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.