Why can't turkeys fly?

Trading physics for empathy

Nov 24, 2021

Tomorrow is Thanksgiving! Beyond eating yourself into stasis and watching your dad fall asleep on the couch, there’s a lot to look forward to. Arguing about Cranberry Sauce’s place on the Thanksgiving table, wondering who actually likes Green Bean Casserole, and trying to figure out why, no matter how hard they try, turkeys can’t seem to get themselves off the ground. I can’t promise we’ll get to all of those questions but we’ll try our best. Happy Holidays.

The first major asterisk in this article is that Turkeys actually can fly. Sort of. Don’t believe me? Watch this video:

Right out of the gate, we have video proof that the title of this article is inaccurate, thank you for taking part in this clickbait study. Nonetheless, I think we can all agree that, while they’re capable of getting off the ground, they can’t really maintain it, let alone soar for miles like their lighter counterparts. Today we’re going to conduct a brief aerodynamic analysis to make sure you, the reader, stay engaged (ha ha).

The average wild turkey is about 20 pounds on a good day. [1] They pair this bulkiness with an average wingspan of 4.5 feet. [1] In order to soar, which we’ll assume is the goal here, turkeys should be able to maintain altitude for a brief period of time without flapping their wings. Think of geese flying in formation. For a large portion of their flight, they can simply stretch out their wings. There’s some more complex vortex shedding going on there but generally, that’s the idea. For simplicity, we’ll examine the video above and estimate that a turkey’s wings can be modeled as a rectangle and that they run about half of the length of the bird. For our analysis, then, their wingspan looks like this from above:

This figure, paired with the equation for the area of a rectangle (base X height), gives an area of 9 square feet. We now have the wing area of our friendly semi-flightless bird. The other two things we’ll need to know are the air density and the lift coefficient of its wings. The air density can be easily determined using the altitude the turkey is flying at. For this, we’ll assume it’s at sea level.

The lift coefficient is a bit harder to quantify. As we’ve discussed before, it’s typically found via testing, but it’s probably pretty hard to get a bird to stay in a wind tunnel for an extended period of time. On top of this, as far as I can tell, no one has done aerodynamic testing on a live turkey. Probably because they don’t fly much and nobody cares. But that’s what we do here at It’s Not Rocket Science, we venture into the unknown. We take risks and explore new horizons. For approximately zero scientific significance.

Thanks to a 1980 paper out of Portland State University, it was found that birds have a lift coefficient anywhere between 0.8 and 1.2. We’ll give turkeys some much-needed love and estimate that, with the right control, they can maintain a lift coefficient of 1.0. [2] Finally, we can use our trusty lift equation to find out how fast turkeys would need to be going to “soar”.

43 feet per second is roughly 30 miles per hour—sadly much faster than they can move. This result can be mitigated a bit by flapping their wings, which we see in the video above is able to get them off the ground. But flying by only flapping your wings is surely exhausting, and unless you get to the point where you can glide, you’re probably going to want to land relatively quickly. Funny enough, turkey wings are extremely cambered (curved), which allows them to generate high lift in short bursts. This means they get off the ground quickly if they need to, but makes it harder to stay there.

But lets say they do get up to 30 mph, they’re not out of the woods just yet. Turkeys are what we would call in the world of aerodynamics “draggy”. This means that air generally has a difficult time getting around them. So, at a high-ish speed like 30 mph, the bird would feel a sizeable drag force, slowing them down, and causing their wings to produce less lift, causing them to descend. This uphill battle seems to be a bit too much for our Earth bound friends, and is why turkeys tend to stay on the ground as much as they can. Other birds have an easier time because they are much lighter relative to their wingspan. This means the lift they need to produce is less and their wings have enough area to do it. Birds like eagles only require about ten miles per hour of speed to glide which makes flying for them, for lack of a better word, a breeze.

All that being said, I hope this gives you a bit more empathy for these beautiful creatures heading into one of my favorite days of the year. Enjoy your time with family, friends, or whomever you spend your holidays with. Happy Thanksgiving.

It's Not Rocket Science

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