Electrically Powered Ultralight Aircraft

In rec.aviation.soaring wrote:
In rec.aviation.piloting Michael Ash wrote:
There is also an advantage which comes from only needing to size the
engine for cruise, not for acceleration, since you can suppliment the
smaller engine with the batteries during acceleration. Smaller engines are
generally more efficient than larger ones when putting out the same amount
of power.

If you are trying to say it takes less power to maintain speed than to
accelerate, yes that is true.

The advantage from the electric engine at cruise is that it uses zero
energy.

There were attempts to increase mileage of gas engines by turning off
uneeded cylinders at cruise. They didn't work that well and you still
had to move the pistons, the big crank, and all the rest of the stuff.

Right, so a hybrid is like that system, except that the undeeded cylinders
are replaced with an electric motor. Instead of, say, having six cylinders
and only running four during cruise, you only *have* four cylinders, and
then you suppliment them with the electric system during acceleration.
That way you aren't moving them around and you get better efficiency from
the smaller engine.

The other advantage is that the engine can stay in the engine's efficiency
band even when the RPM demanded of it is higher (acceleration) or lower
(initial start).

The transmission keeps the engine RPM within a limited range.

Hybrids have no effect on that.

The transmission *tries to* keep the engine RPM within a limited range,
but it doesn't always work.

My car's efficiency band appears to be around 1500-2000RPM since that's
where it stays most of the time. But if I floor it on the highway it'll
easily hit 6000RPM at a great loss of efficiency. On a hybrid that extra
power is going to come from the electrical system.

However, these also don't help nearly as much on aircraft as on cars. The
difference between acceleration and cruise power on an aircraft is much
less than in a car, and aircraft engines tend to spend most of their time
in the efficiency band anyway, especially if there's a constant-speed prop
affixed. The extra drag caused by the extra weight of the batteries and
the rest of the hybrid system would probably outweigh any efficiency gain.

It doesn't help at all on airplanes.

The advantage to hybrids is they get better gas mileage.

They do that by using the deceleration to charge batteries which recovers
some of the kinetic energy instead of using it all to heat the brake linings.

This is true but incomplete. Regenerative braking is *one of the ways*
hybrids get better mileage. They also get better mileage by using smaller
engines and running those engines in a more efficient than would be
possible with a direct-drive system. But the conclusion is the same in the
end: although the last two would help in an aircraft they would not help
nearly enough to make such a system worthwhile.

--
Michael Ash
Rogue Amoeba Software

In rec.aviation.piloting Tim Ward wrote:

wrote in message
...

The advantage from the electric engine at cruise is that it uses zero
energy.

Snippage
--
Jim Pennino

Remove .spam.sux to reply.

You want to support this, somehow?

Tim Ward

At cruise the electric motor is turned off.

The only energy used is some slight bearing friction.

The electric motor is only turned on when more power than the gas
engine can provide is needed.

--
Jim Pennino

Remove .spam.sux to reply.

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 Tue, 7 Aug 2007 11:48:50 -0500, "Neil Gould"
wrote in
:

Recently, Larry Dighera posted:

[snip]
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?

Probably not, but it would mean you'd have significantly more power
available at altitude if the Sterling engine were sized to provide
takeoff power at high density altitudes.

What I was getting at was the author of the articles emphasis on
overcoming the reduced power output of IC engines at lower atmospheric
pressure overlooks its possibly anemic performance (due to minimal air
movement through the heat exchanger and higher ambient temperatures on
the ground) when it is needed most, at takeoff. I find it revealing
that the author failed to mention that point, and it reduces my
confidence in the assertions he made in that article.

It would seem that if this could be achieved, the operating conditions
of the Stirling engine would be mostly understressed.

I am unable to infer your meaning by that statement. Do you mean
under emphasized or less mechanical stress on the engine, or what?


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... ;-)

I'm thinking there would be necessity for some means of conducting the
heat from the engine to a remote heat exchanger, and the resulting
complexity and weight increase would negatively impact the potential
advantages of a Stirling aviation engine. In any event, in addition
to the Stirling engine and its fuel, a heat exchanger of some type
needs to factored into the weight, cost, performance, and efficiency
equations.


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.

There are a lot of down sides to atomic power, but NASA uses it to
power Stirling engines in space.


Here's some information about what NASA successfully has accomplished
with nuclear power:


http://www.grc.nasa.gov/WWW/tmsb/index.html
The Thermo-Mechanical Systems Branch (5490) is responsible for
planning, conducting and directing research and technology
development to advance the state-of-the-art in a variety of
thermal systems for space, aerospace, as well as non-aerospace
applications. The systems of interest include thermal energy
conversion for power systems and solar thermal propulsion systems.
The effort involves working at the component level to develop the
technology, the subsystem level to verify the performance of the
technology, and the system level to ensure that the appropriate
system level impact is achieved with the integrated technology.
System analysis is used to identify high-impact technology areas,
define the critical aspects of the technology that need to be
developed, and characterize the system level impact of the
technology. Specific technology areas of interest include:


