Stability and Control characteristics of the Early Mark Spitfires

[robtek]

Isn't the instability the fact that the Spitfire tightens its turn by itself without further control input???
The pilot has to stabilize the plane by countersteering.
Like a rear wheel driven car in a power slide around a turn, working, but stable is different.

[bongodriver]

Originally Posted by robtek

Isn't the instability the fact that the Spitfire tightens its turn by itself without further control input???
The pilot has to stabilize the plane by countersteering.
Like a rear wheel driven car in a power slide around a turn, working, but stable is different.

It's not an effect that has ever got much mention, pilots are often quite candid about the quirks of aircraft they fly, and this thread is the first place I ever heard of it, it may have happened under certain conditions but I don't think it was a common feature of Spitfire handling.

[Crumpp]

No mention of longitudinal instability being a problem...
and an accident inspector:

Really? It was the second major problem he mentions out of the 68 structural failures.

Isn't the instability the fact that the Spitfire tightens its turn by itself without further control input???
The pilot has to stabilize the plane by countersteering.
Like a rear wheel driven car in a power slide around a turn, working, but stable is different.
Today 02:22 AM

Correct. You have to apply a push force when should be applying a pull force. It is called a force reversal.

So a small input becomes an ever increasing acceleration until arrested by a push force. It is a symptom of the instability.

This is a measured by the NACA and a function of the divergent oscillation stick free measured by the RAE.

At high speed, the aircraft acceleration can overcome the airframe's limits to destruction.

[Crumpp]

Still the "pro Spitfire faction" is trying to push the dispute to a black and white scenario and concentrate to steer the thread to sections where they believe to have valid counter-documentation.

The truth is always grey!

Undisputed should still be the sensitivity and lightness of the longitudal control of the Spitfire.

Also proven is the fact that the longitudal control isn't stable, as it increases the g-load without further pilot input.

Those things should be implemented in game.

If now a player pulls his joystick all the way back in a cruise speed turn, the plane should react accordingly as the resulting g-forces would be way above the structural limits.

The player should be forced to use a small input to initialisize the turn and the to almost neutralize the controls to hold that turn, as the pilots had to to in RL.

In a tightening turn there should be signals (i.e. vibrations) to indicate the beginning of the pre stall buffet, followed by shaking and the loss of energy and increasing turn radius when the turn is further tightened and the buffet is fully entered.

Further tighteneing the turn should lead to a flick-roll.

The disharmony between ailerons and elevators should also be there.

Imo that is a summary that should please any rational view on this thread.

Good Summary

[bongodriver]

Just need to bear in mind that the effects being called for are 'not' conducive to qualities noted for being 'easy to fly', so how do we meet half way on this? how are we going to recreate an alleged instability in an aircraft but retain the ease of flying qualities? or are we really saying that one NACA report on a MkV Spitfire outweighs the accounts of every Spitfire pilot of any Marque that ever lived?

When are we getting the 109 thread?

[Crumpp]

When are we getting the 109 thread?

You guys want to do the Bf-109 next?

I was going to do the Hurricane next.

[Crumpp]

The anti-Spitfire, bad longitudinal instability faction can only see a cloudy, murky-grey, glass half empty scenario where there is no clear evidence that longitudinal instability actually caused in flight structural failure and they don't like black and white evidence being posted to show how doubtful their case is.

But it is not that way.

First, the anti-Spitfire faction exist's only in your mind.

Second, anybody who knows stability and control can read the article to see the characteristics clearly.

The gentleman who was interviewed for the article points out the fact they did not have a good understanding of stability and control engineering at the time.

The article is most interesting because it shows the thought process of the day and not for its engineering conclusions.

You however, take those engineering conclusions as proof. By that thinking, we should be doing meta-center calculations to prove the airplane was stable!!

[bongodriver]

Originally Posted by Crumpp

You guys want to do the Bf-109 next?

I was going to do the Hurricane next.

Why didn't you start threads concurrently?

[Glider]

Crump

Before you start everything I would much prefer it if you used a more complete and modern set of standards for the calculations.

The most recent ones that I had any dealings with were

MIL - STD - 1797A

The fundamental problem that I believe you have, is that something is either stable or unstable. These standards give levels of accaptable stability for different types of combat aircraft. For instance you would expect what is acceptable for a C17 to differ from an F15 or you end up with an F15 which is a sitting duck or a lot of airsick troops in the C17.

I last used these in the late 1980's and there is a better than average chance that they may have changed in that time, so you may want to look into it.

However to carry on with the black and white process that you have is foolish and totally out of kilter with the real world. In the real world its a mixture of theory your preferred approach, how they actually feel to fly which is my approach, plus what are they desinged to do. These are normally combined and we used to refer to the flying qualities.

If I go back to the three gliders I mentioned an age ago.
The Twin Astir was very heavy and as far as aerobatics was only really good in the vertical, but it was excellent for training people to go cross country as it had less need to thermal but was fast.
The K21 was a much better all round glider good at most aerobatics and for training. However it was almost impossible to spin, a major problem in a trainer. So much so we use an old K13 for Spin Training which I loved to fly. The K21 was also good for training all types of flying thermalling and cross country
The Fox was a dedicated aerobatic machine. You certainly didn't want to go cross country or thermal but if you wanted to learn the fine points of aerobatics, this was the machine to use. Excellent roll rate for a glider and very precise in the control.

All design is a balance and as I write this the BOB Lancaster and a Spit have just flown very low over my house at about 5-700 ft

Back to the topic the term we use is the flying quality of the machine, which has to take in the task in mind, how it feels and the theory. These standards cover this combination
The

[NZtyphoon]

Originally Posted by Crumpp

Really? It was the second major problem he mentions out of the 68 structural failures.

Wrong: 20 case of pilots losing control in cloud, 13 structural failures due to oxygen starvation, three due to pilot black-out - in none of these cases is longitudinal instability mentioned as a major or causative factor.

Originally Posted by robtek

Still the "pro Spitfire faction" is trying to push the dispute to a black and white scenario and concentrate to steer the thread to sections where they believe to have valid counter-documentation.

The truth is always grey!

The anti-Spitfire, bad longitudinal instability faction can only see a cloudy, murky-grey, glass half empty scenario where there is no clear evidence that longitudinal instability actually caused in flight structural failure and they don't like valid black and white documentary evidence being posted to show how doubtful their case is.