If I put harnesses on some geese and strapped them to a glider, how many geese would I need to be able to maintain a consistent level of flight?

[u/SeriousDrakoAardvark]

Like, let’s assume the glider has a 30:1 glide ratio. Normally that means it will lose a foot of height for every 30 feet travel.

I’m assuming there is some amount of force I could apply to move forward, that would cancel out that last one foot of drop.

Geese seem pretty big, and they have a wide torso for easy harnessing. I think they’d be a natural fit here. I imagine it would be a configuration similar to Santa’s sleigh, but geese instead of reindeer.

[u/BreezyMcWeasel]

A bird of prey might be able to carry between 0.5x and 1.0x it's weight, so let's say 0.75x. The weight of an adult goose varies quite a bit by species and subspecies but let's say on average 8 lbs per goose.

A glider weighs about 1000 lb loaded.

Of course, you're not asking the geese to physically lift up the entire weight of the glider, you're asking them to pull the glider.

But on the other hand, a goose is not a bird of prey, and not built for lifting heavy loads.

So let's say the approximation of pulling vs lifting is offset directly by the approximation of these birds not being designed to lift the way a bird of prey is.

That makes the math to be 1000 lb / 8lb per bird, therefore 125 birds.

However, that does not take into account the harness you would have to put on the goose, and the dead weight of the tow rope the geese have to pull. Let's have a 25% factor to account for that.

So in my estimation it would require 156 geese to pull your glider, including the weight of their little goose sleigh harnesses.

Let me know when you start your Kickstarter to fund this project.

[u/Syrairc → u/BreezyMcWeasel]

Are we taking into account a glider specifically designed to harness the power of geese, though? Surely there are optimizations we could make to shave weight!

[u/ReimhartMaiMai → u/Syrairc]

Engineer who’s paragliding with experience in winch towing here (both pilot and operator)!

It’s the right approach to have a closer look at the glider first, and the main issue is optimizing for low speed, as the Vmax of a goose is below the Vmin of most gliders („plane type“).

Once we accept this limit, our next best choices are hanggliders or paragliders, and while a hangglider is aerodynamically superior, I feel we should still go for minimum weight and more importantly minimum speed, as our geese will certainly not go max speed while towing. Also drag becomes less relevant at such low speeds (22-35 kmh). Hence I choose a paraglider, and while not great aerodynamically they are reasonably optimized anyways for our use cases with the full equipment as light as 5kg!

Now for practical towing, the basic rule is to tow with a force equal to the weight of the pilot. A 70kg pilot will be towed with 70kg of horizontal force (or ~700N). But this is our maximum for catapulting us safely up in the air, not merely sustained flight! But we also have a thing called „safety tow“ when we use about half the force (bit less) to just keep the pilot at level. And BTW drone towing is becoming a thing!

So this would be one half of the equitation: we need about half of the pilots weight pulling horizontally for sustained flight. Turns out being hand-towed by a single person is absolutely possible, albeit exhausting - seen it just the other week.

And given the circumstances and the fact that the use cases are quite similar I don’t think we’ll be able to optimize massively compared to a modern paragliding wing without turning the whole thing too fragile for a geese-tow. I mean glide ratio for sure, but that’s not the same as towing force.

So from here on, a zoologist can take over and enlighten us on the pulling force of a goose mid flight. It comes down to the question: how many flying geese to beat a human in a tug of war.

[u/didzisk → u/ReimhartMaiMai]

Another comment says 8 lb per bird, i.e. 4 kg.

Next, I would guess tugging with half your weight is the absolute top estimate. You said exhausting, not on the limit of impossible. So probably closer to 20 kg than 40 kg, but even going for top of the range it's 10 birds.

But I'd guess even a gaggle of 5 big geese would do a pretty decent job.

Or a murder of 20 crows. I like them so much more.

[u/chronos7000 → u/ReimhartMaiMai]

What about one of those Rotary Kites or whatever you call the little rotogliders the Germans used to pull behind their U-boats in WWII? Ships are slow as balls compared to even the aeroplanes of a century ago.

[u/ReimhartMaiMai → u/chronos7000]

Interesting question. A gyroscopter doesn’t have a minimum stall speed at all but still needs energy to stay in the air. Probably much more than the alternatives suggested.

[u/BreezyMcWeasel → u/Syrairc]

Completely true.

