So You Think It's to Scale?By Craig Skinner The other day I was thinking about how to make a perfectly scale model in all respects and I realized that it was impossible. Then I thought, that's a good article for the Gazette. Now you all get to sit through my daydream. When we talk about scale we quote fractions "This is my 1/5 scale Cub", but what does this fraction mean? What part of the plane is 1/5? The measurements on an aircraft can be broken down into three categories. One- dimensional measurements are used for lengths such as wingspan or fin height. Two-dimensional measurements are areas such as wing area and finally three dimensional measurements are used for volume or weight.
Now lets say I wanted to reproduce my line, square and cube to ½ scale. Hear is what I would get.
Lets look at what the ½ scale reduction produced. The one-dimensional line is correctly at ½ scale. The area of the square is now at ¼ scale. Perhaps I should have made the sides of the square 2.83 cm to achieve my 8 cm2 ½ scale. Finally the area of the box is now at 1/8 scale. I could have made the sides of the box 3.17 cm to achieve a 32 cm3 ½ scale. As you can see, it gets a bit confusing. You cannot have scale in all three dimensions simultaneously. We modellers use scale in the first dimension and accept the errors in the other two. I decided to take my theory and check it
against a real life example. I compared the Dynaflight Giant PA - 18 Cub at ¼
scale against the real thing. Here are the two web addresses if anyone would
like to check my math (please do).
So what does this tell us? Well, it shows that the area, weight and loading are not to scale and have widely varying ratios from the advertised ¼ scale. It also poses a bunch of questions. What size engine do we use? Do you scale the engine based on the wing area, weight, or wing loading or do you just put on the biggest one that will fit? I thought so. I do not have the answer to this, but if some smart reader would like to continue where I leave off then consider yourself published. One last note. I also ran a comparison with a F4U Corsair and got a much greater divergence in numbers. It was a 1/5.75 scale model comparison and wing area had a ratio of 33, wing loading 10 and weight 341. I suspect that comparing a wooden model to a metal airplane caused the greater difference.
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