Spit IIa

[Crumpp]

I can break the Spitty in two by madly pulling back the stick, something that would be suicidal in the real one with a stick force of a mere 4 lbs / G.

If the unacceptable stability and control characteristics of the Spitfire are not modeled, then you will never have a simulation of the relative dog-fighting capabilities of these airplanes.

Aerodynamically the Spitfire could easily out-turn a Bf-109E series. A pilot dealing with the real world stability and control issues would leave the contest much closer than the aerodynamic analysis on paper.

The stability and control characteristics of the BF-109 were acceptable and actually conformed to a set standard based on Robert R. Gilruth's findings on flying qualities. Germany was ahead of most of the world in adopting such as standard. Japan was also on an acceptable control standard. None of this was known to the Allies until after the war.

It is interesting to note that the NACA adopted a unified stability and control in 1942 but it was not until 1945 that the USAAF (R-1815-A)and USN (SR 119A) printed their own standards using the NACA findings. The first fighter the NACA tested was a Spitfire Mk V. The aircraft failed miserably and was replaced in USAAF service as soon as possible.

[IvanK]

Originally Posted by Crumpp

If the unacceptable stability and control characteristics of the Spitfire are not modeled, then you will never have a simulation of the relative dog-fighting capabilities of these airplanes.

Unacceptable to Who ? A NACA methodology formalised 4 or so years after the aircraft first flew. Didnt a number of US units actually switch from from MKV's to MK VIII's.

As to NACA's evaulation of the MKV the RAE in Technical note No.Aero 1106 made a bit of a rebuttal on the NACA findings. This includes some criticisms in the way NACA carried out its tests. I guess both reports should be read to draw a balanced view. The RAE document refers to NACA reports ARC 6423 and ARC 6422.

Here is the Summary or conclusions of the Langley evaluation of the Spitfire MKVA "Measurements of the Flying Qualties of A Supermarine Spitfire VA Airplane" ... not all exactly bad


Here are the conclusions from the second Langley report "Stalling charcteristics of the Supermarine Spitfire VA Airplane again not all bad:

[Crumpp]

Unacceptable to Who ?

Any stability and control engineer in existence. Remember there was no such person when the Spitfire was designed.

There is a reason why the RAE added bob-weights to correct the stick force gradient. This fixed the control force issue but did not correct the instability itself.

As to NACA's evaulation of the MKV the RAE in Technical note No.Aero 1106 made a bit of a rebuttal on the NACA findings. This includes some criticisms in the way NACA carried out its tests. I guess both reports should be read to draw a balanced view. The RAE document refers to NACA reports ARC 6423 and ARC 6422.

I am aware of the RAE rebuttal. Keep in mind the British were one of the last to adopt any kind of standard on stability and control.

Of course they thought it was fine, there was no established basis for what was acceptable and what was not. A few fatalities later though, the RAE did something about the Spitfire's longitudinal instability. Again, it made it easier to control but did not eliminate the cause of the instability.

[Crumpp]

It is right there.

You know what stick fixed stability is right?

Originally Posted by Crumpp

Aerodynamically the Spitfire could easily out-turn a Bf-109E series. A pilot dealing with the real world stability and control issues would leave the contest much closer than the aerodynamic analysis on paper.

I agree that the fighter pilots would have driven their kites closer to the limits than tought at flight school. As you indicate yourself by your phrase, aerodynamic calculations are never as accurate as to predict reproducable stall speeds. But this may go both ways that is that calculations are either pessimistic (stall would occur later than calculated) or also optimistic (stall would occur sooner than calculated). So it may be the way you stated it (the pilots drove their plane closer to the limits than what calculations would have predicted) but it may also be the other way around.

Principally I would guess that stall speeds taught to the cadets were obtained experimentally. And keep in mind that pilots appreciated when they got a feedback from the plane (e.g. buffeting) when they got close to the stall limit.

[Kurfürst]

I wonder, is there a clear definition of stall at all...?

[CaptainDoggles]

Originally Posted by Kurfürst

I wonder, is there a clear definition of stall at all...?

Stall is defined as the point where the airfoil's critical angle of attack is exceeded.

[Crumpp]

I wonder, is there a clear definition of stall at all...?

Captain Doggles gives a good definition:

Stall is defined as the point where the airfoil's critical angle of attack is exceeded.

The question is not when does the stall occur but rather how much warning the aircraft gives.

That is the conundrum faced by designers. Today stability and control is a well defined science. Aircraft designers have many more tools to take advantage and flying characteristics are a consideration almost from conception. For example, today designers build aircraft with no stall warning at all, these airplanes can be flown at maximum performance right up to CLmax without aerodynamic penalties of a buffet. To warn the pilot he is nearing a stall, an artificial device called a "stick shaker" is used.

To understand that stall warning, one must understand what buffeting is aerodynamically. It is a rapid secession of flow separation and reattachment.

When that boundary layer is not attached to a portion of the wing that portion is stalled, an airplane in turn is no longer turning at maximum rate. If you read the Spitfire Mk I pilots notes it expressly warns the pilot to ensure he experiences no buffeting in a turn. First of all when the airplane is buffeting, the turn rate is reduced even though the airfoil is not at CLmax. Secondly, the Spitfire has an extremely nasty stall that will spin and the aircraft is susceptible to airframe destruction in an aggravated spin.

[Skoshi Tiger]

If the spitfire's stability was unacceptable why would Werner Molders have written

"It handles well, is light on the controls, faultless in the turn and has a performance approaching that of the BF109."

All very subjective I know, but i can only assume that he would have been comparing it to the 109 he flew.

Just because something doesn't comply to a standard doesn't mean it lacks merit, it just means it doesn't comply to a standard.

It's just like if you get a Porche intended for the German market ands try to licence it in Australia, it would fail to meet the Australian safety standard and you wouldn't be able to legaly drive it on our roads. The same car with minor altertations to meet the Australian standards (and given an appropriate compliance plate) would be fine in Australia but in the process render it non-compliant in Germany.

Cheers!

[IvanK]

Originally Posted by Crumpp

You know what stick fixed stability is right?

Err yes, 36 years professional flying, including one high performance type with neutral stability (and 50+ degrees Alpha and controllable capability) and the ability to fly in both FBW and basic manual modes. So I have a basic understanding of keeping the pointy end forward.

My point is your original comment ... "If the unacceptable stability and control characteristics of the Spitfire...." is imo a sweeping one. The spitfire had issues but then so does every aeroplane. In general its handling was pretty straight forward. In addition, adding Bob weights in the pitch circuit was quite a common practice at the time.

As to your comment on the Spitfires stall :

"the Spitfire has an extremely nasty stall that will spin and the aircraft is susceptible to airframe destruction in an aggravated spin."

I think that is a bit loose as well and needs to be put into the context in which this area of handling is discussed in the pilots notes. The pilots notes (MKI anyway) mention is made in the Accelerated (or high speed) stall that if not quickly corrected could lead to structural damage. To my mind this is simply pointing out that at high speed High G departure (accelerated stall) there is a possibility of structural failure, my presumption exceeding Rolling G limits etc. This description is similar to a Flick roll at high speeds. In 1G flight the Spitfire stall was pretty straight forward. A personal work colleague and friend of mine is fortunate to fly the both Spitfire MKVIII,XVI,P51D and P40F on a regular basis. He absolutely raves about the Spitfires slow speed handling and its abilty to just "keep giving" in the high AOA region. It might not meet all the NACA requirements but it still was a very well behaved aeroplane.