Author Topic: Draining E in turns  (Read 12214 times)

Offline gripen

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Draining E in turns
« Reply #240 on: September 09, 2004, 06:14:04 PM »
Quote
Originally posted by Badboy
 
Airplane Performance Stability and Control, by Perkins & Hage, page 73.


This is the only one I have in the hand of those you mentioned and  the graphs in the page 73 actually give correction factors of the rectangular wing against aspect ratio.

In the previous page the writers actually say that:

"For an untwisted wing with elliptical planform shape these correction factors are zero"

If I understand this correctly those formulas you gave above work only for the rectangular wings and we can't determine the shape of the wing from the aspect ratio only.


Quote
Originally posted by Crumpp
Please explain.


I have allready told you several times that my calculation contain exhaust thrust and propeller efficiency check with momentary theory (with link).

Quote
Originally posted by Crumpp
1. Have you thought about the fact the US Navy data is in Nautical miles?


The report gives values in the metric unit too.

gripen

Offline Crumpp

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Draining E in turns
« Reply #241 on: September 09, 2004, 06:55:22 PM »
Quote
I have allready told you several times that my calculation contain exhaust thrust and propeller efficiency check with momentary theory (with link).


Let us see your calculations.

Quote
The report gives values in the metric unit too.


Please disclose the values.

Look Gripen,  My goal in this is not to make you or anybody look silly or to engage in counterproductive flame war.  Your a smart guy who obviously knows quite bit about this stuff.  
What you claim happens to be the opposite from what another  smart guy claims.  Additionally the math backs it up the other claim's.  So that is 2 out of 3 right now.  

I would like to continue this and I will.  I just hope we can set a new tone and discuss this without the silly "oneupmanship".

Crumpp
« Last Edit: September 09, 2004, 07:05:21 PM by Crumpp »

Offline Badboy

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Draining E in turns
« Reply #242 on: September 09, 2004, 07:15:33 PM »
Quote
Originally posted by gripen
This is the only one I have in the hand of those you mentioned and  the graphs in the page 73 actually give correction factors of the rectangular wing against aspect ratio.


Correct, Figure 2-44 (b) shows the relationship of those factors to Aspect Ratio for a rectangular wing, and that illustrates the dependency of e to Aspect Ratio. In the previous graph you see the influence that taper ratio has for an aspect ratio of 6. There are other formulae that also include the taper ratio so that values for non rectangular wings can be estimated also.

Quote

In the previous page the writers actually say that:

"For an untwisted wing with elliptical planform shape these correction factors are zero"


Correct, and that’s why the elliptical planform theoretically has the least induced drag, in that case the efficiency factor e would equal one.  

Quote

If I understand this correctly those formulas you gave above work only for the rectangular wings and we can't determine the shape of the wing from the aspect ratio only.


Partly correct… It is true that formulae that only include aspect ratio only apply to a single taper ratio, it just happens that the graph in Perkins & Hage is for zero taper. The previous graph on the same page illustrates the relationship for both taper ratio and aspect ratio but even so the dependency upon aspect ratio is clear.

However, the formulae presented by Professor Wood is for a taper ratio of 0.57 which yields an almost elliptical lift distribution, which is why it fits the experimental data so closely over a wide range of examples. Most WWII aircraft had a taper ratio close to that value (Me109 was approx 0.52) because the designers knew about the benefits of elliptical lift distribution and that it could be achieved quite closely with a wing of that taper, that’s why a formulae that only includes aspect ratio could still be of such good practical use.  However, other graphs and formulae that include both taper ratio and aspect ratio were common, today it is just as easy to include everything, including twist, camber, and sweep etc.

Hope that helps

Badboy
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Offline Crumpp

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Draining E in turns
« Reply #243 on: September 10, 2004, 08:55:28 PM »
Guess this issue is resolved then.

Thanks for participating!

