Electrically Powered Ultralight Aircraft

On Mon, 06 Aug 2007 09:42:46 -0700, wrote
in .com:

As the invertor can exert more retardation than brakes, the
conventional disc brakes have been discarded altogether.

Oh, boy. Knowing first-hand the reliability of
electrical stuff...


It's a prototype. The choice not to equip the automobile with brakes
demonstrates how effective the regenerative braking is, but apparently
you have to carry chocks when you park it. :-)

There is a fundamental problem with attempting to power an aircraft
with batteries: The propulsion system must not only move the vehicle
forward as it would with an automobile, but it must also
simultaneously maintain the aircraft's altitude;

This is significant at low airspeeds. At higher airspeeds overcoming
wind resistance takes much more power than maintaining altitude.

unlike an automobile
that only requires a small amount of energy to overcome rolling and
wind resistance once in motion, an aircraft can't coast without losing
altitude,

It sure can, until it loses speed and stalls.

Bartek

On Aug 6, 3:16 pm, brtlmj wrote:
There is a fundamental problem with attempting to power an aircraft
with batteries: The propulsion system must not only move the vehicle
forward as it would with an automobile, but it must also
simultaneously maintain the aircraft's altitude;

That is why aircraft engines are so powerful and light; they're
depended-on to fight gravity as well as wind resistance.
Which leads us to the case of airships! They float. They don't
have to work to stay at altitude, they just hang there. Their engines
don't have to hold them up.
But, and it's a big but, since they are so big, they have more
wind resistance than airplanes. Since wind resistance is the log, or
cube? of wind speed, their hull-speeds are quite limited and their
engines remain relatively small as a result.
Enter the less-powerful electric motors! Enter solar photo-
voltaic cells! The big surface area of airships are ideal for mounting
solar arrays. And if you have a cloudy day and don't charge your
batteries up to snuff, well, you will not have to go to ground, as in
an airplane, because you are afloat in your element and you drift with
the breeze for awhile.
Words to the wise about the future of flight. High cheers from
Allen the airshipman

On Sun, 19 Aug 2007 09:53:32 -0700, dirigible designer
wrote in
. com:

On Aug 6, 3:16 pm, brtlmj wrote:

Actually, these are my words from earlier in this message thread. See:
Message-ID: .

There is a fundamental problem with attempting to power an aircraft
with batteries: The propulsion system must not only move the vehicle
forward as it would with an automobile, but it must also
simultaneously maintain the aircraft's altitude;

That is why aircraft engines are so powerful and light; they're
depended-on to fight gravity as well as wind resistance.
Which leads us to the case of airships! They float. They don't
have to work to stay at altitude, they just hang there. Their engines
don't have to hold them up.
But, and it's a big but, since they are so big, they have more
wind resistance than airplanes. Since wind resistance is the log, or
cube? of wind speed, their hull-speeds are quite limited and their
engines remain relatively small as a result.
Enter the less-powerful electric motors! Enter solar photo-
voltaic cells! The big surface area of airships are ideal for mounting
solar arrays. And if you have a cloudy day and don't charge your
batteries up to snuff, well, you will not have to go to ground, as in
an airplane, because you are afloat in your element and you drift with
the breeze for awhile.
Words to the wise about the future of flight. High cheers from
Allen the airshipman

Thank you for mentioning electrically powered airships.

Lighter Than Air craft are excellent candidates for electric power as
is evidenced by:


http://en.wikipedia.org/wiki/Airship
In 1883, the first electric-powered flight was made by Gaston
Tissandier who fitted a 1-1/2 horsepower Siemens electric motor to
an airship. The first fully controllable free-flight was made in a
French Army airship, La France, by Charles Renard and Arthur
Constantin Krebs in 1884 . The 170 foot long, 66,000 cubic foot
airship covered 8 km (5 miles) in 23 minutes with the aid of an
8-1/2 horsepower electric motor.




http://missilethreat.com/missiledefe...tem_detail.asp
...
In September 2003, the Missile Defense Agency (MDA) and the North
American Aerospace Defense Command (NORAD) awarded a $40 million
development contract to Lockheed Martin to build the High Altitude
Airship prototype. Lockheed Martin currently manufactures the
Goodyear blimps that can be seen over big sporting events. These
blimps are approximately 200 feet long with a volume of 200,000
cubic feet. By contrast, the HAA prototype will be 500 feet long,
160 feet in diameter, with a volume of 5.2 million cubic feet,
i.e. more than 25 times the size of the average Goodyear blimp.

