Hey caleb,
the kookas' all have a decided wing kink as well. Just goes to proove the
everything stays the same, it just gets refined a little.
See ya, I'm off to see the Worlds Fastest Indian.
IP
KPST
----- Original Message -----
From: "Caleb White" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Tuesday, June 20, 2006 1:01 PM
Subject: Re: [Aus-soaring] Bent up wing outer panels
Hi Folks,
I think this discussion needs some clarification as to what is referred to
as a ‘kink’. Are we referring the stepped taper (when viewed in plan form
from above) as the ‘kinks’? In which case we are discussing the desire to
achieve an elliptical plan form (with the intent of achieving an
elliptical lift distribution) OR Are we discussing the stepped changes in
dihedral in which case we are talking about achieving elliptical dihedral?
As with all aircraft design the design of sailplane wings is a compromise.
What is desirable is balanced with what is affordable to manufacture. A
stepped planform and dihedral is an excellent example of ‘optimised
compromise’.
Cheers,
Caleb
Kookaburra Precision Soaring Team
-----Original Message-----
From: Mike Borgelt <[EMAIL PROTECTED]>
To: "Discussion of issues relating to Soaring in Australia."
<[email protected]>
Date: Tue, 20 Jun 2006 12:46:06 +1000
Subject: Re: [Aus-soaring] Bent up wing outer panels
At 11:57 AM 20/06/2006, you wrote:
Dear All (Bernard E would read this as 'space' but I'll stay with the
English)
There is the limitation in two dimensional aerodynamics of a minimum
in the induced drag coefficient of:
Cd (induced) = Cl squared divided by (Pi X Aspect
ratio). (Apologies, I haven't the time to write it out clearer.)
So with an ideal lift distribution along the two dimensional wing
planform, that is the lowest you can get the induced drag
coefficient down to. Induced drag relates to drag due to wing tip
vortices (actually more complicated than just tip vortices but let
us leave that for now).
I think somewhere I have in my overloaded filing cabinets an article
from a learned aerospace journal which deals with induced drag for
wings operating in three dimensions. My recollection (unchecked
because the article is somewhere misplaced) was that when the wing
was considered to operate in three dimensions, and computing power
was brought to bear on the calculations, a slender wing with the
outer sections bending upwards and backwards could achieve an
induced drag coefficient BELOW the minimum as determined from two
dimensional aerodynamics.
I remember when the Nimbus 4 first came out and there was a photo of
the 25 m wings bending significantly upwards during steep
thermalling turning. So we have with our sailplanes with higher
aspect ratios and more slender spars wings which are operating in
three dimensions.
So I do not think that wing kinks in the outer wing panels are a
fashion statement or a marketing ploy, but rather founded on serious
efforts to reduce drag.
Beyond that I leave it to some far more knowledgeable person on wing
aerodynamics to provide futher illumination on the matter.
Cheers
Roger Druce
<mailto:[EMAIL PROTECTED]>[EMAIL PROTECTED]
Roger,
I think I have the same article by the late R.T.Jones of NACA and
later NASA reknown. I guess the issue is - does the discontinuity at
the kink increase the profile drag more than the 3D nature of the
bent wing decreases it.
The tendency at a kink is for the leading edge discontinuity to trip
flow to turbulent and for the airfoil to stall earlier although it
would seem you would need a fairly marked kink for this to occur.
Allegedly this is what happened on the F4U Corsair(the earlier stall
in the kink.
Mike
Borgelt Instruments - manufacturers of quality soaring instruments
phone Int'l + 61 746 355784
fax Int'l + 61 746 358796
cellphone Int'l + 61 428 355784
Int'l + 61 429 355784
email: [EMAIL PROTECTED]
website: www.borgeltinstruments.com
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