... I know I am "marking" the wall myself here too but ... this thread is full of info for anyone (e.g : a reminder is a valid info)... Let's step fowrd pass that ugly wall
I always dozed during my theory lessons, but if memory serves compressibility on tail surfaces is the creation of shock waves on the leading edge, which creates a void that makes the control surfaces ineffective because they're outside of the airstream (Viper might give a more educated explanation of it).
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Old 05-12-2011, 03:22 PM
TomcatViP TomcatViP is offline
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Quote:
Originally Posted by Sternjaeger II View Post
LOL I love you man



I always dozed during my theory lessons, but if memory serves compressibility on tail surfaces is the creation of shock waves on the leading edge, which creates a void that makes the control surfaces ineffective because they're outside of the airstream (Viper might give a more educated explanation of it).
No no no..

The tail plane is affected too but this is not the primary prob. In fact it impact the transonic regime by raising the overall drag of the plane as a consequence of the mach shock on the wing itself - e.g : the compressibility - that alrdy affect the plane with a nose down torque.

the thiner is the wing (thickness/cord) , the latter does this occur due to overall smaller camber ratio.
The easiest solution found at the time was to use symmetrical wing section.

Once the wing mach shock wave has been addressed then the tail shock became a problem you are right (take a look to the X1 story)

~S

Last edited by TomcatViP; 05-12-2011 at 03:25 PM.
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