Help with transportation superhighway

[Ernie Rogers]

Originally Posted by ai_vin

BTW that link mentioned the CyberTran system this you can find more about here- CyberTran International

Good job, thanks,

The CyberTran is just about what I had in mind.

Erine Rogers

[Ernie Rogers]

Originally Posted by aerohead

The ideal teardrop form(about 2.7:1 fineness ratio) outside of ground effect has a Cd 0.04.I believe Morelli developed a low drag form of which Aptera borrows from.It was never tested in ground-effect.---- Any lengthening of the ideal teardrop body of revolution exhibits an increase in drag do to skin friction.I believe Cd 0.04 is the limit.Any environmental structure within close proximity will degrade the Cd.

Good job, guys,

Now we are getting somewhere. My Mark's Handbook indicates minimum drag occurs at L/D = 5 and equals Cd = 0.04 at Re = 6 million. It further suggests that Cd rises at higher Re. But, the data are ancient and I'm not ready to trust them.

There are a number of Wortmann airfoils that reach Cd = 0.006 on chord basis, at around Re = 3 million. These published Wortmann sections are about 18% thick. But, I am pretty sure when I worked on this two years ago that I was able to reach half that value, maybe to 0.002 at higher Reynolds numbers using a commercial airfoil calculator. (Don't remember the name, I've got it here somewhere.)

I'm still hoping to find a recent paper or something that has reviewed the situation for bodies of revolution. My handbook is quoting 1930s data.

Ernie Rogers

[Bicycle Bob]

Originally Posted by aerohead

The ideal teardrop form(about 2.7:1 fineness ratio) outside of ground effect has a Cd 0.04.I believe Morelli developed a low drag form of which Aptera borrows from.It was never tested in ground-effect.---- Any lengthening of the ideal teardrop body of revolution exhibits an increase in drag do to skin friction.I believe Cd 0.04 is the limit.Any environmental structure within close proximity will degrade the Cd.

Do you have a reference showing attached flow on such an abrupt shape?

According to "the Theory of Wing Sections" by Abbott & Von Doenhoff, the NACA 66021 has a cd of .0035, but the 66009, twice as fine, gets .003. Even the 63 series is only listed at up to 21% thick, although I think I did OK with a 64025 for a strut.

For a good example of balancing volume with frontal area, I'd look at the Zeppelins. It is unfortunate that so much data on shapes pertains to wings. The earlier NACA series 0010-35 shape, with 10% thickness and a continuous convex curve to the back edge, more like a zeppelin outline, got to .003 cd, but had trouble with pitch instability as a wing.

To modify a pure shape for running near the ground, the bottom is squished in proportion to how low it is. This produces a wing shape, but the lift can be cancelled by a bit of rake and the venturi effect underneath. The overall effect on drag is not as bad as the addition of wheel exposure. Successful LSR cars are not jacked up. One such HPV was made, but it embarrassed the builders.

[Ernie Rogers]

Hello, Bob,

You seem to have more information at your fingertips than I have in my books.

You have been sucked in by a difference between cars and airfoils. Somebody correct me if I get this wrong--

First of all, airfoils are two-dimensional and cars are three dimensional. Here are the drag formulas for both:

Cars: D = Cd A 1/2 rho V^2

Airfoils: D = Cd L 1/2 rho V^2

L is the length of the chord line. So, D for an airfoil has units of force per unit length of wing.

The real problem is that the Cds above have different definitions. It may not be possible to translate from one to the other, but let's try. Suppose the car has a rectangular cross-secion of unit width. Then, you could replace the A in the car formula by H, the height of the car. Equating the two drag formulas above gives--

Cd(car) H = Cd(airf) L,

Cd (car) = L/H Cd(airf) For the airfoil, L/H would be the "fineness"

Okay, so how do I translate for a car with a circular cross-section? Let's say that the car and the airfoil have the same drag when they have the same frontal area. Then, I could write an equation--

Cd(car) A 1/2 rho V^2 = Cd(airf) L W 1/2 rho V^2

and A = HW.

W is the length of the wing, or the width of the rectangular car.

We get the same result as before,

Cd (car) = L/H Cd(airf) For the airfoil, L/H would be the "fineness"

Okay, you say there are airfoils of about Cd = 0.0035 for which L/H = 5 about.

