Spit IIa

[TomcatViP]

Originally Posted by jtd

naca spitfire reports are available here.

thx !!

[Crumpp]

Selective reading, again. The linked document actually states this: (2) For stick controls, W/140 (where W is the maximum weight) or 15 pounds, whichever is greater, except that it need not be greater than 35 pounds.

To be airworthy......

That is not the ideal by any means nor did the Spitfire have unacceptable stick force gradients.

It had a low stick force gradient and that served to aggravated the neutral longitudinal stability issue.

Although steepening the stick for per G gradient was the fix used to increase the pilots ability to safely control the aircraft, the stick force gradient was not the issue with the Spitfire.

The issue was the longitudinal stability was neutral and not positive. That makes for a twitchy airplane that is easy to stall, hard to precisely maintain a load factor in a turn, and easy to overstress the airframe.

3/4 of an inch from cruise to stall is not safe and would not be considered acceptable.

FAA formula for chimp-proof civil aircraft.

That is for all aircraft seeking certification in the United States and since most of us are all on the same standard now, much of the world.

[Crumpp]

Selective reading, again.

Just to clarify. I did read it. You just think my point was the control forces of the Spitfire were bad.

You are mistaken.

They were on the low end of the scale but acceptable. I just illustrated how quickly a pilot could go from cruise to accelerated stall with the neutral stability, tiny stick travel margin, and low stick forces characteristics of the type.

[winny]

It's an interesting point, and from pilot's accounts it seems true.

Time and time again Spitfire pilots say stuff like "you only had to think about moving the stick and she responded" or "the lightest touch was all that was needed". It's also supported by people who flew both Hurri's and Spits most of who say the Hurricane was more stable. The Spitfire was known to be twitchy if flown heavy handed.

I'm not convinced that it was a problem though, technically maybe, but I've never read anything where Spitfire pilot's were complaining about stability (at least up until some of the bigger ones). Isn't a little bit of unstability good for maneuverability?

I suppose it could cause problems in the 'pit if you're throwing it around simply because it must have been hard to stay relaxed on the stick.

[Crumpp]

Isn't a little bit of unstability good for maneuverability?

Not at all. In fact that is big myth.

Remember, a stable airplane can do any maneuver an unstable aircraft can. The stable airplane can do it just as fast and more precisely requiring a less skilled pilot to do the same thing. It can also do things the unstable one cannot. Such as not destroy itself by overloading the airframe, shoot down other airplanes much faster, land with more control and precision, maneuver better in rough air, and hold a precise altitude/heading in instrument conditions.

Unstable just means the airplane is skittish and hard to control.

I'm not convinced that it was a problem though

Sure it was....

The RAE even recognized it attempted to fix it. Eventually it was eliminated in the very late marques with an empennage redesign.

[winny]

Originally Posted by Crumpp

Not at all. In fact that is big myth.

Remember, a stable airplane can do any maneuver an unstable aircraft can. The stable airplane can do it just as fast and more precisely requiring a less skilled pilot to do the same thing. It can also do things the unstable one cannot. Such as not destroy itself by overloading the airframe, shoot down other airplanes much faster, land with more control and precision, maneuver better in rough air, and hold a precise altitude/heading in instrument conditions.

Unstable just means the airplane is skittish and hard to control.



Sure it was....

The RAE even recognized it attempted to fix it. Eventually it was eliminated in the very late marques with an empennage redesign.

So, when someone refers to a Modern Aircraft being unstable (I'm thinking of the ones that need a computer to fly them) are they talking about the same 'unstability'? Is it even true? (I'm not arguing here, I'd just like to know)

About the 'problem', how come the vast majority of Spitfire pilots say it was so easy to fly? How did this problem manifest it's self?

[Crumpp]

Is it even true?

YES!! They are much more maneuverable than if the designer had built a stable aircraft.

They are so twitchy a human being cannot react fast enough to keep them from destroying themselves.

Hence you answered your own question:

I'm thinking of the ones that need a computer to fly them

IIRC, IL2 players complained quite a bit about the P51 Mustang FM's being twitchy.

That is sort of how an airplane with a small enough stability margin to be considered neutral in longitudinal flying qualities will behave.