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Electrified wingsuit from BMW reaches 186MPH on first flight (robbreport.com)
346 points by pseudolus 13 days ago | hide | past | favorite | 191 comments

Lithium-based batteries (and associated tech) are to the 21st century what the internal combustion engine was to the 20th century and what the steam engine was to the 19th century.

There’s a ~90% chance you’re using a device powered by a lithium chemistry battery to read this right now (laptop or tablet or phone). The smartphone alone (enabled by lithium based batteries) has transformed the world. Lithium-based batteries have impacted public health & healthcare (e-cigs vs conventional, medical devices like insulin pump, etc), micromobility (e-scooters, e-bikes, electric wheelchairs, etc), countless accessories (smart watches, smart speakers, wireless earbuds), grid storage, electric cars, electric buses, electric trucks, electric ferries, electric rocket pumps (RocketLab), satellites, submarines, civil drones (like Zipline), and a whole bunch of things that have not yet been invented and perhaps require improved chemistry like lithium metal anode or lithium sulfur or eventually lithium-air (enabling long-haul electric flight, even supersonic flight).

For things like this article described, it will enable more expansion of form factors and reduce costs. Jet suits have been done before but equivalently-specked electric motors are much cheaper than the small, micro turbines used for projects like this. And micro turbines have such atrocious efficiency (about 4.4% for hobby turbine engines... meaning their fuel supply only has a useful specific energy of about 1.9MJ/kg or 525Wh/kg, compared to 0.5 MJ/kg for high-C-rate LiPo, 1MJ/kg for really good production Li-ion and 2MJ/kg for low C rate lithium metal anode cells and lithium sulfur) that after another few decades of battery chemistry improvement, electric microturbines not only will have punchier power but also longer duration.

There’s a ton of undeveloped opportunities out there that will be enabled by the efficiency, convenience, low-cost, high reliability, and oxygen-independence of lithium chemistry batteries.

Allow me my cynicism (this is HN after all): the rise of electric R/C planes and "foamies" has been a fascinating change in the model-airplane hobby but at the same time it has shown that you can practically put an electric motor + lithium cell on anything and it will "fly". So much so that I feel like the art/science of aerodynamics in modeling has fallen by the wayside.

Your run of the mill quadcopter is an ideal example of just throwing together motors + batteries + tech and getting a flying machine out of it. It feels inelegant to me because if any of those systems fails, the entire vehicle drops like the non-fliyng-thing that it is. Even helicopters auto-gyro for a period of time after engine failure and can firefly "fly" to a quick landing.

If there is a continuum running from "flying machine" (like a glider) to "rock", the "wing suit" seems laughably close to the rock end of the spectrum. Throwing electric motors at it.... </rant>

To expose my hypocrisy, I'm a huge fan of the lifting body program out of Dryden Flight Research Center (now Armstrong Flight Research Center) of the 1960's.

> Your run of the mill quadcopter is an ideal example of just throwing together motors + batteries + tech and getting a flying machine out of it.

There's the old saw that airplanes fly using lift, but helicopters fly by beating the air into submission.

Helicopters fly by trying to tear themselves apart, and mostly failing at this.

> the art/science of aerodynamics in modeling has fallen by the wayside.

You are not wrong. That is a valid lament.

But, this is the definition (or at least a very common result) of innovation/progress.

Tech/automation advances to the point that non-artists, non-experts can do a thing competently or even expertly. Photography use to require expensive equipment, skill, and knowledge. Modern advances in digital sensors/lenses/flashes/post-processing makes everyone able to take professional quality photos. There is, of course still masters and talented artists that surpass. But the floor for everyone has been brought up to expert level at least.

Same for film/video, driving, complex maths, and many more.

> Modern advances in digital sensors/lenses/flashes/post-processing makes everyone able to take professional quality photos.

For newspapers, maybe, but the tiny optics on phones rule out a lot of photographic techniques, to say nothing of sensor quality when trying to pull 20+ MP out of a sensor the size of a tab of acid

My iPhone 11 Pro still takes crap pictures compared to my FX (or even DX) camera body, and that's with all of Apple's idiot-proofing AI bullshit

Of course, otherwise those fancy cameras would have no market and disappear. Just like film is pretty much completely gone now, as are glass plate cameras. The truly inferior tech disappears and what's left fits some extreme niche where it surpasses the cheap consumer stuff in some way. There are things you can do with a PC that you can't with a smartphone too.

That's incredibly optimistic of you to call the PC dead. I really, really, hope (and am pretty sure) that you are wrong

I think the death of the PC won’t happen until phones and similar have the same power user capabilities as one. As long as we need a PC to build things for our phones, they’ll exist in some form.

The PC for everyday regular usage though is indeed dying. My girlfriend has an iPad Air with the keyboard case from Apple and it’s her primary computing device!

Not death of the PC! Just the presence of more numerous and cheaper smartphones. They're superior to PCs for most people but not for everyone.

It's a matter of scaling laws. You don't see insects or hummingbirds gliding anywhere, small things fly differently.

Butterflies do glide sometimes.

Dragonflies, too. But it's true that they can only do so for short distances. I don't think I've seen either glide for longer than a meter.


And dangerously. There is no redundancy.

For insects, hummingbirds, and quadcopters of similar size, there’s no danger in dropping from the sky.

J.S. Haldane in “on being the right size”:

“You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object. Divide an animal’s length, breadth, and height each by ten; its weight is reduced to a thousandth, but its surface only a hundredth. So the resistance to falling in the case of the small animal is relatively ten times greater than the driving force.

An insect, therefore, is not afraid of gravity; it can fall without danger, and can cling to the ceiling with remarkably little trouble.”

(These wing suits are man-sized, so they would break their wearer on impact)

> A rat is killed, a man is broken, a horse splashes.

I had thought that cats could fall from any height safely, but that's not quite true: observational studies suggest [0] they have a 50% or 90% survival rate from terminal-velocity height onto hard surfaces, but not without injury.

Still, I'd expect a rat could also "walk away". It's quite a lot smaller than a cat, though it may lack other evolutionary adaptations for falling. And a rat is a mouse, taxonomically: we just informally call the bigger species of mice rats.

[0] http://www.todayifoundout.com/index.php/2010/11/domestic-cat...

The dual taxonomy of so many animals is interesting. The line between a pigeon and a dove seems to be one of judgment, like with rats and mice. Or the slightly more distant mantis and roach.

