Why do Spitfires turn better than Hurricanes?!

[lane]

Stephen Bungay has a chart of turning circles in his book "The Most Dangerous Enemy". It looks to me as if the turning circle at sea level for the Hurricane Mk I is about 660 feet versus about 690 feet for the Spitfire Mk I. (see attached) Great book, I highly recommend it!

I’ve been reading Group Captain Colin Gray's autobiography "Spitfire Patrol". There are some interesting passages related to this thread's topic. Another great book, I highly recommend this one too! Gray flew both Hurricane Mk I and Spitfire Mk 1 in combat and wrote:

"There have been many arguments about the relative merits of Spitfires and Hurricanes, particularly in relation to the mark 1 versions used in the Battle of Britain. As one who has flown both in action, I have no doubt that the Spitfire was superior by quite a margin. It was some 30 to 40 miles per hour faster, climbed quicker, and had a higher service ceiling. Being lighter on the elevators it was quicker and easier to manoeuvre, and contrary to general belief it could out-turn a Hurricane." (see attached)

"The problem of manoeuvrability was of prime importance in enabling one to turn inside the enemy, certainly in fighter versus fighter combats, and thus to get a shot in when on attack, or avoid being shot down when on the defensive – and here the British aircraft had a decided advantage in my experience." (see attached)

Though a bit off topic, though none the less of some interest, Gray also made a rather blanket statement regarding Spitfire and Me 109 turn, in this particular instance describing a Spitfire IX - Me 109 G2 combat which occurred in North Africa during April 1943.

"Just as I completed my turn I saw another aircraft coming towards me at high speed, as he flashed past I recognized a 109G2. He obviously recognized me as hostile because he immediately pulled up into a screaming left-hand turn and attempted to dogfight. This was his big mistake because there was no way a 109 could turn inside a Spitfire." (see attached)

Mr. Gray flew Spitfire Mks I, II, V, IX, XII and XIV in combat and is credited with 27.5 victories, all in Spitfires. He fought over Dunkirk and through the Battle of Britain in 1940; commanded a Spitfire IX squadron in North Africa, then was wing commander during the invasion of Sicily in 1943; and led a Spitfire XIV wing as Wing Commander Flying over France, Belgium, Holland and Germany in late 1944. He earned his say in my opinion and I’ll not be one to take issue with his experience.

The charts are interesting but not really helpfull. The turn radius is at what respective speed? Speed has an extremely strong impact on turn radius (turn around a corner while standing or while running you'll immediately sense the difference. For aircraft it is the same) and at which fill level. For me these are quite futile.

[Sternjaeger II]

Originally Posted by TomcatViP

No problem. The ultimate fighter Pilot is the utmost finest Engineer (this is an awfully wrong statement )

Do you remember the Venturi effect when the air is accelerated through a narrower section ?
Now take a wider look at a wing section. If you focus either on the upper or the lower surface, you will see that regarding to the free stream of air unperturbed by the airfoil, there is a section increase as the thickness of the airfoil increase and the a similar decrease after the point of inflexion.

The direct effect of this (appart from the direct generation of LIFT) is that the air is accelerated and then as the section increased, expended with a rather brutal Pressure increase.

Now imagine that (I am actually singing it) you are flying at a speed nearly 2/3 of the speed of sound.

Due to the imaginary geometry described above, you can understand that the air is accelerated trough this partially materialized venturi. The increase in speed being directly proportional the the section decrease. Hence the more thickness the more the air flow is accelerated

When the speed and the wing's thickness are high enough, the airflow ard the wing reach Mach 1, the speed of sound. As the air goes further back along the chord, the air is expended (the distance btw the free airstram and the airfoil increase) and the air is decelerated bellow Mach one trough a pressure shock. This pressure shock is what we call a shock wave.

Now let say simply that due to he fact that the pressure distribution is modified because of both the shock waves above and bellow the wing, the LIFT moment is modified with a negative upward (relative to the chord) pitch down moment.
What you can see is that the more the wing is thick, the earlier the air ard the airfoil section reach the critical mach number.

Hence the thin airfoil series of the 50's fighters (Starfighter, F105, Mig 21 etc..).

This is why the compressibility affect the wing and not so much the generally thinner tail section.

Interestingly too this is what makes the Spitfire so fast in a dive. What you can see now is the sublime irony of mother nature that turned a wrong design assumption (the elliptical wing) in a wining parameter. I tell you Germany cldn't hve win !

Note : The 47 had an elliptical wing too. And it was also awfully fast in a dive!

~S!

uhmmm it's still a matter of proportions, especially when getting to supersonic speeds.

When doing wind tunnel studies, the transonic/supersonic experiments need to be made on a life size model to make an accurate observation of the shock phenomena, which behave and change dramatically according to the size of models.

I would like to hear Viper's opinion on the matter, do you reckon tail surfaces would hit compressibility before wings or viceversa?

