Two proposals to explore Dynamic Soaring

Dynamic soaring works only when the glider is passing through a path of
changing wind velocity. In this way the glider can gain or loose
energy independent of it's own kinetic and potential energy (as in a
shear or wind gradient). For example on final approach into a 15 knot
headwind, we increase our approach speed because we know as we descend
through the wind shear, we will loose airspeed (energy) and might have
to put the nose down (giving up our potential energy to get kinetic) to
keep the glider flying. Indeed, if we think we are going to be short,
we "dive under the wind" and then bleed off our speed in the weaker
headwind closer to the ground. This is Dynamic soaring that we all
have done.

In order to continuously extract energy from wind gradients or shears
in a closed loop path, our upwind path must be different than our
downwind. For example, of the Albatross was able to "hang a 180"
and fly back along the exact same path to it's starting point, it
would loose exactly the same amount of energy it had gained. It claims
it's free energy from "the area inside the loop" of it's flight
path that contains a gradient.

From a practical perspective, wind gradients are hard to see/feel
unless we have some topology like the ground or a hill for reference,
and even then we are only inferring the boundaries and makeup of the
shear, rather than measuring it directly like airspeed. So even if the
theory works, how do we practice? for example, no matter how sensitive
our backside may be, finding and centering lift is a whole lot harder
without a vario.

Proposal #1
As pilots that want to take advantage of dynamic soaring, we need an
instrument that can measure the rate at which the glider is gaining or
loosing energy independent of the normal Newtonian exchanges of
kinetic, potential and frictional (drag) forces. Such an instrument
could be created based on predicted v.s. actual airspeed. It is
possible to accurately model the dynamic flight parameters of a given
glider such as velocity, rate of sink, angle of attack, etc. in still
air. If we pull back on the stick, increasing the angle of attack by 2
degrees, we can predict what the airspeed will be in 1 second, 5
seconds, 20 seconds, etc.

Now imagine we pull up into a wind shear. Two seconds later, our
airspeed is actually three knots higher than our model predicts. We
are gaining energy! The needle (and tone) in our new instrument starts
to rise. If the airspeed was five knots higher, the needle (tone)
would rise even further. It shows us the rate of energy absorption
through airspeed. Similarly it would show loss, just like a vario.

Of course we could locate convergence lines with this instrument as
well. Who knows, we might even get thermal information from the
ability to detect horizontal gusts.

Proposal #2
While it is possible to design and build this new instrument, and just
how to do it will make an interesting discussion in itself, it will
take some time to perfect it and get it into production. In the mean
time, we want to learn how to use it before we have it. Just like the
albatross has several different techniques for taking advantage of the
same surface shear conditions, there are probably many new ways that
have not been discovered at "full" scale to soar dynamically. What
is the best way to fly in wind gradients that run side to side, rather
than top to bottom? What is the best way to dynamically soar
orthogonal to the wind direction?

While our instrument is difficult to build in the real world, it's a
snap to create in a flight simulator where the glider is already fully
modeled. Lets build a virtual instrument and experiment by flying in
virtual shear using one of the excellent glider flight simulators on
the market. Anyone have an in with the programmers?

Food for a winter discussion,

Matt Herron (jr)

Matt Herron Jr. wrote:

Of course we could locate convergence lines with this instrument as
well. Who knows, we might even get thermal information from the
ability to detect horizontal gusts.

You might already have the instrument you desire. Our total-energy
compensated varios already detect horizontal gusts. In thermal flying,
the trick is to determine the difference between those and air going
vertically. So, I think you ought to proceed immediately to proposal #2.
Perhaps there are simulators with good modeling of a glider's dynamic
flight and allow airflows to be simulated. I suspect you are right, that
it will be much easier to learn on a simulator than in actual flight!
Later, perhaps the instrument characteristics needed will be more
evident, and one could be built.