Rats lack the long legs of cats that allow them to cushion their fall, though. Cats have a ton of adaptations that each help with some aspect of landing from a fall.

a huge portion of that is that humans have a much worse weight to surface area ratio, cats hit at about 60mph and humans at 120 mph. very few humans survive falls in which they reached terminal velocity.

I don't understand the lasting appeal of quadcopters in particular. We can build remote-controlled 'normal' helicopters that have fantastic performance and much greater efficiency (no need for 4x the motors and stubby blades).

The only downside I understand is that R/C helicopters are very difficult to fly, but that should be straightforward to overcome by putting a basic computer + sensors between the controller and the servos - the user could control the helicopter as if it were a quadcopter, and the electronics transforms those inputs with its sensors/gyros to control the helicopter appropriately.

This would seem to save costs due to fewer parts, lower weight, better battery efficiency, etc, but no-one seems to do it. I must be missing something?

Quadcopters are enormously more robust. With an RC helicopter any hard landing probably means replacing hundreds of dollars of finicky bearings and swash plates. Racing drones on the other hand smash into stuff all the time and keep going.

I think a large part is that they’re inherently safer with four smaller propellers rather than one big one. So suddenly applications where you’d need a helicopter are accessible to people with less training and skill. Particularly with the robust flying assists and mechanical simplicity.

Then they also turn out to be a readily accessible tinkering hobby very suited to flying around in areas people have nearby. The whole FPV and racing scenes bought in a demographic shift compared with helicopters and fixed wing. Quads are also fantastically agile so quite a different experience to anything else.

Most quad copter blades won’t go through your skull:


Proper helicopters also require a complicated control linkage on the main rotor and a separate tail rotor. Quad copters (and other multi-blade devices) only need to modulate power to the rotors for control.

I would never ride a quad copter, but they’re better for unmanned use.

I think you are probably correct about creating an easier to fly helicopter using a intermediate processor. I also think the argument of longer flight times due to less power draw may be true also.

But cheaper and fewer parts I'm not so sure, part of the reason drones are so popular is the low parts count and part price.

Most low price hobby copters use 3 motors, driving two opposing rotor blades for stability and a tail blade for steering. There are also several gears and bearings to support their functions. Far easier to strap 4 motors with props to a cross and drive them using a solid state SBC integrated with RF,6 axis gyro and 4 power transistors.

Many of these new hobby drones use all the same parts across several different manufacturers so there is an economy of scale to considet too.

Having 4 weaker motors is generally safer than one big one if something were to hit it, and you can shorten the blades because the lift is spread across 4x as many blades.

Multiple motors is good as well for any motor failures, as quads (if they're well designed) can fly after even multiple motor failures.

With a helicopter, even if you lose the motor (lift) you still have control by adjusting the pitch, angle and ratio of the blades.

A quadcopter depends on the motors for any control. While it is possible to regain control after a single motor failure on a quadcopter, it's extremely difficult and not something a human pilot could do, so you'd be relying on software. Also, if you don't detect the failure instantly, the craft will flip over before the software can react because of the inherent instability.

Any solution where you have some kind of passive lift and inherent stability (eg. parachute, wing, etc.) is always going to be much safer.

Would a proper parachute on a quadcopter be fine in case of motor failure / etc. be okay, then?

Multirotor designs are not limited to 4 motors. You can add more for redundancy. Four is common because it’s the smallest number that has good control characteristics.

Mind explaining that one? To me it seems they have an unnecessary degree of freedom: the "diagonal" one.

What issues do you get with three motors in an equilateral triangle?

EDIT: I managed to find it, with even number of motors you can prevent unwanted yawing, by letting half spin clockwise and other half spin counterclockwise.

Yep. More generally, you can induce the yaw rate you want (up to a limit) in either direction, including zero.

I’m not an expert but IIRC with three rotors you need to be able to control a bit of roll of just one of them to have stable flight control.

As they say "If you're in a helicopter and the fan goes off, you'll start sweating" :)

If you lose power on a quad they become unstable, if you lose power on a heli you can pitch the blades slightly downwards which keeps rotation in them and level out close to the ground landing perfectly smooth. IIRC this is something you practice to get your license. Can be done with both RC helicopters and real ones.

But brushless electric motors are so much more reliable than combustion engines (internal or turbine), the comparison is not even funny. They are basically solid state devices. "Losing power" is simply not much of an error state outside of complete battery failure. And if you still want to be safe from motor failures (or from propeller failures), octocopters exist. I share the "multicopters are boring" attitude, but they are boring for a reason.

Absolutely, as long as they're operating within parameters there's no failing them. I've been running brushless systems in RC cars for the last 7 odd years. The only motor failures has been when It's been subject to extreme abuse, as in the rotor reaching 100+° (internally), going from ~55-60K RPM to 0 in fraction of a second or the rotor being forced through the bearings.

For unmanned flight i do agree on multicopters being the best option. See this[1] video for an example of a multicopter flying with disabled props.

However, as you see this flightmode isn't appropriate for human beings, humans should keep flying helis for now. The swash plate design even though more complex than a prop mounted on a shaft is still a rather simple design, litterally a bearing mounted on a 2 axis system and rods attached to rotate the blades. Multicopters with swash plates are interesting too as they can be simplified not to tilt the plate but only offset it up and down to alter pitch the same way all around the rotation. If. This exerts less force on the bearing, but considering there's still 4 of them rather than one might increse failure rate. With swash plates on multicopters we could have two motors driving one system that drives the props, and do many amazing things with computer aided controls in case of failure.

Idk why i keep on going, TL;DR: Being able to control pitch is key, multirotor or not.

I'm not really with Elon Musk on alot of things, but personal human flight is one thing where i agree with him, It's not going to happen.

[1]: https://www.youtube.com/watch?v=w2itwFJCgFQ

Well, simple propeller pitch control is a lot easier than a swash plate because it's idle when the pitch is kept the same and it's no problem if making it slower simplifies it. A swash plate is active on each rotation and needs to be fast enough to work the blade through a certain range of pitch values within have a rotation interval.

I don't think a quadcopter is controllable with 3 engines.

However, a drone designed to carry pax can be designed with redundancy - the Volocopter, for example, has 18 rotors and engines, and can withstand at least 3 failing.

Mechanical simplicity in not having rotating blades I think is a big part of it. Its a lot easier to just use more motors and a 3d printer for the body then design the complex blade control system for a helicopter.

