Polar with spoilers extended?

Tim Taylor wrote:
High on Final, Summary

Thanks to all that have given input so far. My original intent was to
do some modeling before starting the discussion, but this is RAS and
it has a life of it's own.

So here is the issue. You are high on final and full spoilers are to
enough; what do you do?

List of options so far:

1. Slip
2. "S" turns
3. Dive until intercepting normal angle for spoilers
4. Dive until near the ground, then decelerate
5. Slow down until intercepting normal angle for spoilers
6. 360 degree turn

Unfortunately I still don't have good data for what happens to the
polar as speed increases with the spoilers open. Condor was a good
suggestion, and I am working to see if I can get meaningful data from
it.

John Cochrane brought the discussion back to the real point which is
what would you use in the real world? It is interesting but not that
useful to discuss how you do this at your home airport with 2500 to
9000 feet of runway and know precisely the field elevation. When your
aircraft and your own safety are on the line in a real off-field, what
are you going to do?

What I do must be taken with a grain of salt, because I'm not an
instructor, pretty much learned how to deal with field landings by trial
and error, have 20 or 30 of them under my belt (5 to 10 in "small"
fields), and have yet to do any more damage than scuff up the underside
of the nose.

First, I *never* fly a normal pattern. I fly directly overhead high
enough to make one or more big lazy circles around the field at approach
speed, so I can look carefully for fences, wires, rocks, figure out
which way the field is sloped, get an idea of the actual wind direction,
potential for sink, get a picture of just how high I am above the field,
and pick the spot where I plan to touch down. When it becomes clear
that I won't be able to make another 360 (and I've found that pretty
easy to determine), I shift the circle as needed to approximate an
abbreviated downwind, base, and final, and will use spoilers, landing
flaps, slips, adjustments to the circle, etc., to get myself into the
field as best I can. I never let myself get out of reach or visibility
to the touch down point, and keep plenty of energy in case it becomes
clear that I need to make a last second shift to a different touch down
point (and that has happened more than once). Using this approach, I've
never found myself too high or low to land when I commit to final
approach...

Marc

On Oct 21, 12:13 pm, Tim Taylor wrote:
[...] It is purely an academic exercise from a safety
discussion we had about what are the best steps to follow if you are
high on final. I am trying to look at the difference between several
suggested techniques if full spoilers are not enough.


Since I was a participant in the original discussion, I
feel obliged to throw in my $0.02 even though the thread has
been hijacked. Truth in advertising: while I am a CFI-G,
the vast majority of my dual given has been in powered
airplanes.

First, Tim's method works for him and probably for many
other pilots. This does not mean that it works for all
pilots, or even most pilots. By analogy, some maneuvers might
be a piece-of-cake for a proficient aerobatic
pilot (that would not be me) but deadly for others. The
low airspeed drag-it-in kind of approach that some
have advocated for power planes falls into this category.
One of the skills an instructor must bring to the table
is the ability to figure out what approach is best for the student
and teach that.

The aerodynamics of Tim's maneuver - slow down and
get on the "back side" of the polar - mean that the plane
has lost both potential and kinetic energy. The two methods
lose comparable amounts of potential energy, so the loss of
kinetic energy is significant. Loss of kinetic energy
also means loss of maneuverability in all axes, due to
reduced airflow over the control surfaces. So, a glider
that has slowed and hits big sink will take longer to
recover than one with a higher airspeed, due to
reduced elevator effectiveness.

Also, the slower glider is just a few knots above stall, so
a rather small wind shear (headwind-to-tailwind) will
lead to a stall and more loss of altitude. For this reason alone I
would be uncomfortable teaching it to new pilots.

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.

Author: John Smith Date/Time: 17:40 24 October 2007=
First I thought that you were pulling our legs, but it seems you're actuall=
y serious.Every year a couple of pilots die because they are too slow on ap=
proach. Where I fly, a student will fail his checkride big time if he's onl=
y one knot below the yellow triangle on final.=20
=20
-
=20
Whilst I understand your sentiment, I think this is over the top. The yello=
w triangle is best approach speed at all up weight.
For a glider that takes water ballast, this may well be 2-3 knots higher th=
an the best approach speed at dry weight. ie one knot slower than yellow tr=
iangle may be higher than 1.3x stall speed for particular set-up.
=20
I have found out the hard way about too slow approaches. My SLMG best engin=
e speed is 49 knots which is lower than the approach speed of 55 knots. Whe=
n the engine does not start at low level, with wet wings and an uphill land=
ing, you find out that the extra speed is required to enable a flare, and o=
nly incidentally to prevent a stall/spin.
=20
Rory
__________________________________________________ _______________
Celeb spotting =96 Play CelebMashup and win cool prizes
https://www.celebmashup.com=

"5Z" wrote in message
ups.com...

perhaps a 270 degree turn from base to final. But only if the weather
is considered to be benign. I watched an ASW-22BL do this at a fairly
low altitude while going into a fairly short field on a relatively
calm day and it made sense. Due to the ship's low sink rate, the
pilot was able to drop perhaps 100' and also end up slightly farther
away from the touchdown spot.


My gosh, an honestly new idea (at least to me). In my book, that qualifies
as #7. It would not be my first choice, but if you allow yourself get to the
point where your best choices are behind you, the 270 degree turn from base to
final could be the better of several bad options.

Vaughn

Rory O'Conor wrote:

Whilst I understand your sentiment, I think this is over the top. The yello=
w triangle is best approach speed at all up weight.
For a glider that takes water ballast, this may well be 2-3 knots higher th=
an the best approach speed at dry weight. ie one knot slower than yellow tr=
iangle may be higher than 1.3x stall speed for particular set-up.

The point is not the triangle. The point is that the student has to call
out a target speed and then hold that speed. 5 knots more is tolerated,
but 1 knot below is not. Simply not. No way. Period.

Now if the student calls out a target speed lower than the yellow
triangle, the expert will ask him why. If the student can explain, then
it may be ok. On the other hand, if there is a headwind, the student
must compensate for this. Rule of thumb is add 1/2 wind speed. (And
certainly not slower than without wind, as some other hero suggested.)
Again, the expert will ask what wind speed the student estimates and why.

As for water ballast, well, I've yet to see a student who flyes with
ballast on his checkride.

On Oct 22, 7:57 am, wrote: On Oct 21, 11:13 am, T=
im Taylor wrote:[snip] If you are THAT much too high, wouldn't it also be =
prudent to consider a large 360? It may not be pretty, but let's face it, =
if you have
I would join the crowd voting a 360 turn on final, a score of 0/10.
=20
If you are cool about scratching at 400ft AGL then fine, but if you like to=
terminate your thermalling by 800ft AGL then dont consider it. The workloa=
d when turning low down is enormous and you need to be prepared to push the=
nose groundwards against your instincts if the speed shows any sign of ble=
eding off.
=20
Dont do full turns below the height you would be prepared to do them when s=
cratching.
=20
Rory
__________________________________________________ _______________
Celeb spotting =96 Play CelebMashup and win cool prizes
https://www.celebmashup.com=

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

My gosh, an honestly new idea (at least to me). In my book, that qualifies
as #7. It would not be my first choice, but if you allow yourself get to the
point where your best choices are behind you, the 270 degree turn from base to
final could be the better of several bad options.


My choice, given this situation. would be one or more figure 8's with
all turns toward the runway. In a 270, the first third of the turn is
heading away from the runway - not good down low if you hit unexpected sink.

Tony V. "6N"

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.