Electrically Powered Ultralight Aircraft

In rec.aviation.piloting Dan Luke wrote:

"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?

It takes more power to accelerate the car to cruise speed in a given time.

F=ma

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?

Ummm, no, quite the opposite.

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.

--
Jim Pennino

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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.
I've stood beside a loaded one and watched it deform the tracks. A car
on the road is like a machine rolling across a mattress. Extra weight
pushes the tire down into the mattress and increases the drag. The
energy is going into deforming the tires and heating them. Ask any over
the road trucker what happens when you're hauling 40-tons and you don't
keep your tire pressure up. Tends to light up the night.

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?

--
Jim Pennino

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


Speculate please:

1. Two 3,600 lb cars - good tires
2. Traveling 60 mph (no wind)
3. 4cly - 150 hp (Honda Accords)
3. Flat highway in North Dakota
4. Fuel flow meters hooked up to both vehicles

(Honda #1)
Driver ................ 105 lbs
Fuel .................... 15 lbs
TOTAL .............. 120 lbs (1/30th of 3,600 lb car)

(Honda #2)
Driver ................. 300 lbs
Passengers ........ 700 lbs
Luggage ............. 100 lbs
Fuel ................... 100 lbs
TOTAL ............. 1,200 lbs (1/3 of 3,600 lb car) ....BTW, BTDT! g

If both vehicles were monitored for 50 miles, would their fuel flow be
(approx) the same, in cruise?


Paul-Mont

In rec.aviation.piloting Montblack wrote:
wrote)
In cars, weight matters most in acceleration and doesn't matter in any
significant amount with modern tires in cruise.


Speculate please:

1. Two 3,600 lb cars - good tires
2. Traveling 60 mph (no wind)
3. 4cly - 150 hp (Honda Accords)
3. Flat highway in North Dakota
4. Fuel flow meters hooked up to both vehicles

(Honda #1)
Driver ................ 105 lbs
Fuel .................... 15 lbs
TOTAL .............. 120 lbs (1/30th of 3,600 lb car)

(Honda #2)
Driver ................. 300 lbs
Passengers ........ 700 lbs
Luggage ............. 100 lbs
Fuel ................... 100 lbs
TOTAL ............. 1,200 lbs (1/3 of 3,600 lb car) ....BTW, BTDT! g

If both vehicles were monitored for 50 miles, would their fuel flow be
(approx) the same, in cruise?

A pulled out of my ass, wild assed guess is that since you are
increasing the load by 33%, then yes, you will see a difference,
and at that loading the tires will be visibly deformed.

Now, would you care to calculate the energy required to accelerate
3720 pounds to 60 mph versus accelerating 4800 pounds to 60 mph?

Assume gasoline is 45 megajoules per kilogram and the engine is 38%
efficient.

You may neglect all drag for this calculation and express the energy
in kilograms of gasoline.



--
Jim Pennino

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