Explain this and win the prize!

[gripen]

Originally posted by Crumpp
Way to manipulate words Gripen!

 
Semantics are not subject of this thread. The Spiteful had near elipptical lift distribution as can be proofed with Glauert corrections. Try to live with that.

Originally posted by Crumpp
You keep avoiding the question of how that is possible with the aircraft having near perfect taper ratios and the FW-190 having a significant advantage in Aspect Ratio?

Allready answered above:

"If the tapered wing has about optimal taper ratio it also has near elliptical lift distribution. Now if washout is added, it moves lift distribution inwards which yields less optimal lift distribution as can be seen from Lednicer's chart and can be calculated with Glauert corrections."

Besides the difference between 0,78 and 0,81 is small just like the difference between 0,8 and 0,85.

Originally posted by Crumpp
As for your wooden model, now I am confused about it.  First it was a 1943 report so that it could have used an NACA report calculating corrections of off center flow around the tail which included formulas that brought the model closer to the actual aircraft published in 1937.  

Well, you are certainly confused, it is a 1943 report as can be confirmed from the catalogue of the PRO.

Originally posted by Crumpp

Now it is a Spitfire I?

It is a Spitfire I as can be confirmed from the catalogue of the PRO.

gripen

[Badboy]

Originally posted by gripen
Neither I'm using those values for the WWII fighters. The drag data I have checked so far indicate that the e factor was typically around 0,75-0,8 in the Cl range say 0,2-1,0 (assuming that there was a linear stage around these Cl values). The problem here is that near Clmax (generally around Cl 1,4-1,8), like in the high g maneuvering near corner speed, the Cd/CL^2 curve is no more linear and it's difficult to say if the e factor defined normal way works well for performance calculations in this kind of maneuvering.
gripen

The efficiency factor does work during that kind of maneuvering, what doesn’t work so well is the parabolic drag polar. The fact is that all the theory we have been discussing has evolved around the assumption that the relationships can be fitted with a parabolic polar. That turns out to be a very reasonable assumption for aircraft that have low AoA limits and depend exclusively on conventional lift. However, it is only approximately true, and in situations such as when other forms of lift are involved, or when the flow becomes turbulent near the edge of the envelope, it becomes more difficult to ignore. In those situations, it isn’t the value of e that needs to be modified, something other than a parabolic polar should be used.  

The popularity of parabolic polars, and quadratic relationships and their appeal in aerodynamics stems from the fact that most of the resulting equations can be solved analytically, and generally they do produce good results, and errors are smoothed out to some extent within the coefficients. However, when you work with real aircraft, it isn’t always possible to use those simple relationships, and there are a number of alternatives. Firstly, you can model with non-quadratic relationships, but then the equations do not always have analytical solutions, (but they sometimes do) which doesn’t really matter because you can solve them using numerical methods, it just requires more computer time. There are other ways to match the real curves, very accurately, or at least with any degree of fidelity you wish, but it involves working with large quantities of tabular data. Both of those methods entirely resolve the issues of partial fit discrepancies for parabolic curves and enable very close predictions, even at the extremes of the envelope.  I use those methods when ever I work with real aircraft, for EM analysis for example, but if you are analyzing what is happening in a simulation, such as AH for example, the traditional method is fine, because that is what is being used in the flight model anyway.

Hope that helps…

Badboy

[Crumpp]

Semantics are not subject of this thread. The Spiteful had near elipptical lift distribution as can be proofed with Glauert corrections. Try to live with that.

Your making semantics the subject by accusing other of not understanding what you your self do not understand.

"If the tapered wing has about optimal taper ratio it also has near elliptical lift distribution. Now if washout is added, it moves lift distribution inwards which yields less optimal lift distribution as can be seen from Lednicer's chart and can be calculated with Glauert corrections."

Certainly to control the less desirable stall characteristics of perfect elliptical lift distribution.  

Your attempting to say that that efficiency was completely destroyed down to .78??  Come on, Gripen.

