Tethered aircraft lifting power, low gee world

[DaveC426913]

I may have written myself into a corner. I am not looking forward to your answers.

It involves the very core of my story, so I can't be coy with the deets. I know there are way too many factors for proper analysis, just looking for rough ideas.

There are a couple of parts to this, I'll start with just the first problem.

Setting: 22nd century. Ocean world, thick atmo, with point three gees.

Technology: the best of 22nd century materials - very strong, lightweight, sophisticated, intelligent. No electronics of any sort!

Vehicle: A cross between a glider and a (flying) kayak. Big enough to hold two people plus gear for a trip of several days. Let's say the craft masses 100kg (because: 22c materials!), the occupants 60kg and gear another 30kg. That's 280kg - weighing in at 84kg in .3 gee.

Powerplant: A huge critter like a manta ray that swims through the water with both wings and a powerful tail. (A manta with a 7 metre wingspan masses about 3000kg - weighing 900kg in .3 gee - Gonna have to reduce that substantially.) Can get up to 30km/her (15 knots)

Critter swims in the sea, towing the craft through the air on a tether that can be anywhere from 10m to 80m altitude (because: 22c materials!).

The Critter likes to breach - like dolphins and rays do. They can get, I dunno, a few seconds of air time, spanning maybe 16 - 20 metres at 15 knots.

If the craft increases its alt without letting out any tether, that will pull the craft up and forward until it's almost on top of the critter (i.e. tether is nearly vertical). The critter will have to angle downward somewhat to counteract the lift.

Here's the tricky bit:

The critter powers up to full speed and breaches. The craft must have enough lift to sustain the weight of the critter (flapping uselessly) in the air under it.

Is it plausible, with deft handling of the controls in maintaining a descending glide, to have the critter be carried significantly farther than the un-assisted 16 metres? Or would the critter just drag the craft straight down?

I'm looking for ways to plausibly extend the breaching distance, but there are other factors that limit the size/weight of the craft and its lifting power - as well as the critter - which I will go into momentarily.

 

[Lnewqban]

The critter is the thrust of the aircraft, which is not supporting its weight.
Lift equals the weight of aircraft and load at the speed of that thrust.
Lift is 840 N.
Suddenly, wings must lift additional 9000 N.
Aircraft goes down while critter gets back to swim, then, it reovers and resumes normal flight supporting 840 N.

 

[snorkack]

The critter is the thrust of the aircraft, which is not supporting its weight.
Lift equals the weight of aircraft and load at the speed of that thrust.
Lift is 840 N.
Suddenly, wings must lift additional 9000 N.

In principle, the aircraft can get the extra lift by increasing angle of attack. After all, the lift at the previous condition can be made arbitrarily small - or zero, or negative - by adopting a smaller or zero or negative angle of attack.
You are specifying gravity, and "dense atmosphere", but not specific density.
Note that several diving birds use wings in both water and air. Inefficiently, because of different densities.
7 m wingspn. What is the aspect ratio?

 

[DaveC426913]

You are specifying gravity, and "dense atmosphere", but not specific density.

Whatever it needs to be. Deliberately left vague in the story.

7 m wingspn. What is the aspect ratio?

Whatever it needs to be.

Look at the problem the other way around. It's working (in the story), so what would these various factors have to be for it to be working?

BTW, the 7m wingspan is simply that of an Earth Manta, which I used for comparison.
The critter can have any dimensions necessary to get the story to work.

If there were no other limiting factors, the smaller the better, because then its mass will also decrease, and all my problems go away.

But the lower limit on the critter's mass is set by whatever it plausibly needs to be to tow a glider a long distance without tiring appreciably.

It has huge breathing apparati, like a twin-engine jet plane, but gulping water, so maybe a smaller critter is sufficient to pull the glider.

 

[BillTre]

Here's some possibly relevant biology:

Manta rays are rather solid and heavy. Their "wings" (pectoral fins) are thick, strong, and meaty. Being water animals this is not much of a drawback since their size can make them close to neutrally buoyant while still having a lot of muscle for moving them selves.

