Curve Radius Question

Inkaneer Oct 17, 2019

  1. mtntrainman

    mtntrainman TrainBoard Supporter

    8,569
    4,904
    131
    OH Oh...pick me!! Pick me !!!

    I remember this subject from years back.Superelevation is based on max track speed. In the US...I found some information for 1:1 US railroads that run both freight and passenger trains online and bookmarked it....

    Normally, passenger trains run above the balancing speed, and the difference between the balancing superelevation for the speed and curvature and the actual superelevation on the curve is known as unbalanced superelevation. Track superelevation is usually limited to 6 inches (150 mm), and is often lower on routes with slow heavy freight trains in order to reduce wear on the inner rail. Track unbalanced superelevation in the U.S. is restricted to 3 inches (76 mm), though 6 inches (152 mm) is permissible by waiver. There is no hard maximum set for European railways, some of which have curves with over 11 inches (280 mm) of unbalanced superelevation to permit high-speed transportation.[8]

    The allowed unbalanced superelevation will cause trains to run with normal flange contact. The points of wheel-rail contact are influenced by the tire profile of the wheels. Allowance has to be made for the different speeds of trains. Slower trains will tend to make flange contact with the inner rail on curves, while faster trains will tend to ride outwards and make contact with the outer rail. Either contact causes wear and tear and may lead to derailment if speeds and superelevation are not within the permitted limits. Many high-speed lines do not permit the use of slower freight trains, particularly with heavier axle loads. In some cases, the wear or friction of flange contact on curves is reduced by the use of flange lubrication.
     
    Last edited: Oct 20, 2019
  2. DCESharkman

    DCESharkman TrainBoard Member

    3,793
    835
    58
    So what would happen if you ran a train on a super-elevated track in outer space? Would the cars just float off?

    This was a question from my daughter..........

    I did a very modest elevation of my track on my layout. This was not using the Kato track. It does have a nice look and I have not seen any issues with it.
     
    Hardcoaler and mtntrainman like this.
  3. acptulsa

    acptulsa TrainBoard Member

    2,413
    2,010
    52
    Sounds like a good moment to teach some physics.

    No, if the curve is superelevated enough, a train in space will track right through it. It won't float away until it reaches the straight track!
     
  4. NtheBasement

    NtheBasement TrainBoard Member

    293
    256
    15
    Yes, I stand corrected.
     
  5. DCESharkman

    DCESharkman TrainBoard Member

    3,793
    835
    58
    The correct answer would be that they would peel off over the inside rail due to centripetal acceleration towards the center of the curvature.
     
  6. acptulsa

    acptulsa TrainBoard Member

    2,413
    2,010
    52
    If the superelevation is 90°, there is no inside rail.
     
  7. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

    19,936
    14,565
    243
    This is making my head hurt to ask, but is there a chart of what degree curves is 12"=1' scale equals what radius curves in N scale?
    I'm mulling over an idea, and the prototype has a schwack of back-to-back, reversing 16-degree curves, on a compensated 3% grade (brutal, I know!). I wonder what those curves approximate to in N scale?
     
  8. acptulsa

    acptulsa TrainBoard Member

    2,413
    2,010
    52
    HemiAdda2d likes this.
  9. HemiAdda2d

    HemiAdda2d Staff Member TrainBoard Supporter

    19,936
    14,565
    243
    Crazy, I thought 16° curves in N scale would be tighter than 27" radius. Goes to show just how unrealistically tight model railroad curves are. N scalers like to think 15" radius curves are fairly generous, but it equates to a 28 degree curve!
     
    acptulsa likes this.
  10. mtntrainman

    mtntrainman TrainBoard Supporter

    8,569
    4,904
    131
    All interesting...if you have the room for wider curves. Most however are lucky if they can use a 32 inch wide base. Leaving a +/- 2 inch buffer on each edge for derailments and you end up with 14 inch (max) radius track at the turn around ends. :(

    Selective Compression in any scale is a _____ eh ?? :whistle:

    [​IMG]
    .
     
