Wing Fences on Soviet Fighters?
K129000
so many, the Mig-15, 17 and 19 and good examples.
Are these meant to prevent spanwise flow (or decrease it) at angles of attack
on swept wings?
Why did US designers not add them?
Just wondering.
Chris
Driver 8
> What is the purpose of the wing fences on Soviet aircraft. They are
visible on
> so many, the Mig-15, 17 and 19 and good examples.
> > Are these meant to prevent spanwise flow (or decrease it) at angles of
attack
> on swept wings?
Yes.
> Why did US designers not add them?
U.S. designers did on occasion have to add them. The F-100 is a good
example. Although the fences on the Hun are smaller than those used on many
Soviet fighters. A wing fence or a vortex generator are usually always an
aerodynamic " fix " after post production problems are discovered.
Driver8
merlin falcon-gates
"K129000" <k12...@aol.com> wrote in message
news:20010705230233...@ng-fs1.aol.com...
> What is the purpose of the wing fences on Soviet aircraft. They are
visible on
> so many, the Mig-15, 17 and 19 and good examples.
>
Many US aircraft *do* have wing fences. The A-6, F11F, and 737 come rapidly
to mind.
-m
Ralph Savelsberg
Right. there are more examples. The A-6 is one that springs to mind.
--
Ralph Savelsberg
Fluid Dynamics Laboratory
Eindhoven University of Technology
http://www.fluid.tue.nl/
Cub driver
>Are these meant to prevent spanwise flow (or decrease it) at angles of attack
>on swept wings?
Exactly so. This was a major bafflement in the early days of
swept-wing design.
>Why did US designers not add them?
Dunno. Serendipity--some other feature of the American design made
spanwise flow less of a problem?
(See the dams on the YB-49, which must have been the first American
swept wing if you don't count the XB-35 from which it was derived. In
the case of the 35, the engines and fairings served the same purpose.)
all the best - Dan Ford (email: let...@danford.net)
Glen Edwards and the Flying Wing: http://danford.net/edwards.htm
John Carrier
> aerodynamic " fix " after post production problems are discovered.
I don't think the simple realities of spanwise flow constitutes a "post
production problem." A more elegant solution is the notched leading edge.
R / John
Peter Stickney
k12...@aol.com (K129000) writes:
> What is the purpose of the wing fences on Soviet aircraft. They are visible on
> so many, the Mig-15, 17 and 19 and good examples.
>
> Are these meant to prevent spanwise flow (or decrease it) at angles of attack
> on swept wings?
Yep. It helps keep the stall from starting at the tip, helping to
control pitch-up.
> Why did US designers not add them?
Well, actually, they did. The 6-3 wing F-86s had fences, and the
F-102 had them as well. The thing is, they stick up from the wing and
add drag. They're an easy solution, but there are others. One is to
increase washout at the wing tips. Another is to add a dogtooth, like
the F8U or F-4, to generate a vortex to energize the flow at the tip.
Another solution is a slit in the leading edge (Like a saw kerf). The
F-106 prototypes had fences, but the production airplaned had slits.
--
Pete Stickney Klein bottle for rent -- inquire within.
Pete Zaitcev
> > They are visible on
> > so many, the Mig-15, 17 and 19 and good examples.
> > Are these meant to prevent spanwise flow (or decrease it) at angles of
> > attack
> > on swept wings?
> > Why did US designers not add them?
Soviet design culture of that time considered fences to be
an equivalent of leading edge slats, only non-moving, and thus
cheaper, lighter and more reliable. In that sense they were
not an after-thought as other posters suggested, but a
design feature.
"Razvitije Samoletov Mira" contains several paragraphs on
the subject that describe the development of the fencing
of swept wings in TsAGI research in 1946 and on La-160 in 1947.
Authors sound quite ironic when they describe how stupid Americans
were much too influenced by plungered German ideas and did not
find right solutions to high-AOA performance.
Later Soviet fighter aircraft do feature slats because they
offer less drag and besides, how are you going to use them
on a delta wing anyways?
Bigger transports with swept wings used to have _both_
fencing and slats, for instance the popular Tu-154 does.
-- Pete
Bill Rhodes
> Are these meant to prevent spanwise flow (or decrease it) at angles of
attack
> on swept wings?
Well, an old Cold War joke is that all Soviet fighters had wing fences to
keep the air from
defecting =)
Bill
Maury Markowitz
attack
> on swept wings?
Yup.
> Why did US designers not add them?
Some did, the F-100 for instance. However a "dogtooth" is usually just as
effective, yet has less drag. You see it on planes like the F-4, Arrow, etc.
