World of Science - Aerodynamics - Part 7

I have nothing much to write about the last few lessons. For the last last lesson, the lecturer from NUS talked about start and end vortices induced by airfoils, and how these cause wings to fly. Honestly, it does not make a lot of sense to me, and I have came to a realization that I do not understand how aeroplanes fly based on this circulation around the airfoil explanation completely. However, one thing is for sure, that is I do not know how airplanes fly. Sounds contradictory? Let me elaborate.

When I was really young, I thought that airplanes fly because air hit the wings and get deflected downwards (partially correct). I mean like balls bouncing off the wings and creating a upward momentum. I thought this, because of the phenomena that when I fold the back of the wings of a paper plane up, they tend to go upwards. So I just thought that the 'balls of air' will push the wing and cause the plane to pitch.

However I later found out that a fluid doesn't act like a solid. The path of a fluid curves even before hitting the obstructing surface. So upon learning Bernoulli's Theorem, I thought I knew how wings can fly. This explanation, I thought always correct, and perhaps many others is in fact a misconception: Air flowing above the airfoil takes a longer time to reach the end, while that flowing below the airfoil takes a shorter time, so the air above has to flow faster, thus causing a lower pressure on top.

The flaw in this explanation lies in which, there is no logical explanation as to why the air on top should meet the air below at the same time, so there is no reason for it to be faster.

I found this website in an attempt to understand how wings work. I don't quite get it still, but it is an improvement compared to the wrong stuff that I always thought was correct.

So now I have now upgraded from not knowing what I don't know, to knowing what I don't know.

Next, the lecturer talked abit about animal flight, something I have already listened to during the NUS physics camp. Exact replica. He showed us a few high speed camera videos of birds flying. Some think that its funny, I think that it's really impressive to see stuff like hummingbirds flapping their wings in slow motion. And albatrosses crash landing. And the eagle's precise landing by diving below its eyrie and swooping up again, converting its kinetic energy all into potential for a steady landing.

The following week was a lesson about aircraft stability and control surfaces by Dr Robert Goh from DSO. From the way he speaks, the impression that he gave me was that he knows his stuff much better than the NUS lecturer. The lecture this time was more towards the engineering side, rather than the science and vortices and fluid stuff. So it was quite a lot easier to understand. It didn't really teach a lot, but it was a great exposure to what to expect in the field of aerospace engineering.

I mainly remembered two simple things from the lesson. 1) Dihedral wings give a plane stability because rolling to one side will cause one side of the wing to have greater lift. 2) Found out the use of the tail plane. To correct yawing moments of the plane.

Followed by that we went to the field for a flight demonstration. First we looked at an expert flying a huge R/C plane (maybe around 80cm long) with bulky wings. From the looks of it costs around 300 dollars. The thrust it generates is impressive. The range is 2 km. I have had always a liking for vehicles since a child. By imagining little people just beside the vehicle, and making the vehicle move fast, I place myself in the viewpoint of those little people, and thus they look really magnificent to me. I still can't really believe how 'young at heart' or childish or whatever adjective you use to call a person who a few months ago took a big lego commercial jet flying it around the house and making it take off and land over and over again, I am.

Then the guy showed us a big flapping bird which could not fly as fast, but still it can fly faster than I thought. Not very agile. It attracted a bird which flew near, but it soon flew away when it knew it wasn't a bird.

Lastly, he flew a UFO like thing with 4 propellers. By the looks of it, having to control each propeller individually, it is a hard vehicle to control. Then he tried to do a loop the loop with it, and when it reached the top of the loop it thrusted down towards the ground and smashed.

I really hope I can fly a big model airplane someday. Ironically I wouldn't want to fly in a real one for two reasons.

1) I wouldn't be able to witness it flying from the outside. It will be just a screen, like watching TV if I sit inside the airplane. Maybe a wide surround screen, but still a screen.

2) Maybe looking at screens isn't that boring after all, if you see stuff flying towards you without a need of 3D glasses or if you see grounds spinning towards you. But that isn't really the kind of excitement I am looking for.

World of Science - Aerodynamics - Part 6

My SJChO Silver medal. :) I think their logo is very creative. If you can't see it clearly it's actually 5 benzene rings linked together, just like the olympic rings.

This time we went to the NTU Hanger to look at the aerospace exhibitions. I don't have a camera.

