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Path: utzoo!watmath!clyde!bonnie!dpw
From: dpw@bonnie.UUCP (David P. Williams)
Newsgroups: net.aviation
Subject: Re: X-29
Message-ID: <234@bonnie.UUCP>
Date: Wed, 26-Sep-84 13:37:56 EDT
Article-I.D.: bonnie.234
Posted: Wed Sep 26 13:37:56 1984
Date-Received: Thu, 27-Sep-84 05:17:46 EDT
References: <229@haddock.UUCP>
Organization: AT&T Bell Laboratories Whippany NJ
Lines: 33



With regard to forward-swept wings:

  The aeronautical engineers can put together an aircraft with 
forward-swept wings that is dynamically stable - witness numerous
sailplanes, the Hansa corporate jet (made in Germany), and a bomber
prototype the Germans were working on at the close of World War II.
Advantages of a dynamically unstable aircraft are better maneuverability
and tailoring of the response of the aircraft to different flight
regimes.  The F-16 and Space Shuttle are dynamically unstable and
use different control responses depending on speed, angle of attack,
and other facters.  The penalty is that you have to maintain
redundant control systems for safety.  The X-29 is not a radically
different aircraft for employing new wing technology and dynamic
instability.
  For high speed aircraft, the big advantage of forward-swept wings is
that separation of flow over the wing while maneuvering occurs at
higher angles of attack than for conventional swept wings *if the
wing can be kept from twisting under the load (aeroelastic divergence)*.
Since steel and aluminum are more than happy to twist without a prohibitive
amount of stiffening, forward-swept wings have not been usable until now.
With graphite epoxy and other composites, wings can be tailored to
bend and flex in specific ways by aligning the grain of the cloth
and using varying numbers of layers.  So, it is now practical to
build aircraft with forward-swept wings - many of the designs for
the Advanced Tactical Fighter (ATF) feature them along with canards
for better maneuverability than the current generation of fighters.


David Williams
AT&T Bell Laboratories
Whippany, NJ (bonnie!dpw)