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Eugene Zimmerman

Joined: 10 Jan 2006 Posts: 392
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Posted: Sun Mar 26, 2006 6:26 pm Post subject: Land Shorter VG's on Firestar II |
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On Mar 26, 2006, at 9:54 AM, Chris Mallory wrote:
Quote: | He
said that the reason for this is that because of the VGs, the Wing
wants to
keep flying but the tail wants to stall first, adding the VGs aft will
balance the two flying surfaces and eliminate this tendency.
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Sorry,
Sounds like sales propaganda to me.
Any airplane that stalls tail first would be an extremely dangerous
plane to try to fly.
I can assure you that my VGs do not make my plane stall tail first.
Any increased authority that results form VGs placed on the
horizontal tail surfaces will make the potential to land tail first
even greater not less, because VGs act to increase angel of attack
before stall.
Increased angel of attack means the tail is even lower.
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Thom Riddle

Joined: 10 Jan 2006 Posts: 1597 Location: Buffalo, NY, USA (9G0)
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Posted: Mon Mar 27, 2006 4:40 am Post subject: Re: Land Shorter VG's on Firestar II |
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This JOA guy has lost all credibility with me due to his statement about the tail stalling first causing the tail to be low. The VGs work as described but this guy's knowlege of the purpose of the horizontal stabilizer and elevator is limited at best. I'm sure he has a good product, at least as good as the home made ones, but he is no expert in flight theory or aerodynamics. I'm not either but do know and understand what the experts say.
On ALL succecssful standard configuration aircraft, the tail is designed to continue to fly at speeds below which the wing will be fully stalled, assuming the CG is within limits. Without effective elevator control the pilot cannot get the nose-up pitch and resultant high AOA for the wing to stall. How does he think the pilot gets this high AOA if the tail has stalled?
If the VGs on the BOTTOM of the stabilizer increase downward lift, then the improved downward lift would lower the tail, not raise it. Is this guy even a pilot????
Ignorance is not a sin, but ignorance masquerading as expertise is dangerous.
Thom in Buffalo
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pj.ladd(at)btinternet.com Guest
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Posted: Mon Mar 27, 2006 6:32 am Post subject: Land Shorter VG's on Firestar II |
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If the horizonal stabilizer stalls the tail would go up, not down,...>>
Huh?. VG`s help a flying surface to continue to produce lift past he point
when it would usually stall. In my experience something that suddenly stops
producung lift falls down, not up.
Just as a matter of interest, how much lift does the tail plane produce
anyway. It is not a lifting surface as it is totally flat. I suppose VG`s
on the TOP surface just might hold the boundary layer for just a little
longer which would give more control at slow speeds but I cannot see that
VG`s UNDER the hor. stab do anything at all.
I would like to see some wind tunnel smoke tests.
Cheers
Pat
do not archive
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John Hauck

Joined: 09 Jan 2006 Posts: 4639 Location: Titus, Alabama (hauck's holler)
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David.Lehman

Joined: 10 Jan 2006 Posts: 265 Location: "Lovely" Fresno CA
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Posted: Mon Mar 27, 2006 6:44 am Post subject: Land Shorter VG's on Firestar II |
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Pat...
The way it was told to me is that the "understab" VGs make the elevators
more effective... They're not "lift producers (positive or negative), but
just swirl the air under the elevator... And yep, I have "understab" VGs on
that thing in the garage with 5-rib wings, adjustable elevator trim tab and
a 503 belt drive, the "Hemlock Special"...
Regards...
DVD
On 3/27/06, pat ladd <pj.ladd(at)btinternet.com> wrote:
Quote: |
If the horizonal stabilizer stalls the tail would go up, not down,...>>
Huh?. VG`s help a flying surface to continue to produce lift past he
point
when it would usually stall. In my experience something that suddenly
stops
producung lift falls down, not up.
Just as a matter of interest, how much lift does the tail plane produce
anyway. It is not a lifting surface as it is totally flat. I suppose
VG`s
on the TOP surface just might hold the boundary layer for just a little
longer which would give more control at slow speeds but I cannot see that
VG`s UNDER the hor. stab do anything at all.
I would like to see some wind tunnel smoke tests.
Cheers
Pat
do not archive
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=F4=BF=F4 "I started with nothing... And I still have most of it left!"...
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_________________ ô¿ô
"Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute."
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HShack(at)aol.com Guest
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Posted: Mon Mar 27, 2006 6:57 am Post subject: Land Shorter VG's on Firestar II |
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In a message dated 3/27/2006 9:32:45 AM Eastern Standard Time,
pj.ladd(at)btinternet.com writes:
If the horizonal stabilizer stalls the tail would go up, not down,...>>
Huh?. VG`s help a flying surface to continue to produce lift past he point
when it would usually stall. In my experience something that suddenly stops
producung lift falls down, not up.
Mr. Ladd is correct; our tail feathers hold the tail DOWN in flight since,
on our wing, the center of lift is BEHIND the center of gravity.
I have VG's on the bottom of my horizontal stab; I suspect all they do is
give my Up elevator a little more authority, ie. POWER ELEVATOR.
I think I'm gonna' put 'em on my rudder, to.
Howard Shackleford
FS II
SC
Do not archive
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Ed in JXN
Joined: 24 Mar 2006 Posts: 122
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Posted: Mon Mar 27, 2006 7:31 am Post subject: Land Shorter VG's on Firestar II |
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Hi Thom,
You hit the nail on the head. The tail should have authority after
the wing stalls, and CG then takes over to lower the nose.
Had a stalled tail due to ice once (tail boots quit working on a
C421 in light ice), never want to experience that again. Aircraft wouldn't
stop porpoising, all the way to touchdown.
Ed in JXN
MkII/503
Do not archive.
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Possum
Joined: 12 Jan 2006 Posts: 112 Location: Georgia
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Posted: Mon Mar 27, 2006 7:32 am Post subject: Land Shorter VG's on Firestar II |
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At 07:40 AM 3/27/2006, you wrote:
Quote: |
This JOA guy has lost all credibility with me due to his statement
about the tail stalling first causing the tail to be low.
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I don't know about that - if you do a Google Search on
"horizontal stabilizer" & "vortex generators" you will find out
that everybody recommends putting them on the "bottom" of
the Horizontal stabilizer, not just this JOA guy. Even in the
GA planes.
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Ed in JXN
Joined: 24 Mar 2006 Posts: 122
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Posted: Mon Mar 27, 2006 7:44 am Post subject: Land Shorter VG's on Firestar II |
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Right. The (conventional) tail is an upside-down wing, no? Thus, its lift
vector is downward, and if critical AOA is exceeded, it goes - up - ! (In
level flight). The problem I had, with ice on the tail, is once the
airplane shudders and the nose drops, the natural pilot response is to lower
the nose. This is exactly the wrong thing to do with a tail stall, and
slight aft stick is needed. NASA has a good series of videos on tailplane
icing. They even manage to snap-roll a Twin Otter.
Ed in JXN
Do not archive.
Quote: | > If the horizonal stabilizer stalls the tail would go up, not down,...>>
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Eugene Zimmerman

