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MatC
293316.  Mon Mar 10, 2008 11:56 am Reply with quote

According to an article in Fortean Times 231 (page 14), the anonymous Swiss aerodynamics professor who started the urban myth that “scientists say bumblebees can’t fly” was actually proving that they can’t glide (and he was right).

 
Flash
293331.  Mon Mar 10, 2008 12:12 pm Reply with quote

John McMasters of Boeing:
Quote:
A long time ago [1989] I wrote an article for the journal American Scientist entitled: "The Flight of the Bumblebee and Related Myths of Entomological Engineering" (Am. Sci., Vol. 77, pp. 164-8). In this I gave what still appears to be a correct account of the "Didn't the aerodynamicist prove that the bumblebee can't fly ? [sarcastic ha ha]" story. I too had tried to find the name of "The aerodynamicist" who did this to us. After a long search I was told by a very reputable source that he thought that individual (who was badly misrepresented subsequently by the "press") was the Swiss gas dynamicist Jacob Ackeret - a famous name in supersonic aerodynamics. It was about the right vintage, so I wrote that in my article without naming Ackeret explicitly. Follwoing publication, however, I got mail. Boy did I get mail - including half a dozen xerox copies of portions of the text of the book Le Vol Des Insects (Hermann and Cle, Paris, 1934) by the famous entomologist August Magnan. On page 8 of the introduction, one finds: "Tout d'abord pouss'e par ce qui fait en aviation, j'ai applique' aux insectes les lois de la resistance del'air, et je suis arrive' avec M. SAINTE-LAGUE a cette conclusion que leur vol es impossible." Thus the culprit is finally named: Sainte-Lague, Magnan's lab assistant who was apparently some sort of engineer.


Steven Vogel:
Quote:
The story somehow refuses to die. John H. McMasters (Boeing) gave an account of the back-of-the-envelope calculation in an article in American Scientist a few years ago. Having done a decent survey of the literature on insect flight, I find the account entirely credible. But insect flight aerodynamics are fraught with complexities - 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. All of which makes back-of-envelope calculations next to hopeless. A little over a year ago, Charles Ellington (Cambridge, UK) pretty well tidied up the bumblebee issue, in my opinion. Tricky business, getting sufficiently high lift coefficient, in fact. See paper in Nature, December ?, 1996. Also see two longer papers on bumblebee flight in J. Experimental Biology (1990) by Robert Dudley & Ellington.

 
MatC
293759.  Tue Mar 11, 2008 5:43 am Reply with quote

Following the 11/9 terrorist attacks on New York in 2001, all aeroplanes were grounded for three days (so were headless chickens, no doubt). As a result, the difference between daytime and night time temperatures across the nation became greater. This was because

Quote:
the grounding of aircraft reduced cloud cover produced by condensation trails, the trails of water vapour created in the wake of high altitude aircraft. In response, the diurnal temperature range recorded by a network of weather stations across the US jumped by a factor of three.


S: “The emerald planet” by David Beerling (OUP, 2007) reviewed in Morning Star, 12 March 07.

 
eggshaped
302850.  Wed Mar 26, 2008 5:06 am Reply with quote

It seems that boomerangs fly perfectly well in Space.

Quote:
Astronaut Takao Doi "threw a boomerang and saw it come back" during his free time on March 18 at the International Space Station, a spokeswoman at the Japan Aerospace Exploration Agency said.

Doi threw the boomerang after a request from compatriot Yasuhiro Togai, a world boomerang champion.


http://www.news.com.au/story/0,23599,23412011-13762,00.html

Link to FADS

 
dr.bob
302904.  Wed Mar 26, 2008 6:16 am Reply with quote

Why wouldn't they?

 
Flash
302916.  Wed Mar 26, 2008 6:36 am Reply with quote

Well, here's one possible reason: when I throw a boomerang in an attempt to make it come back to me I angle it upwards so that it returns to me downhill, as it were - ie gravity is one of the forces I'm trying to employ (generally unsuccessfully, though I have occasionally had near misses on people who were standing behind me when I launched).

 
MatC
302953.  Wed Mar 26, 2008 7:24 am Reply with quote

Am I right in thinking it's a Gen Ig that boomerangs are supposed to come back? Ideally, wouldn't each boomerang throw result in a dead animal with a boomerang sitting next to it?

 
eggshaped
302971.  Wed Mar 26, 2008 7:42 am Reply with quote

The oldest known boomerang was found in Poland. It was 20,000 years old and was the first man made object heavier than air to fly.

