Electrically Powered Ultralight Aircraft

In rec.aviation.piloting Charles Vincent wrote:
wrote:
In rec.aviation.piloting Charles Vincent wrote:
wrote:
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

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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.


To carry more weight at the same speed and altitude takes more power, so
you have to account for the energy expended kiting you deadweight
electric takeoff system around the sky as well. Sizing an engine for
cruise has been done, if only backwards. Think JATO. Most JATO's are
actually RATO (rocket assisted takeoff). I expect RATO would beat an
electric system based on energy density and the fact that when it is
done you have reduced your weight by the fuel. I also suspect for a
given amount of thrust the rocket will be lighter than an electric motor
and associated clutches and gearing. In my opinion, at this point in
time it is just as practical for a homebuilt as well as in not.

Well, that's true enough, but the above was about hybrid cars.


Well in cruise in a car, more weight does not increase your aerodynamic
drag like it does on an airplane, but it does increase your rolling
resistance in the real world, so there is no free lunch. Different
tradeoffs for different missions. I guess that is why cheetahs and
sparrows look so different.

Unless the added weight is enough to deform the tires, the increase
in rolling resistance in the total energy expediture can't be found.

--
Jim Pennino

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wrote

Unless the added weight is enough to deform the tires, the increase
in rolling resistance in the total energy expediture can't be found.

Bull hockey.

Just because it is not noticeable, or measurable by the lack of sensitivity
with the instrument you are currently not using, does not mean that it does
not exist.

More weight on the bearings will cause more rolling resistance. That is
fact, not open to dispute. If you say it is, I want to buy the rights to
the bearings you are using, so I can patent them and make a fortune.
--
Jim in NC

In rec.aviation.piloting Morgans wrote:

wrote

Unless the added weight is enough to deform the tires, the increase
in rolling resistance in the total energy expediture can't be found.

Bull hockey.

Just because it is not noticeable, or measurable by the lack of sensitivity
with the instrument you are currently not using, does not mean that it does
not exist.

Perhaps you would like a rephrase:

Unless the added weight is enough to deform the tires, the increase
in rolling resistance compared to the total system energy expediture
is so small that it is negligible.

Or how about:

Unless the added weight is enough to deform the tires, the increase
in rolling resistance compared to the total system energy expediture
has about the same effect as ****ing in Lake Tahoe.

--
Jim Pennino

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Morgans wrote:
wrote

Unless the added weight is enough to deform the tires, the increase
in rolling resistance in the total energy expediture can't be found.

Bull hockey.

Just because it is not noticeable, or measurable by the lack of sensitivity
with the instrument you are currently not using, does not mean that it does
not exist.

More weight on the bearings will cause more rolling resistance. That is
fact, not open to dispute. If you say it is, I want to buy the rights to
the bearings you are using, so I can patent them and make a fortune.

If a bird craps on your windshield, it is more likely to noticeably
influence your aerodynamic drag than rolling resistance.....I took Jim's
"can't be found" to mean lost in the noise. According to SAE studies,
aerodynamic drag accounts for 60% of the resistance that must be
overcome for highway cruise, with tires being 25% and driveline friction
making up the last 15%.

I suspect an electric motor and associated batteries however, are going
to deform the tires. The power companies that I work with are doing
studies on a number of electric vehicles. I have been told that they
run some interesting tires and pressures.

Charles

"Charles Vincent" wrote:

Just because it is not noticeable, or measurable by the lack of sensitivity
with the instrument you are currently not using, does not mean that it does
not exist.

More weight on the bearings will cause more rolling resistance. That is
fact, not open to dispute. If you say it is, I want to buy the rights to
the bearings you are using, so I can patent them and make a fortune.

If a bird craps on your windshield, it is more likely to noticeably
influence your aerodynamic drag than rolling resistance.....I took Jim's
"can't be found" to mean lost in the noise. According to SAE studies,
aerodynamic drag accounts for 60% of the resistance that must be overcome
for highway cruise, with tires being 25% and driveline friction making up
the last 15%.

Pardon the intrusion on this interesting discussion, but just how *does* added
weight in a car impose extra load on the powerplant besides via bearing
friction and tire deformation?

Added weight means the powerplant is doing more work to maintain the same
speed; there's no way around it, the laws of physics demand it. So where's
the extra power going?

--
Dan
T-182T at BFM

("Charles Vincent" wrote)
According to SAE studies, aerodynamic drag accounts for 60% of the
resistance that must be overcome for highway cruise, with tires being 25%
and driveline friction making up the last 15%.


Semi:
Tires ........... 18
Footprint ..... big per tire
Weight ....... 80,000 lbs
Drag .......... HUGE!!
MPG .......... 5 (loaded)

Minivan:
Tires ........... 4
Footprint ..... smaller per tire
Weight ....... 4,000 lbs (for easy math)
Drag .......... MUCH less + no cab/trailer drag
MPG .......... 22

I've never really understood why an 800 lb motorcycle/rider gets (only) 50
mpg and a fully loaded semi can get (about) 5 mpg?

Motorcycle:
Tires ........... 2
Footprint ..... very small per tire
Weight ....... 800 lbs (with rider)
Drag .......... It's a motorcycle! g
MPG ........... 50


Paul-Mont