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With the manuscript as a starting point, Wayne used a combination of engineering theory and trial and error to come up with a working model.
"All right, you'll look out...you get the camera, you'll see from the..."
The prototype looks promising to Marcus Brandt, a carpenter who will help Wayne build the trebuchet. But there is a problem, the model rocks dangerously. This would be a serious flaw in a full-size trebuchet with several tons in motion.
"The machine basically tends to wanna tip forward as that weight comes down, it wants to drop straight down, so it tends to pull the machine forward, making it in this case tilt."
To resolve the problem, Wayne reexamines the medieval illustrations of this type of trebuchet. He's struck by the fact that many have wheels, so he decides to build a new model. Not only do wheels eliminate the tendency for it to tip over, the movement also boosts the trebuchet's performance.
"Shoot it away, Come on..."
Hew doubts that wheels will make a trebuchet throw farther, so he insists on a demonstration. For the first throw, Hew holds down the model, the projectile travels 20 feet.
"Now let's try with letting it loose."
"Letting it loose."
"Yeah, well, certainly better, isn't it? Yes!"
"Yes, I just didn't do enough long..."
When the trebuchet is allowed to roll, the missile goes an extra ten feet, why?
The falling counterweight drives the trebuchet forward like a pitcher stepping forward. This adds momentum to the throw. The forward motion also permits the counterweight to drop further in a straighter line. The closer the counterweight follows this optimal path, the more energy it captures for throwing.
"What I find odd is the idea about it moving and having to move, in order to give more energy to the missile. I would have thought it was, on the face of it, nonsense. But we've seen Wayne has tried it, it goes further, and it can't be argued with."
Now that Wayne has confidence in his model, the project moves to Lock Ness in the Scottish Highlands for the full-scale test. The trials will take place in the shadow of castle Urquhart which may have been besieged with similar weapons during Edward I's Scottish campaigns seven hundred years ago. Wayne and Hew arrive at castle Urquhart, to inspect the timber that is delivered by barge. As in the Middle Ages, heavy-duty English oak is the choice for building the carriage and trestles
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projectile: n. 射弹（如子弹、炮弹等）
pitcher: n. 投手
momentum: n. 动力，动量
barge: n. 驳船
trestle: n. 脚手架
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