Air drafts generated by dragonflight

Question

So, I am working on a project of mine, and have been considering the effects that dragons have in flight upon the air around them. Right now, assume these dragons are perfectly capable of flight, with some even being extremely fast. In general, a dragons wingspan will be double its actual length. Dragons range in size from 15 feet long to 180. Often the biggest of them have even bigger wings.

What I want to know is how their flight would affect others in flight behind and around them, with the creation of downdrafts and other things. I know that a dragon would create massive vortexes in their wake that could both aid and hinder other fliers. How could this be used to aid allies(with formations or other such things) and defend against enemies(i.e., dangerous air currents)? (Edit, to be clear, I am not asking for ideas on specific formations, but more about the physics of the situation and what that would cause. How big vortexes would be, where, etc.)

I have them already making use of V pattern formations in flight, as well as flying directly behind a similar sized dragon, beating at an opposite pace to counteract the downdrafts caused by the lead dragon.

I found this video https://www.youtube.com/watch?v=2sh8_3-R90I on the vortexes created by an owl in flight, which has helped me understand this, but I don't know how these things scale.

UPDATE With a request for more information on how the dragons fly, I am going to provide some of the particulars.

• My dragons have two biological traits, we can call them magical if you want, one called Nal, one called Kwen. Nal makes their bodies lighter, more efficient, etc. Allows for lighter muscles that perform as well or better. Also allows for hollow bones. Kwen makes their muscles and bones denser and tougher. together, these affects combine, making their muscles, bodies, and bones tougher, stronger, lighter, more energy efficient, and more.(Otherwise, they would either be to heavy to function, or to delicate to survive the forces they would produce in flight or landing.)
• As a general rule, my dragons are not using some sort of magic to fly. There are some dragons who use air magic to augment their flying, but that is not the focus of this question.
• Average dragon speeds top at 70 mph, though they range from 50 to 70 mph. The fastest of dragons can achieve bursts of speed up to 150 mph. Any speed achieved beyond that is done by magical means.
• They have an inbuilt system, biomagical, that allows them to deal with the heat generated by their size and flight. Thus, they get around the heat restrictions of the square cube law.
• My dragons are also capable of deriving energy from various sources through magical and biomagical means to empower themselves with extra strength.
• For form and shape, there is variation between kind, but the basics are that most will have their tail comprising half their length, and their neck, head, and body the other half. Usually, the neck and head take up one half of that half, and the body the other. As I said above, wingspan is typically twice the length of the body, so a 30 foot dragon would have between a 60 or 70 foot wingspan, but even bigger ones have been known among more maneuverable dragons.
• Lastly, the bigger the dragon, usually the slower they are and less aerially maneuverable. This is not always the case, but is the trend.

So, does this help? Any other questions?

Answer 1

Minimal opportunities, only in niche circumstances.

RL aircraft face serious, sometimes fatal, dangers from things like propwash, jet blast, and the far more subtle 'wake turbulence.' The latter is typically only a concern when smaller craft follow too closely in the path of a much larger craft. (ATC rules/regs in the US require 3-5 minutes of time to pass in most situations where wake turbulence can apply.)

Everything that flies, however, produces wake turbulence and this can prove fatal even for aircraft of the same size under the wrong conditions.

The catch, for your needs, is that these are threats to RL aircraft because those aircraft have rigid wings that have static critical angles of attack (AoA). The threat from disturbed air currents, such as wake turbulence (vortices produced by wingtips as a function of mass, speed, and wing shape), exist because they can force the relative motion of air over a wing past the critical AoA - thereby causing the wing to stall. (One wing stalling while the other doesn't will cause the aircraft to 'dump the wing' that has stalled, and enter a spin-stall departure from controlled flight. Straight-up deadly if this happens at low altitude as it requires the use of gravity to convert altitude to airspeed to recover. Spin-stalls are a top killer of general aviation pilots.)