MDA plans to deploy the HAA at an altitude of 65,000 feet where
the air is one-twentieth the density that it is near the ground.
One of the biggest challenges facing MDA and Lockheed Martin is
how to get the HAA from the ground to its area of deployment,
since the helium gas inside will expand more than fifteen times as
the blimp rises. To solve this problem, the HAA will be filled
mostly with air when it is close to the ground. As it rises, the
air inside the blimp will be forced out and helium from five small
inner balloons will replace it. This “balloon-within-a-balloon”
concept will allow the HAA to maintain its football-like shape
throughout all stages of flight.

Once deployed, the HAA will generate its own power supply from
thin-film photovoltaic solar cells. It will require 10 kilowatts
of electricity to run its 4,000-pound radar system. The prototype
HAA will include batteries to keep the electricity flowing at
night, although the final version will most likely use lightweight
fuel cells. Four electrically powered engines will each drive two
30-foot-wide propellers that will provide the blimp’s forward
thrust. The propellers will allow the HAA to hover within a mile
of its assigned location, thus maintaining its fixed
“geostationary” nature. ...



http://www.aiaa.org/aerospace/images...es/pdf/LTA.pdf
Zeppelin Luftschifftechnik in Germany resorted to a unique method
of delivering its NT-07 airship to a Japanese customer. The
semirigid air-ship was flown to Italy and, fully inflated, was
put on board a BPDockship for the journey to Kobe, Japan. Tail
surfaces and forward engines were removed. Zeppelin is leasing
another NT-07 to the DeBeers diamond company for two years. It
also was delivered by ship, to South Africa. The air-ship will be
equipped to examine geological formations in southern African
countries. Zeppelin carried 11,000 passengers on sightseeing
flights in Germany during 2004. Work is proceeding on the
development of the 19-passenger NT-14. First flight is expected in
early 2008. Zeppelin has acquired the intellectual property of the
defunct CargoLifter organization.

This will become part of an LTAinstitute for coordinating
activities on scientific and predevelopment levels applicable to
all types of airships. It will be headquartered in
Friedrichshafen.

Japan’s Aerospace Exploration Agency completed its series of eight
flights with the above-mentioned 223-ft-long, 370,755-ft,
un-manned research airship. The objective of these flights was to
verify flight control, operation, and tracking technologies from
takeoff to landing. Geostationary flight at 13,000 ft was realized
with the aid of electrically powered propellers. Data obtained
will be applied to JAXA’s further research into high-altitude
airships.

Another approach to this subject, a “bal-loon robot,” was
investigated by Japan’s National Institute of Advanced Industrial
Science and Technology (AIST). A 92-ft-long model carrying a 3-kg
payload was launched to an altitude of 55,700 ft. Power for
propulsion was supplied by batteries. Data transmission failure
prevented verification of station keeping.

AIST has built a 43-ft-long nonrigid propelled by cycloidal
propellers driven by electricity supplied by batteries. This
unmanned airship can be used for aerial observation and
monitoring of hazardous areas.




http://mae.pennnet.com/Articles/Arti...&KEYWORD=blimp
Latest generation of military airships to use solar electric power
by J.R. Wilson

Peterson AFB, Colo. — The North American Aerospace Defense Command
(NORAD) has joined forces with the U.S. Army and other agencies to
develop the 21st-century High Altitude Airship to help defend U.S.
airspace, control its borders, and possibly provide global
surveillance capability to military theater commanders.

"It's an old idea with new technology applied," explains U.S. Navy
Cmdr. Pat Lyons, chief of ISR and NORAD J-5 Directorate. "This
airship is unmanned, untethered, and electric powered. We expect
it to be composed of solar cells, a fuel cell, and electrolyzer
for nighttime operations."

The new airship's command-and-control links most likely will
involve satellite communications channels. All of these
technologies will probably enable the airship to remain on station
for as long as one year, Lyons says.

Electric power
The airship will be electrically powered — possibly using a
hydrogen fuel cell — with DC brushless motors and propellers as
the likely propulsion system, although the final design will be up
to the contractor; Lyons says there are several other possible
concepts for program managers to consider. That includes the
number of motors, which also would determine the number of
propellers.

