Stability and Control characteristics of the Early Mark Spitfires

[MiG-3U]

Originally Posted by Crumpp

It was actually addressed in the Spitfire Mk V but the longitudinal instability existed from the beginning.

The longitudinal instability existed only if the CoG was in the aft positions as pointed out in the A&AEE report:

(v) Stability - The aircraft is laterally stable at all speeds except in the immediate vicinity of the stall when it is unstable. The aircraft is directionally stable engine 'OFF' and 'ON' at all speeds, but on the climb this is difficult to assess owing to insufficient rudder bias. Longitudinally, the aircraft is stable with centre of gravity forward, but is unstable with centre of gravity normal and aft with engine 'OFF' and 'ON'. Longitudinal stability records are attached

Note that early CoG limits are 5.8" to 8.6" aft the datum point. The revised limits are 5.4" to 7.9" for DeHavilland prop without bob weight (7.5" for Rotol prop).

Originally Posted by Crumpp

They published all the warnings and characteristics of the Longitudinal instability in the Operating Notes.

These warning can be found only from the operating notes of the Spitfire II with Rotol prop (most CoG sensitive combination) before the revised CoG limits and bob weights (which were needed only if CoG was too far aft as was case in the NACA tested Spitfire V).

Originally Posted by Crumpp

It is kind of hard to argue that the NACA was incapable of performing a simple weight and balance when the RAE fixed the same issue and published warnings in the Operating Notes. The truth is they just did not know what the NACA was talking about as the stability and control criteria was classified at the time and Gates had not completed his visit.

1. RAE criticized NACA static longitudinal stability test and for a good reason. Tests were done only at one position of CoG and that position was aft the revised limits.

2. Operational testing and handbooks of the aircraft were made by A&AEE, not by RAE.

Here is the direct link to the document by Gates:

http://aerade.cranfield.ac.uk/ara/dl...rc/rm/2677.pdf

See the page 9. The Spitfire K.9796 was tested at CoG 7" aft the datum point and that is still quite aft given that the range was from 5.4" to 7.9" (revised limits without bobweight and with DeHavilland prop).

Interesting comparison can be made to the Mohawk AX.882 which was tested at CoG 21" behind datum point, rather nose heavy given the range being 19" to 26". And despite forward CoG, the stick force for pull out was about the same as in the case K.9796.

[TomcatViP]

Originally Posted by MiG-3U

Interesting comparison can be made to the Mohawk AX.882 which was tested at CoG 21" behind datum point, rather nose heavy given the range being 19" to 26". And despite forward CoG, the stick force for pull out was about the same as in the case K.9796.

Thx for the link.

The comparison with the Hurri values is more interesting IMOHO

[NZtyphoon]

Here is the NACA Report on Control Characteristics of Spitfire VA specifically stating that the CG of the Spitfire was estimated:



Crumpp can argue black and blue that NACA accurately calculated the cg properly - the report specifically states this was not the case:

Because no accurate drawings of the Spitfire were available, the calculated location of the mean aerodynamic chord may be somewhat in error....The center-of-gravity location with full military load is not known....center-of-gravity location 31.1 inches behind the leading edge of the wing.

and a Spitfire I CG diagram:

Datum point 19.5 in aft of wing leading edge
Maximum aft location of cg was 7.6 in (MiG-3U 7.9 to 8.6 in) aft of datum point, 19.5 in aft of the wing leading edge = 27.1 in aft of leading edge (up to 28.1 in) - NACA calculations = 31.1 in aft of leading edge, enough to make a difference in the longitudinal stability (slightly tail heavy).

[camber]

Thank you for your post, Crumpp

Originally Posted by Crumpp

This thread is going to cover the definable and measure stability and control characteristics of the Spitfire. It is not going to cover opinion outside of stability and control engineers.

Defined like that, any argument is rather moot. If it is defined that the only stability and control engineers at that time were in the US (specifically associated with NACA), and they formulated standards which the Spitfire failed, then the Spitfire failed...as defined in this rather narrow question.

I believe that the work of the pioneering stability and control engineers was interesting and valuable for the future of aviation. But the Spitfire seems to be a bad example to demonstrate that value.

As opposed to the objectively derived flight stability data, the standards that NACA set were subjective (e.g. X inches in control deflection to perform Y). Defensible, intuitively correct, but subjective.

Despite failing these subjective standards, many records exists describing the Spitfire handling as (subjectively) good. Many descriptions exist of Spitfire first flights by novice pilots. Some note the Spitfire pitch issues (e.g "found it easy to black myself out"), but express relief at finding the aircraft benign to fly and push hard.

I realise that you want to exclude all these considerations as being mere anecdotes. But then what it is the argument? I think we all agree that NACA failed the Spitfire on certain aspects of it's flight stability. To determine what that meant, we have to go further.

I think the Spitfire is not a good example of the value of the advances in stability and control. Despite it's rather alarming characteristics in the NACA reports, the young humans sitting inside RAF Spitfires were capable of rapidly adapting to them and making the Spitfire what it was intended to be ..a superlative short range military interceptor.

camber

[Crumpp]

If it is defined that the only stability and control engineers at that time were in the US (specifically associated with NACA), and they formulated standards which the Spitfire failed, then the Spitfire failed...as defined in this rather narrow question.

Gates was not NACA and neither was the RAE when they published the Operating Notes.

Spitfire is not a good example of the value of the advances in stability and control.

It is not meant to be a good example of advances in stability and control. The thread is meant to point out the measureable and definable characteristics so that they can be modeled for the game.

[camber]

Originally Posted by Crumpp

Gates was not NACA and neither was the RAE when they published the Operating Notes.

I read the notes. Do you consider that the warnings against misuse are exceptional for the period, or exceptional compared to later WWII aircraft with better stability characteristics?

Originally Posted by Crumpp

It is not meant to be a good example of advances in stability and control. The thread is meant to point out the measureable and definable characteristics so that they can be modeled for the game.

That is a good idea and worth pursuing, but there is an unfortunate snag. Not only are people using different control hardware to control the same virtual aircraft, they have the option to tune the response between the physical control deflection and the virtual control surface deflection with nonlinear curves. This ability is not under the umbrella of the flight sim software itself. Some people have simulated control surface loading (FFB), some do not, and again the user can quietly do their own stability modifications to make their plane handle differently to what the devs attempt to program.

camber

[CaptainDoggles]

Originally Posted by camber

That is a good idea and worth pursuing, but there is an unfortunate snag. Not only are people using different control hardware to control the same virtual aircraft, they have the option to tune the response between the physical control deflection and the virtual control surface deflection with nonlinear curves. This ability is not under the umbrella of the flight sim software itself. Some people have simulated control surface loading (FFB), some do not, and again the user can quietly do their own stability modifications to make their plane handle differently to what the devs attempt to program.

Yes and no. The user can dampen their inputs to the aircraft (e.g. very flat curve around the center), but the user cannot affect the aircraft's response to said inputs. If the aircraft has a tendency to diverge from equilibrium, then it will still do so regardless of what the user's stick curve looks like. A high-wing monoplane like the Storch will still be very stable in the roll axis due to the keel effect. An aircraft with a lot of anhedral is still going to be largely unstable about the roll axis.

Keeping in mind of course that real control columns have a much greater throw than your average consumer-level HOTAS.

[NZtyphoon]

Originally Posted by Crumpp

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

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

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:

Originally Posted by Crumpp

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.

[CaptainDoggles]

Originally Posted by NZtyphoon

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.

[ATAG_Dutch]

Originally Posted by Crumpp

The early mark Spitfire was a excellent fighter.

He should've stopped there, for all this thread's been worth.