[Viper2000]

Originally Posted by Sternjaeger II

I would like to hear Viper's opinion on the matter, do you reckon tail surfaces would hit compressibility before wings or viceversa?

I think the only reasonable answer to a question like that is "It depends...".

Really this "hit compressibility" concept is horrid. Air is compressible all the time. If you go fast then compressibility becomes more important. But I'd generally be inclined to consider compressibility in calculations for M>0.2 if I wanted accurate answers. Really the Mach number at which you elect to consider compressibility is a bit like the temperature at which you decide to account for variation in the Cp of dry air - it's arbitrary, and depends upon the computational resources available and the effort you're prepared to put in.

I'd generally expect the tail to be lower aspect ratio than the wing. Therefore it can be thinner. I'd also expect it to be at lower absolute CL than the wing. So, if we assume the same amount of sweep for wing and tail, I'd expect the tail to remain subsonic to a higher freestream Mach number than the wing.

But the generalisations associated with the above are dramatic. Control deflection, variations in wing downwash angle and so on could easily make quite a big difference.

In the WWII context, with manual controls you're likely to find that the pilot runs out of bicep before shockwave development over the tail starts to bite.

Here's a quick list of the factors causing "Mach tuck":

• Migration of the wing's centre of pressure
• Changing wing downwash angle
• Rapidly increasing stick force for constant elevator deflection
• Reduced elevator effectiveness due to shock developement over the tail

You can see that 3 out of the 4 don't require shock development over the tail.

OTOH, the underlying problem is the tail; because that's where the control surfaces are, and the problem is a control problem.

So the brute-force approach towards the end of WWII and immediately thereafter was to hydraulically boost everything. Once you do that then the new problems are dealing with the failure modes and providing Q feel so that the pilot doesn't break the aeroplane.

Then you might get into trouble with lack of elevator effectiveness, because the elevator can't affect the pressure distribution upstream of any shock which may have formed over the tail. But really it's unreasonable to think of the flying tail as a "solution" to this problem, because going to a flying tail in 1940 wouldn't have solved fighter stability & control problems. Without irreversible screwjacks to drive the thing, you'd find that either it fluttered off or else the control forces were impossibly high.

Really the concept of the "flying tail" is a sort of marketing thing rather than reality. There's nothing magic about it. The simple reality is that if you're supersonic the you need the movable bit of your control surface to do all the work by itself, and you therefore have to size it appropriately. Note that delta winged fighters do just fine with elevons - no need for the surface to have its own private leading edge to work - it just needs to be big enough and to be driven by a sufficiently strong set of jacks.

In subsonic flight the elevator can be quite a lot smaller because it affects the lift curve slope of the whole surface it's attached to, which is great if you've only got a relatively limited actuating force available. Hence the rapid ubiquitous adoption of the elevator in subsonic aeroplanes quite early in the evolution of the aeroplane.

The other thing which people got used to is the idea that in general a nice set of aerodynamic controls will give you stick free stability which may well mask any nasty stick-fixed behaviour your design may exhibit. During WWII the added friction associated with pressurised cockpits started to show up some of the stick fixed problems that had been lurking under the rug for decades, and this caused people to start working on tweaking the control system itself via bob-weights etc to affect the subjective handling characteristics of the aeroplane, rather than just expecting the pilot to tolerate what he was given.

This gradually took us towards full FBW/manoeuvre demand systems, which allow you to design the apparent handling of aeroplanes to be almost independent of their aerodynamics. Which is great, though it does open all sorts of philosophical cans of worms since you now have to think about what the ideal set of control laws would be, rather than just asking the test pilot whether he can fly the thing or not...

The loss of stick free stability also rather reduced the importance of the fixed portion of the tail from a handling perspective, and since the elevator had to be big enough for the supersonic control task, it was almost always going to end up big enough for the subsonic case and therefore why not just bin the fixed tail?

Actually there are several reasons, especially for larger aeroplanes; essentially a fixed tail with an elevator is likely to be lighter, though you may have to also vary its incidence for trim, which takes some of the advantage away (though the trim change can be an order of magnitude slower than the control trim, since effectively the trim change has to damp the phugoid whilst the control change has to damp the short period oscillation, and therefore the trim actuators can be smaller).

But I digress; time to get a cup of tea & get back to my thesis...

[Viper2000]

Originally Posted by 41Sqn_Stormcrow

For me these are quite futile.

I wouldn't go quite that far, but certainly I'd be much more interested in turn rate than turn radius if I flew fighter aeroplanes for a living.

[Sternjaeger II]

sorry man, that's pilot jargon, the correct question would be "do you reckon that the effects of air compressibility would affect first the control surfaces or the wing?".

Thinking about the effects of compressibility puts the whole research and introduction of delta wings and canard wings into a very interesting perspective

[Viper2000]

Originally Posted by Sternjaeger II

sorry man, that's pilot jargon

No no no! Please watch the following training videos immediately.

