Stability and Control characteristics of the Early Mark Spitfires

[klem]

Originally Posted by Crumpp

Dive to Vne, stomp on the rudder, and pull back as hard as you can.

Fly the airplane in the buffet and time your turn.

Pull back on the stick, release, and note the behavior of the airplane.

Fly at Vmax, pull hard back, hold it at full deflection, and note the behavior.

Fly the airplane trimmed for slow flight, let go of the stick, fire the guns, and note the behavior.

I have played the game and note the behaviors as I play. Just because I don't spend my time making excel spreadsheets does not mean the points are invalid.

What were your five results, what were your expectations and how did you come by them?

[Crumpp]

The must be some pretty smart monkeys.

Yes they are very intelligent, disciplined, and highly educated. It is one of the toughest jobs in existence.

Damn now he has a CFI I say this as before Crump only claimed a PPI.

I am sorry. Do I need your permission to get ratings, train, and get a job flying? You are not hireable as a PPI.


Who do you people think you are????

[Crumpp]

No just your gut feeling not actually measured and or recorded. You post so many charts to support your statements in this thread then jump in the sim and just wing it !

If I had the time I would. Why do you think it has taken so long for me to get the post's out in this thread.

I don't put food on my table by helping to develop realistic flight simulators.

However, I have another source of income, a family to support, and all the things that come with that.

[Crumpp]

In the end it comes down to the last sentence as underlined here, Mr Mel Gough NACA :

Mel Gough was a test pilot for the NACA.
The quote is in the context of the meeting to determine stability and control standards for the individual services, the US Navy and Army Air Corps.

The NACA already had developed stability and control standards and Mel Gough was a co-developer of those standards.

The end result is the document posted below. It did not result in things being left up to "how much instability one can stand".

In fact, Mel Gough was one of the pioneers in eliminating the "pilot opinion" standard.

The handling qualities of all future airplanes would be based on the parameters they outlined. Up to that time a pilot would fly an airplane, and the attitude was, “Well, if you go back and fly it the second time, it must be a good airplane.” Or the pilot would be asked, “What is it that you like about the plane?” And those early-time pioneer pilots would try to describe what it was they liked about the airplane. Whether the stick forces seemed too heavy or if the plane didn’t roll fast enough, etc. It was all kind of subjective stuff based on pilots’ opinions.

Then Mel and Bob decided, “Let’s quantify this. Let’s put some numbers to these opinions.” What is it that a pilot likes in a fighter as well as in all other categories of planes? What does the pilot want to feel? What response is he looking for? How much G [gravitational] force does he want to pull? How much can he handle in a roll? When does he get uncomfortable or reach his limit of physical response. Is any of this different in a fighter or a bomber? Does he expect the same stick forces and rudder forces in a fighter as he does in a bomber?
So all of that became a matter of negotiation, and between the two of them, the pilot and the engineer, they quantified the parameters. They wrote what I call a bible of stability and control and described what ideal handling qualities are in any type of aircraft. It was no longer up to the designer and manufacturer to produce and present a product that was satisfactory to their designers and test pilots. It was a mandate to meet the requirements outlined by NACA.

http://www.google.com/url?sa=t&rct=j...I69j8yvj-7PvKg

The result is attached. It is the quantified answer to the question, "How much instability can one stand?"

In England, Jeffery Quill was the Chief Test Pilot for the development of the Spitfire. If it met his standards in his opinion, without quantification, it went forth despite the some early testing investigating the longitudinal instability, his acknowledgement, and all the warnings found in the Operating Notes that are the result of longitudinal instability.

It was not until the design was evaluated under a set of measured and defined standards that the longitudinal instability was quantified and fixed in the Spitfire.

[IvanK]

And supposedly the clod spitfire doesn't in YOUR opinion meet some standards in your mind that you refer to without quantification.

All this stuff about things being measurable and to defined standards then when asked how you find them in the Sim all we get is:

"Fly the airplane in the buffet and time your turn.

Pull back on the stick, release, and note the behavior of the airplane.

Fly at Vmax, pull hard back, hold it at full deflection, and note the behavior.

Fly the airplane trimmed for slow flight, let go of the stick, fire the guns, and note the behavior.

I have played the game and note the behaviors as I play. Just because I don't spend my time making excel spreadsheets does not mean the points are invalid."

