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#181
10-20-2011, 12:14 PM
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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. 
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#182
10-20-2011, 02:52 PM
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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.
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#183
10-20-2011, 04:31 PM
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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. Quote:
The RAE even recognized it attempted to fix it. Eventually it was eliminated in the very late marques with an empennage redesign.
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#184
10-20-2011, 05:03 PM
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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?
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#185
10-20-2011, 05:27 PM
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They are so twitchy a human being cannot react fast enough to keep them from destroying themselves. Hence you answered your own question: Quote:
 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.
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#186
10-20-2011, 05:35 PM
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In some cases the negative or "relaxed" stability of the aircraft is a consequence of the design, rather than an explicit design goal. I'm thinking here of the F-117 and the B-2, whose fuselages are very unorthodox due to stealth requirements. Aircraft such as these require FBW systems to stay aloft.
In fact I once heard the B-2 described as being "held in the air by sheer computing power"  Other aircraft such as the F-16 are designed to be intentionally unstable. People often get mixed up due to the terms stable/unstable having very specific, prescribed meanings. Last edited by CaptainDoggles; 10-20-2011 at 06:07 PM. Reason: combined 2 posts into 1
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#187
10-20-2011, 05:37 PM
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http://www.google.com/search?q=Cruis...w=1920&bih=941 http://enpub.fulton.asu.edu/aero/mae...ingchapter.pdf "Maximum coefficient of lift" is the term for the CLmax a section can produce and defines the Angle of Attack the airfoil stalls. http://www.google.com/search?q=Cruis...0&bih=941&bs=1
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#188
10-21-2011, 10:22 AM
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F117 is unstable due to the interaction of the uncunventional faceted shape and aerodynamics forces. Ben Rich's team added some FBW rules (out of an F16
 ) to free designer to go much further in the quest for stealth.The unstability of the B2 is more linked to the clean flying wing shape with no vertical surface. With the F16 and the Mirage 2000 the world of high perf fighter begin a new aera were the relaxed stability was the norm. What does it means ? Simply that the balancing forces around the CG were modified to allow a more compact design with the CG moving aft with high pitch authority as a direct benefit. If you look closely at a post 80 design with FBW added you'll see that the jet engines are put at the tip end with no long draggy inner combustion pipe such as in the early jet and mid 60's (draggy because a jet engine blowing in a pipe loose that way its flow momentum due to inner wall friction. Hence a loss in propulsive power). This as freed the designer for a more balanced design improving the overall aero efficiency, lowering the empty weight (hence the direct and OP cost) and increasing the potential modifications in the . What the FBW do ? It simply act where the pilot can't with only minor correction to correct the induced instability of the aircraft. This principle was re-used by Airbus to minimize the tail surface of its design (drag lowered) such as the A320 witch was a seemingly logical step forward with the introduction of airfoils with a reflex zone (that cld be discussed today). SO instability and relaxed stability is not exactly the same thing. In fact you can possibly design an unstable aircraft with relaxed stability ... Or have a stable aircraft with some relaxed stabilty added  Or hve a stable aircraft that can be turned unstable in pitch if you move the ctrl further bckwrd  The best way to asses the Spit instability for everyone here and its uncomfortable 3/4 inch (2cm) stick travel would be to reconfigure your joystick to allow only that travel in the pitch zone. I am sure dozen here will instantly become Spit hatter in a single day !! By the way as ths is a Spit mkIIa thread can Devs stop the annoying characteristic of that bird in CoD that have a better P/W ratio than the 109. Now I see most of the Spit moving in the vertical plan knowing that there is a bug with the FM.  
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#190
10-21-2011, 03:48 PM
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Linear Mode
