Length of one turn of helix T = 2*pi*radiusR, or T=6.28*R
Grade is: vertical separation H / T*100, or G0*H/6.28*R
Min. recommmended H is 1.5 inches, and max recommened grade is 3%. Do
the arithmetic. :-)
Thanks for that. As it happens I have a PhD in mathematics, so I can do the
sums myself. I was rather hoping to benefit from your expertise, not so much
on the steepness, but the effect for the curve in a loco's ability to pull
up the helix, and also on the incidents of derailments. I was also hoping
for some comment on going up and down the helix, as well as what minimum
radius I should use in my design on the flat.
Standard rule, use the largest radius that will fit in your space, it
can never be to large only to small.
Make friends in the hobby.
Garratt photos for the big steam lovers.
Well in that case you can also work out what superelevation (cant,
banking) to use on the curves to make it easier for your stock to go up
(or down) without falling off the track because of the lack of
suspension. As you are no doubt aware, you will only ever have a maximum
of three wheels of a 4-wheel wagon or bogie in contact with the track at
any one time.
I built a "rectangular helix" on my OO layout. The curves are 4 feet
radius, and there is an 8 foot straight between the two semi-circles at
the ends. More details on my web pages (URL in sig, and select "helix"
in the navigation list). The incline works out at about 1 in 75, which
means I should be able to pull rather a lot of coaches/wagons up it
behind my favourite locomotives (Bachmann 56XX 0-6-2T, since you ask).
Derailments should only happen because of your bad tracklaying. Since
you will be taking extra care over laying the track on your helix, you
shouldn't have any bad track. So you shouldn't have any derailments.
You don't say how much space you have. I suggest you use the largest
radius possible that fits in with the rest of your layout. Let us assume
that you are going to use "my" radius (4 ft), but since you are building
it in N, you halve that to 2 ft. Then you are going to build the incline
at 1 in 50 (2%) which is not too steep so you should be able to get a
reasonable train up it. The circumference (on the flat) will be 150
inches, which means the rise for one turn will be 3 inches. The height
from the track on one level to the underside of the support of the next
level will obviously be less than that, say 2.5 inches. Now you have to
consider the future, and maintenance. Is 2.5 inches going to be enough
room for you to get whatever tools you need in there to keep your helix
going whenever things go wrong (as they undoubtedly will sooner or
later). On my helix, the levels are 6 inches apart, and that is too
little sometimes, especially when you want to insert a few more
trackpins, or you want to solder another wire on the wrong (i.e.
inaccessible) side of the track.
OO in the garden http://www.yddraiggoch.demon.co.uk/railway/railway.html
Superelevation becomes a vertical curve on sharp radii curves. I've never
decided if there is any real advantage or disadvantage to it for models.
On trials on my helix, a train of rather expensive rolling stock let go from the
loco right at the top.
I listened to the train circulating and gathering more and more speed down the
helix and at the last moment removed my hand from the bottom exit (guaranteed
destruction) and let it go! The train ran the length of the track along the
baseboard, rounded the 180 degree bend at the end, negotiated the half dozen
turnout throat and rolled to a halt in the staging yard.
I wandered off for a stiff drink and wrote myself a mental note that time spent
carefully laying track is time well spent!
I read on a website that a mere 2% incline will halve the pulling power of
some locomotives while the weight of cars on the descent will increase the
speed and likelihood of a derailment on the curve.
Can't work in percentages but on my first effort I had a 1:30 incline
running down to a set-track 3rd radius curve, very careful driving was
required to prevent a derailment. In the end I re-built the curve, had to
maintain the radius but I super elevated it to around 5 degrees. That cured
he problem, didn't look at all life like though.
And I can't work on 1st, 2nd or 3rd radius curves either as they are
completely nonsensical. What the hell is a 3rd radius curve, why not just
state the diameter?
At least percentage of grade can be worked out. Just divide the percentage
into the 100. 2 in to 100 goes 50 times, grade in UK terms = 1 in 50.
Now, how do I do that for 3rd radius curve?
As for the minimum radius of a helix? Use the largest one you can fit in
but I'd suggest nothing much under 30" radius.
Home of the Great Eastern Railway
It's a setrack measure. If someone has a circle of track using 2nd radius
curves they know they can double the circle by adding either first on the
inside or third on the outside. In that instance, as a measurment device
it does its job perfectly.
http://www.bristol-rail.co.uk : railways around Bristol.
http://www.bugpics.co.uk : DMU/EMU gallery.
The set track thing comes from the train set side of the hobby and to that
extent train sets do have instructions and guides inside with regards to
base sizes yes. As it happens board sold by timber merchants in the UK are
8'x4' (or nearest metric equivalent nowadays) which surprisingly enough are
just the right size to accommodate the plans available to build using set
track components. What a co-incidence. ;-)
"Boards"? People in the UK still build model railways on "boards"? :-)
Yes, just making mock but seriously, do people still build their model
railways on a flat board?
The only place you'll find a "flat board" is under one of my yards. Even
then, the "flat board", 3/4" Good One Side plywood was cut so that the
outside edges flowed with the planned shape of the yard.
Home of the Great Eastern Railway
The helix track base is supported by posts (on the inside, usually),
which are supported by the layout substructure. That's rigid enough, and
It's a question of cost, convenenience, and available skills. For large
layouts, flat table tops are an unnecessary waste of good lumber. For
very small layouts on the order of a couple feet square, such as the
micro-layouts built by some NG freaks, er, sorry, modellers :-), a
corresponding chunk of 3/4" or even 1/2" plywood may be rigid enough as
is. Hollow core doors are very light and rigid, and have been used
successfully as bases for smallish layouts.
See Linn Westcott's book on building benchwork, which introduced the
"L-girder" method. He found (as bridge engineers discovered before him)
that it's not the amount of material but its shape that determines
rigidity and strength.
I guess we each develop our own favourite methods of building baseboards. I
always seem to move before I complete a layout so I build mine to be rigid
enough to be transportable and each section small enough so that I can just
move it by myself. The third factor is that I tend to build from whatever
timber is available - I gather "offcuts" from other jobs and store them long
enough for then to be good and dry. :-)
I'll stand by my call for a rigid board with framing under a helix - mine uses
threaded rods both inside and outside of the circular track bed to allow for
precise height setting and they have to screw into something. The flat board
also allowed me to cut out the center for access. That wouldn't have been
possible with framing/substructure.
My skill at wood-working is about a step above "abysmal" so I plan around
achieving what I need within that skill level and in assuring that dimensional
errors cancel each other out rather than adding together.
All the N.A. articles I've read have the inside of the helix open for
access, I've yet to read about one with a "solid" base. Mind you, all the
ones I've read about have a radius of something like 30 plus inches or more
to achieve a minimum 2%, or 1 in 50, grade on the helix itself, so there is
more than enough room to stand inside the helix structure.
Home of the Great Eastern Railway
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