Explain this and win the prize!

[Dweeb]

Originally posted by gripen
Why the efficiency factor should not be similar among the planes with very similar dimensions?

LOL, you might as well ask why any of the aerodynamic coefficients “should not be similar among planes with very similar dimensions?” but nobody is suggesting they all have the same lift coefficient, or the same drag coefficient, why then do you suppose they have the same efficiency factor? Please prove your argument, as you so often like to say.

Dweeb

[Dweeb]

Originally posted by gripen
I don't see a reason why you post to this thread If you can't bring in relevant data or you can't prove your arguments.

gripen

Gripen, trust me you haven’t proven anything here yourself, despite your pompous claims! None of your endless diatribe constitutes proof, it lacks the transparency and rigour of proper academic exposition and actually qualifies as little more than the ranting of a spoilt child trying to gain influence in a gamers board.

Dweeb

[Angus]

Umm, Dweeb, not quite getting where you're going.
That is regarding this:
"--------------------------------------------------------------------------------
Originally posted by gripen
Why the efficiency factor should not be similar among the planes with very similar dimensions? "

I guess he means RELATIVE dimensions. Correctly scaled that is.
Please enlighten!

[Dweeb]

Originally posted by Angus
I guess he means RELATIVE dimensions. Correctly scaled that is.
Please enlighten!

Yes, Gripen appears to be saying that because the aircraft in question (basically all WWII aircraft) have similar dimensions, they should have similar efficiency factors. The idea is complete nonsense for a number of reasons. Firstly, we are talking about a variety of aircraft and most of their dimensions are not really that similar, despite some common tendencies. The fact that the Aircraft in question have wings with different airfoil sections, means that they all have different maximum lift coefficients, different lift curve slopes, different drag coefficients and so on, does anyone believe those things should all be the same for every aircraft… of course not! And that’s not even including the variety of three dimensional factors like wing taper, sweep and twist, all things that have an influence on the efficiency factor, and when you consider the variety of WWII aircraft, there is no reason to believe the efficiency factor should all be the same, anymore than you would believe they all have the same lift coefficient. And even then we have not included every factor that can influence the results… Yet, Gripen is still happy to claim that they are all dimensionally similar, when they really aren’t, and to claim that is the reason they should all have a constant efficiency factor, which of course they don’t. Nobody believes they do accept him! It just gets more and more laughable every time he posts!

If you want to judge for yourself, just pick up some of the publications mentioned in this thread and realise that if the efficiency factor was constant, they would all be wrong, decades of well established aerodynamics, all down the drain because Gripen has discovered that the efficiency factor is really a constant… The man started with no credibility and has just gone downhill from there.

Dweeb

[gripen]

Originally posted by Dweeb
Why? So you can get a free education?

Determining the e factor from the drag polar or from the value of the K is quite simple as pointed out out in the Perkins& Hage:



If you want to discuss, please point out my errors.

Originally posted by Dweeb
The simple fact is, you have already asked some pretty dumb questions, like the one you opened the thread with, and had some excellent answers by some very knowledgeable people, who according to you are all wrong.

The simple fact is that without several assumptions as with the generalized formulas, there is no way to determine e factor from the aspect ratio only.

Originally posted by Dweeb
Despite the help you have received already, you still claim that the books that explain the theory, even the guy who has had it named after him, and Professor Wood, and Dr Raymer are all wrong, because you claim to have found that the airplane efficiency factor, is not a factor after all, it is a constant!

Please show where I have claimed that Oswald, Wood and Raymer are all wrong. AFAIK they never analyzed WWII fighters but Perkins&Hage and Lednicer actually did.

All I say above is that generalized formulas by Wood and NADC seem to give too high value of the e factor for WWII fighters and this conclusion is backed up by empirical data.

Originally posted by Dweeb
Yes, Gripen appears to be saying that because the aircraft in question (basically all WWII aircraft) have similar dimensions, they should have similar efficiency factors. The idea is complete nonsense for a number of reasons. Firstly, we are talking about a variety of aircraft and most of their dimensions are not really that similar, despite some common tendencies. The fact that the Aircraft in question have wings with different airfoil sections, means that they all have different maximum lift coefficients, different lift curve slopes, different drag coefficients and so on, does anyone believe those things should all be the same for every aircraft… of course not! And that’s not even including the variety of three dimensional factors like wing taper, sweep and twist, all things that have an influence on the efficiency factor, and when you consider the variety of WWII aircraft, there is no reason to believe the efficiency factor should all be the same, anymore than you would believe they all have the same lift coefficient. And even then we have not included every factor that can influence the results… Yet, Gripen is still happy to claim that they are all dimensionally similar, when they really aren’t, and to claim that is the reason they should all have a constant efficiency factor, which of course they don’t. Nobody believes they do accept him! It just gets more and more laughable every time he posts!

The data for the P-80, Bf 109G, Fw products, F4U and F2A is above. Please point out my errors. The Fw series is a good example because it contains three different aspect ratios.

gripen

[Crumpp]

"The close agreement between the low-speed data may be partly fortuitous considering that flight-test was computed from the thrust (the predominate force at low speed) taken from an engine calibration chart."

You honestly have no idea what that sentence is saying do you, Gripen??

