Uzytkownik "Erich Adler" napisal w wiadomosci
m...
I see that no civil discussion can take place here despite the fact
that you "adults" claim to cherish military aviation. So why all the
fuss about German aircraft, jets or otherwise?
I live in America now but don't like the blatant arrogance I see
whenever history is talked about in regards to military aircraft.
Every American I have had discussions with usually end up in disaster
because the ignorant American can't get it through his thick skull
that they owe practically everything to Germany in the field of modern
military aviation.
We could discuss Allied centrifugal jets that lost out in the long
run. German engineers told them that in 1945. We could discuss the US
reliance on German wind tunnel data to build a large variety of
postwar military aircraft and research aircraft.
I don't want to answer all this crap 'Germans invented ALL this decades
(or centuries...) ago', but wind-tunnel testing was my business. I used
to do researches in transonic region - the same which aviation
technology dealt with for the first time in the end of WWII and into
fifties. Unfortunately, Germans HAD NO POSSIBILITY to do any wind-tunnel
tests close to M=1. There was no technology and apparatus to do such
tests in that time. Germans had lots of data up to approx. M=0.7 and
above approx. M=1.15 and BIG STINKING HOLE in between! They had subsonic
and supersonic wind-tunnels but none transonic.
My first job after I finished high school was testing of three airfoils
intended for helicopter use up to M=0.95. The airfoils we NACA 0012
(reference model) NACA 23012 and some modification of the later. It was
during Cold War and long before Internet. I needed some literature so I
dug old NACA and NASA reports which I could find. A friend of mine found
a photocopy of original wartime report of AVA Göttingen upon wind-tunnel
test of NACA 23012 up to M=0.9. These results were totally unreliable
above M=0.7; they even shoved negative (!) lift-curve slope at zero-lift
AoA at M=0.9! It could not be otherwise because the tests were made in
closed test section with SOLID WALLS of circular shape using
conventional finite aspect ratio wing with endplates on external
mechanical balance.
For those unfamiliar with testing technology:
1. However SOLID WALLS are good for subsonic and supersonic tests, they
are inadequate for any transonic tests. Every wind-tunnel with solid
walls has some terminal Mach number (for a given model) above which it
is impossible to increase effective Mach number in the test section. A
shock wave emerges in the throat (usually at model's max. cross section)
between the model and the walls. Nowadays every transonic wind-tunnel
has ventilated test section (slotted, perforated or mix of them).
Ventilation works as a mass-flow nozzle preventing the buildup of said
shock wave and thus achieve Mach numbers up to approx. 1.2 without need
of any convergent-divergent nozzle. I don't remember when ventilated
test section was used for the first time, but this technology was ABSENT
in Germany A.D. 1945.
2. Circular cross section of the test section is not good for
two-dimensional tests. Better is square test section and the best is
rectangular cross-section with H/B1 (H/B=2-3 is widely used) and the
model placed wall-to-wall between side walls. The configuration used in
cited AVA Göttingen tests is tipical for low-speed tests (as presented
in NACA Report 824 for example).
3. Both external balance (with pushrods and strings) and end plates
produce additional forces which have to be tested separatelly and
deducted from model's test results. This technology is proven in low
speeds but in high subsonic speeds those corrections could be higher
than netto force, so the tests become unreliable.
4. As for negative lift-curve slope - this is visible sign of shock wave
between the model and the walls for me. Another argument about
unreliability of German transonic tests.
It would be all from me about these 'superior wind-tunnel data' which US
rely on postwar until today.
[snip rest of the crap]
Peace,
OK! You should RIP, too.
Erich Adler
JasiekS
Warsaw, Poland
PS. What a coincidence! Please compare these two headers (hint -
NNTP-Posting-Host):
----------- Header 1
From:
(Erich Adler)
Newsgroups: rec.aviation.military
Subject: Hey, Germany Invented It... Face It
Date: 17 Feb 2004 09:54:06 -0800
Organization: http://groups.google.com
Lines: 57
Message-ID:
NNTP-Posting-Host: 198.81.26.44
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
X-Trace: posting.google.com 1077040446 4858 127.0.0.1 (17 Feb 2004
17:54:06 GMT)
X-Complaints-To:
NNTP-Posting-Date: Tue, 17 Feb 2004 17:54:06 +0000 (UTC)
----------- Header 2
From: (robert arndt)
Newsgroups: rec.aviation.military
Subject: Hey, Germany Invented It... Face It
Date: 18 Feb 2004 07:16:05 -0800
Organization: http://groups.google.com
Lines: 31
Message-ID:
References:
NNTP-Posting-Host: 198.81.26.44
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
X-Trace: posting.google.com 1077117365 25946 127.0.0.1 (18 Feb 2004
15:16:05 GMT)
X-Complaints-To:
NNTP-Posting-Date: Wed, 18 Feb 2004 15:16:05 +0000 (UTC)