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The Nr Fairy
17th Oct 2018, 19:39
Sorry for the aviation content, but I couldn't resist posting this. The secret physics of dandelion seeds (https://www.nature.com/articles/d41586-018-07103-8) and there's a video:
https://www.youtube.com/watch?v=N2UbaDV9O9Q

WingNut60
18th Oct 2018, 00:49
Beautiful!!

treadigraph
18th Oct 2018, 00:56
So that's how helicopters work. the "they're so ugly the earth repels them" theory debunked...

Karearea
18th Oct 2018, 06:59
Fascinating - thank you!

ORAC
18th Oct 2018, 07:49
Overblown if you ask me......

A_Van
18th Oct 2018, 08:03
Quite impressive, thanks!

DaveReidUK
18th Oct 2018, 08:50
So that's how helicopters work.

Except that mention of a Vortex Ring (as in the video) is enough to give any helicopter pilot palpitations.

ORAC
18th Oct 2018, 08:52
What’s known in the media as a puff piece I presume?

Uplinker
21st Oct 2018, 11:17
So the bristles modify the upwards airflow to effectively form a circular wing which, like a wing, reduces the air pressure above it to provide lift.

ChickenHouse
21st Oct 2018, 11:28
Which license does the kid have to release airborne objects, don't you need a drone permit ;-) ?
Sorry, spent too much time in mental poisoned central continent areas.

WingNut60
22nd Oct 2018, 00:50
So Newton's 3rd Law is not always part of the lift equation,eh.

meadowrun
22nd Oct 2018, 04:01
I think if we had spent more time studying just how birds fly, way back when, we would have been flying a lot sooner. The answers are all there.
Just would have had that portable, self-contained power thing to sort out.

Uplinker
22nd Oct 2018, 11:51
So Newton's 3rd Law is not always part of the lift equation,eh.

Obviously it is.

The dandelion seed is simply acting like a parachute - owing to the upcurrents of air, (or the downward path of the seed through the air), a pressure difference is generated which produces a lift force.. A traditional parachute achieves this by trapping air underneath a canopy which increases its pressure relative to the air above the canopy*. The dandelion seed would appear to achieve a similar pressure difference but does it by reducing the pressure above instead of increasing the pressure below. Same result = lift.

I used to assume the ‘lift’ force was in fact the aerodynamic drag of the hairs, but clearly not.

* modern steerable parachutes are shaped like, and act as, a traditional glider wing of course.

Uplinker
22nd Oct 2018, 11:59
I think if we had spent more time studying just how birds fly, way back when, we would have been flying a lot sooner. The answers are all there.
Just would have had that portable, self-contained power thing to sort out.

Biology, coupled with natural selection is absolutely fascinating. When you watch footage of an eagle flying, for example, you can sometimes see little feathers on the wing upper surface lifting and rippling. This must feed back to the eagle that its wing is approaching the stall. So it senses where its maximum lift is.

WingNut60
22nd Oct 2018, 12:45
Obviously it is.

The dandelion seed is simply acting like a parachute - owing to the upcurrents of air, (or the downward path of the seed through the air), a pressure difference is generated which produces a lift force.. A traditional parachute achieves this by trapping air underneath a canopy which increases its pressure relative to the air above the canopy*. The dandelion seed would appear to achieve a similar pressure difference but does it by reducing the pressure above instead of increasing the pressure below. Same result = lift.

I used to assume the ‘lift’ force was in fact the aerodynamic drag of the hairs, but clearly not.

* modern steerable parachutes are shaped like, and act as, a traditional glider wing of course.

I was looking more for downward deflection of airflow to produce a resultant upward reaction as with a conventional airfoil.
That doesn't seem to be there.

Uplinker
23rd Oct 2018, 07:14
I was looking more for downward deflection of airflow to produce a resultant upward reaction as with a conventional airfoil.
That doesn't seem to be there.

:ok: the parachute and dandelion seed still obey Newtons third law:
From Wikipedia: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

Ancient Observer
23rd Oct 2018, 17:23
Do the CAA issue licenses for this flying?

G-CPTN
23rd Oct 2018, 20:06
I remember travelling in the 'cab' of the Channel hovercraft and the pilot saying that he was neither fish nor fowl.

visibility3miles
23rd Oct 2018, 23:04
Cool. Thanks for posting.

Andrewgr2
24th Oct 2018, 08:55
I think the over simplified video fails to explain some relevant facts. Clearly the vortex ring enables the very lightweight seed to act as an efficient parachute. However it isn't immune from the effect of gravity and, in still air, will drift downwards slowly, despite the drag of the air around it. However, a feature of dandelion seeds is that they are only distributed when acted on by a force - a child blowing them, or more usually in nature, wind. If the wind is blowing, there will be turbulence in the air and some of the air will be moving upwards. Seeds caught in the upward moving air will be carried upwards - although they will still be drifting downwards with respect to the air. Of the myriad of seeds distributed from a single dandelion, some will be carried up enough to drift with upward moving air a long way before falling to the ground. Most will not. However, evolution will have ensured widespread distribution of seeds.

oxenos
24th Oct 2018, 20:41
widespread distribution of seeds.

Is that not the definition of adultery?

GordonR_Cape
25th Oct 2018, 05:35
Dandelions propagate by apomixis (cloning) which is a type of asexual reproduction (virgin birth).

funfly
25th Oct 2018, 19:25
Dandelions propagate by apomixis (cloning) which is a type of asexual reproduction (virgin birth).
Jesus! whatever gave you that idea?

GordonR_Cape
25th Oct 2018, 20:11
Jesus! whatever gave you that idea?

https://en.wikipedia.org/wiki/Taraxacum

Many Taraxacum species produce seeds asexually by apomixis, where the seeds are produced without pollination, resulting in offspring that are genetically identical to the parent plant.

WingNut60
25th Oct 2018, 22:50
Jesus! whatever gave you that idea?

I think he missed the irony, mate.