Helices, gradients, radii etc.

[Dagworth]

A hypothetical question, is it reasonable to expect modern mechanisms (diesel or electric locos in 00 with all wheel drive) to be able to shift ten coach trains from a standing start on a 1 in 72 gradient at 46” radius? I’m thinking of an 8ft diameter helix that would need to rise 4inches on each circuit. 
 

Andi

[The Johnster]

I'd say, hypothetically, yes.  I'd also say, in reality, yes, but that care must be taken to ensure that the helix is very precisely built and that the track is very precisely laid on it, and that the 10 coach train has free running wheelsets in bogies that pivot freely in both planes, do not have issues with contacting buffers, and are not overballasted.  Your hypothetical choice of a relatively wide radius and 4 inch rise per 360 degree run is sensible and should mimimise any potential issues; helii are often used as space savers and setrack curves are sometimes pushing the envelope past the point where reliablility is a given...

 

Be aware, though, that while bogie vehicles should cope with this, the inside rail of the curve rises at a steeper gradient than the outer one, which is why the tracklaying has to be precise and a dead level preseved across the rails at any given point on the spiral.  This will have an impact on any long wheelbase 4 wheeled vehicles and especially 6 wheelers. 

 

 

[roythebus1]

Back in the late 1990s I had a German branch line layout which had a helix down to hidden loops underneath the main station. I use no,2 radius setrack and no3 setrack for the spiral which went round 3 times to reach the lower level. 

 

I didn't have any problem with the German locos and stock of that period starting and stopping on the estimated 1 in 36 gradient. I was using a mictre of the very long DB stock as well as older style Umbauwagen style, long wheelbase goods wagons and a mixture of steam and diesel locos. Admittedly the trains were only 4 or 5 coaches, the most that would fit in the loops. The only steam loco that had problems was a Fleischmann 2-6-4T. I cured that by removing the downward spring form the rear pony truck.

 

Whether modern British outline stock would cope I can't answer. Always use the tighter radius for the going down trains. The gradient is steeper.

 

[spikey]

Don't forget to go up on the outer track if your helix is twin track ...

[DCCconcepts]

You could always think about using DCCconcepts Powerbase plates on the rising line of the helix. Don't forget to also add it to a bit beyond the top of the gradient.

 

Whilst not a replica of your situation:

We have a test track that includes 1 in 30 and 1 in 60 gradients  on a 48" radius curve and a test was carried out with a Bachmann 66 and 14x Dapol HIA hoppers.

The hoppers are relatively heavy and free running.

(You do not mention the coaches that you are using)

 

The 66 was absolutely OK on the 1 in 60, but would wheelslip on the 1 in 30 when all the train was on the gradient/curve. We added a couple of flat magnets under the fuel tanks and the 66 was now a very happy bunny up the 1 in 30.

 

Also consider the weight of the locos. Although they are both 6-axle powered, a Bachmann 70 is far lighter than a Bachmann 66. And we know of a 70 that struggled on a 1in 100 with 21 HHAs, but the 66 was Ok. (We didn't try the Powerbase test on this example)

 

Best Regards,

The DCCconcepts Team

 

[Dagworth]

Has anyone ever built an 8ft diameter portable helix as part of an exhibition layout? 

 

 

[oztrainz]

G'day Dagworth, 

It is not 8' diameter, but check this out:  

Quadzilla by Joey Ricard in the US

 

In some rough distance calculations - an 8' diameter gives you about 24' of train before it loops over itself with your planned 4" rise - This is roughly a 1 in 72 grade or about a 1.4% grade. (Or about as steep as Shap but with a lot more rolling resistance caused by the continuous curve on the helix). A 10 coach train length will probably occupy just over 1/2 of a full revolution on the helix. 

 

While not pushing his product in any way, if you are serious, I'd suggest going to Joey's information centre web page and downloading the Helix Planning Guide. It should give you a good base for further development of your ideas. 

 

The use of the Powerbase plates is also probably a good idea They should add enough extra adhesion so that you are not riding the limit of adhesion on the climb. 

 

 

[Clive Mortimore]

10 hours ago, Dagworth said:

Has anyone ever built an 8ft diameter portable helix as part of an exhibition layout? 

 

 

I know a bloke who is planning one, he keeps asking questions on RM web. Lives somewhere in Gloucestershire if I remember correctly. 

[Dagworth]

1 hour ago, Clive Mortimore said:

bloke who is planning one,

two...

 

Andi

[Michael Hodgson]

1 hour ago, Dagworth said:

two...

 

Andi

One to get up the hill the other to get back down again?

[47406]

An 8 foot diameter helix ?  That is BIG !

 

I have a 4 foot diameter helix that rises a bit over 18 inches on 6 turns & my experience with my fleet is along these lines, including from standing starts part way up:

 

Heljan 47s - 7-10 coach trains & 20+ wagon Speedlink type freights - no problem

Bachmann 47s - same

Bachmann 37s - Don't seem to be quite as sure footed as the 47s in general, most of them seem to have some up/down play in the bogies in terms of the angle they sit at on the track, but most of them are ok with the same size loads

Vitrains 37s & 47s - Don't seem to handle quite the same heavy loads as the others, but 7/8 coach trains ok

Bachmann 2 x 20s with ~24 HAAs with weights added - don't notice the slope at all

Bachmann 25s - definitely less pulling power, no problems with a pair of them together

Hornby 56 & same HAAs - all just fine

Hornby 31s with 20+ wagons - no problems

 

It gets a little more interesting with the Lima 47s, the ones i have modified with improved pickups, extra weight do ok with reasonable length trains. I haven't tried the with the weighted HAA rakes, but they do ok with 7 coach trains. The un-modified 47s are a bit hit and miss, some of them do ok on the helix with medium length trains, others aren't so happy.

 

For a laugh one day i took a resurrected Hornby 25 and tried that, it struggled to get up there on its own !

 

Overall, most of what i have for locos handle the helix just fine. The track on the curves is all Hornby 3rd & 4th radius curves (I did try flexi track initially and quickly abandoned that idea). I also have power feeds onto every level which i think makes a difference.

 

I like to run long trains, so 7-10 coaches for passenger/mail, 24 or so HAAs, ~30 16 tonners, 20+ Speedlink wagons and overall issues with trains going up are few and far between, most of what I have handles it just fine. I would imagine an 8ft helix would be gentler on the loco than what I have.

 

Hope that helps some :-)