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-fo...
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
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
"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."
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.
Unfortunately, the latter are, confusingly, also called called 'calories', despite one nutritional 'calorie' being 1000x of a 'regular' calorie.
6000 to 12000 calories, not kilocalories, per day, means 1.5 g to 3 g per day of sugar, which is plausible for a humming bird.
And it's more like 100lb of hamburger for a human, not 300lb.
If a 10ft bird flaps its wings less than once an hour a plane sized bird would probably fly for days without flapping its wings
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.
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.
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.
To be used on many different imperium planets seem to imply that it operates across an acceptable range of gravities and pressures, etc.
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.
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.
In our universe given enough power there is probably a way to generate an opposite wave to counter the shockwave.
(Same also applies to having force fields, but the whole “slow blade” vs fast blade thing is enough to at least handwave that away)
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.
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.
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.
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.
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..
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.)