Monthly Archives: February 2012

Thanks to the discussion at Burnsland, I was able to refine the pilot truck a bit more:

The equalizer bars were made to be thinner to allow the bottom of the leaf spring to show. Transverse bar and longitudinal bar remodeled, etc.

Interesting that the pilot only has three longitudinal bars. The side with two bars faces the front… I think.

There is now a discussion on Burnsland about the pilot truck, with rare pictures of the truck detached from the engine.

Some observations I took from the thread:

• Disney used almost no bolted connections on the frame itself! Everything appears to be (heavily) welded. In one way it makes some sense given the scale of the truck, but I wonder how easy it is to perform maintenance. For example, if one of the braces crack?
• The transverse bar has a different profile–more trapezoidal than rectangular. That’s easy to fix, but it also appears to be “doubled”–having an inside and outside pair.
• I can finally see the center swing casting–but unfortunately the photos aren’t clear enough to show how it’s assembled. However, I think I have enough to make a good guess.
• I will revise the equalizer bars to be thinner.
• A good point was brought up that I give a bit of thought to previously. In actual pictures of the engine you will see the bottom of the leaf spring, and in the side profile of the truck I made, you do not. I believe this is attributed to the actual weight of the engine flattening the spring. The spring I model is a static solid body, so it cannot compress.

I’ve never drafted suspension system before and I’ll have to think about which state to show: compressed or uncompressed. The purpose of the drawing should govern first, but there’s a question of faithfulness representation of the engine “as seen” by the user.

As there is so little material out there on the Holliday’s pilot truck, what I’ve made is pretty much a guess of what it would look like based on contemporary sources and a few known major dimensions.

The major shapes and look, I think, are at least correct: the flat equalizing bars, the leaf springs, the axle boxes, the squared pedestals. These parts were drawn from the original Holliday drawing. The truck’s profile shows these components: