Stability and Control characteristics of the Early Mark Spitfires

[Crumpp]

http://www.spitfireperformance.com/k9788-stability.jpg

[Crumpp]

slightly longitudinaly unstable

The records are posted above....

You guys understand this is quantifiable and not opinion?

I guess I will run some calcs for you all so you can get a better idea of the effect.

[taildraggernut]

And?........

The graphs show a slight instability, if you cant cope with that level of divergence in 3 minutes then my guess is you'd either be paralysed or in a coma.

[robtek]

There are speed changes of about 70mph in less than 15 second documented, if that doesn't take the pilots attention away from other things i don't know what would.
Of course a pilot can manage to control this instability, but he has to work just to keep his ride in a controlled flight, add other factors as gusts, attacking 109's or else and the workload might become too large.

[taildraggernut]

a cessna 152 will go from 70 to 0 in less than 15 seconds......the point is you have to wait a few minutes before those fluctuations get to that level, within the 1st minute nothing on those graphs looks wildly out of control.

[TomcatViP]

Crummp I think you shld stop answering to them. It goes nowhere. Either this thread shld be locked now if you have finished exposing your point or you might switch to the next step in your argumentation.

Don't take me wrong, I found your point really interesting as many other does.

[Glider]

Part of the problem is that Crumpp doesn't awnser the questions, he quotes the papers which is fair enough but doesn't support it with pilots comments. He said the test pilot reports support his. So let him show any test pilot who said it was difficult or dangerous or uncomfortable to fly, or any test establishment. No one is denying that it didn't have perfect stability but then again whats perfect.

The paper that was posted should be read from beginning to end, after all the man who wrote it had 58 years practical hands on experience. Another important section is as follows:-

I published reports on the Hawker Hurricane (April 1942) (ref. 4.5) followed shortly by one on the Spitfire. The data obtained in these tests served to confirm most of the requirements previously proposed by Gilruth. Other reports followed comparing these results with published data on the German fighter Me109 and with U.S. fighter airplanes. During the war, pilots' lives depended on small differences in performance between the first-line fighters, and continual detailed improvements were made in these fighters. Several research studies were made on improvements, usually on control systems, and close contact was kept with the manufacturers through conferences and preliminary reports.

The tests on the high-speed fighters confirmed the findings of Gilruth that though all the airplanes exhibited instability in the spiral and phugoid modes of motion, these [26] modes did not concern the pilot because his normal control actions prevented the modes from developing to a point that they were noticeable. That is, the airplanes were spirally unstable, but the rate of divergence was small enough that it was not discernible to the pilots. Also, the long-period longitudinal mode might have been a slow divergence or a poorly damped or unstable phugoid oscillation, but the divergence was so slow or the oscillation had such a long period that it was not noticeable in normal flight. The short-period lateral oscillatory mode, the Dutch roll, was noticeable but adequately damped and the short-period longitudinal mode was so well damped that it could not be detected by the pilots. In general, these results applied to most airplanes of this period and explain why successful airplanes could be built without the need to consider theoretical predictions of dynamic stability. On the other hand, Gilruth had found that many of the quantities that could be determined without the need for complex theories, such as control deflections and control forces required in straight flight and maneuvers, trim changes due to power and flap setting, limits of rolling moment due to sideslip, and adequacy of the control effectiveness in maneuvers, were extremely important to the pilot. The tests on the fighter airplanes showed that the longitudinal control force gradient in maneuvers, known as the force per g, was a very important quantity, whereas the control force and position variation with speed in straight flight was of less importance and mainly influenced pilot fatigue on long flights. These airplanes were found to be quite satisfactory in most respects, though the aileron effectiveness at high speeds was low because of the large control force required to deflect the ailerons, which was an adverse characteristic in air combat. The detailed improvements mentioned previously were mainly directed at this aileron effectiveness problem.

Or to put it another way. The imperfections were small enough to be either not noticed or easily dealt with.

[taildraggernut]

http://www.youtube.com/watch?v=EMT6Y...eature=related

[Crumpp]

Crummp I think you shld stop answering to them. It goes nowhere. Either this thread shld be locked now if you have finished exposing your point or you might switch to the next step in your argumentation.

Don't take me wrong, I found your point really interesting as many other does.

I agree. There are no more measureable or definable characteristics to discuss. The only counterpoints are now based on emotion and feelings.

[Crumpp]

The tests on the high-speed fighters confirmed the findings of Gilruth that though all the airplanes exhibited instability in the spiral and phugoid modes of motion, these [26] modes did not concern the pilot because his normal control actions prevented the modes from developing to a point that they were noticeable. That is, the airplanes were spirally unstable, but the rate of divergence was small enough that it was not discernible to the pilots. Also, the long-period longitudinal mode might have been a slow divergence or a poorly damped or unstable phugoid oscillation, but the divergence was so slow or the oscillation had such a long period that it was not noticeable in normal flight. The short-period lateral oscillatory mode, the Dutch roll, was noticeable but adequately damped and the short-period longitudinal mode was so well damped that it could not be detected by the pilots. In general, these results applied to most airplanes of this period and explain why successful airplanes could be built without the need to consider theoretical predictions of dynamic stability. On the other hand, Gilruth had found that many of the quantities that could be determined without the need for complex theories, such as control deflections and control forces required in straight flight and maneuvers, trim changes due to power and flap setting, limits of rolling moment due to sideslip, and adequacy of the control effectiveness in maneuvers, were extremely important to the pilot. The tests on the fighter airplanes showed that the longitudinal control force gradient in maneuvers, known as the force per g, was a very important quantity, whereas the control force and position variation with speed in straight flight was of less importance and mainly influenced pilot fatigue on long flights. These airplanes were found to be quite satisfactory in most respects, though the aileron effectiveness at high speeds was low because of the large control force required to deflect the ailerons, which was an adverse characteristic in air combat. The detailed improvements mentioned previously were mainly directed at this aileron effectiveness problem.

All generality that is not dealing with the Spitfire. The NACA results are published, measured, and available for all to see.

I think the thread has run its course.