[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Fw: Pterosaur size

----- Original Message ----- 
From: "don ohmes" <d_ohmes@yahoo.com>
To: <dinosaur@usc.edu>
Sent: Saturday, December 16, 2006 9:15 PM
Subject: Re: Pterosaur size

> Let me ask a flight question.  Let us arbitrarily assume that you are a
> bird, or a winged whatever, and that from a height of 1000 feet in no-lift
> conditions, you can glide a distance of 20,000 feet.  Now, let's add 15% 
> to
> your weight.  Without flapping, how far can you glide in the same
> conditions?  Now, let's reduce your weight by 15%.  How far?
> --------- Ain't 20:1 high for a whatever? Just asking.

Not particularly.  Diomedea exulans has a glide ratio of about 19-20:1.  I 
rounded off to 20 for convenience in multiplying.
---- that is high, as in upper end.

> Going from thin limits.
> However, remember we agreed about that launch/flight/landing thing
> being what counts? How the hell you get way up there at a 1000'? How do 
> your power requirements vary? I
> don't start my marathon from the halfway point, although I have been 
> called a winged whatever.

Let's say that I dropped you out of an airplane.  Or, alternatively, you got 
up there the same way a wandering albatross gets up there. 

(<=== Relative to how the albatross gets there, see sink rate, minimum stall 
and air circulation patterns through geological time. Last I checked, the air 
circulation trend was more air circulation globally (from past to present), 
which has implications for ancient soarers.)

> When I talk about
> flight or volancy in the context of biosystems, I mean the whole cycle. So 
> I need a more precise term
> that isn't as hard to type as 'ecologically viable volancy' or
> whatever. Flight cycle, maybe?

I repeat my question.  Quantitatively, how does a +/- 15% weight change 
impact gliding range?

-------------- First answer got chopped out, I'll expand. Gets chopped out 
again, I will resend. Dredging this up from memory, if I have been wrong all 
these years, so be it. L/d= glide ratio. Sink rate increases w/ weight, as does 
minimum stall. More to the point w/ biosystems, increase in density = decrease 
in effective weight _WITHOUT LOSS OF POWERMASS OR FAT RESERVES_. Equal power, 
less "weight", lower sink rate/stall speed and more fuel/range. People speak of 
kinematic adjustments. These are MORE beneficial at higher density, as sink 
rate, etc. can ALWAYS be increased through planform adjustment. Also braking 
power is improved. No way this is not massively beneficial to a large bird, 
ESPECIALLY FROM THE ECOLOGICAL PERSPECTIVE. Increases in flight medium density 
(within reason) are beneficial to volant biosystems at Re > 10, period. 15% is 

>> and the Andes. Blackbirds that nest at 2500ʼ have lower
>> wingloads than sealevel nesters.
> Not for any reason to do with flight -- it's actually to do with launch, 
> and
> the variation between individuals or for one individual over time --  
> varies
> by more than the difference in density due to the 2500' change in 
> altitude.
> ----------I don't understand what you mean, but I think I probably 
> disagree.

Let's take Stonker for example.  From memory, when he left Scotland he 
weighed about 26-29 pounds.  Upon arriving in Iceland 2-4 days later, he has 
been weighed at weights on the order of 13 pounds.  That's approximately a 
50% weight change.  On the other hand, the density ratio from sea level to 
2500 feet is 0.929.  That's a change of approximately 7.1%.  Which is 

-------- What counts in selection/evolution is the average _(fill in the 
blank)_. Also, I repeat. You can't expect to see an altitudinal gradient of 
morphological change in a bird that is adapted to high altitude flight. 
Blackbirds are probably optimized to where they nest. They nest at a wide range 
of altitudes, and are functionally equivalent therefore there are altitudinal 

> -------------------- Damn. I was really hoping there was an answer to the 
> max observed launch altitude re cygnus. Think there is one,

Maybe, I dunno.

> or do they launch right on up to .59 atm?

I doubt it.  I don't think any o
ts are at that altitude.


----- That is encouraging.