Formula for working out drag on curves

rusty spike

Registered
4 Aug 2019
99
2
UK
Best answers
0
Country flag
I am almost at track bed stage and as on my previous live steam layout want to incorporate a 16’ dia spiral. Through experimentation I have found my Accucraft (battery) K27 will haul 4 AMS Jackson Sharpe coaches up a STRAIGHT 1:60 gradient. It wheel span at 1:48. The gradient on the spiral would need to be 1:60 but I wonder if the drag on the radius (8’) may tip the balance. I can’t set up a trial spiral without extensive work so wondered if there’s a simple rule of thumb way to find the extra drag.
The coaches could probably do with roller bearings. I have already removed the electrical pickups which made a slight difference.
 

dunnyrail

DOGS, Garden Railways, Steam Trains, Jive Dancing,
Staff member
GSC Moderator
25 Oct 2009
26,076
4,976
75
St.Neots Cambridgeshire UK
Best answers
0
Country flag
Not sure that anyone will be able to come up with a mathematical formula for your problem. But 10/10 if they do, problem is that each coach is likely to have a different rolling resistance and then likely different locomotives will have different pulling powers. You may find perversely that a Stainz may manage your consist with no problems. Being a heavy 0-4-0 helps with pulling power whereas you K27 also has a Tender to lump up the grade.

Why not turn a hinderance to a feature and have a siding for a helper loco to assist the K27 up the Spiral?
 

rusty spike

Registered
4 Aug 2019
99
2
UK
Best answers
0
Country flag
I hadn’t thought of that idea :)
The tender is extremely heavy especially with the batteries etc on board. I could live without the spiral as I could sink part of the layout to keep the whole lot dead level, but not such an interesting line to play with!
 

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
33,455
3,504
Nottingham
Best answers
0
Country flag
Cuttings are a pain! - They collect debris, and can get waterlogged..

And, as you say, you can't see the train! :(
 

Rhinochugger

Retired Oik
27 Oct 2009
36,552
4,234
North West Norfolk
Best answers
0
Country flag
I hadn’t thought of that idea :)
The tender is extremely heavy especially with the batteries etc on board. I could live without the spiral as I could sink part of the layout to keep the whole lot dead level, but not such an interesting line to play with!
I would have thought that at 16 ft diameter, the drag will be fairly minimal. I don't notice any drag at 10ft, but I definitively do on the few 8ft curves that I have (I have some curves that go 10ft - 8ft - 10ft).

Just because I don't notice it, doesn't mean it's not there - equally, I only have one AMS Jackson Sharpe.

However, Murphy's law suggests that the curvature could be the last straw .......................
 

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
33,455
3,504
Nottingham
Best answers
0
Country flag
Flip your stock over, and spin the axles by hand.. - You DO lubricate your axles, don't you?

You sometimes find a tight axle, or two.. These can make one heck of a difference.
Also, any bogies (trucks, US) that do not articulate freely? - All adds to drag..

PhilP.
 

JimmyB

Now retired - trains and fishing
23 Feb 2018
6,891
910
69
Weston-super-Mare
www.tumble-down-falls.co.uk
Best answers
0
Country flag
So don’t forget either the inside or outside wheels will always slip on a curve, any curve, when on a fixed axel, so the friction on the slipping wheels will cause the drag.
 

Gavin Sowry

Garden Railroader and Raconteur
27 Oct 2009
7,840
2,490
70
Hutt Valley, NZ
Best answers
0
Country flag
So don’t forget either the inside or outside wheels will always slip on a curve, any curve, when on a fixed axel, so the friction on the slipping wheels will cause the drag.

Allow me to expand on that comment. That is the reason that railway wheels are not flat, but rather, coned (usually 1 in 20). This is to allow the wheels, fixed on the same axle, to rotate and travel around curves with minimal slippage. The inside rail of a curved track, is a shorter distance than the outside rail. The cone shape of the wheels means that the further away from the flange you are, the smaller the diameter of the wheel. So then, the larger diameter follows the outside (longer) curved rail, and the smaller diameter, the shorter inside rail. This is why we also have gauge widening on curves.... to allow sideways movement of the wheels so that the wheels can adjust their line.
 
8 Mar 2014
7,806
972
San Diego
Country
Armenia
www.elmassian.com
Best answers
0
Country flag
Allow me to expand on that comment. That is the reason that railway wheels are not flat, but rather, coned (usually 1 in 20). This is to allow the wheels, fixed on the same axle, to rotate and travel around curves with minimal slippage. The inside rail of a curved track, is a shorter distance than the outside rail. The cone shape of the wheels means that the further away from the flange you are, the smaller the diameter of the wheel. So then, the larger diameter follows the outside (longer) curved rail, and the smaller diameter, the shorter inside rail. This is why we also have gauge widening on curves.... to allow sideways movement of the wheels so that the wheels can adjust their line.
Allow some further clarification:

The taper in the treads is not for curves, it is for self centering down the straights.

The fillet (between the tread and the base of the flange) provides the larger diameter to allow travel without slippage.

This is one of the reasons we have slippage in our scale, as the fillet is not sufficient to allow a large enough diameter on the outer wheel on our over tight curves, way tighter than prototype.

That's also probably the reason that many wheels don't even have a fillet.

Also the gauge widening on curves is normally to accommodate the wheelbase of the trucks which again is woefully "long" compared to our curves (way tighter than prototype)

(I was schooled by a long time railroad track inspector, who has taught me many things about how stuff works)

Greg
 
  • Like
Reactions: 1 user

Gavin Sowry

Garden Railroader and Raconteur
27 Oct 2009
7,840
2,490
70
Hutt Valley, NZ
Best answers
0
Country flag
Allow some further clarification:

The taper in the treads is not for curves, it is for self centering down the straights.

