Cumberland Times-News

Bob Doyle - Astronomy

March 12, 2009

Human power could help us to get around

All three of our U.S. car manufacturers are facing dropping car sales and the crushing burden of their many retirees, pensions and health care. Business as usual will just lead to further increase in their debts and the need for more government funds.

Discontinuing a number of models is helpful, as fewer cars will be purchased in the next few years. But will the new expensive models be sold in sufficient numbers to keep the companies out of bankruptcy? There are two “out of the box” options that could be beneficial, for keeping more of their workers on the job and for reducing our dependence on foreign oil.

The American public has had an obsession with oversize cars for decades. The key reasons boil down to convenience in carrying stuff and being safer in a crash compared to small cars. But the resale value of these vehicles is dropping and few can afford the new oversize models. The best the car manufacturers can do is help retrofit these larger vehicles with more efficient engines (deliver more miles per gallon).

Here is a dirty little secret about cars; very seldom (1 percent of the time) is the full power of the engine used. When a car is cruising, the engine output is typically 20 horsepower (versus its full 200 horsepower). The need for extra power is when a vehicle is accelerating, either when taking off or passing another vehicle.

So most large vehicles could get by with an engine only half as powerful as the engine that the vehicle came with. This smaller engine would get higher miles per gallon at the sacrifice of acceleration and top speed. This means having to wait longer before entering a highway from an entrance ramp and taking longer to pass a slow moving vehicle.

The cost of the smaller engine would be much less than a new vehicle and probably cheaper than trading in their existing vehicle for a hybrid. There will be some who would never consider this option; this indicates their need for a powerful car engine as an expression of their need to dominate others. This need is as inappropriate as a person who dresses for work wearing combat gear in an attempt to intimidate fellow coworkers and the public.

The second option is for Detroit to develop a light weight hybrid vehicle, licensed for ordinary roads but not highway driving. A standard car at 3,000 pounds has an internal combustion engine that operates at about 20 percent efficiency. If this car is carrying a 150-pound driver, then nearly all of the car engine’s power is devoted to carrying dead weight (of the car), reducing the car’s real efficiency to about 1 percent (as driver is about 1/20th the weight of the car).

So as long as the car is much heavier than its human riders and cargo, most of the car’s energy will be used to push dead weight around. One criticism about ordinary Hybrid cars is that their battery packs are much heavier than the weight saved in reducing the weight of their gasoline/diesel engine.

What vehicle moves humans with the least energy per mile? Surprisingly, it is not walking, but riding a bicycle with energy per mile about one quarter of walking. A more stable platform is a three wheel bicycle or tricycle. Self propelled vehicles (either driven by legs or arms) have much lower motion energy than cars and produce less damage upon collisions, reducing the need for protection such as air bags and bumpers.

When going up a hill, what kind of motor should be used to supplement human pedal power? An electric motor would require a battery pack with more dead weight to push along.

Why not use the fluid that surrounds us — the air? A motor driven by compressed air would have no emissions and you would never run out of air. To compress the air, each tricycle would have a pump, driven by the same set of pedals that propels the vehicle. So before each drive, you would compress air into a tank using the pedals until you had enough pressure to go to your destination or make the round trip.

You then switch the pedals to move the vehicle and begin slowly to roll away using your muscular power. A air-pedal tricycle with protective shocks, air tank and motor might weigh only a few hundred pounds. As you approach a hill, you would turn on the compressed air motor to give you extra power.

Then once on level ground, cut out the air motor and rely on human power. A small generator like those on bicycles would power pulsing LED lights to alert those around you, just as mail trucks and school buses use strobe lights.

Venus drops as spring begins

Catch the brilliant planet Venus as it begins to get dark, for she is setting about 8 minutes earlier each night.

Venus is that striking point of steady light in the western dusk sky that has been on view all through winter.

Venus with her higher orbital speed, is catching up to us, drawing about 150,000 miles closer to Earth each night. On March 27, Venus will have pulled even with the Earth, being 26 million miles away and lost in the sun’s glare. Then in April, Venus can be spied low in the eastern dawn.

There will be no programs at the Frostburg State Planetarium today due to our spring break. Our programs will resume next Sunday. Call (301) 687-7799 to request a free Planetarium/Discovery Center bookmark (with small map) by leaving your name and mailing address on voice mail.

Bob Doyle invites any reader’s comments or questions; call the above number or email him at rdoyle@frostburg.edu .

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Bob Doyle - Astronomy
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