The flying fish I have seem in the Gulf of Mexico are more slender in build. Their wings (pectoral fins) are delicate:

more like a an insect's wings.
On the other hand, they can drag their tail in the water and sweep it back and forth and do a powered skim of the water for hundreds of yards. Really impressive to see.

 

[ChemAir]

Not sure I wouldn't just make the results match what you want and use a little creative license to explain the unique reason why the critters in question can break this rule. I might let them "flap their unique internal spacetime vessel/organ" while in the air to change the distance traveled...Or use the old "nobody knows how or why these creatures can do what they do... They seem to have an internal tie to (insert odd physics phenomena here, incorrectly cited or described) whatever suits the story.

Most stories when they get into a corner like this use the proverbial applied phlebotinum or handwavium. If the story is good, I tend to overlook this. If you spend enough time to make all the math work, the audience will gradually be pared down to goofy people like me, and, based on book reviews, I am in a very distinct minority.

they can drag their tail in the water and sweep it back and forth and do a powered skim of the water for hundreds of yards. Really impressive to see.

Fishing in the Gulf (of Mexico) has given me a great appreciation for flying fish. They are very impressive. I've been hit by flying fish evading predators in my efforts to fish for the predators (usally tuna, sharks, or billfish). You can actually catch them at night in a net at a light, and they are remarkable bait for tuna. It does take some stones to be 80 miles offshore in the dark, attempting to net flying fish while you drift around an exploration rig in a basically tiny boat...

Some of the neatest boat riding/driving I've done was at moderate speed in fairly rolly seas. When you are moving fast, the flying fish will clear the bow and fly by the boat for a nice distance, mostly dragging their tails in the water to keep speed.

 

[DaveC426913]

Not sure I wouldn't just make the results match what you want and use a little creative license to explain the unique reason why the critters in question can break this rule. I might let them "flap their unique internal spacetime vessel/organ" while in the air to change the distance traveled...Or use the old "nobody knows how or why these creatures can do what they do... They seem to have an internal tie to (insert odd physics phenomena here, incorrectly cited or described) whatever suits the story.

That would take the sci-fi to a whole new level, which would diminish the sci-fi already in-place.

A subplot of the story revolves around the likelihood that these critters and all their cousins evolved from the same amino acid building blocks as Earth life.

Most stories when they get into a corner like this use the proverbial applied phlebotinum or handwavium. If the story is good, I tend to overlook this. If you spend enough time to make all the math work, the audience will gradually be pared down to goofy people like me, and, based on book reviews, I am in a very distinct minority.

The actual physics won't be in the story, no more than is necessary so that readers don't go "How is a 100kg glider supposed to lift a 1000-3000kg dead weight?"

Fishing in the Gulf (of Mexico) has given me a great appreciation for flying fish. They are very impressive. I've been hit by flying fish evading predators in my efforts to fish for the predators (usally tuna, sharks, or billfish). You can actually catch them at night in a net at a light, and they are remarkable bait for tuna. It does take some stones to be 80 miles offshore in the dark, attempting to net flying fish while you drift around an exploration rig in a basically tiny boat...

Some of the neatest boat riding/driving I've done was at moderate speed in fairly rolly seas. When you are moving fast, the flying fish will clear the bow and fly by the boat for a nice distance, mostly dragging their tails in the water to keep speed.

Yeah, this has given me some ideas. Maybe my critter is too bulky. I have modeled it on a manta which, as pointed out, is a very bulky critter.

Maybe a combination of making it significantly more svelte and giving it lung power and stamina.

 

[some bloke]

Why not model it as a manta-type creature with fold-out fins for gliding short distances, like a flying fish?

Alternatively, if the manta doesn't have to clear any particular obstacle, they could keep their tail in the water to power them on?

Also alternatively, why not have a deployable kite-like sail on the glider which would generate the lift temporarily? If it's a dramatic feature of the plot, it could be a safety device (like a parachute) and the weather could be very windy - with dense atmosphere and 22nd century strong materials, it would be feasible to drag a large animal into the air for a short while - people get picked up by kites in our atmosphere!

 

[BillTre]

Sadly, actual manta rays don't really have much of a tail and its not muscled for propulsion.
Sting rays use it for defense, by flicking around the stinger in their tail.