The brits went the furthest here, the Victor used the "scimitar" wing
design (as did a few other designs) which changed the angle of the wing
itself to keep the apparent flow constant across the wing.
Maury
Kriegmeister
think would be pretty severe sue to the anhedral design of the wings.
Brian
"merlin falcon-gates" <mjfg...@hotmail.com> wrote in message
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What about the F/A-18? They have those fence sort of things on the aft of
the LERX? Not quite on the wing...but close.
Bill Shatzer
On Fri, 6 Jul 2001, Kriegmeister wrote:
> Yes I believe it is to prevent spanwise airflow over the wings, which I
> think would be pretty severe sue to the anhedral design of the wings.
Why would the anhedral/dihedral make any difference?
Cheers and all,
John Carrier
> the LERX? Not quite on the wing...but close.
I think these were added when LEX airflow at high AOA was found to vibrate
the vertical tails sufficiently to cause cracking. Early OT&E of Bug
discovered some very interesting aero properties.
R / John
Gord Beaman
You saved me from asking Bill...
--
Gord Beaman
PEI, Canada
W. D. Allen Sr.
They did on the Grumman F9F-6 Panther in the 1950s as just one example.
WDA
end
"K129000" <k12...@aol.com> wrote in message
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Mike
W. D. Allen Sr. <ball...@home.com> wrote in message
news:5JI17.26447$QG2.1...@news1.bnapk1.occa.home.com...
> "Why did US designers not add them?"
>
> They did on the Grumman F9F-6 Panther in the 1950s as just one example.
>
> WDA
Cougar?
MMA
TSuglio
>>
>> Just wondering.
>>
>> Chris
>
I was taught that wing fences were to keep the air flow between the fuselage
and the fence. And I believe that the F-4 did have built in fences. It was at
the wing fold. Notice the outboard wing section is angled up. The F-4 ailerons
are just inboard of the wingfold and dump mast. I would think that the wing
fold (fence) would keep air flow over the ailerons for a more stable
maneuvering capability.
Cheers,
Tom
Peter Stickney
Well, the fence keeps the air from flowing outward, so the first part
is true. But I've never seen a real fence on an F-4. The dihedralled
tips don't count as fences, although they do add to the roll and
directional stability. But, the F-4 wing does have a dog-tooth on the
tip, and it does correspond to the wing fold line. The dog tooth will
energize the air over teh tip, and keep it flying longer than the
root. Swept wings have a habit of stalling at the tips first, and
this give you two problems. The first is that the root section is
still lifting, so the airplane wnats to pitch its nose up really bad.
(A particularly nasy example of this was the Bell X-5. For you
Luftwaffe '46 enthusiasts, the Messerscmitt P.1101 that it was derived
from would never have had acceptable handling as a fighter. I'd
expect even worse behavior from the swept Focke-Wolfe jet, with that
T-tail. That thing was a deep stall waiting to happen. (Deep Stall is
when the nose pitches up enough that a high or T-tail is blanketed by
the distubed flow from the wing. It was a problem with the early
T-tailed airliners. I know a prototype BAC-111 was lost to deep
stall, and I think an early 727 was lost to the same cause, as well))
The second problem is that with the tip stalled, control surfaces
located there don't work so well. Since that's where the ailerons
usually are, lateral control is a problem.
TSuglio
>tips don't count as fences, although they do add to the roll and
>directional stability.
Yes Pete you are right, it is not a fence per say, but by virtue of it's sharp
dihedral it would act the same as a fence. If you notice the ailerons were
right at the root of the wingfold. The F-100 also had the ailerons right where
the fence was. In fact the back of the F-100 fences were cut on an angle
because the aileron came up just at the base of the fence and the fence went
behind the wing a few inches.
Cheers,
Tom.
Ross "Roscoe" Dillon
Have read the multitude of answers and frankly I (humbly) believe they
all missed the mark...except for the fact that US designers did in
fact use them as well.
In reality, the fences don't prevent spanwise flow...they depend on
it!!
The point of fences is to take advantage of the spanwise flow to
generate vortices as is "swirls" over the fence. These vortices suck
high energy "free stream" air down into the boundary layer (the slow
moving air "rubbing" on the surface of the wing) to reenergize it.
This prevents the flow from separating from the upper surface as the
angle of attack increases, permitting higher AOA and slower speeds
and/or higher g loading (maneuvering).
Clear as mud, right? <grin>
Roscoe
USAF Flight Tester
(B-1, B-2, T-38, T-37, C-5, QF-106, F-16, F-5...)
