Smallest radius for double track?

[Joseph_Pestell]

At the usual Peco Streamline track-centre to track-centre dimension of 50mm, how tight a radius curve for double track can one achieve when running 76ft (eg BR Mk3) in 00?

 

If I were at home (hopefully later this week to prepare for move), I would have done some practical trials rather than bother folk here.

[TonyMay]

I think your idea of trying it practically is probably best.

 

If you're really stuck for space, you can treat the parallel tracks as like interlaced track for signalling purposes, meaning that no two trains can pass at that point.  If no two trains pass there, they can't collide with each other.

 

Finally, it's quite easy to mix track spacings, e.g. streamline and set-track, as long as there's a slight curve to the track.

[RobinofLoxley]

Joseph if you have Anyrail or something, build a simple section of parallel track and represent the coach by a rectangle having the right footprint. Just move the rectangles around and it will be obvious if there is space or not.

[KingEdwardII]

The NMRA have something comprehensive on this topic, if you're up for a bit of maths 

 

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/tn-7_track_center_and_obstacle_clearance_methodology_jul_2017.pdf

 

Enjoy!

 

Yours,  Mike.

[regme]

Wow, I'd realise you had to go to 6 significant figures on the calculations.

 

[Dungrange]

I think the answer is somewhere in the region of a three foot radius curve.

 

However, the exact answer depends on whether you're prepared for vehicles to almost touch (ie less than 1mm of clearance), or whether you want a scale minimum distance between vehicles on the curve, which I think on the prototype is about 18" (or 6 mm).

 

For my own layout, my minimum radius at each end will be a 2' 6" (762 mm) and I think I'll be using track centres of about 55 mm to give myself something close to a scale clearance between vehicles.  I think it 'might' be possible for me to go as tight as 50 mm track spacing, but the clearances would be negligible and less than I'd want to accept.  I believe that a Heljan Cargowaggon has a slightly greater central overhang than a mark 3 coach and since I like big bogie wagons, I don't want to be working to such tight tolerances that I subsequently buy something that is even more onerous in the clearance requirements.

[DCB]

Its not just the MK3s hanging in on the outer, its the bogie steam locos hanging out on the inner.  Hornby Kings and Triang L1 and M7 are really bad bogie first. Not very obviously Kings and Mk3s operated together in the preservation era but  its probably the worst case scenario. Our layout has its track spacing on the sharpest curve dictated by King to Airfix Auto coach clearance, its fatter than a Mk3 over the handrails but a tad shorter and from memory is around 55mm on an inner radius of 3rd radius or 19".   The main line is at peco 2" or 50mm spacing and 2ft 6" radius  There is no doubt in my mind that narrower spacing looks more realistic but some stock like Hornby 9Fs are 40mm or 10ft wide, whereas the full size railways were about 9ft 3" max for most routes, the C1  Mk1 coach loading gauge.  I like 42 to 44 mm on the straights and it bugs me that 90% of the layout is at 2" or 50mm.

Stock colliding is not ideal but with modern RTR pretty much unavoidable with the tiny flanges etc, and smashing a £200 loco into a £70 coach or six isn't hugely clever.