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FM/DM threads Everything about FM/DM in CoD

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  #101  
Old 07-18-2012, 02:50 PM
NZtyphoon NZtyphoon is offline
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Originally Posted by Crumpp View Post
Amoung the Western Front warring powers during World War II, only two nations had measurable and definable stability and control standards. Stability and control was a young science. Airplanes had simply been two slow and light previously. The forces were small enough such that there was little need. The two nation were the United States and Germany.
Slightly OT, but important to this thread; Unfortunately Crumpp's "historical analysis" is seriously flawed - the British, with the likes of William Lanchester, were pioneers in laying down scientific principles for aeronautics, as shown by this extract: http://rsnr.royalsocietypublishing.o...t/61/1/39.full

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The eponymous university of a vibrant industrial city was an appropriate institution for studies in higher engineering; his father counselled Ludwig to go to Manchester. At the time, English aeronautics was transforming itself from a fledgling, essentially empirical, science to one grounded on firmer principles, taking forward the perceptive concepts of powered aeroplane flight set down by Sir George Cayley a century earlier. Frederick William Lanchester (FRS 1922), who disapproved of trial and error methods, had produced his theoretical calculations for the lift acting on an aircraft wing. His book Aerodynamics was the standard text to be consulted on the subject.

The university had not long been formed from the incorporation of two higher education establishments, Owen's College and Victoria University. It inherited a brilliant academic staff. The Professor of Mathematics was Horace (later Sir Horace) Lamb FRS.7 His classic work Hydrodynamics underpinned the solution of numerous problems arising from the dynamics of an aircraft in flight. A lecturer under Lamb was J. E. Littlewood (FRS 1916), who after spending an unhappy three years at Manchester (1907–10) returned to Cambridge.8 Wittgenstein attended Littlewood's lectures and eventually met up with him again at Cambridge on equal professorial terms.

Another notable at Manchester had been Osborne Reynolds FRS, a longstanding Professor of Engineering who retired a few years before Wittgenstein's arrival but whose work on kinematic viscosity resulted in the Reynolds number, a parameter of vital importance with regard to the onset of turbulent flow within the boundary layer on the surface of an aerofoil. Reynolds's successor, Ernest Petavel FRS, a distinguished physicist, actually learned to fly; in consequence he underwent a severe flying accident.9 In due course he took up the post of Director of the National Physical Laboratory (NPL), an organization also becoming involved with aviation activities, for instance constructing wind tunnels to test models.5 In 1908 the contributions of these Manchester academics to aeronautics were yet to be fully realized.
I would have though that someone who is supposed to be a graduate of aeronautical engineering would have known of William Lanchester:http://www.guggenheimmedal.org/Pages...aspx?Year=1931

Quote:
Aeronautical science to Lanchester was always a spare-time recreation. One of his earliest contributions was an analysis of the dynamical stability of airplane flight, made in 1897, some years before there were any airplanes. So penetrating was the insight shown that this analysis served as the inspiration and foundation for the later work of Bryan, Bairstow, Hunsaker and many others, who were able to apply Lanchester’s precepts while using modern wind tunnels.

He was also the first to propound the vortex theory of flight and its engineering application to the design of airplanes, which was followed up later by Prandtl and others. The vortex theory was the basis of a paper read by Lanchester before the Birmingham National History and Philosophical Society in 1894, and a further paper submitted to the Physical Society of London in 1897.

Lanchester was one of the original members of the Aeronautical Research Com*mittee under the chairmanship of Lord Rayleigh. In 1926 he gave the Wilbur Wright Memorial Lecture on the subject: “Sustentation in Flight.” He died March 8, 1946, at the age of 77.
and also recognised the role of the likes of the Royal Aircraft factory (later Royal Aircraft Establishment) in laying down the principles of scientific analysis later used by NACA; instead we have these types of comments:

Quote:
Originally Posted by Crumpp View Post
The RAE did not have stability and control standards. However, the RAE did agree with the NACA even if they did not know it.
which are complete nonsense. This type of blinkered ignorance about the role of the British, and the Royal Aircraft Factory and RAE, in laying down the principles of scientific aeronautical analysis beggers belief, and Crumpp's idea that only the USA and Germany "had measurable and definable stability and control standards" during WW2 is farcical.

