Standby... Lights! Camera! Action!

Guys naturally delighted to be back in the studio after the Christmas break...

Part 107

Here's the certification for the vehicle that is required to operate it in the US, where it has to be renewed every three years whether flown commercially or purely as a hobby. Ironically it is probably more stringent than building it large enough to carry yourself, so long as it can be controlled from within rather than remotely. Thinking being that if you're up there yourself it's less likely to go AWOL with a pilot on board than if it ever loses radio contact with whomsoever is flying it from the ground.

A second reason for the relative laxity of the piloted as against unpiloted ~ as divulged to me whilst there ~ was that the comparatively stricter constraints on drones dating from their introduction assisted greatly in handing the global market to China. This a mistake that the FAA were reluctant to repeat with people-carrying devices, at least at the level of private ownership.

The distinct problem with designs like the flying phone-box is that it is ideally suited to moving individuals over a short distance for hire. This in turn makes it a commercial operation with all of the certification requires associated with that, most places in the world. As a result capital investment is flowing toward flying taxis that seat between two and six people, as you might as well be slaughtered for a sheep as for a lamb.

This makes personal air vehicles (PAVs) like the Jetson One more likely to be funded by private individuals than corporations, at least in the formative stages. In truth this has ever been the case whether involving the hot-air balloon, airplane or helicopter. each of these struggled between attracting the military on the one hand and people with money to burn on the other at the earliest stage of evolution, though you'd never guess it as you sit back with a gin and packet of peanuts on route for Disneyland.

Half-Scale Build #103

There's sufficient room to store battery-packs in the overhead, this showing how they address the respective ESC. Opted for a top-mounted installation to raise connections clear of the propeller, which now sweeps the area below the drone. The controller, radio receiver and GPS aerial will also be fixed topside (though in the past we've flown them inverted on the underside too).

To secure each ESC I've again used a strip of double-sided tape, reinforced by a pair of cable-ties. These techniques are borrowed from previous builds, the evolution toward a beta-product being a process of continuous improvement. Weight-wise we are up to 11.30kg (or 25lb) with just the Pixhawk controller and propellers remaining to be fitted.

This means we need over 70% thrust just to get airborne. This is marginal and might mean that all we'll get to show is an animated window-display... anyone got Selfridges number?

Half-Scale Build #102

There is so little thread on these motors to engage with, beside the fact 3.0mm bolts are decidedly fiddly anyway, that the easiest solution is to drive the bolts in from the far side. To do so without impacting the windings I've reduced the shanks to 33mm, which in turn means they've probably cross-threaded the bolt-holes on the base of the motor. At the same time I've had to pritt-stick a washer in place to ensure the axle protruding from the base clears the frame. All in all a parlour game which keeps a whole family amused throughout the whole of Boxing Day.

Does though demonstrate the versatility of the design, because from hereon in we can simply flip the drone over to proceed right-foot forward. Alternatively we can leave it as intended and leave the motors mounted inverted on the underside of the airframe. Either way it looks like plastic pushes the envelope when it comes to rigidity, which is why we shall retain an alloy backup for the perimeter sections at least.

I've decided to leave the full length of the cable intact, not least because it saves re-soldering the ends... the cable-tidy was made by wrapping the excess length around a length of double-sided tape stuck to the frame.

A feature of drones which helps all of this is that ~ with computer control ~ it doesn't matter if the motors are not mounted perfectly level. Any tendency to wander due an offset in their level will be remedied by adjusting the RPM of the remaining motors to restore a level hover... something the pilot would have had to do in Christmases past.

Polar Express

Hate at first sight when it came to this motor, mainly because its axle extends beyond the base requiring a shim like this and because there is insufficient depth of thread to play with before the bolts impact the windings. Neither an issue with the U13 model a few grades up ~ this a peril of buying online, its bulk returns and the carbon emissions that go with it.

Does bring proceedings to a halt as I need to know if Loctite will secure that washer or whether I'll need to shop for superglue... which is not the priority come Christmas Eve. In retrospect I should have opened only one set of packaging so the goods could be swapped for more powerful equipment; but like Scott in the Antarctic we're beyond it, and it's do-or-die with a 24-volt set-up.