The oldest aussie boomer was found in Wyrie Swamp, South Australia has been dated at 10,000 years old.

http://www.culturequest.us/aboriginal_tools/boomerang.htm

 
dr.bob
303050.  Wed Mar 26, 2008 8:53 am Reply with quote

Early evidence of Polish emigration?

 
Flash
303053.  Wed Mar 26, 2008 8:58 am Reply with quote

MatC wrote:
Am I right in thinking it's a Gen Ig that boomerangs are supposed to come back? Ideally, wouldn't each boomerang throw result in a dead animal with a boomerang sitting next to it?

We have mused on this before. John Mitchinson thinks that the boomerang is meant to drive game towards the hunter, by making the quarry think there's a hawk overhead. If that's true then there is some kind of logic to the idea of a tool which you don't have to fetch back all the time.

Personally I'm a boomerang agnostic.

Q: What do you call a boomerang that won't come back?
A: A stick.

 
Flash
310161.  Thu Apr 03, 2008 5:37 pm Reply with quote

Flightless birds and Rocket flight from someone who seems to know:
Quote:
Penguins:
Well yes, the mechnisms used by penguins for both propulsion and manouvering in water are pretty well identical to those used by birds for the same purposes in air. It involves using lift developed as a result of the flow of the fluid (water for swimming penguins and air for flying birds) overthe body , tail, feet and wings. This is hardly surprising, given that penguins are actually birds and this is how birds move. The one difference is that birds also need to generate enough lift to oppose gravity, whereas penguins are almost neutrally bouyant in water so they don't need to. This is one reason why penguins have such small wings, the other being that water (being denser than air) develops more lift per given surface area and increment of speed than air. To fluid dynamicists penguins "fly" in water - their motions and behaviours are described by exactly the same equations as aircraft & birds. Of course the *really* controversial bit is that fish do too (even though they have "managed bouyancy"); the distinction is completely artificial from the viewpoint of physics. So you could suggest that penguins don't fly - birds actually swim through the air.

Rockets:
Actually pretty well all rockets "fly" as well. It's true that the initial part of the trajectory (going vertically up) is just sitting on the thrust of the motor, but once they tip over into horizontal flight they remain airbourne due to the lift developed along the boddy of the rocket an (where fitted) by the "fins" (which are actually just small wings). Once significantly away from the vertical, and at constant velocity, the thrust component of the motor alone CANNOT support the weight of the rocket because the motor is not under the centre of gravity (do a diagram of the forces and moments and you'll soon see it). Obviously the cylindrical body and (where fitted) "fins" don't develop any vast amount of lift, but then they don't need to. Lift varies with the square of velocity, so at rocket speeds a small amount of lift coefficient goes an awfully long way. But it does mean that missiles and rockets aren't very manoeuverable.

Some people say "ah, but space rockets only go up!". This is of course not true - they go up for a few miles as quickly as possible to get into the thinner air for less drag, but then they tip over and do most of their accelerating horizontally to get up to the required sub-orbital or orbital speeds.

PDR at post 310100

Q: What's the best way to point a rocket?

 
dr.bob
310334.  Fri Apr 04, 2008 5:18 am Reply with quote

I've not read the thread on the outer forums but, on the rocket point, it's also true that the thrusters on a rocket are steerable to some extent. I wonder how much that's used to keep the rocket going up, and how much is down to the "fins".

PDR does have a tendency to speak very authoritatively on subjects that he's not 100% sure about (in a recent thread about faster than light travel he claimed an imaginary vector would have a negative magnitude, which is incorrect by definition), though I think that aerodynamics is his bag, so I'm not sure here.

I'll try and do an independent check of the rocket thing.

 
Flash
310585.  Fri Apr 04, 2008 8:44 am Reply with quote

Certainly he seems pretty comfortable talking about rocket science, and he does talk about the steerable thrusters but says they're much more difficult to engineer than fins are.

 
dr.bob
310672.  Fri Apr 04, 2008 10:56 am Reply with quote

From a bit of reading up I've done, it seems that lift generated by fins is vital in rocket flight. I retract any scepticism I may have expressed about PDR's views. I can't imagine why I ever doubted him.

 
Flash
310675.  Fri Apr 04, 2008 11:01 am Reply with quote

Maybe the question is about what the fins on a rocket are for, because I imagine everyone thinks they're just for steering. Trouble is, that is indeed part of their function, so it isn't exactly wrong to say so.

IE, this wouldn't work, would it?

What are the fins on a rocket for?

F: Steering

A: Lift

 

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