Electrically Powered Ultralight Aircraft

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

"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

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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