("Photos" are simplified with a few content eliminated due to obvious reaons)

That yellow thing behind the helicopter is a wind tunnel. It is only allowed to be operated up to 15m/s because the glass doors are just in front, which leads into the road)

First we visited a tiny gallery about flight and several experimental set-ups to study aerospace related things. One of them included a set up to test the vibration of different materials and shapes of wings. Then we went into a lab where the guide showed us a water tunnel, sort of like a wind tunnel to test aerofoils, only the medium is water.

There was a white sheet of metal resting on the table folded into the shape of a paper aeroplane. I thought it was paper at first, until the professor picked it up and I heard the sound of metal. A little dangerous for ignorant people.

Then we walked into a warehouse-like room which had this closed circuit wind tunnel. It didn't appear quite as I expected. I was expecting something cyclindrical and sleak looking, the sort of way I imagine particle accelerators to be, but it turned out to look like a line of beautifully arranged shipping containers. It was suppsoed to be really loud when in operation, so the researchers had to be closed in a room with cameras and windows to prevent them from going deaf.

When we were done, another person talked to us about fighter planes, and then brought us to a classroom with flight simulation programmes on computers, fitted with equipment. I'm not sure if it would have happened in real life or if it was just the unrealistic nature of the programme, but my boeing type airplane pitched into the air 90 degrees when I let go of the steering, and it happily proceeded to flip upside down. And the altitude did not drop.

By the time I got the hang of flying the plane, it was time to go.

Finally we listened to a short talk about propulsion, which included the different kinds of jet engines, ion thrusters and solar sails.

The End.

World of Science - Aerodynamics - Part 5

Drag and Lift.

They said that lift might be hard to understand, but drag is in fact harder.

There are two kinds of drag, form drag and skin drag.

Skin drag is the resistance between a moving surface and a viscous fluid. The fluid tends to stick onto the surface, thus causing skin drag. That thin layer of fluid that is directly affected by the presence of a surface is the boundary layer.

Reynold's number is a parameter that measures how much of the flow is controlled by viscousity and how much is affected by speed of the flow. At high values (Speed is more dominant), the boundary layers break away from the surface because they can't change direction along the surface fast enough, and the flow tends to become turbulent. This turbulence (or the wake) appearing behind the moving object causes form drag.

Aerofoil

This link might be useful in understanding turbulent wake flow.

At different Reynold's numbers, different flow patterns occur.

Can't find pictures of flows with increasing reynolds numbers. Instead, here is a link about drag.

I can't say anymore myself because I am not familiar with this topic.

World of Science - Aerodynamics - Part 4

Lesson 4 was an severely crashed course on fluid flow analysis. So crashed, we practically couldn't apply what we learnt. Fluid mechanics really scared the crap out of me this time.

When I am sick, I always have this dream. I wouldn't say dream exactly, but this mental state, where I am half awake, but I perceive the world so complicated that it tortures my mind. Literally, I feel tortured whenever I have this 'dream'. It's like my brain isn't big enough to comprehend whatever I am thinking of, and it is undergoing system errors.

Imagine it this way. Look at your surroundings, resting on the bed, subconsciously aware of them. Everything looks normal. Then, everything suddenly zooms in, your line of sight remains the same, but suddenly, you start seeing things at the molecular level. And you start trying to make sense of each individual molecule working as a part of your surroundings. Thus, your brain now is filled with information the amount of molecules in your room. You are trying to imagine them as lego bricks, and someone at the back of your mind asks you to re-build your surroundings by stacking these molecules, like lego bricks.

Then, you feel so tortured that you fall asleep completely, but you are not let off. Now you float in space, and I cannot recall the details. As you know this happens when I'm sick and I'm sleeping, so I never manage to remember how exactly to describe this horrible feeling. Anyhow, it is a mental torture.

Trying to make sense of fluid mechanics compared to undergoing this sort of mental state is actually nothing. However, it would be good enough to describe fluid mechanics as its counterpart during my consciousness.

I am currently having enough problems in comprehension in very basic E&M, such as Gauss' Law. How I imagine fluid mechanics would work(I might be wrong) is a blend of vector calculus and chaos theory. After all, the vortices I see in pictures of fluid flow really remind me of strange attractors.

DISCLAIMER: Whatever you are going to see from here to there is most probably wrong

Here
Then one day this lecturer comes along, starts off by introducing the Taylor series, and starts deriving the expressions for divergence, vorticity and deformation by assuming there is already a function for the system of fluid flow. I can accept that, but how do you even model a function for the fluids in the first place?