Crumpp

Offline gripen

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Draining E in turns
« Reply #244 on: September 11, 2004, 03:09:04 PM »
Quote
Originally posted by Crumpp

Let us see your calculations.


As noted couple times earlier: Just follow the link and find formula no. 10, collect needed data (speed, altitude, output and propeller diameter), form calculation to the excel and solve the max theoretical efficiency with the solver. As an example the US Navy 190; 537 km/h, sea level, 1740 ps and 3,3 m propeller will result max theoretical efficiency 98,3 %. Effective efficiency is about 10-15 % less than this so 85% seems to be a good aproximate. The exhaust thrust is purely aproximate based on assumption that the exhaust thrust will ad about 15-20% thrust at high speed.

Quote
Originally posted by Crumpp

Please disclose the values.


How can I "disclose" values which you can read directly from the US Navy Fw 190 report?

Quote
Originally posted by Crumpp

What you claim happens to be the opposite from what another smart guy claims. Additionally the math backs it up the other claim's. So that is 2 out of 3 right now.


May I ask what is opposite from what another smart guy claims?

Quote
Originally posted by Badboy

However, the formulae presented by Professor Wood is for a taper ratio of 0.57 which yields an almost elliptical lift distribution, which is why it fits the experimental data so closely over a wide range of examples. Most WWII aircraft had a taper ratio close to that value (Me109 was approx 0.52) because the designers knew about the benefits of elliptical lift distribution and that it could be achieved quite closely with a wing of that taper, that’s why a formulae that only includes aspect ratio could still be of such good practical use.


This is a quite sensible assumption. I have calculated some e factor data for comparison which I will post shortly to the another thread.

gripen
« Last Edit: September 11, 2004, 04:14:20 PM by gripen »

Offline Crumpp

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Draining E in turns
« Reply #245 on: September 11, 2004, 03:24:02 PM »
Quote
As noted couple times earlier: Just follow the link and find formula no. 10, collect needed data (speed, altitude, output and propeller diameter), form calculation to the excel and solve the max theoretical efficiency with the solver. As an example the US Navy 190; 537 km/h, sea level, 1740 ps and 3,3 m propeller will result max theoretical efficiency 98,3 %. Effective efficiency is about 10-15 % less than this so 85% seems to be a good aproximate. The exhaust thrust is purely aproximate based on assumption that the exhaust thrust will ad about 15-20% thrust at high speed.


Your link is busted.

537km/h doesn't agree with any of the Luftwaffe data.  Given the detailed engine trouble the US Navy experienced and the fact the graph agrees with all the performance listing's in the Pilots manual for the FW-190A5 I fail to comprehend why you do not accept the data.  

I am sure that if you use such skewed performance figures as 537kph at full emergency power output you will get skewed results.  You are using the full horsepower ratings the US Navy copied from the FW-190 pilots manual with an engine that is not developing near that amount of power.

Crumpp
« Last Edit: September 11, 2004, 03:47:37 PM by Crumpp »

Offline Crumpp

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« Reply #246 on: September 11, 2004, 03:40:52 PM »
Quote
May I ask what is opposite from what another smart guy claims?


Your flat plate values are totally different from Lednicers.  You claim the Spitfire had less parasitic drag and because of it's induced drag maintained less drag throughout the flight envelope.  That is not what Lednicers says and the calculations confirm.

The only ammo you have left is too try and call into question Oswalds efficiency factor and it's use in the induced drag formula.


Crumpp

Offline gripen

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« Reply #247 on: September 11, 2004, 04:30:52 PM »
Now the link should work.

Regarding US Navy data, it's the best one I know for the Fw 190 which I certainly know to be flight tested.

Regarding flat plate areas; these are calculated with certain assumptions and purpose is not to reach same numbers but that the relative difference between planes is comparable.

And if you look above, I wrote:

" I don't see how it can be used alone to estimate the e factor. Maybe with the taper ratio but not alone."

