Nobody is "attacking the Spitfire". That statement is ridicules and paranoid, deserving of a pointy tin foil hat.
The Longitudinal stability and control of the Spitfire is well documented.
YES, it can kill the pilot and that is why it is "unacceptable". It did kill pilots.
Is the Spitfire a dangerous aircraft that is not airworthy? NONSENSE, of course it is an airworthy aircraft and one the great fighter designs of WWII.
The limitations of that airworthiness are published in the Pilot's Operating Notes.
The arguments over stability and control do not make anybody look intelligent when they don't know what it means. I don't say that to be a jerk, know-it-all, or
I will try to explain the issue with the Spitfire so that it makes more sense.
All aircraft motion is oscillary. There are two categories of oscillations, long period and short. Short period oscillation represents a wide variation in Angle of Attack. Short period oscillation must be dampened in static stability and disappear without pilot input for the aircraft to be airworthy. Long Period oscillation is considered to have a constant Angle of Attack. It really does not but the variation is minor.
The Spitfire's stability issue was with long period oscillation in the longitudinal axis. These are generally not a big deal and the pilot controls them.
Static, Dynamic, stick fixed, and stick free are all different things.
First let's discuss some general stability terms:
Static Stability - The initial tendency of the aircraft movement when displaced. It is the first thing the airplane will do. If it initially moves opposite of the displacement, it has positive static stability. If it moves farther in the direction of displacement, it has negative static stability. If it does not move farther away or attempt to return from its equilibrium position, it has neutral static stability.
Dynamic Stability is the movement of the aircraft with respect to time. If it is disturbed from it equilibrium point and the maximum displacement decreases with time, it has positive Dynamic stability. If it increases with time, it has negative Dynamic stability. If it remains constant with time, the aircraft has neutral dynamic stability.
An aircraft must have positive static stability. The dynamic stability can be positive to be acceptable. The dynamic stability cannot be negative as oscillations over time are divergent or neutral as . That can cause the pilot to lose control or if coupled with accelerations on other axis can destroy the aircraft.
That coupling with yaw-wise pitch up acceleration is what can cause the Spitfire to break apart in the spin.
Control terms:
Stick fixed and stick free are two of the most abused terms in aviation when discussing stability and control. They are control terms and NOT references to stability.
Stick fixed is simply the pilot is in the cockpit, the controls are fixed so that they do not move, and the
mechanical reversible linkage has mass as well as friction.
Stick free is the controls are free to move and the
mechanical linkage has no mass or friction.
Now to the Spitfire early marks....the bold statements are explanations for the NACA language in the Conclusions found in "Measurements of the Flying Qualities of a Supermarine Spitfire Mk VA Airplane."
1. The short period longitudinal oscillation was satisfactorily dampened in all conditions of flight.
The aircraft is positively statically stable and airworthy
2. In all flight conditions the stick fixed longitudinal stability is either neutral or unstable, and therefore failed to meet acceptable standards.
The longitudinal dynamic stability is either neutral or negative. This means over time, the long period oscillations on the longitudinal axis stay the same or grow larger. It is unacceptable and is the stability issue. It is a dynamic stability issue. The requirement for a stable stick force gradient was met in all conditions of flight except for the condition with flaps down, power on.
This describes how the stick forces change as we move away from the trim speed. The Spitfire's stick forces remained on a stable gradient except when the flaps were down and power on. In this condition, the stick forces would change noticeably as we moved farther from trim speed.
3. The stick force gradient in maneuvers was 5.0 pounds per G. The requirement for a force gradient of less than 6lbs per G was therefore satisfied.
Some pilots in the NACA felt it was too light but that is opinion. Measurements reveal it is within standards.
4. The stick motion required to stall in maneuvers was 3/4 inch. This value is much less than the 4 inch stick travel recommended for satisfactory flying qualities.
The Spitfire's elevator required a "two finger" touch. 3/4 of an inch travel to run the gamut of your useable Angle of Attack is not much at all. This is why we see the Operating Notes advising the pilot to brace his elbows on the cockpit sides to steady his hand when maneuvering. Combined with light stick forces, neutral or negative dynamic stability would make the Spitfire squirrely in any kind of chop or gust conditions. The control characteristics aggravate the stability characteristics. Only having 3/4 of an inch stick travel to work with means the pilot will have trouble in any unexpected or violent maneuver being precise. It makes the aircraft more vulnerable to such things as Pilot Induced Oscillations.
http://en.wikipedia.org/wiki/Pilot-induced_oscillation
The rest of the conclusions are normal with the exception of trim characteristics. Here the longitudinal characteristics shine and the aircraft required little trim input from changes in power or configuration.
Ok, so when is all this unacceptable and badness mean in practical terms?
Three common conditions the Longitudinal stability is dangerous are:
1. Steep turns with the gun ports open...
Stall is violent in the condition and without immediate application of the correct control input will result in a spin. We have already covered why spins can destroy the airframe in the Spitfire.
2. High speed maneuvering - Recovery from a dive or hard maneuvering above Va. Any airplane will break and even destroy itself at full control deflections above Va. It is easier to inadvertently make a full elevator control deflection in the Spitfire above Va.
3. Spins...already covered..see Operating Notes and why deliberate spins are prohibited. The Spitfire recovers from a spin very quickly relative to many WWII aircraft if accidently spun. IIRC, it loses about 2000 feet between input and recovery so after pull out you only need the recommended 4000 to 6000 feet altitude. Many WWII aircraft lost anywhere from 4000 to 6000 feet just in recovery resulting in spins being prohibited below 10,000 feet.