Today's Message Index:
----------------------
1. 04:14 AM - Re: Will's picture (dixieshack@webtv.net (Mike and Dixie Shackelford))
2. 05:33 AM - Re: Re: Kolb Snowbirds (Jim and Phyllis Hefner)
3. 07:34 AM - nose heavy mi III (boyd young)
4. 11:39 AM - Re: nose heavy mi III (Richard Pike)
5. 11:53 AM - Re: nose heavy mi III (Christopher Armstrong)
Message 1
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| Subject: | Re: Will's picture |
message of Tue, 4 Mar 2003 23:56:09 -0800
--> Kolb-List message posted by: dixieshack@webtv.net (Mike and Dixie Shackelford)
Great picture, Will...says it all about our sport and our
Kolbs.......and our land.
Mike in WV
do not archive
Message 2
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| Subject: | Re: Re: Kolb Snowbirds |
--> Kolb-List message posted by: "Jim and Phyllis Hefner" <hefners_tucson@hotmail.com>
Will, great shot!! Thanks. I also enjoy trying to capture the beauty of our sport
and our beautiful AZ. Got to get my new miniDV wing mounted for stills and
video clips in flight... will need that at Monument Valley! I've got float mounts
out under the wings on my FF that will work perfectly as camera mounts, either
side.
Jim Hefner
Tucson, AZ
FF#022
Do Not Archive
-- Kolb-List message posted by: <A target=_top href="http://lw9fd.law9.hotmail.msn.com/cgi-bin/compose?curmbox=F000000001a=cc3185cb6baa1e3d91dc776d90d8902cmailto=1to=WillUribe@aol.commsg=MSG1046851361.130start=820034len=24132src=type=x">WillUribe@aol.com
I keep trying to take good pictures, like this one I took with a disposable
camera.
<A target=_blank href="http://64.4.8.250/cgi-bin/linkrd?_lang=ENlah=67aa7876c2ef84c1dbd57f85d848e148lat=1046870034hm___action=http%3a%2f%2fmembers%2eaol%2ecom%2ffirestarn4gu%2fpic14%2ejpg">http://members.aol.com/firestarn4gu/pic14.jpg
Will Uribe
El Paso, TX
FireStar II N4GU
C-172 N2506U
Message 3
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| Subject: | nose heavy mi III |
--> Kolb-List message posted by: "boyd young" <by0ung@brigham.net>
--> Kolb-List message posted by: GeoR38@aol.com
In a message dated 2/27/03 11:18:11 AM Eastern Standard Time,
by0ung@brigham.net writes:
> ps how can i figure where the center of lift is ?????
>
isn't the center of lift always at the thickest part of the airfoil?
George Randolph
Firestar driver from Akron
George.... if the thickest part of the wing is the center of lift. ( on the
mark III it is about 13 inches from the leading edge) and the cg range is 16.5
to 23.1
draw a small picture of your kolb and put a string at 13 inches and lift. remember
that the cg can be 10 inches behind the lift point.... with your picture
in hand tell me is the tail a lifting force or a down force in order to level
the plane?
in my view if you lift forward of the cg the tail must lift..... but in a conventional
plane the tail has a down pressure for stabilization..... aslo if
the lift was forward of the cg when it went into a stall the plane would fall
tail first.... you would not be able to recover.....
i do believe there is a pivit point in the wing about the thickest part of the
wing... but the airadynamic center of lift should be behind the cg..... if not
what am i missing????
boyd
Message 4
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| Subject: | Re: nose heavy mi III |
--> Kolb-List message posted by: Richard Pike <rwpike@charter.net>
No. The center of lift is not always at the thickest part of the airfoil.
But it is probably possible to design and build an airfoil where it could
be the thickest part.
There is a median line between the upper surface of a wing and the lower
surface, and this is the camber line. Typically, it is curved, rising at
the front of the airfoil, reaching it's high point at about a third of the
way back, and then continuing on over, with the back third or sometimes the
back half being almost a straight line. Lift is typically generated from
the high point of that curve to the back end.
Sometimes that camber line is the same as the airfoil itself, such as a
single surface wing, like a Quicksilver MX.
Sometimes that camber line curves back up at the back third, like an Easy
Riser, or most any other flying wing, which gets rid of the pitching moment
of the wing, the airfoil becomes like a wing in front, with a stabilizer at
the back, the back of the airfoil stabilizes the front. But in that case,
the lift quits just ahead of the point at which the reflex begins.