What Badboy pointed out is a quite sensible; the taper ratio should be in the certain ball park in the case of the WWII fighters.

gripen
« Last Edit: September 11, 2004, 04:46:52 PM by gripen »

Offline Crumpp

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« Reply #248 on: September 11, 2004, 05:20:04 PM »
Quote
Regarding US Navy data, it's the best one I know for the Fw 190 which I certainly know to be flight tested.


Yes I understand that but consider this.

1.  The graph I provided is listed as an actual test flight in the FW factory logs.

2.  The data lines up perfectly with the other models of the FW-190A.

Example:

The FW-190A3 could do 365kph at sea level using 1.42ata @ 2400U/min. It weighed 3978kg in that flight with the outboard MGFF's.

The FW-190A5 can do 365kph at sea level using 1.42ata @ 2700U/min.  It weighed 4106kg's and had some aerodynamic refinements to the cooling gills.  The FW-190A3 had gills cut in the side of the fuselage with internal gills that caused some flow problems getting air out of the cowling.  The FW-190A5 moved the gills to the outside behind the cowling.  It did not gain much weight and it gained some power by being able to increase prop rpm and had a reduction in drag.

The FW-190A8 could do 365kph on the deck.  It weighed 4398kg's on take off in that test.  It also had a lot more power at 1.58ata@2700U/min than it's predecessors.   At the same power outputs as the FW-190A5 the FW-190A8 could only manage 545kph on the deck.

So it make perfect sense.  Especially when you consider the fact that the airframe the US Navy test was:

1. A recovered crash that required extensive repairs to both the airframe and the engine.

2.  The Allied personnel doing the work were not technical experts on the design.  Just read the aileron comments on the FW page I reference.  If the FW factory trained personnel had difficulty adjusting certain portions of the plane how can untrained technicians be expected to perform at the same level?

http://www.terra.es/personal2/matias.s/fw190.htm

3.  The engine had problems that are noted in the test.  IMO this was due to the differences in German aviation fuel and US AVGAS.  

Crumpp

Offline Crumpp

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« Reply #249 on: September 12, 2004, 09:28:14 AM »
Quote
Shake hands, and if you ever go touring, come to my place and we'll have a heck of a time


Same goes bro!  If you ever make it to the States you got a place to stay.  The NASM is fairly close.

Crumpp

Offline Crumpp

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« Reply #250 on: September 12, 2004, 09:31:09 AM »
Quote
Regarding flat plate areas; these are calculated with certain assumptions and purpose is not to reach same numbers but that the relative difference between planes is comparable.


That is correct.  Your CONCLUSIONS are totally different.  However, the more detailed we make the calculations the more Lednicers conclusions are shown to be correct.

Crumpp

Offline gripen

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« Reply #251 on: September 12, 2004, 09:41:49 AM »
Quote
Originally posted by Crumpp
Your CONCLUSIONS are totally different.  However, the more detailed we make the calculations the more Lednicers conclusions are shown to be correct.


Hm... I wonder what do you mean? Lednicer's flat plate area values for the Spitfire and the Fw 190 are within 3,4 % from each other. I have pointed out that variation among tested Spitfires was far larger than this.

Besides this has nothing to do with the subject of this thread.

gripen

Offline Crumpp

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« Reply #252 on: September 12, 2004, 10:51:59 AM »
Yes and that variation is high enough to lend a drag advantage to ONE Spitfire MK IX with a new air intake design.  ALL OF THE OTHERS lose the drag advantage race and none ever win the parasitic drag race.  One model is close enough that it's induced drag advantage counts and brings the planes to equality drag wise at high speeds.

Given that same variation you will find many FW-190's that widen that gap even more and a few who completely close it.  On average, given the number of Spitfire Mk IX's the FW-190 has less drag than, you can concluded FW-190's had less parasitic drag than the Spitfire.  

Especially when the FW-190A8 in question is not "filled and polished" but rather "primed and painted".  A frontline fighter finish.

