Do winglets produce thrust?

"Todd Pattist" wrote in message
This is an interesting winter-we-can't-fly debate. The wing
on a glider in steady motion through the air produces a
total aerodynamic force. That total aerodynamic force is
exactly vertical and exactly equal to the gravitational
force. By convention, we resolve this total aerodynamic
force into two components called lift and drag. The lift
component is always perpendicular to the flight path, and
the drag component is always parallel to it. By the usual
convention, "thrust" is either parallel to the flight path,
or is the non-aerodynamic force produced by an engine of
some sort. Thus, "lift" cannot produce "thrust." Either
the lift is perpendicular to the path, while thrust is
parallel, or it's an aerodynamic force and is excluded. For
a glider with winglets attached, when you are talking about
the total lift and drag forces, winglets cannot produce any
"thrust" by the definitions.

Good post Todd,
Isn't that what I said earlier??
Winglets produce lift, with a vector. The vector direction
can be perpendicular to the winglet surface, fwd or aft.
That is dependant on how it is shaped and mounted.
A lift vector facing the nose (fwd) being called thrust
might be a mishmash of terms, but it happens.
I usually think of thrust as a motive force acting on the vehicle.
Winglet vectors are recovery of lost energy by reshaping flow
to our advantage. Good idea, yes, thrust...... probably not
a really good description of what is happening........

Scott.

I'm amazed at the complete lack of understanding of the basic principles of
physics displayed by some posters in this thread. No wonder people can still
sell constant motion engines to investors!

Ian

"Todd Pattist" schreef in bericht
...
This is an interesting winter-we-can't-fly debate. The wing
on a glider in steady motion through the air produces a
total aerodynamic force. That total aerodynamic force is
exactly vertical and exactly equal to the gravitational
force. By convention, we resolve this total aerodynamic
force into two components called lift and drag. The lift
component is always perpendicular to the flight path, and
the drag component is always parallel to it. By the usual
convention, "thrust" is either parallel to the flight path,
or is the non-aerodynamic force produced by an engine of
some sort. Thus, "lift" cannot produce "thrust." Either
the lift is perpendicular to the path, while thrust is
parallel, or it's an aerodynamic force and is excluded. For
a glider with winglets attached, when you are talking about
the total lift and drag forces, winglets cannot produce any
"thrust" by the definitions.

You are exactly right Todd. The lift of the wing is perpendicular to the
flight path and the drag is pointing backwards parallel to the flightpath.
You may deduce these vectors from the total aerodynamic force acting on the
glider as you do. However I never state that this total force counteracts
the weight of the glider, which is true of course. I always tell my glider
friends that the lift counteracts the weight component perpendicular to the
flightpath while the drag is counteracted by the weightcomponent in the
direction of the flightpath. Four vectors in a sketch gliding forward on the
glidepath making an angle like 2 degrees with the horizon completes the
story. In fact back to earth all the time.

Karel
V-2cxT

tango4 wrote:

I'm amazed at the complete lack of understanding of the basic principles of
physics displayed by some posters in this thread. No wonder people can still
sell constant motion engines to investors!

Surely you don't mean Bernhard (my newsreader shows you replying to his
post)? His diagrams look correct.

--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

Bernhard's diagrams are spot on, but whether you call
it thrust or a reduction in drag is up to you. My Aeronautical
Engineering textbook uses both as alternative ways
of describing it. It all depends on how you choose
your frame of reference. The winglet produces a vorce
vector which consists of drag and lift, but when this
force vector is considered with the sailplane as the
frame of reference then its components could be considered
as a thrust force and a lateral force. I feel that
this is the easier way to describe the way they reduce
overall drag, but if you want to be pedantic........

"Libelle Driver" wrote in message ...
The glider is always sliding "downhill", the updrafts, thermals, ridge lift,
all just change the height of the hill. The wing just changes the slope of
the hill, a 1-26 has a steep slope and an ASH-25 has a shallow slope. We
are all sliding downhill when we soar.

What if the glider isn't falling, but moving at a constant altitude
while ridge or wave soaring? What powers it then? I think it's the wind,
like a sailboat.




I can't believe you are so confused about Thrust and Lift? EG?

......For the libelle Driver: Normally an aircraft get's its thrust
from an engine, which pulls it's wings through the air and makes the
aircraft fly. Wings create lift! If your engine quitts, or you do not
have one, you will not necessarily quitt flying. You can glide! The
energy, thrust, is your altitude and gravity.

This is why we first NEED a towplane, in order to get altitude,
energy! then we can glide till we find lift! 3 kinds: Thermal, ridge
or Wave! Possibly one more..... When the lift is stronger than the
sinkrate (energy) we can soar, climb or fly streight, managing that
energy.