When others actually go out there test and document and show their results you jump on them questioning every detail of their efforts. ... what were the conditions etc etc.

Please give us a break and at least practice what you preach !

[DC338]

It was not until the design was evaluated under a set of measured and defined standards that the longitudinal instability was quantified and fixed in the Spitfire.

Can you explain this further. Fixed As a result of NACA? How? Surely not.

Can we have a analysis of figures 16 17 & 18 pointing to the instability in these test? It would appear tha 15 is an anomaly when compared to the later test.

[Crumpp]

Can we have a analysis of figures 16 17 & 18 pointing to the instability in these test? It would appear tha 15 is an anomaly when compared to the later test.

It is different conditions.

In Figure 15 we see the result of the pilot just pulling the stick back and entering a turn. That is the inherent stability of the aircraft without pilot input. It tells us the workload the pilot needs to exert.

In figure 16, he pushes the stick forward in the measuring equipment.

In figure 17 and 18, he demonstrates the stability thru careful flying.

Figure 15, In other words it is the measured results of what happens if you are new player and you turn the Spitfire and keep the stick pulled back like a stable aircraft to maintain the turn.

In figure 16 we see the proficient but not the expert at controlling the aircraft. He pushes forward and his ability to control the aircraft improves. He still is not getting that steady level of acceleration.

In figure 17 and 18, we see the pilot carefully matches the unstable accelerations to produce a steady level of acceleration.

Klem,

The aircraft in the game acts stable both static and dynamic. It returns to trim and dampens the oscillation. Only in a steady state climb does it begin to act neutral.

I don't know the games code, but it seems like they made it "just statically stable" in level flight without the dynamic instability. When an aircraft enters a climb, the stability margin is reduced so we see the neutral static stability.

The spin modeling is excellent for a game. It took an average of at least two turns to recover when correct input was held. I liked it.

The stall behavior when reached is good too.

The issue is the amount of control required to maintain a turn is not representative of the longitudinal instability.

The inability to exceed the airframe limits. You can pull as hard as you want on the stick without fear of breaking the airplane.

The buffet effects are under modeled. In the game, The turn rate improves IN the buffet without any advantage for correctly flying a maximum turn rate performance turn. The turn performance does not begin to taper off until just before the stall when the slope becomes rather steep. That is not correct. Turn rate should decay in the buffet as a function of the strength of the buffet.

The buffet itself is under modeled. It is like a nibble when we see from the NACA report it imparted noticeable accelerations on the aircraft. Those accelerations are quantified in figures 13 and 14 of the NACA report.

In other words, your turn rate in the game improves in the buffet until just before the stall point and the airplane does not shake as the real thing.

That is part of the stall warning. The idea is to have it so you know to back off and not stall. It is essential to the control of an longitudinally unstable aircraft to have that large and distinct stall warning as well as the ability to maintain control in it. The large accelerations warn of the impending stall and increase the power required to make the turn. This also encourages realism. He rewards the players that fly on the edge to the nibble and back off to smooth air. It has the added benefit of precisely defining that point to an experience player.

[klem]

Originally Posted by Crumpp

It is different conditions.

In Figure 15 we see the result of the pilot just pulling the stick back and entering a turn. That is the inherent stability of the aircraft without pilot input. It tells us the workload the pilot needs to exert.

In figure 16, he pushes the stick forward in the measuring equipment.

In figure 17 and 18, he demonstrates the stability thru careful flying.

Figure 15, In other words it is the measured results of what happens if you are new player and you turn the Spitfire and keep the stick pulled back like a stable aircraft to maintain the turn.

In figure 16 we see the proficient but not the expert at controlling the aircraft. He pushes forward and his ability to control the aircraft improves. He still is not getting that steady level of acceleration.

In figure 17 and 18, we see the pilot carefully matches the unstable accelerations to produce a steady level of acceleration.

Klem,

The aircraft in the game acts stable both static and dynamic. It returns to trim and dampens the oscillation. Only in a steady state climb does it begin to act neutral.

I don't know the games code, but it seems like they made it "just statically stable" in level flight without the dynamic instability. When an aircraft enters a climb, the stability margin is reduced so we see the neutral static stability.

The spin modeling is excellent for a game. It took an average of at least two turns to recover when correct input was held. I liked it.

The stall behavior when reached is good too.

The issue is the amount of control required to maintain a turn is not representative of the longitudinal instability.

