Polar with spoilers extended?

bagmaker wrote:
I have to add my thinking, open to scrutiny.
1- whatever needs to be done to get the a/c to an acceptable landing
position above and before the field needs to be done early, to minimise
ground effects. (theoretically, if this is adhered to, the problems
wouldnt eventuate, as the pilot would have noticed his/her extra
altitude before arriving at final and modified the curcuit to suit.)

Good point. No-one has mentioned using airbrakes on the base leg, or
even the downwind leg. I often do this if the sink is less than I
anticipated or I hit lift. Once a pilot has some experience it's really
easy to see at this stage if you will be too high, and losing the excess
height early makes the last part of base and the approach much easier
than if you leave all the excess height to be lost in the approach.

I recall that when being trained, I was told not to use airbrakes until
I'd turned finals (though also that in post-solo training it was pointed
out to me that I could now break this rule).

Is it possible that we are too heavily conditioned not to use airbrakes
before the final turn?

In my Open Cirrus I'd rather turn finals a *little* too low, as if I fly
the first part of the approach without brakes I'll soon intercept the
approach funnel. Turning too high is always more difficult. Note that in
a K8 the opposite is true - too low might not be fixable and losing
height is easy (and often not optional!). One of the points which comes
out clearly from this thread is that the answers are very glider-specific.

So I guess my preferred answer is:

0. Lose the excess height before making the final turn, in whatever way
works for you.

[PS For those blessed with a tailchute, I can highly recommend
practising opening the tailchute towards the end of the downwind leg. If
you need it for a real field landing, the approach is too late - what if
it fails to deploy? The feeling of despair as you are clearly too low is
balanced by the elation when you realise that you will make the field
after all. Anyone trying this will need to fly a curved path from end of
downwind to touchdown, as a formal circuit is *far* too scary and will
probably leave you short.]

Bruce wrote:

This is the kind of rigid thinking that kills people.

You can't be rigid enough when it comes to final approach speed.

If you teach that the
needle has to be ON the yellow triangle, what happens to the pilot when
he suddenly notices the glider he is in doesn't have one.

Yeah, yeah, yeah. I would expect from a glider pilot that he doesn't
"suddenly" discover on short final that there isn't such a triangle, but
that he familiarizes himself with the glider before the flight. If he
doesn't, then many other things have gone wrong during his training.

For every weight and configuration there is a stall speed.

Of course. But the other poster proposed to slow down to the point where
you get a steeper approach. For me, this is a *very* rigid no-no. I
don't think that rigidness in this point kills people. I even tend to
think the contrary.

Bill Daniels wrote:

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.


In other words, the Duo "airbrakes" are not very effective. Lots of big,
heavy, fast aircraft do have effective spoilers/speedbrakes/"airbrakes",
or whatever you want to call them, that make the desired changes in
speed/rate of descent promptly.

Every car's acceleration from 35 to 65 for merging into Interstate
highway traffic is adequate--if you are willing to wait for it.

I learned to "plan ahead" when passing on two lane roads in my VW
Beetles and early un-blown Corvairs. I know what planning ahead means
and that is not "performance" as we like to think of it. The same goes
for sailplane spoilers whose effects are not prompt, and rudders which
are not effective enough to allow a good steep high descent-rate slip.


Jack

BB wrote:

As fun as the high parasitic drag maneuver is, I wonder if anyone has
ever actually used it in combat. Has anyone been so flustered and out
of synch to get monstrously high in an off field landing, then had the
presence of mind and skill left to dive to the ground at near VNE,
aiming several hundreds of yards short of the intended small paddock
with fence at the far end, and had it work? The mental attitude that
gets to the problem seems incompatible with the attitude needed to
pull this one off.


In "combat"? In a Duo?

There are a number of real combat stories about people keeping the speed
high in damaged aircraft to get down out of the fight, through clouds,
etc. to find a safer area for a forced landing or bailout--so as not to
be hosed while under canopy, or to avoid setting up a big slow pattern
that would make them a sitting duck--but I think that diverges from what
you are asking.

I don't think fighter pilots get a chance to practice engine out
landings much, so yes, they adapt. The best adaptation is that for which
the mental groundwork is laid _on_ the ground.

Sailplane pilots have the incomparable advantage of doing their
preparation on the ground _and_ in the air by planning and practicing
both low- and high-energy approaches, as has been outlined here in
previous postings by several contributors.


Jack

Tim Taylor wrote:


The situation: You are 70 miles from home over unfamiliar territory
(read not sure of exact elevation of the terrain below, your altimeter
is useless now). You have gone for a Cu over a dry lake bed and it
doesn't work. You have selected a landing site in the lake bed that
is about 350 feet long and 100 feet wide that looks safe to land.
There are tree stumps and other object in other parts of the lakebed.
There are no obstructions on the ends of the site so you can do a
normal approach. The winds are 15 to 20mph out of the south so you
are landing from the north to south. As you drop lower you make a
rectangular pattern over the site checking for any missed obstacles.
The downwind is fast with the tailwind, as you turn base you estimate
you are 400 feet. Your adrenaline is pumping as you prepare for a
fairly technical landing. You want to keep it close so that you don't
end up short back into the wind and you turn base a little too soon.
You are on short final about 350 feet, but about 100 feet over full
spoilers decent. What do you do?


Tim,

We've already screwed up a bunch of things to get ourselves here, but
then we may do that from time to time, so:

S-turns.

In this situation I want more time: to achieve the necessary descent
while flying the ship in the way I most frequently fly it--this is not
the time for something completely different--even though I can
_probably_ do a "360" from that height with a "clean" wing. _Know_ what
your configuration is. Gear? Spoilers? If there is any cross-wind, turn
into the wind initially, using anything from a 45 to 120 degree turn
depending on conditions, but I'll be more comfortable with 60 to 80
degrees; keep the touchdown area in sight; control speed carefully; do
not hurry the process; continually assess drift, obstructions, and
condition of roll-out space as your vantage point changes while crossing
the extended runway centerline.

Do not continue maneuvering below a safe altitude. The last 100 feet
should look as normal as any you've ever done. If not you've been in too
much of a hurry to get to the runway. Just relax and fly around until
you get to where everything looks about right again--really, thats what
we always do, isn't it? That's why we must be able fly the pattern very
comfortably without reference to the altimeter.

When airliners need more spacing on final approach, something similar to
this method is surprisingly effective without disturbing the customers
too much.

One more note: if every approach we fly at our home field looks just the
same as every other one, we may not be learning enough. Mix it up a
little. Where I fly that's rarely a problem, though, and I think that's
good for us in the long run.


Jack

In article , J a c k wrote:
Bill Daniels wrote:

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.


In other words, the Duo "airbrakes" are not very effective. Lots of big,
heavy, fast aircraft do have effective spoilers/speedbrakes/"airbrakes",
or whatever you want to call them, that make the desired changes in
speed/rate of descent promptly.

The Duo's airbrakes are effective. I fly a DG1000 and Duo's a lot. The DG1000
airbrakes _feel_ much more effective than the Duo's, but they both work about
the same. I've descended from the wave wingtip to wingtip with the DG1000
and a Duo, both with full brake, and they go down at the same rate.

I'll be most interested in how the Duo X compares.

--
Philip Plane _____
|
---------------( )---------------
Glider pilots have no visible means of support