Explain this and win the prize!

[Crumpp]

Anyway, from some source (think it was a pilot) I heard that actually the Spitfire wing would NOT stall all at once, which would then be a normal sideffect, since a complete ellipse should stall all at the same time. Am I right there?

That is exactly why it was twisted.  To destroy some of the ellipse.

Check your email.

Crumpp

[gripen]

Originally posted by Crumpp
Read Lednicer's quote on the fact designers were well aware of the benefits of elliptical distribution and it was easily achieved by twisting the wings.  This occurred in the later designs of the FW-190 and the P51.

While some amount of washout can  improve lift distribution of the rectangular wing, it can be seen from Lednicer's lift distribution chart that the Fw 190 and P-51 have too much washout for optimal lift distribution:



With less washout the lift distribution would have been much closer elliptical. Therefore it's easy to see that reason for the amount of wing twist in the Fw 190 and P-51 is same as in the Spitfire; to get the wing root stall before the tip.

Originally posted by Crumpp
Thereby bringing all three aircraft in a similar catagory for wingtip efficiency.

The lift distribution chart is quite clear, the Spitfire has "the most optimum of the three". This can be also verified from the wind tunnel and FW data.

Originally posted by Crumpp
It's lower wingloading is the main contributor to it's fighting characteristics not it's efficiency factor.

Well, here I agree. If we compare planes, generally the one with lowest wing loading has lowest drag rise when the g load increases. But that is a bit out of subject of this thread.

gripen

[Crumpp]

Thanks for clipping the chart from the article.  It illustrates perfectly what is going on with the FW-190 vs Spitfire wing.


At low speeds the Spitfire does have the advantage.  At high speeds the efficiency gap closes dramatically.  Just as the Spitfire moves farther away at high speed from the "elliptical shape", the FW-190 moves closer and eventually surpasses the Spitfire in the last bit of the envelope.

According to your calculations that never happens.  According to Lednicers data, the drag polars, and other aeronautical engineers figures it does.



Crumpp

[gripen]

Originally posted by Crumpp
Thanks for clipping the chart from the article.  It illustrates perfectly what is going on with the FW-190 vs Spitfire wing.

Well, I don't know why you want to make yourself laughable but "´Semispan Fraction" means relative location along the wing half. It has absolute nothing to do with the speed.

gripen

[stantond]

Hi,

Here is an explanation which may or may not have the level of detail you require.  Lift is generally described mathematically, or through the mathematical abstraction, as circulation.  This circulation is a function of the shape of the wing, not the wing area vs span ratio.  As an example of how the wing Coefficient of lift varies along its span, here is a url: http://www.nurflugel.com/Nurflugel/Horten_Nurflugels/theory/theory.html

The concept of vorticity and circulation is not physically easy to grasp, and I make no claim to have that insight.  However, circulation is what creates the lift in the inviscid (non viscous) flow regimes.  This circulation theory provides an elliptical distribution (for vorticity) giving a minimum resistance due to vortex downwash.  This elliptical distribution is for the wing along its span and the aspect ratio can vary.  

My apologies if all this is way too abstract but it is how I was taught.  There are several papers by Prandtl from 1918 to the early 20's that are on the NACA server at   .  He first made this connection in mathematical terms between wing shape, lift, and drag.

Regards,

Malta

[Crumpp]

Thanks Stantond.  Great explaination.  Now to apply it to this chart.

So one end is the wingtip, correct?  I certainly don't see where the Spitfire has any advantages if that is the case.

Crumpp

[gripen]

Originally posted by Crumpp
So one end is the wingtip, correct?  I certainly don't see where the Spitfire has any advantages if that is the case.

At least Lednicer, me and probably everyone else can see the diffrerence the Spitfire "being the most optimum of the three".

gripen

[Angus]

How can twisting an elliptical wing destroy it any more than twisting a tapered wing?
After all, that part is about washout right? And that is a drag issue more than a lift issue.
I always thought the Spitfire wing was not a complete ellipse in shape, i.e. a total ellipse would have meant a bit wider chord.
Or am I in the dark here?

[gripen]

Originally posted by Angus
How can twisting an elliptical wing destroy it any more than twisting a tapered wing?

It's quite simple; without washout elliptical wing has optimal lift distribution and washout makes it less optimal. Lift distribution of the tapered wing can be improved with some amount of washout (in some cases) but in the case of the Fw 190 and the P-51 it can be clearly seen that that these have too much washout for optimal lift distribution.

Basicly in the all three cases the main reason for the washout is to improve stalling characters of the plane and in all three cases amount of washout decrease efficiency of the wing.

gripen

[Kurfürst]

So appearantly the best way is to use wings with slats and no washout to have both optimum stall characterstics AND good lift effiency.

[gripen]

Originally posted by Kurfürst
So appearantly the best way is to use wings with slats and no washout to have both optimum stall characterstics AND good lift effiency.

That's one way to do it. The e factor of the Bf 109 appear to be in the same ballpark with the P-51 and Fw 190 but it generally had the better stall characters.

gripen

[Angus]

And then enters the dihedral

[Kurfürst]

Originally posted by Angus
And then enters the dihedral

Hmm, the dihedral (V-stellung) supposed to increase the stability of the aircraft, this being important for low mounted wings, ie. fighters with neutral roll axis stability... is there anything else?

[Crumpp]

Depending on which end is the wingtip....



The spitfire does have a more efficient wing on the whole that was never in doubt.  It is the wingtip though that determines induced drag though and the twist destroyed the elliptical shape of the lifting surface at the tip.  You can see that by this chart.

Just as David Lednicer says.  The Spitfire is the most optimum of the three.  It does not have the commanding lead you want to give it, nor does always have less drag than the 190 no matter what portion of the flight envelope.  As you picture it.

And then enters the dihedral

The Spitfires roll was not as stable??

Crumpp

[Crumpp]

In fact I would veture to say that if this guy:

http://www.grc.nasa.gov/WWW/K-12/airplane/benson.html

Doesn't know a way to calculate wingtip efficiency or gain any insights into it off of the above chart. I would say we are spinning our wheels with this.  

Gripen didn't you use this chart to figure out the FW-190's wingtip efficiency earlier in this thread?


My question:

Is there anyway to figure out the exact Wingtip efficiency factor of the Aircraft using this chart?
Not asking you to figure it out.  Just confirm whether you could do it off this chart or gain any insight.  Using the forumla for Oswalds Efficiency factor, the FW-190, P51D and the Spitfire are extremely close.

Tom says:
There probably is .. but I don't know it.

Crumpp