I’ve been looking into the angle of the steam boiler on a traction engine relative to the surface that the engine sits on. This angle is always biased downwards towards the firebox.
Having measured a few angles from different sources I get:
- 0.66° Henry Greenly’s working model traction engine
- 1.26° Burrell 6NHP drawing
- 2.35° Ruston Proctor – Live Steam Models
The angle is calculated as the difference between the groundline and the front and rear wheel centres along with the distance between wheel centres. Hence:
Angle = tan-1((Frheight-Rrheight) / wheelbase)
Why do we need the angled boiler, here is what I believe, but I don’t have references to back them up:
The angle of the boiler is such to bias the water towards the firebox end of the boiler over a range of road inclinations and to avoid the crown of the firebox being uncovered when the engine is descending a hill. If there is any doubt then the engine should be stopped before the descent and the water-level raised to a safe point. Note that the engine should be kept in gear to avoid any chance of it rolling away (this is because the engine itself provides the most powerful brake on a traction engine.
The top of the firebox to the water level will be different between engine designs and so this diagram will vary.
The boiler is angle so that any condensation in the flue drains towards the firebox end of the boiler.I originally thought this might be a reason for the angle of the boiler, but cannot find any evidence to support it.
When operating the traction engine to drive machinery it is best to arrange it so that the smokebox is slightly higher than the firebox end. This will result in drier steam as the pickup will be slightly further away from the water level. It will also ensure that the crown of the firebox is covered even at a lower water level.
So, the steam boiler angle is important to maintain safe operation of the engine. For my miniature traction engine design with the simplified boiler I’m going to set the angle at 0.5°, having no firebox crown covered in water I only need a hint of an angle for the overall aesthetics.
If you know of any drawings, texts etc that give a calculation or more data on this then please forward to me: [email protected]