Totally different from the picture you are creating on your calculator.

Crumpp
« Last Edit: September 12, 2004, 02:08:44 PM by Crumpp »

Offline Crumpp

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« Reply #253 on: September 12, 2004, 10:55:29 AM »
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Besides this has nothing to do with the subject of this thread.


It has everything to with this thread and is the focus of the matter at hand.

Crumpp

Offline Crumpp

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« Reply #254 on: September 13, 2004, 03:36:50 PM »
"Reality Strikes" September - October, 1944

September 13, 1944

Oberflächenschutzliste 8 Os 155:

Released by Blohm & Voss and approved by the RLM, designating the 'green' 81/82 camouflage scheme to be applied to the BV 155. The colours were designated as "Olivbraun 81" and "Hellguen 82" (Hitchcock, 1990, inside front cover & p.19). The following is an exact translation of this document, courtesy of Kenneth Merrick:

Sch/01 Advance announcement B&V 13 Sept. 1944

Camouflage BV155

The E-stelle Travermuende authority provides the following:

The BV155 shall have on the uppersurface the colours 81 Olivebrown and 82 Light Green. The mottling spacing and placement should be similar to the Bf 109 camouflage scheme. The fuselage sides, side of the vertical tail and leading edge of the wing and horizontal stabilizer should be painted in colour 76 (no name given). Hereafter, except for the wing and horizontal stabilizer’s leading edge, the aircraft should be then in a cloudy overspray with colour tones 81 and 82. Also, we look ahead to simplify the paint schemes which we should know shortly and will publish. Afterwards, the above mentioned aircraft which will be used for day service, camouflage on the undersurfaces should be deleted.

With the mottle scheme, it should be applied on the aircraft sheet metal between the camouflage and its painted line. The pattern is to be soft flowing lines. The colour scheme is to be sprayed on at the present time. In case of needed puttying, (aircraft putty 7270.99) it should be applied on bare metal beyond the border lines of the paint scheme and the bare metal should be polished in the usual way but no camouflage on top of the putty. The painting of the undersurface is being deleted to economize.

A/c materials test division for surface protection.

 

COMMENT: Here is what the author believes is a perfect example of a camouflage document typical of the period. It is important in that it is the first to describe the use of colours 81 and 82, and provides evidence that the descriptive names of these shades were assigned by the manufacturer. Significantly, such was the supply crisis that even at this early date it was ordered that the undersides of the aircraft were to remain unpainted. Another point to ponder: Could "Olivbraun" in fact be RLM 80 Olivgrün, which could have been inserted as a substitute from excess and redundant stocks for the as yet still officially un-described colour RLM 81

September 1944

Factory Camouflage Directive, Fw 190 A:

It is most probable that this document or a related order (possibly a document only and not an Oberflächenschutzliste), existed in some form and specified the 75/83 scheme for the Fw 190 D-9 as well (see above comments).

 

COMMENT: First operational use of the Dora took place in early October 1944 with III./JG 54 whose aircraft were camouflaged in the 75/83 scheme that is well documented with photographic evidence.(Smith and Creek, 1986, p.10). However, a change occurred in the camouflage colours used in early 1945, from the standard 75/83 scheme to the 81/82 combination, and it is most probable that a variety of transition schemes existed (e.g., 81/83, 82/83, 75/81, etc.) Furthermore, the seperate production and finishing of the Jumo 213 engines in RLM 83 (or possibly 71) would have also complicated the prescribed and transitional camouflaged schemes

http://www.clubhyper.com/reference/luftcamdb_3.htm


In fact it is the opposite.  Filled and Polished is more the standard while "primed and painted" is a substandard Luftwaffe A/C finish.

Makes sense.  If you were an A/C company competing for design contracts wouldn't you want the greatest performance gains possible in your new design over the old one?

Crumpp
« Last Edit: September 14, 2004, 06:41:27 AM by Crumpp »