Proposal #2
While it is possible to design and build this new instrument, and just
how to do it will make an interesting discussion in itself, it will
take some time to perfect it and get it into production. In the mean
time, we want to learn how to use it before we have it. Just like the
albatross has several different techniques for taking advantage of the
same surface shear conditions, there are probably many new ways that
have not been discovered at "full" scale to soar dynamically. What
is the best way to fly in wind gradients that run side to side, rather
than top to bottom? What is the best way to dynamically soar
orthogonal to the wind direction?

While our instrument is difficult to build in the real world, it's a
snap to create in a flight simulator where the glider is already fully
modeled. Lets build a virtual instrument and experiment by flying in
virtual shear using one of the excellent glider flight simulators on
the market. Anyone have an in with the programmers?

I suspect a practical problem will be finding shear large enough for the
typical glider. Birds do it, model airplanes do it, maybe a microlight
glider can do it, but these all turn quite sharply compared to our 15 m
and up gliders.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Actually, the desired instrument is the "MEMS Inertial Variometer" currently
under development by al least one European group. Total energy variometry
in the inertial domain needs no air data and so displays the rate of energy
gain or loss without gust sensitivity. It might be interesting or even
useful to display the difference between this and an air data based TE vario
but the inertial TE vario would give the needed data.

Bill Daniels


"Eric Greenwell" wrote in message
news:uDcsh.693$Kf.554@trndny07...
Matt Herron Jr. wrote:

Of course we could locate convergence lines with this instrument as
well. Who knows, we might even get thermal information from the
ability to detect horizontal gusts.

You might already have the instrument you desire. Our total-energy
compensated varios already detect horizontal gusts. In thermal flying, the
trick is to determine the difference between those and air going
vertically. So, I think you ought to proceed immediately to proposal #2.
Perhaps there are simulators with good modeling of a glider's dynamic
flight and allow airflows to be simulated. I suspect you are right, that
it will be much easier to learn on a simulator than in actual flight!
Later, perhaps the instrument characteristics needed will be more evident,
and one could be built.


Proposal #2
While it is possible to design and build this new instrument, and just
how to do it will make an interesting discussion in itself, it will
take some time to perfect it and get it into production. In the mean
time, we want to learn how to use it before we have it. Just like the
albatross has several different techniques for taking advantage of the
same surface shear conditions, there are probably many new ways that
have not been discovered at "full" scale to soar dynamically. What
is the best way to fly in wind gradients that run side to side, rather
than top to bottom? What is the best way to dynamically soar
orthogonal to the wind direction?

While our instrument is difficult to build in the real world, it's a
snap to create in a flight simulator where the glider is already fully
modeled. Lets build a virtual instrument and experiment by flying in
virtual shear using one of the excellent glider flight simulators on
the market. Anyone have an in with the programmers?

I suspect a practical problem will be finding shear large enough for the
typical glider. Birds do it, model airplanes do it, maybe a microlight
glider can do it, but these all turn quite sharply compared to our 15 m
and up gliders.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

OK,

So I tried Dynamic Soaring using a flight simulator and it works! I
used X-Plane on a mac, and a Fox glider as it has a large working range
for speed. I set up a wind gradiant that was stil air from the ground
to 5000 feet, and then 30 knots/1000 feet above that. So at 7000 feet
there was a 60 kt wind from the North. Not very realistic, but I just
wanted to see if it would work.

Starting at 7000 ft I dove steeply strait downwind until I hit about
200 kts at 5500 ft. then I banked sharply into the wind and was doing
about 220 kts at 5000 (where there was no wind). I then immediately
climbed steeply until I was down to 100 kts at which point I did a
climbing turn to the right and ended up pointed downwind, leveled off
at 80 knots. But this time I was at 7500 feet! I had gained 500 ft in
one hairly circle. However I had drifted downwind from my original
starting point. I repeated this routine and quickly climbed to 11000
feet, always diving about 2000 feet below my starting altitude. As I
climbed my average headwind was increasing, and so I was drifting
downwind faster and faster.

