The 'Great Debate' - Spitfire vs BF109

[taildraggernut]

Originally Posted by Crumpp

Not sure what you mean here. The aerodynamic center does not change with AoA.

The Center of Pressure moves forward with increased angle of attack and disapates at the stall.

Is that what you mean? The CP moves forward, the AC is stationary and when the CP is gone, down the wing comes about the AC.

Cause otherwise you have it backwards, the CP moves backwards in infinity as we approach zero lift AoA.

One of the reason's why CP is obsolete.

I assure you I have nothing 'backward', I said nothing about Aerodynamic centre.
as the AoA increases the CP moves forward until the departure, the CP then moves to the back of the wing and doesn't dissapear, CP may be an obsolete mathematical model but the real world low pressure we know as the CP behaves as I describe, again I'm wondering where all the aerodynamic lessons are taking us?

Originally Posted by Crumpp

All true. Some airplanes the turbulence is the predominate factor. As a general rule though, it is the buffet.

In fact, it is really not good design to put the tail in the wings wake. It can lead to an unrecoverable stall condition. That is the big issue with T-tails.

Near the stall incidence, in most airplanes, the tail by design is in clean air.

as you said all true, not sure where T-tails bear relevance here.

Originally Posted by Crumpp

Well it is the co-efficients not the forces. In level flight we are lucky our lift force remains constant.

The co-efficients have a direct relationship. So as the airplane's co-efficient of lift increases, the co-efficient of drag increases.

Drag, unlike lift does not remain constant. So when our CL increases lift force stays the same but our drag force goes up.

How does this answer my question? you didn't explain how drag inceases lift.

[Crumpp]

CP may be an obsolete mathematical model

Yes it is because it does NOT accurately describe what happens in the real world.


As a general rule though, it is the buffet.

It is not good design to put the tail in the wings wake.

you didn't explain how drag inceases lift.

I certainly did explain it. What part did you not understand? Exam these graphs and maybe you will understand.

[Crumpp]

drag inceases lift.

Look at the AoA chart. If the wings AoA increases, then our lift co-efficient increases and so does our drag coefficient.

If we add drag, then our wing will change angle of attack to compensate because it requires more power. Our lift coefficient will increase.

The relationship of lift to drag is fixed by design.

[TomcatViP]

Originally Posted by Fenrir

Okay tomcat, my bad, you have my apologies. I only scan read the links and didn't get what you actually communicating. It was late and I was tired but still, should have made sure I understood your post before replying. Interesting stuff, now that I've read it properly.

Sorry again for the flippant response.

Thumb up M8

[taildraggernut]

Yes it is because it does NOT accurately describe what happens in the real world.

But is 'does'

As a general rule though, it is the buffet.

It is not good design to put the tail in the wings wake.

the buffet as a result of the turbulence impinging on the tailplane yes, we are talking about conventional aircraft here, you know the ones with the tail at the back like almost every aircraft flying even today has it, where the empennage is very much in the wake of the wings.

I certainly did explain it. What part did you not understand? Exam these graphs and maybe you will understand.

I see a Cd curve which continues on a smooth path and seems unaffected by anything, a Cl curve falling off at the stall and a standard L/D arc that also seems pretty unremarkeable but nothing showing how drag increases lift.

If we add drag, then our wing will change angle of attack to compensate because it requires more power. Our lift coefficient will increase.

the wing changes AoA all by itself? where does the 'more power' come from, these things don't happen unless demanded by the pilot and you certainly don't seem to be suggesting that.

The relationship of lift to drag is fixed by design.

yes it is, the L/D curve is the combined effect of Cd and Cl, in all your little graphs all I can see is the drag continually rising but lift dropping off at the stall, where exactly am I supposed to be looking if I want to see drag increasing lift.....am I being too litteral? I am only asking because you said verbatim 'drag increases lift'

[CaptainDoggles]

Originally Posted by taildraggernut

the buffet as a result of the turbulence impinging on the tailplane yes, we are talking about conventional aircraft here, you know the ones with the tail at the back like almost every aircraft flying even today has it, where the empennage is very much in the wake of the wings.

