Polar with spoilers extended?

That's how this whole discussion got started.

What, RAS going around in circles (in sink!) ? Unheard of!

I haven't tried the high parasitic drag maneuver in a duo yet. When
demonstrated by Marty Eiler in an ASK 21, it consisted of a near VNE
dive to the ground well short of the intended landing area, and then
bleeding off the speed quite low. The key is that you lose so much
energy near VNE with spoilers out, you can afford now to bleed off
speed, even in ground effect. Most of our duo discussions have not
invovlved such high speeds -- I'm curious how it might work. I know
that being high, 80 knots and aiming at the spot in a duo is a bad
combination, but that's not what we're taling about!

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. If you don't aim short enough in the dive, you just
crash into the far fence at really high speed. But I'd be curious to
hear a "it worked for me" story.

John Cochrane

On Oct 23, 6:29 pm, Marc Ramsey wrote:
BB wrote:
[snip]
That's how this whole discussion got started. Someone suggested that
the best thing to do when high on final is to dive with full spoilers,
pull up above ground effect and wait for the speed to bleed off. I said
that won't work too well with a Duo, as with full spoilers it isn't all
that draggy, will accelerate relatively quickly, and bleed off speed
slowly. Others said nonsense, the Duo has wonderful spoilers. And so
on, and so on...

Marc

Then why don't you slip it in? The Duo slips quite well.

Darryl


(Sorry Marc I could not resist :-) )

"BB" wrote in message
ups.com...
That's how this whole discussion got started.

What, RAS going around in circles (in sink!) ? Unheard of!

I haven't tried the high parasitic drag maneuver in a duo yet. When
demonstrated by Marty Eiler in an ASK 21, it consisted of a near VNE
dive to the ground well short of the intended landing area, and then
bleeding off the speed quite low. The key is that you lose so much
energy near VNE with spoilers out, you can afford now to bleed off
speed, even in ground effect. Most of our duo discussions have not
invovlved such high speeds -- I'm curious how it might work. I know
that being high, 80 knots and aiming at the spot in a duo is a bad
combination, but that's not what we're taling about!

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. If you don't aim short enough in the dive, you just
crash into the far fence at really high speed. But I'd be curious to
hear a "it worked for me" story.

John Cochrane


I have tried it with my big wing glider and for me the 'high parasite drag'
approach doesn't work unless you shift to a airspeed stabilized approach no
lower than 100 feet AGL.

My reasoning is that the ground effect starts at about a wingspan above the
ground so the bigger the wing the higher it starts. Just above the runway,
ground effect roughly doubles the L/D, (i.e. ~7:1 with full spoilers becomes
14:1) so in ground effect is a bad place to try to scrub off energy.

The key to the Duo spoilers seems to be a stabilized approach. It's a
really slippery glider and it's easy to let the airspeed creep up once your
eyes are on the aim point. In low wind/low turbulence conditions, nailing
the airspeed right on the yellow triangle while holding the glideslope to
the aim point can result in a fairly short landing. You can fly much higher
airspeed in the patern and on long final as long as the airspeed is reduced
to the calculated reference airspeed on short final.

Bill Daniels

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. If you don't aim short enough in the dive, you just
crash into the far fence at really high speed. But I'd be curious to
hear a "it worked for me" story.

In reality, I almost always have too little altitude rather than too
much when I'm trying to sneek into a field. I did use this sort of
technique with my Ventus a couple of times to get over trees and into
short fields, but it had trailing edge dive brakes that would allow me
to hold 60 to 65 knots in a dive, then round out, slow down, and plop it
in. There is no way I could make that work in a Duo, or most other
gliders...

Marc

Back to Tim's original question ---- it appears that the effectiveness of
the high parasite drag (HPD) approach varies depending on the glider. Even
if we don't have the absolute speed polar of a given glider with the
spoilers out, we should be able to figure out a relative measurement that
gives us some idea of a "good" HPD glider vs a "not so good" HPD glider.
It's been about 26 years since my last aero course, but I think I remember
that the term we care about here is wetted area; however you smarter people
please correct me as needed. The measure I propose would be:

Wetted area clean / wetted area with full spoilers, then multiply by the
wing loading. The bigger the number - the less effective the HPD maneuver
in that glider. Maybe we don't even need the wing loading - I'm not
certain, but it would seem reasonable to me that the HPD maneuver would be
progressively less effective with higher wing loadings.

