Ah, chemistry; I never did that either. Shoulda tried Wikipedia first; was
sure it was some sort of shortened up slang. Thanks.


At 15:13 16 March 2009, Bruce wrote:
monomer
Dimer
Trimer
....


Nyal Williams wrote:
I know this is not alt.usage.english, but what is the etymology of
this
word? Is it slang? Jargon? Engineer language? Is it Di-mer or
Dim-er
or
dimer... something or other? I'm just a poor musicologist trying to
figure
stuff out.

At 14:27 16 March 2009, Bruce wrote:
Sorry Nyal - excessive vocab use. Dimer == related pair of.

In this case two vortices - one off each wingtip that interact to
create

a roughly symmetrical "geared disk" shape behind the wing. With the

downward part of the vortex from each wingtip merging with the
downward

flow from the other.

If you drive behind a (modern / streamlined not SUV) car in the rain
or

snow you can see the dimer it creates. Formula one and Nascar rear
wings

also create impressive examples...



Nyal Williams wrote:
Help; what is "dimer" ?


At 14:09 15 March 2009, Bruce wrote:
Paul

There is a large scale vortex dimer operating behind any aircraft,
and

particularly behind high wing loading, heavy short winged things
like

Pawnees.

The wake we fly above in high tow is the turbulent propeller wake,
but

we would have to be impossibly high and/or far back to avoid the
downward moving centre section of the dimer.

I saw a picture using smoke trails that demonstrates the scale and
power
of this some years back -
http://www.nasa.gov/audience/forstud...ry/Vortex.html

There is a more impressive video at
http://www.youtube.com/watch?v=uy0hgG2pkUs&NR=1

So - given that you are flying in a field of air that has a
significant
downward component, maybe you do have a higher angle of attack on
the

wings.


Bottom line is that even in the smooth air above the propwash you
are

still in air affected by the tug.

Bruce


sisu1a wrote:
Agreed. My money is on the towplane wake.
I put my monies on the elevator authority/AoA ratio. We fly
above
the wing wake (USA...) in most cases, in relatively clean air, but
sometimes in the clean air below it. Box the wake, it will tell
you
where it is and where it isn't...

But typically glider's noses, on tow, are unnaturally high (and
thus
AoA is higher...) for a given airspeed, in addition to being more
forcefully held there, both effects of course due to the rope's
pull. The elevator is the same size whether on tow or free
flight
though, so the authority it can exert against the countering
forces
is
proportionately lower than in free flight...

The fix is the same regardless of why though- more speed...
please!
(wings rocking in vain...)

-Paul