Electrically Powered Ultralight Aircraft

In rec.aviation.soaring wrote:
In rec.aviation.piloting Phil wrote:
I wonder if anyone has done any experiments with a hybrid drive system
for an aircraft. I am thinking of something like a 3-cylinder diesel
engine providing enough power for cruise, supplemented with a battery
pack and motor for takeoff and climb.

The advantage for hybrids comes from stop and go driving where the
battery is charged by regenerative braking.

There isn't much stop and go flying.

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.

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).

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.

--
Michael Ash
Rogue Amoeba Software

"Michael Ash" wrote in message
...
In rec.aviation.soaring wrote:
In rec.aviation.piloting Phil wrote:
I wonder if anyone has done any experiments with a hybrid drive system
for an aircraft. I am thinking of something like a 3-cylinder diesel
engine providing enough power for cruise, supplemented with a battery
pack and motor for takeoff and climb.

The advantage for hybrids comes from stop and go driving where the
battery is charged by regenerative braking.

There isn't much stop and go flying.

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.

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).

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.

--
Michael Ash

There is, I believe, a UAV using hybrid power. The idea is to switch off
the gas engine and run on electric power for a stealthy approach to a
"location of interest".

Bill Daniels
Rogue Amoeba Software

"Michael Ash" wrote

The extra drag caused by the extra weight of the batteries and
the rest of the hybrid system would probably outweigh any efficiency gain.

Probably? You are being far too kind. A redundant power system, only
helping at takeoff is GOING to waste efficiency. There is no way to avoid
that fact unless then cruise speed is going to be painfully slow.
--
Jim in NC

In rec.aviation.soaring Morgans wrote:

"Michael Ash" wrote

The extra drag caused by the extra weight of the batteries and
the rest of the hybrid system would probably outweigh any efficiency gain.

Probably? You are being far too kind. A redundant power system, only
helping at takeoff is GOING to waste efficiency. There is no way to avoid
that fact unless then cruise speed is going to be painfully slow.

I don't doubt you in any way, and in fact my general feeling is in
complete agreement with you. But I'm not speaking from a position of great
knowledge so I used a weasel word to indicate that.

--
Michael Ash
Rogue Amoeba Software

In rec.aviation.piloting Michael Ash wrote:
In rec.aviation.soaring wrote:
In rec.aviation.piloting Phil wrote:
I wonder if anyone has done any experiments with a hybrid drive system
for an aircraft. I am thinking of something like a 3-cylinder diesel
engine providing enough power for cruise, supplemented with a battery
pack and motor for takeoff and climb.

The advantage for hybrids comes from stop and go driving where the
battery is charged by regenerative braking.

There isn't much stop and go flying.

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.

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.

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.

--
Jim Pennino

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

Come on, it's not like there isn't sufficient motivation out there
now and it isn't coming from battlebots. If anyone comes up with a
battery that can power and automobile for 4 hours at highway speeds
and is affordable to produce they will be very wealthy.

If they can make one that is as efficient as a tank of gasoline they
will shortly become very, very wealthy.

I agree. It's on the way. Wasn't too long ago that terms like
"lithium ion" and "nickle metal hydride" were unheard of to the
common consumer.
Five or six years ago your choices were Hawker Genesis-style Sealed
Lead Acid or custom-built NiCad battery arrays which is what we used.
NiMH and lithium ion weren't available or affordable but the
proliferation of power chairs, stuff like the Segway, electric
scooters and so forth have really pushed the demand for lightweigh,
high performance batteries.
-c

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?

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

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.

On Mon, 6 Aug 2007 20:43:47 -0500, "Maxwell" wrote
in :


"Larry Dighera" wrote in message
.. .

Personally, I'd like to see an electrically powered parachute
(http://skyhighflying.com/homepage.html) design attempted. Surly the
lighter weight would require less power. It would seem that
lithium-ion polymer batteries are a potential enabling technology.


They might be lightweight and strong, but I think they would be far too
inefficent. All the canopies I have been around have had a very poor L/D
when compared to something like a sailplane.

The web site below mentions an L/D of four to one.

I always assumed they were so popular because they were so strong, portable
and quick to set-up. But I'm thinking their fuel mileage would be very poor.

I would be more interested in the specific horsepower required to
operate powered parachutes than their efficiency. This web site
mentions 50 HP to 65 HP:
http://www.all-about-powered-parachutes.com/faq.htm

There is a 14 HP Powered Paraglider (PPG) engine offered he
http://www.poweredparasports.com/Par...#Jet%20Details
They also state that the weight of their engines ranges from 46 lbs.
to 68 lbs.

If a 14 HP electric propulsion system weighing 46 lbs could be
constructed, apparently it would permit the use of PPGs by pilots up
to 180 lbs.