Ian,

If we draw vector force diagrams of two identical gliders, one with flaps
extended, and the other with flaps retracted, we can easily see that
"lift" is essentially the same in both cases.

The direction of flight will be steeper with flaps extended, and drag will
be signifigantly greater.

As for spoilers, vector diagrams will also show lift is not reduced
(except for a tiny, tiny amount) but drag is greatly increased and the
fligth path is steepened.

Remember were are talking about stabilized unaccelerated flight here.

Sudden application or retraction of flaps might have MOMENTARY changes in
lift, but not once stabilized unacellerated flight is resumed.

Misconceptions commonly found in publications and professed by many
"experts":

Gravity powers a glider and provides forward motion.
Flaps increase lift
Spoilers reduce lift
Centrifugal force turns a glider
Aircraft climb due to increased lift
Aircraft descend due to reduced lift

Any more?

Cookie



At 01:00 20 March 2009, Bob Cook wrote:
OK. badly worded question.

Here I was trying to point out that DRAG is the major difference between
a
40:1 glider and a 20: glider. Not lift, not gravity.


Drag determines the direction of flight.

More drag= steeper glide (spoilers, flaps)

Less drag = flatter glide

Cookie



At 18:23 19 March 2009, The Real Doctor wrote:
On 19 Mar, 12:15, Bob Cook wrote:

Spoilers redistribute lift, but not reduce lift.

They reduce the lift over part of the wing. Whether the overall lift
increases, decreases or stays the same depends on what the pilot does.

Flaps change the coeffecient of lift, but not lift.

If you keep everything else the same then they do change lift. Every
tried dumping your landing flap just before the flare ...?

Q) =A0Two gliders, one is 40:1 racer and glider two is 20:1 trainer.
Both
weigh 800#

Glider one has twice the lift of glider two. =A0True or flase and
why.

Depends what they are doing.

Ian