Alright --- ready to be shot full of holes.

Lou McDonald
"LM"





"Tim Taylor" wrote in message
ps.com...
I am working though some calculations and need the sink rate as a
function of speed with the spoilers fully extended. Does anyone know
of such data for a glider? How do spoilers extended affect sink rate
as a function of speed?

Thanks,

Tim

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?

This is where I find teaching some of these other techniques
interesting, but possibly dangerous. The rule of primacy for learning
or as the Doobie Brothers album from the 70's title "What were once
vices are now habits" suggests we will do in an emergency what we have
practiced. Is someone really going to dive a glider to the ground and
pull out to land in a short off field landing? Is there really a need
to be on the ground 10 seconds faster than using some of the other
techniques? Maybe only if a severe thunderstorm is approaching and
you must be on the ground now. I think in general the high parasitic
drag technique being taught by some schools is a hyped method that may
give some less experienced pilots the idea this is a good technique to
use for off-field landings. I think it is time to get back to basics
and teach sound techniques that provide the best tools for pilots to
use day in and day out.

The dive until intercepting normal angle for spoilers has some merit,
but I still think should be used with caution. Why, because we train
to look at landings from a specific angle for a narrow range of
landing speeds. To dive at high speed leaves the aircraft with a much
greater kinetic energy that must still be lost someplace. Depending
on the ship type some may take much longer to dissipate this excess
and make it more difficult to precisely hit a touch down point. Often
the greater sink rate is held up as the reason for using this
technique. It is true that sink rate goes up with speed, but the
actual decent angle does not go up nearly as much. For my Ventus B at
45 knots descent rate is 122 ft/min while at 135 knots it is 894 ft/
min, but actual loss per nautical mile is 163 ft/ktm verses 397 ft/
ktm. The other thing we don't mention is the average pilot going to
handle the decision making process better at higher speeds and less
time? At stable speeds it takes about 11 seconds to lose 300 feet at
135 knots with the spoilers out verses 22 seconds at 45 knots. Do we
need that extra time to make proper judgment and fine adjustments to
hit a target for a tight off-field landing?

Ok, lets try a hypothetical (well maybe not, been there done that ;-)
off-field landing.

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?

Slip?
"S" turns?
Dive until intercepting normal angle for spoilers?
Dive until near the ground, and then decelerate?
Slow down until intercepting normal angle for spoilers?
360 degree turn?

In the real world nearly 15 years ago this was in a 1970 "A" model
Standard Cirrus. If you think the Duo will float try the Standard
Cirrus. What should we be teaching students? You are somewhere
between 11 and 30 seconds from being on the ground and that 100 extra
feet will take you past the whole safe landing area and into the tree
stumps.

Dive until intercepting normal angle for spoilers?

Maybe, but can you dive, lose the altitude, decelerate and get it on
the ground for a tail wheel first, full stall landing? I would give
this a 6 out of 10. This also shortens the time available to make
adjustments and requires rapid and precise decisions.

Dive until near the ground, and then decelerate?

My guess is your chances are slim that you can pull this off and get
the ship stopped. Especially, if you were flying my Std. Cirrus. My
rating is a 1 out of 10.

360 degree turn?

I never like to turn my back on a field. Low and with the winds a
good result is not likely. My rating is a 0 out of 10.

Slow down until intercepting normal angle for spoilers?

This technique is useful for very high approaches, but must be broken
off before 300 feet agl because you must have height to accelerate and
be able to recover from any inadvertent stalls. From about 1000 feet
to 500 feet this technique has the advantage of giving a higher decent
rate and giving the pilot more time to evaluate the situation, but the
pilot must be ready to respond to any sign of stall. My rating is a 0
out of 10 here.

"S" turns?

This might be useful. You are low, but may have time to extend the
your descent. Any turn at this point will require nearly at least 180
degrees of turning (45 away, 90 back and 45 back to final.) and up to
360 degrees with three changes in direction and roll. The advantage
is your speed stays constant and you can see the touchdown point the
whole time. A disadvantages is you are no longer lined up on the
target so your perception changes as you roll and move to the side.
My rating is a 7 out of 10 here.

