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

Remove .spam.sux to reply.

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

Remove .spam.sux to reply.

wrote)
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...


So you're saying zeppelins should take advantage of jam-jet propulsion
technology?

....when in season, of course


Paul-Mont
Usually needs to snow twice before I get the drift ~~~~

On Aug 11, 9:47 pm, "Bill Daniels" bildan@comcast-dot-net wrote:
...
I've already made a cell holder for A123 Systems "A1" cells. That's the
lithium phosphate nano cathode one used in 36V DeWalt power tools. You can
buy a couple of new DeWalt 36V power packs for $50 or so on Ebay. Then,
dismantle the pack to retrieve the individual cells. My pack will be 13.8
volts and 11AH weighing 3 pounds. It will be the same size as a 7AH 12V SLA
but weigh less than half as much.

Don't forget to add a brick of lead to the bottom of your
new battery pack, to keep the CG in the right place ;-)
Best Regards, Dave "YO"

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

("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

Montblack wrote:
("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

Motorcycles have a terrible coefficient of drag given their shape and
the shape of the rider. A fully faired bike is much better, but still
much worse than most cars. My K1200LT is one of the better motorcycles
and its Cd is above 0.5 with the windshield fully lowered and I believe
it is closer to 0.6 with the windshield at the highest setting.

So even with the relatively small frontal area as compared to a car
(although not as much smaller as you might think as the bike is taller
than most cars), the drag coefficient is so high that the total drag is
quite high in comparison.

Matt