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Hi Steve & All,
Front wing spread is just a convenient and conventional (Opler &
Malikul, Eastern Butterflies) measure of size.
No doubt size is just one element in flight versus wind but remember how
even nearly imperceptible wind flow (to us) keeps tiny insects like
no-see-ums grounded and slight air movement discourages mosquitoes; lessons
quickly learned if you decide to sleep in sheltered lake- or stream-side
thickets. And yes, there clearly are downsides to excessive size in insects
and no doubt one of these is large wings acting as sails in high wind.
And as you observed Steve, a bit of flight wobble is acceptable & normal
for Leps other than at the instant of landing.
Yt, DW
----- Original Message -----
From: "Stephen Shaw" <srshaw@Dal.Ca>
To: <naturens@chebucto.ns.ca>
Sent: Sunday, June 14, 2015 1:14 AM
Subject: RE: [NatureNS] Tiger Swallowtail flying in strong wind- How?
> Hi Nancy, Dave,
> Re Dave's comment on front wings alone, the front and hind wings of
> butterflies and most other winged insects (but not all) are closely linked
> together by a series of hooks etc, so while they don't always act as a
> single rigid structure, they can't be considered as independent actuators
> acting in flight either.
>
> The mechanism of insect flight has been clarified in recent years by the
> work of C. P. Ellington, Michael Dickinson and also robotics groups trying
> to emulate insects. It is not closely similar to that involved in
> generating lift using a steady airflow over the fixed aerofoils of an
> aircraft, involves several complex variables, can't be summarized in a
> couple of sentences, and is not completely understood. A good
> introduction on flight mechanisms can be found in the middle section of
> 'Insect Wings' in Wikipedia, obviously written or edited by someone in the
> field, and in part quite technical. One look at this should tell you that
> predicting how a butterfly of any size will respond in locally turbulent
> air currents is not possible to second-guess.
>
> This area has received a lot of attention because of hoped-for practical
> spin-off: having a sub-miniature camera carried by a tiny artificial
> flying robo-insect, much smaller than the current quadcopters, would have
> surveillance possibilities appealing to military sources that fund some of
> this (one could fly in through your half-open window and read your snail
> mail). Low power density in all current battery technologies is one
> (thankfully?) unsolved problem. A recent issue of the journal Nature has
> a section on such robotics. Or follow the links in the Wikipedia article
> to RoboBee, and Delfly (3 grams, 2 minutes flight time).
>
> In part the original question is apples and oranges. The hummingbird
> trying to hover at a feeder is an example of failure to stay on a very
> precise target because of wind turbulence. Conversely, it's not likely
> that the swallowtail has a single distinct target that requires precise
> navigation to get there, until the last few seconds of arriving
> fortuitously near a nectar source or a leaf on which to lay eggs. So it
> may not be a problem to be blown around a bit by variable wind gusts, some
> (+) and some (-) anyway.
>
> The usual assumption about the evolution of tails on hind wings is that
> they are supposed to confuse a predatory bird as to which end is the head,
> so can be sacrificed to save the owner's real head. They possibly might
> add aerodynamic stability as well, in line with the speculation for this
> function of long feathered tails in the early dinosaur group that likely
> made glide jumps off trees, before they evolved powered flight as 'birds'.
> Did you find that anyone had looked at the aerodynamics of tailed
> butterflies?
> Steve (Hfx)
> ________________________________________
> From: naturens-owner@chebucto.ns.ca [naturens-owner@chebucto.ns.ca] on
> behalf of David & Alison Webster [dwebster@glinx.com]
> Sent: Saturday, June 13, 2015 8:41 PM
> To: naturens@chebucto.ns.ca
> Subject: Re: [NatureNS] Tiger Swallowtail flying in strong wind- How?
>
> Hi Nancy & All, June 13, 2015
> I have no idea what the conventional wisdom is on such questions but
> logically the significant unit of wind speed should not be in absolute
> units
> (e.g.M/sec) but wing dimension/sec.
>
> And for example, expressing wind speed as front wing spreads per second
> (FWS/S), a Lep with a FWS of 15 cm would be expected to cope with an
> absolute wind speed ten times as great as would a Lep with a FWS of 1.5
> cm.
> In addition, wing muscle performance would be expected to some function,
> probably a linear function, of total wing area.
>
> So larger Leps, with dimensions and strength in their corner, should
> have good flight stability in conditions which would overwhelm
> sufficiently
> smaller Leps.
> Yt, DW, Kentville
>
>
>
> ----- Original Message -----
> From: "nancy dowd" <nancypdowd@gmail.com>
> To: <naturens@chebucto.ns.ca>
> Sent: Saturday, June 13, 2015 6:03 PM
> Subject: [NatureNS] Tiger Swallowtail flying in strong wind- How?
>
>
>> Friday was extremely windy here on L Torment. So windy that the
>> Hummingbirds could not manage to hover or land on the perches of the
>> feeder despite several attempts and the windfish was straight out
>> horizontal most of the day. Such strong winds are not unusual at this
>> location.
>>
>> What surprised me was watching a Tiger Swallowtail flapping merrily along
>> in its up-and-down flight seemingly oblivious to the gales. I was only 6'
>> from it, having a hard time holding a book's pages steady. I am not sure
>> how the Swallowtail is able to fly in such windy conditions and looked
>> online for answers. I only found some info on the tail helping
>> aerodynamically but not much. Anyone here have any idea?
>>
>> Nancy
>>
>>
>>
>>
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>
>
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