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Re: vaulting pterosaur launch, questions



> It seems to me to be an easier mode than running, but the
> two are not mutually exclusive.
I think the physical requirements for a standing/leaping launch are greater 
than a running launch. While it may be easier for a bird with the neccesary 
adaptations, I would think a standing launch would be a more derived form of 
flight, and the basal launch technique would either be running into the wind, 
down a slope, or dropping from a high perch.

> > Birds always take off into the wind,
> As an aviation-related example, when taking off from and landing on the 
> sandbars on the
> Mississippi and White Rivers, you usually have to do it downriver no 
> matter the direction of the wind, due to the saw-tooth shape of the 
> ripples and dunes (they will take your landing gear off if you hit them > 
> going upstream, while you jump them like jumping off a ski jump when 
> going downstream)

(ok, birds don't ALWAYS do it, but I'd say 99% of the time any appreciable wind 
is present)

I question the applicability of this example, due to the large differences in 
scale, weight/wing loading, airspeed, and landing aparatus (feet vs wheels).
I can gaurantee the preferable landing direction in an HG would be into the 
wind - even in no wind, properly executed technique results in 0 ground speed 
when your feet touch the ground.
The onlt situation landing into the wind is not preferable, is if it results in 
trying to land on a downhill slope, or there is no LZ where the widest axis is 
parrellel to the wind direction, in which case a crosswind landing is called 
for. (downwind uphill landings are also viable in some cases)

> > a 9 mph wind would be enough to make up the difference
> > between the 2 m/s running speed, and 6 m/s stall speed.
> 
> Only until the wind decelerates the animal so that it's
> 'rest' speed matched that of the wind.  Steady wind can help with 
> launch, but not with sustained flight.  
But archeaoptyrx could sustain flight, the problem was getting airborne and the 
trouble it would have flapping its wings on the ground, right? a running start 
into a head wind could be sufficient to get airborne to allow for weak flapping 
to do the rest.


> Orographic lift would do more good in the long
> run. It can also make up the difference between a 2 m/s leaping
> speed and a 6 m/s stall speed (diminishing as the animal decelerates 
> due to drag.

True, but I think any animal that does a leaping takeoff from the ground, is 
already adapted for flight, I have a hard time beleiving it is the basal launch 
technique


> There also has to be a purpose for the flight, and though shear can 
> provide energy for flight, it can also make control more difficult
> (I can takeoff and land a Piper J3 in direct crosswinds gusting to more
> than 30 knots, but 
> I sure don't enjoy it or search out the experience.
    I'm not talking shear here (30 knots consistent straight in is at my limit, 
if not just above it), but smooth laminar flow over elevated coastal terrain. 
At Marina beach, I can cruise for dozens of miles along the ridge exerting 
almost no energy, the dunes are only a 100' climb to relaunch should I find 
myself landing on the beach for whatever reason- I often spot miscilaneous 
washed up dead things on the beach.
Like seabirds today, the seashore has a lot to offer, and the ability to 
traverse it with little energy expenditure does have a lot of value

Coastal lift is the most consistent lift I know of, and presents in my view the 
lowest barrier to controlled flight. This doesn't mean thats how it happened, 
but I wouldn't be surprized if controlled flight arose from pterosaurs or 
therepods living near the beach, or consistent wind.

I should note there are ridges in the Utah desert that also have very reliable 
and consistent wind for ridge soaring - of course I see such an environment as 
less likely to host the first flying animals because of the much lower 
availability of any food source.

> they were deliberately lookng for orographic lift. 
> Birds can can and could do that as well, but it is not a requirement.
Of course birds do that as well, and it isn't a requirement. However, as with 
the Wright brothers, you can't very well have powered flight until you can have 
controlled flight.
The transition form has to be viable, and I think a coastal soaring unpowered 
flight form is viable. 
At least more viable than something clumsily flapping to extend its glide 
between trees.

Among human foot launched flight, a lot of the time all you need to do is walk 
to the edge of a coastal dune with a neutral/negative angle of attack, and then 
increase angle of attack at the edge, and away you go- no leaping or running 
required at all. It should get even easier as it is scaled down.
A an early bird or pterosaur need not neccesarily run or leap at at all, just 
waddle up to the edge and unfold its wings