Author Topic: Explain this and win the prize! (Read 21986 times)

gripen · « **Reply #30 on:** September 12, 2004, 01:40:21 PM »

Crumpp,
Well, you are presenting quite a logic here; first you bring Lednicer in this thread and after I point out that Lednicer said quite little about the span loading and did not determine Oswald's efficiency at all, you blame me for skirting around the issue.

gripen

Crumpp · « **Reply #31 on:** September 12, 2004, 02:03:34 PM »

Quote

after I point out that Lednicer said quite little about the span loading and did not determine Oswald's efficiency at all

Actually he says quite a bit about span loading and how the wing twist of the aircraft effect the wet lifting surfaces. It is covered in the first part of the article and is quite informative. That is the whole reason the Spitfire does not develop a truly elliptical wing.

He mentions the "e" factor and states it is better than the other fighters but not by much. Not nearly as large a gap as the "guestimates".

Quote

e = 1.78(1- .045*AR^.68) - .64

Is the formula in Zigrat's spreadsheet. If you find another formula you think will be "better" let me know and I will recalculate the figures.

Crumpp

gripen · « **Reply #32 on:** September 12, 2004, 02:16:17 PM »

Crumpp,
I wonder what is your point now, basicly you are repeating what I said above and actually Tango allready claimed that formula above too (as well as me).

Have you tested that formula if it gives similar values as the drag polars?

gripen

Crumpp · « **Reply #33 on:** September 12, 2004, 02:43:57 PM »

No I haven't Gripen.

What is the data you are using for the Bf-109G and I will run it through.

Crumpp

Badboy · « **Reply #34 on:** September 12, 2004, 02:58:40 PM »

Quote

Originally posted by Crumpp
Is the formula in Zigrat's spreadsheet. If you find another formula you think will be "better" let me know and I will recalculate the figures.
Crumpp

The empirical formulae used by zigrat appears to have been derived some 20 years after WWII ended so it is possible that the data used to produce it might not be as representative as this formulae

e = 1/(0.9676+0.033*AR)

Which was derived in 1935 using data current at that time, and was quite possibly used in the design of fighters that saw service during the war. Here is a comparison of the values from each formulae, notice particularly the values for AR of 1 and 2, because that's a clue as to which formulae might be more appropriate. However, I will admit that given the sacrifices already made in the assumptions used to derive these equations, this is a bit like splitting hairs

AR___NADC___Wood
1____1.06____1.00
2____1.01____0.97
3____0.97____0.94
4____0.93____0.91
5____0.90____0.88
6____0.87____0.86
7____0.84____0.83
8____0.81____0.81
9____0.78____0.79
10___0.75____0.77
11___0.73____0.75
12___0.70____0.73

Hope that helps...

Badboy

gripen · « **Reply #35 on:** September 12, 2004, 03:01:31 PM »

The data is VL and MTT data as claimed above. The first is from the VL archives and later is from the NASM.

gripen

Crumpp · « **Reply #36 on:** September 12, 2004, 04:00:10 PM »

Quote

e = 1/(0.9676+0.033*AR)

It changes both the Spitfires and the FW-190's "e" factor in the exact same proportion as:

Quote

e = 1.78(1- .045*AR^.68) - .64

Different values with the same spread.

I will run some test calculations but I think the conclusions will be exactly the same suing either formula.

Crumpp

madness · « **Reply #37 on:** September 12, 2004, 07:05:46 PM »

Tango!? Is that you bud? Are ya the same tango from ww2ol that flew with 8th af?

dtango · « **Reply #38 on:** September 12, 2004, 09:53:40 PM »

madness:

Sorry not the same tango. I've never played WW2OL.

Tango, XO
412th FS Braunco Mustangs

gripen · « **Reply #39 on:** September 12, 2004, 10:23:54 PM »

Crumpp,
You don't seem to understand how to tests these formulas; you need a drag polar of a certain plane to make comparison, see Perkins&Hage p. 90-94.

gripen

madness · « **Reply #40 on:** September 12, 2004, 10:27:45 PM »

Ahh ok, thought you were somebody else

oh well. Thanks for explaining that jibberish

.

S!

Crumpp · « **Reply #41 on:** September 12, 2004, 11:12:26 PM »

You mean this one?

http://www.wiley.com/WileyCDA/WileyTitle/productCd-047168046X.html

Crumpp

gripen · « **Reply #42 on:** September 12, 2004, 11:17:21 PM »

Yep, that's the reference regarding WWII fighter performance estimation.

gripen

Crumpp · « **Reply #43 on:** September 13, 2004, 05:47:59 AM »

Got it on order. Should be here in a couple of days.

Crumpp

Starbird · « **Reply #44 on:** September 13, 2004, 09:22:57 AM »

I can't quite follow all of this, but do you guys have any suggestions on books or papers where these formula are explained?

[edit]Other than what has already been linked to.