Fantastic performance as in? Quadcopters routinely reach 60km/h, and cheap racing models can go over 100km/h. I doubt any kind of heli will ever perform like that

One could argue that the increase in hardware performance of computers has led to the art of software design falling by the wayside. Horribly inefficient software runs because the hardware performance hides the truth under the hood.

That in theory gives a programmer who does care about performance an edge: they can leverage the amazing performance of modern day chips in a way that the average product doesn’t, and it should mean a business advantage...

In practice it seems more complex than that — but I have experienced a softer version of that idea in practice with my own work. Performance does matter, but it isn’t the only factor.

Unfortunately, you lose that advantage because in days of yore, people knew the implementation details of their hardware, and would optimize around that. With microcode. and the sheer size of certain instruction sets, it is very difficult to do the same thing, particularly mow that the philosophy of programming/computing has shifted to accomodate the industry as an omnipresent actor in your execution environment, and furthermore one with even more rights to observable machine state than you, the owner of the damn thing.

Your point on inefficient code stands, but there is far more at play than mere "programmers aren't skilled enough" and "imagine the possibilities!"

I'll wager a true Mel would not be an easy thing to reoccur nowadays.


Wingsuits are much closer to gliders than rocks aerodynamically. They can generate lift and fly upwards for a short time. Ram air wingsuits have only been around for less than 25 years but have developed dramatically during that time, even without power. They are amazing gliding craft.

Quadcopters also usually have terribly autonomy. Gliding is a lot more efficient at conserving energy so there's still a lot good engineering to be had in aerodynamics whenever you need to be in the air for more than a handful of minutes at a time.

That's why if you look at professional drones you generally only see quadcopters when being able to hover and/or execute very precise motions is required, for the rest wings are still generally superior.

It seems to me like there's a good future for electric VTOL. Whether for package delivery or for carrying people, you can take off vertically, and then transition to a horizontal flight regime using wings that's more energy efficient, so you can get more range.

This feels like the golden path to me, too. Lilium is claiming 300km range at 300km/hour, and appears to transition nicely to horizontal flight. Maybe not a great glide ratio on those stubby little wings, but it looks safer than quadcopters. They don't need all 36 ducted fans for normal flight, so eating a bird shouldn't spell death.

Has anybody else shown off similar craft? Uber Air's eVTOL looks about 50% CGI/50% hype, but maybe I've missed something.

My layman's aerodynamic hunch says that Lilium is on the right design track for practical, reliable, long-range electric VTOL aircraft.

There's two critical ingredients: Transitioning out of powered lift immediately after takeoff, and having a battery mass fraction that's as high as possible. Obviously, VTOL & payload limits the latter.

Multicopter designs won't work; their power requirements are too high.

That's what they're hoping for at Joby Aviation: https://www.jobyaviation.com/

I fly FPV drones and can confirm the propellers and motor technology has come quite far. Not to mention the leaps and bounds of flight controllers in the last few years. There seems to increasingly few things that can go wrong with my drone. Bent prop/motor shaft; no problem. Missing parts of propellers; you can still fly home. Its aerodynamics, materials and software... and most of those things are off the shelf, just an afterthought for the drone builder and pilot. Its cool to be able to shift focus to flying but agree heavily its a different craft now.

This reminds me of various videos I've seen where people strap the guts of a quadcopter to various lightweight things to make them fly (the most recent being the Corridor Crew video on making a flying Nerf gun), and they just...work. (With much shorter battery life.) Of course, that's almost entirely thanks to the control electronics - that sort of active stabilization enables almost anything to fly. You couldn't do the same thing with a passively-stable R/C airplane, for example (speaking from experience).

What is the difference between what you are describing and a helicopter? Obviously comparing quad drones to fixed wing aircraft is going to make it seem that the quad drones thrown out 100 years of innovation and theory, but they are very different things.

If you are so inclined to answer, I’d live to know why lithium batteries and not some other form of battery? That is, do other elements not have the right properties? Are they too rare? Are they dangerous? You sort of answer a bit in your last paragraph.

Why did it take until now to get to lithium batteries? Why way NiCad the thing before? Will lithium continue to dominate, or are there other competitive solutions just one breakthrough away? What about hydrogen cells?

The periodic table is limited. Of all metals, lithium is the lightest. It also has the highest mass-specific conductivity and the highest chemical specific energy of all the metals.

Hydrogen is not a solid or a liquid at room temperature and is also too volumetrically in-dense.

I have never really understood the hydrogen hype train, because liquid hydrogen is terrible in so many ways.

A bucket of gasoline contains more hydrogen atoms than a bucket of liquid hydrogen, it contains more chemical energy, and you can actually keep it in a bucket at room temperature without anything terrible happening.

Sure, liquid hydrogen has a lot of energy by weight, but energy storage needs to be good by weight and by volume, and hydrogen is terrible by volume.

There are cases for using hydrogen as your energy storage, but if your thing is smaller than a truck, it's probably not one of them. There's just so much wishful thinking around.

You are absolutely right. The great appeal of hydrogen is that you can get it straightforwardly from water and it oxidizes back to water. Hard to imagine a cleaner energy cycle, subject to the extraction energy source but that’s in common with the alternatives.

Pretty much everything else about it is bad. Shame.

Hydrogen storage becomes quite easy when you forget about H2 for a while and focus on the energy content instead. Add some other atoms into the mix and you get something much more benign with little energy loss. Methane (CH4) is the obvious first candidate because it's so close to what we are used to burn, but ammonium (NH4) is also a good "storage hydrogen" (this one you'd want to split before burning, but it's easier to make because there's far more N than C in the air). Ammonium liquefies at easily achievable -33C or at room temperature under pressures no higher than what you find in certain bicycle tires. Some are even exploring the viability of iron dust as an energy storage medium: it oxidizes quite violently and would be recycled from the resulting iron oxide dust with hydrogen.

So hydrogen electrolysis would be the root of renewable chemistry just like fossil hydrocarbon is the root of almost all current chemistry (where even processes that use hydrogen are sourcing that from fossil hydrocarbons). You can have a "hydrogen based economy" even without any meaningful amount of H2 ever stored or leaving the power-to-x plant.

Usage site H2 applications are a dead-end, that's something I would have signed ever since the "hydrogen economy" proposed by George W. Bush (funny how benign hindsight looks at him post-Trump). Admittedly, back then I was also completely unaware that "hydrogen based economy" wouldn't necessarily mean "H2 to the home", I was just shooting down that idea with basically the same inevitability arguments as yours.