Did you forget that wave and ridge lift, IS lift also, air that is
moving UP just like thermals!?? Eric?

soarski wrote:
I can't believe you are so confused about Thrust and Lift? EG?

snip

This is why we first NEED a towplane, in order to get altitude,
energy! then we can glide till we find lift! 3 kinds: Thermal, ridge
or Wave! Possibly one more..... When the lift is stronger than the
sinkrate (energy) we can soar, climb or fly streight, managing that
energy.

I think you are repeating my point: we don't get energy from gravity, we
just use gravity's field to store energy in the glider. When the glider
is sitting on the ground, it has no energy. As you point out, it gets
energy from first the towplane, then we release and get energy from
thermals or wind (ridge and wave).

Did you forget that wave and ridge lift, IS lift also, air that is
moving UP just like thermals!?? Eric?

We call them "lift", but they aren't aerodynamic lift like the lift from
a wing or winglets, which is what we've been discussing. The movement of
the airmass is really a separate issue from whether a wing or winglet
produces thrust. Except for dynamic soaring, the airmass motion is
simply superimposed on the aerodynamic motion of the glider through the air.

--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

Nope not at all! ( Sorry Bernhard ) and that's why I cut out his posting

I just wanted to add to the tail of the 'discussion.'

Ian


"Eric Greenwell" wrote in message
...
tango4 wrote:

I'm amazed at the complete lack of understanding of the basic principles
of
physics displayed by some posters in this thread. No wonder people can
still
sell constant motion engines to investors!

Surely you don't mean Bernhard (my newsreader shows you replying to his
post)? His diagrams look correct.

--
-----
Replace "SPAM" with "charter" to email me directly

Eric Greenwell
Washington State
USA

Correct Todd. Two vectors (weight and aerodynamic force) cancel each other
out so according to the first law of Newton
the glider maintains its direction and speed. But it is not obvious from
this model which force is pulling the glider forward. This was the basic
problem put up some days ago.
From the four vector model relative to the glidepath it is clear at first
sight that the component of the weight in the direction of the glidepath is
the force that pulls the glider forward.

As far as winglets are concerned one can say that when during flight
winglets are installed at the wingtips (a little difficult of course) the
total flowpattern of the wing, especially at the wingtip area is improved in
such a way that total drag is reduced. The glider will therefore accellerate
to a new somewhat higher velocity until the previous value of total drag is
achieved again. Therefore one can say that winglets have a "thrusting"
effect on the glider. However this is not a very sound way of reasoning. In
the same way one can say that "bugs" on the wing have a decellerating effect
on the glider. But the bugs are dead; the only thing they can still do is
spoil the nice laminar flow over the leading edge of the wing.. As a result
drag increases and the performance of the glider is reduced.
A sound statement I think is that winglets improve the general flow pattern
over the wing, especially at the wingtip area, thereby reducing induced drag
and therefore improving the performance (polar curve) of the glider.

Regards,

Karel
V-2cxT




"Todd Pattist" schreef in bericht
...
"K.P. Termaat" wrote:

I never state that this total force counteracts
the weight of the glider, which is true of course. I always tell my
glider
friends that the lift counteracts the weight component perpendicular to
the
flightpath while the drag is counteracted by the weightcomponent in the
direction of the flightpath.

And you do as almost everyone else does. In fact, that's why
I made the point that the total force is simply a vector
that exactly opposes gravity - it often comes as a surprise
to someone trained in the conventional FAA
four-balanced-forces model. That model is so prevalent that
you almost never hear of the simpler two-forces description.

Gravity points down, aerodynamic force points up.
Everything is balanced and the glider maintains constant
speed. Lift and drag are just two vector components of the
total aerodynamic force that we've chosen for convenience.
I'm not saying the four-forces model isn't good - it is, but
there are times when it's useful to keep the basic
definitions of lift and drag in the back of your mind.

Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

Jon Meyer wrote:

You could describe it as 'interfering with the formation
of the tip vortex and thereby reducing drag', but an
easier to understand explanation (and just as accurate)
is that of the Thrust component of the force vector
produced by the winglet. The crossflow component generated
by the tip vortex means that the angle of incidence
of the winglet relative to the flow is different to
that relative to the line of flight. If this angle
is large enough then the winglet itself will no longer
produce a force component opposing the direction of
travel, but will instead produce a small 'Thrust' component
in the direction of travel. The fact that the winglet
is in fact producing a force in the direction of travel
is why the term 'Thrust' is perfectly correct.
Its easier to explain using a diagram, and plenty of
textbooks have them if you really are that interested.
The important thing to remember is that because of
the influence of the tip vortex, the flow striking
the winglet is not travelling in the same direction
as the freestream velocity. Thats what makes it all
possible.

Ok, so my diagram of the winglet isn?t ok, because the airflow has an
inbound direction. And so it?s possible that it?s lift can be divided
into a inbound component an a thrust-component. I think now I got it.
See also: http://www.ich-habs-doch-gleich-gesagt.de/winglet2.gif

Greetings

Bernhard