"The concepts we've seen show speeds up to 100 knots for the
objective airship," Lyons explains. "The winds at 70,000 feet are
fairly benign; you're above the weather and the jet stream, but
occasionally, depending on where you are, they can get up to 100
knots, building for 24 hours, peaking for a day, then diminishing
for a day. With a 100-knot airspeed, the airship can remain
geostationary," Lyons says.

A variety of sensors are being considered for the airship's
Advanced Concept Technology Demonstration (ACTD), including a
small communications relay. In operation, the vehicle could be
used to enable communications 600 or more miles apart, including
over a mountain. Currently, ground troops with handheld
communications must post a relay unit on a water tower or other
tall structure to avoid losing contact in the field. ...

Military & Aerospace Electronics August, 2002
Author(s) : J.R. Wilson

On Aug 7, 3:39 am, Larry Dighera wrote:
Are external combustion engines as efficient as internal combustion
engines? Stirling engines are great for converting waste heat to
mechanical energy, but I'm not sure how appropriate they would be for
aircraft propulsion.

In theory, I think that stirling engines are quite well suited to
aircraft, all it needs is a source of "hot" and a source of "cold",
the cold is in abundance (stick a heatsink in the wind, higher you go,
colder it gets, more power the engine can deliver, directly the
opposite of IC), the hot could be provided with any number of
combustables (and some oxygen delivery system).

I found yesterday after writing my initial post an article about
exactly this - http://www.qrmc.com/fourpartstirling.html "Why Aviation
Needs the Stirling Engine by Darryl Phillips" from 1993/1994.

Given what was said in the article, I'm kind of surprised that nobody
has come up with a working protoype actually.

James Sleeman wrote:

stick a heatsink in the wind, higher you go,
colder it gets, more power the engine can deliver, directly the
opposite of IC

What I didn't get from the article: Where does the "hot" come from? A fuel
burner, probably, which would have the same problems with altitude as an IC
engine, wouldn't it?

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On Mon, 06 Aug 2007 18:22:41 -0700, James Sleeman
wrote in
.com:

On Aug 7, 3:39 am, Larry Dighera wrote:
Are external combustion engines as efficient as internal combustion
engines? Stirling engines are great for converting waste heat to
mechanical energy, but I'm not sure how appropriate they would be for
aircraft propulsion.

In theory, I think that stirling engines are quite well suited to
aircraft, all it needs is a source of "hot" and a source of "cold",
the cold is in abundance (stick a heatsink in the wind, higher you go,
colder it gets, more power the engine can deliver, directly the
opposite of IC), the hot could be provided with any number of
combustables (and some oxygen delivery system).

I see what you mean. Unfortunately, the highest power requirements of
aircraft engines are during the takeoff and climb phases of flight.
Power requirements are even greater when the ambient temperature rises
resulting in less air density or a higher density altitude. That is
when the most power is required for takeoff, but that would be a
situation where the Stirling engine would have its minimum power
production.

I would also like to see a comparison of the efficiencies of IC and EC
engines and their relative weight and size per horsepower compared.

Unlike electrical motors, that must be constructed with heavy iron, IC
and EC engines can be constructed of lighter materials like aluminum,
but electrical motors are usually 80% to 95% efficient. With the
Stirling aircraft engine there is a requirement for what I would
imagine would be a large heat sink or heat exchanger located in the
slip stream. The weight of this heat exchanger and its drag penalty
must also be considered.

I found yesterday after writing my initial post an article about
exactly this - http://www.qrmc.com/fourpartstirling.html "Why Aviation
Needs the Stirling Engine by Darryl Phillips" from 1993/1994.

Given what was said in the article, I'm kind of surprised that nobody
has come up with a working protoype actually.

The article is interesting; thank you for mentioning it. I am
e-mailing a copy of this followup article to the author Darryl
Phillips.

There might be one advantage to using Sterling external combustion
engines for aviation: the use of atomic energy as a fuel source if the
weight of the lead shielding were not too great. Imagine an aircraft
that effectively never runs out of fuel! There'd be no more fuel
exhaustion mishaps.

Recently, Larry Dighera posted:

On Mon, 06 Aug 2007 18:22:41 -0700, James Sleeman
wrote in
.com:

On Aug 7, 3:39 am, Larry Dighera wrote:
Are external combustion engines as efficient as internal combustion
engines? Stirling engines are great for converting waste heat to
mechanical energy, but I'm not sure how appropriate they would be
for aircraft propulsion.