NiCd is actually more capable than NiMh, but suffers from memory issues (capacity decreases significantly if not carefully discharged and recharged; ie you cannot “top them off” without sacrificing capacity.

Again, speaking from my lived experience, NiCd pushed to the limit resulted in many gnarly fires in high performance RC use, NiMh was never a contender given low output (again low discharge rates). LiPo is king here, both in terms of output and weight/power, but overcharging or excessive discharging results in thermal runaway. Lithium ion is far safer, but less effective.

As a non-performance (including weight) practical matter as well, cadmium is just plain a rather toxic heavy metal. IIRC the EU has outright banned NiCd batteries entirely with a few very minimal legacy exceptions (medical devices I think?). Even though in principle part of the price is supposed to cover proper disposal EOL, people being people plenty got tossed and it's nasty stuff to have in a landfill even let alone elsewhere. There isn't any real treatment for it either as far as I know, normal heavy metal treatments like chelation therapy don't really work with Cd.

So I think yet another benefit of lithium is also that it's relatively easier to deal with over its whole life cycle. Elemental lithium is of course quite reactive, don't want to be directly exposed to it, but it doesn't stay that way in nature. That it's extremely abundant and distributed doesn't hurt either. While for economic reasons it makes sense to get it initial from naturally highly concentrated sources, and to recycle lithium packs, it'd be perfectly viable to pull it right out of the ocean with solar power if there was ever a need.

LiPo is a type of Li-ion battery and they have much the same safety characteristics. Lithium iron phosphate (LiFePO4) batteries are much safer, they don't tend to run away.

What about lithium and memory? Do lithium batteries have big memory issues, or is all the stuff rattling around in my head about batteries having memories mostly because I grew up when NiCd and NiMh were all the rage?

If you grew up with both you must remember how NiMH was initially championed as "no memory effect". It was still there, but so weak compared to NiCd that the claim wasn't really disputed. Lithium are at least another step of that size better than that, if they have memory effect at all. If they do have a tiny little memory effect left it's probably smaller than the extra cell aging one deep cycle would cause compared to to two smaller cycles of the same total capacity, as least as long as the smaller cycles are taking place somewhat close to nominal voltage. That would at least make memory effect irrelevant for all practical purposes.

Lithium doesn’t have any memory effect.

Asimov promised me miniaturized nuclear batteries. Sad face.

They were supposed to fit in a belt buckle!

Hydrogen cells will always have 10x+ the inefficiency of a lithium battery. They will always be niche for cost reasons.

A NiCd cell has 1.2V per cell, a lithium cell has 3.2-3.7V per cell, so they need to have three times the electron density just to break even. They are about 1.5-2.0x higher IIRC and aren't getting better, while we are still improving lithium slowly.

It's funny but I happen to be reading this on a desktop with an AGM (sealed lead acid in fiberglass) battery backup.

Congratulations, you are one of the less than 1 out of 10. AGM is great for stationary batteries, and has a place in vehicles but they will probably be replaced by lithium chemistry batteries in the coming decades as well as cost is coming down further.

It’s rather pedestrian in the shadow of this soaring sermon, but I found these Lithium Batteries in the shape of traditional D cells.

They put out 1.5v just like regular Ds but the end screws off slightly to reveal a micro usb to charge them! I wish I had these for my stuff when I was a kid.

I use them to power my automatic cat feeder. It’s great.


I’m not going to post the link but they are called Twharf D Cell Batteries 1.5V/5000mAh D Batteries Micro.

I really could not believe it when I charged them for the first time. Here is a pic https://i.imgur.com/2LoyZlR.jpg

Those look incredibly useful. I'll be ordering some in the future if they are still around and don't seem to have any reliability/safety issues (I'm slightly wary of Lithium batteries being crammed into places that haven't been thoroughly tested for that application, given the tendency of these things to catch fire. A Mag-lite with lithium batteries would be great but resembles a pipe-bomb a little too much for comfort until they're proven.)

I don’t know about their reliability, but the sheer novelty of recharging them is something else.

I’ve only done it once in six months for the cat feeder and it hadn’t run out.

No fires yet. Presumably the danger would be in the wiring and power electronics. I’d guess the battery is off the shelf, though I haven’t torn one down—they aren’t exactly cheap.

My favorite part is the action on opening the end. It is slightly spring loaded, but also limited, it won’t come apart. Someone clever designed it.

They have other standard sizes as well, but I haven’t tried them.

I really like your observation of a "lithium battery age".

But people tend to greatly overestimate how much lithium batteries improve: we remember a class of battery powered devices that ran on NiMH, then at some point LiIon became cheap enough for that use case so that the next generation that we got was so much better. We then extrapolated a fantasy battery improvement speed from that one-time jump and this mistake is rarely corrected. Instead it was supported by the next device class that got absorbed by the ever shrinking lithium price threshold. This process is now about finished, very few NiMH applications left to get "lithiumized". But the fantasy also supported, one a lower intensity but enough to impede corrections, by how the actual actual progress within lithium batteries (not quite as big as we wish, outside of price at least) gets complemented by devices becoming more efficient (think LED flashlights) and devices dedicating an increasing fraction of their mass/volume to the battery (smartphones, laptops, also cars if you compare to pre-Tesla electrics)

Lithium ion cannot output enough (low C) to make this feasible (yet). Much more likely using Li-Po cells, which are far more adept at emptying themselves at high load—but thermal runaway (eg insanely hot fires) is all too real with Li-Po, though less so today than say 6 years ago!

From Wikipedia: A lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated as LiPo, LIP, Li-poly, lithium-poly and others), is a rechargeable battery of lithium-ion technology using a polymer electrolyte instead of a liquid electrolyte.

You’d be surprised. There are some high-C lithium ion cells, but they’re not as easily available as LiPo. If you need to dump your power over 4-10 minutes or longer at peak power, there are lithium ion cells available. Less than 4 minutes, LiPo is still better for now.

Totally agree. My use case: 3 seconds max (launch), 3 seconds in-flight would be out of sight— total power on time between charges is well below one minute. I’m tempted to guess that this would be the most efficient way of converting electricity in wing suit applications as well.

That is more supercapacitor territory than batteries, especially if you do not require long-term energy storage (can accept relatively high self-discharge). The energy recovery systems in Formula 1 racing (KERS) are examples.

