Aerial Technologies, Lesson 3: BDG

Post by Steven Dale

The Ngong Ping 360 is a high profile example of bicable technology.

Note: This post was updated on May 30, 2011. These revisions reflect the most current and available knowledge we have but do not guarantee the validity of the claims made. As always, it’s best to use the information contained herein as a guide.

Bicable Detachable Gondolas (BDG) are a less common form of gondola than Monocables (MDG). Originally, BDGs were a superior technology to the MDG, but advancements in MDG technology have rendered the BDG obsolete in all but the most specific of situations.

The difference between MDG and BDG is straightforward. Whereas Monocable systems are both propelled and suspended by the same cable, Bicable systems provide those two separate functions with two separate cables.

One cable is stationary and doesn’t move. It’s this cable that gives the gondola support. This cable acts much like a rail would for a traditional transit vehicle. A wheeled bogey attached to the gripping mechanism of the gondola runs along this cable much as train’s wheels would run along rails.

The second cable is not stationary. It runs in a loop and is powered by bullwheels at the terminals. The gondola grips attach and detach from this moving cable, thereby providing propulsion.

BDG Stats:

  • Maximum Speed: 27 km/hr (revised upwards from 24 km/hr).
  • Maximum Capacity: ~4,000 pphpd (revised downwards from 6,000 pphpd).
  • Vehicle Capacity: Up to 17.
  • Wind Stability: Operational in winds up to 70 km/hr.
  • Maximum Span Between Towers: Up to 1,000 meters (conditional on capacity).
  • Cost: $15 – 25 million (US) / kilometre. (estimate).

While Bicable systems are more expensive than Monocable systems, this added cost is not really justified. The only two real advantages of a Bicable as compared to an MDG are as follows:

  • Bicables can travel at greater maximum speeds than the MDG. This speed premium, however, amounts to only 5.4 km/hr.
  • Longer spans without need of intermediary stations. Like above, this premium is modest. Whereas an MDG can span 700 meters without need of an intermediary tower, the BDG can span 1,000 meters.

These modest advantages are offset by the following:

  • Higher capital cost
  • Larger station size
  • Larger tower profile.

Because of their higher capital costs as compared to an MDG, with little real advantage, Bicables are increasingly becoming an abandoned technology in the cable transit world.

The Teleferico Madrid is an old but strong example of bicable technology.

Proceed to Aerial Technologies, Lesson 4: Funitels

Return to Aerial Technologies, Lesson 2: MDG

Creative Commons images by jaaron and Shadowgate.

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  1. Hi there, Thank you for for using my photograph in this post! Please attribute the photograph to Duncan Rawlinson and link to me @ http://www.TheLastMinuteBlog.com Thank you.
  2. José Rodrigues
    Please send more details about CPT to my e-mail Regards
  3. Jose, Please send me an email (in the comments section) and tell me what you're interested in. I will be happy to respond.
  4. José Rodrigues
    electrosistemas@netmadeira.com Hello Steven Dale I have two CPT platforms working on rails on two farms to carry agricultural products, suported on rails like a russian montain. Now another Farmer wants me to do another one suported on cable, as it shall have three diferent directions.... It is not so eazy to solve... Maybe you can help? Regards José Rodrigues
  5. Hello Steven. I´m after detail plans and sections (3d would be nice too) of a bicable gondola for an Uni poject. Can you maybe help me out here? Thanks a bunch
  6. Rubes, That's something you'd have to talk to the industry about. At the same time, I'm fairly certain they wouldn't release detailed blueprints due to the intellectual property issues involved.
  7. I could offer some informations about measurements if you would need those. But I think taking a look at photos of existing BDG's in the internet should also work. However the most important thing is the cable itself: the parellel distance between one direction and the other is 6.2 m. The cabin runs almost in the middle of the rope, so depending on your cabin size you will know where the platform begins. The technology itself is a package of around 20 meter length and positioned 4 meter or 4.5 above with a height of around 2 meter. That's basically all. Hope I could help you a little.
  8. Hi Steven, You mention that the BDG can handle faster wind speeds than the MDG. How much faster? Thanks!
  9. Hi Julia, That post is rather out dated. What I'm hearing from the industry is this: Technology developments with MDG systems have kind of rendered BDGs obsolete. They just don't have that much of a wind speed premium anymore. If you were looking for wind speed resistance, you'd probably want to look at a Funitel or 3S.
  10. What about maximum capacities? Back when these were written, MDGs were listed at 3000 PPHD, BDGs at 6000 PPHD. That's a big difference, and potentially highly relevant to urban applications. Has that gap also been eliminated?
  11. @ BrianTH, I think those two posts are going to have to be revised. In the year since they were written, I've learned that MDGs are now capable of carrying 4,000pphpd and BDGs are really just not recommended by the industry any more. Really, if you want the bump up in capacity, probably best to go with a Funitel or 3S/TDG.
  12. @ Julia "Hi Steven, You mention that the BDG can handle faster wind speeds than the MDG. How much faster? Thanks!" MDG can handle about the same wind speeds like an BDG, but a BDG can transport more people.