FOUR ARMS GOOD
We left off then with a ludicrous plan on paper that involved figuratively ‘teleporting’ an individual from one urban location to another based solely on, say, entry of a postcode. Or so you would have thought? Reviewing the hits on the handful of videos featuring a number of different layouts as an alternative to the ‘flying phone-box’ however, that one featuring precisely that (albeit in model form) still outnumbers every other by a factor of over ten to one. In other words, people are still motivated by the notion ~ not least from having seen any number of episodes of either Star Trek or Doctor Who ~ of stepping into a GPO phone-booth that is able to connect them physically with someone beside being able to do so on the end of a telephone line. The good news is, that remains a longer-term goal and one that is facilitated anyway by everything that is being done within the current round of development.
Nonetheless in terms of the timeline (and these things invariably take years rather than months), it would not be that much longer having filed a patent specification from force of habit if nothing else, before I became aware of the fact that someone in the US was in the process of organising a global meet for the nascent ‘personal air vehicle’ industry. In fairness, the founder of Opener and its BlackFly would be among the first to appreciate how a convergence of technologies was about to enable electrical vertical take-off and landing (eVTOL) vehicles. Nonetheless it would be the same concatenation of technical evolution that would inspire Gwen Lighter to found the ‘GoFly Challenge’. As a Harvard-educated lawyer, her forte would lie in the broader organisation of the event moreso than the nuts-and-bolts of flight itself; and given many number of contestants would be strangers to the nuts-and-bolts of flight this would hardly matter. In fact it is precisely the people outside an industry that go on to pioneer its evolution, in the way for instance that IBM were slow off the mark with personal computing and Kodak would be left behind altogether in the field of digital photography.
The challenge itself, as you might expect from a lawyer, was probably overly constrained by the red-tape from the outset. Whereas aviation had always progressed through broad competition, in simpler and more swashbuckling ages these might involve meeting the simplest goals like crossing the English Channel, or later the Atlantic. When you consider the pioneers of flight, this was altogether practical, in that you either stayed in the air or else ended up in the water. As the current challenge came off the back however of a century or more of flight, and stretched to 854 teams who mostly had zero experience of aviation practise, then the finer points had to be addressed. In this case, this would be by reference to experts in the field with the knowledge of the available technologies and how best and safest to apply them.
As we joined at the Phase Two stage, involving considered prototypes rather than pictures on the classroom wall, we had to meet any number of conditions and lay these out in a readable form for review: at which point the proposed prototype would fall at the first fence. Recalling the content of the original concept from the previous chapter, this might have taken the form of an upright passenger booth around which an eight-motored rig or platform would levitate itself around the passenger into the overhead, from where it would engage the payload and raise it into flight… or so the theory went.
Nonetheless in so far as the available technology was concerned, this presented not inconsiderable problems from the outset. Upon advice I had selected Pixhawk’s flight controller to modulate the power emanating from each motor, and this required to be mounted in a central location. A hobbyist device, it had sprung from a need to program increasingly sophisticated radio-control aeroplanes and helicopters, from whence it would be adapted to the newly-emerging drones.
The vast bulk of these were quadcopters that featured a motor and propeller in each of its corners, configured in a broadly square outline. So far as what the controller considered a drone to be, this was a broadly flat airframe much like a starfish without the extra leg. Containing sophisticated gyros and accelerometers derived from mobile phones, these had ideally to be placed in a central nexus that represented the precise centre of the physical outline (which was essentially flat or two-dimensional anyway), beside its centre of gravity (which I would only discover at a much later date).
This was a punch to the solar plexus, as in a flying phone-box that physical and gravitational centre is occupied by you or me and not by the drone itself. Later I would in fact discover that a degree of offset is available to the controller, but that this condition is decidedly sub-optimal. Like the earliest PCs that I had had to deal with, this technology is decidedly temperamental unless set up precisely, whereas I had spent half a lifetime flying aircraft that were practically bullet-proof so far as failure redundancy was concerned. In fact the reason the current (and hopefully future-proof) design has departed from the original vision is that it is effectively a physical manifestation of what is most likely to work sustainably given the budget and equipment available.
Nonetheless it was prior to entering the second phase of the challenge that the decision had been made ~ given the difficulties of incorporating a ‘sliding’ power-rig ~ to ditch the concept in favour of fixed means of power-installation. The obvious solution was to array the motors both above the ‘phone-booth’ around its dome, and below it around the base. The reason for this distribution was wholly practical, in that the bulk of the unladen weight of all such designs lies in the electrical motors and battery-packs, and to set these around the top end of a phone booth that was not anchored to the ground was to invite it to topple over. Distributing motors and power-packs above head-height and around foot-level would mean that it was adequately ballasted on the ground, and better balanced in flight from the aerodynamic point of view.
Basically a quadcopter above and one below, this would also that there was a better failure case in that given sufficient power, any one of these could continue the vehicle in controlled flight even given a total failure of the other. At the same time if you have two multicopters vertically separated, that pitches the centre of thrust around what would be the centre of gravity, enhancing its manoeuvrability. In short, this would give it a ‘low polar moment of inertia’ which is what for example you would want in your car to best protect it from spinning off around bends. Except this is the same in three dimensions instead of two.
