gradient?

[djrobot]

hi moving on with my track design i now have started to work out some gradient issues.
basically i have a narrow garden so am going to have a return loop 10' diameter at each end but in the middle i intend to drop the level of the track via a helix with roughly 1 and 3/4 full revolutions (630 degrees) . I need to drop 30cm / 1' in that helix . what is the maximum gradient recommended to run aristocrat dash9/ sd45 or usa trains sd70 on? i have for some reason 1:42 e.g. 1 foot gained in 42 feet travelled...is this correct...if so i think I'm good with using 2 x pye x radius and 630 degrees of rotation (1 and 3/4 circles)

anyone familiar with this sort of maths could they confirm or in deed shot me down on my calculations ;-] cheers Rob

 

[bobg]

1:40 is a tough-ish grade in a straight line, it'll pull even harder on a curve. Achievable grades depends mostly on how much you want to pull up them. Lay a test line on a plank and jack up one end a bit at a time (bricks?). If you can start the train from dead, it should be able to manage well enough at a run.

 

[stockers]

I agree with Bob = a test track is a good idea and remember that pulling on a curve will add significantly.
1 in 40 is certainly workable but it does depend on what you want to run. Long American style freights wont get up it unless you add locos (which could be a nice idea). Bucolic style contry trains would have little problem.

10ft diameter will give you about 32 foot circumference. 1.75 turns will make this 56ft (approx). 1 in 56 is getting a lot more workable and should also give you clearance for the helix going over itself (you need about 8 inches but check your stock (and your mates stock!)

 

[ntpntpntp]

... clearance for the helix going over itself (you need about 8 inches but check your stock (and your mates stock!)...

If you're running American stock such as USA Trains double-stack you'll need something more like 10 inches clearance I reckon!

 

[kedwards]

To get my track layout in I was forced to put in a long gradient at 1:29. Most of it is straight but there is one 90 degree curve at about LGB radius 4. Very long trains struggle on the curve, but Thomas the Tank Engine running off a 12V battery pack can pull 10 trucks up it with ease.
There's a video on YouTube with the gradient on it at http://youtu.be/Fydtr7ueVd8. Obviously wet rails create a bit of a problem!