Spit IIa

[RAF74_Winger]

Originally Posted by IvanK

Max performance turning is done "On the Buzz". A standard exercise is to do this whilst airspeed and G are changing whilst holding the aeroplane on the Buzz throughout without reference to AOA instrumentation etc ... just by feel.

I was taught to pull to the 'nibble', just a slightly different colloquialism I suspect.

The 'depth' of the buffet is due to washout I suspect, and very indicative of the progressive nature of the stall along the span. With light buffet, a very small inboard section of the wing has actually exceeded alpha max, but the remainder of the wing is at or near CLmax.

W.

[Crumpp]

Crump you are mixing terms

Nobody is mixing terms.

Aggravated in terms of aerodynamics is not a common term.

Sure it is a common term.

Simone Zuccher∗ and Sergio De Ponte†
Politecnico di Milano, 20158 Milano, Italy.
DOI: 10.2514/1.25389

The spin of an airplane occurs for angles of attack beyond stall, where nonlinear aerodynamics dominates and where complex and unpredictable behaviors might induce to question whether or not such a motion is chaotic. To find an answer to this issue, wind-tunnel tests are carried out on a model of a fighter attached by its center of gravity through an universal joint that allows only the three rotations. These degrees of freedom are analyzed according to modern techniques for the study of “supposedly chaotic data.” It is found that, for increasing Reynolds number, successive bifurcations take place with a consequent more complex structure of the attractor, which reveals some features typical of quasi-periodic systems evolving toward chaos. The model is tested also in other configurations (different nose and/or leading-edge extensions, presence or absence of tail planes) so as to verify the dependence of the motion on some details. It is found that unpredictability and strong dependence on the initial conditions characterize
the basic configuration, whereas a blunt nose and leading-edge extensions make the motion extremely regular. Even though the system might be on its route to chaos, a fully developed chaotic behavior is not observed.


Nomenclature
c = wing mean chord, m
f = frequency, Hz
k = reduced frequency, fc=U1
Re = Reynolds number, U1c=
t = time, s
U = wind-tunnel streamwise velocity, m=s
t = time interval, s
= kinematic viscosity, m2=s
= time delay
’, , = degrees of freedom (roll, pitch, and yaw), deg
Subscript
1 = asymptotic (freestream) conditions


I. Introduction
SPIN is an aggravated stall that results in autorotation [1].

http://profs.sci.univr.it/~zuccher/d...DS_JOA2007.pdf

A standard copybook 1G stall and spin entry has you arriving at the Critical AOA in 1G flight with close to full backstick. As the stall develops (ideally a nanofart before) you smoothly apply and hold full rudder (I guess you could say this is "aggravating" the stall ).

Any stall under any acceleration is aggravated. Anytime you have uncoordinated flight, you have lateral acceleration.

http://books.google.com/books?id=nxb...flight&f=false

The primary cause of an inadvertent spin is exceeding the critical AOA while applying excessive or insufficient rudder and, to a lesser extent, aileron. Insufficient or excessive control inputs to correct for Power Factor (PF), or asymmetric propeller loading, could aggravate the precipitation of a spin. At a high AOA the downward moving blade, which is normally on the right side of the propeller arc, has a higher AOA and therefore higher thrust than the upward moving blade on the left. This results in a tendency for the airplane to yaw around the vertical axis to the left. If insufficient or excessive rudder correction is applied to counteract PF, uncoordinated flight may result.

http://faculty.chicagobooth.edu/john...C%2061-67C.pdf

[Crumpp]

Sounds pretty standard to me, Max turn performance in a conventional straight wing aeroplane.

It is and I did not ask you to post it because of some abnormality. I asked you to post it because it specifically warns the pilot NOT to fly in the buffet zone and even to ease off the stick by pushing it forward.

Max performance turning is done "On the Buzz". A standard exercise is to do this whilst airspeed and G are changing whilst holding the aeroplane on the Buzz throughout without reference to AOA instrumentation etc ... just by feel.

Only in modern FBW....

Aerodynamic buffeting will not increase your turn performance, it will degrade it.

In the more modern types (FBW with active leading and trailing edge flaps etc) high AOA capabilty and aerodynamic configuration has you in a lot of buffet any time you are close to max turn performance ..

And that "buffet" has nothing to do with the aerodynamics of the aircraft. It is a programed stick shaker placed there by the engineers to let the pilot know he is nearing stall speed and is "On the Buzz" at the point the stability and control engineers put it.

[Crumpp]

Watch from 3:50 on to get a better idea what we are discussing. When you see those little pieces of sting stand straight up and then reverse, that portion of the wing is stalled.

That stall progresses if the pilot continues to increase angle of attack to CLmax until the wing can not longer support the weight of the aircraft and is no longer flying.