Looking ahead therefore I check the weight of the payload viz. completed transporter including mannekin. It comes to 5.90kg or thirteen pounds, which is fairly remarkable for what is practically a two-third scale iteration. At 75% we've theoretically fourteen kilos of thrust, though that's well beyond what you'd want thrust settings to be in the hover. There's still the weight of the drone to consider too, though it should come in well under the payload.

Worst case we'll dump the mannekin, halving the payload at a stroke. We'd all still get the picture knowing the power can be upped. Whichever form of transport we use ~ whether car, aeroplane or all else ~ started off with power that was a fraction of what it would later become. And so now it must be time for old Mr Fezziwig to clear the factory floor, don his best breeches and set the tables for an evening of merriment... and God bless us, one and all.

Half-Scale Build #101

The passenger is secured at the top of the box. In order to fly their heads are shaved, and velcro taped to the crown in a drug-fuelled initiation ceremony in the jungle.

Half-Scale Build #100

A view of one of the landing rods in place. Advantage of prototyping is learning lessons that are carried forward into the next build: the M5 bolts should have been relieved of their heads prior insertion, so that their uncut ends protrude. Nonetheless the idea of speculative builds like this is to achieve the big picture, the broad outline of a design that looks like it's literally going to be a flyer at whichever scale.

Their means of attachment for instance is probably sub-optimal... pair of brackets, one of which is drilled out to allow the rod to be slid into place and fixed with a wing-nut. We could have riveted plastic conduit clamps to the footwell panels in order to form a guideway. In fact I did order M8 P-clips for precisely this reason, but they proved to be too tight a fit once closed by the pop-rivet.

Previous iterations of the box featured an 'H' arrangement of rods like helicopter skids, but then they need to perform running landings, while VTOLs don't. Principally though, despite the sacrifice of an element of ground-stability the attraction of this fit is that it remains consistent with our design strategy: limiting part count to a bare minimum and inter-operability of parts.

The landing rods are fitted like the arms of the drone above, which they complement. Ensure that brackets are fitted at the correct corners, else otherwise the rods extend from along the wrong side of the frame. The vehicle's arms and feet are arranged left-foot forward because they appear better that way, but don't ask why ~ perhaps they look better the other way to left-handed people?

If you wish to reverse the look, flip the drone other side up prior to fitting the motors.

Half-Scale Build #99

Days you don't feel like doing any of this, and this is one of them. Nonetheless cannot let a day go by without advancing the cause, and a gentle pursuit is the preparation of landing gear. This takes the form of 8mm GRP rods which served well on the earlier build shipped to California. In one end there are 5mm bolts whose heads are removed later and at the other, door-knobs to stop the rods from impaling landing surfaces.

The length of each rod has been reduced from one metre to 30" so as to extend just 6" beyond the outline of the airframe. It would perhaps look better were it to match the length of the drone's cantilevers, but we'll err on the safe side throughout. They'll look nice either way once sprayed red.

Half-Scale Build #98

Devil is truly in the detail and there are days when progress slows to a snail-pace as a variety of different fixes are tried out. In the event ~ apart from putting my back out as I lean over ~ I decide to remove the battery-packs topside to simplify matters. This in turn allows the phone and drone to be close-coupled, and by way of attachment I use a pair of angle-brackets at each corner. One is secured using the 6mm bolt at the end of each cantilever, whilst its opposite number is simply riveted to the framework.

These brackets suit M4 bolts and have to be drilled out to fit an M6. Out in the field they could be attached with nuts and bolts though we'll likely use cable-ties instead. Deceptively strong, they are used as hand-cuffs for unruly passengers; so it won't be the first time they've taken to the skies.

Half-Scale Build #97

Got to get on message, and if you scale this to A4 size it suits our current build. I do four because phone boxes were not designed to fly people ~ with the exception of Doctor Who ~ and had a back where ours does not. In fact the only way you can figure which way is forward is whichever way its passenger is facing, and even that can be changed whilst the air vehicle remains stationary.

It has that advantage over helicopters or eVTOLs like the Jetson ~ one reason we'll be pitching it for video and observation. The typeface is Arial Bold, because we're both.

