Bill

Generally they are treated interchangeably so your LD 33 ( K6e on
Gliderpilot ) is the same as 1:33 glide angle.

A Nimbus 4 has an L/D of 1:60 or a glide angle of 1:60 ( 60 bits of lift
for one bit of drag 60' forward for 1' of altitude lost )

Generally the figure quoted refers to the best glide angle that the aircraft
can acheive, there is no standard speed at which this is quoted so its a bit
misleading.

What everyone works from is the gliders 'polar diagram'. A plot of speeds
against sinkrate.

A few examples can be found at the SSA site
http://www.ssa.org/Magazines/Johnson.asp

These days the manufacturers still aim to develop good L/D ratios ( around
1:50 seems to be the mark for todays 18m ships ) but the game seems to be to
get the polar as flat as possible and to try to maintain good glide ratios
into the 150 kph or 80 kts range and higher.

Given two gliders with the same LD, say 1:42 ( 2nd generation glass ships )
one has best L/D at 90 kph the other at say 95 kph the theory is that the
second must win all the tasks ( higher average speed )

Reichmans 'cross country soaring' is great for filling your head with the
theory of all this. Well worth a copy even at the newbie end of your flying
career!

Ian



"Bill Gribble" wrote in
message .. .
Completely daft newbie question that I'm hoping will have a simple
answer.

Mention is frequently made of the term L/D, which I know is an
abbreviation of Lift / Drag. For example, the L/D cited in an advert for
a Ka6 recently was "L/d 33"

If L/D is the Lift/Drag ratio, why are the figures accompanying it
frequently not ratios? For instance, in the above, what is the "33"?

Is L/D used as the best Lift/Drag ratio the glider in question can
achieve? How does this translate in real terms? Does it describe the
best glide speed, or relate to the glide ratio in any way?

The glide ratio (eg. An ASH25 has a glide ratio of 60:1) seems a great
way of describing certain aspects of the performance of a glider. Yet
most the specifications I read describing gliders don't give this figure
in quite such a straight forward way. Is this information somehow
derived from other information given? Or is it too variable to generally
provide as a generic statistic (eg. One ASH25 might have a 60:1 ratio,
another less at 45:1)?

Am I managing to make any sense, or am I completely confusing myself (in
which case, no worries - more time, exposure and experience will
eventually rattle all this out for me, I'm sure)?

--
Bill Gribble

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