Joined: 10 Jan 2006 Posts: 392
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Posted: Mon Mar 27, 2006 7:48 am Post subject: Land Shorter VG's on Firestar II |
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On Mar 27, 2006, at 9:56 AM, HShack(at)aol.com wrote:
Quote: | I think I'm gonna' put 'em on my rudder, to.
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Howard,
I think that could make a lot of sense.
All single seat Kolbs I ever flew had more than enough up elevator
control authority to stall the wing even with VGs. Any more up
control is totally useless, however there are times when it would be
good to have more rudder authority for cross wind landings.
The Kolb planes that would benefit most by having VGs on the
horizontal tail surfaces would be the early twinstar and Mark II
flying two up because of their smaller tail surfaces. The Mark III
was given larger tail surfaces and some feel that even they, in
certain situations, are marginal and could possibly receive some
benefit from additional up control by adding VGs to the bottom of
horizontal tail surface.
Gene
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n79rt(at)kilocharlie.us Guest
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Posted: Mon Mar 27, 2006 7:55 am Post subject: Land Shorter VG's on Firestar II |
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In normal configuration aircraft (i.e. non-canard or tandem wing
(Quickie)) the tail produces DOWN force...the center of lift is behind
the aircraft CG. The center of lift, being the fulcrum, being behind
the CG (i.e. the load being lifted) has to have a balancing load DOWN on
the tail to keep everything level. I hope there was just some
misunderstanding of these posts cause this should have been basic
groundschool to get any form of a pilots license.
Elevator "stall" and elevator "effectiveness" are possibly being
interchanged inappropriately here but the net result is the same...the
tail can't pull the nose up...
In regards to tail stalling...yes it can and does happen. I have seen
videos of the testing of an ATR passenger aircraft that was setup to
create icing on the tail...the look on the test pilots face was sheer
panic as the nose dropped and he was fully expecting it to happen.
Other forms of tailplane stall is common on tandem aircraft like the
RANS S7 I used to fly. Flying solo (front seat) and light fuel meant CG
was right at the forward limit...this meant that getting a 3 point
landing (i.e. full stall) was dang near impossible. This doesn't make
sense right? I mean heavy (2 up, heavy fuel) stalls faster right? Of
course it does, but heavy also moved the CG back which required less
downforce from the tail to balance everything. Flown heavy the plane
landed itself...flown solo and light meant you better wheel land it. As
you would go to flare the higher downforce requirements of the forward
CG and the slower speed (less ability of the tail to generate DOWNforce
or DOWNWARD LIFT...meant the tail wasn't capable of bringing the nose
up. The extreme limits of up elevator can cause the bottom surface of
the elevator you basically stall do to the air not being able to make
the bend around the fairly level horizontal stab and then around the
upward deflected elevator...VG's on the underside of the horizontal stab
can sometimes help this. (in defense of RANS around '96 or so they
enlarged the tail a bit and made the tail considerably more
powerful...was easy to get a full stall landing in any configuration...)
Remember the Ercoupe? It's main claim to fame of being unable to be
spun was just a function of limiting the elevator travel to the point
that it could not generate enough downforce to raise the nose high
enough to exceed the wings critical angle of attack...i.e. you couldn't
stall it...if you can't stall it you can't spin it.
Personally I think spins are fun...at least with some altitude they
are...
Jeremy Casey
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slyck(at)frontiernet.net Guest
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Posted: Mon Mar 27, 2006 8:31 am Post subject: Land Shorter VG's on Firestar II |
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Although Thom already said it once, let's repeat:
on a conventional airplane (non canard) the tail is always pushing
DOWN in flight. When trimming for slow flight and landing configuration
you pull back on the stick to compensate for the lack of down force
via less airflow over the tail. Some planes have a real inverted
airfoil to help out. The Zenith aircraft CH-701 for example:
http://www.zenithair.com/stolch701/7-design-tail.html
So then the tail doesn't actually fly, you could move a lead weight in
and
out on a track to accomplish the same thing.
There have been a few tailless designs.
Might not work too well at stall though, in which case the horizontal
stab acts more like the feather on an arrow or a lawn dart to help the
rear end stay up a little during the time you start falling nose down.
-BB
do not archive
On 27, Mar 2006, at 10:31 AM, possums wrote:
Quote: |
At 07:40 AM 3/27/2006, you wrote:
>
>
> This JOA guy has lost all credibility with me due to his statement
> about the tail stalling first causing the tail to be low.
I don't know about that - if you do a Google Search on
"horizontal stabilizer" & "vortex generators" you will find out
that everybody recommends putting them on the "bottom" of
the Horizontal stabilizer, not just this JOA guy. Even in the
GA planes.
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pj.ladd(at)btinternet.com Guest
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pj.ladd(at)btinternet.com Guest
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Posted: Mon Mar 27, 2006 1:19 pm Post subject: Land Shorter VG's on Firestar II |
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, the "Hemlock Special"...
David,
love the name.
Pat
do not archive
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pj.ladd(at)btinternet.com Guest
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Posted: Mon Mar 27, 2006 1:19 pm Post subject: Land Shorter VG's on Firestar II |
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"lift producers (positive or negative), butjust swirl the air under the
elevator...>>
Hi David,
I would have thought that `swirling the air` is just what they DONT do. The
boundary layer on a surface as far as we are concerned is required to
`stick` and flow smoothly. The VG`s help this to happen after the flow would
normally have `broken away`.
Can anybody get access to or contrive a wind tunnel? The Wrights made one
out of a cardboard box. Surely with all the talent on the list some `real`
answers can be obtained. We are all arguing theory here, each of us `as we
understand it` some dragging up basic theory we have not thought seriously
about in years. Did we remember correctly what that instructor said?
Cheers
Pat
do not archive
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pj.ladd(at)btinternet.com Guest
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Posted: Mon Mar 27, 2006 1:21 pm Post subject: Land Shorter VG's on Firestar II |
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Depends on which direction it is lifting.>>
Hi John,
irrispective of which side of the road I drive on, gravity, which usually we
are lifting against, points down.
Space stations excluded!
Pat
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Earl Zimmerman

