Stability and Control characteristics of the Early Mark Spitfires

[robtek]

Originally Posted by 41Sqn_Banks

So basically what should be implement is:
- Structural g limit for all aircraft
- Light elevator at high speed for Spitfire

Now let's figure out if both features are already implement and if not submit a feature request.

Agreed, but the elevator was not only light but also sensible. (short travel-large reaction)

[ACE-OF-ACES]

There is a point where we all have to realise this it not real..

There are so many things we simmers don't have access to that real pilots had access to

Such that it would be silly to expect us to deal with every aspects of 'reality' in a 'simulation'

On the flip side, we never have to worry about a .50 cal hitting us in the neck while flying

So many things are done in software to make up for this fact.. But I would not refer to them as a bug (make up for the fact it aint real)

Take buffets for example..

In reality in some cases you would probally 'feel' it..

A buzz in your pants or the stick before you 'see' it in real life..

But since the sim can not simulate this (minus those with FFBJS)

The software inserts a screen shake and/or sound to cue the sim pilot into the fact that he is near a stall

At the same time there are so many things (like this topic) that can not be done in software.. But I woudl not refer to them as bugs either (limitations)

In short

No flight simulation ever WAS, IS, or WILL BE REAL!

[Crumpp]

buffet can be simulated with head shake and g with increasing tunnel vision.

To simulate the buffet realistically, the aircraft turn performance should be reduced if one tries to fly in it.

It takes more power to fly in the buffet than it does in smooth air.

The harder an aircraft buffets and more stall warning it delivers, the more power it takes to produce the buffet.

This is exactly why you see aircraft with little to no stall warning and the advent of artificial stall warning devices like stick shakers. With the advent of stick shakers, designers are freed from providing aerodynamic stall warning and can maximize aerodynamic performance.

[IvanK]

Originally Posted by Crumpp

To simulate the buffet realistically, the aircraft turn performance should be reduced if one tries to fly in it.

It takes more power to fly in the buffet than it does in smooth air.

The harder an aircraft buffets and more stall warning it delivers, the more power it takes to produce the buffet.

This is exactly why you see aircraft with little to no stall warning and the advent of artificial stall warning devices like stick shakers. With the advent of stick shakers, designers are freed from providing aerodynamic stall warning and can maximize aerodynamic performance.

We have been here before ! As has been stated before Buffet has depth. The very first onset is referred to as the the "Buzz" or the "Tickle" The current RAAF PC-9 Flight manual uses the term "Light Pre Stall Buffet". It is a standard technique (and was in WWII as stated by Geoffery Wellum in his book First light) when trying to get the best out of the aeroplane to smoothly pull to then hold on the "buzz". This is a STANDARD technique taught in most air forces even to this day. Whole training sequences in Military pilots courses are devoted to max performance turning. It is also a standard technique used by Glider pilots trying to get the best out of their machines as well in the thermal centering etc.

Stick Shakers are a relatively new device and have little to do with WWII era aviation. Stick shakers were designed to provide Stall warning as a primary goal not as a device to enable max performance turning..... AOA indicators do a better job in this department. Trying to fly an aeroplane on the shaker (like in a wind shear or GPWS event) is not an easy task as you are in and out of the shaker all the time. In general Stick Shakers are the preserve of the larger transport types from say the DASH 8, B757,B767 with conventional non FBW flight controls. Though some predominately Russian fighter types with conventional flight controls (early MIG29) do have similar devices (including pedal shakers) to provide Max AOA cueing.

We all know flying in deep buffet requires more power. I think you will find Energy bleed in CLOD is increased quite significantly IN the buffet.

Flying on the buzz is a valid technique to get the best turn performance out of the aeroplane.

I posed a situation before when this was the subject of another of these Mammoth "intellectual" threads... the answer was avoided. Picture this situation.

You find yourself in your Spitfire MKI 90 degrees nose down at very low altitude. You are not sure if you have the turning room to avoid the ground.
Your only chance is to get the absolute minimum radius turn RFN... how are YOU going to fly the turn .. no time to think ... delay compounds the issue.... FAILURE = DEATH.

[bongodriver]

Originally Posted by robtek

Agreed, but the elevator was not only light but also sensible. (short travel-large reaction)

Not at all speeds though, only at very high speed and only documented on a Spitfire Va on one NACA test.

[Crumpp]

Please note that this happens with a full bomb load (1,000 lb) and the extra rear internal fuel tank. Obviously neither of these were around until late 1944

Right and has nothing to do with piles of bent wings at the repair depots during the Battle of Britain.

[bongodriver]

Originally Posted by Crumpp

Right and has nothing to do with piles of bent wings at the repair depots during the Battle of Britain.

That are purely anecdotal

[Crumpp]

must be 'Joe Average' for all pilots,

The NACA did a study as part of the stability and control standards on the forces an average pilot can exert.

I am sure that data could easily build an "average joe" pilot.

It would be easy to implement a fatigue model as well.

It is very interesting, btw.

The current FAR's are based in this same research. The formula for minimum stick force per G required in a stick control column aircraft is:



(Weight of Aircraft / 140lbs) / (structural damage limit - 1)

So a 6500lbs aircraft using a stick as the control input and is fully aerobatic at a structural damage limit of 6G:

(6500lbs/140) / 5 = 9.28Lbs per G minimum required.

[NZtyphoon]

Originally Posted by Crumpp

The NACA did a study as part of the stability and control standards on the forces an average pilot can exert.

I am sure that data could easily build an "average joe" pilot.

It would be easy to implement a fatigue model as well.

It is very interesting, btw.

The current FAR's are based in this same research. The formula for minimum stick force per G required in a stick control column aircraft is:



(Weight of Aircraft / 140lbs) / (structural damage limit - 1)

So a 6500lbs aircraft using a stick as the control input and is fully aerobatic at a structural damage limit of 6G:

(6500lbs/140) / 5 = 9.28Lbs per G minimum required.

Please explain how this translates to a computer sim, and how will the developers adapt this formula to cater for the different types of joysticks/rudder pedals used by members of the IL2 community?

[Crumpp]

PS I do owe you an apology.
You said that the design of the Spitfire wing was done at a number of colleges and I asked you which to which you gave me a number. It was a trick question which you fell for.
You may or may not know what is taught at the establishments you named, but you would not know what they use in their lectures unless you had done the course so your list must have been made up.
Also you said Cambridge as one of the establishments. Cambridge isn't a place where you study. Cambridge is in effect an admin centre for 31 Colleges or to be more precise seats of learning and none of them do aerodynamics.

I can tell you that Cranfield is the premier University for Aerospace in the UK its very advanced with their own test fleet of aircraft. We had visiting lecturers from Cranfield come to HMS Daedalus for some of our studies which included Hovercraft

Which has what to do with anything?

I never claimed to go to Cambridge. I went to Embry Riddle. I do have friends who went to other colleges and they also know of the Spitfire's instability.

What does your point have to do with that fact or any fact relevant to this discussion?

Or the fact, it is Cambridge University that published the book??

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