Imagine a dragon as tall as average adult horse with a wing span of 12m long measuring from tip to tip. I wonder what evolutionary traits or techniques could allow the dragon to lift itself off the ground and fly in the air without making sound audible to a human being? I suspect among these dragons some might have evolved or developed ingenious way to take off without startling a dog but this is left as an exercise for hardcore reader only.
Kindly use magic sparingly.
Owls & co. already do this, thanks to the particular structure of their feather. Since I imagine your dragons don't have feather, they might have some structure leading to the same result.
Another option can be that they simply start flying with a dive, like birds nesting on cliffs do. Just spread their wings and jump, gaining velocity thanks to gravity and then flying.
Use its wings to trap hot ascending air underneath?
Like make the dragon heat the air under its wings and generate its own thermoclines. Or make a hot air pocket with the skin of its wings and then climb as a hot air balloon.
Kindly use magic sparingly.
Perhaps heat the belly of the dragon so high that the force of the emitted dragon's black-belly radiation will lift the dragon. Feel free to use whatever amount of magic necessary to make the black-belly radiation more potent than the black body one.
without making sound audible to a human being
Consider the dragon flapping its wings at ultrasonic frequencies?
Or, I don't know, make it take off at hyper-sonic speeds, by the time the humans or dogs hear the noise it's already too late.
without making sound audible to a human being
Take a page from Manowar and play metal louder than hell™.
What your dragon needs is the capacity to give out a very shrill, very loud shout. Something like my morning alarm ringtone, but at 180 dB and without any warning signs. For added effect, make the dragon nocturnal, mostly active after midnight.
Prior to takeoff, the dragon shouts. Any nearby humans or dogs will either die of heart attack or go temporarily but practically, absolutely deaf for a couple minutes, give or take. In any case they won't be able to hear wings flapping.
Being a headbanger who constantly got exposed to music at over 120 dB I can tell you that exposure desensitizes your eardrums for a while. And don't forget that decibels are logharitmic, so I'm suggesting a sound about 6 orders of magnitude (1,000,000x) louder than a drumkit at point blank range. Even deaf people might hear it because it will shake their inner ear bones very strongly.
ingenious way to take off without startling a dog
Taking off will not startle dogs because they will already be startled by the shout.
If your goal is to have a stealthy dragon, just remember that people hearing this will generally have an instinct to hide their sorry selves in their homes, from where they mostly won't be able to see anything. They will blame the fact that the goat's milk turned into yogurt inside the she-goat's udder out of a scare onto some mythological entity such as Baba Yaga.
I see the evolution tag. My explanation as.to how the dragon evolved this shouting ability is that it's much easier to catch prey when the prey is paralyzed out of terror.
We can assume dragons don't have feathers, but there is a possibility of some feather-like evolution qualities.
Look at the evolution of this owls feather though.
The National Audubon Society accounts for a leading-edge comb in the feathers being the reason why owls fly and land silently.
Something like this evolves as a means of survival, in this case, hunting food silently. If dragons needed something similar to the leading-edge comb during evolution, there would be something very similar to this, but on their wings.
dragons are rather large animals and would have a lot of air whipping up during take-off and flying.
so they would definitely need something like this.
Really, with this question, an owl comparison is 100% called for,
I hope you take this into consideration.
Dragons are not powered in flight by their wings...
They are instead blimps, with special hydrogen sacs along the length of their body that inflate (making the dragon appear far larger than it really is).
The wings are their as rudders and stabilisers.
The hydrogen is a by product of a chemical reaction which is generally very quiet, and incidentally allows the dragon to breath fire.
Many answers have discussed exotic and/or magical ways to reduce sound, as well as some great ideas like loud deafening sounds. But from the perspective of aviation engineering, I had a different idea.
An important factor in airplane design is wing loading. This is simply a measure of how much weight is supported by a certain area of wing. In the context of flapping wings, high wing loading(small wings/large weight) means the creature will have to flap fast and hard, while low wing loading(big wings/small weight) means that flapping less hard is suitable.
Now with a dragon, many ideas of dragons show a large armored body with absurdly small wings, yielding an extremely high wing loading. Impossibly high. But a dragon with a small(at least relatively) body and humongous wings would be very capable of flight in the real world, and it would be quieter. Here's why.
As I explained above, low wing loading means you don't have to flap so hard. But flapping hard is loud. Insects like bees flap their wings really fast, and they are quite loud for their size; imagine the sound of a dragon-sized bee! The lower the wing loading, the gentler flapping, the quieter the flapping, the quieter takeoff. So to make a dragon quiet at takeoff(and in all parts of flight) it just needs to have really really hugely ginormous wings compared to its weight.
