Weights and road speeds of model engines

Member Trevor Clay who owns Burrell 3″ scale traction engine “Bill” provides some interesting information on weights and speeds:

Comparing scale weights and speeds of miniatures against full size weights and speeds

I have often wondered about how hard miniature engines have to work when being driven around rally fields, lanes, hills etc so I have tried to establish the scaled up speeds and towed weights that are typical of miniature traction engines.
I have made some tables that should provide an understanding of the relationship between the different scales and a full size engine.

For example:-  Quite often, when I am giving rides, I have got a typical towed weight of 750lbs behind my 3” Burrell.  This is made up by the following:-  2 trailers (total weight 150lbs), myself (200lbs) and a load consisting of 2 adults (200lbs each) or 4 children (100lbs each) , and can be pulled over soft wet grass at a speed of 2 to 2.5 mph.  Tarmac is better as a speed of up to 3.5 mph is possible with ease whilst on the flat.  These weights are approximate and can easily be exceeded.  This equates to just over 21 tons and with a speed for a full size engine equating to 8 to 10 mph on grass or 14 mph on tarmac.

Some more comparisons

If you take a 2” engine and assume it is on tarmac or dry hard ground. With a speed of 1 to 1.5mph and a typical load of 200lbs to 250lbs this equates to 6 to 9mph with a load of 19.3 to 24.1 tons with a full size engine.

  • A 3” engine’s driver and driving trolley weighs typically about 275lbs or 7.9 tons if scaled up.
  • A 4.5” engine’s driver and driving trolley weighs typically about 275lbs or 2.3 tons if scaled up.

Below are two tables that give examples of various weights and scales.

Table showing:- Scale weight to true weight.

Scale Scale Weight (lbs) Conversion Factor Scaled up Weight (lbs) Weight (tons)
 (“/ft)
1 500 1728 864000 385.7
2 500 216 108000 48.2
3 500 64 32000 14.3
4 500 27 13500 6.03
4.5 500 19 9481 4.23
5 500 14 6912 3.09
6 500 8 4000 1.79

Table showing:- True weight to scale weight.

Scale True Weight (tons) Conversion Factor Scale Weight (as lbs) Scale Weight (as tons)
(“/ft)
1 10 1728 13 0.01
2 10 216 104 0.05
3 10 64 350 0.16
4 10 27 830 0.37
4.5 10 19 1181 0.53
5 10 14 1620 0.72
6 10 8 2800 1.25

It looks like the smaller scale engines are most likely to be worked hardest, even if the driver only is being pulled.  I have heard about a 1” Minnie pulling a car back in the 1950/60s and that equated to a lot of weight if you scale it up.

With the speed, it is very simple to convert from scale speed to the equivalent speed of a full engine,  you just multiply by the speed of the model by it’s scale, ie

  • 1” scale you multiply by 12
  • 2” scale you multiply by 6
  • 3” scale you multiply by 4
  • 4” scale you multiply by 3
  • 4.5” scale you multiply by 2.67

Table showing actual road speed to scale speed.

Road speed (mph) scale “/foot
1” 2” 3” 4” 4.5” 5” 6”
1 12 6 4 3 2.67 2.4 2
2 24 12 8 6 5.33 4.8 4
3 36 18 12 9 8 7.2 6
4 48 24 16 12 10.67 9.6 8
5 60 30 20 15 13.33 12 10
6 72 36 24 18 16 14.4 12
7 84 42 28 21 18.67 16.8 14
8 96 48 32 24 21.33 19.2 16
9 108 54 36 27 24 21.6 18
10 120 60 40 30 26.67 24 20

I have used an excel spreadsheet to convert scale weights or speeds to and from true weights or speeds and this could be available via email. If you would like a copy then contact alittleandoften@gmail.com.

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About tvtecbeta

Thames Valley Traction Engine Club Website manager
This entry was posted in model steam, Technical topics and tagged , . Bookmark the permalink.

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