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Old 03-27-2003, 02:53 PM's Avatar is offline Moderator
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[quote]Originally posted by stonedchihuahua:
<strong>Okay I just worked out the real car by multiplying all sides by 18 if it were a solid block of steel. Now it works out to over 23 000 lbs. Maybe I'm just dumb </strong><hr></blockquote>

You are in the right track here. The model is 1/18 scale which means it is 18 times smaller than the prototype in three dimensions. The linear dimension conversion in any one direction is 18. However, the volume (weight too) conversion is 18x18x18 = 5832.

The problem with you trying to scale the model up to full size comes with your assumption that the model is an exact scale copy of the real car. The model is actually far too heavy to be an exact replica. The body metal on the model is probably at least twice as thick as the real car's sheet metal when it should be 1/18th as thick (remember, the effect is cubed!). However, this is impossible to scale correctly since that would make the model body 0.12"/18 =0.0067", like extra-heavy aluminum foil. Likewise, the solid tires are probably many times heavier in scale than the real pneumatic tires would be. Your assumption that the scale plastic parts on the model are lighter than the steel components is wrong also. Plastic is less dense than steel and thus lighter IF the two components have the same amount of material in them. The model has many times more plastic in scale terms in it's components than the full sized car has steel.

You should be looking at the problem in reverse - ask, "how much should an exact scale model weigh?" Assuming your real car weighs 3000#, then a 1/18 scale model would weigh 3000#/5832 = 0.56#(half a pound)! A model of a real 50# tire should weigh 0.0085# or 3/8 ounce. The model tires probably weigh in at 5 or 6 ounces. Rather than being too heavy to lift, an EXACT scale model would seem feather light.

There are professional engineers who make a career of finding ways to scale down real world problems to run physical experiments on them. Have you have seen engineers doing physical model expeirments on model boats in a wave pool on shows on the Discovery Channel? EVERYTHING in those experiments must be scaled down, not just the overall dimensions of the ship. Viscosity of the water, density of the water, strength of the materials in the model, weight of the model, frequency of the waves, roughness of the surface finish on the model's hull, velocity of the ship, etc., etc., etc., must me scaled correctly. That is why digital computers are taking over this task since it has become MUCH easier to account for all of the physical parameters there than in a physical model chamber.

[ March 27, 2003: Message edited by: ]</p>
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