Stability and Control characteristics of the Early Mark Spitfires

[taildraggernut]

Originally Posted by Crumpp

I will be happy to take to PM and explain the results for the few who have questions.

Feel free to send me one.

Why all the 'cloak and dagger' secrecy of PM's, this is a forum, why can't people ask you a question and you answer them?

[taildraggernut]

Originally Posted by Crumpp

DEFINE what you do not understand.

Posting "It flew great and was easy" is not an argument nor definable. It is opinion.

I don't understand what you are trying to prove with this thread, I don't need to PM you to get that accross.

it seems to me that if we wen't down the road of how you would like the Spitfire 'defined' then it wouldnt fly so great and be easy.......which seems at odds with real world oppinion.

[Crumpp]

odds with real world oppinion

Just because these people put a ruler to it and measured against a definable standard, it is invalid because folks flew the plane around the pattern???

RAE Cm graphs, NACA measurements, RAE oscillation graphs, Operating Notes, and pilot reports

[taildraggernut]

folks flew the plane around the pattern???

Pattern?.....are you equating air to air combat during WWII to flying a cirquit pattern?

[Crumpp]

Let's get back on topic:

This thread defines the characteristic that can submitted for the bugtracker.

Great document Lane!!

It gives us a measurement of the divergence and the slope of the Cm increase.

Exactly, one of the quirks of the Spit was the extreme easy elevator

Not only that, it is unstable. That means your coefficient of moment increases each cycle instead of decreasing.

So if you pull a 6 G turn and did nothing except hold the stick fixed, the next oscillation will exceed 6G and continue to increase with each cycle until the airframe is destroyed.

That is the reason why "flick" maneuvers were not allowed in it.

Let's summarize the behavior that occur at normal and aft CG positions and categorize them to be implemented in the game. Then we can build a list for the bug tracker. These are all at NORMAL CG. If the game models a shifting CG then they increase in severity at aft CG positions.

The take away is:

1. The large accelerations change for very little elevator movement.
2. The very rapid rate at which the pilot was able to load the airframe to 5G's.
3. The equally rapid rate at which the airframe unloaded down to 2G's when the pre-stall buffet was encountered. In 1 second, the aircraft went from 5G's to 2G's due to buffet losses. This means a rapid decay in turn rate resulted.
4. The violence of the pre-stall buffet combined with the longitudinal stability and control caused large fluctuations in the accelerations on the aircraft.
5. The violent accelerated stall behavior resulting in spin/loss of height

1. The large accelerations change for very little elevator movement.

1. The Spitfire should be twitchy and unstable gun platform. IIRC, in IL2, people used to complain about the "twitchy" behavior or the Corsair and P-51's so I am sure it is within the games engine to model a twitchy airplane.

It should take very careful and small stick movements to get the gun sight on target. That means a Spitfire pilot will require more skill to hit a maneuvering target than he would need in a stable platform such as the Hurricane.

2. Above Va, large or abrupt elevator control can more easily exceed the airframe limitations of 6G for damage. Currently, it is impossible to stall the Spitfire in a turn or a dive. The reality is it requires careful flying so as NOT to induce an accelerated stall or exceed the airframe limitations.

3. In the turn, the violent buffet is a double edged sword. There is no such thing as a free lunch especially in physics. In the NACA measured results, encountering the buffet represents a change in available angle of bank. The airplane goes from 78.5 degrees of bank to 60 degrees of bank in one second.

****5G @ 147.73KIAS:

ROT = 1091*tan(78.5) divided by 147.73 KIAS = 36.2 degrees a second

****2G @ 141.647 KIAS:

ROT = 1091*tan(60) divided by 141.647 = 13.34 degrees a second

As a quick ballpark using IAS to get an idea of the scope of the effect on turn performance, we see the rate of turn drop from 36.2 degrees a second to 13.34 degrees a second. That means our time to complete a 360 degree turn changes from 10 seconds to 27 seconds!!!

As the Operating Notes relate, you do not want to turn any airplane in the buffet. Energy cannot be created or destroyed, all the energy that was being used to achieve an instantaneous performance rate of turn of 36.2 degrees a second from our ballpark went to warn the pilot of an impending stall, taking the aircraft right down well inside its sustainable performance envelope of 13.34 degrees a second.

The longitudinal stability characteristics of the Spitfire requires skilled flying to achieve a maximum performance turn. In a stable airplane, the pilot would have a much easier time keeping the aircraft at the maximum rate of turn velocity and a less violent buffet would have subsequently reduced effects on the turn performance.

4. Below Va, the Longitudinal instability of the Spitfire make it more difficult for the average pilot to prevent an acelerated stall or overcontrol the aircraft by pulling deeper into the buffet zone.

I think the fact that you have to return the stick almost to neutral after entering a high g turn (>3 g) to prevent oversteering in a Spitfire should be in game, also the very sensible elevator with large reaction for small inputs and the roll rate as documented.
This will be a problem for ham-handed pilots, but a delight for the virtuosos, as it was in RL.
I don't see that as "porking" the Spit further, but to give it the characteristics that made it famous.
Every aircraft in CoD should reflect its pro's and con's as they where documented then.