At the same time as I would substitute a single sliding rig for two fixed units above and below, practical build considerations meant that I would prefer cantilevered arms (motors on sticks, basically) over ducted fans. If you are unfamiliar with the later, a ducted fan is more like a bathroom extractor than a desk-top fan in that it includes a moulded surround that improves its efficiency and allows it to be smaller than it would be otherwise. You most often use these when you go in holiday, as airliner engines are invariably fans albeit driven by a jet-engine. The problem is, they have to be produced very precisely and at great expense so as not to allow the fan to rub catastrophically on its surrounds (as ultimately caused the Boeing 737 accident at Kegworth in the UK).
Accordingly, these two conditions stemming from a practical application of the originator’s vision viz. a pair of fixed quadcopters vertically separated on the one hand, and set upon arms rather than sunk into ducts on the other. Given all of this, you get what is pictured at the start of this chapter and indeed what still appears at time of writing on the entry to the challenge appearing on HeroX’s platform.
That was the good news. The bad would be that it failed to jibe with the extensive conditions associated with the GoFly Challenge itself. Specifically, these dictated that the airframe had to be contained within 2.60 meter dimension all-round, and worse this constituted a virtual sphere rather than a cube. Worse again, the height of the vehicle once the operator was included did not count, which put us at a disadvantage because whereas our operator would be wholly encapsulated in the airframe, any number of the other entries featured a flying-platform that the operator stood upon and whose own height was not included. In other words if we had flown under a low-bridge and some to grief we would be penalised, whereas anyone stood on top of a flying machine who was dismounted by the same collision would remain within the rules.
What a swizz! But there would only be one answer to this if it meant sticking to the original vision of flying phone-box, and that would be to scale the outline down and take it to the competition in the guise of a proof-of-concept in place of thoroughgoing entry to the competition itself. There were, after all, prizes for the most outlandish iteration (disruptor was their preferred moniker) worth a not inconsiderable sum. At the same time I also figured that it would fly a child, and there were actually no stipulations that related to the age of the pilot-operator, which was surprising itself coming from a lawyer. The weight of same had however to amount to a hefty ninety kilos, although this could be achieved by means of a wearable ballast. I even at one stage considered an advert in Flight magazine petitioning the services of a dwarf who wanted to go flying in a phone-box. I mean if people are up for a real-life Squid Game then surely there’d be a candidate out there?
Before moving on to consider how best to accommodate a phone-box and its tentacles to the confines of an 8.50 foot sphere, it is perhaps worth considering the challenges involved in assuring its structural strength whist at the same time preserving the essential quality of levity afforded all flying machines from the outset. Smaller drones have the benefit that they can be injection moulded in plastic so as to form what is called a monocoque structure, much like the starfish previously referenced. This provides for an internal volume for components, beside a measure of depth that helps support the arms, which are known to engineers technically as cantilevers (supported as they are at only one end).
Once drones began to have a commercial value in their proliferating use as survey or quality video equipment, they inevitably grew in size to support the extra payload for one thing and to provide more range or endurance for another. Larger forms of transport be they ships or aeroplanes tend to have more range, not least as Brunel discovered with his steamships that the cube law means that they can carry a disproportionate increase in fuel load as they are stretched in each dimension. To make injection-moulded product however requires vast sales in order to justify the tooling, whilst at the same time that tooling becomes progressively more expensive as with size increases. Beside this, the increasing spheres of operation and range of applications that had to be met called for more flexibility in locating components.
This would mean that commercial drone operators would as often as not build to order, invariably using stock electrical components like the aforesaid Pixhawk flight controller. At the same time they needed to keep weight to a minimum, which steered builders to carbon fibre. This is expensive, but not prohibitively so in view of the fact these were not unduly large flying machines (and are limited generally to around 25kg or 55lb). That said prices are rarely quoted because they are almost invariably custom-built ~ although the mass manufacturers are encroaching on the market too ~ and as a result cost tens of thousands of pounds as against hundreds. This is unsurprising given the survey cameras they carry might cost over thirty thousand pounds,, and you don’t want it falling out of the sky.
How then scale these devices to proportions which suit flying the average quarter-back round an airfield, instead of HD cameras the size of a cockroach?
This would mean that commercial drone operators would as often as not build to order, invariably using stock electrical components like the aforesaid Pixhawk flight controller. At the same time they needed to keep weight to a minimum, which steered builders to carbon fibre. This is expensive, but not prohibitively so in view of the fact these were not unduly large flying machines (and are limited generally to around 25kg or 55lb). That said prices are rarely quoted because they are almost invariably custom-built ~ although the mass manufacturers are encroaching on the market too ~ and as a result cost tens of thousands of pounds as against hundreds. This is unsurprising given the survey cameras they carry might cost over thirty thousand pounds,, and you don’t want it falling out of the sky.
How then scale these devices to proportions which suit flying the average quarter-back round an airfield, instead of HD cameras the size of a cockroach?
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| One day son, all phone boxes will be like this |