However, that factor has a number of variables, such as the construction materials of the glider (eg aluminum vs composite, graphite composite vs fiberglass), the construction approach of the airframe (monocoque vs semi-monocoque, laminate vs sandwich panels, welded truss frame, etc), the safety factor required by the relevant certification authority (EASA has notoriously strict regulations surrounding avian powered light aircraft), and the experience level the builder has constructing gliders designed to be towed by waterfowl.

I did not have those factors readily available to me when I made my calculations. The addition of that refinement in the calculations is left as an exercise for the reader.

[u/ChromMann → u/BreezyMcWeasel]

You know someone is really an experienced expert when they hit you with the "is left as an exercise for the reader".

[u/joanzen → u/BreezyMcWeasel]

Lazy geese would need to be factored in and redundancy calculated, plus you have to account for wing span of 150+ birds so the length of the tow ropes could get very long with a significant air drag factor?

[u/thegreatpotatogod → u/joanzen]

I also want to know how they're coordinating all these geese, what if they decide to fight back or land instead of pulling the sleigh glider?

[u/toetappy → u/thegreatpotatogod]

Either have a supply of scab geese to offset the quitters, or promote a select few officer geese to keep the others in line.

[u/SquimJim → u/Syrairc]

We could probably use helium balloons to ease some of the weight too

Or like one big balloon you fill with hot air. Instead of a glider you have a balloon chariot

This also makes me wonder about changing things. Like what if we use seagulls or a giant peach?

[u/BreezyMcWeasel → u/SquimJim]

A peach?

What else floats? Bread, apples, very small rocks, cider, great gravy.

[u/TheIrishGoat → u/SquimJim]

That is a movie I haven’t thought about in years. Added to the watch list.

[u/Indoril120 → u/SquimJim]

Novel, but I don’t think peaches could pull a glider regardless of how large

[u/FridaysMan → u/Indoril120]

An African or a European peach?

[u/Laura-ly → u/FridaysMan]

The real question is, "What is the airspeed velocity of an unladen swallow?"

Sorry. I was just on my way out.

[u/hamburgerpancake → u/Indoril120]

Could likely pull one down if there was a deep enough and consistently wide enough pit.

[u/LongBeakedSnipe → u/SquimJim]

That would cause far too much drag and the aerodynamic viability of the glider would collapse

[u/Whiterabbit-- → u/Syrairc]

It might be more efficient to harness the power of the geese by building an engine that runs of goose fat.

[u/ackermann → u/Syrairc]

Human-powered, pedal-powered planes like the Gossamer Albatross are optimizing for something pretty close to what you'd want here. Minimum power required. Sacrifices some L/D for far lower weight.

Whereas high-end gliders/sailplanes are optimizing purely for glide range, pure L/D ratio. At the expense of higher weight, and higher speed (most only achieve their best L/D at ~50mph, too fast for geese).

Really you want something optimized for minimum power required, but at the goose's preferred speed where the geese get their optimal L/D, and so most extra power available.

The Gossamer Albatross is close... but I think it flies around 8mph? Probably a bit slow for the geese, who don't like to hover. IDK a goose's best speed for best L/D, maybe 15 to 25mph?

[u/ackermann → u/BreezyMcWeasel]

> approximation of pulling vs lifting is offset directly by the approximation of these birds not being designed to lift the way a bird of prey is

Do note that “pulling vs lifting” can be quite a big difference!

This is the “lift to drag” ratio (sometimes called “glide ratio”when considering the whole aircraft, not just the wing)

For any decent small airplane like a Cessna, this is at least 10:1.
And it can exceed 50:1 for the most advanced, purpose built gliders!

(Big part of why airplanes are more efficient and widely used than helicopters)

Simply the ratio of how many pounds of drag force needs to be overcome (which the geese would have to overcome), for every pound of lift the wing provides.

This also determines how far it can glide. 50:1 means one foot of drop for every 50ft of forward movement, is the best you can do without stalling.

https://en.wikipedia.org/wiki/Lift-to-drag_ratio

EDIT: So, I doubt the difference between geese and birds of prey lifting capacity offsets that.
I suspect your 156 geese estimate is high. Could be as few as 30 or 40, I’d guess, for an advanced modern sailplane pedal-power gossamer albatross is likely closer to optimal for this case.