Slip?

The forward slip can be very effective at bringing "most" ships down.
Check you flight manual of your aircraft and practice at altitude.
The old joke about you could always tell who the Std. Cirrus and
Libelle pilots were because they were slipping on final is true. But
we got very good at it. It would nearly double the sink rate and when
kicked out you were nearly at the correct speed. The Std. Cirrus if
flown even 5 knots too fast would float a long way before settling.
The nice thing about a slip is your speed and angles all stay the same
without speeding up the process. You can use your trained judgment to
say the angle looks about right here and kick out of the slip and
proceed with a normal landing. My rating is a 10 out of 10 here.


Summary
Each situation is different, but I think we should focus on teaching
techniques that are robust and give that average pilot the best
opportunity to have a good outcome in an off-field landing. I know of
very few off-field landings that start at 1000 feet at the end of down
wind. If I have found that much lift on downwind I have cycled the
gear and am climbing out, not landing. Any technique that requires
bleeding speed in ground effect should not be taught as anything other
than a curiosity and never considered for off-filed landings.

On Oct 23, 3:12 pm, Nyal Williams
A fully locked rudder slip won't allow much opposite aileron before it starts to turn off course.

Was that comment related to a specific type or was it a general
comment on characteristics of all gliders?

Specific to the ASW-19B (that I owned and with the CG I flew it at) -
I could sustain a stable slip with full airbrakes, gear down, with
the rudder on the stop and the stick hard in the opposite corner. I
practiced this at the start of every season and it saved a couple of
very tight off airport landings for me.

Andy

On Oct 21, 12:23 am, Tim Taylor wrote:
I am working though some calculations and need the sink rate as a
function of speed with the spoilers fully extended. Does anyone know
of such data for a glider? How do spoilers extended affect sink rate
as a function of speed?

I have one data point for the ASW 19B. Gear down, full airbrake, IAS
90kts, sink 3,300fpm. Flight data 4/20/91 EW barograph.


Andy

On Oct 24, 5:36 am, 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?

This is where I find teaching some of these other techniques
interesting, but possibly dangerous. The rule of primacy for learning
or as the Doobie Brothers album from the 70's title "What were once
vices are now habits" suggests we will do in an emergency what we have
practiced. Is someone really going to dive a glider to the ground and
pull out to land in a short off field landing? Is there really a need
to be on the ground 10 seconds faster than using some of the other
techniques? Maybe only if a severe thunderstorm is approaching and
you must be on the ground now. I think in general the high parasitic
drag technique being taught by some schools is a hyped method that may
give some less experienced pilots the idea this is a good technique to
use for off-field landings. I think it is time to get back to basics
and teach sound techniques that provide the best tools for pilots to
use day in and day out.

The dive until intercepting normal angle for spoilers has some merit,
but I still think should be used with caution. Why, because we train
to look at landings from a specific angle for a narrow range of
landing speeds. To dive at high speed leaves the aircraft with a much
greater kinetic energy that must still be lost someplace. Depending
on the ship type some may take much longer to dissipate this excess
and make it more difficult to precisely hit a touch down point. Often
the greater sink rate is held up as the reason for using this
technique. It is true that sink rate goes up with speed, but the
actual decent angle does not go up nearly as much. For my Ventus B at
45 knots descent rate is 122 ft/min while at 135 knots it is 894 ft/
min, but actual loss per nautical mile is 163 ft/ktm verses 397 ft/
ktm. The other thing we don't mention is the average pilot going to
handle the decision making process better at higher speeds and less
time? At stable speeds it takes about 11 seconds to lose 300 feet at
135 knots with the spoilers out verses 22 seconds at 45 knots. Do we
need that extra time to make proper judgment and fine adjustments to
hit a target for a tight off-field landing?

Ok, lets try a hypothetical (well maybe not, been there done that ;-)
off-field landing.

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?

Slip?
"S" turns?
Dive until intercepting normal angle for spoilers?
Dive until near the ground, and then decelerate?
Slow down until intercepting normal angle for spoilers?
360 degree turn?

In the real world nearly 15 years ago this was in a 1970 "A" model
Standard Cirrus. If you think the Duo will float try the Standard
Cirrus. What should we be teaching students? You are somewhere
between 11 and 30 seconds from being on the ground and that 100 extra
feet will take you past the whole safe landing area and into the tree
stumps.

