Question of the day

In article , says...
Eric Greenwell wrote:
The heavier glider is flying at a higher L/D than the lighter one, so

I don't think that can be right.
The heavier glider will achieve the same max L/D ratio than the lighter
one, but at a higher speed.

It's true they will have the same max L/D ratio; however, at any speed
above the ballasted glider's max L/D, the ballasted glider will have
an L/D better than the unballasted glider (same speed, lower sink
rate). That L/D will be lower than the max L/D, of course, since it is
flying faster the max L/D speed.

Take a look at a polar plot for a glider that shows the both the
unballasted and ballasted polars, compare them for the same speed, and
you will see what I mean.
--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

Eric Greenwell wrote:
It's true they will have the same max L/D ratio; however, at any speed
above the ballasted glider's max L/D, the ballasted glider will have
an L/D better than the unballasted glider (same speed, lower sink

Oh yes, of course. On the other hand, at a speed slower than max L/D
speed for the lighter, the sink rate will be smaller for the lighter
glider. And the gliders will have the same sink rate at a speed
somewhere between their max L/D speeds.

So, during a manouver where two gliders pull up from a speed greater
than max L/D speed for the heavier one to a speed slower than max L/D
speed for the lighter, the altitude difference is a function of the
speed profile during the manouver. It's quite hard to compare the
altitude gains without heavy calculations, but I wouldn't say the effect
would clearly benefit either glider. What it _does_ say, in my opinion,
is that the pilot should probably only pull up to the max L/D speed or
minimum sink speed (depending on the situation) for _his_ glider.

Jere

jere at iki.fi