SoLong Solar-Electric UAV 48 hour flight

On 19 Oct 2005 20:47:6 -0500, "Ash Wyllie" wrote in
::

Larry Dighera opined

I ran across this flight earlier. there is less here than meets the eye. During
the day the pilots, all of whom are experienced RC glider pilots, used thermals
so all the solar power collected could be used to charge the batteries for the
night time.

Where did you get that bit of information?

If the aircraft had had to circle over the same spot, the flight would have
been much shorter.

Agreed, if atmospheric convective lift was indeed used to sustain the
aircraft during daylight hours. While it's still solar power, but not
photovoltaic, it would not be of practical use for sustaining the
aircraft indefinitely.

Solar cell efficiency and battery storage density need to at least double before
true stay aloft forever is going to happen.

How did you calculate that factor?

Triple-Junction Gallium Arsenide solar cells with efficiencies of
about 31% under terrestrial conditions are the most efficient of which
I am awa

http://www.boeing.com/news/releases/...r_030725s.html

HIGH-EFFICIENCY SOLAR CELLS
July 25, 2003
News Release
A Spectrolab, Inc. associate places wafers on platters for epitaxial
growth. The wafers are then fabricated into solar cells that will be
capable of an unprecedented 36.9 percent efficiency in converting
sunlight to energy when exposed to concentrated sunlight. Spectrolab,
a Boeing subsidiary, uses these state-of-the-art photovoltaic solar
cells in concentrator modules of various sizes and power-generating
capabilities. Several modules are already being tested throughout the
world by photovoltaic concentrator system manufacturers. These
Spectrolab products could be part of terrestrial systems that
dramatically reduce the cost of generating electricity from solar
energy.

Contact:
Spectrolab, Inc.
Public Relations Department
P.O. Box 92919 (S10/S323)
Los Angeles, CA 90009
Public Relations (310) 364-6363
www.boeing.com/satellite
http://www.spectrolab.com/

Triple-Junction with a minimum average efficiency of 26.5%) developed
and manufactured at Spectrolab. Ultra-Triple-Junction solar cells,
with a minimum average efficiency of 28.3%, are now in production

http://www.spectrolab.com/stores/
Spectrolab has a variety of solar cells in inventory and available in
limited quantities. Some of these solar cells are rejects from the
production line, others are surplus material from space programs. All
are limited to small batches and sold on a first-come first-serve
basis.

Improved Triple-Junction Gallium Arsenide with efficiencies of about
26.8% (AM0) or about 31% under terrestrial conditions.


Some of these solar cells are in excellent condition while others are
functionally limited to a certain type of application. Call Mike
Kalachian at (818) 898-7540 or send an e-mail to: Mike Kalachian to
inquire about what is currently available.


If you are ready to place an order, please download the appropriate
form, fill it out appropriately and fax it to Mr. Kalachian's
attention at: (818) 361-5102

The era of silent, zero emission flight is upon us. Never run out of
fuel again.


http://www.acpropulsion.com/whats_new.htm
AC Propulsion SoLong UAV Flies for 48 Hours on Sunlight
Two Nights Aloft Opens New Era of Sustainable Flight
[...]

Larry Dighera opined

On 19 Oct 2005 20:47:6 -0500, "Ash Wyllie" wrote in
::

Larry Dighera opined

I ran across this flight earlier. there is less here than meets the eye.
During the day the pilots, all of whom are experienced RC glider pilots,
used thermals so all the solar power collected could be used to charge the
batteries for the night time.

Where did you get that bit of information?

Aviation Wek and Space Technologies, IIRC. I probably didn't keep that issue.

If the aircraft had had to circle over the same spot, the flight would have
been much shorter.

Agreed, if atmospheric convective lift was indeed used to sustain the
aircraft during daylight hours. While it's still solar power, but not
photovoltaic, it would not be of practical use for sustaining the
aircraft indefinitely.

Solar cell efficiency and battery storage density need to at least double
before true stay aloft forever is going to happen.

How did you calculate that factor?

It was in the article.