So, Cd(car) = 5 x 0.0035 = 0.0175, close to my initial guess. Well, I have settled on the suggestion from (who said it?) and used Cd = 0.025 for analysing the super-efficient rail-car.

Thanks, Bob, your words have been very helpful.

Ernie Rogers

Originally Posted by Bicycle Bob

Do you have a reference showing attached flow on such an abrupt shape?

According to "the Theory of Wing Sections" by Abbott & Von Doenhoff, the NACA 66021 has a cd of .0035, but the 66009, twice as fine, gets .003. Even the 63 series is only listed at up to 21% thick, although I think I did OK with a 64025 for a strut.

For a good example of balancing volume with frontal area, I'd look at the Zeppelins. It is unfortunate that so much data on shapes pertains to wings. The earlier NACA series 0010-35 shape, with 10% thickness and a continuous convex curve to the back edge, more like a zeppelin outline, got to .003 cd, but had trouble with pitch instability as a wing.

To modify a pure shape for running near the ground, the bottom is squished in proportion to how low it is. This produces a wing shape, but the lift can be cancelled by a bit of rake and the venturi effect underneath. The overall effect on drag is not as bad as the addition of wheel exposure. Successful LSR cars are not jacked up. One such HPV was made, but it embarrassed the builders.

[jamesqf]

Instead of putting your theoretical future transportation system up in the air, run it underground, in a tube - a larger version of an oil or gas pipeline. Then you evacuate the pipeline, and air drag becomes moot.

[Bicycle Bob]

A tube does not have to be buried to be evacuated. It could even be clear. However, even long, dedicated holes like the Chunnel have never traded the fuss for the savings.

[jamesqf]

Originally Posted by Bicycle Bob

A tube does not have to be buried to be evacuated.

True enough: my idea on that was to get it out of the way of other stuff, for what I assume is the same reason (but even more so) that the original concept was elevated on pylons.

As for trading fuss for savings, I don't think the original concept does that. I'm a great fan of trains in their proper place, but that place is where you have lots of people wanting to get from one place to another. Building all that dedicated infrastructure to move just a few passengers seems counter-productive, especially as you'd have to have some other way (roads?) to move heavy/bulky objects.

[Bicycle Bob]

Ahh, if only we were starting from scratch, with lots of money, and helicopters to get started with. :-) If you connect any two points on earth of equal altitude with a straight, evacuated tube and a frictionless track, and let gravity power the cars, they go anywhere in 42 minutes!
Overall, I think that reducing the need for long commutes and freight routes is the way to go, but it might still produce branching or grid systems with high-volume corridors. To get the best features of cars and trains in one system, small units can be combined into short railway trains under automatic control. They can be private cars that also have road wheels, or dedicated public transit cars that enter from stations. These stations could also dispatch cars filled with a few pallets of freight, robotically handled for most of their journey. The pallets, in turn, might be loaded with small containers or standard, bar-coded boxes for courier delivery.
To keep the merging lanes short from the road system, the entrance ramps could have progressively flashing LEDs, run by the RR traffic sensors. Stay beside a green zone of "moving lights," and you can merge gracefully.
One of my favourite pipe-dreams has been a transit device divided into a double or triple decker, so that people can drive on and off in velomobiles, and relax in their own space while on board.

[jamesqf]

Originally Posted by Bicycle Bob

Overall, I think that reducing the need for long commutes and freight routes is the way to go...

True, especially for the commuting. My 186,000 mps telecommute beats your 47 minutes :-) The problem with the rail system comes at the other end. When I leave my house (which itself is not where there's what anyone would call a lot of traffic), it's often to go to someplace like a lake or trailhead that might not get visited by more than a few people a week. Hardly economic to build rail there.

As you get less & less need for people to physically commute to job locations, though there'll be an overall decrease in traffic volume, a larger share of what remains will be trips with one or both ends at less-dense locations.

[ai_vin]

Something Bicyclebob said reminded me of this-

http://www.youtube.com/watch?v=rtrB8...eature=related

To get the best features of cars and trains in one system, small units can be combined into short railway trains under automatic control. They can be private cars that also have road wheels, or dedicated public transit cars that enter from stations. These stations could also dispatch cars filled with a few pallets of freight, robotically handled for most of their journey. The pallets, in turn, might be loaded with small containers or standard, bar-coded boxes for courier delivery.

The pedal powered version-The Shweeb – World’s First Human Powered Monorail Racetrack, Rotorua