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timspaceman
29586.  Sat Nov 05, 2005 9:29 am Reply with quote

In an early episode of QI, it was claimed that although there are many theories, nobody can provide written proof that Jumbo Jets can fly. I mentioned this to a friend of mine (an aeronautical engineer) and he called me naive for believing nonsense on comedy quiz shows.
Am I remembering the episode incorrectly, or can somebody please explain to me what that was all about?
Cheers, Tim

 
Frederick The Monk
29604.  Sat Nov 05, 2005 1:42 pm Reply with quote

You should certainly never automatically believe quiz shows.......BUT nor should you automatically believe aeronautical engineers.

Now Jumbo Jets certainly fly, I think we can all agree on that but there is a great deal of argument still about why they fly. For instance David Anderson, who is a physicists at Fermilab has written a book called Understanding Flight in which he claims:
Quote:
The standard explanation of how we fly is mostly mythóit's just wrong, but it has such a life of its own that you even see it on NASA websites and in physics books.


There was a very interesting interview with him on the subject in New Scientist issue 2289, 05 May 2001, page 40 which is available online here . We'd all be interested to know what your aeronautical friend thinks about it.

 
Flash
29607.  Sat Nov 05, 2005 5:09 pm Reply with quote

If you need a soundbite, I believe this question is supposed to make aeronautical engineers giggle nervously: If an aeroplane's lift is explained by the Bernouilli Principle, how come they can fly upside-down?

 
laidbacklazyman
29614.  Sat Nov 05, 2005 6:04 pm Reply with quote

I recently watched a programme about suicide pilots, those that apparently dive their planes deliberately into the ground. The "expert opinion" in these cases said that Jumbo jets do have a natural tendancy to fly and the reason they can say that the pilot is responsible for these crashes is that it takes a lot of work to get a plane to dive, it will always make every effort to correct itself

 
JumpingJack
29637.  Sat Nov 05, 2005 11:37 pm Reply with quote

timspaceman

This reminds me of telling a friend that female kangaroos have three vaginas and him asking his friend who is a zoologist who, like your friend the aeronautical engineer, said it was rubbish because he had never heard of t.

It was, and is, nevertheless, quite true.

The Encyclopaedia Britannica was my original source for the 'fact' that there are currently five serious theories as to why planes stay up in the air but that aeronautical engineers cannot agree which (if any) is the right one.

 
Kevino7
29674.  Sun Nov 06, 2005 8:36 am Reply with quote

It's a bit like Bumblebees then.

 
dr.bob
29885.  Mon Nov 07, 2005 10:37 am Reply with quote

Bumblebees have been shown long ago to be theoretically capable of flight.

Which I'm sure was of some relief to them :)

The fact that, long ago, an extremely simplistic examination of the forces involved suggested that it shouldn't be possible is often used to suggest that scientists clearly know nothing. This kind of thing often gets right up the noses of said scientists, especially when they have to explain yet again why it isn't true.

 
JumpingJack
29963.  Mon Nov 07, 2005 4:56 pm Reply with quote

I'm glad you said that, dr.bob.

I was going to post something similar but it seems I'm getting a reputation for nagging, so I'm trying to be a bit less critical.

 
Natalie
29972.  Mon Nov 07, 2005 5:15 pm Reply with quote

The word "bumblebee" is quite cute.

That's a fact.

 
Flash
29974.  Mon Nov 07, 2005 5:19 pm Reply with quote

We think we nailed down the origin of the "bumblebees can't fly" thing, incidentally: it seems to be from a 1934 book by entomologist Antoine Magnan, who refers to a calculation by his assistant Andrť Sainte-LaguŽ, who was an engineer. The conclusion was apparently based on the fact that the maximum possible lift produced by aircraft wings as small as a bumblebee's wings and traveling as slowly as a bee in flight would be much less than the weight of a bee.

 
JumpingJack
29986.  Mon Nov 07, 2005 5:44 pm Reply with quote

Flapping aircraft wings?

Or did they miss that tiny detail?

 
Flash
29993.  Mon Nov 07, 2005 5:59 pm Reply with quote

No, I think the point is that nobody missed anything - Sainte-LaguŽ just made the QI observation that if they were built to function like aircraft wings, they wouldn't work - they had to build in the complexities of insect aerodynamics to explain it: continuously changing angles of attack, interactions of opposite wings at the top of the stroke, issues of how many chord lengths of travel are needed for full lift to be developed, vortex shedding and reformation (with opposite sign) at the bottom of the stroke, spanwise flow, etc, etc.

 
JumpingJack
30050.  Mon Nov 07, 2005 7:02 pm Reply with quote

Fair enough.

So wonderful to come across a chap who really understands 'vortex shredding' at last.

We can have hours of fun chewing that over with a Meerschaum and a large Lagavulin in hand.

 
Flash
30056.  Mon Nov 07, 2005 7:08 pm Reply with quote

There's an animation of vortex shedding here. Actually, I thought it was a kind of flat-packed garden hut kit from Scandinavia.

 
JumpingJack
30060.  Mon Nov 07, 2005 7:25 pm Reply with quote

Ha ha ha. Very good.

 

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