5 ms·

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 bird

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.
  - cgriswald 5y ago
    All these conversations are lacking a discussion about the atmosphere on Arrakis. We have only hints about the composition and density of the atmosphere. We can assume that the atmosphere isn't toxic and contains quantities of oxygen and carbon dioxide that make breathing both possible and comfortable. We can be sure it doesn't crush humans or explode their lungs. We also don't know the gravity of the planet. It might be 1.2g or 0.85g. So we don't know how much lift is generated per stroke, how much lift is required, or what the speed of sound actually is on the planet.
    - philipswood 5y ago
      Ornithopters seem to be an Imperium-wide vehicle and not a Arrakis-only device which blunts the urgency of these questions and variances. To be used on many different imperium planets seem to imply that it operates across an acceptable range of gravities and pressures, etc.
      - cgriswald 5y ago
        Ornithopter is a type of vehicle. It's unlikely any specific vehicle of the type would be generic enough to operate across the variety of planets that likely exist within the Imperium without modification to the design. This particular branch of the discussion was focusing specifically on the feasibility of the 'dragonfly' ornithopters operating on Arrakis as represented in the new film.
- 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.

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.
- cgriswald 5y ago
  All these conversations are lacking a discussion about the atmosphere on Arrakis. We have only hints about the composition and density of the atmosphere. We can assume that the atmosphere isn't toxic and contains quantities of oxygen and carbon dioxide that make breathing both possible and comfortable. We can be sure it doesn't crush humans or explode their lungs. We also don't know the gravity of the planet. It might be 1.2g or 0.85g. So we don't know how much lift is generated per stroke, how much lift is required, or what the speed of sound actually is on the planet.
  - philipswood 5y ago
    Ornithopters seem to be an Imperium-wide vehicle and not a Arrakis-only device which blunts the urgency of these questions and variances. To be used on many different imperium planets seem to imply that it operates across an acceptable range of gravities and pressures, etc.
    - cgriswald 5y ago
      Ornithopter is a type of vehicle. It's unlikely any specific vehicle of the type would be generic enough to operate across the variety of planets that likely exist within the Imperium without modification to the design. This particular branch of the discussion was focusing specifically on the feasibility of the 'dragonfly' ornithopters operating on Arrakis as represented in the new film.
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.