That flow reversal over a portion of the wing is what causes aerodynamic stall buffeting.

At 4:29 the test pilot begins recording a "light" buffet. Observe the tufts and imagine a "heavy" buffet....

http://www.youtube.com/watch?v=dUj6rmgku10

An airplane does not increase its turn rate if it experiences aerodynamic buffeting. An airplane that buffets will decrease it's turn rate when the buffeting begins.

When artificial means such as stick shaker were not available, the only choice a designer had was to reduce the amount of stall warning he gave the pilot. The less buffet, the closer the pilot can fly to CLmax without degrading his turn performance due to aerodynamic buffeting.

[Fenrir]

Your efforts Crump are becoming tiresome, and frankly your arguments about the spitfires 'Dangerous Instability' are verging on laughable. Every post that you put up serves only to advertise your bigotry and deepen your alienation of the rest of the forum.

I'll leave on this;

1) A pitch unstable aircraft is not pleasent to fly; it tightens in turns and does not settle automatically from a disturbed path. IT is VERY hard work. EVERY pilot who has flown a Spitfire, particularly those who have flown in combat say time and again the similar thing; words like DELIGHTFUL, EASY and WONDERFUL are repeatedly used to describe the handling and time and again they use the analogy that you didn't get into a Spitfire YOU PUT IT ON. Not to labour the point, but how on earth is there any correlation between these two factors? Cos apparently according to you they co-exist in the same airframe.

In case you missed it the first time, I'll write it again: Spitfires stability was MARGINAL. That does NOT make it UNSTABLE. You, with your self proclaimed expertise on aerodynamics should know this.

2) This bob weight stuff you seem hung up on is a poor argument; I have already related as to how it only affected Mk.V variants - thats Mark Five by the way; introduced many months after the Mk I & II in game - and was a result of increasing amounts of ancilliary equipment that was loaded into these a/c being poorly loaded at squadron level. But yet AGAIN you seem to have missed or ignored someones counter argument when it doesn't fit your model. So, yet AGAIN I'll direct you to Jeffrey Quill's excellent book on the subject. But somehow I get the feeling you won't read it; might not fall into line with some of your 'well founded' opinions.

Crump, your only working to serve your increasing reputation as a stuck up opinionated blowhard. One of these days you're gonna post something ace, a real piece of pukka gen as the old saying goes, and know one round here's gonna give a monkeys cos your credibility is vanishing with every cherry picked argument you present. But please, if you wish to continue shooting yourself in the foot......

[Crumpp]

spitfires 'Dangerous Instability' are verging on laughable.

Pilots died from it....

A pitch unstable aircraft is not pleasent to fly; it tightens in turns and does not settle automatically from a disturbed path.

Like this??

From the Spitfire Mk II Pilot Operating Notes:



The same warning is in the Spitfire Mk I which contains even more details.

If you want I will scan the pages from my college text from my stability and control classes. They deal a lot with the Spitfire and the DC-3 as both are famous icons that lack the most basic of stability, longitudinal. Unfortunately, Stability and Control engineering was new science at the time and nobody collected data on just how many accidents could have been prevented had these airplanes had acceptable longitudinal stability.

There is no agenda or bias, bud. You can learn something or not.

Notice, this is not MY opinion.....









Here is part of that text book. Read the last myth on a stable aircraft being less maneuverable than an unstable one.

http://books.google.com/books?id=D-c...0myths&f=false

[Fenrir]

What kind of verification do you have for these sources Crummp? As far as I know you've written that stuff on an old typewriter and scanned it. Besides, when it says 'failed to meet requirements' - whose?! What requirements? For all I know the Spitfire fails to meet requirements for a heavy lift wide body! Context man, for pitys sake.

Besides, if what you infer is correct we'd have seen spitfires and DC-3s - or more accurately, there constituent parts - scattered all over the landscape because every single one was an inherently dangerous saftey hazard. Take a look how many survive into the modern day and are flown regularly and aerobatted reguularly without incident. Look at the war record of these a/c. Since when on either type is it apparent that they were falling out of the sky in pieces with a methodical regularity?

Do I have to point out that the pictoral example of a structural failure that you provide IS A BLOODY Mk. FIVE again.

Gimme strength!

Besides which where on that photo/drawing does it show that this breakup was caused by excessive g due to instability? Oh that's right, it doesnt. It could have been faulty construction, metal fatigue, flutter, any number of causes. You just assume that it's down to some inherent flaw with Spitfires stability because you've got your axe to grind.