All the working aeronautical engineers looking at the same data you have already say it is .87.  Much more reasonable given the Taper Ratio and the Aspect Ratio.  The FW-190's wing as listed on Badboys chart with NO twist yields an efficiency of .91.  

Aeronautical engineers at the time of the FW-190's design were well aware of the benefits of elliptical wingtip distribution and how to attain it.

It is easy to see from this lift distribution chart that the FW-190 and the P51 were closer to elliptical distribution at the wingtips than the Spitfires.



The wingtips being the most important part of wing efficiency, this would go a long way towards correcting the rest of the elliptical departure in the wing structure.  This is shown by every accepted formula in aeronautics.

Your value of .78 is calculated from your half-baked "Lift distribution" calculations and has no place in the real world.

I don't believe for an instant you even calculated off that FW-190 chart.  

Especially when compared to your results from the Spitefuls wing.  Taper ratio are within .03 between the two and the FW-190 has a decisive Aspect Ratio advantage of .21.  You come up with a .84 result for the Spiteful!  Poppycock on your FW-190 results.  Your manipulating data in an attempt for recover from the "Draining E turns Thread".

Crumpp

[gripen]

Originally posted by Badboy
The efficiency factor does work during that kind of maneuvering, what doesn’t work so well is the parabolic drag polar.

I can't really follow now, a constant value of the e results perfectly parabolic drag polar. As an example we can assume a plane with rectangular wing with AR 6 and e factor 0,75, the formula for the drag rise written with e factor is then:

Cd = Cd0 + Cl^2/(pi*6*0,75)

Same can be also written in the form of the simple polar as:

Cd = Cd0 + 0,07073553*Cl^2

It can be also written in the form of the  e factor formula (Glauert correction factor 0,05):

Cd = Cd0 + 0,0150313*Cl^2 +  Cl^2/(pi*6)*(1+0,05)

All these three ways to calculate drag rise results exactly similar perfectly parabolic drag polar which does not work particularly well near Clmax in most cases.
 

Originally posted by Crumpp

Certainly to control the less desirable stall characteristics of perfect elliptical lift distribution.

This thread is not about the stalling characters.

Originally posted by Crumpp
Your attempting to say that that efficiency was completely destroyed down to .78??

No one says that the efficiency was completely destroyded, 0,78 is typical value for the WWII fighter.

Originally posted by Crumpp
All the working aeronautical engineers looking at the same data you have already say it is .87.

Who? There is other answer than 0,78 for the value of the K 1,24 in the Fw chart.

Originally posted by Crumpp
Much more reasonable given the Taper Ratio and the Aspect Ratio.  The FW-190's wing as listed on Badboys chart with NO twist yields an efficiency of .91.  

There is no Fw 190 wing in that chart.

Originally posted by Crumpp
It is easy to see from this lift distribution chart that the FW-190 and the P51 were closer to elliptical distribution at the wingtips than the Spitfires.

Lednicer about the lift distribution of the Spitfire:

"... loading distribution is not elliptical, though it is probably most optimum of three from the induced drag standpoint."

Originally posted by Crumpp
You come up with a .84 result for the Spiteful!

Nonsense, the wind tunnel data results 0,81, the value 0,84 is just a test result to check validity of the formula with  approximated value of K.

gripen

[Crumpp]

This thread is not about the stalling characters.

Again you don't read.  My point was not about stalling, Gripen.  It was the FACT that lift distribution beyond the wingtip has little effect on efficiency, just like the aeronautical engineers say.

There is no Fw 190 wing in that chart.

The NACA 230015-009 is the FW-190 Wing, Gripen, minus 2 degrees of twist.

"... loading distribution is not elliptical, though it is probably most optimum of three from the induced drag standpoint."

Exactly.  Once again you completely miss the mark on the point.  You have a talent for completely ignoring data which does not suite your vision and twisting the words of others.

Crumpp says:
It is easy to see from this lift distribution chart that the FW-190 and the P51 were closer to elliptical distribution at the wingtips than the Spitfires.

Completely different meaning that what your trying to twist out of it.

Since wingtip elliptical distribution is the MOST important part of induced drag reduction, it's not hard to see why the Spitfire was not that far ahead of either the P51 or the FW-190.  No matter what formula the spread remains the same between the three.

