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I just watched the new movie today; it's good. The dragonfly-like wings were an interesting choice. It seems like they'd be less efficient at lift than a join

by elihu 5y ago

I just watched the new movie today; it's good. The dragonfly-like wings were an interesting choice. It seems like they'd be less efficient at lift than a jointed wing, but then I thought, maybe an unusual wing surface material could be used? The problem is that when the wings go up, they're pushing air in the wrong direction and propelling the ornithopter down. But suppose the wing was covered in tiny little hinged flaps that close on a downstroke, but open on an upstroke? That way the upstroke would push the aircraft down much less than the downstroke lifts.. (These wouldn't even need to be controlled in any way, they could just be passive flaps. Though being able to lock them closed might be useful for certain acrobatic maneuvers.)

generalizations 5y ago
You just change the angle of the wing on the upstroke so it's slicing through the air. It's not actually a problem. :) Same thing real dragonflies and even birds do (though birds fold up their wings too).
- elihu 5y ago
  I kind of assumed that's what actual dragonflies do (I mean, they have to get lift somehow), but for a very large wing that rotation must cause quite a bit of drag in itself. In the movie, the ornithopter wings are maybe 50 to 100 feet long and usually moving too fast to see. I would tend to assume that the aerodynamics would be different for something that huge than an insect, but I don't have any good intuition for what would be most efficient. Maybe a combination of wing rotation and self-opening flaps would be best? Or a wing that splits itself into multiple parallel wings on the upstroke and combines into one on the downstroke? It's interesting that dragonfly wings are so long and thin, which I suppose minimizes the amount of drag as they rotate between the downstroke angle and the upstroke angle.
  - sandworm101 5y ago
    >> the aerodynamics would be different for something that huge With such a large moving airfoil there are inefficiencies. Pretending that the wing is a solid object, very quickly the tips will be moving faster than the speed of sound. At such speeds void/shockwaves start to form, radically changing everything. The root of the wing is barely moving, the tips are supersonic, and somewhere along the middle is a transition zone that moves back and forth depending on speed. Good luck designing that airfoil. (This is what makes the TU-95 Bear so loud. Its propeller tips are supersonic while the rest of the aircraft isn't.) There is a Russian saying about helicopters: You can place every problem in all aerodynamics on the tip of a rotor blade.
    - Joeri 5y ago
      In the dune universe they have some kind of antigravity technology, so perhaps this is used to dampen the shockwave at the tips? In our universe given enough power there is probably a way to generate an opposite wave to counter the shockwave.
      - ben_w 5y ago
        But if you have antigravity, why do you need wings? (Same also applies to having force fields, but the whole “slow blade” vs fast blade thing is enough to at least handwave that away)
        simonh 5y ago
        Possibly cost. But also suspensors only seem to give lift, or very small amounts of lateral thrust. All the pure suspensor vehicles we see move extremely slowly. It's possible the 'thopters use suspensors for primary lift, maybe 80% of vehicle weight, and the wings are just for manoeuvring lift and thrust.
        jon-wood 5y ago
        The aversion to using force fields is more about their interaction with laser guns, when shot by one they cause an explosion equivalent to a small nuclear weapon. Not ideal to have wrapping a vehicle you may be flying in formation on an attack run.
    - adrian_b 5y ago
      The problem with the supersonic tips is identical for normal aircraft propellers. For aircraft with fixed wings for generating lift, the propellers can be small, so supersonic speed is reached only at a higher rpm, but for a helicopter there is no difference from this point of view compared with an ornithopter. The blades of a helicopter propeller must also be able to rotate along their longitudinal axis, like those of an ornithopter, but nonetheless they are more efficient than flapping wings, because there is no dead time and no energy lost for the reversing motions, and the fatigue resistance need not be as extreme as it would be required for flapping wings.
  - deleted 5y ago
    [deleted]
  - adrian_b 5y ago
    In real insects there is no problem with the drag for wing rotation, because the rotation is not an active motion, but a passive motion caused by the flow of the air. The insect wings have a rigid front edge, which is moved up and down, while the rest of the wing is flexible. When the front edge goes down, the rear part of the wing is pushed by the air upwards until it assumes a slanted position that pushes the air backwards. The reverse happens on the upwards beat. So in most insects only the rigid front edge of the wing is moved actively while the rest of the wing assumes passively various shapes that are determined by the distribution of rigid veins and flexible membranes in the wing, which ensure that the shape of the wing is the right one for good efficiency.