In the next test I wanted to see if I could maintain my upwind position
rather than drifting downwind. I started the same way, diving
downwind from 7000 ft and banking sharply to end up at 5000 ft (where
the headwind was zero) heading upwind. This time I held it level for a
while to make some upwind progress without a headwind. When my speed
dropped to 200 kts, I pulled up sharply and climbed, made my climbing
turn at 100 kts and ended up at about the same altitude and location as
I had started doing 80. I know this because X-Plane can leave a wire
flightpath trail in 3D. I was able to repeat this circuit many times,
maintaining my altitude and holding my position into an average 30 kt
headwind. X-Plane can also display wind vectors in the air, handy for
orienting myself in flight. One can imagine if I turned left at the
bottom instead of right I could make crosswind progress without loosing
altitude or drifting downwind as well.

In the next test, I tried dolphining into the wind without turning. I
dove steeply, and climbed more slowly. While I obviously made progres
upwind, I was unable to maintain my altitude and soon droped out of the
bottom of the shear at 5000 ft.

Finally, I tried looping into the wind. I wasn't able to make this
work, but I suspect it was because my flying sucked and I usually ended
up stalling at the top of the loop. I imagine you would need a fairly
sharp pullover when vertical, and then a sharp pullout when heading
strait down, but I haven't proven it yet.

The next test will be to see how weak I can make the shear before I
can't maintain my altitude (while drifting downwind). I would also
like to try a horizontal shear with the headwind being stronger to the
right and weaker to the left. Plain old flat circles between these
areas would probably work, and you might even gain altitude if you
pulled up on one side of the turn. this type of shear might arrise
downwind, and at the edge of a ridge, etc. Unfortunately X-Plane can't
model this. It would also be interesting to fly behind the vertical
shear created by an obsticle, but X-Plane can't model this either.

I would be interested to see if anyone else could confirm these
experiments, or try them with a different simulator. I will also see
if I can take a movie of the sim and post it.

Cheers,

Matt

Ingo Renner accomplished dynamic soaring in Australia in the 80's using a
ballasted open class glider. He towed above an inversion in which a few
hundred feet separated still air from strong winds. He was able to make some
upwind progress using the dive downwind turn and pull up into the wind, the
same way albatrosses fly.

Karl Striedieck


"Matt Herron Jr." wrote in message
oups.com...
OK,

So I tried Dynamic Soaring using a flight simulator and it works! I
used X-Plane on a mac, and a Fox glider as it has a large working range
for speed. I set up a wind gradiant that was stil air from the ground
to 5000 feet, and then 30 knots/1000 feet above that. So at 7000 feet
there was a 60 kt wind from the North. Not very realistic, but I just
wanted to see if it would work.

Starting at 7000 ft I dove steeply strait downwind until I hit about
200 kts at 5500 ft. then I banked sharply into the wind and was doing
about 220 kts at 5000 (where there was no wind). I then immediately
climbed steeply until I was down to 100 kts at which point I did a
climbing turn to the right and ended up pointed downwind, leveled off
at 80 knots. But this time I was at 7500 feet! I had gained 500 ft in
one hairly circle. However I had drifted downwind from my original
starting point. I repeated this routine and quickly climbed to 11000
feet, always diving about 2000 feet below my starting altitude. As I
climbed my average headwind was increasing, and so I was drifting
downwind faster and faster.

In the next test I wanted to see if I could maintain my upwind position
rather than drifting downwind. I started the same way, diving
downwind from 7000 ft and banking sharply to end up at 5000 ft (where
the headwind was zero) heading upwind. This time I held it level for a
while to make some upwind progress without a headwind. When my speed
dropped to 200 kts, I pulled up sharply and climbed, made my climbing
turn at 100 kts and ended up at about the same altitude and location as
I had started doing 80. I know this because X-Plane can leave a wire
flightpath trail in 3D. I was able to repeat this circuit many times,
maintaining my altitude and holding my position into an average 30 kt
headwind. X-Plane can also display wind vectors in the air, handy for
orienting myself in flight. One can imagine if I turned left at the
bottom instead of right I could make crosswind progress without loosing
altitude or drifting downwind as well.

