Polar with spoilers extended?

as an ex Duo owner I agree with Dave Nadler and Bill
Daniels; the Duo airbrakes are better than their reputation:

The manual says the give a glide angle of 6.7:1 (which
fits with my measurements of 800fpm descent rate) at
approach speed which isn't barn door but should be
adequate. My D2cT manual quotes the same approach
glide angle (I observe the same sink rate of 800fpm)
- and reviewers assess the D2c airbrakes as very good.
I made the same observation as Bill about the Duo
brakes taking a couple of seconds for the drag to build
up - I thought it had something to do with a more turbulent
airflow as the trim changes nose down with the brakes
deployed(??)

The Duo airbrakes need a very strong pull to fully
open them - but this is aided on later ones by a mod
to the control linkage (also available as a simple
retrofit)

Also, our Duo was delivered with the airbrake lever
actuated hydraulic wheel brake picking up well before
full airbrake and I initially found it almost impossible
to pull full airbrake - it is easy to adjust the wheelbrake
and this, along with the linkage mod, helped a lot.

However our wheel brake was so effective that if the
glider touched down on grass with the wheel brake fully
on then the wheel didn't turn and the glider bounced
as if it had hit a rock. As a result I always had to
close the airbrakes a little before touch down which
increased float.

John Galloway


At 15:18 23 October 2007, Bert Willing wrote:
There are other big heavier gliders with lots of inertia,
and they react
very well and immediately to the deployment of airbreaks.
Those on the original DuoDiscus are just a very bad
design. But, as Marc
pointed out, a sideslip works well AND gets you a visual
on the airfield
from the back seat (the second very bad design glitch
of the Duo).

Bert

'Bill Daniels' wrote in message I think the Duo's

airbrakes are better than many people think. The Duo
is a
big heavy glider with lots of inertia. It doesn't
like to change
direction quickly. That includes its behavior on
sudden airbrake
deployment. You don't get a lot of sink right away.

My first reaction was that the airbrakes were weak
but a little more
experience showed me that with a little patience,
the brakes took effect
and produced a respectable decent rate. The Duo just
makes you plan ahead
a little more than with a light single seater.

Bill Daniels