    BNSF FAN likes this.
  11. Grey One

    Grey One TrainBoard Supporter

    8,290
    995
    109
    Arnt degrees the amount of curvature.
    There are four 45 degree curves in a circle.
    Radius is 1/2 the diameter.
    1:160 = 1/160 = .00625
    If you know the radius of the prototype then wouldn't you multiply it by .00625? and Convert to inches?
    So
    A 1 mile radus curve
    63,360" x .00625 = 396"
    Or did I miss something?
     
  12. acptulsa

    acptulsa TrainBoard Member

    2,413
    2,010
    52
    No, you didn't miss anything.
     
  13. Grey One

    Grey One TrainBoard Supporter

    8,290
    995
    109
    @acptulsa Thanks, I've been mentoring the grandson in math and we just finished fractions / decimals and ratios. I was afraid I mis-understood.
    For 'S' curves I suggest:
    A straight track the length of the longest car between each curve
    Shorter trains
    Slower speeds
    Better rolling cars
    More relyable couplers.

    I am currently playing with double 'S' curves more from curioslty and to see what I can get away with than anything else.
     
  14. Point353

    Point353 TrainBoard Member

    2,245
    2,035
    53
    Aren't there also four more?
     
    Shortround likes this.
  15. Grey One

    Grey One TrainBoard Supporter

    8,290
    995
    109
    @Point353 Oooops. Thanks, please don't tell the grandson. ☻
     
    Inkaneer likes this.
  16. rschaffter

    rschaffter TrainBoard Member

    242
    3
    22
    They would not, because a train could not move in zero gravity; since there is no normal force, the tractive effort of any locomotive would therefore be zero...
     
  17. acptulsa

    acptulsa TrainBoard Member

    2,413
    2,010
    52
    Tractive effort?

    [​IMG]

    We don't need no stinking tractive effort.
     
    mtntrainman, bremner and Sepp K like this.
  18. Inkaneer

    Inkaneer TrainBoard Member

    3,890
    614
    64
    I did not like the tight radius curves either and that is why I joined an NTRAK club. An NTRAK three foot corner has curves of 24", 25.5" and 27". But be forewarned now I am thinking of four foot corners with curves of 39", 37.5" and 36". Recently there has been some stirrings in NTRAK of even larger radii curves.
     
    bremner and Sepp K like this.
  19. BigJake

    BigJake TrainBoard Member

    916
    845
    21
    IINM, these jet engines simply spun electric generators to run conventional traction motors. And it doesn't look like there are any thrust reversers installed on these. Jet engines themselves are not reversible.

    And I'm pretty sure the diesel is pulling the jet on this train, not the other way around...

    I'll bet those babies were loud, but they sure were sexy in their day! By today's standards, those jets are incredibly inefficient. Their application to rail transportation was a great example of form over function.

    BTW, it also looks like they had to install a wind deflector at the brow of the sloped cab front, to reduce interference with the jet intake airflow when travelling at speed.
     
    Grey One likes this.
  20. acptulsa

    acptulsa TrainBoard Member

    2,413
    2,010
    52
    That would have made it the only Budd RDC-3 with traction motors. They didn't have that much time, to completely re-engineer a Budd diesel-hydraulic. Perlman wanted a publicity stunt by yesterday, not a prototype Turbotrain.

    I'm not saying it was impossible. After all, the New Haven had two customized RDC-1s and four RDC-9s with traction motors and third rail shoes for the Park Avenue tunnel (to the best of my knowledge, the only ones ever to have them). I'm just saying there's a reason you don't see NYC M-497 on any of the lists of history's turbine-electric rolling stock.

    This might help you out:

    https://oldmachinepress.com/2015/04/29/new-york-central-m-497-black-beetle/

    And yes, no doubt the RS is hauling it. But no, it didn't haul it up to 183.68 miles per hour. Yes, those old military no-bypass turbojets were seriously inefficient, even by the low standards of the day. But they did produce some thrust (like 10,000 pounds between them). That day, that thing didn't make no stinking tractive effort, and didn't need none.
     
    Last edited: Sep 23, 2021
    Sepp K likes this.

Share This Page