Triple-Junction Gallium Arsenide solar cells with efficiencies of
about 31% under terrestrial conditions are the most efficient of which
I am awa

http://www.boeing.com/news/releases/...r_030725s.html

HIGH-EFFICIENCY SOLAR CELLS
July 25, 2003
News Release
A Spectrolab, Inc. associate places wafers on platters for epitaxial
growth. The wafers are then fabricated into solar cells that will be
capable of an unprecedented 36.9 percent efficiency in converting
sunlight to energy when exposed to concentrated sunlight. Spectrolab,
a Boeing subsidiary, uses these state-of-the-art photovoltaic solar
cells in concentrator modules of various sizes and power-generating
capabilities. Several modules are already being tested throughout the
world by photovoltaic concentrator system manufacturers. These
Spectrolab products could be part of terrestrial systems that
dramatically reduce the cost of generating electricity from solar
energy.

Contact:
Spectrolab, Inc.
Public Relations Department
P.O. Box 92919 (S10/S323)
Los Angeles, CA 90009
Public Relations (310) 364-6363
www.boeing.com/satellite
http://www.spectrolab.com/

Triple-Junction with a minimum average efficiency of 26.5%) developed
and manufactured at Spectrolab. Ultra-Triple-Junction solar cells,
with a minimum average efficiency of 28.3%, are now in production

http://www.spectrolab.com/stores/
Spectrolab has a variety of solar cells in inventory and available in
limited quantities. Some of these solar cells are rejects from the
production line, others are surplus material from space programs. All
are limited to small batches and sold on a first-come first-serve
basis.

Improved Triple-Junction Gallium Arsenide with efficiencies of about
26.8% (AM0) or about 31% under terrestrial conditions.


Some of these solar cells are in excellent condition while others are
functionally limited to a certain type of application. Call Mike
Kalachian at (818) 898-7540 or send an e-mail to: Mike Kalachian to
inquire about what is currently available.


If you are ready to place an order, please download the appropriate
form, fill it out appropriately and fax it to Mr. Kalachian's
attention at: (818) 361-5102

Weight and flexibility arealso important as well.

It's not that the goal is impossible, just a little bit off.

The era of silent, zero emission flight is upon us. Never run out of
fuel again.


http://www.acpropulsion.com/whats_new.htm
AC Propulsion SoLong UAV Flies for 48 Hours on Sunlight
Two Nights Aloft Opens New Era of Sustainable Flight
[...]


-ash
Cthulhu in 2005!
Why wait for nature?

On 20 Oct 2005 15:46:26 -0500, "Ash Wyllie" wrote in
::


Larry Dighera opined

On 19 Oct 2005 20:47:6 -0500, "Ash Wyllie" wrote in
::

Larry Dighera opined

I ran across this flight earlier. there is less here than meets the eye.
During the day the pilots, all of whom are experienced RC glider pilots,
used thermals so all the solar power collected could be used to charge the
batteries for the night time.

Where did you get that bit of information?

Aviation Wek and Space Technologies, IIRC. I probably didn't keep that issue.

Thanks for the pointer. There is a lot more information in that
article:

http://www.aviationweek.com/avnow/se...2F06275p01.xml
SoLong Solar-Powered Drone Stays Aloft for 48 Hr.
By Michael A. Dornheim
06/26/2005 03:05:12 PM


PERPETUAL MOTION

People have long dreamed of perpetual flight, and the tipping point
was reached earlier this month when a solar-powered drone stayed aloft
for 48 hr.

It showed that enough energy could be stored during the day to fly the
aircraft at night, for at least several days. All that's needed are
small, near-term improvements in technology to tip this feat into
flights lasting reliably for months.

One application, albeit much harder, would be as a radio tower in the
sky, giving line-of-sight access across a city.

AC Propulsion, a small research company in San Dimas, Calif., made the
flight after several years of dedicated effort by its founder, Alan G.
Cocconi. Semi-perpetual flight has been sought after for years, most
notably by AeroVironment and its solar-powered Helios drone with fuel
cell storage (AW&ST Feb. 28, 2000, p. 58). More recently the company
has been working on a pure fuel cell week-long flier (see p. 52).

