sliding wings?

"kd5sak" wrote

Isn't that pretty much how the B-2 is controlled?

Not really. On a B-2, there is a plain flap, or spoiler, on the top and the
bottom of the wing, out towards the tip. Yaw is done by extending the top
and bottom flap, about equally. You turn to that side, in a flat turn,
though.

To roll and turn left, the spoiler on the top left goes up. Fine tuning of
the yaw and roll, and so-forth, is done with the other flaps, with the fly
by wire doing all ot the thinking.

This is all a gross over simplification, of course.
--
Jim in NC

wrote in message
oups.com...

when I look at my eyeglass case, I see two closely overlapping
wing-type shapes that are being pulled apart for opening.

why would it not be worthwhile to extend wings this way for landing and
departure?

/iaw


But, wouldn't the eyeglasses fall out onto the runway?

:-)
--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

Bryan Martin wrote:

Fowler flaps, like those found on most single engined Cessnas and most
airliners, do increase the area of the wing as they deploy. They extend
backward as they deploy, acting to increase the wing chord instead of the
wing span.

True, of course.
The extra area of the flap equipped part of the wing adds surface.
But seldom in excess of .2 to .3 chord - and that only on the flapped
area of the wing.

The real pay off is the increased CLmax.

Abbott & Von Doenhoff has a very detailed study of various flap systems.

The example shown is a 65-210 section.
RN = 8 meg.

Basic section CLmax is about 1.4.

With fully extended Fowler type flap that goes up to a little over 2.4.

However, the angle of attack at CLmax actually goes DOWN!

From peak at about 15 degrees plain to roughly 8 at full deflection.

That one even surprised me...


in article ,
at wrote on 2/26/06 11:25 AM:


(snip)

richard---it was my misunderstanding that I thought they primarily
change the angle of attack. but compared to more wing, they seem
somewhat "limited."

/iaw


The deciding factor will be weight and structural difficulties.

One thought - fat airfoils don't like to go fast.
Thin airfoils don't like to go slow.

Seems like we'd have to have a fat airfoil for the main section so
that the thin airfoil could fit inside.

Just about exactly backwards...

Might be why we don't see very many telescoping wings around?

Richard

But it sure works great for eyeglass cases!

One thought - fat airfoils don't like to go fast. Thin airfoils don't like to go slow.
Seems like we'd have to have a fat airfoil for the main section so that the thin airfoil could fit inside.

next stupid question for the day. if this is so, why not have wings
that change shape? flaps, I know---but again, flaps seems pretty
rudimentary. there must be some better solutions, now that building
materials have become a lot better than they were 80 years ago.

actually, all my questions are ignorant of the very first question---is
it possible to estimate how much faster would an ordinary piston
airplane, say a C172, would be if we eliminated *all* wing drag? [and,
yes, presume it is still flying and not straight down, where my
eyeglasses have fallen into ;-)] if the answer is not much, then I am
to blame for having started a useless discussion.

Rich S. wrote:
wrote in message
oups.com...

when I look at my eyeglass case, I see two closely overlapping
wing-type shapes that are being pulled apart for opening.

why would it not be worthwhile to extend wings this way for landing and
departure?

This is a solution in search of a problem.


Doesn't a swing wing accomplish pretty much the same thing?

--

FF

wrote in message
oups.com...

Rich S. wrote:
wrote in message
oups.com...

when I look at my eyeglass case, I see two closely overlapping
wing-type shapes that are being pulled apart for opening.

why would it not be worthwhile to extend wings this way for landing and
departure?

This is a solution in search of a problem.


Doesn't a swing wing accomplish pretty much the same thing?

--

FF

Yes, for supersonic fighters. Swept wings aren't a good choice for light
aircraft.

For slow propeller airplanes, the telescoping wing does have its
attractions. It's a way to keep the slow stall speed required for single
engine airplanes and stilll get a fast economical cruise. It probably
wouldn't help the venerable C-172 but an airplane that was already
aerodynamically clean might benefit quite a lot.

