Spit IIa

[Crumpp]

The Spitfire was at about 5 lb/g, requirements were around 8 lb/g. So it was too light on the elevator.

It would be unstable if it was <=0 lb/g. It wasn't.

That is not even close to correct. You can easily have a zero static margin for a condition of flight as the NACA determined.

Cable and hinge pressure alone can give you 5lb/G.

[Crumpp]

Do you mean inverted ctrl ?

He is confused.

He does not understand that classifying control characteristics as Neutral does not mean they are at the Neutral Point with a margin of zero as the engineering definition.

The airplane would be unflyable and that is not what the NACA or anyone else who tested and measured the stability and control of the early Spitfires concluded.

The classification is based on the what control inputs by the pilot, that is why it is termed "flying qualities".

For static that is generally the airplanes reaction to a disturbance. If the airplane returns to last trimmed condition of flight with the stick free, it has positive static stability.

If it does not return but just stays on its disturbed course, it is neutral. That is why the NACA classified the aircraft as poor in rough air. It stays on whatever course the disturbance sets it on for practical purposes.

In this case the low positive static margin is stability is probably eaten up by hinge moments or balances leaving the system neutral for all practical purposes. Certainly it would eventually return to course but the time required is longer than the parameters set for positive stability.

If the disturbance increases, it is divergent or negative.

[TomcatViP]

Originally Posted by Crumpp

He is confused.

I was too

Poor post than mine. Will delete/correct content

~S