In the next test, I tried dolphining into the wind without turning. I
dove steeply, and climbed more slowly. While I obviously made progres
upwind, I was unable to maintain my altitude and soon droped out of the
bottom of the shear at 5000 ft.

Finally, I tried looping into the wind. I wasn't able to make this
work, but I suspect it was because my flying sucked and I usually ended
up stalling at the top of the loop. I imagine you would need a fairly
sharp pullover when vertical, and then a sharp pullout when heading
strait down, but I haven't proven it yet.

The next test will be to see how weak I can make the shear before I
can't maintain my altitude (while drifting downwind). I would also
like to try a horizontal shear with the headwind being stronger to the
right and weaker to the left. Plain old flat circles between these
areas would probably work, and you might even gain altitude if you
pulled up on one side of the turn. this type of shear might arrise
downwind, and at the edge of a ridge, etc. Unfortunately X-Plane can't
model this. It would also be interesting to fly behind the vertical
shear created by an obsticle, but X-Plane can't model this either.

I would be interested to see if anyone else could confirm these
experiments, or try them with a different simulator. I will also see
if I can take a movie of the sim and post it.

Cheers,

Matt

The theoretical analyses of this sort of thing I've read point to
somewhat different maneuvers.

First, you don't really want to slow down. The only reason for slowing
down is to expoit a vertical wind shear. If the shear were discrete,
i.e. 30 kts above 1000' and 0 below, then you wouldn't slow down much
at all: you'd do the into wind turn at 1001 feet, 100 kts, and the
downwind turn at 999 feet, 99 kts. You would not pull way back and go
up to 1500 feet at 40 kts.

You gain more energy the faster you're going. Think of a tennis ball
gaining energy by being swatted back and forth between two rackets.
That's what we're doing here. You gain more energy the more massive the
ball, and the faster it goes.

In "real life" the shear is not so discrete. So there's a tradeoff: the
higher you go, the greater the wind difference, but the less energy you
gain since you're going slower. The optimum is not, though, to rise up
to near stall and then dive down. The upwind turn should still be a
high speed, high bank, high g affair.

Second, circles are not optimal. The model airplanes we've seen do this
because they need to stay near the guy with the transmitter. The
optimal path changes course as little as possible. It's more efficient
to do S turns, ideally in a heavily ballasted glider going pretty fast.


Where might we actually use this in real life? My winter day dreaming
has me trying to make an upwind transition on a ridge day, realizing
I'm not going to make it, and then turning sideways, dynamic soaring in
the lee of the upwind ridge, doing S turns parallel to the ridge but
slowly moving upwind, until I gain enough energy to clear the top of
the ridge. We know model airplanes can dynamic soar in the lee of
ridges; we need to find out if the shear is strong enough and well
enough defined a mile or so downwind of the ridge to make this useful
for sailplanes.

If someone gets motivated to try it this winter, let us know. Matt: how
about programming something like this in the simulator, and let's see
if you can pick up enough energy in a 15-20 kt shear over say 500
vertical feet to make progress upwind?

John Cochrane BB

I will give the 500 ft/ 15-20 kt shear a try. Since the speed range
won't be as high, I will try using a more conventional glass ship like
the ASW27. I like your scenario for cresting a ridge. Clearly DS can
work at full scale as pointed out by karl and others under certain
conditions. We need to see if can work in more common conditions in
order for it to be actually practical. Otherwise is stays in the
category of the exotic, like thermalling in steam geysers, etc.

One other scenario that might be practical is trying to make it home
late in the day when the wind is up and the thermals have died or been
broken up. One might use DS to fly perpendicular to the wind without
loosing altitude to get to the field.

Matt.

One other scenario that might be practical is trying to make it home
late in the day when the wind is up and the thermals have died or been
broken up. One might use DS to fly perpendicular to the wind without
loosing altitude to get to the field.

Matt.

I've thought of this one a bit too. It's most likely to work pretty
late, when the atmosphere has decoupled, i.e. the ground is cooling
fast. The biggest problem for me at least is that you'd need a vast
area of very landable terrain!

John Cochrane