Polar with spoilers extended?

On 22 Oct, 22:33, John Smith wrote:
Brian wrote:
Frightening? Really? It actually works very well with a bit of head
wind. Backcountry power pilots occasionally use this technique as
well.

It's a completely different thing in a power plane. (Although I wouldn't
recommend it with power planes, either.)

A short look at a typical glider polar is all that is needed to
understand why your "technique" is a no-no. If you continue using it,
then it's only a question of time that we'll hear about you in the news.

Anyone tried option 4?

Stuffing the nose right down for 3 or 4 seconds will easily lose you
50m or more with only a small increase in airspeed since Newton gets
involved in the exercise. A bit of increased spoiler will overcome
that increase quickly. What's more you are playing with the safe side
of the energy curve!

To the poster who said that condor may not be a good tool to test
this. I suggest you try a copy. It really is a great sim and the
flight dynamics are superb. I believe that Lasham gliding club took
one ab-initio student right to solo standard on a sim before one or
two real circuits to get him away. Sims have come a long way.

Ian M

On Oct 23, 6:30 am, nimbusgb wrote:
....snip...
To the poster who said that condor may not be a good tool to test
this. I suggest you try a copy. It really is a great sim and the
flight dynamics are superb. I believe that Lasham gliding club took
one ab-initio student right to solo standard on a sim before one or
two real circuits to get him away. Sims have come a long way.

Ian M

I am planning on buying a copy and for general flying and basic
training I see great value in simulators. But the original posting
was about doing a flight test to determine performance such as descent
rates with spoilers extended, turns back to the airport, etc. Any
such data requires that not only does the simulator have all the right
aerodynamics models, but that it has complete and accurate data for
your specific model of glider. I doubt that Condor has test flown
every glider model extensively enough to confirm the accuracy of their
results.

BTW, I program flight simulators for SIkorsky AIrcraft. One of my
bosses has a rule "all simulators are guilty until proven innocent"

Todd Smith

On Oct 22, 9:12 am, Nyal Williams
Forward slip in glass gliders won't get you much descent;

The ASW-19 and ASW-28 have a huge increase in sink rate in a full
rudder slip compared with airbrakes alone. What glass gliders are
you flying that do not slip well? Can you maintain a full rudder
slip, and I mean rudder on the stop and never comes off it until you
choose to exit the slip?


Andy

I first learned it in Minden and then refined it in
Cal City.

What the objecters have not realized is just how fast
you can bleed off tons of excess speed by lifting the
nose to the horizon with full spoilers out.

And again, the maneuver need not necessarily be carried
out to the threshold, even, much less to the round
out. You can use it to bleed off 200ft or 500ft when
you are at 1000ft on final [No, this is not the everyday
pattern or practice] and then you can lift the nose
and lose the speed when it looks like you are at the
normal height for that distance from the touchdown
point. When the speed drops to proper approach speed
you just adjust the spoilers and continue as normal.
Once you have done it it no longer appears to be a
dare-devil ride; it is entirely predictable.

At 00:12 23 October 2007, 5z wrote:
On Oct 22, 4:52 pm, Tom Gardner wrote:
And I take the point that it's not usually necessary
to finish the
manoeuvre at ground level.

IMHO, it's useful to demonstrate this on final approach,
but a better
place to apply it in real life would be earlier in
the landing
pattern. For example huge amounts of lift on downwind,
so dive off
the altitude on base.

In the US southwest, where downbursts and the associated
huge sink and
sometimes lift can happen, I've found myself turning
a high final
expecting 40-50 knots headwind and it's vanished.
I've also
experienced huge lift on base / final as the outflow
curl decided to
position itself right at the end of the runway. So
these are the
cases where I might be tempted to use the dive while
on final
approach.

-Tom

Nyal Williams wrote:
I first learned it in Minden and then refined it in
Cal City.

What the objecters have not realized is just how fast
you can bleed off tons of excess speed by lifting the
nose to the horizon with full spoilers out.

The objectors are pointing that there are some gliders whose spoilers
don't produce quite enough drag to manage this maneuver effectively. In
a glider that has effective spoilers (like a Ventus B) it's a blast.
But, in my experience (which were usually at 8000+ foot density
altitude), a Duo will accelerate rather quickly in a dive with full
spoilers, then take you halfway down the runway while you bleed off 15
or 20 knots of excess speed, even out of ground effect. If you bleed it
off more quickly, you're going up. I found a slipping turn to final
that is held for as long as needed to be far more effective. Your
mileage may vary...

Marc

Certainly there are some gliders with inadequate divebrakes.
A modification was applied to the Cirrus. I've not
flown a Duo; perhaps it needs a mod; thin airfoils
are not conducive to installing wide vertical plates.

At 02:12 23 October 2007, Marc Ramsey wrote:
Nyal Williams wrote:
I first learned it in Minden and then refined it in
Cal City.

What the objecters have not realized is just how fast
you can bleed off tons of excess speed by lifting
the
nose to the horizon with full spoilers out.

The objectors are pointing that there are some gliders
whose spoilers
don't produce quite enough drag to manage this maneuver
effectively. In
a glider that has effective spoilers (like a Ventus
B) it's a blast.
But, in my experience (which were usually at 8000+
foot density
altitude), a Duo will accelerate rather quickly in
a dive with full
spoilers, then take you halfway down the runway while
you bleed off 15
or 20 knots of excess speed, even out of ground effect.
If you bleed it
off more quickly, you're going up. I found a slipping
turn to final
that is held for as long as needed to be far more effective.
Your
mileage may vary...

Marc

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

John Galloway schrieb:

The manual says the give a glide angle of 6.7:1 (which
fits with my measurements of 800fpm descent rate) at
approach speed

Very interesting, indeed:

JAR 22.75 Descent, approach
It must be shown that the sailplane has a glide
slope not flatter than one in seven at a speed of
1·3 VS0 with air brakes extended at maximum
weight.

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

Well, clearly, not all current and former Duo owners agree. Perhaps I'm
used to gliders with very effective spoilers, including various DG
models, ASW20s, Ventus Bs, etc. But, after 200 or so hours in our Duo
(and a couple of others in the area), I'll simply say that the spoilers
were workable with proper approach planning and airspeed, and that it
remains the only glider I've ever felt the need to slip on a routine
basis...

Marc

On Oct 23, 2:00 pm, Marc Ramsey wrote:
John Galloway wrote:
as an ex Duo owner I agree with Dave Nadler and Bill
Daniels; the Duo airbrakes are better than their reputation:

Well, clearly, not all current and former Duo owners agree.

My 2c: (Our club has a duo, so based on some experience.) The actual
glide angle of the duo, with full spoilers out and at a stable
approach speed, is decently steep. Looking at this angle at altitude
is instructive. The duo seems not to lose speed as quickly as other
gliders when you open the spoilers, especially in ground effect. "Too
high" really often means "too fast". I think a lot of the perception
that the duo has poor divebreakes is realy that it does not slow down
fast, rather than the actual steady state glide angle is shallow.

This all makes some aerodynamic sense. The duo is heavier than basic
trainers, and much heavier than the single seaters we are used to.
"Spoilers" work as much by "spoiling lift" as by "increasing drag",
and much of the latter is induced drag due to the gap in the lift
distribution anyway.


John Cochrane