What's the scalability of this flying strategy?

Question

So, a quick rundown:

Giant pterosaurs lived during the Cretaceous period before some a-hole wiped the server clean. These pterosaurs ranged in appearance and lifestyle from sorta-scavengers, like the long-necked Arambourgiania and the Quetzalcoatlus, to the Hateg islands' monster, the Hatzegopteryx Thambena with a short but T H I C C neck and a more proactive predatory lifestyle.

Most paleontologists, like Mark Witton, Michael Habib, etc... attribute their large size to quad-launch.

You see, since launching is the hardest part of flying, it takes some power to do. Birds use mostly their legs to initiate the launch. The problem with that is that those beefy (and rather heavy) legs become a dead weight during flight.

So, what bats and pterosaurs did was to use their flight muscles to take off, basically pole-vaulting into the air. This means that increasing the power of the flight muscles increases the power available to launch. These muscles were most likely fast-glycolytic, very powerful but tire quickly.

So, if you see "realistic" dragons (read: wyverns) that don't quad-launch, it's probably the Dunning-Kruger effect.

Rant aside, it IS a neat launch strategy, I'm just not sure if it can be scaled further "by default" to achieve flying creatures heavier than even giant pterosaurs.

What do I mean by "default"? Simple, really:

1. Let's assume we have lightweight materials with the right mechanical properties to be made into wings, bones, etc, and they aren't going to fail under very heavy loads.
2. Handwave metabolism. To be fair, at this size, our fliers will probably be soaring for most of the time. They'd only flap their wings when they need to go really fast, or when they're climbing out to cruising (?) altitude.

So, in terms of variables, we're left with the shape of the muscles and the wings. We're gonna assume the wings won't break, no matter what, but their shape and aerodynamics will still affect how much muscle-power is needed to flap with them.

Given these circumstances, how scalable would this flight strategy be?

Here's a link to a video of how quad-launch probably looked like for pterosaurs.

And here's a vampire bat taking off.

Papers We'll be referencing:

From damselflies to pterosaurs: How burst and sustainable flight performance scale with size:

https://www.researchgate.net/publication/15014212_From_damselflies_to_pterosaurs_How_burst_and_sustainable_flight_performance_scale_with_size

Why we think giant pterosaurs could fly:

https://markwitton-com.blogspot.com/2018/05/why-we-think-giant-pterosaurs-could-fly.html

Constraining the Air Giants: Limits on Size in Flying Animals as an Example of Constraint-Based Biomechanical Theories of Form:

https://www.academia.edu/12192191/Constraining_the_air_giants_limits_on_size_in_flying_animals_as_an_example_of_constraint_based_biomechanical_theories_of_form

Note:

It seems like clearance is a big problem for wings larger than 12-ish meters. The question then becomes whether we can increase the wing loading or change the wing's shape (and lower the aspect ratio) without negatively impacting the creature's soaring capability.

Answer 1

According to models 9-10m wingspan is the limit for a run-and-flap-wings takeoff of these creaturs, but there are great uncertainties since we have no working model and all flight manuals are lost ;-). Jump and flap doesn't work, no forward speed, even for an Albatros' take-off-run it's advisable to have some headwind and a slope down from the threshold for departure (see funny yt videos).

But a similar technique - run along a flat surface until lift kicks in - could potentially bring even (slightly, 12m wingspan) larger creatures into the air. Once airborn, they could have glided dynamically for days or weeks like some modern day species do.

Huge wingspan, high aspect ratio, an empty stomach and take off in dry air at sea level can help reducing take-off-speed.

Newer work, involving modeling and functional morphology, seems to suggest they didn't jump and instead needed some taxiway.

https://www.sciencemag.org/news/2014/11/launch-limit-pterosaur-flight

https://royalsocietypublishing.org/doi/10.1098/rspb.2018.0727

So, 12m seems to be the limit under current view for the real world creature.

For a fantasy scenario and a bit of a stretch one could go higher, turn a few screws on atmospheric oxygen levels (energy for the muscles), pressure, gravity, etc. So, maybe 15m wingspan i'd say, if the creature is able to run at a large cat's or steppe herd animal's, raptor like velocity (balance when running, no tail, and all that) and no T-Rexes or other predators are waiting at the end of the runway. Btw., seeing the bat in the video try to get airborne from ground instead of hanging overhead, if I was a cat I knew where to wait for food to come to me, just a little down from the threshold :-)

One must also keep in mind, the material can't be scaled endlessly. If that fourth finger that spans the flight membrane breaks from forces in flight that's the end of the creature.