Half-Scale Build #96

Here's a nice top-view of the battery-bay. Not wanting to waste any precious lengths of extrusion I've used metre lengths for each upright, and the tube-connectors add a further five centimetres to those in terms of height. Though we could fit the standby mannekin in the transporter 'as is' we've selected the unarticulated one for the lunar mission and in fact I'm tempted to call him Neil Armstrong for that reason. I've had to make a cut-out to accommodate the crown of his head within the confines of the bay, and the CAA have kindly provided an exemption from use of the firewall in the event he's dead already. We shall though be providing a baseball cap as a mark of respect.

The battery-bay incidentally is simply supported four-square by brackets along each of the shorter extrusions that you see in the photo. Accordingly it can be removed so we are able to drop the mannekin in place, with him being unable to step inside, love, as Cilla Black was oft known to sing. All four six-inch footwell panels have been riveted to the box prior to all of this, in order to render the space-frame suitably rigid for the handling required.

Battery-packs sit proud of the frame by around a half-inch, so that lugs are required in order to raise the drone clear of the box during the pre-flight manual docking. The gap will be used to route those cables up to each speed-controller (ESC) situated on the adjacent cantilever. We just need to add the TELEDRONE panels round the top-side prior to the airframe going down the line to the paint-shop.

I've omitted both flying-boots and underlay from the base of the transporter, settling for a simple plug that engages with Monty's left foot to secure. He's as unhappy about launching in 'Woodstock' footwear as he is to have no helmet tho' I point out it could be worse. Until recently he'd be flying in the buff, and as it stands he'll still be going commando.

Nothing new either about tailoring safety-cell to pilot like this. F1 driver Nigel Mansell used to need the toes of his shoes cut off to fit inside the cockpit, and I suspect he's not been the only one.

Half-Scale Build #95

We know how to assemble the transporter now, don't we, as it's all been done before during the alloy build? All I would say as you're fetching vaseline from the bathroom is that these three-way tube-connectors are two-part mouldings, and I recommend that those prongs with joins form shorter edges of the box, whilst the solid (seen here with logo on top) support each column.

Half-Scale Build #94

To my knowledge the only vehicles tailored to the pilot's height are space-capsules, F1 racing cars and my drone. Measure your test-pilot with a set-square and standing on whatever might be used as a base in the phone-box, like the leftover foam here. Note too how that resin-gauze repair will ensure that Monty's head won't fall off in flight ~ few people besides Henry VIII would want to see their loved one's head come off at Christmas.

Half-Scale Build #93

Here are the templates in place ready for drilling. You may wish to use a centre-punch on aluminium frames in particular, though I do so to take me back to those metalwork classes at school that I so enjoyed. Though he might not be with us any more, we thank Mr. Powell wherever he may be. Meanwhile back at the ranch I recommend that you warm the plastic frame up if it has overnighted in the garage, to suffer life's slings and arrows (and not least, drill-bits) more readily.

(When I trained to teach pilots in the simulator how to fly jet airliners, my instructor at the time had operated F-16s in Alaska, where cold made the metal switches so brittle that they would snap off at his finger-tips.)

Here too I cracked open a prop to make sure we've sufficient clearance. In case you're wondering too, there's always more clearance between a pair of props if they clear the centre-body, assuming you've used the rule-of-thumb that the centre-body is a third the size of the outer frame.

The propellers are lavishly packaged; something we owe a debt of gratitude for to the late Steve Jobs, who insisted every Apple product should be as great a pleasure to unwrap as to use. The propellers come with a velvet sleeve which looks uncannily like a Christmas willy-warmer, albeit for those of us with a 22" member.

Half-Scale Build #92

The easiest way to mount the motors is to create a template in either Word or Pages, and import a JPEG image drawn from the manufacturer's website. Here I've overlain a circle (in red) of the required diameter (30mm) to match the bolt-holes on the base of each motor, and sized the JPEG overlay to suit.

All that remains to do is to cut these templates out and stick them on the airframe in a way that matches the orientation of each motor. In our case we'll mount the motor with the wires facing the nearest cantilever, with two bolts through the airframe and two through the adjacent bracket: using our template to guide the 3.0mm drill-bit.

(Alternatively you may wish to spend £2500 and upwards on a laser-cutter to make a pattern in carbon-fibre sheet that can be fixed to the airframe, along with the motor.)

