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-   -   Why a Swept-Wing? (http://www.aviationbanter.com/showthread.php?t=7652)

James Dandy January 11th 04 02:39 PM

Why a Swept-Wing?
 
Pardon my ignorance on all matters concerning modern aviation but just
why the hell would you want to sweep a wing forward?

Doesn't that make any aircraft unstable? If so, why would any pilot
feel safe in it?

Has anyone ever made one work?

James Dandy

Simon Robbins January 11th 04 02:56 PM

"James Dandy" wrote in message
m...
Doesn't that make any aircraft unstable? If so, why would any pilot
feel safe in it?


I imagine it would move the centre of lift forward of the centre of gravity,
which might help to increase lift at slow speed or high angle of attack. (I
think..)

Si



Mike Marron January 11th 04 03:23 PM

(James Dandy) wrote:

Pardon my ignorance on all matters concerning modern aviation but just
why the hell would you want to sweep a wing forward?


Depending on the type of aircraft, there are lots of good reasons
to sweep the wing forward as opposed to aft. I'm only familiar with
the reasons the Blanik L23 sailplane has forward swept wings and
that is to allow for more weight placed forward of the main wing spar.

Doesn't that make any aircraft unstable? If so, why would any pilot
feel safe in it?


The Blanik is stable in all 3 axes (e.g: pitch, roll, and yaw) and
aerobatics in it are a delight. It's an all-metal sailplane that's
been around for decades and countless pilots, including me,
feel perfectly safe in it.

Has anyone ever made one work?


The Blanik is the USAF Academy's basic sailplane trainer of choice.



C Knowles January 11th 04 03:47 PM

This is taken from Aerospace web
http://www.aerospaceweb.org/aircraft/fighter/s37/

"The advantages of forward sweep have long been known as such wings offer
lower wave drag, reduced bending moments, and delayed stall when compared to
more traditional wing shapes. Unfortunately, forward sweep also induces
twisting strong enough to rip the wings off an aircraft built of
conventional materials. To solve this problem, the Su-47 makes use of
composite materials carefully tailored to resist twisting while still
allowing the wing to bend for improved aerodynamic behavior. "

"However, Sukhoi has apparently decided to abandon the forward-swept wings
of the S-37, and the future production model will return to a more
conventional wing layout. If true, Sukhoi may have reached the same
conclusion as NASA did following testing of the X-29--the benefits of
forward-swept wings are just not worth the extra cost and complexity
associated with their design and manufacture."

Curt

"James Dandy" wrote in message
m...
Pardon my ignorance on all matters concerning modern aviation but just
why the hell would you want to sweep a wing forward?

Doesn't that make any aircraft unstable? If so, why would any pilot
feel safe in it?

Has anyone ever made one work?

James Dandy




Air Force Jayhawk January 11th 04 03:55 PM

On 11 Jan 2004 05:39:04 -0800, (James Dandy)
wrote:

Pardon my ignorance on all matters concerning modern aviation but just
why the hell would you want to sweep a wing forward?

Doesn't that make any aircraft unstable? If so, why would any pilot
feel safe in it?

Has anyone ever made one work?

James Dandy


An aircraft is only unstable if the aerodynamic center is forward of
the center of gravity. If the wing root is sufficiently aft and the
AC stays aft of the CG, stability remains.

Why? Well it was tried with the X-29 but I never have read why no one
has pursued it since. The advantage was supposed to be that the
boundary layer (the thick air right next to the surface caused by
friction and very annoying) builds up as the air moves aftward along
the wing. With a FSW, the thickest part of the BL is at the root
rather than near the control surfaces, enhancing control while at high
angles of attack. There are other advantages but it's been a while so
I can't recall them off the top of my head.

I knew the USAF pilot on the X-29 project...he said it flew fine and
had no issues with it.

Ross "Roscoe" Dillon
USAF Flight Tester
(B-2, F-16, F-15, F-5, T-37, T-38, C-5, QF-106)

patrick mitchel January 11th 04 06:16 PM

The Hansa jet had forward sweep- the one pilot that had flown said type
stated no unkind words on the plane. Pat



Tarver Engineering January 11th 04 06:57 PM


"C Knowles" wrote in message
m...
This is taken from Aerospace web
http://www.aerospaceweb.org/aircraft/fighter/s37/

"The advantages of forward sweep have long been known as such wings offer
lower wave drag, reduced bending moments, and delayed stall when compared

to
more traditional wing shapes. Unfortunately, forward sweep also induces
twisting strong enough to rip the wings off an aircraft built of
conventional materials. To solve this problem, the Su-47 makes use of
composite materials carefully tailored to resist twisting while still
allowing the wing to bend for improved aerodynamic behavior. "

"However, Sukhoi has apparently decided to abandon the forward-swept wings
of the S-37, and the future production model will return to a more
conventional wing layout. If true, Sukhoi may have reached the same
conclusion as NASA did following testing of the X-29--the benefits of
forward-swept wings are just not worth the extra cost and complexity
associated with their design and manufacture."


