Reindeer are pretty earthbound. They've got no wings, and weigh way more than dandelion puffs. But when it comes to those in Santa's service, it seems that sprinkling some gravity-defying magic dust on them does the trick.
Now, what if the magic dust you have is past its due date, and doesn't give the reindeer the lift they need? Is there another way to get reindeer to fly? We turned to Chris Damaren, an aerospace engineer at the University of Toronto, for help. After all, Santa needs a backup plan.
In short, Rudolph needs wings strapped on for lift to get him off the ground, along with an engine or two for thrust to move him forward in the air. (For our purposes, we'll assume Santa's reindeer are shielded from the effects of high altitudes and near light-speeds.)
"Reindeer aren't very aerodynamic, so, they would need a lot of help. At least they're fairly narrow, which helps," he said.
There are a variety of wing and engine combinations to pick from, depending on what type of performance you want, Damaren says. Each comes with its own trade-offs. Bigger wings produce more lift, making it easier for Rudolph to take off. But bigger wings create more drag, which means slower flight speeds. Some kids will have to wait for their toys.
With small wings, you get more speed and maneuverability. Sharp turns are easy. But landing is fast and hard. Landing at high speeds means Santa's reindeers would crash through rooftops. Parents will be annoyed at having to call in a roofer.
But how big a wing and engine would be needed? To figure that out, Damaren assumed Rudolph weighs about 200 kilograms (440 pounds), is 2 meters long (6.5 feet) and 150 centimetres (5 feet) tall.
"The length of each wing length needs to be at least the length of the body of the reindeer," he said. For Rudolph, this means a wing length of 2 metres on each side would be adequate, but doubling that works too. That presents more trade-offs: With longer wings, you can fit a bigger engine underneath each one. But the reindeer couldn't do any sharp turns. Smaller wings means using a smaller engine, which could mean less power.
Damaren suggests opting for longer wings of around 4 metres (13 feet) on each side, along with two small engines, one under each wing. Damaren said the prop engines that are used for Dash-8 airplanes would do the job. This might be overkill, for the job, he admits. However, spoken like a true engineer, it's better to have too much than too little. Right?
With this general set-up, a reindeer in its quasi-airplane get-up would travel at about 144 kilometres (90 miles) per hour, which is a lot slower than Santa's dust-powered supersonic speeds. Toy deliveries would be late, but at least the rooftop landings won't be as catastrophic.