Another thing that comes to my mind is that fluid behaves really weirdly and it seems that no two times will I exactly see my bowl of soup behaving the same way. This led me to think that fluid (especially at high speeds) can exhibit chaotic nature, and now even my only pillar for security, the function which we assumed we already know, becomes hazy.

And if you haven't noticed, we (or at least I) have no idea what is going on in vector analysis, as you can see on the chart. It is just mind boggling to imagine infinitely many vectors associated to every point in a field.

I have no idea whether what I said was correct, but to sum it all up, I 'learnt' fluid flow analysis in two pages of notes. In other words, I learnt practically nothing.

This are the 4 main nothings that we learnt in the lecture.

Divergence: The supposedly rate of area change
Vorticity: How fast it spins
Deformation: Squash squash squash

THERE

Although my understanding did not increase much, the lecturer then started talking about real life applications, and it FEELED like that I started to understand certain phenomena such as cyclones better on an extremely shallow level after an hour of exposure to fluid dynamic jargon and pictures.

I know I haven't. My feeling then was that this was a topic that I will never understand and learn in my life because it was too bizarre for the mind to contemplate. But again, this was the feeling I had when I was in primary school after being told that with something called Integration, you can find the PRECISE area of a mathematical shape without any error.

Here are some interesting videos my lecturer showed us. Don't ask me how they work.

World of Science - Aerodynamics - Part 3

SECTION 1 - CREATING YOUR OWN REACH IN FISH TANK

This is how you create a 'reach in' fish tank.

Start off with this tank. It is really simple, just a tank with a hole at the side. But with just a hole, air will bubblie in, so let's make the wall penetrate downwards a bit more so that the air will have a harder time bubbling in.

WARNING: Provided the height of water is low enough such that the pressure at the depth of the whole is less than atmospheric pressure. the water will (hopefully) not flow out. However, if the column of water is too high, atmospheric pressure will not be able to support the weight.

Atmospheric pressure is 760 mmHg. Since mercury is 13.5 times denser than water, 1 atmosphere will hold up 10260 mm = 10 metres of water. As long as you conform to that height limit, the tank is safe.
Next you add your fish and plants and stuff inside the tank. Now visitors to your interactive tank will be able to feed your fish and touch your fish.

Warning: Ventilating your tank with an oxygen pump is NOT a good idea. The oxygen will soon displace the water and your fish will be soon swimming in air. Instead, be sure to get someone to design an extremely complicated system for channeling the water out of your tank and aerating it in a chamber independent of the tank, then pumping it back in.

Warning: Do not place exotic fishes in your tank. People might steal them.

And you're done! Probably the worst thing that can happen now would be this.So just make sure that you keep a lookout every now and then.

SECTION 2 - THE BALOONEY EQUATION (sorry I found the common mispronunciation so funny that I just had to put it down)

In a closed system, energy has to be conserved. This basically means that the gravitational potential energy, kinetic energy and pressure exerted perpendicular to the direction of liquid flow is more or less the same.

In other words: Pressure + Density*gravitational acceleration*height+0/5*density *velocity^2 is a constant throughout the system.

Whatever that means, just now that the faster something flows the less pressure it exerts and the lower its height the faster it flows. Makes sense doesn't it? Things go faster as it go downhill.

Just as usual, the lecture was boring.

The demonstrations were just a tad more interesting.


Erm... I guess many of us had seen this many times. Air flows around the ball, causing a region of low pressure around it. When it goes out of balance, the surrounding stationary air with higher pressure pushes it back in.



Atomizer. Water gets sucked up and a cocktail of body fluids and water is sprayed out.


Some burrow design by prairie dogs. Different shape of entrances to allow different flow speeds at different entraces, resulting in a pressure difference that allows ventilation.

I hope the next lesson will be more interesting.

World of Science - Aerodynamics - Part 2

Last Tuesday was a lecture about hydrostatic pressure.

It was really boring. For around 45 minutes the professor tried to explain why pressure throughout a liquid of same depth is constant. I wanted to sleep, but it would seem rude

However, the applications and demonstrations of hydrostatic pressure were rather interesting, yet simple.

1) Land surveying

With a main water tank and pole filled with water connected to the tank with a hose, altitude at which the pole is can be read via markings of the pole. Of course we have to make the water in the tank a lot compared to that in the connecting tube and the pole, so that the change in datum (water level in the tank) is negligible.