Ron
>generate vortices as is "swirls" over the fence. These vortices suck
>high energy "free stream" air down into the boundary layer (the slow
>moving air "rubbing" on the surface of the wing) to reenergize it.
>This prevents the flow from separating from the upper surface as the
>angle of attack increases, permitting higher AOA and slower speeds
>and/or higher g loading (maneuvering).
>
Sounds exactly like the vortex generators on the Cessna 340 I fly. They have
the same purpose but we have lots of little ones, as opposed to a few big ones.
They are above the deicing boots on the leading edge, and on the tail
Ron Chambless
Pilot C-340 - Weather Modification
Edwards Aquifer Precipitation Enhancement Program
Peter Stickney
Yah, in the long (Albium Cut) version of my post, I waxed on the
vagarities of aileron placement, and, of course,the F-100 featured.
Basically, the problems of aeroelasticity (A fancy way of saying that
the airplane could get bent if you played too rough) started showing
up in the early transonic aircraft, like the F-86, and the B-47,
where the forces on the aileron would bend the wing, rather than roll
the airplane, leading to a lowered roll rate, or, eventually, a roll
reversal, (When the aileron acted like a trim tab for the flexible
wing) In some aircraft, a fast roll at a high IAS could permanently
warp the wings.
North American really didn't want that for the F-100. So, in the
early models, they put the ailerons inboard, where you'd expect the
flaps to be, and left the flaps in the hangar. (Well, they kinda added
little flaps to the F-100D, but they didn't change much in the way the
airplane behaved). I've never heard of an F-100 suffering roll
reversal. Vought did something similar with the F8U, but was a little
more clever, and used the ailerons as flaps, as well. Republic use
spoilers for roll on the F-105, as did North American's F-107
competitor.
McDonnell decided tht the best thing was to include both. An F-4 had
spoilers on the upper surface, just inboard of the fold, and ailerons
on the trailing edge, again, just inboard of the fold. The unusual
thing is that the ailerons only deflect down, so for a roght roll,
the right spoiler deflects up, and the left aileron deflects down.
Nowadays, you'd think it would be simpler, what with roll control
being by differential stabilizer movement, & all, but watching the
control checks on an F-18 drives me bats. slodge the stick over, and
every movable surface on the airplane makes some sort of arcane wiggle.
Ken Duffey
Wasn't the extreme dihedral on the outer panels on the F-4 added late in the
design ??
IIRC, the original proposal from McDonnell had a 'straight' wing (as viewed from
the front) but wind tunnel testing revealed the need for more dihedral - which
would have necessitated a longer main undercarriage, had the dihedral been
incorporated at the wing root..
So McDonnel took the simpler expedient of applying increased dihedral to the outer
panels only - just at the fold line.
So their effect as 'wing fences' must have been purely coincidental ???
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Ken Duffey - Flanker Freak & Russian Aviation Enthusiast
Flankers - http://www.flankers.co.uk/
S-37 Model - http://www.samolet.co.uk/s37model.html
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Jan Skowronski
I wouln't agree with you. You interchanged cause and result. Both wing
fences and LE vortex generators (dogtooth), along with other devices (LE
notches, fairings/nacelles as in most Tupolev sweptwing a/c, BL suction
etc.) were PRIMARILY used to prevent spanwise flow, which caused thickening
of boundary layer on the outboard section of sweptback wing. Thick boundary
layer is more sensitive and separates rapidly. So, spanwise flow increased
hazard of flow separation in the outboard (AILERON!) wing section and
classical approach (geometric and/or aerodynamic twist) could be not
sufficient. Folks didn't know about vortex lift these days (about forties).
Strake wing was designed significantly later. Even for the double-delta
wings (such as Swedish Draken fighter), which resemble nowadays strake wing,
vortex lift wasn't taken into consideration.
Jan Skowronski
Warsaw, Poland
Uzytkownik "Ross "Roscoe" Dillon" <rossd...@home.com> napisal w wiadomosci
news:piokktc91s3p1m1v2...@4ax.com...
> On 06 Jul 2001 03:02:33 GMT, k12...@aol.com (K129000) wrote:
[cut...]
Jan Skowronski
spanwise flow causes THINNING of boundary layer in the O/B wing sections and
THICKENING of BL in the I/B wing sections, so flow separation is shifted to
the wing's root. Why they didn't use forward sweep from the start? Because
of aeroelasticity and some stability problems.
Jan Skowronski
Warsaw, Poland
Ken Duffey
Just looking at a poster of the Sukhoi S-37 on my office wall............