Now let's tie this to Kolbs: The Kolb airfoil has a curved median line from
the leading edge to about two - four inches behind the main spar, and then
is pretty much a straight line to the back of the flaps or the ailerons.
When the flaps are down, then the median line gets an additional curve at
the back end. This has the effect of moving the center of lift farther
back, imagine the wing "growing" a much bigger chord toward the back,
because it has a bigger median overall curve line, greater total camber,
except that the back part is chopped off, but it still moves the center of
lift toward the back. And the airplane feels nose heavier, because the CG
stayed the same, but the center of lift moved aft as the overall proportion
of the camber line moves aft.
Reflex the flaps upward past normal, and the airfoil becomes like a flying
wing airfoil, the back part quits making lift as the lifting part of the
median curve moves forward, consequently whatever lift there is comes from
farther forward on the wing. And the airplane feels tail heavier.
And it is correct that the CG has to always be ahead of the center of lift,
unless you are in a canard like a Long Eze or similar.
Hope this makes sense, if I flubbed any of the terminology or details,
Topher can always bail us out...
Richard Pike
MKIII N420P (420ldPoops)
At 07:34 AM 3/5/03 -0800, you wrote:
>--> Kolb-List message posted by: "boyd young" <by0ung@brigham.net>
>
>
>--> Kolb-List message posted by: GeoR38@aol.com
>
>In a message dated 2/27/03 11:18:11 AM Eastern Standard Time,
>by0ung@brigham.net writes:
>
> > ps how can i figure where the center of lift is ?????
> >
>
>isn't the center of lift always at the thickest part of the airfoil?
>George Randolph
>Firestar driver from Akron
>
>
>George.... if the thickest part of the wing is the center of lift. ( on
>the mark III it is about 13 inches from the leading edge) and the cg
>range is 16.5 to 23.1
>
>draw a small picture of your kolb and put a string at 13 inches and lift.
>remember that the cg can be 10 inches behind the lift point.... with your
>picture in hand tell me is the tail a lifting force or a down force in
>order to level the plane?
>
>in my view if you lift forward of the cg the tail must lift..... but in
>a conventional plane the tail has a down pressure for
>stabilization..... aslo if the lift was forward of the cg when it went
>into a stall the plane would fall tail first.... you would not be able
>to recover.....
>
>i do believe there is a pivit point in the wing about the thickest part of
>the wing... but the airadynamic center of lift should be behind the
>cg..... if not what am i missing????
>
>boyd
Message 5
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| Subject: | nose heavy mi III |
--> Kolb-List message posted by: "Christopher Armstrong" <cen33475@CenturyTel.net>
i do believe there is a pivit point in the wing about the thickest part of
the wing... but the airadynamic center of lift should be behind the cg.....
if not what am i missing????
boyd
Don't believe, know... I think you will find that knowing is much more
valuable the believing.
what are you missing? the tail. the fuselage. they contribute to the
center of lift. the ac of a wing is at the quarter chord, not the thickest
part. so you start out at 25% and then you add the contribution from the
tail, and rest of the plane. the tails on Kolb's aren't very big, lets say
they are ~1/10 of the size of the wing... but they are way back there, so
they move the center of lift of the plane back a fair bit. the thickest
part of the wing has nothing to do with it what so ever, on an old
ultralight with a 2 inch round tube for a leading edge and a single piece of
fabric going to the back the thickest part of the wing would be 1 inch from
the leading edge... no, the wing would not pivot around that point. wings
and anything else not constrained by pivot points pivot about there cg...
not the ac the cg.
there is no possibility that the cg of the Kolb is behind the ac of the
plane. that is not possible, because if it was the plane would be
statically unstable and you or even the great John H could not fly it for
more then 5 seconds before it swapped ends on you and flew backwards. the
fins are at the back of the dart. throw a dart backwards and it swaps ends
and hits the dartboard going point (cg) first. cg is in front of ac.
always... except
I worked on the f-16 for 8 years. it is statically unstable at speeds
greater then around 400 knots, neutrally stable or very slightly stable
below that. supersonic it is very unstable. the ac moves aft from the 1/4
chord to 1/2 chord when your supersonic. we have triple redundant fly by
wire on the f-16, cause even at the best case it would be unflyable without
the computers feeding back to the controls to provide artificial stability.
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