- simonh 5y ago
  >You just change the angle of the wing on the upstroke In fact we see that the wing joints can do this in the movie. When the wings fold up for deployment, the joint rotates them into orientation.
- ganzuul 5y ago
  The fatigue life seems to be the biggest problem next to power production. Superelastic alloys might survive though. If the intuition is some kind of supersonic reverberation that lets the wings operate in a local low air density then it might not be that hard to find an envelope of lift in that regime.
- Sharlin 5y ago
  However, momentum is a problem. The vibrations, and thus stresses, induced on the body of the thopter must be ludicrous. When the wings go up, the body must go down, and vice versa.
  - adrian_b 5y ago
    Actually this can be an explanation for the fact that in the movie the ornithopters have 8 wings instead of 4, like an insect. On each wing position there are a pair of wings, one above the other. If when one goes up, the other goes down, and vice-versa, that eliminates the vertical oscillation of the body.
    - Sharlin 5y ago
      Good point!
    - elihu 5y ago
      Interesting, I hadn't noticed that the ornithopters in the movie had 8 wings rather than 4.
carabiner 5y ago
Yeah, it's horribly inefficient to do this (flapping wings) at larger sizes. Birds, bats, insects actually evolved to flap less as they get larger: https://www.researchgate.net/figure/Wingbeat-frequency-versus-wing-length-For-comparison-the-slopes-of-two-predicted_fig3_13904663 https://www.researchgate.net/figure/Wingbeat-frequency-versu... A condor with a 10-ft wingspan might not flap for hours - so it glides, just like an airplane: https://www.sciencealert.com/giant-andean-condors-can-fly-for-five-hours-without-flapping-their-wings-even-once https://www.sciencealert.com/giant-andean-condors-can-fly-fo... A hummingbird (4 inch wingspan) flaps at 60 Hz though. It can hover too, just like an insect.
- trhway 5y ago
  >A hummingbird (4 inch wingspan) flaps at 60 Hz though. It can hover too, just like an insect. during hover hummingbird doesn't flap the wings up/down, instead it flaps it in horizontal plane. On each stroke, back and forward, the wing is set at an angle of attack and thus is kind of like propeller during each flapping stroke pushing air down : https://youtu.be/naE7fK-gCPs?t=110 https://youtu.be/naE7fK-gCPs?t=110 Hummingbird weights 3 grams. An APC 4x4 prop at 3000 rpm would generate 4 grams thrust consuming 0.2 Watt. Such energy density would mean 6 KWt for human, ie. 60x our regular power. So no wonder : https://www.lib.niu.edu/2000/oi000811.html https://www.lib.niu.edu/2000/oi000811.html "Hummingbirds are sugar addicts. Their metabolism is so incredibly fast that they need to refuel about every 10 minutes. Each day they consume 50 percent of their body weight just to maintain their normal weight. Hummingbirds burn from 6,600 to 12,000 calories per day. If a man had the metabolism of a hummingbird, he would have to eat almost 300 pounds of hamburger a day to keep from wasting away."
  - straphka 5y ago
    Just so you know, those numbers are way off. If you think about it how would a hummingbird consume that amount of calories in half its bodyweight? See https://www.birdspot.co.uk/bird-brain/how-many-calories-do-hummingbirds-eat-in-a-day https://www.birdspot.co.uk/bird-brain/how-many-calories-do-h... I mean, when extrapolated to human size it's still 125k calories a day, but 6600 for a bird of 3g is just not possible.
fareesh 5y ago
The dragonfly wings were in the video games too I think
- skhr0680 5y ago
  Dune2’s ornithopter has bird-like wings. That game had a really unique aesthetic
ohiovr 5y ago
You might like this post also from today describes a simple science fair like way to demonstrate the effects of hinged flap surfaces. I called it a Venetian valve wing but whatever.. https://news.ycombinator.com/item?id=28950161 https://news.ycombinator.com/item?id=28950161 I thought about it a year ago but put it away due to no interest from my peers. I only brought it up to news.ycombinator recently because of the cut scenes from the new dune movie. You can try the experiment for yourself. It does in fact work. The only immediate benefit I see so far is that trust power does not get sheered at the edges with super sonic helicopter edges. Meaning the flaps, even if they are traveling at a whopping 100 meters per second are moving far less than would cause a super sonic shock wave like helicopter blades. An aircraft built around it would be more maneuverable, and have more lift power than similar sized aircraft. I can almost picture an ornithopter picking up a tank and transporting it to the battle field with the lift these things can develop. I'd animate it but there seems little point. This thing is going to show up soon and neither of us will get credit for the idea. But it does work..