What’s interesting is that in many cases, LiPos can equal the specific power of supercapacitors!

Did you know there were electric cars and they were more popular before ICE cars became more wide spread.

>after another few decades of battery chemistry improvement

How do you know we aren't near the end of what is possible with batteries already? I assume that people in the steam and internal combustion era thought things would just keep improving forever as well.

I don’t have any experience with Steam engines, but IC engines have made huge improvements in efficiency in the last 10 years or so.

>> I assume that people in the steam and internal combustion era thought things would just keep improving forever

Maybe at the beginning of steam, but as early as 1824 Carnot had put a theoretical limit on it.

Because of where we are in the lab for better chemistries.


This only goes to 2005 and is plateauing at 200. I checked and a Tesla is 250-260 or so. Seems rapid growth is definitely over and we are at the asymptote.

Isn't the efficiency of jet turbines, even microjets, wildly dependent on velocity? I don't know how you can calculate an efficiency without qualification.

I used figures from a hobby turboprop which gives mechanical power output in kilowatts (or horsepower, if you prefer) and it’s basically independent of velocity.

Well yes, that's a turboprop. But fossil fuel wingsuits don't use turboprops, they use turbojets, whose efficiency very much depends on speed, which in practice means that they are most efficient right before their peak mach, up to around mach 2.

Does this mean when we run out of lithium we will fall into some kind of dark age?

The lith in lithium is the same word that describes the Earth’s crust.

To a reasonable approximation, the day we run out of lithium is the day we’ve mined the entire planetary surface.

We will never run out. Lithium is infinitely recyclable, is common in underground brines and some rocks all over the world, and has sufficient concentration in seawater that it can usefully be extracted (for non-insane cost) if for whatever reason all other sources are exhausted.


Certain kinds of lithium batteries can be limited by the availability of other elements used in them, which are less abundant than Li, e.g. cobalt.

There are efforts to reduce or eliminate the use of such elements.

Yup, and worth pointing out such chemistries are already common, although slightly heavier. Lithium iron phosphate, for instance, which also tends to be safer and have longer cycle life, has improved to the point that Tesla is planning on using it for low cost versions of Model 3 (and/or whatever their $25k model will be called), as is already common for electric cars there. Iron and phosphorous are very common and cheap.

So there are lots of alternative batter chemistries that all have lithium as the common element.

LiFePo4 is a fantastic middle ground between Li-ion and LiPo—I made out like a bandit at the end of the Obama administration when all the green startups went belly-up; Chinese LiFePo4 cells were a dirt cheap and ubiquitous in California back then. I still use some of those cells to charge Lipo cells in the field.

Internal combustion engines don't degrade to uselessness after three years

Nor do electric motors.

Rings, cylinders, valve seats, there are plenty of ICE components that wear out or coke up long before anything on a brushless electric motor will.

It makes more sense to compare batteries to tires and brakes; they're wear items. And their cost will keep dropping as their scale of manufacture increases exponentially until the economics start resembling tires too.

Are you joking? Electrical motors can go for decades before they need replacing if they're built well. Same with electronics. Contrary to HN bits don't rot, electronics fail though over time depending on robustness. Just because you don't update to the latest and greatest every couple of weeks doesn't mean anything if the device you're using is serving it's purpose well enough. I'm not sure where you're getting "3 years and you're done" from.

Are you joking?

The kinds of electric motors that go for decades with just a couple pumps of grease are reserved for industrial applications because their economics doesn't make sense for consumers most of the time.

I like my cordless drills and grinder but I'm not delusional enough to compare them to industrial motors that are twice (or more, they tend to have massive cases) as heavy for the power output and live for decades. I have a 15hp motor kicking around that dwarfs a Tesla motor in every way except output. That kind of stuff is monumentally inefficient for any non-stationary use.

3yr and you're done sounds about right for consumer battery degradation in hard use. How long a battery lasts is basically a reflection of how nice you are to it in terms of charge and discharge cycles and how much reserve capacity you want to tote around.

We've got electric motors pretty much down and can build them for just about any use case but for a given longevity vs power output batteries are still pretty bulky for the output you get.

> Are you joking? Electrical motors can go for decades before they need replacing if they're built well. Same with electronics. Contrary to HN bits don't rot, electronics fail though over time depending on robustness.

This is a mighty big "if."

Re: electronics, the electronics are by far the highest-failure item in ICE cars and in the mechanical appliances I own. Indeed, every failure I've had in cars I own and those of my family owns has in the past ~15 years been an electronic problem. That's only usually been the case with appliances and tools.

Nondegrading motors and electronics are indeed fine if you never leave the range defined by you -charging- pardon operating cable.

It says something about wingsuit flying that strapping a 25,000 rpm motor to one's chest and pointing it only slightly away from one's groin isn't even close to the biggest risk factor in this activity.

I guess his arms are fixed into the suit, but it still looks like if you relaxed your arms a little too much you could get your hands into the turbine...

> BMW says the electric wingsuit enabled Salzmann to accelerate faster than his mates at a peak speed of 186 mph. (Normal wingsuit operators typically reach horizontal speeds around 62 mph.)

Very cool; it appears to be an assist, however, without the power to actually do a takeoff.

15kW should be enough to easily lift an adult human, but the stability implications are a good reason this is an assisted wingsuit and not a jetpack.

Another thing to consider is that saying it has 15kW motors and 5 minutes of thrust does not necessarily mean 5 minutes at 15Kw. That would work out to 1.2kWH weighing what I guess to be about 40 pounds in batteries alone.

I'm really impressed by wingsuits, and strapping a motor onto one just makes it that much cooler.

> That would work out to 1.2kWH weighing what I guess to be about 40 pounds in batteries alone.

Absolutely not. Sony VTC4s are early 2010s cells that do 30 amps continuous with 2000 mAh capacity[1]. 172 cells weigh in at 17 lbs, 1.2 kWh, and a whopping 16.5 kW continuous rated output.

For lower power applications, higher-capacity cells like the NCR18650G[2] weigh below 10 lbs per kWh.

[1]: https://cdn.shopify.com/s/files/1/0674/3651/files/Sony_VTC4....

[2]: https://www.imrbatteries.com/content/panasonic_ncr18650g.pdf

> Normal wingsuit operators typically reach horizontal speeds around 62 mph.

Normal wingsuits can easily reach ground speeds up to 250kmh/155mph.

