Q1. What is the maximum gradient a train of six bogie coaches can manage ?
a) (Mike Boydon, N-Gauge) This depends to a great extent on the loco, e.g. a Grafar 4P out of the box might manage 6 downhill, whereas a Fleischmann 7161 with Langley S15 white metal body kit will manage 30 bogies on 1in30. I would suggest nothing steeper than 1in30.
b) (Ken Howard, N-Gauge) I had gradients of 1in40 on my last layout. No problem with Farish coaches but Minitrix were far too heavy.
c) (John A Arkell, SEmG) It depends on many things not least of which is the tractive effort of the locomotive and the rolling resistance of the coaches. Tractive effort can be affected by the materials used for the wheels and the power developed by the motor. I use steel rimmed wheels (Sharman) on my kit and scratchbuilt locomotives. I think they have a greater friction between wheel and rail than polished nickel plated or nickel rimmed wheels such as Romford or those found on commercial ready to run locomotives. What you will have to do is set up a plank with a length of the track you wish to use and experiment with different locomotives and coaches. You will soon find what your set-up will cope with and what needs banking assistance.
d) (Colin Duff, SEmG) I have gone through a sharp learning curve (gradient??) with my current layout. All my previous layouts, save a Triang-Hornby one I built when I was about 10 years old which had an up and over girder bridge with a frighteningly sharp gradient which relied upon Magnahesion, have been level. However my current layout has three levels. As a general principle any gradient should be as shallow as possible. In other words you need as long a run up as you can achieve to gain the required altitude. Apologies to all who do not like the North American/Continental use of percentages but I am afraid that is what I think in these days. Even 1% ( a vertical rise of 1 inch in 8ft 4in) on the real railway is troublesome. To put this into perspective the gradient from Exeter St Davids to Exeter Central is circa 2.7%. It is much the same with models. Trying to squeeze 3 levels into a 12ft x 8ft space on my layout I have gradients of 4% (a vertical rise of 3.5 inches in 7ft) and most of the rise is on curves with a minimum radius of 2ft . This is of course horrendous but it works, if only because in the space I have I only intend running a maximum of a loco with 5 coaches or up to a 5 car EMU. (By the way I am working in 4mm scale and I am not sure how experience in this scale follows for 2mm, what with locos, etc, being lighter.) I suggest you do what I did and run a series of trials with your rolling stock on a test variable gradient. I used a 4ft strip of plywood 2 inches wide with track on it using various size risers calculated and placed by trigonometry to set particular gradients. That way you can find out what your stock is capable of on various steepnesses. I found within reason the power of a model loco is proportional to its real life capabilities - of course excepting models with really weak or strong motors. Thus up my 4% round a 2ft radius curve a Terrier can manage one mk1 coach, an M7 two, a BR Std class 4 three-four, a WC/LN five-six.
e) (Richard Giles, SEmG) The max gradient depends on the loco!! Farish steam locos have no traction tyres and within the range some locos are worse than others - e.g. 8F, Castle, Hall. Diesel locos will normally pull anything up anything!! 1in30 or 1in35 is about max but reduce to about 1in40 to 1in45 on curves. Remember that in a figure of 8 you can have both an incline and decline thus reducing gradients!!
f) (Paul Severs, SEmG) I had the misfortune some years ago to design an N-gauge layout for my father-in-law, based on Riccarton Jcn. and it had gradients to hidden sidings below. It was designed on the basis of a 4mm design reduced by ½. When he began to build it, we realised that there are greater problems in N-gauge than we envisaged. In spite of using a special Peco gradient track [? is it still available] which had a serated rail head to aid adhesion, only very short trains could manage the gradients, and the particular difficulties were on the curves [which were down to the minimum, ~ 12" radius]. It seems that the increased friction on the curves, together with the lack of weight in typical locos, made hill-climbing too difficult.Now admittedly in the tight space he had available to him - ~ 2'6" x 8'0", the gradients were of the order of 1in30.
Q2. What special precautions (if any) have to be taken with gradients on curves, and what would be the minimum advisable radius on a gradient ?
a) (Mike Boydon, N-Gauge) Curves on gradients are best avoided if at all possible, if they have to be included then ease the gradient to 1in45 or better.
b) (Noel Leaver, N-Gauge) I would definitely try to change gradient only on straight track to avoid compounding problems.
c) (Ken Howard, N-Gauge) I had 15" radius curves on the gradients and had one serious problem. Peco wagons would invariably uncouple when going down grade. When the loco entered the curves it would slow and the rest of the train would bunch up and some of the Peco couplers would stand up in the uncoupling position. Then as the loco came out of the curve it would accelerate and the train would pull apart before the couplers could return to the horizontal. I had to fit brakes to the axles of all my brake vans.
d) (John A Arkell, SEmG) I try not to lay curves of less than three feet radius on any layout but that is because I work in EM and some of my locomotives are not designed to go round less.
e) (Colin Duff, SEmG) Curves cause extra resistance which on a rising gradient adds to the force of gravity, thus best to avoid, but again I suggest it is far better to test with your stock than rely on any theory or advice from another. It is best to avoid starting and finishing a gradient on a curve - this is not possible on my layout but I have got away with it by using gradual vertical transitions into and out of the gradients. Just as it is best to use a transition curve into a constant radius curve it is best to do the same with gradient changes. It can now be admitted (and some SEmG'ers already know this) that due to a change of track plan I made whilst construction was underway, and thus it was not thought through properly, I ended up with the middle of a reverse curve happening just as a gradient peaked. Unsurprisingly this was a cause of regular derailments particularly with long wheelbase locos which just wanted to carry straight on, which brings us onto your next question!
f) (Richard Giles, SEmG) Curves should not be less than 15" radius (for N gauge) to be safe. I tend to work with a baseboard width of 2' but if you are doing a figure of 8, you need 30" minimum.
g) (Paul Severs, SEmG) See answer to question 1.
