The 'Great Debate' - Spitfire vs BF109

[Crumpp]

The Buffet is not a double edged sword.

Sure it is and you understand you don't fly in it for maximum turn performance.

It is easily and immediately recognisable and resolving the issue is equally easy and immediately effective, all you do is ease off the stick until the buffet goes. It is easy to fly on the edge, you 'feel' for the start of the buffet and ease off as applicable, the normal process is to hold it on the edge with gentle movements once you have found the buffet. You don't fly in the buffet, you can fly to the buffet

Absolute 110% agree. You are absolute right.

It is easy to do in a stable airplane.

To pull through the buffet would be dangerous, stupid and also difficult to do, the vibration would rattle your teeth and its impossible to miss it.

Not really, In fact accelerated stalls are a testable maneuver for a Commercial rating, now.

The amount and energy of the buffet depends on the airplane design too. Some airplanes don't even buffet before the stall. You get just a nibble and its gone!

[Crumpp]

No when the boundary layer separates the center of lift moves aft and flow on the undeside of the wing is allowed to curl up over the trailing edge, this simly causes turbulence behind the wing.

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One of the reason's why CP is obsolete.

Light buffet comes from the separation but for most aircraft the significant stall buffet is from the turbulent air impinging on the tailplane.

Washout is what prevents the tips of the wing stalling before the inboard.

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.

I have never heard of an increase in drag inceasing lift

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.

[Glider]

Originally Posted by Crumpp

Sure it is and you understand you don't fly in it for maximum turn performance.



Absolute 110% agree. You are absolute right.

It is easy to do in a stable airplane.

Clearly I have no experience in a Spit but I do have some in aerobatic gliders which are close to the edge. The best are borderline unstable as are fighters, it isn't difficult to recover and they also have very light controls. All you have to do is ease off the stick a touch and you will immediatly recover. Its an almost instinctive reaction.

Stable gliders and I assume fighters are hard work, the physical effort involved can be very tiring and that in itself can make flying close to the edge of the envelope difficult. Some of my first aerobatic lessons were done in a Twin Astir and you had to really haul it around, she was too stable. Close to the edge the lighter touch gives you a better 'feel' for what is going on with the aircraft.

[Crumpp]

The best are borderline unstable as are fighters,

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".

[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.

[TomcatViP]

Originally Posted by 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.

Naca & RAE curves describe instrumented flights were the test pilot had to follow a predetermined trajectory. Nothing like what most of the fighter pilot will try to do.

Still it is interesting that it give us an indication that the ctrls were not the one we have in the sim where the Spitfire act like an F18.

Attention to details and imperfections are what makes a great sim.

Originally Posted by Glider

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.

I hve always said that I do believe that the 109 was more difficult to master than the Spit. It's an evidence for me.

What you told us about your experience in gliders is interesting. Thank you for the feed-back.

Originally Posted by Glider

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.

I was talking of the travel range in roll that shld be more or less the same as the one in pitch -ie control harmonization - sry for my bad English

It would be interesting (and relatively easy) to hve it implemented in the Spit model.

[Crumpp]

Originally Posted by 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.

The German report also notes the longitudinal instability. It does NOT note the CG position of the aircraft.

Quick changes of the trajectory along the vertical axis cause especially with the Spitfire load changes around the cranial axis, coming from high longitudinal thrust momemtum, and significantly disturb the aiming.

http://kurfurst.org/Tactical_trials/...g_Aug1940.html

[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.