The fillet (between the tread and the base of the flange) provides the larger diameter to allow travel without slippage.

This is one of the reasons we have slippage in our scale, as the fillet is not sufficient to allow a large enough diameter on the outer wheel on our over tight curves, way tighter than prototype.

That's also probably the reason that many wheels don't even have a fillet.

Also the gauge widening on curves is normally to accommodate the wheelbase of the trucks which again is woefully "long" compared to our curves (way tighter than prototype)

(I was schooled by a long time railroad track inspector, who has taught me many things about how stuff works)

Greg

That's what I said, in a different form of English. I was trying to keep it in simple terms, so folks could understand it. Yes, your man has taught you well.
I started my career in railway track engineering 49 years, 4 months, 3 weeks, and 2 days ago........
 

dunnyrail

DOGS, Garden Railways, Steam Trains, Jive Dancing,
Staff member
GSC Moderator
25 Oct 2009
26,076
4,976
75
St.Neots Cambridgeshire UK
Best answers
0
Country flag
A common language separated and differentiated by a big pond.
 

Rhinochugger

Retired Oik
27 Oct 2009
36,552
4,234
North West Norfolk
Best answers
0
Country flag
Allow me to expand on that comment. That is the reason that railway wheels are not flat, but rather, coned (usually 1 in 20). This is to allow the wheels, fixed on the same axle, to rotate and travel around curves with minimal slippage. The inside rail of a curved track, is a shorter distance than the outside rail. The cone shape of the wheels means that the further away from the flange you are, the smaller the diameter of the wheel. So then, the larger diameter follows the outside (longer) curved rail, and the smaller diameter, the shorter inside rail. This is why we also have gauge widening on curves.... to allow sideways movement of the wheels so that the wheels can adjust their line.
Allow some further clarification:

The taper in the treads is not for curves, it is for self centering down the straights.

The fillet (between the tread and the base of the flange) provides the larger diameter to allow travel without slippage.

This is one of the reasons we have slippage in our scale, as the fillet is not sufficient to allow a large enough diameter on the outer wheel on our over tight curves, way tighter than prototype.

That's also probably the reason that many wheels don't even have a fillet.

Also the gauge widening on curves is normally to accommodate the wheelbase of the trucks which again is woefully "long" compared to our curves (way tighter than prototype)

(I was schooled by a long time railroad track inspector, who has taught me many things about how stuff works)

Greg
Which is why (slightly off-piste) you need to ensure that axles have a little side play, and we're back to making sure they're well lubricated.
 

David1226

Registered
24 Oct 2009
7,831
7,859
74
Abingdon, Oxfordshire
Country
United-States
Best answers
0
Country flag
That's what I said, in a different form of English. I was trying to keep it in simple terms, so folks could understand it. Yes, your man has taught you well.
I started my career in railway track engineering 49 years, 4 months, 3 weeks, and 2 days ago........

You have been taught well Obi Wan, the force is strong in you....

David
 
Last edited:

Paradise

Registered
28 Jan 2010
1,244
299
Back Yard
Country
Australia
Best answers
0
Country flag
A common language separated and differentiated by a big pond.

And the term 'sinusoidal oscillation' wasn't even uttered once. ;)
All I can say about that is...

Hunting_oscillation_section_ja_150px.gif
Hunting_oscillation_plan_ja_150px.gif
 
Last edited:
  • Wow
Reactions: 1 user

trammayo

Interested in vintage commercial vehicle, trams, t
24 Oct 2009
22,659
4,665
75
Co. Mayo
Country
Ireland
Best answers
0
Country flag
And the term 'sinusoidal oscillation' wasn't even uttered once. ;)
All I can say about that is...

Hunting_oscillation_section_ja_150px.gif
Hunting_oscillation_plan_ja_150px.gif

Another term would be "hunting"!
 

Rhinochugger

Retired Oik
27 Oct 2009
36,552
4,234
North West Norfolk
Best answers
0
Country flag
And the term 'sinusoidal oscillation' wasn't even uttered once. ;)
All I can say about that is...

Hunting_oscillation_section_ja_150px.gif
Hunting_oscillation_plan_ja_150px.gif
Vic Mitchell (of Middleton Press and Ffestiniog Railway fame) built an axle with a large pair of truncated cones - no flanges - to demonstrate at the Midhurst Model Engineering Exhibition how train wheels stay on a track.

Not only, but also - the Docklands Light Railway (in London) has wheels that have a more pronounced slope (dunno the proper term) to enable trains to go around sharper curves, but the trade-off is that speed is limited to 50 mph (if my memory serves me well).
 

Paradise

Registered
28 Jan 2010
1,244
299
Back Yard
Country
Australia
Best answers
0
Country flag
I think the treads on railway wheels are typically about 3% taper but that proved unstable for high speed trains so they made tolerances smaller and had far less angle to the tread taper to keep them on the track.

 
Last edited:

dunnyrail

DOGS, Garden Railways, Steam Trains, Jive Dancing,
Staff member
GSC Moderator
25 Oct 2009
26,076
4,976
75
St.Neots Cambridgeshire UK
Best answers
0
Country flag
They even used some G Scale Track for the cone tests. Wonder what skip that went into or perhaps Cpt. Slow purloined it for a G scale railway.
 

Paradise

Registered
28 Jan 2010
1,244
299
Back Yard
Country
Australia
Best answers
0
Country flag
They even used some G Scale Track for the cone tests. Wonder what skip that went into or perhaps Cpt. Slow purloined it for a G scale railway.

No roundy roundy. Just a short line layout. :giggle: