DSK wrote:
Nav wrote:

If set up with dihedral or when heeled, yes they can -but its small as
their area is small.


I'm not saying you're wrong, but the wing keel designers I've talked
with have never mentioned it. First of all the winglet is mostly
horizontal. Here is where Jax's favorite, the 'sine function' comes
in... if the winglets produce a net lift, then it is going to be mostly
up or down unless the dihedral and/or heel angle gets very large, like
greater than 45 degrees.

Yes, that was my point. Did you see the dihedral on current IACC
winglets? It's up to about 30 degrees (by eye). That neans when the heel
is 30 degrees (a typical 'powered up' design heel angle) one winglet is
horizontal the other within 30 degrees of vertical. The latter winglet
adds some useful keel area. The question I ask you to think about is
which one is controlling the keel tip vortex by a plate effect... The
answer is, of course, that they are too small to do that well and they
are really workin in conjunction with the bulb (that provides an
endplate effect). I don't think I'm giving TNZ design secrets away but,
what these long thin winglets are doing "flying" in the keel vortex
which is why they are at the back of the bulb. They extract lift and
energy from the vortes and increase overall keel efficiency. If they
actually generate a lift (or a torque) in a direction oppostite to that
of the votex then they rob it of energy and return energy to the keel
system (or reduce parasitic drag if you prefer). Second they are not
symmetrical in section. The winglet with the negative angle of attack
generates less negative lift in the vortex than that with the postive
angle. The net effect is postive lift and again vortex energy robbing.

OK?

Cheers MC