"Derek Copeland" wrote in message
...
In free unaccelerated flight with no thrust, i.e. no aerotow, winch, or
turbo, a glider IS essentially gravity powered. The resultant force of
gravity plus wing lift, angled very slightly forward, opposes drag. Thus a
glider runs down a very slight slope through the air. The less drag there
is, the flatter the glide angle becomes.

Both airbrakes and large positive flap angles increase the drag, so the
glider has to run down a steeper slope to maintain speed.

Airbrakes both reduce lift, by disrupting the airflow over part of the
wing, and increase drag, so the answer to that question is obvious.

Large amounts of positive flap increases lift, but also increases drag to
a much greater extent.

Derek Copeland


Just to add a bit to Derek's analysis. I fly a HP-14 which doesn't have
spoilers and totally relies of large span flaps for glide slope control.
The increase in lift is negligible as the flaps are extended beyond 45
degrees to 90 degrees. However, the increase in the drag produced is
massive.

At 50 kts with flaps set at 0 my HP-14 has a glide ratio about 38:1;
however, with the flaps at 90 degrees the glide ratio at 50 kts is some
where between 2:1 to 3:1.

http://www.soaridaho.com/Schreder/St...r_on_Flaps.htm

Wayne
HP-14 "6F"
http://www.soaridaho.com/Schreder


At 12:30 18 March 2009, Bob Cook wrote:
Well, at least I did learn a lot from the previous thread, thanks mostly
to
Ian who helped me "tidy up" some of my conceptions.

Yes this is Jr High physics. I think if we took the final exam, Ian
would
get an "A", while I would get a "C" and most of the guys would do
worse!


Since everybody liked my "gravity" question so much, here is more from
my pet peeve department.

Q) Two identical gliders on final approach. Glider A has spoilers
closed.
Glider B opens spoilers. Glider B will make a steeper approach because
"spoilers reduce lift". True or false? And why.

Q) Two identical gliders on final approach. Glider A has flaps
retracted.
Glider B has flaps extended. Glider B will make a steeper approach
because "flaps increase lift". True or false? And why.

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