Crumpp

[gripen]

Crumpp,
Let's look at the whole text:

"The agreement of the flight and wind-tunnel data is excellent at all Mach numbers of the test. The close agreement between the low-speed data may be partly fortuitous considering that flight-test was computed from the thrust (the predominate force at low speed) taken from an engine calibration chart. The drag data at high Mach numbers are on a better basis for comparison because the flight-test drag weas computed principally from from gravitaional components, jet thrust being of secondary importance. The flight results are taken from data previouysly issued in preliminary form. Refinements in calibration of the flight-test instruments have been made since the data were first issued."

Shortly it says that the agreement between the data sets is excellent, they had some doubts about low speed data (due to used thrust data) but the at high mach numbers data sets should be very comparable.

Besides it should be noted that used thrust values do not affect lift distribution.

gripen

[gripen]

Here is a chart which shows how the all data points mentioned above as well as above mentioned formulas fit in the AR/e chart, note that in this chart all the datapoints are calculated using least square method to fit linear line  (the only notable difference is the Mtt data for the Bf 109G, e being 0,69 with this method):



It can be easily seen that in the case of the tapered winged WWII fighters generalized formulas by Wood and NADC give allways too high value of the e. Only in the case of the wind tunnel data for the Spitfire (elliptical winged) these give about right value.

Another thing which can be easily seen is that aspect ratio explains poorly differences in the e factor regardless the used formula. Including the Spitfire, the value of the R^2 is about 0,2 in the best case. However in the case of the tapered winged planes (exluding Mtt data), the value of the R^2 is about 0,5 using the e-f formula (which can be easily altered further if more relevant data comes in).

gripen

[Crumpp]

Text says:

"The agreement of the flight and wind-tunnel data is excellent at all Mach numbers of the test. The close agreement between the low-speed data may be partly fortuitous considering that flight-test was computed from the thrust (the predominate force at low speed) taken from an engine calibration chart.  

Gripen says:

Shortly it says that the agreement between the data sets is excellent, they had some doubts about low speed data (due to used thrust data) but the at high mach numbers data sets should be very comparable.

And attempts to pass off this off as proof that wooden models can be compared to actual aircraft of a different design here:

Regarding accuracy of the wind tunnel data, this report gives also interesting read:
"The agreement of the flight and wind-tunnel data is excellent at all Mach numbers of the test"

As for your repeated request to show your math errors:

Please point out my errors.

That would be a complete waste of time.  It is not a math error your making but a conceptual one.  Showing any error committed on your part is like beating your head against the wall.  Look how many times the "waxed and polished" came up.  You still contest the Focke Wulf performance data especially when it comes from FOCKE WULF!  You would rather take the allies even when it proven the data is bad.  

Crumpp

[gripen]

Originally posted by Crumpp
And attempts to pass off this off as proof that wooden models can be compared to actual aircraft of a different design here:

The NACA report compares the model and the real aircraft of the same design, and found out that the agreement was excellent.

Originally posted by Crumpp
As for your repeated request blaah blaah

Well, my calculations as well as used data are above for all who really want to discuss as well as for those who don't want to discuss (namely you and Dweep). In the case of the Dweep this apparently means that e factor is some how forbidden subject and bringing in data on this is same as claiming everything written on e factor not true.

gripen

[Crumpp]

The NACA report compares the model and the real aircraft of the same design, and found out that the agreement was excellent.

So this is a basis for saying all wooden models can now be directly compared with actual aircraft of a different design?

Well, my calculations as well as used data are above for all who really want to discuss as well as for those who don't want to discuss (namely you and Dweep).

What part of your concepts are flawed and not your math do you not pick up on?

Crumpp

[gripen]

Originally posted by Crumpp
So this is a basis for saying all wooden models can now be directly compared with actual aircraft of a different design?

The lift distribution and the form drag should be about the same regardsless the size of the model in the wind tunnel regardsless differences in the viscous drag, given the corrections are right. So I don't see the reason why the e factor determined from the wind tunnel data should not be comparable with another wind tunnel data.

Besides as noted above, the Fw data is probably determined with the models.

Originally posted by Crumpp
What part of your concepts are flawed and not your math do you not pick up on?

The data is above, feel free to play with it.

gripen

[Crumpp]

The lift distribution and the form drag should be about the same regardsless the size of the model in the wind tunnel regardslessdifferences in the viscous drag, given the corrections are right. So I don't see the reason why the e factor determined from the wind tunnel data should not be comparable with another wind tunnel data.

 

Besides as noted above, the Fw data is probably determined with the models.

And the wheel goes round and round and round and round.....

You got a copy of the full report?  

The data is above, feel free to play with it.

YOUR data is above.  Why "play with it" when it is based on flawed science.  Garbage in Garbage out.

Crumpp

[Crumpp]

Tell me Gripen,

What are the differences between the Mach and Low Speed Realm of flight?

Crumpp

[gripen]

Originally posted by Crumpp
And the wheel goes round and round and round and round.....

Well, you are most wellcome to post relevant data. I have seen pictures of a Fw 190 in the Chalais-Meudon but not pictures of Ta 152s in the large scale tunnel. Besides all WWII era large scale tunnels were low speed tunnels, maximum air flow around 50-60 m/s.

gripen