You may find that a slightly oversized drill-bit works better for mounting the motor, as the hand-tool is not as accurate as the power-pillar drill few of us have in the garage. In the past I've used a half-millimetre over-size and have yet to experience an in-flight separation of any sort. Use the regular bit first and then adjust whichever bolt-hole(s) are off-centre, rather than use an over-size bit at the outset.

Bored Meeting

At 16:00 I halt work on the factory floor and call a board meeting for an interim risk assessment. With my engineering cap on I get quite exercised, refusing to commit the lives of mannequins to 'Outer Somerset' in a plastic spacecraft which does appear to flex that bit more than 1/16th alloy. Flex is good, flutter is bad in aerospace and the drone is no exception and especially as it is scaled up. If the flight computer detects vibration that it tries to dampen and that vibration harmonises with its clock-speed, then it can exacerbate rather than cure the problem... like applying a force to a child on a swing too late, so as to speed it up rather than slow it down.

Any number of experimental electrical aircraft on YouTube show how many prototypes fly better with stabilisation turned off. The modern eVTOL is like an orchestra that is sublime when synchronised but unbearable when not. Unlike a concert orchestra, however, aircraft suffering 'divergent' stability are prone to break up.

As CEO with no hat on, I point out to myself that air transport at the end of the day is about 'bums on seats' even though strictly speaking we've no seat to consider. Were I Elon Musk I would have fired me by now, but instead we come to a compromise in the best spirit of Christmas present. We shall build a back-up rig of the same size but in alloy, to which we can transfer the electricals as necessary and have another go.

There is nothing new in this, any number of prototypes often accompanying the design and testing of aircraft (until relatively recently when it could all be done on computer). Wikipedia says no less than six Concordes were built for development and another fourteen intended for service, whereas nowadays there may be just one or two prior to several thousand entering service.

Interestingly Boeing's Dreamliner experienced problems with (a) a new type of battery (b) supply-chain issues related to rivets (c) new methods of working in carbon-fibre composite instead of aluminium alloy. Echoing that, our prototyping has also suffered from supply-chain issues delaying the mannequin's shoes, the process of learning with different materials and getting to grips with the lithium-based batteries.

I'll admit that issues of these sort won't be having quite the same consequences as the 737 Max had on Boeing's then-CEO, though.

In aerospace, small can be beautiful.

Half-Scale Build #91

Here's the bracket being riveted to the inside edge of the airframe. It is better for any overhang to be located inside the outline of the airframe as it makes handling, storage and transport that much easier. Be careful not to let the drill-bit impinge on the other side of the extrusion, however, as it is likely to crack and need patching. New material requires new methods but are worth the love and tenderness in the end; for example the new generation of airline cabins are a plastic composite and as a result are lighter and stronger ~ this in turn reduces fuel usage and provides a more comfortable cabin pressurised to a lower altitude.

Half-Scale Build #90

We're going to mount the motor four-square on the bolt-holes, straddling the airframe as well as a 1" angle-alloy. These angle sections come in plastic but I'll use left-overs for our build. A pain-in-the-ass feature of the U7 motor is the fact the axle appears below its base, which will need a shim or washer around the bolts to clear the frame.

Looking at the picture below I've flipped the motor over in order to trace the outline, as we'll cut the motor-mount to suit. These babies are going to run HOT according to the manufacturer's own data, which is why they're top-mounted to benefit from the downwash from each propeller. Notice that a pair of bricks prove ideal for the exercise and these were available from my local scientific instrument store ~ and always insist on PILOT marker pens for aerospace builds like this.

Note also what it says on the tin: a 280KV motor runs at 280 rpm per volt. This is the slowest running of the three U7 variants and designed to drive a big ol' lazy 22" prop at a lower speed but higher (and hotter) torque. The batteries we collected yesterday are advertised at 3.70 volts apiece and are likely to die if run down below around 3.00 volts, so you're looking at an operating range of 3.20 and 3.70 volts for commercial ops with passengers.

