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Working as a continuation of the concept I mentioned in my previous question, my character is building a flying robot, which has wings which function much like those of a bat. The robot in question weights 150 kg, is 2.7 meters tall, has a wingspan of around 16 meters and a wing loading of around 93.75 kg/m^2.

The main issue here is: the robot is not meant to be only capable of flight, it should also be able to move on the ground, which, when you have 8 meter long wings attached to your back region, can be a tricky matter. To mitigate this issue, I planned to make the rods equivalent in position with a bat's ulna and radius bones each capable of collapsing, shrinking to a size slightly longer than 1/3 of their original length, as hopefully represented below:

enter image description here

enter image description here

Given this scenario, is such telescopic wing actually possible without compromising the wing structure altogether? I planned this wing "Skeleton" to be made out of a titanium alloy and control the compression and elongation of the wing via either hydraulic or pneumatic mechanisms, but before I started to question which would be the best method, I started doubting if it was even possible to begin with.

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  • $\begingroup$ Does this have to be "bat-like"? Bats have that wing shape because they're coming from a peculiar configuration that they've inherited and can't abandon, but a machine can be designed with any shape that can be imagined... or brute-forced via algorithm. A simpler, single beam might telescope, and have the membrane "roll up" as the beam itself retracts. $\endgroup$
    – John O
    Dec 4, 2020 at 14:27
  • $\begingroup$ @JohnO the reason why I chose a wing much like that of a bat is maneuverability. Regarding the ornithopter wing designs provided by evolution (insect, bat, bird and pterosaur styled wings), the bat wing is widely considered as one of the best vertebrate wings concerning maneuverability and energy efficiency in active flapping flight, which is a trait I wished my robot to have (of course, we're not limited in the number of "fingers", although I still think 3 would be the bare minimum to get the desired wing maneuvering). $\endgroup$
    – ProjectApex
    Dec 4, 2020 at 14:44
  • $\begingroup$ Some aircraft designed for use on aircraft carriers have folding wings. If metal birds can do it, so can protein birds. $\endgroup$
    – AlexP
    Dec 4, 2020 at 15:51

2 Answers 2

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I think the main problem you will face is how to keep the leading edge of the wing surface.

Using the telescopic implementation of the "bones", when switching between the "all in" and "all out" configuration you will have to ensure that also the wing membrane accommodates for the movement.

But since the membrane cannot go inside the structure, you might end up having a gap between the bone and the membrane, in the region I marked in blue below.

enter image description here

Such a gap might be detrimental for the wing performance (membranes are sensible to turbulences, you don't want it to flap like a flag in the air stream).

You might solve the issue giving enough tension and proper stiffness to the membrane, but you will need to ensure that the whole things can also withstand being wrinkled in the "all in" position.

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  • $\begingroup$ Do you think that a thick elastic string within that region, similar to the patagial tendon on a bird's wing, would help mitigate this issue? $\endgroup$
    – ProjectApex
    Dec 5, 2020 at 15:22
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This is not an answer, but an animation I made to give an insight as to how the folding process might work:

enter image description here

I'm aware that the telescope didn't fold.

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  • $\begingroup$ Could you please tell me which program you used to make it? $\endgroup$
    – ProjectApex
    Dec 5, 2020 at 11:16
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    $\begingroup$ @ProjectApex Blender. $\endgroup$
    – user80961
    Dec 5, 2020 at 13:06

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