However, fictional world, modifications should be OK.

Manta rays are like cows of the ocean. They filter feed plankton (like a whale shark or baleen whales).
Large size prevents a lot of predation. Not sure how that works with the smaller young.
The flying fish are smaller fish with larger fish predators (thus their escape behavior mentioned by @ChemAir). They eat smaller fish and probably zooplankton (larger plankton that eat smaller plankton).
A good reason for a behavior to evolve, provides a more plausible story, in my view.

 

[member 656954]

I'm with @ChemAir, here, @DaveC426913.

Peter F. Hamilton and Iain M. Banks are two examples of many successful sci-fi authors who use tons of not even handwavium, but ignoritentirelyium. If the story is engaging and the characters are compelling, you can't write yourself into a corner because only a tiny fraction of readers will care enough - and be knowledgeable enough - to even question your description of the elephant ray dragging a passenger kite across the immense distances of Waterworld. They'll be more engrossed with the visceral reaction of the newbie who is trying hard not to throw up as the kite dips and flips, while being laughed at by the old-timer who could have trimmed it for level flight, but enjoys seeing if people puke more than providing a comfortable ride!

And if you're concerned about it not being 'real', consider Dune. How likely are giant sandworms, really? They 'swim' through the sand and eat spice for the plankton (don't ask what the plankton eat ), but as soon as you start drilling into that, the ecological house of cards collapses. People don't care though, because the story is so awesome!

 

[DaveC426913]

OK, but just couple of caveats:

If the story is engaging and the characters are compelling, you can't write yourself into a corner because only a tiny fraction of readers will care enough - and be knowledgeable enough - to even question your description of the elephant ray dragging a passenger kite across the immense distances of Waterworld.

It's a kind of nit-picky story - like The Martian. A lot of the story is about the sailing and the boat and husbandry of the critter.

And if you're concerned about it not being 'real', consider Dune. How likely are giant sandworms, really?

Yeah, but the laws of physics are pretty unforgiving here. It's not too hard to draw a maximum on the dead weight that could be lifted by the craft. And this story is set way closer to Earth sensibilities than Dune. Basically Earth, but a century in the future.

I'll thin the critter down and figure out how it can have such a high endurance.

 

[jim mcnamara]

Just a question. How can you have a dense atmosphere with gravity at "point three gees"? I am assuming dense=>760mm Hg. Clearly I am missing something.

 

[DaveC426913]

Just a question. How can you have a dense atmosphere with gravity at "point three gees"? I am assuming dense=>760mm Hg. Clearly I am missing something.

That's one of the things I can hand wave.

 

[member 656954]

I'll thin the critter down and figure out how it can have such a high endurance.

Maybe some previous civilization generically engineered this? That's acceptable handwavium for most stories.

It's a kind of nit-picky story - like The Martian. A lot of the story is about the sailing and the boat and husbandry of the critter.

Ah, that makes it harder. Though, with The Martian there is a real planet with lots of data for people to compare to. You get to manipulate your world, somewhat at least, but if you are waving the atmospheric density away, it seems an arbitrary line so I'd still focus on the characters and the story and let the physics slip on by.

 

[stefan r]

There are kite sail kits that can be attached to boats currently in existence. Skysails. The kite and harness can be used to pull the fish. Some sort of filter feeder animal would benefit tremendously. Anytime they are traveling down wind or perpendicular the fish can relax while packing on fat.

Energy can be stored up by manipulating wind or waves. Perhaps have your fish swim down a wave while pulling tension. Lock in the tension. Then wind up slack while the fish is swimming up a wave.

The glider can have a ridged aerodynamic wing. Bending the wings like a bow or crossbow might slightly reduce the optimal flight performance. But it probably does not matter much over a short distance. The fuselage may also have the ability to hold tension by either bending or crunching like a spring. Some types of tether cable stretch like a rubberband, perhaps use spider silk. You need 9000 N to achieve suspension of the fish but perhaps the wing/bow can ratchet up to 90,000N. Various medival devices like bows, torsion catapults, balista.