Just check out the elliptical planform wing 4412 on Badboys chart.  It's  e factor is .92 and the 230015-009 is .91.

Crumpp

[gripen]

Originally posted by Crumpp
Again you don't read.  My point was not about stalling, Gripen.  It was the FACT that lift distribution beyond the wingtip has little effect on efficiency, just like the aeronautical engineers say.

The lift distribution is function of the entire wing as pointed out by Prandtl, Glauert and entire wing theory. Try to live with that.

Originally posted by Crumpp
The NACA 230015-009 is the FW-190 Wing, Gripen, minus 2 degrees of twist.

Nonsense, this wing just has same profile but not same characters (washout, shape etc.).
 

Originally posted by Crumpp
 You have a talent for completely ignoring data which does not suite your vision and twisting the words of others.

You are the one who can't accept what Lednicer says.

Originally posted by Crumpp
Just check out the elliptical planform wing 4412 on Badboys chart.  It's  e factor is .92 and the 230015-009 is .91.

The 4412 is a wing profile and again it has no washout. Besides the source of the chart is not documented and we are talking about the e factor of the entire airframe not just wing.

gripen

[Crumpp]

Besides the source of the chart is not documented and we are talking about the e factor of the entire airframe not just wing.

Oh now the chart is bad, huh?

The lift distribution is function of the entire wing as pointed out by Prandtl, Glauert and entire wing theory. Try to live with that.

Again you twist what others say.

NASA Says:
The wing-tip shape, being at the point of production of the tip vortices, appears to be of more importance in minimizing tip vortex formation and thus minimizing induced drag.

http://history.nasa.gov/SP-367/chapt4.htm#f62

NASA says:
Taper and twist are perhaps of greater importance when the problem of stalling is discussed later.

http://history.nasa.gov/SP-367/chapt4.htm#f62

Is the light bulb on Gripen?

Nonsense, this wing just has same profile but not same characters (washout, shape etc.).

Afraid it is Gripen.  As I pointed out earlier, it the FW-190 wing without the 2 degree twist to improve the stall.

Crumpp

[gripen]

Originally posted by Crumpp
Oh now the chart is bad, huh?

Generally if some one brings in the data the source should be noted. In this case I found the source myself.

Actually it confirms what I said about the e factor near Clmax as well as gives the reason for e value of the 4412 wing:

"This curve is typical for the wings and shows how the efficiency-factor curve departs from the Cd curves below Cl=0.2 to 0,4 and above Cl=1.0. Reference to table I shows that that NACA 24-30-8.50 and 2R1-15-8.50 wings which have the largest Clopt, have values of e equal to and larger than e, respectively, for the elliptical NACA 4412 wing. This result is obtained because shifting the Cde curve to the right makes it fit a flatter e curve, and hence one with a higher value of e. If Clop, had been zero for all the wings and they had differed only in plan form, the values of e would indicate the departure of the drag of the wings from that of the ideal elliptical wing. The wings, in fact are sufficiently similar and the variations of the Cd0 values with lift are near enough alike so that there is a general reduction of e as the wings depart from the elliptical plan form toward the wings of high taper."

Originally posted by Crumpp
Blaah Blaah...

The situation is very simple here; your theories against Lednicer's calculations and word, data from Fw and RAE as well theory from Prandtl and Glauert. Entire wing generate vortices and very small differences near wing tip are neglible as can be proofed from the Glauert's book, note that half tapered wing has nearly same e as elliptical despite differences in the lift distribution:



Besides no one else than you is comparing planes here, all the data here is just to show what was the normal range of e for WWII.  If you don't like the data, it's not my problem nor subject of this thread.

gripen

[Crumpp]

The situation is very simple here; your theories against Lednicer's calculations and word, data from Fw and RAE as well theory from Prandtl and Glauert.

That's funny!  It's not my theories, its the exact folks your quoting above backed up by NASA.  

Nice attempt at a bait and switch.