Do you actually even read what gets posted or do you just pick out bits and pieces? It's blatantly obvious that "putting the tail in the wake" was referring to the wake of a wing at high AoA, where the elevators won't be able to get you out of a stall.

Same with your post in the other thread. "Are you equating combat flying with flying a circuit pattern?" Ummm... NO. Read all the sentences that are posted, not just bits and pieces, and then maybe you won't get so worked up about it.

[taildraggernut]

Do you actually even read what gets posted

Very much so.....do you?

It's blatantly obvious that "putting the tail in the wake" was referring to the wake of a wing at high AoA, where the elevators won't be able to get you out of a stall

is that so?.......why are we discussing a condition that does not relate to the Spitfire then? Crumpp said it himself 'deep stall' (that's what it's called) is a condition relating to T-tails......name me a common T-tailed WWII fighter, either way the tailplanes on conventional aircraft feel the turbulence from the stalled wing and that is the heavy buffet, this will vary according to aircraft but it's the more common situation.

Same with your post in the other thread. "Are you equating combat flying with flying a circuit pattern?" Ummm... NO

Then why did he say anything about flying a pattern?......oooohh sarcasm of course....well in which case I had the right to treat it with contempt.

NO. Read all the sentences that are posted, not just bits and pieces, and then maybe you won't get so worked up about it.

Don't tell me what to do, I read everything I need to, what is your excuse for getting worked up?....now back on topic please.

[Glider]

Originally Posted by Crumpp

It is a complete fallacy that manueverability and stability are linked by an inverse relationship.

"Just statically stable" has nothing in common with "borderline unstable".

Sorry Crumpp but this statement is totally wrong. A Ground Attack aircraft is normally very stable as it spends a lot of time at very low altitude where the air is rougher. However it is normally less responsive to inputs from the controls as the wing is designed to soak up rough air.

A fighter has a lighter touch and the reponse times are more immediate.

To use the Glider examples the Twin Astir was used to teach basic aerobatics but it was hard work. Most of the training was done on a K21 a very popular glider which incidently was almost impossible to spin. When I did an advanced course we used a Fox glider, a dedicated aerobatic glider. This was very sensitive and needed a gentle touch.

I have no doubt that all three were technically stable but the dedicated aerobatic Fox was far more sensitive, and responded to any input.

I work on the basis that the SPitfire was like other fighters the equal of the Fox.

[TomcatViP]

Glider, if they wanted to make it unstable or even neutraly stable, they would hve taken great care that the ailerons had the same sensitivity. It's quite unpleasant to have to make wide move in the roll axis when you've got a narrow travel range longitudinally.

The fact is that many bi-plans were marginally stable (inherent to their shape and short fuselage). Perhaps that experienced professional military pilots with years of flying the biplans in the 30's didn't bother that much that Spit annoying characteristic in regard of the general perfs improvement.

[Glider]

Tomcat
Find any pilot of any nation including German ones, who found the Spitfire difficult or unpleasent to fly. If it was as difficult as people are making out you should be able to find someone.

Just remember that Molders described the SPitfire as being faultless in a turn and childishly easy to take off and land. He found it much easier that the Me109.

Stability depends on what you want out of the aircraft. As I tried to show with the different Gliders, the dedicated aerobatic Fox was far more sensitive than the others. A Fighter needs to be more sensative than any other type of fighting machine because of what it does.
This goes back to the first air combats in WW1. Generally speaking the first RFC fighting aircraft were too stable and couldn't mix it with the German fighters. This trend was broken with later fighters until the Camel which was probably too far the other way. Even here the establishment SE5a was more stable than the Camel. Stability is't one measurement, there are degrees of stability. Many bi-plans were marginally stable as you say, but many were very stable it depended what you wanted out of the design.

I admit that I don't understand your statement they would hve taken great care that the ailerons had the same sensitivity The ailerons are the same in each wing, but its late and I might be missing something obvious.