With the crash-test dummy (sorry, mannekin) on board however we'll be pumping iron in the form of 4.20 volts per cell... think TOGA on your Airbus with its ten minute limit. Therefore we've a total of 25.20 volts down the line, which is 1.20 volts over the 'book' figure for max thrust, our own Tmax. Thus 25.20 times by 280KV is a theoretical RPM of 7056, at which speed the propeller tips are turning at 462 m.p.h. according to back-of-the-serviette calculations: well inside the subsonic regime and the reason slower props run quieter whilst optimising thrust.

Half-Scale Build #89

The 36" rig weighs in at 2.10kg (4.60lb), nearer the mark for our choice of motors. The plastic deforms a little around the bolts but a bit of flex and deformation comes with the aeronautical territory. The 737s I flew often had ripples in the skin around the rear baggage hold (which is what they did) and the fastest jet in the shape of the Blackbird used to leak fuel at the seams.

The material is less forgiving than alloy when it comes to metal-bashing in the form of stripping and re-building prototypes, but then that won't be an issue in the fabrication of a beta-product. Meantimes prior to it's removal to the paint-shop (aka garage) we'll look at fixing the motor-mounts for those mighty 600w units.

Half-Scale Build #88

Sinclair and Rush have the three-metre extrusions delivered first thing this morning as it turns out Santa had dropped the previous down the wrong chimney. To optimise the use of these sections I've run with the 36" frame and 12" centre-body converted into metric measures, and you'll find the optimum procedure is to cut each length in half and then divide the remaining 1500mm into lengths of 580mm and 920mm apiece.

Thus two of the three-metre lengths will produce the entire frame, as seen here. One advantage of a switch to plastic, aside from the cost and weight savings, is that these extrusions come in white, which requires only a top-coat to render in Post Office red, or black which is suitable for drones 'as is'. In each event therefore we move closer to a consumer product.

The tube-connectors are a tight fit, nonetheless manageable for anyone with a rubber mallet and a tub of vaseline ~ stop the sniggering NOW please, not big nor clever. The M6 threaded tube-inserts to terminate the cantilevers are a push-fit but are unlikely to need reinforcing with pop-rivets. in fact there are nylon M8 inserts too, so that everything seen here could be 100% plastic. (Ed. If you think it's a good idea, ask your local turtle.)

Using a Mark 1 eyeball and averaging four measures, a 6mm drill-hole at 607mm from the end of each perimeter section (excluding connectors) should work. Meanwhile for the cantilevers, 310mm from the outboard ends (excluding inserts) works equally well. Plastic flexes even more than alloy, and therefore corrects any errors in measurement at the prototyping stage, where we are working to nearest millimetres rather than microns.

Christmas Wishlist

It's the time of year when the unsound of mind are trying to get a people-carrying drone built by Christmas. For everyone else it's about buying shit that their nearest and dearest neither need nor want, in order to celebrate the birth of someone who said that we didn't need anything.

Sinclair and Rush are on first thing to re-supply extruded tubes and agree to upgrade the order to three-metre lengths; such that I feel bad about letting them have both barrels to the chest with the TrustPilot review. They're a valuable partner not least for being US-based, where so many of the drones will ideally be marketed.

Overlander too pull out the stops to supply the battery-packs and fix connectors to the loose ends of the ESCs too, saving me the bother of learning to solder. Nearby I collect another overall for our standby mannekin, with a view to a pre-launch SpaceX-style team-photo with everyone suited and booted.

Meanwhile Santa's elves have left four 8mm GRP spars in the garage, which we shall use as the lightweight landing gear for our all-plastic, super-compact phone n' drone.

The principal inventory thus far reads:

(a)        Pairs of 22" props, 2 off.

(b)        80A speed controllers, 4 off.

(c)        800W motors, 4 off.

(d)        2900mAh LiPo battery-packs, 4-off.

(e)        Space-suits, 2-off.

(f)        Crash-test dummies (don't call them that), 2 off.

(g)        1000 x 8mm GRP tubes, 4 off.

(h)        3000 x 25 x 25mm plastic extrusion, 5 off.

(j)         Pair of flying-boots (ASDA not NASA), 2-off.

(k)        3-way tube-connectors, 8 off.

(l)         2-way tube-connectors, 4 off.

My mission now ~ should I choose to accept it ~ is to assemble all of these parts into a scale Star-Trek transporter able to beam people up whether with or without Scottie.