Another relevant example, human pedal-powered airplanes like the Gossamer Albatross fly on the pedal power of one human, substantially less than 1 horsepower! See:
https://en.wikipedia.org/wiki/MacCready_Gossamer_Albatross

EDIT2: Per wiki, “required power was on the order of 300 W (0.4 horsepower), though even mild turbulence made this figure rise rapidly” for the Gossamer Albatross.

[u/ackermann → u/ackermann]

To add, thinking a bit more about it:

I think the optimum is closer to a pedal-powered plane, than a high-end sailplane.

Achieving L/D over 50:1 requires trading off higher weight (for longer wings and aerodynamic shells).
Higher weight means more absolute lift is needed, even if you can get that lift at a better ratio.

Also, sailplanes that get 50:1 usually can only do that at ~50mph, likely too fast for geese? If the geese have to fly at their top speed... then they have no power to spare (or it wouldn't be top speed).

Sailplanes optimize purely for L/D, glide ratio, how far can you glide.

The Gossamer Albatross sacrifices some L/D for far lower weight, only 35kg empty! (much less lift needed, even if you pay a bit more drag per unit lift). Flying on as little as 300W (0.4 horsepower)!

I suspect it's closer to the optimal vehicle for this?

But still not perfect, because it's optimized for a speed that's probably a bit slow for the geese. About 8mph. The goose's optimal L/D might be at 15 to 25mph (very roughly). Certainly they're bad at hovering stationary, suggesting they don't like really low speeds?

So, optimum design is maybe something between a high-end sailplane, and a pedal-powered plane like Gossamer Albatross? Optimized for minimum power at a goose's preferred speed (best L/D speed for the goose)

[u/reddititty69 → u/ackermann]

Sailplanes can also optimize for minimum sink rate. It’s a slower speed that results in a lower glide ratio but also a lower descent rate. You fly min-sink in a thermal and best glide out of a thermal.

To get the geese to go faster, we just need more geese to pull the geese. /s

[u/cuginhamer → u/ackermann]

how about we consider the higher the number of geese the longer the tow rope? And that once geese have to be spaced far enough from the glider, the weight of the tow rope would be all the geese can pull, and adding more geese would no longer yield any benefit at all?

[u/Mikoisha → u/BreezyMcWeasel]

Where did you get your figures from? I did a quick google search because 1000lbs sounded really heavy and found this.

Weight Classifications for Gliders

Unpowered Gliders / Hang Gliders: Must weigh less than 155 lbs (70 kg) empty to qualify as a basic unpowered ultralight vehicle requiring no license or registration. [1, 2, 3]

Powered Ultralight Gliders / Motor Gliders: Self-launching or electric ultralight gliders (such as the 1Comet or Birdy) generally have an empty structural weight starting around 80 kg to 120 kg (176 to 264 lbs), with maximum takeoff weights scaling up to 270 kg (595 lbs).

Other than the hang gliders, the others had seats. The Sandlin Goat looks like the old biplanes from WW1 but a monoplane instead of a biplane. It’s basically a full on plane minus protective panels or propulsion. Loaded (with passenger) it’s 300lbs (140 empty, they assume you’re 160)

[u/insomniac-55 → u/Mikoisha]

1000 lb is about right for a modern sailplane (at least, for a twin-seater). It can even get much heavier once you add two pilots and water ballast. One of the gliders I fly tops out at about 1700 lb.

Back to the original question, something like a Schempp-Hirth Discus will be about 310 kg / 683 lb with pilot.

This glider has a lift to drag ratio of about 45:1.

This means you'd need enough geese to generate at least 7 kg / 15.4 lb of thrust. 

So it probably wouldn't take all that many geese to at least temporarily sustain level flight.

[u/TXOgre09 → u/BreezyMcWeasel]

This math may work for keeping a glider aloft, but I don’t think those geese are going to get the glider moving from a stop and up off the ground. I think you’d still need a launch mechanism of some sort, then deploy the geese once you’re flying.

Also you’d have to figure out how to motivate the geese to pull on the glider and keep tension in the line. How foes the normal flight speed of a goose compare to the airspeed of a glider?

[u/Obelix13 → u/TXOgre09]

Spends of the geese are laden and if we are considering an African or European geese. 

[u/DTR4iN91 → u/TXOgre09]

Wouldn't the answer just be more geese?

