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Murmur
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 Posted: Fri Jul 06, 2007 7:42 pm Post subject: Induced drag in supersonic flight? |
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1) If an aircraft is travelling at M>1, but the airflow is slowed to
subsonic speed by shockwaves ahead of the wing, is there induced drag?
2) A swept-wing aircraft is travelling at M>1. The airflow is slowed down by
oblique shockwaves, but still supersonic. The chordwise component of the
airflow on the swept wing is subsonic though. Is there induced drag? |
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Tom S.
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| Posted: Fri Jul 06, 2007 9:37 pm Post subject: Re: Induced drag in supersonic flight? |
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"Murmur" <Murmur@Murmur.invalid> wrote:
[quote]1) If an aircraft is travelling at M>1, but the airflow is slowed to
subsonic speed by shockwaves ahead of the wing, is there induced drag?
[/quote]
Yes. The wing is flying in subsonic flow.
[quote]2) A swept-wing aircraft is travelling at M>1. The airflow is slowed down
by oblique shockwaves, but still supersonic. The chordwise component of
the airflow on the swept wing is subsonic though. Is there induced drag?
[/quote]
There would still be induced drag because the transit time over the wing
isn>t zero, but that effect would be localized to a very small area at the
wing tip. I>m having a tougher time picturing this situation in my head
but, since the local flow is supersonic the air ahead of the wing can>t see
the wing coming, there should would be very limited opportunity for induced
drag. Lots of wave drag though...
Tom. |
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marika
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| Posted: Sat Jul 07, 2007 8:17 am Post subject: Re: Induced drag in supersonic flight? |
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Tom S. wrote in message ...
[quote]"Murmur" <Murmur@Murmur.invalid> wrote:
1) If an aircraft is travelling at M>1, but the airflow is slowed to
subsonic speed by shockwaves ahead of the wing, is there induced drag?
Yes. The wing is flying in subsonic flow.
2) A swept-wing aircraft is travelling at M>1. The airflow is slowed down
by oblique shockwaves, but still supersonic. The chordwise component of
the airflow on the swept wing is subsonic though. Is there induced drag?
There would still be induced drag because the transit time over the wing
isn>t zero, but that effect would be localized to a very small area at the
wing tip. I>m having a tougher time picturing this situation in my head
but, since the local flow is supersonic the air ahead of the wing can>t see
the wing coming, there should would be very limited opportunity for induced
drag. Lots of wave drag though...
[/quote]
This is oh, so too darn funny. I just rolled around the floor I was
laughing so hard . Thanks. I have to send this to a friend
mk5000
"building up like storms,
bursting in mid-air"--david heavenor. sign in a stranger |
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Murmur
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| Posted: Sun Jul 08, 2007 4:06 pm Post subject: Re: Induced drag in supersonic flight? |
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"Tom S." <tdscanuck@yahoo.com> ha scritto nel messaggio
news:JKrnJA.2qL@news.boeing.com...
[CUT]
Thanks Tom, you seem to have a good intuitive understanding of fluid
dynamics.
I have another question, let>s consider the same situation:
swept wing, supersonic flow, subsonic chordwise component.
Will the aerodynamic center of the wing shift from 25 to 50%?
Will shockwaves form on wing leading and trailing edge etc?
Marco |
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Tom S.
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| Posted: Mon Jul 09, 2007 1:22 pm Post subject: Re: Induced drag in supersonic flight? |
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"Murmur" <Murmur@Murmur.invalid> wrote:
[quote]I have another question, let>s consider the same situation:
swept wing, supersonic flow, subsonic chordwise component.
Will the aerodynamic center of the wing shift from 25 to 50%?
[/quote]
I believe so. Been a while since I worked any of this type of stuff but the
transition from sub to supersonic flow is accompanied by an aft shift in
center of lift. The changed flow regime alters the pressure distribution
around the airfoil.
[quote]Will shockwaves form on wing leading and trailing edge etc?
[/quote]
There will always be shockwaves (no way to avoid it) but the location and
type are going to be very geometry and speed dependant.
Tom. |
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Murmur
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| Posted: Mon Jul 09, 2007 8:06 pm Post subject: Re: Induced drag in supersonic flight? |
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"Tom S." <tdscanuck@yahoo.com> ha scritto nel messaggio
news:JKwKLy.6Jy@news.boeing.com...