It has what LOOKS like a small fence at the wing root - just outboard of where
the wing l/e sweeps sharply forward to meet the LERX. You can see it in the
fourth photo at :- http://www.flankerman.fsnet.co.uk/s-37.htm
Jan Skowronski
Yes, I see SOMETHING in the fourth, eight and tenth (wing's lower side)
photo, but I wouldn't call it 'fence'.
First - it is too small. As I recall from the reports I have read, fence has
to be high some percent (2% or 5% - I cannot to check now) of the chord to
work.
Second - I don't see anything in the front view, because this SOMETHING is
in line with fins.
My GUESS - it is some vortex generator intended to improve flow at fins at
high alpha (less probable) or linked with LE flaps, which inboard edge
coincides with this SOMETHING (compare photos 13 and 14). I have to see this
to decide.
Jan Skowronski
Warsaw, Poland
PS. Ken! I am fan of your site for a long time.
Uzytkownik "Ken Duffey" <k...@nerc.ac.uk> napisal w wiadomosci
news:3B4ADFB1...@nerc.ac.uk...
[cut...]
Ken Sykes
> Just looking at a poster of the Sukhoi S-37 on my office wall............
>
> It has what LOOKS like a small fence at the wing root - just outboard of where
> the wing l/e sweeps sharply forward to meet the LERX. You can see it in the
> fourth photo at :- http://www.flankerman.fsnet.co.uk/s-37.htm
>
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Ken Duffey - Flanker Freak & Russian Aviation Enthusiast
> Flankers - http://www.flankers.co.uk/
> S-37 Model - http://www.samolet.co.uk/s37model.html
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
That's a gap in fit of the leading edge flap. Look at photos
lower down the page.
Tallyho!
KS
Kurt Plummer
At least on the E/F, post slat, there is in fact a small slat just inboard of the
dogtooth, at it's root.
Kurt Plummer
TSuglio
>control checks on an F-18 drives me bats. slodge the stick over, and
>every movable surface on the airplane makes some sort of arcane wiggle.
Yes, and other aircraft with seperate horizontal stabs do the same thing, i.e.
F-14, F-15. Thats real integrated flight controls when the horizontal stabs can
also work like ailerons. Here is a small quote out of the F-15 Dash one
speaking about Lateral Control. "Lateral stick motion positions ailerons,
rudders and stabilators to provide roll control. The ratio of
aileron/differential stabilator deflection to lateral stick motion (roll ratio)
is adjusted automatically for different airspeeds, longitudinal stick position
and gear position." It goes on to describe how the rudder is tied through the
aileron rudder interconnect.
So yes, when you see pictures of F-14s and F-18s landing on a flight deck, you
can see a lot of flight control movement in very short bursts that the pilot is
NOT doing, but the PRC is controlling.
Cheers,
Tom
Ralph Savelsberg
Isn't this one of the reasons why the F-14 is sometimes called the Turkey? It
looks a little ungainly with everything hanging and in addition has all these
control surfaces moving seemingly at random, like a Turkey's feathers in a breeze.
Regards,
Ralph Savelsberg
Fluid Dynamics Laboratory
Eindhoven University of Technology
http://www.fluid.tue.nl/
Peter Stickney
It's not so much that all the various pieces/parts move, but that they
move in directions that seem to be unrelated to what the Crew Chief's
hand signals tell me he want's the Stick Actuator to do. That tells
me that the Bug has a lot of oddbal local airflow, or some really
strange responses. I started my professional career (Well, the
Technician part, anyway) putting things in the back end of FB-111s,
and trying to make them work. I thought I'd seen everything.
TSuglio
>looks a little ungainly with everything hanging and in addition has all these
>control surfaces moving seemingly at random, like a Turkey's feathers in a
>breeze.
>
>Regards,
>Ralph Savelsberg
I had never heard of the "Turkey" till I came to this NG, but yes, I guess it
does look like a turkey.
This was also a reason why the Israli F-15 was able to fly home without a
right wing after a mid-air. The stabilators were acting as ailerons, along with
some other factors having to do with hydraulics and lift from the fuselage,
etc.
Cheers,
Tom
TSuglio
>move in directions that seem to be unrelated to what the Crew Chief's
>hand signals tell me he want's the Stick Actuator to do.
>
>Pete Stickney
Pete, you hit the nail on the head. If you watch especially the horizontal
stabs when a F-14 pr F-18 is landing on a flight deck, they are moving in both
directions yet the plane seems to be making a very smooth landing, doesn't look
like the sink rate is changing at all.
Cheers,
Tom