Raving Review

Who'd build a personal air vehicle, doing so over and over expecting different results?

Funnier raving reviews to appear on www.raving.reviews

Half-Scale Build #87

No surprise that arrival proved timely, DHL being operated by Deutsche Post in the UK, where if it works it's probably German. One problem with the kit-built people-carrier is that it is about where the PC was when Jobs and Gates sold stuff from their garage; user information being much like playing a game of Cluedo.

I last worked with larger U13 motors that came with stub cables, whereas this has the 'Full Monty' attached. There are (very few) motors out of there with built-in ESCs and you have to wonder whether things will go that way, just as computers once had pop-in circuit boards and no longer do in order that the average chimpanzee can use one.

Like the gaming chips that my son prefers to dad's shit, however, these things all run hot given the current and are finned like the motorcycle cylinders of my youth. We could park the ESC next to the motor and open that up to wire it direct, though that would invalidate the warranty. We could also mount them on the centre-section so as to conceal the workings in a fancy dome, just like those guys spending millions of OPM (other people's money) on speculative air taxis.

Pays at this stage to stick to the knitting tho' and mount the controllers some place where there's an ample draught from the propeller, which to my mind is about where I've put it ~ if in doubt, use a half-way point. Bear in mind too that these cables would normally run down the tubes, whereas that would be silly on a prototype. It's the reason Jetson took a whole year and a lot of money to prepare a vehicle for sale... and they recently flipped from a kit offering to an ex-works strategy, doubtless in view of the potential cock-ups in assembling something more complex than IKEA's MALM.

Whatever happens it looks like we do not need any extra lead-length on the batteries and in fact we've more cable than we need: an embarrassment of riches. We do need thought to know which of the finer control-cables is which, one being longer than the other. Motors and controllers used in robots or cars require a feedback loop that allows them to work accurately at lower speeds, tho' drones use one-way logic to let the motor do its thing. One of said cables is therefore redundant, but which?

I say Professor Plum, with the soldering-gun, in the Hall-effect.

Half-Scale Build #86

Whilst we wait for the kit for the rig to arrive we can draft the outline on the back of a Christmas wrapping-paper (Bah, humbug... best use for it). Then we can overlay motor and speed-controller, which come with stock lengths of cable attached, so as to work out what length of lead we would like on each battery pack.

Quadcopters are normally defined by the diagonal length between each axis, bearing in mind non-people-carrying drones fly with a prop at each corner. For anyone with a flying phone-box there has to be a more logical measurement that we can use to draft builds on the floor. Bear in mind this is what they did at yards in Belfast and Glasgow, which once produced a third of the world's tonnage of shipping... so don't knock it.

Accordingly we'll make the measure the square on which axes of motors are mounted: in our case 36". A reason for defining it this way is that it disregards the thickness of whichever tubing used in construction. Note the arc of the 22" propellers, which seem a good fit. The manufacturers actually do a super-light version of this carbon-fibre prop, which to my mind is like providing the option of lipstick on pigs.

One reason I chose U7 motors is they come with an optional prop-fitting using a single nut fixed on the axle. In turn it means we can run with wooden props if we choose, they being a fraction of the price and more forgiving. If we'd blade damage on the jet airliners I flew, the engineers would just sand them smooth. Rolls-Royce notoriously were bankrupted by an effort to switch to carbon-fibre, having to be baled out by that gift which keeps on giving... the tax-payer.

Battery Park

It's normally at four in the morning when sleep evades me that I draft these designs in my head, and consistent with this I fix upon the ideal arrangement. I'm unable to use the previous location (a bay within the top of the phone-box) because you'll recall to avoid purchasing plastic tubing in bulk we were limited to lengths of one metre each. This in turn means that there is no head-space within the box available to store the batteries as we wished.