Using 2 kites would open up some options. The lead glider can be across the obstacle and at higher altitude. The cable runs through the pulley and connects the trailing glider and the fish. All three can be moving forward at max. The trailing glider pulls up vertical as if to do a loop/stall. It is effectively a parachute. The lead glider still has full forward momentum so the cable moves through the pulley lifting on the fish. We can get leverage by using compound pulley systems. Since the front glider is ahead of the obstacle the fish is hanging on a pendulum.

Using 2 fish might allow creative jumps. Again use a pulley. Suspend a gear box. When one fish is jumping the other fish is pulling both the glider and the jumping fish. The glider will lose altitude rapidly. The gears take up extra cable leading to the glider. The second fish is still swimming and pulling cable which gives the jumper lift. Once the fist jumper clears the obstacle the glider builds up altitude and the fish switch roles so the second one also clears the obstacle.

 

[DaveC426913]

There are kite sail kits that can be attached to boats currently in existence. Skysails. The kite and harness can be used to pull the fish. Some sort of filter feeder animal would benefit tremendously. Anytime they are traveling down wind or perpendicular the fish can relax while packing on fat.

Energy can be stored up by manipulating wind or waves. Perhaps have your fish swim down a wave while pulling tension. Lock in the tension. Then wind up slack while the fish is swimming up a wave.

The glider can have a ridged aerodynamic wing. Bending the wings like a bow or crossbow might slightly reduce the optimal flight performance. But it probably does not matter much over a short distance. The fuselage may also have the ability to hold tension by either bending or crunching like a spring. Some types of tether cable stretch like a rubberband, perhaps use spider silk. You need 9000 N to achieve suspension of the fish but perhaps the wing/bow can ratchet up to 90,000N. Various medival devices like bows, torsion catapults, balista.

Using 2 kites would open up some options. The lead glider can be across the obstacle and at higher altitude. The cable runs through the pulley and connects the trailing glider and the fish. All three can be moving forward at max. The trailing glider pulls up vertical as if to do a loop/stall. It is effectively a parachute. The lead glider still has full forward momentum so the cable moves through the pulley lifting on the fish. We can get leverage by using compound pulley systems. Since the front glider is ahead of the obstacle the fish is hanging on a pendulum.

Using 2 fish might allow creative jumps. Again use a pulley. Suspend a gear box. When one fish is jumping the other fish is pulling both the glider and the jumping fish. The glider will lose altitude rapidly. The gears take up extra cable leading to the glider. The second fish is still swimming and pulling cable which gives the jumper lift. Once the fist jumper clears the obstacle the glider builds up altitude and the fish switch roles so the second one also clears the obstacle.

These are some amazing ideas, thank you!

Especially the idea of reversing the effort when going downwind to have the craft pull the critter.
(Wind direction and variable points of sail have not been addressed in the story. This is a great way to do so.)

 

[snorkack]

A thick-billed murre weighs 700...1500 g. Its wingspan is 64...81 cm, and it is the heaviest auk who can fly as well as the heaviest surviving auk.
Note that thick-billed murre is a notably poor flier. Its wings are short for its weight, suited for diving and poorly suited for flight. But not completely unfit. The murre must spend a lot of energy to flap the small wings rapidly.
Garefowl weighs about 5 kg. Its wings are shorter than that of a murre - the garefowl cannot fly at all.
Little blue penguin weighs about 1,5 kg. Like garefowl, cannot fly at all. And no heavier than the murre - but the penguin´ s wings are better for swimming.
Nor is garefowl heavier than a swan, who does fly.

When you have a critter with one pair of flippers suited for swimming, not flying, it may already have the propulsive power to fly - just not the lifting surface. Which you are adding.

 

[Nik_2213]

If you have a dense atmosphere, it lends itself to ballooning. Hot-atmosphere balloon needs a power source, if only solar. Hydrogen is not recommended, you'll only get a few percent into mix before it becomes too flammable. Given the hinted geology, Helium would have to be shipped in. But, what is the atmospheric composition ? If includes a sufficient proportion of eg neon to allow easy distillation, that would help. Probably easiest is ammonia, which may be conveniently liquefied for storage.

So, an aerostat shaped to a flying wing with lifting bags filled with ammonia gas ??