First of all, HOn3 is not the

First of all, HOn3 is not the same gauge as standard gauge N.  HOn3 is 10.5mm gauge, while N is 9mm (which is the same as HOn30).

To answer your question though, you are still in HO scale, so that dimension is the relevant one.
 

Scale

Hi Pete,

You would use the HO scale radius, as you are still in HO Scale -- even if you are using N scale track

Andrew

Thanks!

Thanks for the help! This helps tremendously.

Pete

Yep, you are modeling in HOn30.

I learned my lesson from the guys here on the forums.  I considered HOn30 as I have a huge amount of N scale, but after much consideration I have decide to do HOn3.  You will find many items for HOn30 on Shapeways.com for HOn30.  Take a look here;

http://www.shapeways.com/search?q=HOn30

There are kits offered to convert N scale locos to HOn30.  ​i hope this helps.  

​Den

" Modeling in HOn3 I'm in HO

Yeah, you are correct, the 10 degree prototype curve would be 79 inches in 1:87  (HO scale) but that's way bigger than most folks would use for a narrow gauge layout. Tehachapi Loop is probably about a 10 degree curve for instance and it looks huge even though it's considered sharp in prototype mainline terms. I'm not very experienced with  HO narrow gauge  but I'd guess 30 inch radius would be plenty big enough for most purposes and something like 24 inch more common? .DaveB

...

You can run almost everything through 24", but some brass may be fininky.  26" is a pretty good guarantee that everything will be fine.  Also, keep it to a 2% grade, you'll be better off than trying to do 4%.

Sharp Radius NG

If you are modeling H0n30 and are looking for a correct radius for that scale working from the prototype. Here is an example from a true 2'6" railway the Victorian Railways in Australia now widely known as Puffing Billy.

The VR NG line from Upper Ferntree Gully (now from Belgrave) to Gembrook was blocked by a land slide at what is now appropriately known as Landslide and a new line was laid to get passed this point. Tto do so the sharpest possible curve the Baldwin 2-6-2T locos would traverse was used. This being 2 chains (44 yards or 132 feet). when you scale this to HO it works out to be a tad over 18" radius. This goes to show how small the radii we as modelers use actually are!

Click here for a picture of Landslide http://wiki.prov.vic.gov.au/index.php/VPRS_12800_P1_H_4821

By the way "Tad" is a technical term for a measurement somewhere between a "Smidgen" and a "Bit"!!

Of course if you want really tight radius....

we used to get this consist

around 18' radius on 2' gauge in 1:1 scale. 

I'll let you all work out how many degrees that is and what actual radius it scales out at in model form. 

Yes narrow-gauge can get into some really tight places, and yes this consist has been modelled.