Vampire vs Me 262

delcyros · 02-14-2008, 05:29 PM

Quote:

Originally Posted by Soren

Delcyros,

Why do you keep talking about the Me-262's wing tip ?? What does that have to do with anything ??

The wing tip always has the lowest Clmax & critical AoA, hence the use of wing twist (Wash out) and slats on outer wing sections.

The Me-262's wing root thickness ratio is 11% from where it gradually decreases along the span to 9% at the wing tip. The Vampire's wing thickness ratio decreases more sharply starting at 14% and ending at 9%.

The automatic LE slats on the Me-262 help increase the lift & critical AoA by 25%.

As to the Aspect Ratio of the wings, well you totally blew it there Delcyros!

The Aspect Ratio of a wing is calculated likewise: Span * Span / Wing Area, very true.

Me-262: A = 21.7 m^2 Span = 12.51 m
DH Vampire. A = 24.34 m^2 Span = 11.58 m

So the Me-262's wing's AR is 7.23, and the Vampire's is 5.5 !

Actually I'm quite surprised you could ever screw that up Delcyros as just by looking at the two wings it should've been very clear to you that the ARs of the two wings are VERY different!

Any meaningful discussion HAS to include the outer wings, not just the wingtips. You don´t want to have a stall there (...and the plane would enter a spin) so the reynolds number for the outer wing sections are non neglectable factors for lattice vortex analysis. The Me-262´s reynolds numbers for each section are ranging from 1.48 mill (wingroots) to about 0.8 mill., resulting in a mean, actual Cl-max in the range of in between 1.03 and 1.05 for Mach 0.1. without and around CL-max=1.29 with LE slats deployed (note that the actual Cl-max is lower as the maneuvering speed is higher than Mach=0.1 and thus the Cl-max is lower, too). In comparison the Cl-max of the EC 1240 under it´s re limitations is 1.19. THIS HAS SUBSTANTIAL IMPORTANCE FOR THE DISCUSSION. THE LE-SLATS DO NOT GIVE A 25% ADVANTAGE TO THE ME-262 (for each m^2 wingarea) BUT ONLY AN 8.2% ADVANTAGE. At 6.400 Kg combat weight, the Me-262´s wingload is 295 Kg/m^2 (adjusted for Cl-max of 1.29 at fully deployed LE-slats = 228 Kg/m^2) opposed to 259 Kg/m^2 at 5.430 Kg combat weight of the Vampire MK I (adjusted for Cl-max of 1.19 = 217 Kg/m^2). So despite LE-slats, the Me-262 has a higher, lift adjusted wingload. These results are derived from FORTRAN, Profill 2.20, Xwing and Mr. Ranis vortex software and adjusted for EC 1240/0640 (14% wingroot, 9 % wingtips) and NACA 0009 (11% wingroot and 9% wingtips) and their respective planforms.

span^2 is the mathematical expression of span * span. Your ar calculation of the Vampire I is based on wrong facts.

RCAF.com : The Aircraft : deHavilland VAMPIRE

Vampire MK I:
span: 12.19m; wing area: 20.99m^2
aspect ratio: 7.08 (12,19^2 = 148,5961 / 20,99 = 7.07937...)

Soren · 02-14-2008, 05:45 PM

I believe you're the one relying on incorrect data Delcyros. Just from looking at the a/c it's exceedingly clear that the AR of the Vampire's wing isn't even close to 7, the wing would be ALLOT more slender if that were the case.

All the sources I have indicate a Span of 11.58m and a wing area of 24.34 m^2.

Vampire

Now as to your CL estimates, well they're just as screwed up. You're simply not correctly reading the charts you yourself presented Delcyros, cause they clearly illustrate the high similarity in Cl between both airfoils at all speeds & Reynolds numbers.

delcyros · 02-15-2008, 04:06 AM

Quote:

Originally Posted by Soren

I believe you're the one relying on incorrect data Delcyros. Just from looking at the a/c it's exceedingly clear that the AR of the Vampire's wing isn't even close to 7, the wing would be ALLOT more slender if that were the case.

All the sources I have indicate a Span of 11.58m and a wing area of 24.34 m^2.

Vampire

Bottom line is that Your source relate to the Vampire FB V, not our Vampire F MK I. I quote from Your link:

Quote:

Applies to:

de Havilland Vampire FB.5

Type:

Single seat jet propelled twin boom fighter

(...)

Wing Area:

262 sq ft

For the F MK I use the reference, I listed above.

Quote:

Now as to your CL estimates, well they're just as screwed up. You're simply not correctly reading the charts you yourself presented Delcyros, cause they clearly illustrate the high similarity in Cl between both airfoils at all speeds & Reynolds numbers.

No, they don´t.

