This is a big red button wired up to seven
actual rocket emojis that are primed and ready for launch. When they ignite we’ll know once and for
all what is the best tech company in the world or at least which is the best at designing
emoji rockets. This whole insane video idea came to me when
I realised that the rockets we see in social media don’t look anything like the ones
that actually go to space and I wanted to find out why. In addition to 3D printing and designing these
rockets I also went to a chemistry lab and two types of wind tunnel to get a crash course
in rocket science. Obviously, don’t try anything you’re about
to see me do at home. Not only did I have to go through half an
hour of training, but… I’m also wearing safety glasses. Before we look at aerodynamics or fancy stability
we first need to get our rocket off the ground. We do that using rocket fuel. There are a few different types we could use,
but for today I’m using solid propellant since it’s relatively cheap and I can access
it without being put on a government watchlist. To see how rocket fuel works I’ve submerged
one of our engines into this graduated cylinder and filled it with water. When I press this button, current from the
battery should flow through the wire and into an electronic match which, when it ignites,
will set off the black powder mixture inside the engine producing a huge amount of carbon
dioxide, nitrogen gas, and potassium sulphide. On three then. 3 - 2- 1. Wow! That is a lot of gas. Actually, far more than I was expecting. We flooded the table and now the entire room
smells of rotten eggs. Let's head somewhere else to explain why we
needed all of that exhaust. It's this exhaust which makes the rocket move
according to the impulse equation. Using the equation, we know if we want to
increase the power of our rocket we could increase the amount of gas being produced
per unit time or by making the velocity of that gas really fast. Rocket emojis are typically quite round. This is good because it means we can fit more
fuel in there, allowing it to reach higher heights, but the comically large portholes
suggest that not all of the space is actually put towards fuel. In Wallace & Gromit’s “A Grand Day Out”
we see that they fit an entire living room inside their rocket, leaving pretty much no
room for fuel at all. Even without much fuel we can still get pretty
good thrust by increasing the velocity of those exhaust gasses. To see how we do that, let's take a cross
section of one of our rocket engines. Here we have the black-powder charge, over
here we would in theory have some sort of cap - although when I cut it in half the cap
sort of fell out - and encasing it we have a cardboard tube. At this bottom end, where all the exhaust
gasses are going to be forced out, we have a plug but with a very small hole in the middle. Like with a hosepipe, if we restrict the flow
by partially plugging it with a finger or adding in a clay throat piece, then we increase
the speed of that escaping gas. Roughly speaking, the same amount of fluid
comes out, the only thing changing is its velocity. We can keep making throat diameter tighter
and tighter until eventually the exhaust gasses are travelling at the local speed of sound. If we were to make the throat even tighter
still then they’d still be exiting at the speed of sound, but there would just be less
of them. The reason I talk about the local speed limit
is because this value changes based on local density as well as temperature. In the high-pressure, super-high temperature
exhaust gasses of a rocket this means that the speed of sound actually increases to 900
m/s. In Freedom Units of Going to the Moon, that
is equivalent to about 2,000 miles per hour. At the moment our exhaust gasses are under
extremely high pressure and are also pretty hot. However this isn’t very good at moving our
rocket forward. So to do that we need to increase the speed
and can get rid of these other unimportant factors. We do that by having an expanding bell nozzle
at the back of the rocket. What this does is it forcibly expands the
exhaust; reducing the pressure and the temperature while increasing speed. With this technique, the exhaust gasses coming
out of a SpaceX’s Merlin engine can achieve an exit speed of more than 3,000 metres per
second, but with an exit pressure of only around 0.6 bar. In theory, the most efficient engine is one
that has an exit pressure equal to the ambient pressure. From what we can see of our rocket emojis
we can tell that some designers have elected to include both the converging and diverging
components of the nozzle, others have just done the converging, and some have no nozzle
at all. Because of this we’re going to have two
separate launches. In the first, everyone is being powered by
a D motor. This is the highest power engine that I can
access in Perth. The next launch, we’re going to account
