Electrically Powered Ultralight Aircraft

wrote:


The biggest source of drag on a car is air followed by tires.

Of course the makers are going to put hard tires on as well as
streamline the vehicle to get mileage up.

The less drag, the less gas the vehicle uses.

What's your point?


That is only true in cruise on the highway. In stop and go city driving
driveline friction is the majority, followed by inertia. Air and tire
is a small percentage combined.

Charles

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


The biggest source of drag on a car is air followed by tires.

Of course the makers are going to put hard tires on as well as
streamline the vehicle to get mileage up.

The less drag, the less gas the vehicle uses.

What's your point?


That is only true in cruise on the highway. In stop and go city driving
driveline friction is the majority, followed by inertia. Air and tire
is a small percentage combined.

Inertia is not drag.

Inertia is F=ma.

In stop and go driving, F=ma dominates.

If it didn't, hybrids converting the F in deceleration into energy in
the batteries instead of heat in the brakes wouldn't get their high
mileage numbers.


--
Jim Pennino

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"Phil" wrote

I know you're only half serious,

Yep, only half, until you really start to think about it.

but yes, that would have to be
considered. That's a risk in hybrid autos as well. EMTs and
firefighters are taking special training to handle the wrecks of these
cars. And the gasoline we use for our current airplanes poses the
risk of incinerating the occupants in a crash. I am not sure that an
electric plane would actually pose more risk.

I think there is a higher risk, perhaps by many times.

Ever seen a LiPo Battery have a catestrophic failure? One of the primary
ways a LiPo can be caused to fail in that way is physical damage. Ask the
electric RC guys. Most of them would never think of putting even a slightly
physically damaged LiPo back into service, unless it was a really cheap
plane that they wanted to see destroyed.

Now imagine a battery many thousands (or even a few hundred) times larger,
and larger capacity to match.

I'll take my chances with the gasoline fire, thanks, ANY day. That speaks
nothing of the chance of electrocution, or chemical burns or injury due to
the cell's chemestry.

I would think that the
increased reliability of the propulsion system would decrease the risk
overall. How many people are killed every year in crashes caused by
engine failures?

How much more reliable is an electric of that size ( to run a decent sized
airplane with decent performance) and power going to be, especially if it is
designed with lightness as a major design consideration? That remains yet
to be seen.

OK, even if we give the electric a given reliability superiority, that is
not going to save all that many lives. Most power failures in I.C. powered
airplanes are not that big of deal, and many times never even reported. Far
more die due to stupid pilot tricks (a broad spectrum category to lump a
bunch of other things together) than loss of power.

Nope, lots of problems to consider before we start considering an electric
aircraft. Lots more than we can maybe even consider, at the moment, even if
we were to figure out a way to make a practical airplane electric powered,
don't you think?
--
Jim in NC

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

The biggest source of drag on a car is air followed by tires.

Of course the makers are going to put hard tires on as well as
streamline the vehicle to get mileage up.

The less drag, the less gas the vehicle uses.

What's your point?


That is only true in cruise on the highway. In stop and go city driving
driveline friction is the majority, followed by inertia. Air and tire
is a small percentage combined.

Inertia is not drag.

Inertia is F=ma.

In stop and go driving, F=ma dominates.

If it didn't, hybrids converting the F in deceleration into energy in
the batteries instead of heat in the brakes wouldn't get their high
mileage numbers.


Yes Jim, I knew the difference, and I see you know too. I had assumed
you also knew the difference between aerodynamic drag and rolling
friction when you lumped then together in your statement "The biggest
source of drag on a car is air followed by tires." I figured you were
using drag in a more generalized way rather than jumping to the
conclusion you just didn't know the difference. Since you are insisting
on being pedantic, then I will have to point out that inertia is really
just the m in F=ma, the formula just establishes a relationship between
the property of mass called inertia and force and acceleration. I
expect that the manufacturers are working to reduce all of the
"retarding" forces on their vehicles, which benefit them without regard
to the motive source. Electric vehicles can have an advantage in the
regime where inertia is the dominate "retarding" force and a
disadvantage where it is not.

Charles

wrote:
In rec.aviation.piloting Ernest Christley wrote:
wrote:

The laws of physics say once an object is in motion it takes no energy
to maintain the velocity UNLESS there is some other force at work
that would cause the velocity to decrease.

Since at a constant speed, the a in F=ma is zero, the force is zero
no matter the mass.

Once at speed in a car (or airplane or rocket ship) the only energy
needed to maintain speed is that equal to any drag forces that
would otherwise slow the car down.

Have you looked at the current crop of high mileage cars?

They all have very aerodynamic profiles to get the air drag down.


They also have very narrow, hard tires. Unfortunately, the DOT has laws
against solid rubber tires or they could be made even harder.

Your analysis would be mostly correct if we were talking about trains.

My analysis of what?

The biggest source of drag on a car is air followed by tires.

Of course the makers are going to put hard tires on as well as
streamline the vehicle to get mileage up.

The less drag, the less gas the vehicle uses.

What's your point?


The point is that weight matters...even in land-locked vehicles.

In rec.aviation.piloting Ernest Christley wrote:
wrote:
In rec.aviation.piloting Ernest Christley wrote:
wrote:

The laws of physics say once an object is in motion it takes no energy
to maintain the velocity UNLESS there is some other force at work
that would cause the velocity to decrease.

Since at a constant speed, the a in F=ma is zero, the force is zero
no matter the mass.

Once at speed in a car (or airplane or rocket ship) the only energy
needed to maintain speed is that equal to any drag forces that
would otherwise slow the car down.

Have you looked at the current crop of high mileage cars?

They all have very aerodynamic profiles to get the air drag down.


They also have very narrow, hard tires. Unfortunately, the DOT has laws
against solid rubber tires or they could be made even harder.

Your analysis would be mostly correct if we were talking about trains.

My analysis of what?

The biggest source of drag on a car is air followed by tires.

Of course the makers are going to put hard tires on as well as
streamline the vehicle to get mileage up.

The less drag, the less gas the vehicle uses.

What's your point?


The point is that weight matters...even in land-locked vehicles.

In cars, weight matters most in acceleration and doesn't matter in
any significant amount with modern tires in cruise.

--
Jim Pennino

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jimp wrote

This is probably a historic moment.

Normally what happens when thread drift begins is that it increases
at an increasing rate such that what was originally zepplin aerodynamics
becomes the best recipe for strawberry preserves...

LoL !

Thanks, I needed that!
--
Jim in NC

"Dan Luke" wrote

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?

It isn't. He failed to include bearing resistance (only tire deformation)
in the original assessment of increased rolling resistance.
--
Jim in NC

On Aug 18, 12:24 am, "Morgans" wrote:

Nope, lots of problems to consider before we start considering an electric
aircraft. Lots more than we can maybe even consider, at the moment, even if
we were to figure out a way to make a practical airplane electric powered,
don't you think?
--
Jim in NC

Oh, definitely. We are nowhere near a practical electric airplane.
But I think the potential is there (no pun intended), and I hope they
keep working on it.

In rec.aviation.piloting Morgans wrote:

"Dan Luke" wrote

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?

It isn't. He failed to include bearing resistance (only tire deformation)
in the original assessment of increased rolling resistance.

I didn't include it because the increase in wheel bearing friction (the
only bearing friction effected by weight) is negligable in modern
vehicles.

The total bearing friction, i.e. all the bearings in the vehicle is
around 10% of the total drag forces trying to slow a car.

Adding a little weight to a 2000 to 3000 pound car causes an insignificant
change in the wheel bearing friction.


--
Jim Pennino

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