by elihu 5y ago

generalizations 5y ago

You just change the angle of the wing on the upstroke so it's slicing through the air. It's not actually a problem. :) Same thing real dragonflies and even birds do (though birds fold up their wings too).

elihu 5y ago
I kind of assumed that's what actual dragonflies do (I mean, they have to get lift somehow), but for a very large wing that rotation must cause quite a bit of drag in itself. In the movie, the ornithopter wings are maybe 50 to 100 feet long and usually moving too fast to see. I would tend to assume that the aerodynamics would be different for something that huge than an insect, but I don't have any good intuition for what would be most efficient. Maybe a combination of wing rotation and self-opening flaps would be best? Or a wing that splits itself into multiple parallel wings on the upstroke and combines into one on the downstroke? It's interesting that dragonfly wings are so long and thin, which I suppose minimizes the amount of drag as they rotate between the downstroke angle and the upstroke angle.
- sandworm101 5y ago
  >> the aerodynamics would be different for something that huge With such a large moving airfoil there are inefficiencies. Pretending that the wing is a solid object, very quickly the tips will be moving faster than the speed of sound. At such speeds void/shockwaves start to form, radically changing everything. The root of the wing is barely moving, the tips are supersonic, and somewhere along the middle is a transition zone that moves back and forth depending on speed. Good luck designing that airfoil. (This is what makes the TU-95 Bear so loud. Its propeller tips are supersonic while the rest of the aircraft isn't.) There is a Russian saying about helicopters: You can place every problem in all aerodynamics on the tip of a rotor blade.
  - Joeri 5y ago
    In the dune universe they have some kind of antigravity technology, so perhaps this is used to dampen the shockwave at the tips? In our universe given enough power there is probably a way to generate an opposite wave to counter the shockwave.
    - ben_w 5y ago
      But if you have antigravity, why do you need wings? (Same also applies to having force fields, but the whole “slow blade” vs fast blade thing is enough to at least handwave that away)
      - simonh 5y ago
        Possibly cost. But also suspensors only seem to give lift, or very small amounts of lateral thrust. All the pure suspensor vehicles we see move extremely slowly. It's possible the 'thopters use suspensors for primary lift, maybe 80% of vehicle weight, and the wings are just for manoeuvring lift and thrust.
      - jon-wood 5y ago
        The aversion to using force fields is more about their interaction with laser guns, when shot by one they cause an explosion equivalent to a small nuclear weapon. Not ideal to have wrapping a vehicle you may be flying in formation on an attack run.
  - adrian_b 5y ago
    The problem with the supersonic tips is identical for normal aircraft propellers. For aircraft with fixed wings for generating lift, the propellers can be small, so supersonic speed is reached only at a higher rpm, but for a helicopter there is no difference from this point of view compared with an ornithopter. The blades of a helicopter propeller must also be able to rotate along their longitudinal axis, like those of an ornithopter, but nonetheless they are more efficient than flapping wings, because there is no dead time and no energy lost for the reversing motions, and the fatigue resistance need not be as extreme as it would be required for flapping wings.
- deleted 5y ago
  [deleted]
- adrian_b 5y ago
  In real insects there is no problem with the drag for wing rotation, because the rotation is not an active motion, but a passive motion caused by the flow of the air. The insect wings have a rigid front edge, which is moved up and down, while the rest of the wing is flexible. When the front edge goes down, the rear part of the wing is pushed by the air upwards until it assumes a slanted position that pushes the air backwards. The reverse happens on the upwards beat. So in most insects only the rigid front edge of the wing is moved actively while the rest of the wing assumes passively various shapes that are determined by the distribution of rigid veins and flexible membranes in the wing, which ensure that the shape of the wing is the right one for good efficiency.
simonh 5y ago
>You just change the angle of the wing on the upstroke In fact we see that the wing joints can do this in the movie. When the wings fold up for deployment, the joint rotates them into orientation.
ganzuul 5y ago
The fatigue life seems to be the biggest problem next to power production. Superelastic alloys might survive though. If the intuition is some kind of supersonic reverberation that lets the wings operate in a local low air density then it might not be that hard to find an envelope of lift in that regime.
Sharlin 5y ago
However, momentum is a problem. The vibrations, and thus stresses, induced on the body of the thopter must be ludicrous. When the wings go up, the body must go down, and vice versa.
- adrian_b 5y ago
  Actually this can be an explanation for the fact that in the movie the ornithopters have 8 wings instead of 4, like an insect. On each wing position there are a pair of wings, one above the other. If when one goes up, the other goes down, and vice-versa, that eliminates the vertical oscillation of the body.
  - Sharlin 5y ago
    Good point!
  - elihu 5y ago
    Interesting, I hadn't noticed that the ornithopters in the movie had 8 wings rather than 4.

