A general question about maneuverability

[klemchen]

Hello everyone,

in aviation literature maneuverability is often treated as something unambiguous. However, there are different ways of determining this quality: For instance, one could ask for the smallest possible circle an aircraft can fly, with or without loss of altitude permitted at any or at some specified altitude, or one could consider the shortest time which an aircraft needs to fly a full circle, with corresponding variations.
By logic, these concepts are clearly not the same, but they still could be factually equivalent. This would mean that, by laws of physics, if of any two aircrafttypes 1 and 2 one turns out to be better according to mode A it also does according to mode B. In other words, modes A and B would not be (factually) equivalent, if there are instances of two aircraft types 1 and 2 where type 1 is better according to mode A but type 2 is better according to mode B.
I would expect that not all reasonable concepts of maneuverability are factually equivalent, but I do not know this for sure. If this asumption is correct, then what kind of maneuverability is most important concerning air combat? -
It is generally agreed that the Spitfire and the Hurricane were distinctly more maneuverable than the Me 109. In spite of this, Len Deighton in his book "Fighters" stated just the opposite. I do not have the book but some time ago I read the passages on the maneuverability of those fighters. If I remember it correctly, Deighton took as criterion the smallest possible circle that could be flown at a certain rather high speed. I have read statements that Deighton is downright wrong, but could it be that instead he was also right, except that his claims are based on a rather unusual criterion?
Any answer will be greatly appreciated.

Best regards,
klemchen

[Graham Boak]

No, Deighton was just plain wrong, because the assumptions that went into his calculations were incorrect. The matter was studied by the University of Manchester, who published a report in the Royal Aero Society's Journal. I'm sorry, I can't quote the precise reference.

The usually-quoted parameters are
Sustained Turn Rate (or Radius) which is the maximum turn rate that can be acheived without loss of speed or height.
Attained Turn Rate (or Radius) which is an absolute maximum found at CLmax, but during which spped/altitiude is being lost dramatically.
Specific Excess Power, which is a measure of the maximum acceleration or climb rate at any given point in the envelope.

Most turning combats will descend in altitude and reduce in speed as each pilot tries to out-turn the other.

However, these are far from the only relevant matters. For example, Rate of Roll can be significant, and indeed transients such as the time taken to achieve that rate of roll. This was significant in 1941, where the Fw190 had such good ailerons that it could reach its maximum rate of roll sooner than the Spitfire. If caught at a disadvantage, it could roll and dive away, beng gone out of reach before the Spitfire could follow.

I'm sure that other examples, different in detail, can be found.

[chuckschmitz]

You also need to throw into the mix altitude, speed and acceleration.

Chuck

[DavidIsby]

two other good sources:

Francis J. Hale, Introduction to Aircraft Performance,
Selection and Design (New York: John Wiley & Sons, 1984), pp. 103-109. Sustained Spitfire and Bf 109E performance: AVIA 6/2394. Messerschmitt Me. 109,
Handling and Maneuverability Tests, Royal Aircraft Establishment, Farnborough,
September, 1940, National Archives (UK).

[DavidIsby]

The journal article mentioned in the above post by Gray Boak is:

J.A.D. Ackroyd and P.J. Lamont, ‘A Comparison of Turning Radii for four Battle of Britain Fighter Aircraft’, The Aeronautical Journal, January 2000, pp. 53-58.

[klemchen]

Hello,

thank you all very much for your answers.

Best wishes,
klemchen