Actually it confirms what I said about the e factor near Clmax as well as gives the reason for e value of the 4412 wing:

Which has nothing to do with our discussion.

Generally if some one brings in the data the source should be noted. In this case I found the source myself.

So now it is good.  Make sure you tell Badboy about the source standards.  Is that the same standard as your Spitfire wooden model report?

Actually it confirms what I said about the e factor near Clmax as well as gives the reason for e value of the 4412 wing:

No one is arguing this Gripen.  Your a master of the obvious and seriously attempting a straw man rebuttal.

Gripen says:
Entire wing generate vortices and very small differences near wing tip are neglible as can be proofed from the Glauert's book, note that half tapered wing has nearly same e as elliptical despite differences in the lift distribution:

You need to inform NASA cause they are not on the same sheet of music.  It's the tip vortices that are the main contributor to induced drag.

NASA Says:
The wing-tip shape, being at the point of production of the tip vortices, appears to be of more importance in minimizing tip vortex formation and thus minimizing induced drag.

http://history.nasa.gov/SP-367/chapt4.htm#f61

Sure your not making up another Gripen Theory of Aerodynamics?

Crumpp

[gripen]

Originally posted by Crumpp
It's not my theories, its the exact folks your quoting above backed up by NASA.

The difference in 1/10 part of the wing in the Lednicers lift distribution chart is much smaller than the difference in the Glauert chart which did no difference. NASA site claims nothing about small differences in the lift distribution chart, but Lednicer's opinion on his data is known as well as backed up by data from Fw and RAE and also supported by theory.

Besides, according to Lednicer's chart Mustang does the smallest tip vortices  and Fw the largest of the three.

Originally posted by Crumpp
Which has nothing to do with our discussion.

Basicly it says that to compare the plan form characters of the wing all other characters (like profile) should be equall, that was not case when you compared other wings to elliptical wing.

Originally posted by Crumpp
Make sure you tell Badboy about the source standards. Is that the same standard as your Spitfire wooden model report?

It's allways a good standard to identify sources and I have given the source of the report on Spitfire I.

gripen

[Crumpp]

The difference in 1/10 part of the wing in the Lednicers lift distribution chart is much smaller than the difference in the Glauert chart which did no difference.

So what Gripen?  The difference is the most important part of lift distribution for induced drag production.  Think of it like wing loading is to turn performance. It is just one of the factors. However wing loading is the most important factor in turn performance and you can get a feel for turn performance looking at it.

1/10th is kind of an exaggeration too. 20 percent at the tip Gripen and that is not counting the other 20 percent at the root were the FW-190 is equal or better.

but Lednicer's opinion on his data is known as well as backed up by data from Fw and RAEand also supported by theory.

Only problem with any of this is YOUR THEORY.  You need to fit your world to the facts and not the facts to your world.

Lednicer's opinion is published in his article that you seem to read much more into than what he says about efficiency factor differences.  His main point is the Spitfire does not have the elliptical lift distribution commonly attributed to it.



So based on the calculations and the chart, the Spitfire does have a better efficiency.  Because it's wingtip lift distribution is the farthest from elliptical due to its uniform twist, though it's advantage is not huge.  In fact is close enough that Lednicer refrains from calling it a fact that the Spitfire has the advantage.  

Just as NASA says.  Wingtip lift distribution is the main contributing factor to induced drag formation.  The rest of the lift distribution is a minor contributor and commonly the wing design is manipulated AWAY from elliptical to improve the stall.

Crumpp

[Badboy]

Originally posted by gripen
All these three ways to calculate drag rise results exactly similar perfectly parabolic drag polar which does not work particularly well near Clmax in most cases.