The airfoil could be any reasonable one for light aircraft. The outer wing
wouldn't make the innner wing more than an inch thicker. In addition to the
speed, another benefit would be a softer ride in turbulence with the much
higher wing loading.

Bill Daniels

wrote:
One thought - fat airfoils don't like to go fast. Thin airfoils don't like to go slow.
Seems like we'd have to have a fat airfoil for the main section so that the thin airfoil could fit inside.


next stupid question for the day. if this is so, why not have wings
that change shape? flaps, I know---but again, flaps seems pretty
rudimentary. there must be some better solutions, now that building
materials have become a lot better than they were 80 years ago.

actually, all my questions are ignorant of the very first question---is
it possible to estimate how much faster would an ordinary piston
airplane, say a C172, would be if we eliminated *all* wing drag? [and,
yes, presume it is still flying and not straight down, where my
eyeglasses have fallen into ;-)] if the answer is not much, then I am
to blame for having started a useless discussion.


Well, admission is the first step in recovery :^)

Wing drag comes in two flavors:

There is induced drag from the creation of lift
and parasitic drag, which is a catch all for everything else.


Induced drag will vary directly according to CL.
Think of it as:
Di = Cdi q S

or another way:

Di = (CL^2 / Pi AR) S q

whe
AR = b^2 /S
b = wing span
Cd = coefficient of drag
Cdi = Cd induced
q (rho - not Que) = dynamic pressure (psf)
S = wing Surface (area)


Parasitic drag (Dp) is a little tougher to get an accurate handle on.
First step is to estimate a coefficient for it (Cd).
For wing only, we can refer to the lift/drag curves for a starting guess.

Dp = Cdp S q

then:

Dtotal = Di + Dp

To answer the 172 example we need to know the airfoil and area
Plug and grind, and out will pop - an estimate.

There is an added complication as Cessna uses neither a constant
chord - nor a constant airfoil.

That would mean doing a span wise summation of Cdx to get a better
guess. Messy and WAY beyond anything I want to type up this early
in the morning.

But for true masochists, refer to "Theory of Wing Sections" by
Abbott and Von Doenhoff.

Might be a good idea to have MathCad handy too...


Richard

wrote:
hmm...what would happen if the ailerons were mid-wing, rather than
end-of-wing?

Instead of having a smaller outer panel extend out of a larger fixed
section, how about having the larger section (with the ailerons) slide
out over a smaller fixed section?

Yeah, I know the control linkages could get interesting, but there are
ways to do this mechanically, hopefully without too much of a weight
penalty. Or, fly-by-wire, perhaps?

Rob

Bill Daniels wrote:
wrote in message
oups.com...

Rich S. wrote:
...
This is a solution in search of a problem.


Doesn't a swing wing accomplish pretty much the same thing?

--

FF

Yes, for supersonic fighters. Swept wings aren't a good choice for light
aircraft.

IIUC, sweeping the wing backwards has an adverse effect on stall
which is often offset with washout or twist.

How about swinging the wing forward instead?


For slow propeller airplanes, the telescoping wing does have its
attractions. It's a way to keep the slow stall speed required for single
engine airplanes and stilll get a fast economical cruise. It probably
wouldn't help the venerable C-172 but an airplane that was already
aerodynamically clean might benefit quite a lot.

The airfoil could be any reasonable one for light aircraft. The outer wing
wouldn't make the innner wing more than an inch thicker.

It would be easier to have the outer wing be the moving part from
a structural perspective, but then you have a longer chord on the
wing tip.

Another even more exotic alternative would be to design a wing
that could shape to higher or lower lift and drag airfoils. Actually
the Wright Brothers sort of did that.

Always happy to muddy the waters.

--

FF

I think this telescoping wing idea is interesting from an academic
standpoint, but I don't think the engineering challenges are going to
make it practical.

However, for the sake of discussion, what about telescoping the wings at
the fuselage instead of the outboard ends? Could dovetailed spars be
strong enough to allow the wings to be extended during TOAL and extended
for cruise? Would a cabin width of extra wingspan suffice to accomplish
the rather nebulous objectives?