Dragons, however, do not have rigid airfoils to produce lift - they beat their wings, instead. Flexible wings, operated by natural flyers, are not subject to critical AoA failure because they can independently shift the shape/position of the wing to compensate for the change in airflow. Thus, birds are essentially incapable of spin-stall accidents unless they've been injured or are otherwise impaired.

Offense use of wingtip vortices (wake turbulence) or the wingbeat equivalent of 'propwash/jet blast' is therefore difficult to the point of futility. The only dragon you could meaningfully disrupt with wake turbulence is one in a gliding regime - which they can immediately and instinctively exit as soon as they encounter your wake, which they will only do for a moment.

Using the downwash of your wingbeats to stall an enemy's wings would require you to be close enough that you'd be more effective engaging in melee combat, instead - greater chance of causing meaningful injury.

Dragons under powered flight could use v-formation the way migrating birds do, but gliding dragons will spread out to avoid each other's wake.

Military jets, by the way, use formation for unit cohesion and mutual support NOT for efficiency. Flying that close in rigid-winged aircraft is actually quite dangerous and requires considerable skill. The operational benefits end up worth the training effort in that context.

The TL;DR here is that the only dragon vulnerable to aircurrent effects is one very near the ground, distracted, and in a gliding regime (unlikely near the ground). There's no real reason to defend, as a result. A massive dragon could present a brief threat to a swarm of smaller flyers, but by your stipulations they're more maneuverable so they'd likely be able to avoid.

There's niche cases where mutual support can help with things like energy efficiency for long-haul flying under power, but biological wings are simply too flexible and responsive to be meaningfully disruptable.

If, however, there's ever anyone stupid enough to try and share the skies with a rigid airfoil wing while there's hostile dragons of their size or larger? Putting them into a spin-stall would be so easy that it's likely to be a cruel sort of sport: "Lol, look at this scrub with his hide-covered hang glider... watch this..."

Answer 2

It would be helpful to be able to estimate how fast a downdraft the dragon's wings could produce.

If the dragon's wings are exerting on average a constant force, this must be produced by throwing air molecules in the opposite direction. The faster they throw the air molecules, and the more mass of air molecules they throw per second, the more force is produced. The mass of air molecules they throw per second is (density of air) * (volume thrown per second) = (density of air) * (area of wing) * v.

So F = v * (density of air) * (area of wing) * v. Or v = sqrt(F / ((density of air) * (area of wing))).

For example, suppose a fast dragon is capable of not only hovering, but accelerating upwards with 1 gravity of acceleration, which makes 2 gs of acceleration total. Say the dragon weighs 2000 kg and has a wing area of 100 m^2. The force is 2 * 9.8 m/s^2 * 2000 kg, so v = sqrt(2 * 9.8 m/s^2 * 2000 kg / ((density of air) * (100 m^2))) = 17.5 m/s or around 40 mph.

That's a strong gust of wind, but if the enemy is also able to accelerate at 2 gs, it's not exactly going to knock them out of the air or anything. The wind would also swiftly dissipate the farther you get from the dragon. It could be a tactical consideration sometimes in close quarter air combat, to use a flap of wings to get distance from the enemy or push on them (although striking them directly with a claw or wing might be more effective).

Airplane, helicopter, or jet engine drafts are probably a lot stronger than a dragon's backdraft would be, because a dragon likely has a lot more wing area than the disc swept out by an airplane propeller. The larger the area, the slower the backdraft.

On the other hand, dragons may be more massive relative to their wing area than an airplane. This would increase backdraft speed. Because of their large mass-to-wing-area, in most settings dragons could never fly anyway on aerodynamics alone, so you basically could set their backdraft to be whatever you want, because they're magic.

Answer 3

Geese fly in a 'V' formation. The lead goose has to work harder than the others, who can use their wake. This works for geese because they take turns at going first. Working harder for 10% of the time is more efficient for birds. Aircraft are most efficient when cruising steadily, so they do not travel in 'V' formation.

We don't know what dragons do, or how their energy budgets work. My guess would be that the largest animals would glide and rise on thermals when travelling large distances, and probably not fly in formation.