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Re: Pterosaur Takeoffs (Under-rated Bats)




bh480@scn.org wrote:

> Speculation on pterosaur take-offs in the literature seems
> to be overlooking some recent research on species of bats
> that move about on the ground and can get into the air
> directly from a flat surface without climbing to some
> higher perch. Vampire bats can do this by leaping into the
> air.

JimC response:

It hasn't been overlooked.  I first publicly described the probable
similarities between the launches of Quetzalcoatlus and Desmondus
rotundus (sp?) in a talk I gave last February at SSA'99 at Knoxville, in
response to a request by Paul MacCready to talk about Quetzalcoatlus
flight mechanics, and I've been working with Wann Langston on
Quetzalcoatlus launch and flight mechanics for a bit over two years
now.  Actually, Q's apparent launch mechanism looks a bit more like a
mix between the bat D rotundus and a Cuban Tree Frog, with the leap
being oriented at about 25-35 degrees off the ground rather than the
almost vertical launch the bat uses.  I was planning to briefly mention
the mechanism in my SVP talk at Denver (which I've had to cancel due to
conflicts with my 'Day Job'.  I'm attaching exerpts from a private post
I sent Betty in response to her post about the albatross launch a couple
of days ago.

> Betty Cunningham wrote:
>
> > This might work also with inland rivers with fast current (water
> > creating it's own wind in this cases), but would not work with lake or
> > pond dwellers.
>
> Jim Cunningham responded:
>
> Right.  And both Q's were fresh water lake skimmers that didn't land to
> feed.  Steady state stall speed for northropi was close to 35 mph, only
> about 3 mph less than my Piper Cub.  He took off from flat ground, couldn't
> run, and couldn't afford to wait on a breeze for fear of becoming lunch
> (many of the Q remains bear teeth marks -- big teeth).  A bird-like takeoff
> from a standing start would have taken about 6 horsepower, which was more
> than he had available.  Muscle attachments and skeletal reinforcement in Q
> species indicate launch style for it and northropi remotely resembled a
> cross between Desmondus rotundus and a Cuban Tree Frog, powered first by the
> hindquarters with the front leg (inner wing) wadded up and loading tendons
> through adverse mechanical advantage.  Then about midway through the leap,
> geometry shifted so mechanical advantage could allow the stored energy in
> the front leg tendons to start kicking in.  The back foot cleared ground
> first, with the front leg clearing shortly thereafter, at which point the
> front leg (wing) started a modified upstroke till it reached a point where
> the tip could extend without striking the ground.  Thereafter, the upstroke
> was normal, and airspeed was above stall speed when the first downstroke
> began.  Launch was at about 25-35 degrees above ground level.  Average
> acceleration was a bit over two g's, well within the range of normal load
> factors, and loosely, about half the launch power was provided by the legs,
> the other half by the wings.  I haven't finished the force curves yet to
> determine maximum load factors for each, but it doesn't appear they will be
> severe.  All this happened quickly enough that anaerobic power was available
> all the way up to cruise speed, at which point the 1.3 horsepower needed to
> maintain level flight was usually provided by atmospheric lift.
>
(insert) At this point, it should be noted that Quetzalcoatlus replicas
are generally mounted in a configuration that requires about 4.0
horsepower to maintain level flight.

> I don't know how any other pterosaurs launched, not having
> examined their skeletons and muscle attachments.
>
> I'm not going to be able to make SVP (suddenly gotta work for a living), and
> have had to cancel my talk on Azhdarchids.  Made me sick, but maybe another
> time.  Tell everyone I said hi.
>
> Jim
>

 bh480 wrote:

> Any discussion of the take-off capabilities of
> quadrupedal pterosaurs should  consider how nimble bats
> can be despite having back legs that are much less
> developed than in pterosaurs.

Indeed it should.

> I would guess pterosaurs had
> little problem hopping into the air.

You are quite right.  Accelerations and power required were well within
the normal capabilities for Quetzalcoatlus species and Quetzalcoatlus
northropi.

> Whether they could do
> it from water, of course, is a tricker question. Although
> some bats catch fish with their clawed feet, they can't
> get back in the air if they land in the water.  Some
> pterosaurs appear to have had webbing between their hand
> fingers (mentioned in a recent post from Darren Naish),
> which could have been used for paddling if the function
> was not purely aerodynamic.

Correct.  I tend to doubt swimming in Quetzalcoatlus because of skeletal
restrictions in the achievable positions of the neck and head, but it
may well have been possible in other pterosaurs.

Your post and observations were most astute. Thanks!!

Best wishes to All,
Jim Cunningham