This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
An ordinary hand sled can be easily converted into a sled that can be guided like a bobsled by the addition of one extra runner. To attach this runner, a piece of wood is fastened to the under side and in the center at the front end of the sled top. A runner with a crosspiece on top is pivoted to the extending wood piece, which should be of a length to make the position comfortable when the coaster, sitting on the sled top, has his feet on the ends of the crosspiece. Careful measurements should be made to have the lower edge of the runner on a level with or a little lower than the sled runners.
Ill: The Extra Runner in Front is Pivoted, and When Turned, Guides the Sled