Functional mechanical wings allowing to fly and to go underwater?

Question

In my world, there is a race of small humanoids (average : 1.3m for 40kg) living on cliffs, they have designed mechanical wings that can make them fly or that can fold, and turn around their body acting like propeller to help them move easily underwater.

I wanted to know how would you design these wings (size, attachment to the body, weight, propulsion system, etc.) given that it's better if they are exclusively mechanical (the energy source can be magical)

Thanks in advance for your ideas, feel free to ask if you need any more details about how would the wings work =)

Answer 1

How about a set of wings with winglets on the end to reduce drag. For water use, the wings fold around the operator and create an elongated, streamlined shape, and the winglets from each wing lock together and form a propeller for underwater use. The inside of the leading edge of the wings contain the shafts that drive the propeller.

To transition to water, you just fold the wings back like a pelican diving for fish, or you just glide and land on the surface, then reconfigure for water.

Transitioning back from water to air is more difficult. Somehow, you have to get out of the water and get up to flying speed. How about the root of the wings reconfiguring themselves into a hydrofoil, which also lowers the propeller so it stays in the water while the contraption is skimming along on its foils. Think of an inverted gull wing shape, like a Corsair WWII fighter, except at this point the wings are still connected at the tips, to form the propeller. So more of a diamond shape, yet bent to form hydrofoils. You then go to the surface, reconfigue, and get up to speed on the hydrofoils. This configuration gives you enough lift to get into ground effect, then you can separate the wings at the back, stretch them out, and fly away. Or, if you don't need to fly you can just stay in hydrofoil mode and travel that way.

The big problem will be energy. It takes a lot of energy to fly under power, and to move at high speeds underwater. Moving slowly under water can be done almost for free, by inflating and collapsing bladders that allow you to dive and rise repeatedly, traveling directionally while doing so. So one answer to the energy problem could be that flying time is strictly limited, and all serious distance traveling is done by water with the wings used basically to get to and from the water. Or, if batteries are used, the wings could be covered in solar cells and the creatures travel in hops - landing on the water long enough to recharge batteries just enough to get them to an altitude where they can glide a few miles. Then they land and repeat.

Answer 2

Unfortunately, the wingspan of your small humanoid will be quite large, to pick up the weight of 40kg and allow you to fly (unless you only want him/her to glide).

The heaviest flying bird of current times is the Mute Swan (Cygnus Olor) of 23 kg and it was questioned if it really does 'fly'.

Of course, it is possible to have heavier masses flying - as indicated with extinct species, but wingspans get larger. Pteranodons could get quite heavy but their wingspans were 5.6m.

Then underwater the dynamics of the wings are quite different. I would expect large wings become cumbersome and create a lot of drag. Flying Fish as an example only have small wings/fins as underwater they become a hindrance. To reduce this you would have to tuck them or wrap them tightly to the body.

Propellers underwater are wholly different in terms of fluid dynamics to aerodynamics, the shapes are 'screw like', flatter with larger contact with water, and more circular. Therefore only a portion (perhaps the tip) of your tucked in wing need to detach, driven with a spring or other powered mechanism, to create the right circular screw shape.

Drag is a major factor, so your screw propeller should be behind you to prevent water pushing over your own body. Unfolding your huge wings and taking off again will be a challenge though, as I doubt you could speed up enough from your propeller (look at how ungainly an Albatross tries to take off), you may need to come to shore to take off again.

Answer 3

The first image that came to mind is a sting-ray. Maybe the wings act like a sugar-glider's membrane in the air, and the humanoids are able to manipulate wind with magic, to keep them afloat. Then, in the water, they move by literally flapping their arms?