In theory, I think that stirling engines are quite well suited to
aircraft, all it needs is a source of "hot" and a source of "cold",
the cold is in abundance (stick a heatsink in the wind, higher you
go, colder it gets, more power the engine can deliver, directly the
opposite of IC), the hot could be provided with any number of
combustables (and some oxygen delivery system).

I see what you mean. Unfortunately, the highest power requirements of
aircraft engines are during the takeoff and climb phases of flight.
Power requirements are even greater when the ambient temperature rises
resulting in less air density or a higher density altitude. That is
when the most power is required for takeoff, but that would be a
situation where the Stirling engine would have its minimum power
production.

If an engine's minimum power production is greater than the power required
for takeoff, would it matter? It would seem that if this could be
achieved, the operating conditions of the Stirling engine would be mostly
understressed.

I would also like to see a comparison of the efficiencies of IC and EC
engines and their relative weight and size per horsepower compared.

Unlike electrical motors, that must be constructed with heavy iron, IC
and EC engines can be constructed of lighter materials like aluminum,
but electrical motors are usually 80% to 95% efficient. With the
Stirling aircraft engine there is a requirement for what I would
imagine would be a large heat sink or heat exchanger located in the
slip stream. The weight of this heat exchanger and its drag penalty
must also be considered.

Why couldn't the heat exchanger be an integral part of the airframe? Wings
come to mind... ;-)

There might be one advantage to using Sterling external combustion
engines for aviation: the use of atomic energy as a fuel source if the
weight of the lead shielding were not too great. Imagine an aircraft
that effectively never runs out of fuel! There'd be no more fuel
exhaustion mishaps.

One downside would be the hazardous materials that could be dispersed in a
crash. I'd like to see a prototype Stirling using conventional fuels
before exploring more exotic options.

Neil

On Aug 8, 2:21 am, Larry Dighera wrote:
I see what you mean. Unfortunately, the highest power requirements of
aircraft engines are during the takeoff and climb phases of flight.

Hence why i was thinking more along the lines of a electric motor +
reasonable battery coupled to a stirling. The battery provides the
oompfh for takeoff (and other moments of urgency) from stored energy.
The stirling charges the battery, or passes current through to the
motor when the battery is at peak charge (hand waving the bajillion
technical details which I don't know), it doesn't matter that the
stirling doesn't run at peak efficiency at all times, in cruise mode
you'd want it to be at peak and providing more than enough current to
the motor with some spare to charge the battery.

The article I linked to was more along the lines of a direct-drive,
but I think hooking the output shaft from a stirling straight to a
gearbox/prop would not be a good idea, you are stuck with too many
disadvantages and it makes the engine design more complicated than
necessary.

The main advantage of the stirling+battery versus just battery, is
that you remove the requirement for major infrastructure change
(abundant charging points at airports), the stirling just needs some
fuel (which could be anything from mogas to radiant solar heat) and
that's it, no infrastructure change is necessary in the interim, and
minimal in the long term. As an added benefit, you get much better
cruise endurance than battery alone.

James Sleeman opined

On Aug 7, 3:39 am, Larry Dighera wrote:
Are external combustion engines as efficient as internal combustion
engines? Stirling engines are great for converting waste heat to
mechanical energy, but I'm not sure how appropriate they would be for
aircraft propulsion.

In theory, I think that stirling engines are quite well suited to
aircraft, all it needs is a source of "hot" and a source of "cold",
the cold is in abundance (stick a heatsink in the wind, higher you go,
colder it gets, more power the engine can deliver, directly the
opposite of IC), the hot could be provided with any number of
combustables (and some oxygen delivery system).

I found yesterday after writing my initial post an article about
exactly this - http://www.qrmc.com/fourpartstirling.html "Why Aviation
Needs the Stirling Engine by Darryl Phillips" from 1993/1994.

Given what was said in the article, I'm kind of surprised that nobody
has come up with a working protoype actually.

I see 2 problems. First is that although the temperature at 30,000' is low, so
is the air density, so the size of the heat sink is smaller than one might
think. Second is heat generated by compression of airby the high true airspeeds
at altitude.


-ash
Cthulhu in 2007!
Why wait for nature?