Source: https://ppc.paralog.net/listtracks.php?sort=Speed&record=C

An electric ducted fan (EDF) is highly inefficient, had they put similar wattage through a gearbox to say a folding prop, efficiency may have doubled (albeit an admittedly more onerous form factor). This is just the beginning of electric assist single passenger flight!

Reference: plenty of experience pushing 8KW+ through 2KG RC gliders (F5B) and far slower EDF models.

> had they put similar wattage through a gearbox to say a folding prop, efficiency may have doubled (albeit an admittedly more onerous form factor)

They chose not to do this because the more onerous form factor results in amputation of the pilot's viscera and legs.

> results in amputation of the pilot's viscera and legs.

Granted, that could be an issue, but once the government contracts for production of a few thousand units such minor flaws can be addressed with a field upgrade package, barely tripling the unit cost.

It's true that big, slow things are, all other things being equal, more efficient than small, fast things. Momentum is mv, but kinetic energy is 1/2 mv^2, so that squared term means it's cheaper to move a lot of mass(m) slowly than a little of it quickly. You can build big, slow ducted fans, but you do hit size limits much earlier than with free props because of the shroud.

HOWEVER, efficiency is maximized when outlet velocity matches airspeed (or you have wasted momentum that will dissipate into heat, when your outlet stream mingles with the rest of the atmosphere). For your slow gliders, a small ducted fan with a high outlet velocity will indeed be quite inefficient. But this guy, traveling at hundreds of mph, needs a propulsion unit with a similarly high outlet velocity. A big, slow thing isn't going to cut it for that. A big, fast thing would, but would also blow their power budget. Within their design constraints, this is pretty close to the optimal solution.[1]

There's also the small matter of free props being horrifically dangerous :)

[1] They've helpfully given us enough information to work out some basic aerodynamics of their fans. At 7.5 Kw each, assuming 90% efficiency each of the motors and ESCs, and eyeballing the duct and hub diameters as 18cm and 8cm each respectively (could be off, here), we should expect an outlet velocity of about 230 mph. The guy reached an airspeed of nearly 190mph, or over 80% of the outlet velocity, so they aren't doing badly at all considering the drag.

If someone wanted to learn all this stuff in a "for dummies" class, what course would they look for, among the MOOCs?

I liked this course: Introduction to Aeronautical Engineering, by Technical University Delft in the Netherlands, on edX. It assumes basic physics and maths, but then gives a nice overview about all the fundamentals - aerostatics, aerodynamics, propulsion, materials, structure of aircraft, etc.


If you're specifically looking at autonomous flight of drones, then the Udacity Flying Car nano degree is not bad (it contains several mistakes, but takes you through quite some material with neat exercises). It presupposes a bit more maths and programming. I was free (for a month) during the early stages of the pandemic, now I think it's back to normal prices.



I'm also open to the idea that a HN'er teaches us.

Yes, I know what I'm asking.

You don't have to do it ;-)

It would just be really nice :)

Bit of an aside, but are you saying you are flying an EDF glider?

Haven’t bothered :) Only “toy” EDF models, performance from an 8KW system revving at 60K rpm at 10S (10 lipo cells in series) swinging a 19” folding prop is on par with a mini turbine in terms of performance (0-> 180mph+ in under 2 seconds). Granted this is for 2 meter gliders, but I would expect similar efficiencies in larger scale applications (the bmw EDF is not that much larger than RC).

That's crazy. For a non-RC dude, how much thrust does that produce, and how much did it cost?

The $ sounds high, but it’s nothing compared to the time that goes into building and preparing... https://youtu.be/oCS84I8vJK8

"electric assist single passenger flight"

If electric is assist, what would be the main power source?

I thought efficiency of a fan < 2 counterrotating stacked fans < ducted fan?

Amusingly that’s actually much slower than the world record for unpowered wingsuit horizontal speed of 246.6 mph.

Tho that was not what was tested, this is about having additional thrust to regain altitude and fly longer distances:

> “I found the idea of being able to jump from my local mountain wearing the wingsuit and land in my garden fascinating.”

Sure, I just find it funny how in most cases 180MPH is fast, but that’s about the minimum speed for horizontal wingsuit flight. You really can strap a get engine to a brick and get it to fly, but you can’t stick a jet engine to a brick and get it to fly slowly.

EX: F-15 landed safely with just one wing. A little cough propaganda, but still interesting: https://www.youtube.com/watch?v=M359poNjvVA.

I don't fly wingsuits, but from a bit of quick research it seems that 180 MPH is fast even for a wingsuit.

The article itself mentions typical horizontal speeds of around 62 mph.

The Wikipedia article on wingsuit flying says:

> A typical skydiver's terminal velocity in belly to earth orientation ranges from 180 to 225 km/h (110 to 140 mph). A wingsuit can reduce these speeds dramatically. A vertical instantaneous velocity of 40 km/h (25 mph) has been recorded. However the speed at which the body advances forward through the air is still much higher (up to 100 km/h [62 mph]).

Even mentions another jetpowered attempt with hydrogen peroxide rockets reaching a horizontal speed of 160 mph, back in 2007.


I run a small site/app where wingsuit pilots upload gps tracks for analysis. 180mph is fast but can be achieved/sustained without a jet.

In practice that is difficult to do on most BASE jumps as you need to sustain a steep angle for 10-15 seconds to hit that speed. Density altitude will greatly affect performance as well.

What's cool is being able to sustain 180mph while not losing altitude, which it sounds like BMW+Salzmann have accomplished. From the article:

"While Salzmann’s first flight was a resounding success, it appears he’s not resting on his laurels. According to BMW, the daredevil wants to fly between the skyscrapers of South Korea next."

I've dreamed of being able to zigzag through downtown skyscrapers for more than 10-15 seconds. The Jetman project is astounding. From a friend who is working on a copycat, the costs are close to 100k to replicate. Eager to see experimentation+progress on any projects with the promise of making hybrid human+wing flight more accessible (cheaper).

Minimum level flight speed is called an aircraft’s stall speeds, which is different than their ideal glide speeds. Wingsuits have a glide ratio of ~2.5:1 (horizontal:vertical) which is not that much better than just falling as a normal skydiver can hit 1:1.

To maintain level flight they need to generate a lot more lift, while carrying the extra weight of an engine. By comparison a 747 has a glide ratio of 15:1 and depending on specific model and how much weight it has onboard it will stall in level flight around 180MPH. While many aircraft can fly at much lower speeds, a wingsuit is a terrible aircraft.

