Help with transportation superhighway
 

Hello, guys,

About a week ago, I was asking for help on a little project, to predict the ideal high-efficiency car. Well, I have labeled that job "complete" and I'm on to a new one. (The document from the last project was posted today in the general efficiency forum.)

New project: To define the ultimate public transportation vehicle. Something better than a train, better than a bus, faster than a plane for short distances, say up to 200 miles. The premise of the new vehicle is that it will operate in a "transportation superhighway," a network with distributed control, with traffic routed for maximum throughput and efficiency.

The vehicle is presumed to travel on a rail and be small enough to provide near-point-to-point transportation. I am imagining a body of revolution sized to carry eight passengers--

7.8 ft diameter x 35 ft long (D/L = 0.21?)
200 mph design speed
Up in the air, no ground effect. Re = 20 million? (from memory)

My question: I guessed that a drag coefficient (based on frontal area) of Cd = 0.02 should be achievable. Could somebody help with this, verifying or improving this number? I was unable to find a place to get the information.

Ernie Rogers

Ernie, you got your Cd figure wrong for sure. Maybe you meant CdA, since you mentioned frontal area, but even then 0.02 figure does not seem right.

Honestly, what's wrong with trains? I traveled to Italy last year, taking the train for more or less 200 miles everyday. There were trains every 15 minutes during peak hours and those things travel up to 100 mph with no traffic! And it was insanely cheap!

I agree, the number sounds wrong.

And I also wonder how another form a rail transport could improve on trains dramatically, since the cost will be much higher for multiple smaller vehicles and as far as CD goes trains will win over shorter vehicles because of the length.

My grandma says one of the biggest problems with America is that it did not take trains to the level of integration that Europe did.

The reason for that is that the automakers and big oil lobbied against railroads, and in favor of government building more highways.

superhighway
 

I did two or three posts on trains.The data was from Hoerner.If you can chase those down with the search engine,there might be some preliminary info to get you started.-------- Cd0.02 would be a passenger airliner wing.That would be hard to pull off.--------- The rail system,cross-ties,girders,and pylons would still create some ground-effect interference.----------- An exposed underside would aggravate lift,especially with a truly "light" rail system and the velocities you're talking about.---------- Since power varies as the cube of velocity,I believe there are already concessions made to speed,as there becomes a point where the cost of some velocity can not be justified in fares.---------- Since you are describing an unknown quantity,there won't be any real empirical data to guide you.--------- You may want to study roller-coasters.Coaster-based systems can operate mostly on gravity.Empty"trains" lifted with renewable energy.Passengers ride up to load from elevators run on renewable energy.Any 34-story building (there are over 55 cities in N.America with them) can provide the base structure which receives the add-ons.Once loaded,the cars accelerate to over 100 mph on gravitational pull alone,and can coast great distances when aero-maximized.Rolling resistance is already the lowest known,short of Mag-lev.The infrastructure requires a very small footprint across the landscape.Many possibilities.

If you have control over your lane, as with a railway, you don't need heavy crash protection. With less weight, there's less incentive for steel wheels, although they are wonderfully slender. In any event, adding wheels and a ground plane will have a lot of effect on the CD. To get those .0___ cd ratings, you need flawless shapes. Maybe our kids will think of trains as something that you can run your fingernails along without feeling anything until the little tick for the door seam, near the back, but it is a stretch for me. If fit and finish can save half our oil, it seems like a noble crusade.

Around here and in other major cities, there also used to be much more extensive public transit with street cars, but those tracks were torn up in the early '20's so more automobiles could be sold.

Hi, Tas,

You aren't facing the question. Do you have a source for drag coefficients of bodies of revolution in incompressible flow and high Reynolds numbers?

Access to a CFD program should allow calculation of a Cd, but that's more work than I would expect.

I calculated the Reynolds number:

Sea level
200 mph
35 ft long ------> Re = 65.5 million

Ernie

Okay, guys,

I think you have wandered off the topic. (It was aerodynamics of a high speed car without ground effect.)

But, let me join in. Here are CO2 emissions for different transportation choices, including the new "aerocar" high speed 8-passenger "tear drop."

Shinkansen Bullet Train....................100 gm CO2 /passenger mile
U.S. Train.......................................95
Transit Bus.....................................64
Prius (two people)..........................131
Airlines.........................................3 23
X Prize car (100 mpg, 2 people)..........59

New 8 passenger rail car...................13 gm CO2e /mile

/Ernie Rogers
Some of the data are from here:
"High Speed Rail and Greenhouse Gas Emissions in the U.S."
Center for Clean Air Policy and Center for Neighborhood Technology