Stability and Control characteristics of the Early Mark Spitfires

[CaptainDoggles]

Originally Posted by NZtyphoon

"In a word, the relationship of longitudinal stability to maneuverability is inverse. As one increases, the other decreases and vice versa." ?

First of all, I'm going to disregard things like Active Stability, where you have the computer making lightning-quick corrections to the unstable aircraft to keep it in controlled flight, because I think that this is beyond the scope of what we're talking about here. If we want to get into a discussion on the characteristics of FBW systems and supermaneuverability then we should open a new thread.

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I think it depends greatly on

a) which stability mode we're considering; if it's the short period or the phugoid mode

and

b) what you consider to be "maneuverable".

I think that if you were to reword that statement to read "the relationship of longitudinal stability to agility is inverse. As one increases, the other decreases and vice versa" then I would absolutely agree.

If an aircraft is unstable, then it will by definition be difficult or impossible for the pilot to precisely control the aircraft during a maneuver. By this I mean the pilot won't be able to hold a constant G-level through a turn, or to keep his guns on target.

I would consider such an aircraft to be highly agile, because it can re-orient its lift and nose vectors quickly and easily. This makes intuitive sense, because an unstable aircraft always wants to depart from equilibrium.

But I don't think that the aforementioned aircraft is particularly maneuverable, because I would define maneuverability as being easy to maneuver precisely and accurately through a wide range of maneuvers. In my opinion, if you have to fight the aircraft making corrections the whole time, then it's harder to get it to do what you want it to do, and so it's not very maneuverable, and so I would not consider an aircraft with negative stability to be very maneuverable.