Note: the Helix page has lots of photos. To ease the load for those of you on dial-up connections, I have split the page in several pages. Just hit the "Next Page" link at the bottom of the page to go to the next page.

Status
We usually have just one overall photo for the area discussed on the page, but there isn't much to see anymore now that the helix has a Masonite board jacket on. The Masonite board is 30 inches (76cm) tall. Below you will see the most recent overall photo (first one), and the helix before it got dressed (second one). These photos were taken with a wide angle lens from under the Allegheny Mountain.

The helix is finished. The track is done. The visible track on the top of the structure has been ballasted. The two tracks of the helix have been connected to the rest of the layout via Shire Oaks. Once Pogo Mountain is built (the center, top opening of the helix), we will complete the scenery work on the helix tracks. What is not readily visible are the infrared detection circuits we built to report the train movements inside the helix. On the front of the helix' Masonite board (far right in the photo below) are twenty LED's that turn on when a train passes through the corresponding infrared light path. For more info about these circuits, see the Helix Elevator article. This photo shows the helix painted in black, matching the rest of the layout's fascia.




(taken on August 13th, 2002)

Design
The helix starts by encircling Pogo Mountain as it starts its decent down. It is a double track helix so that we can handle large, slow trains and fast trains, as well as one train moving down while another moves up the helix. The outside radius is 19 inches (48cm) with an effective grade of 1.75%, and the inside radius is 17 inches (43cm) with an effective grade of 1.95%. This should be sufficient clearance for even the long passenger cars we have. Given the total length of the run per rung, we will have a vertical separation of 2.5 inches (6.35cm). Each rung has 23 feet (7m) of track on it, making for a total (with lead-ins) of around 254 feet (77.4m) of track!

The diagram on the left shows the track plan of the top rung of the helix. The A - A tunnel area indicates approximately where the track will disappear under the Pogo Mountain area. The diagram on the right shows the bottom rung as it gets ready to enter the Altoona Yard area.

Progress
The next collection of photos shows the progress of this part of layout over the duration of the layout.

Our first attempt at building the helix (started on April 9th) was flagged as a prototype :-). The next set of diagrams shows the various designs we have done up front to determine what materials we need and to visualize what the unit is going to look like. The first diagram shows the top view of one level of the helix. It gives the overall dimensions of the subroadbed (luan board) material. We will be cutting two halves and two straight sections.


Knowing what the subroadbed needs to look like, the next diagram shows the top and side profile of the base frame. This is where the vertical supports and the subroadbed will be attached to. There will be two pieces of 1/2" plywood attached to each other via 1" x 2" stock wood strips. These strips will be spread throughout the structure to provide rigidity to the structure, and to provide ample surface for attaching the vertical posts that hold the subroadbed. The strips will be offset 1/4" away from the edges of the plywood so that the vertical posts will not have to have large areas of wood removed (these will "hang over" the edges of the subroadbed luan board).


This diagram represents the cutting pattern for the base frame plywood parts.


This diagram represents the cutting pattern for the subroadbed luan parts (except for the bottom and top rungs of the helix - they are custom cut).


In the diagram below we have super-imposed the vertical strips made out of high-quality 1" x 2" stock pine. These will have grooves cut into them to support themselves against the base frame and to support the subroadbed luan board. The sizes listed next to each strip indicates the relative offset that the subroadbed grooves need to be, measured from the top of the base frame. In other words, this is the implementation of the grade of the subroadbed. The "entry point" is where the distance says 0" and goes around clock-wise. We came up with these numbers by measuring the distance between the vertical strips and, with the desired grade, calculated the relative rise that needs to occur at each vertical strip location. Some small round-off was included to make measuring these distances managable (see table below for the values calculated in Excel). The last entry, #8, was just for verify my logic. The Distance From Entry Point is the inside radius of the curves.

The last design diagram is that of the vertical pine boards that will provide the support of the subroadbed. The areas which are indicated by "varies" are where the subroadbed level changes are going to be implemented (i.e. implementation of the grade). The boards will all be attached to the base frame a half inch below the frame. The 1/4" grooves will vary vertically based on the spacing indicated in the table above. In the future we will have masonite board to wrap the outside of the helix and that will be attached to the outside vertical boards.