Exactly. That is our goal to recreate the flying qualities of all of these aircraft.

In this thread we have focused primarily on the Longitudinal stability. Most of the Spitfires issues stem from that.

For example, the heavy lateral control forces would not be an issue if the control forces were equal on all axes. The control harmony was poor in the Spitfire and Gimpy raises a good point:

well personally I would expect a much lower Roll rate at speed, and a very sensitive Unbalanced Elevator (unbalanced meaning it needs much more roll input than pitch).

The pilots ability to apply lateral control would be reduced by the longitudinal control characteristics.


*****Not a silly argument on actual turn performance, just a quick ballpark so readers understand the importance and general effect of encountering the buffet on turn performance.

[robtek]

Could please a mod put a stop to the personal attacks and the derailing of this thread?

[taildraggernut]

Not only that, it is unstable. That means your coefficient of moment increases each cycle instead of decreasing.

An unremarkable quality shared with many other types.

So if you pull a 6 G turn and did nothing except hold the stick fixed, the next oscillation will exceed 6G and continue to increase with each cycle until the airframe is destroyed.

Above Va, large or abrupt elevator control can more easily exceed the airframe limitations of 6G for damage

inconsistency, first quote you are already at 6G and expect airframe failure beyond that, second quote you say the limit is 6G, the limit was more like 10G

That is the reason why "flick" maneuvers were not allowed in it.

incorrect, the MkII low speed flick manouvers were permitted.

1. The Spitfire should be twitchy and unstable gun platform. IIRC, in IL2, people used to complain about the "twitchy" behavior or the Corsair and P-51's so I am sure it is within the games engine to model a twitchy airplane.

It should take very careful and small stick movements to get the gun sight on target. That means a Spitfire pilot will require more skill to hit a maneuvering target than he would need in a stable platform such as the Hurricane.

interestingly enough the Hurricane pilots notes describe a very similar longitudinal stability to the Spitfire

The longitudinal stability characteristics of the Spitfire requires skilled flying to achieve a maximum performance turn. In a stable airplane, the pilot would have a much easier time keeping the aircraft at the maximum rate of turn velocity and a less violent buffet would have subsequently reduced effects on the turn performance.

Below Va, the Longitudinal instability of the Spitfire make it more difficult for the average pilot to prevent an acelerated stall or overcontrol the aircraft by pulling deeper into the buffet zone.

Why? the elevator controls were light, requring much less effort on the part of the pilot to correct.

In this thread we have focused primarily on the Longitudinal stability. Most of the Spitfires issues stem from that.

What issues? the Spitfire never built up a reputation for any 'issues', can you at least give me the benefit of the doubt and provide some examples of documented events which gave the Spitfire any sort of bad reputation, it's a fair question.

For example, the heavy lateral control forces would not be an issue if the control forces were equal on all axes. The control harmony was poor in the Spitfire and Gimpy raises a good point:

it states clearly in the pilots notes that the exeptionally heavy ailerons were only apparent at very high speed, certainly not the sort of speeds one is likely doing in a combat turn where the speed is more likely decreasing, in a sustained turn there is little need for constant aileron correction, bad harmonisation is of no consequence here.

The pilots ability to apply lateral control would be reduced by the longitudinal control characteristics.

Again, only you seem to be able to understand this, just explain it in simple terms, how does elevator affect aileron control?

*****Not a silly argument on actual turn performance, just a quick ballpark so readers understand the importance and general effect of encountering the buffet on turn performance.

Quite right, no silly arguments here, just a need to have some very counter intuitive statements explained, Glider is 'spot on' when he said that buffet simply acts as a device to say 'hey bud ease off the back pressure a little'

[taildraggernut]

Originally Posted by robtek

Could please a mod put a stop to the personal attacks and the derailing of this thread?

I don't see any 'personal' attacks....unless asking questions or having a different oppinion is classed as an attack?

[Robo.]

Originally Posted by Crumpp

1. The Spitfire should be twitchy and unstable gun platform. IIRC, in IL2, people used to complain about the "twitchy" behavior or the Corsair and P-51's so I am sure it is within the games engine to model a twitchy airplane.

It should take very careful and small stick movements to get the gun sight on target. That means a Spitfire pilot will require more skill to hit a maneuvering target than he would need in a stable platform such as the Hurricane.

I am sure that you're aware that this is already the case in the sim.

[lane]

Originally Posted by winny

Ok.. NACA report on stalling characteristics of the same MK V





Further on in the report

Nice post winny. See also related R.A.E. Technical Note No.Aero 1106 - Comments on N.A.C.A. Advance Confidential Report Nos.A.R.C. 6423 and 6422 - "Stalling charteristics of a Supermarine Spitfire VA airplane" and "Measurments of the flying qualities of a Supermarine Spitfire VA airplane"