Joined: 13 Jan 2006 Posts: 35 Location: Elizabethtown, PA
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Posted: Mon Mar 27, 2006 5:39 pm Post subject: Land Shorter VG's on Firestar II |
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Thom Riddle wrote:
Quote: |
This JOA guy has lost all credibility with me due to his statement about the tail stalling first causing the tail to be low.
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Is this guy even a pilot????
Thom,
I think there must be some misunderstanding or misinterpretation here!
Joa owns and flys a Rans S7. www.landshorter.com ~ Earl
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beauford(at)tampabay.rr.c Guest
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Posted: Mon Mar 27, 2006 6:37 pm Post subject: Land Shorter VG's on Firestar II |
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Did I hear someone call for a wind tunnel....?
I am at your service, Sir....
..Moving right along... Fer whatever it's worth, I stuck six of
Brother Shackleford's semi-patented
VG's on the bottom of the Firefly's horizontal stabs about 18 months
ago... three on a side... just forward
of the elevators... objective was to increase elevator authority in
full stall
landings... they work like a charm... major improvement... I'm a
believer...
Barely worth what ye paid fer it...
Stalled Beauford
FF#076
Brandon, FL
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John Hauck

Joined: 09 Jan 2006 Posts: 4639 Location: Titus, Alabama (hauck's holler)
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Posted: Mon Mar 27, 2006 6:44 pm Post subject: Land Shorter VG's on Firestar II |
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| objective was to increase elevator authority in
| full stall
| landings... they work like a charm... major improvement... I'm a
| believer...
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| Barely worth what ye paid fer it...
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| Stalled Beauford
Beauford:
Was that positive or negative stall?
john h
MKIII barely able to get past the stall.
DO NOT ARCHIVE
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_________________ John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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beauford(at)tampabay.rr.c Guest
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Posted: Mon Mar 27, 2006 7:58 pm Post subject: Land Shorter VG's on Firestar II |
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Yessir, it was....
B.
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