Alright so several months ago we took a deep dive and learned exactly how bird wings work.
And it was pretty cool, so go check it out if you want, but, a couple of you
had the audacity to ask me how bat wings work and I didn't know the answer.
So you hear that behind me right? It's a waterfall. It's called Blowing Wind Cave, and there are thousands
of bats overhead right now flying to the river to eat for the night. You see those little
dots? They're all bats... All of them.
That's pretty crazy isn't it? So here's the deal. I'm gonna send you to the Peruvian Amazon rainforest with
ignorant Destin from several months ago, and a Phantom high-speed camera. So go
make observations and when you get back, me and you are gonna talk about bat-wing biomechanics by looking
at data from Brown University's bat wing wind tunnel
It's amazing. I'll see you on the flip side. This is worth your time. I'm going to the cave.
So bats... Amazon rainforest, they live everywhere.
They live in the top of hollow trees, like this one, which
I can understand because right now I'm about, oh I don't know, 30
40 feet off the ground? Here's Phil. Phil what kind of tree are we in?
(Phil) We are in a strangler fig, which means that basically
the figs start off as a vine, and then strangle the tree that used to live in this hollow space
(Destin) Here, I'll hand this off to you. (Phil) Cool. - There's some high speed
video we're gonna shoot of bats that live near a lake nearby, so we're gonna go check that
out. Right now, let's just try to get video of this. Getting Smarter Every Day.
See em? - Oh yeah nice!
- There he is... You don't like me being here do you?
Oh man!
The joker just peed in my mouth. Stop. I need to clarify, that was
a lie. The bat didn't actually poop in my mouth. He pooped towards my mouth and
it was deflected by my moustache and then it hit me on the mole here. So, good thing I had a moustache.
That's cool.
Our guide Gerson grew up in the area so he knew the exact log that bats like to hang out
on. So that's where the bat is huh?
[music]
So how do
bats fly differently than birds? That's the question I want to answer here.
So when I started researching the topic, several papers lead me to the real
life dynamic duo Dr Kim Breuer, who's an engineer, and Dr Sharon Swartz who's a biologist.
They work together at Brown University school of engineering animal flight
wind tunnel to unravel the mysteries of bat flight. Now most people's knowledge of how bats fly
stops at echo location, but I want to go much further than that. If you look back at the
high speed you'll notice that when the bat strikes the other bat in the head his entire body starts to roll
to one side. Now at first blush it looks like he might be countering the aerodynamic lift
of that open wing by rolling his body. But if you look at this footage that I captured
of macaws, you can see when one of the macaws strikes another one in the head, he doesn't
roll his body like the bat does. Now what's the difference in the bat and the macaw?
The answer is mass. Bats have 12-20% of their entire body weight
in each one of their wings. This means that inertial forces play a much bigger role
in bat flight than they do in bird flight because birds are much lower than that. If you think about it,
the ability to react against their own wing mass allows bats to do maneuvers that birds
can't. For example, go from full speed flight to an upside down and sideways
twist in order to gently grab the top of a cave. Don't let this freak you out
There's this place I like to go where owls will drop their prey and they decompose.
What's so cool about that is the soft tissue will decompose in the same position as it usuallt
is relative to the bones. Now on this duck that means we can check out the
wing structure really well. Look at this. You can see the major bones here.
What I think's cool is you can see that there's no bones that go down into the wing. Bats have
an entire hand built into the wing. That means a bat has a lot more precision
control over the shape of the wing relative to a bird who basically just has a few major
joints and the ability to pitch each individual feather. So when you use a wind tunnel typically you
put a model right in the middle and then you'll measure the airflow over the surfaces of the model.
But what do you do if your model is actually a bat and it can fly wherever it wants? How do you know where to measure?
Well the answer is you put dots on the model, or in this case a bat.
Using multiple camera angles and a little math researchers track the position of each individual dot
and can recreate a simulation of how the finger joints in the wing open and close
the wing. This doesn't answer our airflow question though.
(Son speaking, unintelligible) That's right. Particle image
velocimitery is a pretty interesting way of measuring a flow field, so right now at springtime
in Alabama and there's pollen all over my driveway. So as my son pours this water
out, if you look you can see this pollen moving along with the water. It's pretty awesome
because it lets you see things in the flow that you couldn't see before like this little vortex.
This is exactly what the researchers are doing with the bats. They put
particles in the wind tunnel and then they illuminate the particles with a laser. They then take these images
and calculate the local vorticity omega. By plugging
omega in and integrating over a defined area you can get circulation, or gamma. Gamma goes
into one last equation and there you have it. The lift generated by a bat wing while in flight.
Imagine how useful this could be if you're doing something awesome like oh...
I don't know... Developing a robotic bat wing. Yep.
That's happening. So did I answer your question? Bats have more mass in their wings
so they maneuver using inertia. They're more agile than birds, they can even hover.
They control their wing geometry better so on the back stroke instead of delaminating
the wing they umbrella fold and slide the wing along their body. Heck they even
fly before they can fly. They're mammals, their moms carry them. Here's a question for you in the comments.
Some bats have tail membranes and some don't. So how do you think that affects flight?
So big thanks to Dr Breuer and Dr Swartz for letting us use your research video. I think
a good way of ending this would be to couple that with some music that Gordon wrote that reminds me
of Castlevania. Quick warning though, there's a little nightmare fuel in this. Anyway, I'm Destin,
you're getting Smarter Every Day. Please subscribe. Have a good one.
[music]
[ Captions by Andrew Jackson ] captionsbyandrew.wordpress.com
Captioning in different languages welcome. Please contact Destin if you can help.