What do your dragons look like? This question could derail this entire answer, but given the description you do have, I think this could fit.
Your dragons have the equivalent leg strength of the grasshopper (or flea, or pick you favorite jumping insect)1.
The dragon has the ability to quickly wrap it's wings around it tightly, creating a near perfectly aerodynamic form - twisting it's body roughly 720o each time it takes off2.
So your dragons simply jump to take off silently. The turning forces air off the ground to follow the dragon up and fill the vaccum left more smoothly. So there's still some leaves rustling, and some air movement for 100ft along the ground3
See notes below4
1Yes, whatever bio-fibers make up their legs will have to be something that doesn't actually exist from a physics/reality standpoint - at least that we know of or can dream of so far.
2 At full strength this does indeed create a sonic boom, but if attempting to, the dragon knows the correct strength to use to get itself just high enough it's wing noise isn't audible to a human, without creating said sonic boom. This is pure speculation, it could easily not be possible for a creature of this size to leave the ground with enough speed to get high enough without creating a sonic boom. This would depend on gravity, air density, etc. Not sure if we're assuming all physics are identical to ours?
3 Estimated, hopefully obviously.
4 Yes, yes I did just find the superscript/subscript tags for SE
Into the wind. Just hold out your wings straight and angle yourself into a decent-strength wind. Hilltops should work, mountain saddles even better.
Albatrosses do this aready on their (windy) islands. Paragliders are another good example.
Some running might be needed when the wind is down.
For those who say that an animal of this size could not fly without magic, here is a link to the wikipedia entry for a very large pterosaur (note the comparison to a Cessna!)
https://en.wikipedia.org/wiki/Quetzalcoatlus
The better an animal is at gliding, the less noise it will make (as it will expend less effort flying.) So you are looking at minimizing wing loading, by the same techniques as used by pterosaurs and birds. Principally, hollow bones and a lightweight skull, combined with large wing area.
Taking off by running into the wind will help.
Kindly use magic sparingly.
A lot of answers/questions on this SE delve into how dragons could work and how to make them realistic etc. In general, such large flying beasts, especially if they should somewhat resemble the typical dragon are not realistic at all. So I do think that magic should be part of the answer.
As L.Dutch stated it already, Owls achieve this effect with their special feathers and your dragons could have similar features built into their wings too.
Adding to that or just on its own I'd say they achieve a silent takeoff and for that matter a silent flight (and glide) via magic. Dragons, in general (Hollywood, modern fantasy), are depicted as passive or natural magic users and so are your dragons. They control the air around them to allow for flight in the first place but also to stop sonic waves from forming. A kind of magical ANC which could/should also be applied when flying around or at least when approaching prey. Owls are also not just very silent while taking off.
Takeoff already takes quite some physical and magical effort so adding additional strain to do it silently does not matter that much especially as it's a moment of vulnerability. Not giving away your position matters a lot if you try to catch some prey. So those dragons which were more silent when taking off and when flying around did catch more prey, meaning more food, meaning higher chances of survival. It is also quite handy if you are the prey and need to get away unnoticed.
If you add in some rivalry with other species their control over making/not making sound could be also used while attacking. Canceling out the sounds of cries and combat, in general, would definitely come in handy. If they need to they can also stop the noise cancellation and cry for help. So a natural selection favoring those dragons with better natural ways of making less sound and those which did create less sound is very likely.
They run fast to take off. Their mastery in hunting has made their feet's movement super stealthy, even when they are running. They can run on a rigid surface or a place full of houses. They know where to keep their feet without making any noise, for this they take help of their sharp eyes - to spot objects which could make noise and avoid putting feet on them.
Their agility and sharp eyes have helped them to fly silently without falling into the eyes of humans, for thousands of years.
Russian Sci-Fi strikes back!
A book series with quite scientific dragons has the dragons with reduced wing span as compared to the physical requirements by
Although the initial design (yep, they are designed, and the design description is a part of the plot) saw antigravs responsible for up to 90% of mass, later books reveal that using some concentration (similar to us preparing to lift a heavy object) and with some previous training, a dragon can lift off without using their wings, on biological antigravs only.
So, basically, the solution is to let the dragons have antigravs in their bodies. Those devices would also help with lowering wingspan and general flying.
If you want a more understandable hint to that series, give your sentient and human-level (or even above-human level) intellectual dragons appropriate dragon-sized protection goggles with an eye tracker for computer controls.