The inability to exceed the airframe limits. You can pull as hard as you want on the stick without fear of breaking the airplane.

The buffet effects are under modeled. In the game, The turn rate improves IN the buffet without any advantage for correctly flying a maximum turn rate performance turn. The turn performance does not begin to taper off until just before the stall when the slope becomes rather steep. That is not correct. Turn rate should decay in the buffet as a function of the strength of the buffet.

The buffet itself is under modeled. It is like a nibble when we see from the NACA report it imparted noticeable accelerations on the aircraft. Those accelerations are quantified in figures 13 and 14 of the NACA report.

In other words, your turn rate in the game improves in the buffet until just before the stall point and the airplane does not shake as the real thing.

That is part of the stall warning. The idea is to have it so you know to back off and not stall. It is essential to the control of an longitudinally unstable aircraft to have that large and distinct stall warning as well as the ability to maintain control in it. The large accelerations warn of the impending stall and increase the power required to make the turn. This also encourages realism. He rewards the players that fly on the edge to the nibble and back off to smooth air. It has the added benefit of precisely defining that point to an experience player.

OK, let me stick my neck out a mile and try to find some common ground.

I'm no aerodynamicist but all Crump is saying is that the low level of longitudinal stability of the Spitfire is not properly represented in the game and the buffet/stall characteristics are not right. I haven't tried it or flown it on the edge (I've only flown it once since the patch) so I don't know but it would be nice to have the characteristic and helpful pre-stall buffet and I think what Crump is saying is that the FM doesn't provide it.

However I think most of us are currently concerned with more significant issues like it is (was?) too damn slow and perhaps that has led to a low tolerance level for this particular issue. Again, I haven't tried the Spit more than one sortie because I've been concentrating on the Hurricane which is also too slow. Whether it is the power modelling of the Merlin III, prop modelling, drag modelling or some other aspect we don't know either but that's another thread.


I think the basic argument may have value but what does come across is entrenched attitudes on a personal level and arguments about whether NACA findings should or should not be used. Apparently these came much later but should they be used as a reference if they are correct for the Spit MkI/II? Their validity has been challenged because of NACA's own admissions about possible errors. OK, forgive me for not trawling through all 94 pages of the thread but where are the relevant RAE or A&AEE or other British data for the same problem? If longitudinal instability was a fact the data should show that and the thread could come back on track.

Perhaps instead of binding himself to NACA Crump would accept historical data other than NACA's and use that in his explanation of "Stability and Control characteristics of the Early Mark Spitfires". His point should hold good if the basic premise is correct, i.e. longitudinal stability is not modelled properly.

The real shame of the thread, whether you agree with NACA or not, is that Crump set out to explain something and it has been shoved off track by arguments of various kinds including red herrings like differences in players joysticks. As several early posts said, its something worth pursuing in the battle to get the FM as near correct as possible. Just need to agree the data.

[Crumpp]

you jump on them questioning every detail of their efforts.

I am sorry if that is your perception. It is not the case or my intention.

I only post to try and help the testor's efforts.

For example, posting aircraft performance test's without the conditions for both aircraft and atmosphere does not tell one if the airplane is performing at it should under other conditions.

It should not be surprising that those questions come up when the information is not presented only the results.

[NZtyphoon]

Originally Posted by Crumpp

In England, Jeffery Quill was the Chief Test Pilot for the development of the Spitfire. If it met his standards in his opinion, without quantification, it went forth despite the some early testing investigating the longitudinal instability, his acknowledgement, and all the warnings found in the Operating Notes that are the result of longitudinal instability.

It was not until the design was evaluated under a set of measured and defined standards that the longitudinal instability was quantified and fixed in the Spitfire.

Alas Jeffrey Quill - he spent thousands of hours in flight, testing and developing real Spitfires in real conditions, and thus we find out that he had no idea of what he was doing by an American sitting in front of a computer who had "tested" the Spitfire a couple of times on a flight sim and he did find it wanting. And because of Quill Spitfires went forth unstable and drunken in their flight.

Thus it was the Yanks who came to the rescue and fixed the hitherto unstable machine by waving their magic flight reports and inertia weights and speaking in unison "Fix this Spitfire it does not meet our standards!" The British quavered and lo! they fixed the Spitfire forever. And the tale told by Quill, that the inertia weights were fitted after the discovery of badly loaded Spitfire Vs in Fighter Command service was horse pucky.