On Fri, 05 Jun 2015 06:35:11 -0700, platypterus101 wrote:

What do you need to do with the stick to hold a constant airspeed as you
open the spoilers in wings-level flight?

That's dependent in what glider you're flying:

- If you're in a Puchacz you give the stick a healthy shove forward as
you open the brakes. If you don't, it will loose at least 5 kts almost
instantly.

- if you're in a Libelle, SZD Junior or an ASK-21 there's little
immediate speed change.

- in a Grob G103 you pull back a bit because these drop their nose and
pick up speed when you open the brakes.

Is the heart of the matter simply that for a given airspeed in
wings-level at any given bank angle, including zero degrees bank, the
stick needs to be positioned further aft with the spoilers open than
with the spoilers closed?

No. The main effect of well-designed airbrakes is to reduce effective
lifting surface, but, as a side effect is to add drag, most gliders will
need the stick to be eased forward a little to keep the airspeed
constant. However, the wind gradient and turbulence will probably be more
significant: you'll think you're correcting for these factors rather than
for the extra drag from the brakes. But, as I said above, it does depend
on the glider. For the G103 to behave as it does, its drag must reduce
along with the lift as you open the brakes. Conversely, the Puchacz has
huge speed-limiting upper and lower surface brakes: so much so that it
would be surprising if shoving those out in the breeze didn't show it
down.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |