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EGBKFLYER
7th Feb 2006, 16:36
Friend of mine who knows about such things just told me that an Emperor Dragonfly can stop in its own body length from its cruise speed of around 35mph. By my calculations, that means a deceleration of about 350g. :eek: So how come it survives? :ooh:

This isn't a plane-on-a-conveyor type question BTW - genuinely intrigued.

G-CPTN
7th Feb 2006, 16:40
I've never seen a dragon fly.

Lord Snot
7th Feb 2006, 16:44
It's because of the relatively low mass and high-strength, semi-monocoque style construction of the dragonfly's empennage. You know, the tail section.

It's the same reason you sometimes see a wrecked aircraft smashed into "non-survivable" dimensions except for the tail section with is relatively undamaged.

EGBKFLYER
7th Feb 2006, 16:47
Yeah, but 345g?!!!!:eek:

Onan the Clumsy
7th Feb 2006, 16:57
I've never seen a dragon fly.
Me neither, though I have seen one angered :ouch:

Farmer 1
7th Feb 2006, 17:15
It's one of those things that vary as the cube of the length, if you see what I mean. Double the length, and you multiply the weight by eight. Likewise, halve the length, and divide the weight by eight.

So, if you divide yourself down to the size of a dragonfly, your weight will be about - well, about the weight of a dragonfly, i.e. a few milligrammes. So, if you multiply that by 345, or even 350, you're still not going to have much more than a gramme or two, and it's the force which matters, not the g.

It's like statements like "If a human could jump as high as a flea he could clear the Empire State Building (or whatever)." Well, he could, if he was the size of a flea. It's a completely fatuous statement, and amazes only morons. Pretty amazing, all the same.

Lord Snot
7th Feb 2006, 17:26
the force which matters, not the gGravity is the force being applied - and acts on everything equally, except for fat people.

I'm still backing my own argument (which I made up on the spot) until someone smarter or full of better-quality bullshit comes along...

tony draper
7th Feb 2006, 17:38
I find the quoted speed of 35 mph a tad doubtful, sounds a bit like the legendary Deer Bott fly although that had a reported top speed of around 300 mph,and actually made it into old encyclopedias as the fastest animal in the world.

Cool_Hand
7th Feb 2006, 17:39
Gravity is the acceleration, the force is the mass times the acceleration.

airship
7th Feb 2006, 17:53
For your information: dragonflies don't use mph, they use knots.

This is because they start out life as aquatic larvae...

Dragonflies can also turn on a pin-head. They do this by breathing out heavily through just one side of their abdomen.

Empty Cruise
7th Feb 2006, 18:14
Only polar bears have a higher deceleration capacity then dragonflies - they can manage just under 500 G when jumping on hapless seals.

Killer fact!

BALIX
7th Feb 2006, 18:59
When I saw the title of the thread

Why don't dragonflies collapse?

I assumed that the the question referred to collapsing with exhaustion. Let's face it, if you waggled your arms at the same speed as a dragon fly flaps its wings, you would be shagged out pretty damn quick. :hmm:

tony draper
7th Feb 2006, 19:10
All well and good,but how does a fly land upside down on the ceiling?, confounds the lift overcoming gravity thingy dun it?
:uhoh:

Bern Oulli
7th Feb 2006, 21:21
Tony, see http://www.coolquiz.com/trivia/explain/docs/flies.asp

G-CPTN
7th Feb 2006, 21:27
All well and good,but how does a fly land upside down on the ceiling?, confounds the lift overcoming gravity thingy dun it?
:uhoh:


They coat their feet in sh1t (which, as you know will even stick to a blanket), then they can land and walk upside down (and vertically on glass).

tony draper
7th Feb 2006, 21:31
One knows a pig farmer who's footwear is often coated thus,yet he is restricted to walking about on the ground.
:rolleyes:

Noah Zark.
7th Feb 2006, 21:56
Digressing somewhat, have you seen the name of the new adhesive from Evo Stik? It is literally called "Sticks like Sh*t"!
True!
Incidentally, Dragonflies only live for a day, so the chance of the airframe getting knacked out with all the hairy-ar$ed stopping is a bit remote!

Conan the Librarian
8th Feb 2006, 01:14
Mr. Draper,

have you considered donating your body to science? Your brain certainly deserves posterity in at least, a glass jar. But not for a few years yet, eh?

Conan

Farmer 1
8th Feb 2006, 06:17
"Incidentally, Dragonflies only live for a day, so the chance of the airframe getting knacked out with all the hairy-ar$ed stopping is a bit remote!"


Just for once, I thought I'd be pedantic, and pooh-pooh Noah's rash statement, but I couldn't find a definitive statement to contradict him. Mayflies only live for a day, and have no mouths or stomachs, but dragonflies have both.

However, talking of pooh-poohing, I came up with the following riveting piece of information, courtesy of Encyclopaedia Britannica:

[Dragonfly] Larvae absorb oxygen from the water using gills inside the rectum. The abdomen draws water in and pumps it out again through the anus.

Can you imagine a conversation between two dragonfly larvae? Whatever one says, the other is bound to say, "You talk a load of pooh-pooh"(?)

Marvin the Robot
8th Feb 2006, 06:20
http://www.dragonflysoc.org.uk/frameset.htm?home&home

Describes life cycle, amongst many other fascinating facts (click on "FAQ").

One of the most beautiful of creatures, IMHO. Note that they don't sting. So don't go killing them out of fear. Hopefully that info will save a few from death by ignorance.

They've been on this planet for a darn sight longer than we have. It's just as much theirs as ours, arguably moreso.

tony draper
8th Feb 2006, 07:14
As one understands it when Dragonflies change from tadpoles into err dragonflies, they are not suppled with a mouth,ergo they have to get their business done before they starve to death,perhaps that is the reason for them pissing about at 35 mph,( a velocity which incidently one still has difficulty believing)
:cool:

G-CPTN
8th Feb 2006, 07:44
pissing about at 35 mph,

Do you mean that they excrete water whilst flying?

chornedsnorkack
8th Feb 2006, 08:42
Gravity is the force being applied - and acts on everything equally, except for fat people.
I'm still backing my own argument (which I made up on the spot) until someone smarter or full of better-quality bullshit comes along...

OK, I think that what matters most is the pressure. Which is height times acceleration (times density, but this is near constant).

If you fly and suffer 3g or 4g, or 5g when standing up, head over 6 feet above your feet, there are nasty effects to blood pressure, greyouts, blackouts, G-LOC. As well as being uncomfortable for knees. Somewhat similar effects happen if it is just your part above buttocks that is propped up nearly upright (so you could see out of cockpit windscreen) by the seatback and 5-point harnesses.

Whereas if you lie fully flat on a soft bed, head level with feet and nothing over a feet above your back, you are much more comfortable with moderate g-s.

A dragonfly being (much) less than an inch in thickness could easily withstand 100 times higher g forces than a human... the pressures and stresses would wind up being comparable.

As for flies... Well, propellers of aircraft can have reverse pitch on landing.

A helicopter might have reverse pitch on main rotor and fly with rotor down, but this might cause problems with stability and controllability. The wings of a fly offer more control options, so flying inverted, hovering inverted and landing inverted would be feasible...

Oldjet Jockey
8th Feb 2006, 12:45
Have seen a dragonfly stop in its own length. Some 50 years ago was in the sea in a little rubber dinghy when a dragonfly approached and stopped over head with out any problem. down was winched a cable and I was lifted up into the dragonfly and returned to my carrier. Westlands had developed the dragonfly from a Sikorsky S51 design and built many for the Navy.
Didn't show any signs of stress or too much G. So it is quite possible for a dragonfly to stop in its own length from a forward speed of 35mph or knots as the case may be. So there.

OJJ