Exactly, and that’s as good as it gets, the situation actually gets worse for many other wing configurations and the departure from a parabolic polar increases. However, what is failing is not the efficiency factor, but the parabolic drag polar. It was only ever approximately true, and in situations where other forms of lift are involved, or near the edge of the envelope, the parabolic relationship can no longer be used.  When you said:

Originally posted by gripen
The problem here is that near Clmax (generally around Cl 1,4-1,8), like in the high g maneuvering near corner speed, the Cd/CL^2 curve is no more linear and it's difficult to say if the e factor defined normal way works well for performance calculations in this kind of maneuvering.
gripen

It sounded to me as though you were thinking that it was the e factor that might need to be defined differently, when it is the parabolic relationship at fault. There are other methods to match the real curves with any degree of fidelity you wish, but not with quadratics. Those methods don’t suffer from the issues of partial fit discrepancies (that occur because parabolic curves are only good for non-turbulent flow and traditional lift) and are able to provide very close predictions, even at the extremes of the envelope.  

However, parabolic polars, and quadratic relationships are popular, and their appeal in aerodynamics stems from the fact that most of the resulting equations can be solved analytically, and can be manipulated easily in order to learn about the relationships involved. Also, they do generally produce good results, and errors are smoothed out to some extent within the coefficients, so that they are satisfactory for most practical purposes.

All I’m saying is that when that relationship breaks down, as it does near the extremes of the envelope and even more widely in many other wing configurations, you simply can’t rely on quadratic equations any more, and need to use other methods.  

Hope that helps…

Badboy

[Badboy]

Originally posted by gripen
Generally if some one brings in the data the source should be noted. In this case I found the source myself.

gripen

My apologies… I thought I had posted the link.

Did you notice the author’s comments that he was specifically trying to find an efficiency factor comparable to the airplane efficiency factor, and he then provides a reference to Oswald’s paper to support his point. But he then appears to have tested wings without the fuselage, I guess folk have been confused on that point for a long time. I’ve seen it done both ways almost indiscriminately for many years

Badboy

PS
But I don't feel too bad about forgetting the source, after all I've given you some very good ones

Edited in the PS

[Angus]

OMG, this thread is getting so big, that it is actually THREATENING the Spit-Messer thread

Anyway, I saw you mentioning the wing tip configurations as ell as the Spitfire wing.

Well, for what it's worth, AFAIK, clipping that wing would increase roll rate incredibly, speed slightly, climb would fall, zoom would rise, and turning would drop by some margin, stall would be more vicious.

Would it fit? I'd think yes ...

[gripen]

Originally posted by Crumpp
The difference is the most important part of lift distribution for induced drag production.

The tip vortices are the result of the pressure difference between top and bottom of the wing and therefore a wing with lot of lift near tip produce larger tip vortices than a wing with less lift near tip. The elliptical lift distribution means constant downwash along the wingspan. Funny thing in your theory is that if your favorite plane has more lift (downwash) near tip than some others, it also produces larger tip vortices. In addition it should be noted that if there is no constant downwash in the rest of the wing, there is no such in the tip. Generally a wing with least variation of downwash along the span produces least induced drag.

Originally posted by Badboy
However, what is failing is not the efficiency factor, but the parabolic drag polar. It was only ever approximately true, and in situations where other forms of lift are involved, or near the edge of the envelope, the parabolic relationship can no longer be used.

The good point in the parabolic drag polar is that it has a theoretical explanation in the lifting line theory. I could form a formula, say the form Cd=Cd0+X1*Cl^3+X2*Cl^2 (X1 and X2 being constants) or something, which might work better at low and high Cl values, but such formula has no theoretical background.

Anyway, I've been under impression that in the AH the drag rise is modeled with AoA ie not by making some kind of Cl based model.

Originally posted by Badboy
Did you notice the author’s comments that he was specifically trying to find an efficiency factor comparable to the airplane efficiency factor, and he then provides a reference to Oswald’s paper to support his point. But he then appears to have tested wings without the fuselage, I guess folk have been confused on that point for a long time. I’ve seen it done both ways almost indiscriminately for many years

Yep, generally the e factor for the wing only can be estimated good enough but muddy waters start when estimating the rest of the airfame so. Wood gave one solution but it's difficult to say if it works generally well. RAE wind tunnel data for the Mustang I contains drag data for the wing only which result value of e about 0,88 for the wing, while the entire airframe has value of e about 0,77. Other planes were not tested with wing only at higher Cl range.

Angus,
Start a new thread if you want to compare planes.

gripen