Re: Do winglets produce thrust?

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" <[EMAIL PROTECTED]> schreef in bericht
news:[EMAIL PROTECTED]
> "K.P. Termaat" <[EMAIL PROTECTED]> 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.)