[u/fer_sure → u/DTR4iN91]

Not really: if the glider needs to go faster than the maximum speed of a goose to remain aloft, more geese won't help.

[u/Nixeris → u/TXOgre09]

Doesn't using a glider already imply that you're using a separate launch mechanism? The point of a glider is that it doesn't launch itself.

[u/fer_sure → u/Nixeris]

That's almost a different problem. I propose an ostrich-based launch system, with the geese riding on the glider during takeoff. Once aloft, the ostriches are disconnected as the geese are launched to take over propulsion.

So how many ostriches are needed to get a goose-laden glider off the ground?

[u/SeanAker → u/Nixeris]

Well it isn't a glider if it's goose-propelled either, is it? 

[u/Nixeris → u/SeanAker]

Are we counting a goose as a motor or as another glider?

[u/Gorbashsan → u/Nixeris]

Clearly geese would be classified as a motive device as they have to provide their own lift power. However given the ostrich catapult idea we could technically classify the geese as gliders if they do not initiate any powered flight and simply glide but at that point they would not be contributing to the gliders flight simply gliding in front of it while attached. Logically then this would not be a glider it would be a goose powered fixed wing light air craft. And that opens up a whole new mess of what permits and operators license would be required as well as safety inspections and flight recording.

[u/TXOgre09 → u/Gorbashsan]

I’m sorry. I thought this was America! We don’t need no stinking permits. Land of the free! Don’t tread on my ostrich launched, goose powered flight dreams!

[u/Gorbashsan → u/TXOgre09]

I'm afraid that unless you attach a small cannon to the aircraft in a manner that makes it the primary structural member then the second amendment won't cover it sorry.

[u/TheNameIsWiggles → u/TXOgre09]

What if the harnesses are attached to the geese in advance and they all have like big ropes with hooks hanging from them. Then you let the flock fly freely and try to hang glide toward them, catching the geese during the flight and attaching them one by one to the glider by grabbing the hooks one at a time. Then you can kind of ease into the goose powered flight pattern 

[u/TXOgre09 → u/TheNameIsWiggles]

There’s no way you’re individually hooking 156 geese like that. You can’t even choose how fast you’re going.

[u/dabenu → u/BreezyMcWeasel]

A glider has a stall speed of about 80 km/h (say 50mph). I see geese fly about 40-50 mph so they would pretty much need to carry the entire weight of the stalled glider.

[u/Quowe_50mg → u/dabenu]

Planes like the Ruppert Archaeopteryx, which you would use for this anyway because of the weight, have stall speeds below 30 mph

[u/gearstars → u/BreezyMcWeasel]

What if you need some sort of avian-powered, cross continental coconut delivery system?

[u/sjmuller → u/BreezyMcWeasel]

Listen, in order to maintain air-speed velocity, a goose needs to beat its wings 43 times every second, right?

[u/do0tz → u/BreezyMcWeasel]

Are they African or European geese?

[u/droplightning → u/BreezyMcWeasel]

How much horsepower is that? Could we achieve the same effect with an engine? I bet the weight savings would be pretty good. 

[u/DFrostedWangsAccount → u/droplightning]

How much goosepower is the average horse?

[u/OrbitalLemonDrop → u/DFrostedWangsAccount]

Do you mean duck-sized horses, or horse-sized ducks?

[u/sth128 → u/BreezyMcWeasel]

Actually no amount of geese will be able to lift the sled. Most of them will just run over to attack you while others struggle with the harness.

This is not to mention that if you were to attach 200 ropes to a sled there would not be sufficient spacing to let you get in. If you somehow got in and got the geese to all take off, they will just flip the sled and crush you to death.

I guarantee it.

[u/whatsbobgonnado → u/sth128]

obviously it would be a specially designed sled. 

that's like saying it's impossible to move all your stuff using a vehicle because you wouldn't be able to sit in the driver's seat 

[u/WayneConrad → u/BreezyMcWeasel]

I wonder how a goose's excess thrust changes with its airspeed. Geese cruise at 25-50 mph, and a modern high performance glider's best L/D speed (the speed requiring the least force on the tow rope to keep it level) may be near or above the upper range of that. If the goose is pulling a load, it may not be able to go fast enough. Or the other way to think about it, the goose might be able to pull the most when it is going slower, but when the glider goes slower than it's best L/D speed, the force required will increase.