Horizontal speed =/= level. The average wingsuit with a forward velocity component of 62mph is still dropping in altitude quite fast.

IIRC terminal velocity for a skydiver in free-fall is approx 180mph. (It's at least in that vicinity.) So the direction of "flight" certainly matters a lot in making sense of numbers.

Also, when I was in 5th or 6th grade (over 30 years ago) I was obsessed with the F-15. Talk about thrust:weight ratio. The idea that you could take off, point the nose to vertical, and accelerate past the speed of sound, then level off and get to mach 2.4 or so... simply amazing machines.

First a belly down skydiver falls at about 120 MPH. Face down with streamlining they can do up to about 300MPH.

So someone starting with a deep dive in a wingsuit can level out and get very fast horizontal movement. There are a few videos of people doing this and reaching almost level flight though their slowing down. It’s maintaining speed that requires thrust, but speed is enough for level flight.

Also, while you could effectively balance on a jet engine to hover, that amount of thrust would also allow you to do not just level horizontal flight but rapidly gain altitude, making it kind of a meaningless from a minimum speed to requirements for minimum thrust perspective.

Base jumping has a ridiculously high fatality rate (~1 in 60 people who try it die). I wonder if adding engines makes it safer or less safe.


It's more active jumpers over their jumping career than just people who try it once. It varies wildly jumper to jumper based on the types of jumps done (cliffs are more deadly than bridges) and how often. Most people jump for a period of 3-6 years and quit.

My wife and I were pretty active jumping in the era of wingsuit videos on YouTube. In her first year we had one good friend die and 9 people we'd met or hung out with a short time. It is basically comparable in danger to spaceflight.

Didn't expect to find one here at Hacker News. 698... so you must have started around the early 00:s or thereabouts?

Unfortunately I share your same statistics: I was very active in the early 2010:s and in that period I lost about 10 friends/acquaintances. Since then even more people I've hung out with are gone.

So yeah: wingsuiting is dangerous. But BASE itself can be done "reasonably" safely I think: personally I was always more fond of slider down (low) stuff, like buildings, and in my mind that's a safer sport than wingsuit BASE.

Yeah 2000 was first BASE jump. There are a few on here. Brendan W and a few others pop up on these threads.

probably depends on whether you're buzzing mountains and not deploying a chute till 1000ft.

in this vid he's jumping out at 10k ft which makes it closer to skydiving.

This appears to provide an additional 5 minutes of boost to traditional wingsuits [1], a specialized form of skydiving.

[1] https://en.wikipedia.org/wiki/Wingsuit_flying

For anyone interested in wingsuits in general, check out Jetman (Yves Rossy):



Obviously cool if you can do similar things with electric as well.

Meanwhile, Tesla is gobbling up BMW's luxury car marketshare. I mean, this is exciting and all, but as a BMW owner with a 6 year old car, I'd appreciate if there were any non-dumb options in your lineup, BMW. Instead we're getting humongous grilles and wingsuits. How stupid do you think your customers are?

First sentence in video: "What does it take to shape the future?"

Me: turns off sound

For non-Americans, that's 300 km/h.

And I just read on Wikipedia the fastest speed ever recorded was 396.86 km/h. And the fastest average horizontal speed over 1000m: 325.4 km/h.


Why does this, of all things, have to be electric? It's a wing suit. They're basically strap-on death. Their glide ratio is somewhere between a really bad plane and a brick, they're unusable in any shape or form for real transportation. They could've had gone with a jet or even a rocket engine and it wouldn't have made the thing more dangerous or less green or anything.

Don't get me wrong, I love it, but I don't really see what they were seeing when they made this.

Rockets or jets would limit your candidates for a sponsoring contract to Red Bull and Red Bull. If you are making a bit of a career out of BASE and/or wingsuit you are probably tired of them by now, or they are tired of you or both. It's a very small market and surely weird given that the buyer has a monopoly, whatever that means.

With electric, apparently BMW becomes another candidate (who seem to be desperately looking for ways to get their name visible in a context that somehow combines "electric" and "exciting").

Minor headline nitpick: It should be electric-powered. An electrified wingsuit has electricity coursing through the whole thing. EDIT: More of a BMW PR nitpick I guess.

Does anyone know why it's not strapped at the back like a jetpack?

Most obvious is parachute goes on the back, and you really don’t want to mess with that. But, you’re also going to get a lot more turbulence on someone’s back.

I guess extrados is much more important than intrados in terms of aerodynamics (planes "never" carry anything above their wings, only below them)

No, that's not even remotely some sort of design rule. Business jets commonly have their engines mounted above the wings. Doing so can enhance lift in some situations. Here's one of Boeing's models using this idea to enhance the lift of a blended wing body: https://www.youtube.com/watch?v=28blrKKg0Uo

Interesting. But propulsion is strapped to his body (fuselage) and not his wings. Planes have things attached above fuselage AWACS have huge dish. The Space Shuttle transporter too. A-10's have engines above wings (although they are not attached to them).

I'm genuinely wondering when I can buy a personal, commercially available, vehicle that will let me fly (or maybe sail) over the Hudson river on my commute into NYC. What are the stoppers for something like this? Landing? Economics? Regulation? I'd pay more money than a car for something like this.

You can buy a helicopter. They're expensive, loud, and dangerous.

The noise is really bad and one of the reasons I'll vote against any local ordinance that would make heli-transit more available.

Or you can buy a canoe - GP was willing to sail instead of fly. Cheap, quiet, safe-ish - paddling across the shipping lanes of the Hudson is probably mostly fine, but if you do it every day you'll have some close calls.

The Hudson River is less than a mile across at Manhattan. This could be faster than car/train/ferry/bike for some very specific commutes.

It's very much doable: https://edition.cnn.com/2016/11/01/americas/zach-schwitzky-c...

"Living in Hoboken, New Jersey, the other side of the Hudson river to Manhattan, Schwitzky kayaks across the water in around 20 minutes."

a pilots license

For people wondering what is this for. BMW has just announced a new electric SUV (iNEXT) and started production on another one (iX3) so they are hyping their electric technology. In my opinion, they could do much better by just allowing their plugin hybrids to charge at the full rate of a lv2 charger.

A PHEV X5 could be the killer product with the X5 already being one of the best selling cars in its segment except it takes 6 hours to charge on a lv2 for the full 30 miles range due to the current limitation. The battery itself seems to be able to handle much higher current when it charges off the engine so it seems like an artificial limitations to prevent the PHEVs from competing with the few BEVs they struggle to move.