Dive until intercepting normal angle for spoilers?

Maybe, but can you dive, lose the altitude, decelerate and get it on
the ground for a tail wheel first, full stall landing? I would give
this a 6 out of 10. This also shortens the time available to make
adjustments and requires rapid and precise decisions.

Dive until near the ground, and then decelerate?

My guess is your chances are slim that you can pull this off and get
the ship stopped. Especially, if you were flying my Std. Cirrus. My
rating is a 1 out of 10.

360 degree turn?

I never like to turn my back on a field. Low and with the winds a
good result is not likely. My rating is a 0 out of 10.

Slow down until intercepting normal angle for spoilers?

This technique is useful for very high approaches, but must be broken
off before 300 feet agl because you must have height to accelerate and
be able to recover from any inadvertent stalls. From about 1000 feet
to 500 feet this technique has the advantage of giving a higher decent
rate and giving the pilot more time to evaluate the situation, but the
pilot must be ready to respond to any sign of stall. My rating is a 0
out of 10 here.

"S" turns?

This might be useful. You are low, but may have time to extend the
your descent. Any turn at this point will require nearly at least 180
degrees of turning (45 away, 90 back and 45 back to final.) and up to
360 degrees with three changes in direction and roll. The advantage
is your speed stays constant and you can see the touchdown point the
whole time. A disadvantages is you are no longer lined up on the
target so your perception changes as you roll and move to the side.
My rating is a 7 out of 10 here.

Slip?

The forward slip can be very effective at bringing "most" ships down.
Check you flight manual of your aircraft and practice at altitude.
The old joke about you could always tell who the Std. Cirrus and
Libelle pilots were because they were slipping on final is true. But
we got very good at it. It would nearly double the sink rate and when
kicked out you were nearly at the correct speed. The Std. Cirrus if
flown even 5 knots too fast would float a long way before settling.
The nice thing about a slip is your speed and angles all stay the same
without speeding up the process. You can use your trained judgment to
say the angle looks about right here and kick out of the slip and
proceed with a normal landing. My rating is a 10 out of 10 here.

Summary
Each situation is different, but I think we should focus on teaching
techniques that are robust and give that average pilot the best
opportunity to have a good outcome in an off-field landing. I know of
very few off-field landings that start at 1000 feet at the end of down
wind. If I have found that much lift on downwind I have cycled the
gear and am climbing out, not landing. Any technique that requires
bleeding speed in ground effect should not be taught as anything other
than a curiosity and never considered for off-filed landings.

Great summary Tim !

To further your point on training: One thing we need to do in
training is demonstrate the effect of flying the final too fast.
Back-to-back pattern flights with different final speeds and
the same aim point really help pilots internalize this.
Especially for transition pilots (Cirrus, 1-35 come to mind),
practicing this on an appropriately long runway brings
religion to pattern energy management like no amount
of briefing...

Be careful out there,
Best Regards, Dave "YO"

On Oct 24, 7:09 am, wrote:
Great summary Tim !

I agree.

A quick response to the above choices would be based on how much too
high I was. And Tim's list is pretty much in the correct order:

1. Slip
2. "S" turns
The first one likely being an overshoot of the turn to final, then a
120-180 back toward the runway, repeat if necessary, then line up on
the runway.

3. Dive until intercepting normal angle for spoilers
4. Dive until near the ground, then decelerate
Not sure if I like this one... I think #3 is the proper way to do
it. Though, if one is REALLY high, then the proper angle for 'normal'
final would be pretty close to the ground. I would be in this
situation if there are strong winds and chance of downbursts (been
there, done that). Turn final way high expecting the 40+ headwind to
be there (perhaps downburst since the storm is nearby), but instead
the wind quits! In my ASW-20B, I just did a full flap, full spoiler
slip with the nose way below the horizon, so it really was a diving
slip - remember I was WAAAY high. Ended up stopping at my intended
spot even though there was a slight 2-3 knot tailwind.

5. Slow down until intercepting normal angle for spoilers
Perhaps

6. 360 degree turn
Actually, I doubt one would be on final when this decision is made, so
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.

-Tom