But AC Propulsion used lithium-ion laptop computer batteries for
storage instead of fuel cells, as well as an overall simpler approach,
to become the first to fly through two full nights under solar power
(AW&ST Sept. 15, 2003, p. 66). It's a friendly rivalry, as Cocconi has
been an important collaborator on several AeroVironment projects.

The aircraft is called SoLong and is a powered sailplane of Cocconi's
own design with solar cells built into the wing. It weighs 28.2 lb.,
has a 15.6-ft. span, and takes off with its own 1-hp. motor from a
wheeled dolly. The control system includes a sophisticated autopilot
with inertial, barometric and GPS references; a television camera
gives an over-the-nose pilot's-eye view. It's easy to dismiss the
project due to the small size of the aircraft and the 5 X 8-ft. ground
station, but the flight system is equal to those many times larger.

Still, Cocconi is quick to point out the limitations of the
achievement. There was no mission flexibility. The six skilled glider
pilots were focused only on soaring to keep the motor off most of the
day in order to put more solar power into the battery. No payload was
carried, though the TV camera is good for simple reconnaissance. A
mostly cloud-free sky on a long summer day and reasonable weather were
required.

But the flight probably could have lasted a third night, and perhaps a
fourth and a fifth. Cocconi landed after 48 hr. 16 min. because the
pilots were exhausted, not because the battery was low on juice. The
flight started at 4:08 p.m. PDT June 1 with a charged battery; two
days later at that time, the charge was down less than 5%. The landing
was made at 4:24 p.m. at the Desert Center airport operating base in
southeastern California.

SoLong is reasonably tough. It has been flown in 30-mph. winds and
desert turbulence, and has landed at night with the aid of a pair of
1/2-watt LED "landing lights" in the wing and a set of $2 runway edge
lights. The aircraft has flown more than 250 hr. in 60+ flights
without being seriously damaged--not bad for a drone.

AC Propulsion's multiday flight effort was self-funded and hence less
ambitious than AeroVironment's, which was covered by
multimillion-dollar contracts from NASA. Helios performance was
challenging because it operated in the thin air at 50,000 ft., where
more power is needed to loiter because of the high true airspeeds. The
benefits of that altitude are that it is above the clouds and the
winds are fairly low. Cocconi has an easier job loitering near sea
level, though his drone has to be stronger to withstand the frequent
turbulence there. Helios could carry some payload, and SoLong hasn't.
Helios' regenerative fuel cells were a major headache, and
AeroVironment and its contractors were not able to make them work.
SoLong's battery has less energy per pound--but it works. Helios was
destroyed in a crash in June 2003 (AW&ST Sept. 27, 2004, p. 59).

Rather than trying to do everything at once, Cocconi decided to focus
on the simplest path to multi-day flight, then build from there. He
estimates he spent $20,000-30,000 developing SoLong during a two-year
period, the majority of it full-time.

Key parameters for endurance are the energy density of the batteries,
the efficiency of the solar cells, and other efficiencies such as
round-trip battery storage and motor economy at loiter thrust. These
are on top of the usual parameters like lift-to-drag ratio, structural
weight and propeller efficiency.

Technology is improving in two key areas--the solar cells and the
batteries. Cocconi made the first 24-hr. flight here with SoLong on
Apr. 21-22, comprising two half-nights (AW&ST May 2, p. 19). The
100-cell, 800 watt-hr. battery was not quite big enough for a full
night and could not absorb all the day's solar energy. It used LG Chem
18650-size lithium-ion laptop cells storing 185 watt-hr. per kilogram.
In late May, Cocconi received Sanyo 18650 cells that could hold 214
watt-hr./kg., a 15% improvement. That, and increasing the battery to
120 cells, tipped performance to the current edge of being barely
capable of multi-day flights. The pace of battery improvement has
indeed been rapid.

