Electrically Powered Ultralight Aircraft

("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

Montblack wrote:

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

Check this: http://www.bgsoflex.com/airdragchart.html

Matt

In rec.aviation.piloting 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


The coefficient of drag for motorcycles is usually pretty bad unless
they are faired, and it still ain't great.

The power required to overcome drag is 1/2(p*v^3*A*C)

p is the densitity of the fluid
v is the airspeed
A is the area
C is the coefficient of drag


--
Jim Pennino

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wrote:

The coefficient of drag for motorcycles is usually pretty bad unless
they are faired, and it still ain't great.

Yes.


The power required to overcome drag is 1/2(p*v^3*A*C)

No. It is v^2 unless they have changed the physics since I was an aero
engineering student back in the 70s.

Matt

In rec.aviation.piloting Matt Whiting wrote:
wrote:

The coefficient of drag for motorcycles is usually pretty bad unless
they are faired, and it still ain't great.

Yes.


The power required to overcome drag is 1/2(p*v^3*A*C)

No. It is v^2 unless they have changed the physics since I was an aero
engineering student back in the 70s.

Yes.

The drag goes up with the square of velocity, the POWER required to
overcome the drag goes up as the cube.

Force: Fd = 1/2(p*v^2*A*C)

Power: Pd = Fd * v = 1/2(p*v^3*A*C)

--
Jim Pennino

Remove .spam.sux to reply.

wrote:
In rec.aviation.piloting Matt Whiting wrote:
wrote:

The coefficient of drag for motorcycles is usually pretty bad unless
they are faired, and it still ain't great.

Yes.


The power required to overcome drag is 1/2(p*v^3*A*C)

No. It is v^2 unless they have changed the physics since I was an aero
engineering student back in the 70s.

Yes.

The drag goes up with the square of velocity, the POWER required to
overcome the drag goes up as the cube.

Force: Fd = 1/2(p*v^2*A*C)

Power: Pd = Fd * v = 1/2(p*v^3*A*C)

Ah, yes, I didn't read "power" when I looked at the formula. Sorry
about that.

Matt

wrote)
The coefficient of drag for motorcycles is usually pretty bad unless they
are faired, and it still ain't great.
The power required to overcome drag is 1/2(p*v^3*A*C)

p is the densitity of the fluid
v is the airspeed
A is the area
C is the coefficient of drag


80-ft length of the semi
(vs.)
8-ft length of the motorcycle

Does this play (much) of a role here?

Is that role expressed (adequately/sufficiently) in the above formula,
through "C" ...drag?


Paul-Mont
http://www.totalmotorcycle.com/motorcyclespecshandbook/1MotorcycleManufacturer.htm
Fun site - make / model / year. My Yamahoppers were both in there.

In rec.aviation.piloting Montblack wrote:
wrote)
The coefficient of drag for motorcycles is usually pretty bad unless they
are faired, and it still ain't great.
The power required to overcome drag is 1/2(p*v^3*A*C)

p is the densitity of the fluid
v is the airspeed
A is the area
C is the coefficient of drag


80-ft length of the semi
(vs.)
8-ft length of the motorcycle

Does this play (much) of a role here?

Is that role expressed (adequately/sufficiently) in the above formula,
through "C" ...drag?

The C is the catchall variable that is determinded by the object's
overall shape and for all but the most simple shapes (i.e. flat plate,
sphere, etc.) determined by measurement.

As to what length does specifically, it depends.

Smooth sides are going to be less "draggy" than lumpy sides.

A flat back end is going to be more "draggy" than a tapered back end.


--
Jim Pennino

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