Last edited by NZtyphoon; 07-18-2012 at 03:09 PM.
  #102  
Old 07-18-2012, 03:05 PM
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Great document Lane!!

It gives us a measurement of the divergence and the slope of the Cm increase.

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Exactly, one of the quirks of the Spit was the extreme easy elevator
Not only that, it is unstable. That means your coefficient of moment increases each cycle instead of decreasing.

So if you pull a 6 G turn and did nothing except hold the stick fixed, the next oscillation will exceed 6G and continue to increase with each cycle until the airframe is destroyed.

That is the reason why "flick" maneuvers were not allowed in it.

Let's summarize the behavior that occur at normal and aft CG positions and categorize them to be implemented in the game. Then we can build a list for the bug tracker. These are all at NORMAL CG. If the game models a shifting CG then they increase in severity at aft CG positions.

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The take away is:

1. The large accelerations change for very little elevator movement.
2. The very rapid rate at which the pilot was able to load the airframe to 5G's.
3. The equally rapid rate at which the airframe unloaded down to 2G's when the pre-stall buffet was encountered. In 1 second, the aircraft went from 5G's to 2G's due to buffet losses. This means a rapid decay in turn rate resulted.
4. The violence of the pre-stall buffet combined with the longitudinal stability and control caused large fluctuations in the accelerations on the aircraft.
5. The violent accelerated stall behavior resulting in spin/loss of height
Quote:
1. The large accelerations change for very little elevator movement.
1. The Spitfire should be twitchy and unstable gun platform. IIRC, in IL2, people used to complain about the "twitchy" behavior or the Corsair and P-51's so I am sure it is within the games engine to model a twitchy airplane.

It should take very careful and small stick movements to get the gun sight on target. That means a Spitfire pilot will require more skill to hit a maneuvering target than he would need in a stable platform such as the Hurricane.

2. Above Va, large or abrupt elevator control can more easily exceed the airframe limitations of 6G for damage. Currently, it is impossible to stall the Spitfire in a turn or a dive. The reality is it requires careful flying so as NOT to induce an accelerated stall or exceed the airframe limitations.

3. In the turn, the violent buffet is a double edged sword. There is no such thing as a free lunch especially in physics. In the NACA measured results, encountering the buffet represents a change in available angle of bank. The airplane goes from 78.5 degrees of bank to 60 degrees of bank in one second.

****5G @ 147.73KIAS:

ROT = 1091*tan(78.5) divided by 147.73 KIAS = 36.2 degrees a second

****2G @ 141.647 KIAS:

ROT = 1091*tan(60) divided by 141.647 = 13.34 degrees a second

As a quick ballpark using IAS to get an idea of the scope of the effect on turn performance, we see the rate of turn drop from 36.2 degrees a second to 13.34 degrees a second. That means our time to complete a 360 degree turn changes from 10 seconds to 27 seconds!!!

As the Operating Notes relate, you do not want to turn any airplane in the buffet. Energy cannot be created or destroyed, all the energy that was being used to achieve an instantaneous performance rate of turn of 36.2 degrees a second from our ballpark went to warn the pilot of an impending stall, taking the aircraft right down well inside its sustainable performance envelope of 13.34 degrees a second.

The longitudinal stability characteristics of the Spitfire requires skilled flying to achieve a maximum performance turn. In a stable airplane, the pilot would have a much easier time keeping the aircraft at the maximum rate of turn velocity and a less violent buffet would have subsequently reduced effects on the turn performance.

4. Below Va, the Longitudinal instability of the Spitfire make it more difficult for the average pilot to prevent an acelerated stall or overcontrol the aircraft by pulling deeper into the buffet zone.

Quote:
I think the fact that you have to return the stick almost to neutral after entering a high g turn (>3 g) to prevent oversteering in a Spitfire should be in game, also the very sensible elevator with large reaction for small inputs and the roll rate as documented.
This will be a problem for ham-handed pilots, but a delight for the virtuosos, as it was in RL.
I don't see that as "porking" the Spit further, but to give it the characteristics that made it famous.
Every aircraft in CoD should reflect its pro's and con's as they where documented then.
Exactly. That is our goal to recreate the flying qualities of all of these aircraft.

In this thread we have focused primarily on the Longitudinal stability. Most of the Spitfires issues stem from that.