As for your quote on the Mk. II that buffeting can cause large variation in stick travel and g - wow, revelation. Any one who's read into the spitfire knows how sensitive the elevators were. At what what point does it say ANYWHERE in that text that the a/c is longitudinally unstable or prone to taking itself to pieces in that text? It does not. You're extrapolating, badly while your at it, tying it in with other flawed and irrelevant data.

The simple fact is your opinion extrapolated from text book teachings do not correlate with the historical record from a massive amount of disparate sources. And your one textbook evidence - whose validity I suspect - is not only being qouted without context - again WHAT & WHOSE requirements - but upon re-reading them it even agrees with me - NOTE the passage that you underlined 'the small static longitudinal stability',

It says small. It does not say none. It says the stick was very sensitive to movement in pitch.

It does not say Spitfires were falling apart all over the sky.

AT NO POINT DOES IT SAY THAT A SPITFIRE IS DANGEROUSLY AND INHERENTLY UNSTABLE.

[IvanK]

Crump you said :

"It is and I did not ask you to post it because of some abnormality. I asked you to post it because it specifically warns the pilot NOT to fly in the buffet zone and even to ease off the stick by pushing it forward."

Guess what you do when you go past the Buzz and get into the buffet ... you ease the back pressure off to get back into the Buzz .... Ideally the very first hint of it. Thats the art of max performance turning.

Then in response to my statement:

"Max performance turning is done "On the Buzz". A standard exercise is to do this whilst airspeed and G are changing whilst holding the aeroplane on the Buzz throughout without reference to AOA instrumentation etc ... just by feel."

You said:
"Only in modern FBW...."

Ok you are really off the plot in this response and thats just wrong.
I learnt to fly on the "Buzz" in a Winjeel and then on MB326H aircraft. Both Cable and or Manual push rod controls no Hydraulics or FBW. I also do it regularly in a YAK52. Whether you like it or not thats the way you practically get max turn performance in conventional straight wing aircraft. You want to get pretty close to Clmax to do achieve that, without an AOA gauge the first onset or the buzz IS the cue that is used. I am not the only one posting here to that effect.... see RAF_Wingers post.


You then said
"Aerodynamic buffeting will not increase your turn performance,it will degrade it."
No argument I didnt say that.... but see above response.....

You then said;
"And that "buffet" has nothing to do with the aerodynamics of the aircraft. It is a programed stick shaker placed there by the engineers to let the pilot know he is nearing stall speed and is "On the Buzz" at the point the stability and control engineers put it."

Sorry mate but with respect thats just total crap, and shows you dont really know what you are talking about. The fighters I have flown operationally the Mirage III and F18 Buffet like hell as soon as you start to get some Alpha on the jet. The Mirage III is even in buffet in the circuit ! ..... nature of the beast..... neither type has a Stick shaker or Stick Pusher system

As to Stick shakers I have flown 2 types that were equipped with these ... both commercial transports that required them certification wise both conventional Hydro mechanical controls.

Now I dont know your background Crummp but if you had some practical experience in realitvely high performance straight wing aerobatic aircraft and had been taught how to get the maximum out of it you wouldnt be saying the things you are.

[IvanK]

Here is someone elese's view on this. The text is from a civilian Aerobatics manual. The author a qualified Military Test pilot and graduate of ETPS... and even referring to an Aeroplane with a typical WWII type wing.
The last line says it all.



Lets put this into a practical example that is a realistic life or death situation that requires your best possible turn performance in this case Min radius.

Lets say you find yourself 90 degrees nose down pointing at the ground. You are unsure if you have sufficient height to pull out you may or may not but you must give it your best shot. How would you fly the recovery ? Any delay makes the problem worse, you need your best Turn RFN. Get it right you live get it wrong you DIE.

[RAF74_Winger]

Originally Posted by Crumpp

I asked you to post it because it specifically warns the pilot NOT to fly in the buffet zone and even to ease off the stick by pushing it forward.

Well, it doesn't actually say that - as given: "Even if the aeroplane does not begin to shudder or otherwise indicate an imminent stall, it may not be turning quite as quickly as it would if the stick is very slightly eased forward."

As has been said before - the buffet region of flight has 'depth' due to washout and the progressive nature of the stall across the wingspan. It's possible for a pilot experienced on type to know how much he can pull through the buffet before a full-blown stall & consequent stall and/or flick will occur.

The 'buzz' or 'nibble' does not necessarily presage an imminent stall, it just indicates that the inner part of the wing has exceeded max AoA, the airflow has separated from that surface and is impinging on the elevator.

Originally Posted by Crumpp

Aerodynamic buffeting will not increase your turn performance, it will degrade it.

That's sort of true, but not completely. For a wing with washout, max turn performance might not occur until some portion of the inner part of the wing is stalled and the wing as a whole has reached CLmax.

W.