Nonetheless this configuration has, if anything, more to recommend it:

(a)    6s packs of around this size come in a range of capacities and sizes

(b)    the weight is entirely centred and arrangement wholly symmetrical

(c)    it eliminates the need for a battery-bus or power distribution board

(d)    replacement costs are lower in the event of a single-cell failure

(e)    it uses little extra space because it surrounds the Pixhawk cube

(f)    everything remains top-mounted on the drone for easy access

(g)    which also means that the drone and box are closely coupled

(h)    the battery leads can be specified to required lengths to suit

Fortunately in Lancashire we've a supplier who assembles packs from individual cells, allowing lengths of leads to be matched to suit the implementation. We are unable though to proceed as yet until the airframe has been re-built and the motors and ESCs fitted, so that we can determine exactly what length of lead we are talking about.

The worst time to be doing all this of course is in the run-up to Christmas, during an Arctic freeze and any number of postal strikes... but it was Richard Branson who said the best time to start in business was during a recession, because nobody else would be stupid enough.

What we can do whilst we wait however is to recalculate the sort of packs we might need in view of size, weight and flight-endurance constraints. I've always been bigger on the practical build than the calculations and wholly moreso than the accounts, but needs must if all of this is to succeed.

Deathly Hollows!

Returned from the hardware store to find the test-pilot with his head in the oven and worried sick that the pressures of the project had overwhelmed the mannekin. "Monty, Monty!" I shrieked, but turns out it was a rapid cure for that operation to restore his fractured neck with a polyester-resin dressing...

Final Answer?

Weighing everything up ~ quite literally ~ I settle on the final build. For every prototype there is a point where a spec has to be frozen so as not to be chasing a moving target. Accordingly I decided to replace alloy sections with plastic to bring the gross weight to within the range that smaller motors (the U7) can be used instead of larger. This in turn lowers the operating voltage and allows for lighter batteries within a virtual circle.

The plastic is supplied in metre lengths or three; the latter requiring a bulk purchase. Accordingly the columns around the phone-box are reduced again to the former dimension. At this height either mannekin will fit and so I revert to the lighter. An impromptu X-ray reveals a severe neck-fracture, however, which needs repairing with a gauze dressing set with resin of the sort sold at auto shops... a simple procedure that need not require a suspension of flying duties.

Meanwhile beside plastic another order has gone out for equipment to motorise the prototype i.e. four U7s and 80A ESCs, plus two pairs of 22x6.6" propellers. A perusal of the performance on the manufacturer's site shows that this largest of the available propellers for the motor in question rotates slowest and draws the lowest amperage, whilst producing much the same thrust.

Larger diameter propellers provide disproportionate improvements in performance ~ a helicopter being around twenty times more efficient in the hover than a Harrier jet for instance. Nonetheless the U7 motor clearly struggles with the torque required to turn the 22" prop and while operating temperatures are quoted for smaller sizes, this one is recorded in the table as simply being HOT.

Nonetheless we'll be pushing those babies to the max, for as the late Colin Chapman was prone to say at Lotus, the ideal Formula One racing car is one which falls apart when the race is finished.

Now if you'll excuse me I must get scrubbed up for an operation...

Half-Scale Build #85

Here's the battery-bay, with which I'm well pleased. Note the packs are wired in series and the remaining terminals will connect to the battery-bus (power distribution board in drone-speak) and from thence to the four electronic speed controllers... and that's PDB and ESC for the three-letter acronym (TLA) fans amongst you. Under no circs join those remaining terminals together; as I have done twice, discharging all the available energy in a facial-hair-singeing-singularity.

In production transporters the battery bay will be lined with a firewall and there'll be an associated drill to execute in the event of BATTERY BAY OVERHEAT master caution. Though any fire is directed away from the crew, if it proves uncontrollable there's a FIRE, SEVERE DAMAGE OR SEPARATION drill (and should it fail you'll release the floor and bale).

Whatever they say, electrical aircraft crash and fail like every other. It's a forewarning that was associated with every new form of transport up to and including RMS Titanic.

Half-Scale Build #84

As I cannot get the stock brackets I need, I've made four using the angle-alloy. This is the dome of the transporter and notice that I have set it roughly in place before fixing the brackets, as it's a one-way operation and won't be removable subsequently.

Half-Scale Build #83

We need to drill a three-quarter inch hole, which can be a fairly violent operation with a hand-drill... plus of course we are adapting as we go along and therefore none of it is being done in sequence. In the fulness of time anyway this will be plastic or carbon fibre sheet that can be laser-cut anyhow. In the interim however I've clamped timber off-cuts either side, which takes the sting out of these super-sized drill-bits.