Graeme · 02-15-2008, 06:36 AM

Quote:

Originally Posted by Arsenal VG-33

I vaguely recall on the assembly sheet, the short aircraft history mentioning something about the Vampire/Mistral being capable of carrier takeoff/landing (or could be easily modified to do so). Anyone else heard of this? If it were true, that would be an advantage over the 262.

I'm unaware of the Mistral being carrier capable, but as you know the Aquilon (Venom) certainly was, but now we're talking early 50's. However the FAA produced the Sea Vampire (F 20 and F 21) at the end of the war. The F 21 was used in trials on HMS Warrior involving undercarriageless landings on rubber matting. Eric Brown landed a modified Vampire on HMS Ocean on 3 December 1945...

Soren · 02-15-2008, 10:29 AM

For crying out loud !

Delcyros, the only difference between the FB.5 and FB.1's wing is that one has square wing tips and the other has rounded wing tips, span and wing area is similar!

The site you reference simply by mistake misplaced the numbers 2 & 6 in the wing area specification, writing 226 sq.ft. instead of the true 262 sq.ft. and then converted that into metric getting 20.99 m^2 instead of the true 24.34 m^2.

The real specs for the Mk.I and onwards are:

Wing span: 11.58 m
Wing area: 24.34 m^2

Look at every other site for this, and if you're still not convinced then look at the profile of the different Vampire marks and compare them, and furthermore try comparing them to the Me-262's profile. That should be more than enough for anyone to realize that the AR's of both a/c are VERY different!

Bottom line, the Vampire's wing is not even close to having an AR of 7!

Soren · 02-15-2008, 10:57 AM

Vampire Mk.I top profile:

Me-262 top profile:

Should be endlessly simple and easy to note the big difference in AR between the two a/c's wings!

delcyros · 02-16-2008, 07:13 AM

Quote:

Originally Posted by Soren

Delcyros, the only difference between the FB.5 and FB.1's wing is that one has square wing tips and the other has rounded wing tips, span and wing area is similar!

No. The FB V has basically a F MK III wing with clipped wingtips, which has different properties with regards to planform in order to allow a larger internal fuel capacity. This new wing (originally with rounded tips in the Vampire F MK III) was first tested on a modified Vampire MK I in june 1945. Altough I have little geometric datas on the differences between old & new wing, I am not in the position to proof them. Since You have casted them in doubt, it´s Your task. Note that IF the planforms were identic between FB V and F I wing, than the clipped wingtips would have made a LARGER wingarea for the unclipped FI wing necessary (in between 272 and 274 ft^2, ca. 25.2-25.3m^2). 226 ft^2 therefore hardly is a typo from 27x ft^2, my friend. It is not credible to use the shorter wingspan of the clipped MK V wings for MK I performance estimations, too.

de Havilland D.H. 100 Vampire I — Canada Aviation Museum
RCAF.com : The Aircraft : deHavilland VAMPIRE
Comox Air Force Museum Vampire

Btw, the max. overloaded fighter weight seems to be only 4.754 Kg without external stores! So even if You are right with the wingarea -from what I have been not convinced- the aspect ratio would be more like 5.8 to 5.9, but the wingload at overloaded fighter configuration drops from 259 Kg/m^2 of my original estimation (20.99m^2 wingarea and 5430 Kg MTOW) to only 188 Kg/m^2 (25.26 m^2 wingarea and 4.754 Kg MTOW). My lattice vortex computations would need to be redone for such a wing and I expect a Cl-max in the range of in between 1.13 and 1.16 for such a wing, which would end up the adjusted lift corrected wingload to only 165 Kg/m^2. Congratulations, Soren! You have found a way to show that the lift adjusted wingload of "Your" Vampire is even far lower than that of mine! It will turn rings around a Me-262 anytime!

BTW, comparing pictures from swept and unswept planes with regards to aspect ratio is given false impressions. although the aspect ratio as such is only a secondary indicator. The wingspan is the crucial component of the performance. This is because an airplane derives its lift from a roughly cylindrical tube of air that is affected by the craft as it moves, and the diameter of that cylindrical tube is equal to the wingspan. A swept back wing with thin chord has a notably lower aspect ratio than would the same wing have if it would be unswept.

Soren · 02-16-2008, 05:24 PM

Nope, you don't fool me mr. spin doctor.

I don't buy your Cl estmations either, as the Cl of both wings are very similar as both have similar LE sweep & Cl figures for the airfoils under similar conditions.

Also you can choose to ignore the facts about wing span and area if you like but then you're just making stuff up from then on.

Finally let me ask you; Do you have any idea how the wing on the Vampire would look like if it had an AR of 7 ??!

Please play a little more with that program of yours to get an idea of how AR affects the shape of a wing and then compare the profile you get with the real thing, that should open your eyes.

Still can't believe you can't even see it with your own eyes from just looking and comparing shapes, geeez... even the FW190 & Bf-109 have more slender wings!