Polar with spoilers extended?

First I thought that you were pulling our legs, but it seems you're
actually serious.

Every year a couple of pilots die because they are too slow on approach.
Where I fly, a student will fail his checkride big time if he's only one
knot below the yellow triangle on final. *Especially* with a headwind.
If you don't understand this, I *strongly* recommend you talk to a
knowledgeble instructor.

I will be the first to agree that pilots die every year because they
are too slow on the approach. However I have not been able to find any
evidence that any of these were caused by the pilot intentinally
flying the approach slower than normal. In fact in nearly every case
I have examined it appears more likely that pilot was flying by sight
and feel and not paying any attention at all to the airspeed. Often
they are landing or flying downwind which gives the illusion of
airspeed, as does flying close to the ground. If fact the few pilots I
have been able to interview or read their description of the accident
described it as feeling like the controls went limp and had no effect.
The didn't make any mention of airspeed. It is not hard to find this
description in NTSB reports for power aircraft. I believe nearly all
Stall Spin Accidents are caused by the illusion of speed. The pilot
thinks he going fast so he doesn't look at the airspeed indicator and
he is not thinking about a stall or a spin.

Brian

On Oct 24, 8:44 pm, Brian wrote:
First I thought that you were pulling our legs, but it seems you're
actually serious.

Every year a couple of pilots die because they are too slow on approach.
Where I fly, a student will fail his checkride big time if he's only one
knot below the yellow triangle on final. *Especially* with a headwind.
If you don't understand this, I *strongly* recommend you talk to a
knowledgeble instructor.

I will be the first to agree that pilots die every year because they
are too slow on the approach. However I have not been able to find any
evidence that any of these were caused by the pilot intentinally
flying the approach slower than normal. In fact in nearly every case
I have examined it appears more likely that pilot was flying by sight
and feel and not paying any attention at all to the airspeed. Often
they are landing or flying downwind which gives the illusion of
airspeed, as does flying close to the ground. If fact the few pilots I
have been able to interview or read their description of the accident
described it as feeling like the controls went limp and had no effect.
The didn't make any mention of airspeed. It is not hard to find this
description in NTSB reports for power aircraft. I believe nearly all
Stall Spin Accidents are caused by the illusion of speed. The pilot
thinks he going fast so he doesn't look at the airspeed indicator and
he is not thinking about a stall or a spin.

Brian

I'm pretty sure that's not a true. I know of at least a couple of
accidents where the pilot was knowingly flying as slow as possible and/
or s-turning on final to get into a tight spot. Both were fatal.

I think the best way to think about this is in terms of energy
dissipation between wherever you start and some fixed touchdown point
(or stopping point if you are willing to plant the glider on the
ground and use the wheel brake too). Frankly if I am looking at a
finite distance to an unpleasent end of the field I will do whatever I
can to burn energy - before and after touchdown.

For starters I took a look at my ASW-27B factory polar. It turns out
that I will fly the same L/D spoilers closed at 37 knots (stall) as at
86 knots. This is basically the breakeven tradeoff between between
high induced and and high parasitic drag manuevers. If I add spoilers
I am adding a parasitic drag device which increases in effectiveness
with the square of velocity. That means that the breakeven speed for
the parasitic maneuver has to be lower than 86 knots. You don't need
to get to Vne to do better by going faster - even 70-75 knots is
probably better.

The ground effect argument has some merit I think, but keep in mind
that you can always stop the manuever before you get into ground
effect and bleeed off airspeed at 100' or so - you will still be
ahead. The altitude you consume slowing form the higher speed will be
roughly equal to the altitude you burned getting to the higher speed.

This is for still air. If I add headwind the breakeven airspeed for
speeding up versus slowing down goes up, but in most cases I'd be hard
pressed to believe that with spoilers out you will get a better energy
dissipation going slow than fast. At some point there will be a
crossover as headwind goes up. Just think of a headwind that is
greater than your stall speed to convince yourself.

Theory aside, I am convinced that as a practical matter making the
glider as draggy as possible and adding speed is almost always a more
practical and safe solution to slowing down and maneuvering at low
altitude. Stall/spin is a buzz-kill.

Lastl;y, I have done the parasitic drag maneuver down to touchdown in
a G-103 with spoilers closed and convinced myself that it is the
preferred method. I 'm guessing a Duo with the boards out is at least
as draggy as a G-103 clean.

My 2c.

9B

Brian wrote:

I will be the first to agree that pilots die every year because they
are too slow on the approach. However I have not been able to find any
evidence that any of these were caused by the pilot intentinally
flying the approach slower than normal.

It's hard to tell after a fatal accident whether he was intentionally or
accidentally too slow... :-/ But if you're actually correct, well, then
you'll be the first.

Brian wrote:

However I have not been able to find any
evidence that any of these were caused by the pilot intentinally
flying the approach slower than normal.

After a fatal accident, it's usually hard to tell whether he was
intentionally or accidentally too slow... :-/

But if you're correct, well, then you'll be the first... :-/

This is the kind of rigid thinking that kills people.

While I entirely concur that being too slow on final approach is dangerous, one
has to understand the variables. 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. While under pressure in a difficult situation.

For every weight and configuration there is a stall speed.
For every wind condition there is a different factor to add to stall to get to a
safe approach speed.

Personally I would far rather fly with someone who knows exactly why he/she is
trying to maintain a particular speed, than someone who is a master at nailing
some arbitrary speed. Which happens to be perfect for one set of conditions.

As a Std Cirrus driver (pre serial 75) I can vouch for the wisdom of being at
the right speed. Too fast by even a small margin and you will float forever, and
PIO if you try to fly it on. Too slow and the handling gets very interesting if
there is turbulence. That right speed varies widely depending on the wind and
other circumstances.

Maybe we make it too complicated - our rule is you have to be able to decide an
appropriate approach speed, explain why you chose it, and then keep within 5km/h
of it.

John Smith wrote:
Brian wrote:

Looking at a polar is exactly why it works. It is called Speed to fly.
It really only works well when you have some headwind. It does work
somewhat in calm conditions but is really not very effective. It
probably doesn't work at all in a tailwind condition.

First I thought that you were pulling our legs, but it seems you're
actually serious.

Every year a couple of pilots die because they are too slow on approach.
Where I fly, a student will fail his checkride big time if he's only one
knot below the yellow triangle on final. *Especially* with a headwind.
If you don't understand this, I *strongly* recommend you talk to a
knowledgeble instructor.

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.

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