Half-Scale Build #82

These inch-alloy brackets will help to secure the packs in place. Ordinarily they would be strapped down with Velcro too, though that should not be necessary here.

Half-Scale Build #81

We embark now upon the battery bay, and here's a bit of scrap sheet that already has albeit over-sized cutouts for the columns at each corner of the transporter. Now mark a border around the packs ~ these are stock six-cell LiPo batteries of 22,000mAh each. In view of the fact they will be wired in series to produce 45v, that rating is the final figure for calculating the flight time.

Half-Scale Build #80

I've had to adjust the height of the flight-deck to suit Monty, here demonstrating the boarding sequence ~ firstly inserting its forward half before lowering it into the locked position. Turns out that we can fit the assembly within the outlines of the transporter after all, which is a bonus.

The adjustments do though highlight the importance of having the booth tailored to your personal physique, though a 'Pret-a-Transporter' range will be available off the peg. We do recommend the services of one of our accredited tailors in Savile Row, for customers unable to upload a 3D scan.

Consistent with this philosophy the booth may be fitted to height requirements, Monty choosing to fly in a relaxed forty-two inch number... "Suits you, Sir!"

Half-Scale Build #79

With sub-zero temperatures in the workshop some elements of the build have to be conducted indoors, where I've set the temperature to a balmy 14°C. I've also recalled Monty to test-flying duties, which he gracefully acceded to.

He has insisted on a number of conditions, one being the restoration of a flight-deck-come safety restraint. He also requires a dual side-stick option, which will involve an extension to the front half of the restraint. This time however we shall retain it inside the outline of the transporter (aka phone-box), as it makes for easier handling beside providing the opportunity for all-round glazing.

I've used two lengths of sixteenth-inch angle alloy with cut-outs to accommodate the columns, at the same time countersinking the 9mm ply in order to accept 12mm rivet.

Weight Loss Program

As a part of the weight-loss program that caused the unpleasantness featured in the previous post, I turn to managing the materials... and something of a relief. Arranged here are samples of 1.20mm plastic tubing, beside sixteenth inch, 1.20mm and long-abandoned 2.00mm alloy sections.

1/16" is easily remembered as it is equivalent to 1.60mm, the gauge I have chosen on past experience and because of its glove-like fit into the tube-connectors. The sample plastic is well up to scratch in all departments, however, and on a like-for-like basis is exactly half the weight. Plastic sheet is likewise less than half the weight, so that if we were to build entirely in plastics then the advantages would be spectacular.

Nonetheless I decline to do so at this stage for five reasons:

(a)    Have bust my ass on producing the current prototype

(b)    Extra weight compensates for its lack in the mannekin

(c)    I refuse to spend the extra cash

(d)    Regulators are in love with alloys

(e)    We flew them successfully prior.

Nonetheless I make a note to self: this will be the way to go with full-size iterations in future, and perhaps beyond.

Still unimpressed with the carbon-fibre that so many others feel obliged to use so as to be taken seriously. Plastics and alloys bend but rarely break, like me.

And palm trees.

The Apprentice

In the Captain Kirk lookalike section of. the test-pilot screening program we had to let Monty go, on one of the hardest days of my life. When I pointed out he was overweight and that Kirk lacked prosthetics regardless of diversity policies, he photo-bombed our latest PR shoot. I told him that all the tech companies were struggling at the moment, but he didn't take it at all well.

Monty worked his way up from the window at Mothercare to attend the Empire Test-Pilot School before joining us at Teledrone and training at the Baikonaur cosmodrome. As CEO I thanked him for all he'd done for us, and presented him with his belongings in a black bin-liner.

Weight Loss Program

Mannequins meet to debate the drone 

As part of the effort to reduce the planned gross weight of the scale model for testing I visit the UK's largest repository of retired mannequins, which is itself something of a YouTube sensation and in fact is so large as to occupy a fair proportion of what was once RAF (and USAAF) Fulbeck. There was naturally some debate about the pros and cons of sending a juvenile into what for them must seem like space, but following an impromptu board meeting I was given their blessing and sent upon my way. Possibly though the worst case of manspreading I've yet to witness.