Dynamic Power Systems: Brayton, Rankine and Stirling Convertors,
Solar Receivers and Thermal Energy Storage
Primary Solar Concentrators: Thin film, SRP and Rigid
Secondary Solar Concentrators: Refractive and Reflective
Thermal Management: Radiators, Electronics Packaging, and Heat
Pipe Technology


http://www.grc.nasa.gov/WWW/tmsb/stirling.html
Animation of a 55 We Stirling TDC
(click on image to view)


http://www.grc.nasa.gov/WWW/tmsb/sti...adisotope.html
AVAILABLE TODAY FOR TOMORROW'S NEEDS
NASA Glenn Research Center and the Department of Energy (DOE) are
developing a Stirling convertor for an advanced radioisotope power
system to provide spacecraft on-board electric power for NASA deep
space missions. Stirling is being evaluated as an alternative to
replace Radioisotope Thermoelectric Generators (RTGs) with a
high-efficiency power source. The efficiency of the Stirling
system, in excess of 20%, will reduce the necessary isotope
inventory by a factor of at least 3 compared to RTGs. Stirling is
the most developed convertor option of the advanced power concepts
under consideration [1,2].


http://www.grc.nasa.gov/WWW/tmsb/sti...ng_bckgrd.html
However, about this time NASA became interested in development of
free-piston Stirling engines for space power applications. These
engines use helium as the working fluid, drive linear alternators
to produce electricity and are hermetically sealed. These 12.5 kWe
per cylinder engines were intended for use with a nuclear reactor
power system; the Space Demonstrator Engine (or SPDE) was the
earliest 12.5 kWe per cylinder engine that was designed, built and
tested by MTI. A later engine of this size, the Component Test
Power Convertor (or CTPC), used a "Starfish" heat-pipe heater
head, instead of the pumped-loop used by the SPDE. Recently, in
the 1992-93 time period, this work was terminated due to the
termination of the related SP-100 nuclear power system work and
NASA's new emphasis on "better, faster, cheaper" systems and
missions.


http://www.spacedaily.com/news/outerplanets-00a2.html
Europa Orbiter was replanned to use a new "Sterling" nuclear
generator design which would use less plutonium



http://www.cndyorks.gn.apc.org/yspac...heed_offer.htm
Boeing, Lockheed Offer NASA Two Choices for Nuclear Power

"Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in message
...

Do me a favor Gattman. What is the weight of the most effeicent battery
that could power an automobile at highway speed and how long will it do so
and how long to recharge?

Well, if I tried to answer that I'd sound like mx. I don't know what the
"most efficient" battery is for that purpose. It's a hell of a lot heavier
than the 250-250 pound machines I worked with. I think 4-6 SLAs--possibly
the least efficient--would pull a vehicle, but I doubt it would make highway
speed and if if it did it wouldn't be for more than a few minutes. Charge
time for each battery would probably be a couple of hours, maybe longer.

I bet it would weigh a hell of a lot more than a Rotax. Internal combustion
is still the most bang for the buck this side of nuclear.

I think the most realistic use of an electric motor in an aircraft would be
in the context of something like a glider, for maintaining altitude or
finding a thermal or just getting home. It would be fun to fly an
ultralight around the pattern under electrical power, but I wouldn't stray
very far.

-c

Recently, Larry Dighera posted:

On Tue, 7 Aug 2007 11:48:50 -0500, "Neil Gould"
wrote:

Recently, Larry Dighera posted:

[snip]
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?

Probably not, but it would mean you'd have significantly more power
available at altitude if the Sterling engine were sized to provide
takeoff power at high density altitudes.

Exactly, but I don't see that as a negative... ;-)

What I was getting at was the author of the articles emphasis on
overcoming the reduced power output of IC engines at lower atmospheric
pressure overlooks its possibly anemic performance (due to minimal air
movement through the heat exchanger and higher ambient temperatures on
the ground) when it is needed most, at takeoff. I find it revealing
that the author failed to mention that point, and it reduces my
confidence in the assertions he made in that article.

I understand your perspective, which is what prompted my reply. If there
is sufficient power to take off, then the issue should be moot, unless I'm
overlooking something. It should be reasonable to presume that any
practical aircraft engine would have sufficient power to take off, right?
;-)

It would seem that if this could be achieved, the operating
conditions of the Stirling engine would be mostly understressed.

I am unable to infer your meaning by that statement. Do you mean
under emphasized or less mechanical stress on the engine, or what?

Less mechanical stress due to operating well below maximum power settings
under normal cruise. That should provide plenty of reserve power at
altitude and increase the fuel efficiency as well.

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... ;-)

I'm thinking there would be necessity for some means of conducting the
heat from the engine to a remote heat exchanger, and the resulting
complexity and weight increase would negatively impact the potential
advantages of a Stirling aviation engine. In any event, in addition
to the Stirling engine and its fuel, a heat exchanger of some type
needs to factored into the weight, cost, performance, and efficiency
equations.

Of course, but I don't see a lot of reason why that couldn't be
incorporated into the overall design. My point is that heat exchangers
need not be heavy, and could probably double as structural and/or
aerodynamic components, further reducing (and possibly enhancing) their
impact.

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.