for the different types of nozzle and give some which have a really good nozzle the more
powerful D motor, and others which have a bit of the nozzle the less powerful C, and
some which have no nozzle at all the least powerful B motor. First though we need to be sure that these
rockets are actually going to fly. This is Shoey; an actual high powered rocket
built by one of my friends. She's launched in the United States, Australia,
and New Zealand. On the other hand, Mr Spotty is a PVC pipe
with delusions of grandeur. He also doesn’t have any fins. We’re in the wind tunnel to find out if
that makes a difference. The first thing we need to consider is centre
of mass. We can find it experimentally on the rod by
having your fingers at either end and then moving them in towards the middle until the
entire rod balances on a single finger. You can think of it as the entire object’s
mass is acting through this point. We also have a centre of mass on Shoey and
Mr Spotty. I’ve balanced the rockets on this centre
of mass and included a pivot joint. This allows them to rotate freely as the air
moves them left and right. Next, we need to consider the centre of pressure. If we were to consider just a 2D cross section
of the rocket and hold it against the wind, the center of pressure is the point at which
the total sum of pressure fields act on the body, causing a force to act through that
point. Roughly speaking, the surface area in front
of the centre of pressure equals the surface area behind the centre of pressure. Mr Spotty has a centre of pressure much further
forward than its centre of mass. Shoey’s fins on the other hand have pulled
its centre of pressure much further back. To see what difference that makes, let's turn
on the wind tunnel. Now that we have the wind tunnel up to speed,
we can see how Shoey operates in the wind. Because we have the centre of mass ahead of
the centre of pressure, even if it deviates one way, then because the wind is pushing
on that centre of pressure we have a restorative torque being formed which pushes the entire
thing back into alignment. On the other hand, Mr Spotty’s centre of
pressure is much further ahead than it’s centre of mass. This means that the wind just spins it around. There is a restorative torque, but it's really
pushing the other way. It’s incredibly unstable. From these tests we can conclude that a safe
rocket is one with a centre of mass ahead of the centre of pressure. Ok Vlad, let's shut it down. Thanks so much! In addition to these factors, a large diameter
makes it harder for the restorative torque to push the structure back into alignment. Using a mathematical description of stability,
centre of mass minus centre of pressure over diameter, we can rank the emojis. For reference, Shoey has a stability of 1.9,
which is roughly an order of magnitude better than the emojis. Although at least the centre of pressure and
mass are the right way around. Given their relatively poor stability, when
they launch get ready for a few of these emojis to just start spinning. For those that do manage to survive we have
one final topic to cover in a wind tunnel that doesn’t use wind. In order to quantitatively compare the aerodynamics
for each of our rockets we need to perform some sort of test. When they leave the launch rail the rockets
should be travelling at about 50 m/s. This is way too fast to simulate in the 8
m/s speed limit of the tunnel from earlier. So I got thinking, what about rather than
using the low density, low viscosity, but very fast air in a wind tunnel instead we
used something much more viscous, a lot more dense, and made it go a little bit slower. Perhaps we could put our rocket inside this
medium and pull it up, measuring the drag experienced when it does so. But what could we use? Well, water has been used before but that's
a bit boring. Perhaps we could use golden syrup. Let's give it a shot. Here's how to construct your very-own wind
tunnel that doesn’t use wind. I’ve looped a piece of string around some
pulleys. On one end we have a constant mass, namely
a pancake flipper, and on the other end we have a mini version of one of our rockets. This is the Microsoft emoji. All we need to do now is fill up our two litre
graduated cylinder with golden syrup and we’re good to let the experiment begin. In what is sure to become the next big spectator
sport we have Microsoft versus Twitter. As you can see, Twitter’s low profile and
streamlined sides give it the least drag. Allowing her to zip past Microsoft at a truly
demanding pace. With a bit of fluid dynamics we can convert
our data into useful drag statistics. However, rather than repeating what is the
stickiest experiment I’ve ever been involved in, I'm going to use a dedicated simulation
package designed for just this sort of fluid flow problem. Apple with its large fins and bulbous body
