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Re: SPECULATION: pterosaur extinction versus bird survival
Demetrios Vital wrote:
> Demetrios Vital replies:
> Sorry I was unclear. Here goes... Longer, stiffer, thicker wings are
> better suited to fly in denser atmospheric conditions.
Why? In what way?
> The Boeing 747 has
> to achieve a very high speed to fly with its wings and size.
Oh. I thought this was because of its extremely high wing loading and
consequent need for high dynamic pressure.
> A _Q.
> northropi_ today would also have to achieve higher speeds or strong wind
> currents to fly efficiently.
Well, assuming that the late Cretaceous atmosphere was more dense (I don't
particularly doubt that it was, but don't consider it to be proven), the animals
would still need to achieve the same dynamic pressure to remain aloft, so would
fly at pretty much the same indicated airspeed. True airspeed would be
different, but that would affect them more during launch and landing than during
flight. There are some other differences in power required, but they are not
all that significant for the relatively minor differences in density altitude
that one might expect in the late-Cretaceous.
> In the Cretaceous, however, my theory is that
> not only were oxygen leves higher, but the atmosphere in total was denser.
Very speculatively, maybe 20-25% more oxygen and a few times more carbon
dioxide, combined with slightly higher temperatures, for a total decrease in
density altitude on the loose order of perhaps 10% -- something I consider to be
possible, but unproven. But even if true, that isn't enough difference to put
Quetz below the margin for flight or launch in today's atmosphere, or even
particularly close to it.
> And it was more dense than our atmosphere by an amount that definitely
> affects pterosaur flying.
In what way? Note that I'm not saying that it didn't affect flight. If true,
it would have, to some extent. But why would it have made it any more difficult
for northropi, for example, to fly in today's atmosphere than it is for the
WoodStock and Carbon Dragon sailplanes, which have weight, size, wing loading,
and other flight performance parameters similar to northropi? The Carbon Dragon
flies well enough that it presently holds a number of world's records (mostly
with Gary Osoba as the pilot).
> So because of the denser air and consequently
> stronger currents, _Q. northropi_ (again, only an example) would be able to
> fly at lower speeds and would need to expend less energy to do so, than if
> it lived today.
Considering that required dynamic pressure and indicated airspeed remain pretty
much the same for relatively small changes in density, in what specific ways
does the denser air reduce the energy expenditure?
> Birds' wing structure, however, obviuously is and was able to accomodate to
> the lower atmospheric density, for many reasons.
Of course. But, my point is that current atmospheric density is entirely
sufficient for the big pterosaurs to fly and fly just as well as similarly sized
modern aircraft. And the small ones too, for that matter. I would speculate
that it may have been conditions during the transition that got 'em (whatever
the cause of the transition) and not the eventual reduced density (if the
density is indeed reduced). As an example, Gary Osoba recently used his
Woodstock sailplane to simulate a skimming run for the similarly sized Q
northropi. He managed 600 yards of penetration against a 10 knot headwind, and
could have done about 1000 yards if he had flown in the opposite direction.
> I hope I've cleared my ststement up.