SoLong is now fitted with Sunpower A300 single-crystal silicon solar
cells about 20% efficient. Each wing has a series string of 38 cells
and they cover a total of about 13 sq. ft. producing a nominal 225
watts. They weigh about 2.3 lb. Bending the thin silicon cells to fit
the wing contour is tricky and Cocconi has devised techniques to avoid
breaking them. "It's like bending a 5-in. square of microscope slide
glass," he says.

Right now, 28% efficient space-grade cells are available, making 40%
more power, but cost about 100 times as much. Covering the wing with
them would cost about $150,000, Cocconi says. But that boost in power,
along with the next generation of laptop batteries, would make SoLong
a no-brainer multi-day airplane with no glider soaring required. Solar
cell prices can only go down, and the reality of this craft is close.

SoLong was recently modified to include a variable-pitch propeller,
and inflight tuning has gained about 10% propeller efficiency. A load
cell in the motor mounts, cannibalized from a postal scale, sends
real-time thrust readings back to the ground. Pitch is automatically
scheduled in flight but can be manually tweaked. The 23-in. prop folds
back when not in use.

An important factor is to maintain motor efficiency when operating at
low loiter power settings. Maximum input is 800 watts for 1-hp.
output, but minimum loiter is 95 watts. Cocconi built a special
nine-phase motor controller that is 88% efficient at loiter power,
including motor geartrain losses, instead of a typical 70-75%.

The hollow wings are ribless with stiff sandwich skins to hold the
airfoil shape. The solar cells are under the fiberglass outer skin.
The fuselage is made of Kevlar and carbon-fiber composites.

The lift-to-drag ratio is roughly 20, and the loiter speed is about 28
mph., or 2-3 mph. above stall speed. The autopilot can fly a constant
lift coefficient to ease operating on the edge of stall. The ground
station plots areas of rising and falling air from telemetry, giving a
map to assist the pilots. On the first day, they were aggressively
hand-flying to seek the best air; but when they tired on the second
day, they would usually tell the autopilot to orbit a GPS waypoint at
a defined radius in a good area. The second night was more turbulent
and difficult than the first.

An ingenious barometric roll sensor picks up static pressures near
both wingtips and calculates the bank angle by measuring the flow due
to differential pressure between the wingtips. Running the autopilot,
flight controls, strobe lights and 5-mi.-range, 23-channel telemetry
and TV transmitter takes only 7 watts.

Cocconi would like to build a larger aircraft that can fly higher, but
both those objectives would make the job more difficult and require
bigger improvements in solar cell efficiency, battery energy density
and lightweight structure. And that would make him face more of the
problems that were tackled by Helios.

Energy Budget Per Day

(June 1-3 at 33.75 deg. N. Lat.)

(estimated by Aviation Week & Space Technology)

BATTERY CHARGING
(approx. 9 a.m. to 7 p.m. 10 hr.)
Solar power in 1.55 kw.-hr.
used to charge battery 1.1-1.2 kw.-hr.
used for housekeeping(7 watts X 10 hr.) 0.07 kw.-hr.
used for motor (95 watts X ~4 hr.) 0.38 kw.-hr.

BATTERY DISCHARGING
(approx. 7 p.m. to 9 a.m. 14 hr.)
Available in battery 1.2 kw.-hr.
used for housekeeping (7 watts X 14 hr.) 0.1 kw.-hr.
used for motor (95 watts X ~9.5-11.0 hr.) 0.9-1.05 kw.-hr.


DIMENSIONS
Wingspan 15.6 ft.
Wing area 16.1 sq. ft.
WEIGHTS
Gross weight 28.2 lb.
Battery 12.3 lb.
Solar cells 2.3 lb.
COMPONENTS
Battery 120 Sanyo 18650
Li-Ion cells
Battery capacity 1,200 watt-hr.
Solar array 76 Sunpower A300
solar cells
Nominal solar power 225 watts
Powerplant Kontronik 800-watt
electric
PERFORMANCE
Speed range 28-50 mph.
Min. loiter power 95 watts
Max. climb rate 490 fpm.
(Battery power alone can climb
to approx. 50,000 ft.)
Control and telemetry range 5 mi.