Actually, once the notch filter was adjusted such that the wing did not
delaminate, there was no benifit to forward swept wings. The program
falsified X-29 flight test data and USAF was quite punative in blackballing
the whole group. Perhaps Mary would like to speak to that issue, as she was
very close.

"James Dandy" wrote in message
m...
Pardon my ignorance on all matters concerning modern aviation but just
why the hell would you want to sweep a wing forward?

Doesn't that make any aircraft unstable? If so, why would any pilot
feel safe in it?

Has anyone ever made one work?

James Dandy






Tarver Engineering January 11th 04 07:10 PM


"Air Force Jayhawk" wrote in message
...
On 11 Jan 2004 05:39:04 -0800, (James Dandy)
wrote:

Pardon my ignorance on all matters concerning modern aviation but just
why the hell would you want to sweep a wing forward?

Doesn't that make any aircraft unstable? If so, why would any pilot
feel safe in it?

Has anyone ever made one work?

James Dandy


An aircraft is only unstable if the aerodynamic center is forward of
the center of gravity. If the wing root is sufficiently aft and the
AC stays aft of the CG, stability remains.

Why? Well it was tried with the X-29 but I never have read why no one
has pursued it since. The advantage was supposed to be that the
boundary layer (the thick air right next to the surface caused by
friction and very annoying) builds up as the air moves aftward along
the wing. With a FSW, the thickest part of the BL is at the root
rather than near the control surfaces, enhancing control while at high
angles of attack. There are other advantages but it's been a while so
I can't recall them off the top of my head.

I knew the USAF pilot on the X-29 project...he said it flew fine and
had no issues with it.


USAF got shafted on the X-29 and would have never built the second airframe,
had they known about the flutter problem. NASA falsified the flight test
reports such that they indicated the wing flutter sensor was within limits,
when in fact, the data went full scale and drew a straight line.

What would a pilot know about a vehicle? You've been there Rosco, how could
they possibly know?



Ed Rasimus January 11th 04 07:20 PM

On Sun, 11 Jan 2004 09:55:02 -0500, Air Force Jayhawk
wrote:

An aircraft is only unstable if the aerodynamic center is forward of
the center of gravity. If the wing root is sufficiently aft and the
AC stays aft of the CG, stability remains.

Why? Well it was tried with the X-29 but I never have read why no one
has pursued it since. The advantage was supposed to be that the
boundary layer (the thick air right next to the surface caused by
friction and very annoying) builds up as the air moves aftward along
the wing. With a FSW, the thickest part of the BL is at the root
rather than near the control surfaces, enhancing control while at high
angles of attack. There are other advantages but it's been a while so
I can't recall them off the top of my head.

I knew the USAF pilot on the X-29 project...he said it flew fine and
had no issues with it.


As I recall the X-29 project, one of the objectives was evaluation of
the instability as a means of gaining agility for future highly
maneuverable aircraft. The "urban legend" was that the aircraft
required minimum of triple redundant FBW augmentation as loss of the
augmentation would result in immediate excursions from stable flight
and structural failure within seconds. The ultimate in "JC maneuvers".

Always thought it made for an extremely ugly airplane.

Wasn't the basic structure from an F-16A?



Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
Smithsonian Institution Press
ISBN #1-58834-103-8

Ed Rasimus January 11th 04 07:24 PM

On Sun, 11 Jan 2004 09:55:02 -0500, Air Force Jayhawk
wrote:

An aircraft is only unstable if the aerodynamic center is forward of
the center of gravity. If the wing root is sufficiently aft and the
AC stays aft of the CG, stability remains.

Why? Well it was tried with the X-29 but I never have read why no one
has pursued it since. The advantage was supposed to be that the
boundary layer (the thick air right next to the surface caused by
friction and very annoying) builds up as the air moves aftward along
the wing. With a FSW, the thickest part of the BL is at the root
rather than near the control surfaces, enhancing control while at high
angles of attack. There are other advantages but it's been a while so
I can't recall them off the top of my head.

I knew the USAF pilot on the X-29 project...he said it flew fine and
had no issues with it.


As I recall the X-29 project, one of the objectives was evaluation of
the instability as a means of gaining agility for future highly
maneuverable aircraft. The "urban legend" was that the aircraft
required minimum of triple redundant FBW augmentation as loss of the
augmentation would result in immediate excursions from stable flight
and structural failure within seconds. The ultimate in "JC maneuvers".

Always thought it made for an extremely ugly airplane.

Wasn't the basic structure from an F-16A?



Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
Smithsonian Institution Press
ISBN #1-58834-103-8


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