carabiner 5y ago

Yeah, it's horribly inefficient to do this (flapping wings) at larger sizes. Birds, bats, insects actually evolved to flap less as they get larger: https://www.researchgate.net/figure/Wingbeat-frequency-versus-wing-length-For-comparison-the-slopes-of-two-predicted_fig3_13904663 https://www.researchgate.net/figure/Wingbeat-frequency-versu... A condor with a 10-ft wingspan might not flap for hours - so it glides, just like an airplane: https://www.sciencealert.com/giant-andean-condors-can-fly-for-five-hours-without-flapping-their-wings-even-once https://www.sciencealert.com/giant-andean-condors-can-fly-fo... A hummingbird (4 inch wingspan) flaps at 60 Hz though. It can hover too, just like an insect.

trhway 5y ago
>A hummingbird (4 inch wingspan) flaps at 60 Hz though. It can hover too, just like an insect. during hover hummingbird doesn't flap the wings up/down, instead it flaps it in horizontal plane. On each stroke, back and forward, the wing is set at an angle of attack and thus is kind of like propeller during each flapping stroke pushing air down : https://youtu.be/naE7fK-gCPs?t=110 https://youtu.be/naE7fK-gCPs?t=110 Hummingbird weights 3 grams. An APC 4x4 prop at 3000 rpm would generate 4 grams thrust consuming 0.2 Watt. Such energy density would mean 6 KWt for human, ie. 60x our regular power. So no wonder : https://www.lib.niu.edu/2000/oi000811.html https://www.lib.niu.edu/2000/oi000811.html "Hummingbirds are sugar addicts. Their metabolism is so incredibly fast that they need to refuel about every 10 minutes. Each day they consume 50 percent of their body weight just to maintain their normal weight. Hummingbirds burn from 6,600 to 12,000 calories per day. If a man had the metabolism of a hummingbird, he would have to eat almost 300 pounds of hamburger a day to keep from wasting away."
- straphka 5y ago
  Just so you know, those numbers are way off. If you think about it how would a hummingbird consume that amount of calories in half its bodyweight? See https://www.birdspot.co.uk/bird-brain/how-many-calories-do-hummingbirds-eat-in-a-day https://www.birdspot.co.uk/bird-brain/how-many-calories-do-h... I mean, when extrapolated to human size it's still 125k calories a day, but 6600 for a bird of 3g is just not possible.

fareesh 5y ago

The dragonfly wings were in the video games too I think

skhr0680 5y ago
Dune2’s ornithopter has bird-like wings. That game had a really unique aesthetic

ohiovr 5y ago

You might like this post also from today describes a simple science fair like way to demonstrate the effects of hinged flap surfaces. I called it a Venetian valve wing but whatever.. https://news.ycombinator.com/item?id=28950161 https://news.ycombinator.com/item?id=28950161 I thought about it a year ago but put it away due to no interest from my peers. I only brought it up to news.ycombinator recently because of the cut scenes from the new dune movie. You can try the experiment for yourself. It does in fact work. The only immediate benefit I see so far is that trust power does not get sheered at the edges with super sonic helicopter edges. Meaning the flaps, even if they are traveling at a whopping 100 meters per second are moving far less than would cause a super sonic shock wave like helicopter blades. An aircraft built around it would be more maneuverable, and have more lift power than similar sized aircraft. I can almost picture an ornithopter picking up a tank and transporting it to the battle field with the lift these things can develop. I'd animate it but there seems little point. This thing is going to show up soon and neither of us will get credit for the idea. But it does work..