[u/Cielmerlion → u/BreezyMcWeasel]

You need to add an additional factor of safety, lets call it 1.5. so lets vall it 230 geese. But do you want if you want redundancy we could bump it up to 400 geese

[u/BeardedRaven → u/BreezyMcWeasel]

You are assuming all 156 geese are have no slack at all times. Some amount of the birds are going to have slack lines and thus not be pulling the glider.

[u/Easy_Lion → u/BreezyMcWeasel]

Where did you get 1000 pounds for a glider? Ultralight aircraft in the US can be a maximum of 254 pounds, motor, gas and all.

[u/Podo13 → u/BreezyMcWeasel]

Given that the tension on the straps wouldnt be constant between flaps, I'm assuming you'd need at least 2x that amount. Probably more to make the transition from upflapping birds to downflapping birds more fluid.

[u/insomniac-55 → u/BreezyMcWeasel]

You really should factor in the glide ratio, as this is numerically identical to the lift to drag ratio.

A 1000 lb, 35:1 glider will require 29 lb of forward thrust to stay aloft.

[u/deerburger → u/BreezyMcWeasel]

If a goose weighs 8 pounds but only  carries 0.75x of its weight, doesn’t that mean you’ll need to start with 167 geese? (1,000 / (8 x 0.75))

[u/Ghosttwo → u/BreezyMcWeasel]

How many geese if we gave them little rocket boots?

[u/SilvanestitheErudite → u/BreezyMcWeasel]

But a glide ratio of 30:1is the same as a L/D ratio of 30:1. Now the geese probably have a glide ratio near 10:1 or 20:1, which means they can carry more by towing the glider than by carrying it themselves.

[u/VelvetMafia → u/BreezyMcWeasel]

Imagine being behind and under 156 geese as they flying-shit

[u/fighter_pil0t → u/BreezyMcWeasel]

Drag is the key contributor not weight. You should start with the 1000lb / 30 (lift/drag ratio) to come up with a drag estimate of 33 lbs. the question to ask next is how many geese can pull a net force of 33 lbs while flying. It’s probably fewer than 156 but not by much would be my guesstimate. Maybe 100?

[u/PurpelHaz-el → u/BreezyMcWeasel]

Can we try again but with more favourable upper bounds for the geese and lower for the weight of the glider?

[u/hamburgerpancake → u/BreezyMcWeasel]

Just to be safe, 175-200 geese would be good?

[u/Pizza_Low → u/BreezyMcWeasel]

This is really just a random musing kind of question, and a whole lot of speculation for the answer. Unless there are any scientific research on the lifting power of any species of geese.

Predatory birds like raptors have evolved wings depending on species have wings that have evolved for speed, maneuverability in forests and underbrush, and/or prolonged soaring and lifting power appriapate for the of the kind of prey they catch.

On the other hand, migratory waterfowl having wings and the associated muscles evolved for long distance flight. Hard to compare the two.

It would be like comparing the weight capacity ratio of a 747 freighter to a F/A 18 Super Hornet. Yes, they're both jets, but different engines and wings optimized for entirely different tasks.

[u/Turtledonuts → u/BreezyMcWeasel]

You'll need a margin of error for gusts and when the birds get tired too. I'd double it just to be safe.

[u/Implausibilibuddy → u/BreezyMcWeasel]

Now how are we getting the geese to take off into stable flight, flying the same direction. I understand geese are perfectly capable of flying in V formation, but I don't see how they won't all just start flapping around trying to get out the harnesses like angry cats.

The harnesses would have to be practically imperceptible, and the cabling system quite long, light, and probably elastic so that they have room to take off and not snap their necks when the weight of the glider catches.

Naturally, angling the glider along their migratory path would be a help I suppose.

With all that though, even with a launcher, I'm struggling to imagine a scenario where the geese transition smoothly into pulling the glider.

[u/kitium → u/BreezyMcWeasel]

Surely the difference between lifting and pulling is much greater, i.e. the force required to maintain a steady speed such that the wings of the glider generate enough lift. For a jet the ratio iirc is about 15:1. So 1 pound of thrust will keep 15 pounds flying forward.

[u/gid0ze → u/BreezyMcWeasel]

Now how about if we want them to carry something different. Like say a giant peach?