Stability and Control characteristics of the Early Mark Spitfires

[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.

[taildraggernut]

Originally Posted by Crumpp

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.

Yes, it ran it's course a while ago....anyway looking forward to the 109 debate, is is coming soon?

[Al Schlageter]

Originally Posted by taildraggernut

Yes, it ran it's course a while ago....anyway looking forward to the 109 debate, is is coming soon?

There won't be one as the 109 was perfection personified as it is German.

[Crumpp]

Typhoon I

Yep and notice the Typhoon Operating Notes lack the warnings of the Early Mark Spitfire notes.

1. No bracing in turns required

2. Lack of warnings about overloading the airframe

IIRC, the Typhoon's issues did not stem from stability and control design but low velocity flutter in the tail.

It was reported in a couple of flights as longitudinal stability issues but not measured.

It turned out to be a q-limit issue. I think early Typhoon's even had a few structural failures because of it.

[NZtyphoon]

Originally Posted by Crumpp

IIRC, the Typhoon's issues did not stem from stability and control design but low velocity flutter in the tail.

Wrong, once again - the tests observe that the Typhoon had fore and aft instability (page 2 para 5), no mention of your "low velocity tail flutter" - as it was the Typhoon's operational history showed that it did make a good GA aircraft. The Tempest, which had no sign of "low velocity tail flutter" also exhibited the same characteristics, contradicting your statement:

Sir Sydney Camm may not have understood swept wing theoy during the war but he was a master of stability and control design. The Hurricane was a wonderful gun platform and had near perfect longitudinal stability. His other major designs, the Typhoon and Tempest also exhibited the same characteristics.

[Crumpp]

The "instability" was low velocity flutter and was not caught until the end of the war.

The tail problems turned out to be due to elevator flutter and were cured by modifying elevator balance, but that didn't happen until very near to the end of the war.

http://www.airvectors.net/avcfury.html

The RAE did not have a standard for stability and control.

ONCE again, there is nothing else in the Operating Notes in either the Typhoon or the Tempest that pertain to any kind of longitudinal stability issue. Had their been an issue, it would reflect in the cautions.

This is in sharp contrast to the early Mark Spitfires whose Operating Notes are filled with warnings of symptoms that are the result of longitudinal stability.

[camber]

Crumpp,

I keep hoping you will try and answer Glider's question. If the Spit had such objectional handling characteristics, why is there such a huge body of pilot's reports stating otherwise?

Your position seems to be to me that all such reports don't warrant any thought or comment as they do not represent hard data. I disagree, and don't seem to be alone on this. I don't see how you can convince many others including myself unless you try to come up with some explanation and try to address the discrepancy. Don't you have an opinion?

If you were a young pioneering stability control engineer in 1940, what would YOUR approach be? Judging from this thread, you would collect hard data with precision and evolve intuitively appropriate standards. Then you would ignore all test pilot's feedback of whether or not your proposed changes were desirable. After all, they are not control and stability engineers and cannot understand how their combat aircraft should operate. I don't think you would be playing much of a role in the future of aviation after that.

camber

[NZtyphoon]

Originally Posted by Crumpp

The RAE did not have a standard for stability and control.

ONCE again, there is nothing else in the Operating Notes in either the Typhoon or the Tempest that pertain to any kind of longitudinal stability issue. Had their been an issue, it would reflect in the cautions.

This is in sharp contrast to the early Mark Spitfires whose Operating Notes are filled with warnings of symptoms that are the result of longitudinal stability.

The tail problems turned out to be due to elevator flutter and were cured by modifying elevator balance, but that didn't happen until very near to the end of the war.

The Typhoon's tail problems had nothing to do with the longitudinal instability described in the Pilot's Notes. The Tempest did not suffer from "low velocity tail flutter" yet also displayed slight longitudinal instability.

And, BTW the website is completely wrong - the rudder balances, which were at the root of the tail problems, were modified in 1943 - there was no problem with the elevator balances. From early 1944 new production Typhoons, and some earlier ones, adopted Hawker Tempest horizontal tailplanes and elevators which had a larger area - with the small tailplanes and a full weapons load of either 8 RP-3s or 1,000 lb bombs the longitudinal stability deteriorated.

Your comment was the Hurricane, Typhoon and Tempest had near perfect longitudinal stability - no comment about a "longitudinal stability issue." Fact is you were wrong, once again - both aircraft were slightly unstable longitudinally.

If the RAE had no standards for stability and control it meant they were unable to comment on the stability and control of aircraft they tested - read the 1938 report carefully, it is most illuminating.

The Spitfire PNs describe control and g-limits in rough air and caution pilots against making high-speed manœuvres in such conditions, something also covered in Pilot's Notes General.

[winny]

Originally Posted by Crumpp

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

For a MK V

[Glider]

Originally Posted by Crumpp

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.

I think you forgot this part

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.

I think you also forgot this part posted earlier

FIGURE 4.5. Supermarine Spitfire airplane. A high-performance fighter noted for its role in the Battle of Britain and throughout WW II, the Spitfire had desirably light elevator control forces in maneuvers and near neutral longitudinal stability. Its greatest deficiency from the combat standpoint was heavy aileron forces and sluggish roll response at high speeds.