33.5" radius HO Helix?

LKandO's picture
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If my math is right a 33.5" radius helix with 4" separation is just shy of a 2% grade. I have found several formula for effective grade each yielding slightly different results but all seem to work out to be somewhere around 2.5%.

From your experience would a 33.5" radius helix be reasonably trouble free with 6 axle diesel, 50' rolling stock, 16 car train length, and track work that is up to par?




bear creek's picture

You probably won't have

You probably won't have troubles with keeping the train on the tracks. However, a train on a  33.5" radius will probably have enough extra drag (from having the whole train on a curve) to make it appear that the grade is almost a percent steeper.  Depending on the loco, you might need to add one more loco to get up the corkscrew.

If you have space, mock up a 3.5% grade and put your loco and the 16 cars on it. If it goes up that grade without trouble your helix will likely work fine. If the loco slips its wheels, you'll probably need to douible head your power.

The extra drag from going around corners comes from the inner and outer wheels on an axle needing to travel different distances. Since both wheels must turn at the same rate, one or both of the wheels needs to slip instead of rolling freely. The tighter the radius the more pronounced the extra drag.

Best regards,

Charlie

 Contributing Editor, Model Railroad Hobbyist magazine

ddrever70's picture

Pushers

I've always thought that a helix would be a perfect opportunity to model a helper district.

- Derek

The Crowsnest & Kootenay Railroad

bear creek's picture

Pushers might be tricky in a

Pushers might be tricky in a helix unless you are using speed matched locos (same brand, same model, same decoder, same programming) MUed together on one throttle.

If you use separate helper crews, lack of visibility can be a major problem...

Chalie

 Contributing Editor, Model Railroad Hobbyist magazine

SNL

Edit per Emily Littella: Never mind.

Dave Stewart

LKandO's picture

Helix Optional

The grade down to staging on both ends will be strained for clearance. I was playing around with a helix under the Brittain Yard end to alleviate the problem.

Charlie, I can't test. I don't have my DCC system yet. I figured with all the MRH readers someone is bound to have a helix of this size in operation.

Alan

All the details: www.LKOrailroad.com        Just the highlights: MRH blog

When I was a kid... no wait, I still do that. HO, 28x32, double deck, 1969, RailPro

ddrever70's picture

Interesting ...

I hadn't considered that different models of even the same manufacturer could have speed differences. When you calculate grades in a curve, do you use track centerline or the inside or outside rail?

- Derek

The Crowsnest & Kootenay Railroad

wp8thsub's picture

Re: 33.5" radius HO Helix

The staging helix on the west end of my mainline is 29" radius with 4" vertical separation, so about a 2.2% grade.  I have no problem running typical trains for my layout through it - two powered locos with either four or six axles, plus 20 cars and a caboose.

Rob Spangler  MRH Blog

LKandO's picture

Reassuring

Thanks Rob, I knew someone had to have in operation a helix this size. And it is you! Am I surprised? Nope. You seem to be a wealth of valuable experience garnered information. Thank you.

Do you have pics of your layout somewhere... web site, Photobucket, Flickr, Facebook, etc.?

Alan

All the details: www.LKOrailroad.com        Just the highlights: MRH blog

When I was a kid... no wait, I still do that. HO, 28x32, double deck, 1969, RailPro

On dc I've seen the variation of speed by same manufacturer

mostly with open frame motors.  Old Athearn Blue Box was especially prone to differences in speeds of similar models.  In the case of Athearn, it didn't really need to be different versions of the same models since the gearing and motors are identical (notable exception being Sw models) throughout the line regardless of what body or side frames were on the trucks.  Sometimes the difference would be due to flash on gears, and sometimes it was in the motor, perhaps a weaker magnetic field on the stator magnets?  I haven't seen that sort of difference on models powered by can motors, although different can motors and different gearing might mean that locomotives from different manufacturers might not like to work together.  Of course, with dcc you can synchronize speeds with adjustments to the speed table.

There is a misconception

There is a misconception about wheel slipping.
The tapered tread of the wheelsets (just like the prototype) takes care of the difference between the distance differential between the inner and outer rails, not wheel slippage.

Pete


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