Pilots use banter.

http://www.youtube.com/watch?v=5rKYL0tW-Ek

Only engineers are allowed to use jargon.

http://www.youtube.com/watch?v=bOV0v1Uq5CY

[TomcatViP]

Originally Posted by Viper2000

I think the only reasonable answer to a question like that is "It depends...".

Really this "hit compressibility" concept is horrid. Air is compressible all the time. If you go fast then compressibility becomes more important. But I'd generally be inclined to consider compressibility in calculations for M>0.2 if I wanted accurate answers. Really the Mach number at which you elect to consider compressibility is a bit like the temperature at which you decide to account for variation in the Cp of dry air - it's arbitrary, and depends upon the computational resources available and the effort you're prepared to put in.

I'd generally expect the tail to be lower aspect ratio than the wing. Therefore it can be thinner. I'd also expect it to be at lower absolute CL than the wing. So, if we assume the same amount of sweep for wing and tail, I'd expect the tail to remain subsonic to a higher freestream Mach number than the wing.

But the generalisations associated with the above are dramatic. Control deflection, variations in wing downwash angle and so on could easily make quite a big difference.

In the WWII context, with manual controls you're likely to find that the pilot runs out of bicep before shockwave development over the tail starts to bite.

Here's a quick list of the factors causing "Mach tuck":

• Migration of the wing's centre of pressure
• Changing wing downwash angle
• Rapidly increasing stick force for constant elevator deflection
• Reduced elevator effectiveness due to shock developement over the tail

You can see that 3 out of the 4 don't require shock development over the tail.

OTOH, the underlying problem is the tail; because that's where the control surfaces are, and the problem is a control problem.

So the brute-force approach towards the end of WWII and immediately thereafter was to hydraulically boost everything. Once you do that then the new problems are dealing with the failure modes and providing Q feel so that the pilot doesn't break the aeroplane.

Then you might get into trouble with lack of elevator effectiveness, because the elevator can't affect the pressure distribution upstream of any shock which may have formed over the tail. But really it's unreasonable to think of the flying tail as a "solution" to this problem, because going to a flying tail in 1940 wouldn't have solved fighter stability & control problems. Without irreversible screwjacks to drive the thing, you'd find that either it fluttered off or else the control forces were impossibly high.

Really the concept of the "flying tail" is a sort of marketing thing rather than reality. There's nothing magic about it. The simple reality is that if you're supersonic the you need the movable bit of your control surface to do all the work by itself, and you therefore have to size it appropriately. Note that delta winged fighters do just fine with elevons - no need for the surface to have its own private leading edge to work - it just needs to be big enough and to be driven by a sufficiently strong set of jacks.

In subsonic flight the elevator can be quite a lot smaller because it affects the lift curve slope of the whole surface it's attached to, which is great if you've only got a relatively limited actuating force available. Hence the rapid ubiquitous adoption of the elevator in subsonic aeroplanes quite early in the evolution of the aeroplane.

The other thing which people got used to is the idea that in general a nice set of aerodynamic controls will give you stick free stability which may well mask any nasty stick-fixed behaviour your design may exhibit. During WWII the added friction associated with pressurised cockpits started to show up some of the stick fixed problems that had been lurking under the rug for decades, and this caused people to start working on tweaking the control system itself via bob-weights etc to affect the subjective handling characteristics of the aeroplane, rather than just expecting the pilot to tolerate what he was given.

This gradually took us towards full FBW/manoeuvre demand systems, which allow you to design the apparent handling of aeroplanes to be almost independent of their aerodynamics. Which is great, though it does open all sorts of philosophical cans of worms since you now have to think about what the ideal set of control laws would be, rather than just asking the test pilot whether he can fly the thing or not...

The loss of stick free stability also rather reduced the importance of the fixed portion of the tail from a handling perspective, and since the elevator had to be big enough for the supersonic control task, it was almost always going to end up big enough for the subsonic case and therefore why not just bin the fixed tail?

Actually there are several reasons, especially for larger aeroplanes; essentially a fixed tail with an elevator is likely to be lighter, though you may have to also vary its incidence for trim, which takes some of the advantage away (though the trim change can be an order of magnitude slower than the control trim, since effectively the trim change has to damp the phugoid whilst the control change has to damp the short period oscillation, and therefore the trim actuators can be smaller).

But I digress; time to get a cup of tea & get back to my thesis...

Any how I managed to write it down it seems that the tail has to be looked with suspiciousness.

When it comes to fluid mechanics don't be obsessed by tail's story



Just to make thing more clear and easier : the path to supersonic speed at those time went troughs symmetrical airfoils then to the all flying tail (AFT) unit. I am not sure that a full array of Bell and NACA engineers would hve been fooled such a way to design the X1 with a conventional tail if it could hve not fly faster than Mach 0.66 (compressibility).

idem for the F86 with thckness ratio decrease then AFT

[Danelov]

Why do Spitfires turn better than Hurricanes?!

Easy, the magic wings of Mr Reginald Mitchell, that is all.

A better question is why do Hurricanes out climb and are faster in level flight than 1a spits...