Stability and Control characteristics of the Early Mark Spitfires

[winny]

Originally Posted by CaptainDoggles

I read the entire article. Are you denying that a stable aircraft can be maneuverable?

This is a bit of a loaded statement. It ignores half of the argument.

The question is: Is a stable aircraft more or less maneuverable than an unstable one. Of course you can have a maneuverable stable aircraft but, are unstable aircraft more maneuverable than that?

The other big question is how detrimental to the Spitfires performance was the instability?

[fruitbat]

Originally Posted by winny

This is a bit of a loaded statement. It ignores half of the argument.

The question is: Is a stable aircraft more or less maneuverable than an unstable one. Of course you can have a maneuverable stable aircraft but, are unstable aircraft more maneuverable than that?

exactly.

[CaptainDoggles]

Originally Posted by NZtyphoon

"In a word, the relationship of longitudinal stability to maneuverability is inverse. As one increases, the other decreases and vice versa." ?

First of all, I'm going to disregard things like Active Stability, where you have the computer making lightning-quick corrections to the unstable aircraft to keep it in controlled flight, because I think that this is beyond the scope of what we're talking about here. If we want to get into a discussion on the characteristics of FBW systems and supermaneuverability then we should open a new thread.

--

I think it depends greatly on

a) which stability mode we're considering; if it's the short period or the phugoid mode

and

b) what you consider to be "maneuverable".

I think that if you were to reword that statement to read "the relationship of longitudinal stability to agility is inverse. As one increases, the other decreases and vice versa" then I would absolutely agree.

If an aircraft is unstable, then it will by definition be difficult or impossible for the pilot to precisely control the aircraft during a maneuver. By this I mean the pilot won't be able to hold a constant G-level through a turn, or to keep his guns on target.

I would consider such an aircraft to be highly agile, because it can re-orient its lift and nose vectors quickly and easily. This makes intuitive sense, because an unstable aircraft always wants to depart from equilibrium.

But I don't think that the aforementioned aircraft is particularly maneuverable, because I would define maneuverability as being easy to maneuver precisely and accurately through a wide range of maneuvers. In my opinion, if you have to fight the aircraft making corrections the whole time, then it's harder to get it to do what you want it to do, and so it's not very maneuverable, and so I would not consider an aircraft with negative stability to be very maneuverable.

[CaptainDoggles]

Coming back to the Navy textbook quote and FBW systems for a moment:

I think that they ascribe an inverse relationship to stability vs maneuverability because their aircraft have FBW capabilities. If the airframe is actually unstable, but you have a computer making corrections thousands of times per second, then all of a sudden your aircraft appears very stable to the pilot. In this context, the quote is accurate.

Obviously this lets them combine agility and maneuverability into one, and I think this is why the quote says what it does.

[winny]

Here's a quote written about the F-16

The CG is located aft of the aerodynamic center to reduce longitudinal stability
in favor of maneuverability, and help the horizontal tail
add to the lift while maintaining longitudinal trim...

From : JOURNAL OF AEROSPACE SCIENCES & TECHNOLOGIES VOL. 58, No. 2

[NZtyphoon]

Originally Posted by CaptainDoggles

First of all, I'm going to disregard things like Active Stability, where you have the computer making lightning-quick corrections to the unstable aircraft to keep it in controlled flight, because I think that this is beyond the scope of what we're talking about here. If we want to get into a discussion on the characteristics of FBW systems and supermaneuverability then we should open a new thread.

Fair enough, we are discussing an aircraft without FBW and supermanœvreability

Originally Posted by CaptainDoggles

If an aircraft is unstable, then it will by definition be difficult or impossible for the pilot to precisely control the aircraft during a maneuver. By this I mean the pilot won't be able to hold a constant G-level through a turn, or to keep his guns on target.

I would consider such an aircraft to be highly agile, because it can re-orient its lift and nose vectors quickly and easily. This makes intuitive sense, because an unstable aircraft always wants to depart from equilibrium.

But I don't think that the aforementioned aircraft is particularly maneuverable, because I would define maneuverability as being easy to maneuver precisely and accurately through a wide range of maneuvers. In my opinion, if you have to fight the aircraft the whole time, then it's not very maneuverable, and so I would not consider an aircraft with negative stability to be very maneuverable.