There are a lot of down sides to atomic power, but NASA uses it to
power Stirling engines in space.

Understandable, but their expectation is that catastrophic destruction
would disperse the nuclear material harmlessly. That can't be presumed for
light aircraft.


Neil

Gattman wrote:
"Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in message
...

Do me a favor Gattman. What is the weight of the most effeicent
battery that could power an automobile at highway speed and how long
will it do so and how long to recharge?

Well, if I tried to answer that I'd sound like mx. I don't know
what the "most efficient" battery is for that purpose. It's a hell
of a lot heavier than the 250-250 pound machines I worked with. I
think 4-6 SLAs--possibly the least efficient--would pull a vehicle,
but I doubt it would make highway speed and if if it did it wouldn't
be for more than a few minutes. Charge time for each battery would
probably be a couple of hours, maybe longer.
I bet it would weigh a hell of a lot more than a Rotax. Internal
combustion is still the most bang for the buck this side of nuclear.

I think the most realistic use of an electric motor in an aircraft
would be in the context of something like a glider, for maintaining
altitude or finding a thermal or just getting home. It would be fun
to fly an ultralight around the pattern under electrical power, but I
wouldn't stray very far.

-c


I understand and thank you for not MXing us. But the point isn't the weight
of the battery as compaired to a Rotax or any other engine. The issue I had
been getting at is the weight of the battery in comparison to the weight of
full load of gasoline.

Let's take my 601XL. 2 aluminum 12 gallon tanks each tank ways let's say 10
pounds add in 145 lbs of fuel and you have 165 pounds of transportable
energy that will produce ~100HP for about 4 hours.

My question to anyone is what is the lightest battery that is capable of
powering any motor that will produce the equivilent power for and equal
amount of time?

check out the article on regenerative soaring at www.esoaring.com I
think I may have heard that Taras Kiceniuk will be giving a talk on
this subject at Tehachapi this Labor Day. He's been working on this
idea for a while...
Bill

In rec.aviation.piloting Gig 601XL Builder wrDOTgiaconaATsuddenlink.net wrote:
Gattman wrote:
"Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in message
...

Do me a favor Gattman. What is the weight of the most effeicent
battery that could power an automobile at highway speed and how long
will it do so and how long to recharge?

Well, if I tried to answer that I'd sound like mx. I don't know
what the "most efficient" battery is for that purpose. It's a hell
of a lot heavier than the 250-250 pound machines I worked with. I
think 4-6 SLAs--possibly the least efficient--would pull a vehicle,
but I doubt it would make highway speed and if if it did it wouldn't
be for more than a few minutes. Charge time for each battery would
probably be a couple of hours, maybe longer.
I bet it would weigh a hell of a lot more than a Rotax. Internal
combustion is still the most bang for the buck this side of nuclear.

I think the most realistic use of an electric motor in an aircraft
would be in the context of something like a glider, for maintaining
altitude or finding a thermal or just getting home. It would be fun
to fly an ultralight around the pattern under electrical power, but I
wouldn't stray very far.

-c


I understand and thank you for not MXing us. But the point isn't the weight
of the battery as compaired to a Rotax or any other engine. The issue I had
been getting at is the weight of the battery in comparison to the weight of
full load of gasoline.

Let's take my 601XL. 2 aluminum 12 gallon tanks each tank ways let's say 10
pounds add in 145 lbs of fuel and you have 165 pounds of transportable
energy that will produce ~100HP for about 4 hours.

My question to anyone is what is the lightest battery that is capable of
powering any motor that will produce the equivilent power for and equal
amount of time?

If you go to http://xtronics.com/reference/energy_density.htm you find
the energy densities of a lot of things.


Propane (liquid) 13,900 Wh/kg
Diesel 13,762 Wh/kg
gasoline 12,200 Wh/kg
Ethanol 7,850 Wh/kg
Methanol 6,400 Wh/kg
Secondary Lithium - ion Polymer 130 - 1200 Wh/kg
Primary Zinc-Air 300 Wh/kg
Lead Acid Battery 25 Wh/kg

So batteries have to improve by a factor of 10 to match gasoline.




--
Jim Pennino

Remove .spam.sux to reply.

"Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in message
...

Let's take my 601XL. 2 aluminum 12 gallon tanks each tank ways let's say
10 pounds add in 145 lbs of fuel and you have 165 pounds of transportable
energy that will produce ~100HP for about 4 hours.

My question to anyone is what is the lightest battery that is capable of
powering any motor that will produce the equivilent power for and equal
amount of time?

Well, depending on which end of the gearbox it's measured, 40+ pounds of
NiCAD batteries got between 1-4 HP at maybe 70% motor power for 20 minutes
max before the battery output began to taper off. For perspective, the
Etek motor used on the ultralight in the link is probably about twice as
powerful as the motors we were using, so maybe for a ballpark measurement I
could double the battery time for the same weight. Theoretically if you
managed and cooled your batteries correctly you could get ~30 minutes for
that 40 pounds of batteries, or maybe two hours if you quadrupled it for
your ~160 pounds. Max.

Too much weight for an ultralight, and no way it's gonna get near 100HP.
Again, that's just a ballpark estimate.

-c