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!