I don't see any indications of pilots having to "fight" the Spitfire all the time, so it wouldn't come into your definition of agile but not manœuvreble -

Here are some comments from Alex Henshaw on flying the Spitfire:
http://www.theaviationindex.com/publ...pilots-defence

"With a brief pause for the undercarriage to retract and at 135 m.p.h IAS, the machine would be pulled up into a vertical climb for the first half of a loop. On reaching almost the extremity of the climb it could then be gently coaxed over at something like 10-15 m.p.h below its normal stalling speed. During this sensitive manœuvre the ailerons would be hard up against the stops but still effective....
The Spitfire would then continue with a series of loops and half-rolls to gain height over the airfield to between 4,000 and 5,000ft. Depending on the precise position of the aircraft in relation to the airfield, the usual procedure was to dive to 450-470 mph in front of the flight shed and then pull out and complete an upward roll to the left, one to the right and a half-roll left. This manœuvre might be repeated or continued with a vertical dive with aileron turns."

"It is generally accepted that the Hurricane made a better gun platform than the Spitfire. I have never fired the guns of a Hurricane, but those top-scoring pilots with whom I have discussed the subject all say that the marvellous feature of the Spitfire was the speed at which the guns could be brought to bear on the target. Their reply to the accusation of "hosing' was that the pilot concerned was a poor shot."

[robtek]

I'd like to repeat that being unstable or negative stability is NOT desirable for any airplane, as the pilot, or today electronics and hydraulics, have to work all the time for a controlled flight.
For commercial planes, were safety is the highest priority, positive stability is desirable.
For fighters, or aerobatic planes, neutral stability is the non plus ultra.

[Crumpp]

During WW2, however, the demands of production testing thousands of aircraft meant that each factory adopted its own techniques, designed to test aircraft to an acceptable standard, as quickly as possible, before delivery: this did not mean that there wasn't a standard set by the RAE, simply a divergence of ways in which it was done at a production level. The same thing happened in the 'States, each factory adopted a testing regime broadly following the NACA guidelines.

Once again, a standard is a standard. The Air Ministry and the RAE did not have one.

The United States had a standard during the war. That does not mean every airplane met that standard. Most aircraft were designed before the standard was adopted. It does mean, they designed to meet, tested to meet it, and implemented design corrections to meet the adopted standard. Part of that report and standard is included in the very first post in this thread.

The design firms in the United States were obligated to meet a standard. Supermarine was under NO Obligation to correct the Spitfire. It as already in production and service. It took the NACA, Gates, and mounds of evidence of the instability before a simple correction was adopted.

With the right information, figuring out how much weight to add to your elevator bellcrank is no different than a weight and balance. Once more, a designer can add springs, bungees, weights, and other devices to increase or decrease the control force as he wants.

Facts are the RAE relied upon the individual talent of the engineers and the opinion of the pilots.

Not all engineers are equal. For example, Sir Sydney Camm was very talented with stability and control design. His designs reflect that. RJ Mitchell certainly missed the mark on the Spitfire.

Is a stable aircraft more or less maneuverable than an unstable one.

It does not matter how maneuverable an aircraft is if the pilot cannot control it.


That is the Spitfire's issue. Nobody is claiming it should be less maneuverable. The longitudinal axis should be so maneuverable as to be very difficult to precisely control.

Generally speaking, all aircraft above Va can exceed their airframe limitations. You can do it more easily in the Spitfire.

It is also harder to precisely control in a turn. The strength of the buffet determines the scope of the effects of the stick shaker zone. Hitting stick shaker in a Spitfire is easier due to the longitudinal instability.

Properly modeled, the Spitfire has world beating performance. While not the most agile fighter, it is fast, climbs well, and excellent rate of steady state turn.

The majority of fighter pilots in World War II never got into a single dogfight. Most kills occurred without the "victim" even knowing the opponent was there behind them.

So all those anecdotes about "easy to fly" are worthless without the context and a comparison of pilot skill. I would love to fly a Spitfire and throw it around the sky on a sunny afternoon.

That is not the same as dog fighting. Dogfighting is what you do in this game and it has very little if anything at all to do with the actual events or history. An actual simulation of WWII would be zero fun. For the vast majority of pilots, it was lots of tedious flying to be killed without ever seeing who did it. For a few, it was a few seconds of terrified maneuvering before death and for a rare few that we still talk about today, the thrill of the hunt.

The NACA and the RAE agree that the aircraft was difficult to precisely control in a turn. It was twitchy airplane. The airplanes characteristics are measureable, definable, and everyone who was involved with the airplane agreed upon them.

The Spitfire should take time and skill to master. Once mastered, reward its aficionados with the performance they expect.


I think this thread has about run its course. Time to submitt the bugtracker.

[Crumpp]

Please start into my use of "stick shaker"....

[Crumpp]

Alex Henshaw on flying the Spitfire

How many actual dogfights did Henshaw get into in an early mark Spitfire??

None.

How many in any Spitfire??

What Mark of Spitfire is that on the magazine cover?? What Mark was the topic of this thread??