[quote]I believe so. Been a while since I worked any of this type of stuff but
the transition from sub to supersonic flow is accompanied by an aft shift
in center of lift. The changed flow regime alters the pressure
distribution around the airfoil.
[/quote]
I>m trying to picture the situation myself.
My conclusion is that if we consider the theoretical case of an infinite
swept wing, the pressure distribution should remain unchanged until the
chordwise component exceeds Mcr.
Hence we should have induced drag and no a.c. shift even if the incoming
flow is supersonic.
The case of a finite wing maybe a completely different story though.
Marco |
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Tom S.
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| Posted: Mon Jul 09, 2007 9:12 pm Post subject: Re: Induced drag in supersonic flight? |
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"Murmur" <Murmur@Murmur.invalid> wrote:
[quote]My conclusion is that if we consider the theoretical case of an infinite
swept wing, the pressure distribution should remain unchanged until the
chordwise component exceeds Mcr.
[/quote]
It will start to shift considerably before the chordwide component goes
supersonic because you will get local supersonic exceedences even if the
bulk flow is subsonic. This is the whole problem with transonic airfoil
design.
[quote]Hence we should have induced drag and no a.c. shift even if the incoming
flow is supersonic.
[/quote]
If you have an infinite wing, of any sweep, why would you be getting any
induced drag?
Tom. |
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Murmur
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| Posted: Mon Jul 09, 2007 9:48 pm Post subject: Re: Induced drag in supersonic flight? |
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--
-------------------------------------------------
Don>t look-up. Do fly. X-Plane.
-------------------------------------------------
"Tom S." <tdscanuck@yahoo.com> ha scritto nel messaggio
news:JKx6C6.H4o@news.boeing.com...
[quote]It will start to shift considerably before the chordwide component goes
supersonic because you will get local supersonic exceedences even if the
bulk flow is subsonic. This is the whole problem with transonic airfoil
design.
[/quote]
What I meant is, if the chordwise velocity is below Mach critical, I think
the airfoil (infinite wing) should still retain a subsonic behaviour,
despite a supersonic streamwise flow.
[quote]If you have an infinite wing, of any sweep, why would you be getting any
induced drag?
[/quote]
D>oh, you>re right!
I should have said: we should have upwash even if the incoming flow is
supersonic (see first part of repsonse).
What do you think?
Marco |
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Tom S.
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| Posted: Tue Jul 10, 2007 9:34 pm Post subject: Re: Induced drag in supersonic flight? |
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"Murmur" <Murmur@Murmur.invalid> wrote:
[quote]What I meant is, if the chordwise velocity is below Mach critical, I think
the airfoil (infinite wing) should still retain a subsonic behaviour,
despite a supersonic streamwise flow.
[/quote]
If you have supersonic streamwise flow, you>re going to have a shock off the
leading edge. I think that will throw the whole airfoil pressure
distribution off what you>d see with subsonic flow.
[quote]If you have an infinite wing, of any sweep, why would you be getting any
induced drag?
D>oh, you>re right!
I should have said: we should have upwash even if the incoming flow is
supersonic (see first part of repsonse).
[/quote]
Not sure how that would work, physically. If the wing is swept at less than
the Mach angle, no air ahead of the wing can "see" the wing coming. That
means, I think, no wash (in any direction).
Tom. |
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Murmur
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| Posted: Tue Jul 10, 2007 11:47 pm Post subject: Re: Induced drag in supersonic flight? |
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"Tom S." <tdscanuck@yahoo.com> ha scritto nel messaggio
news:JKz21w.IyK@news.boeing.com...
[quote]If you have supersonic streamwise flow, you>re going to have a shock off
the leading edge. I think that will throw the whole airfoil pressure
distribution off what you>d see with subsonic flow.
[/quote]
Hi Tom,
finally I found references on the subject, some NACA technical reports.
Actually my intuition was right: in an ideal case of an infinite wing swept
beyond mach cone, pressure distribution is subsonic.
So there should be upwash, induced by the infinite mach waves originating
from every other point (on the leading edge) that is upstream of the current
point.
In the real case it>s basically supersonic at wing root, and approaches
subsonic distribution the more we move farther from wing root.
[quote]Not sure how that would work, physically. If the wing is swept at less
than the Mach angle, no air ahead of the wing can "see" the wing coming.
That means, I think, no wash (in any direction).
[/quote]
That>s right, in all my examples I was referring to a wing swept beyond mach
cone.
Marco |
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