Are these way safer than say the base jumping type wing suits?

Obviously they're powered so they're different, but I remember a lot of wing suit debates where even professionals felt that the envelope between 'safe' and disaster on wing suits was way too small for even professionals to use. A lot of that seem to have to do with the jumper's sense of how stable they are / compared to how stable they actually are and how that could get way off at times and even pro's weren't able to manage them well enough.

Just to clarify, he's jumping a BASE rig with a wingsuit - albeit technically a skydive (jumping from a helicopter).

It's a BASE rig since it only has one parachute, and the sole canopy is designed to deploy quickly and consistently.

Another clarification - BASE rigs with wingsuits are not inherently dangerous. In fact, BASE/wingsuit gear failure as a cause of death is extremely low. It's correlation vs causation - BASE rigs are used almost always (except for certain stunts like this) used in a BASE environment flying close to land, where the margin of error (time to impact) is extremely low compared to a skydiving environment.

In a skydiving environment, you can do everything wrong, even do nothing and likely live (automatic activation device triggered deployment of your reserve canopy). But with BASE, oftentimes you are flying so close to terrain that you cannot deploy your canopy and live, and your only option is to continue flying your wingsuit to a safe place to deploy - which is a problem if you stall, take a slightly wrong line down the mountain, etc.

Source: I'm a parachute rigger and I wingsuit (in a skydiving environment).

Batteries -> electric motors -> ducted fans seems inefficient to me. If I were building this myself I would go with a hybrid rocket engine.

Though electric motors are notoriously efficient (much more so than ICEs), and my understanding was that ducted fans are also efficient (particularly with 2 stacked counterrotating props).

Still not up to King of the Rocket Men standard. I think take off has to be included in these 'first flights'.

Does anybody else think it is way too small to produce any real thrust? If it put out serious thrust, I'd expect it to be less flimsy...the video made it look kind of floppy on the guy. I think BMW needs to publish the thrust produced vs use numbers that aren't truly comparable.

This is why they cannot use the EDF for launch—nowhere near enough thrust. But thrust is far less important for sustained speed, where pitch speed becomes the critical element.

I guess I can see military and extreme sports applications, but is there a mass market application I'm missing?

Looks like a lot of fun.

The cheesy music and SFX put me off.

Is that exhaust smoke from an internal-combustion engine trailing behind them?

No, they're just wearing smoke bombs/sticks so that you can see the trails in the footage.

My first thought is that this would plausibly explain the recent appearances of mid-altitude jetpack sightings by airline pilots around LAX.

Something seems suspect here.

There is just no way that small unit could generate near enough thrust to make a real difference.

I think we need to look deeper into this claim

He's starting from a plane, so his flight is mostly powered by the fall and the updraft of the wingsuit. Additionally, it may look as if he's soaring when just gliding with a small change in perspective


Fans that small put out enough force to literally push you straight up. Jetcat has an engine 23 cm wide which can pull 110 kg. For the same size an electric fan passes much more air.


those are jets, not EDF

Are you sure? Those small EDFs can generate 12-25kg of thrust.

The fastest wingsuit flight almost topped 400km/h so maybe the real question is how much extra speed was gained with those little EDFs.

Even without additional power it's possible to gain a small amount of altitude with a wingsuit[0]. Modern suits can be very powerful with proper technique.

[0] https://squirrel.ws/learn/wingsuit-deployments

Humans are amazing animals

that looks fun. is this something i can pay to do?

now just get me to flying altitude

Wow.. Some people have managed to build a seriously high tolerance for risk.

Boredom causes people (presumably not just me) to go to great lengths to feel alive again.

I saw this on the news a couple of days ago. It stated that flight time is about five minutes before the battery runs out.

That time in "flight" doesn't seem much different than the time it would take to plummet to your death. The only material difference seems to be the not dying part.

5 minutes in addition to the normal time you get when flying a wingsuit would feel like forever. Even 2 minutes (my average) starts to feel strange towards the end after being used to a typical 60 second skydive.

You could use these suits to help pilots who can’t land their plane - they literally only need a few moments of “burn” close to the surface

As a wingsuit pilot I would disagree. Donning the suit is a little more complicated than just strapping on a skydiving rig and you need a fair amount of experience to successfully fly one to begin with. Your parachute system threads through the wingsuit, you still need to tighten leg straps inside the suit before zipping up, tighten a chest strap after zipping up, then zip the arm and leg wings and exit the aircraft with a correct body position and delay to avoid slamming into the tail depending on what type of aircraft it is. It takes a few minutes to put everything on while on the ground, I can't imagine trying to put everything on while a plane is out of control and get it all adjusted properly during an aircraft emergency. Wingsuiters suit up on the ground before boarding so all that's left is to zip up your arm wings and leave the aircraft.

We already have those, they're called "parachutes". They're easier to operate, safer and don't require power.

I just need you all to pony up and buy me one. Presume that’s ok?

I mean... It's only like, really cool.

On a side note, I think it's going to be an interesting decade for all sorts of sports. Different variants enabled by technology, and every-improving athletes and engineers are going to be working on very interesting demonstrations I bet.

Nice to see they aren't bothering with social distancing. I mean, sure, they might be spreading a deadly virus, but how else are they gonna talk about how bad-ass that wingsuit flight was? Totally worth killing immunocompromised people.

This sounds like a "Karen" comment. Do you really think a few guys flying in turbulent air will spread covid? Have you seen all of the people who gather in parks in San Fransisco? This flying experiment is not even comparable to other vectors of the virus that immunocompromised people are exposed to on a daily basis.

It's not so much a 'Karen comment' as actually respecting human life. But sure, let's all spread the disease whenever we feel like it just because other people spread it worse.

It's amazing how little morals people have nowadays when I have to defend not wanting people to die.

Coughing at 10,000 feet is completely harmless. That sort of turbulence/condition is an unviable transmission vector for a virus as it reduces the PPM beyond effectiveness.

They're outside and (in the last congratulatory shot) almost all wearing masks. I think that is defensible.

It's not defensible, because you still have to social distance even when outside.

FWIW, this paper (on the danger of thanksgiving dinners...) has some graphs showing the difference between transmission during indoors vs. outdoor meetings. The difference is tremendous.

Slide 6 - the barely visible brown line hugging the x-axis is outdoors.


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