For example, the heavy lateral control forces would not be an issue if the control forces were equal on all axes. The control harmony was poor in the Spitfire and Gimpy raises a good point:

Quote:
well personally I would expect a much lower Roll rate at speed, and a very sensitive Unbalanced Elevator (unbalanced meaning it needs much more roll input than pitch).
The pilots ability to apply lateral control would be reduced by the longitudinal control characteristics.


*****Not a silly argument on actual turn performance, just a quick ballpark so readers understand the importance and general effect of encountering the buffet on turn performance.
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Last edited by Crumpp; 07-18-2012 at 03:09 PM.
  #103  
Old 07-18-2012, 03:22 PM
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Quote:
the British, with the likes of William Lanchester, were pioneers in laying down scientific principles for aeronautics,


You are confused about this whole subject. Of course, there were some brilliant British engineers.

What does he have to with an adopted measureable standard for stability and control????

You understand, an engineer in the United States or German designing a fighter could go look to see the measured characteristics that he must meet.

Gates was the British engineer who tried to shoulder that task of getting the Air Ministry to adopt a measureable standard. He eventually achieved it in the post war.
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  #104  
Old 07-18-2012, 03:37 PM
taildraggernut taildraggernut is offline
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So why was the Mustang III considered longitudinaly unstable too?

Last edited by taildraggernut; 07-19-2012 at 09:05 AM.
  #105  
Old 07-18-2012, 05:28 PM
winny winny is offline
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So, now all we need is the same data for a MK I and II.
Because, correct me if I'm wrong, they didn't test them at NACA.

I'm pretty sure that if I came on here saying that the 109 E was wrong, and used an F or G's data I'd get laughed out of here. Especially by you.

So I'd like some hard data on the same phenomenon in I's and II's, please.

Thanks.

Edit: and bear in mind that the spitfire in lanes docs is around 300lb lighter than a spit in BoB trim.

Last edited by winny; 07-18-2012 at 05:31 PM.
  #106  
Old 07-18-2012, 05:38 PM
JtD JtD is offline
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It was designed for a load factor of 10, not 6. Calculation showed wing to be the weakest point, it was tested and met specification. Specification was changed to 12 for later marks.

Last edited by JtD; 07-18-2012 at 05:41 PM.
  #107  
Old 07-18-2012, 05:54 PM
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Quote:
Originally Posted by NZtyphoon View Post
Slightly OT, but important to this thread; Unfortunately Crumpp's "historical analysis" is seriously flawed - the British, with the likes of William Lanchester, were pioneers in laying down scientific principles for aeronautics, as shown by this extract: http://rsnr.royalsocietypublishing.o...t/61/1/39.full

...

I would have though that someone who is supposed to be a graduate of aeronautical engineering would have known of William Lanchester:http://www.guggenheimmedal.org/Pages...aspx?Year=1931
This is being disingenuous; your argument is flawed. The fact that someone didn't mention Lanchester when discussing a subject that was mostly unrelated to him doesn't mean that that person has never heard of Lanchester.
  #108  
Old 07-18-2012, 08:06 PM
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Quote:
Originally Posted by winny View Post
So, now all we need is the same data for a MK I and II.
Because, correct me if I'm wrong, they didn't test them at NACA.

I'm pretty sure that if I came on here saying that the 109 E was wrong, and used an F or G's data I'd get laughed out of here. Especially by you.

So I'd like some hard data on the same phenomenon in I's and II's, please.

Thanks.

Edit: and bear in mind that the spitfire in lanes docs is around 300lb lighter than a spit in BoB trim.
The airframe of the Mk Va is similar to the Mk I and II
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  #109  
Old 07-18-2012, 08:15 PM
taildraggernut taildraggernut is offline
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Quote:
Originally Posted by robtek View Post
The airframe of the Mk Va is similar to the Mk I and II
is similar a good enough benchmark? even the Mk9 airframe was similar.

I think Winny's point is valid, would it be accepted if the aircraft being analysed was a 109?
  #110  
Old 07-18-2012, 09:30 PM
taildraggernut taildraggernut is offline
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Quote:
Originally Posted by Crumpp View Post
That is the reason why "flick" maneuvers were not allowed in it.
Flick manouvres were permitted in the Mk2 (from pilots' notes) at slow speeds, there are several other aircraft including the P-40 which were prohibited from 'flick' rolls and intentional spinning.
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