Monday, February 26, 2007

Lift

This is about a ‘stupid’ thought, due to ‘lack of memory’ and the result.
If you want to skip this and go to the outcome of discussion click - Brief description of flight

The discussion on this topic happened in college after some guys got back having had their industrial training in HAL Helicopter division. We were discussing one funny answer given by one of my friend in the interview regarding IT.

Q : How is speed of rotation of helicopter wings controlled? (I don’t remember exactly)
Answer was expected to be ‘by gearing’
But by the profile of the person asked by the person, and because he usually don’t ask such simple question, my friend gave a complex answer.
A : The speed is controlled such that the velocity at the tip of the blade doesn’t exceed the mach limit. So and so…
Question was repeated and confused, he dint give the answer.

That limit was a new knowledge for me…

Started a boring class…

I asked whether the blades are similar to that of a fan? He said yes.
I also remembered that fan will get lift by deflecting air.

That time my mind strayed into aircrafts and I tried to recollect the wing shape. My powerful memory – I could not recollect the aerofoil…
So I tried something similar to fan blade for the wing. I found myself drawing some airflow in notebook.

Class over…

I checked with one of my friend. He did draw an aerofoil. Yeah now I remember. But how this create a lift? ‘Wow you forgot Bernoulli’s theorem and the equal time principle’…

But I argued that it can’t be so much different from a helicopter. Because I stand with Einstein – “God doesn’t play dice” – or he???

But why should both reach at the same time?? Why not the air be pulled from somewhere else, if vacuum formation is the problem?

He said he also don’t believe in equal time principle, but Bernoulli’s is giving a somewhat satisfactory answer.

So we started our search for answer. Posted in one physics forum www.advancedphysics.org, one site I really love.

Immediate responses… Not purely Bernoulli, but Newton’s and Coanda effect… If it is you just can’t explain – Inverted flight, Importance of angle of attack and so many things. And a webpage – which is hosted by authors of a book.

Now the page is now longer available, but I have a copy hosted in a page of my blog – A brief description of flight.

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