Polar with spoilers extended?

On Oct 22, 10:12 am, Nyal Williams
wrote:
Frightening! That you would slow down to decrease
forward motion. What happens with downdrafts or wind
shear after you have given up the option for altitude
that speed gives you.

snip

Frightening? Really? It actually works very well with a bit of head
wind. Backcountry power pilots occasionally use this technique as
well.

It could be "Frightening" on a normal approach but remember the
context. A Downdraft or Windshear would be welcomed as the whole point
is to lose altitude. It does requires some expertise in slow flight
and stall awareness. But then glider pilots or at least soaring pilots
are supposed to be the experts at slow flight. Once you get down
close to a normal approach angle simply accelerate (which will bleed
off some more altitude) to your normal approach speed and fly the
remaining part of the approach normally. In fact it is necessary that
at about 200 feet AGL or higher that you do accelerate to a normal
approach speed so that you will have enough energy to flare with.

I would strongly recommend practicing it with an instructor and in the
specific airplane before having to use it. Usually with gliders there
are other, as good, or better options to this technique.



Brian

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.

On Oct 22, 3:33 pm, 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.

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.

As noted gliders usually have a better ways of dealing with being
high. And since most people aren't excessivly high with a headwind it
does have limited use in gliders. There are really only two things
that can go wrong with using the technique and both should be easily
controllable. These are a Stall/Spin or continuing the slow approach
to too low of altitude to recover back to a normal approach speed.

Personally I seldom use it, The High Parasitic Drag approach and/or
Slips described above is usually more effective in a wider range of
conditions.

Brian

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.

Tims summary is a good one, thanks!
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.)
So, slips, s turns etc, must be initiated as soon as the over-energy issue is recognised.
2-if the pilot is high-energy when arriving in the flare it is way too late, a long or harsh landing is inevitable.

concluding the above, s turns are going to be a logical option, as you are just extending your base turn, then back again toward the field and repeat at a reasonable altitude, into the wind. Unfortunately, the turns will be at a higher speed, sloppily co-ordinated with the brakes out, so if you survive them, you will probably land correctly!

The issue is one of observation, the fact is there has been previos mis-observation, so, will the pilot suddenly realise? - possibly not. The more time that is taken to realise it, the more serios the problem results.

Quite the conundrum!

thanks for a great post

bagger

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.]

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.

Assuming the U.S., not likely. I admit that being slow on final is bad
news, but the Practical Test Standard for the private pilot exam calls
for +10/-5 knots as being acceptable for a final approach speed (page
1-16 - see below). If one of my students was "pink slipped" for being
one knot slow on final, I would advise him to challenge the failure -
and he would win. An examiner simply does not have that kind of
latitude. If the applicant flies to the PTS, he gets his license. I
agree that if there is a headwind, "recommended approach airspeed" will
be higher than the "yellow trangle".

Tony V.

LANDINGS
Q. TASK: NORMAL AND CROSSWIND LANDING
NOTE: If a crosswind condition does not exist, the applicant’s
knowledge of crosswind elements shall be evaluated through oral
testing.
REFERENCES: Soaring Flight Manual, Glider Flight Manual.
Objective. To determine that the applicant:
1. Exhibits knowledge of the elements related to normal and
crosswind approach and landing procedures.
2. Adjusts flaps, spoilers, or dive brakes, as appropriate.
3. Maintains recommended approach airspeed, +10/-5 knots.

Tony Verhulst wrote:

Assuming the U.S., not likely.

You're assuming wrong.

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