has the highest drag while shark-like Twitter has the lowest. Now that we have the theory, let's put it
into practice. We’re back at the launch range. On launchpad number one we have our search
engine emojis; Mozilla and Google. Of all the emojis, Mozilla has the equal worst
nozzle design while Google tied for best. Its converging and diverging sections will
allow its exhaust to go supersonic. For the first launch all of the rockets are
using the same D-class engine. Now, none of the rockets have parachutes attached
so I’m not sure how many will survive, but for those that do we’re going to have a
second launch where we take into account the differences in nozzles. On launchpad two we have our social media
emojis; Facebook, Twitter, and WhatsApp. Facebook looks like the quintessential rocket
and my dad has already dibsed it to go on his piano once we’re done filming. The remaining six however I’ll be randomly
sending to new subscribers and anyone who comments on the video. I had to make some interesting design choices
with twitter. The 2D emoji looked a lot more like Old Bessie
from Futurama than the more rotationally symmetric rocket in Wallace & Gromit, so I represented
this with a flattened profile. Twitter has a really low drag coefficient,
although I expect it will spin wildly out of control because of its unbalanced design. On launchpad three we have the operating systems;
Apple and Microsoft. Coincidentally, Apple has the highest stability
of all the rockets and Microsoft’s has the worst. It’s the most likely to cra------
After an insane amount of preparation, the rockets are primed and ready to go. 3 - 2 - 1. First to leave the pad is WhatsApp closely followed
by Apple and Twitter. Then comes Microsoft. Emerging from the smoke we see Facebook, Google,
and finally Mozilla. Long launch rails ensure that the rockets
get off the pad going pretty straight, however soon many of them turn or spin wildly out
of control. As you can see; Mozilla, WhatsApp and Apple
have taken out the top three spots. So that was pretty exciting and we only damaged
a few of the rockets. Infact, I think we can super glue this back
together and be ready for another launch. So on that first launch, everyone was going
on a D motor; it's the most powerful and looks really cool, but doesn’t take into account
different nozzle designs. For that on our second launch we’re going
to have three different engines. With the new engines loaded its time for launch
number two. Hopefully with a little bit less thrust a
few of them can be a bit more stable. On three then. 3 -2 - 1. WhatsApp and Google still go pretty well,
they stayed on the D so that does makes sense. Expectedly, the Cs and Bs go a little bit
worse, although Twitter's decent design allows it to go quite high. Plotting the results we see that more thrust
makes the rocket go higher. Considering just the data from the first launch,
we see that better stability generally results in a higher apogee. That makes sense; a rocket that doesn’t
spend half the flight doing loops-the-loops is probably going to go higher than one that
does. Our drag results are a bit more confusing. They suggest that the more drag that you have
the higher you can go. Rather than fundamentally rewriting all of
rocket science, I think this is actually just illustrating that other factors just had more
of an influence. You could have the most streamline rocket
ever designed, but if it's not pointing in the right direction then that doesn’t really
matter. Unfortunately Mozilla wasn’t able to make
it to a second launch. However, given that it was on the lowest power
B motor we can be confident that it wouldn’t have gotten very far. For these reasons, I’m declaring WhatsApp
as the creators of the world’s best rocket emoji. So does this mean that WhatsApp is going to
be replacing SpaceX’s Starship for the next moon landing? Maybe. But, to be serious there is a reason why we
have graphic designers design emojis and rocket scientists design rockets. For the final launch of the day we have WhatsApp
versus an actual model rocket. Until next time this has been James Dingley
from the Atomic Frontier. Keep Looking Up. This video could not have been made without
the huge amount of support from the folks at the University of Western Australia as
well as members from the UWA Aerospace rocket team. In particular I’d like to thank Thomas who
did all our 3D printing, the lab technicians who let us mess around in their laboratories,
and - of course - to Adam for the chemicals and general lab equipment. I’d also like to thank our Patrons, without
whom we could not have afforded to make such a really ridiculous video. And, if you’ve made it to this point, you
might want to jump over to the Discord server where we discuss the videos, talk about rocketry
stuff, and generally have quite a fun time. Seeya then!