2) Hydraulic jack

I always thought that hydraulic jacks were gigantic pieces of equipment controlled by machines, because the great difference between the force humans apply and the weight of the truck is so large, in order to gain sufficient mechanical advantage, one will have to go to the top of the empire state building, hold onto a handle of the same height, and jump off the building in order to lift anything. Turns out that I had the wrong idea. People wouldn't be that stupid. Instead they suck hydraulic liquid from another chamber when needed, so we can push the pump back and forth, drawing liquid and pushing it, instead getting a darwin award.



3) Siphon. Water sucker. Found out about the siphoning effect years ago, but never really thought about how it worked.





4) Magdeburg Water bridge.

As one walk across a conventional bridge, center of mass shifts from one pillar to another. However, in a water bridge, pressure throughout the fluid remains the same, so assuming that there is little turbulence, the force is always evenly spread out across all pillars.

Magdeburg Water bridge

A water bridge in Germany, 918 metres long, the longest aqueduct in whole of Europe. It has been planned for 80 years, but put off after the splitting of East and West Germany. Now, it is used to connect Berlin's inland harbour and ports along the Rhine.



5) Lastly, we were given the task of coming up with a design for a fish tank which allows people to put their hand through a hole at the side to touch the fish. I heard of something like that in Underwater World in Sentosa sometime ago. However I found nothing when I searched the internet. Even went to Yahoo answers, but people gave me useless answers like reach your hand from the top, or have a pump that continuously pumps water back in as it spills out.

Here are some more ideas.

1) Vortex. Vortex tank creates a vortex in front of the opening like a washing machine, so the water does not spill out. Reaching your hand inside might disturb it though, so this 'reach in tank' is a see no touch


2) Plastic gloves. Transparent gloves makes it look as if your hand is reaching in. Gloves are coloured in picture for easier viewing. You can't feed to fish in here, because fish food does not pass through plastic.

Any more ideas on how this might work?

World of Science - Aerodynamics

Woke up at six on tuesday, and I was almost late for school. Fortunately my judgement did not fail me, and I alighted at Dover MRT station, ran to school in the rain. After that, had fits of sneezing during the national anthem, but I was relieved that my sneezing stopped after "Expelling the 'yin' out of my body"(Do not take this seriously, please).

Went to DSO in the afternoon, and ate mee goreng. For the umpteenth time, I know I cannot take spicy food, but I keep on eating them. When I got home, I got the same burning sensation when I poop, supposedly caused by the chemical capsaicin as I have read up, found strands of tough long shits and an orange block which looked rather much like a carrot, and the water in the toilet filled to the brim after an unsuccessful attempt to flush it.

After an hour of watching the lego nxt robot making rounds, jk and I left. It makes many frequent and minor analytical errors and assumptions, due to the rather simplistic hardware and code we used.

Speaking of which the next day, Wednesday, we went there again and kept on running the robot and made changes to parameters, as if hoping that the robot will finally learn how to do its task right after enough trials. Almost fell asleep under the table...

I left and went back to school for aerodynamics. Almost late, and had to run from the Singapore Polytechnic bus stop back to school. Then I found that my bag was trapped in class and ran to the general office trying to rescue my bag. By the time I got to Aerodynamics I was really sweaty, so sweaty that I could smell my own stink (People usually are oblivious to their own smell)

About aerodynamics. I was rather unsure about this at first, because after attending the aerodynamics lecture during the physics camp day 1, I found that I did not understand anything about fluid mechanics. So I regretted it and hoped that I had taken up cryptography instead.

But surprisingly, I found the module really good, so far at least. Tonnes better than the Artificial Intelligence module. And the funny thing was that the lecturer who lectured aerodynamics at the NUS physics Camp was the same one lecturing this module, and the slides he used were exactly the same.

However, ever since I went for the aerodynamics lecture, I came to realise that if aerodynamics and fluid mechanics was to be understood by secondary school students, our air spaces would not be safe at all. So I had my expectations drop really low and I no longer find it discouraging if I do not understand aerodynamics.

As I looked at the course outline, it was similar to the lecture at physics camp, only the topics were more in depth, and spanned across some 10 weeks. So I was rather happy for that glimpse of hope of me being able to understand something.

After the lecture of the first lesson, we played with paper airplanes. A really childish yet fun session.

I am looking forward to the next lesson and upcoming field trips for aerodynamics.