Pound for Pound?

In many ways the development of eVTOLs re-visits that of the PC (which itself evolved into the smartphone), in that both the data and equipment are becoming integrated. So whereas you once had to build computers out of components and find out as you went along how to put them together ~ whereas now it is all on a plate ~ slowly the technology behind multicopters is beginning to be rationalised in the same way.

Which makes it easy for dummies like me and you. Accordingly here at the outset I've  approached things in a scientific and disciplined manner, which is a personal first.

The above selection of motor, propeller and speed controller provide around 26 kilos of installed thrust at a throttle setting of 60% according to the data. Thrust settings of that sort are what are required to keep something 'in hand' with which to address the contingencies of both steering a trajectory as well as engine failure.

This amount of lift happily accords with what is broadly becoming an internationally recognised limit to the gross weight of drones before things get more complicated to register i.e. 25 kilos. This in turn means we can build a sizeable scale prototype, and subtracting whatever its airframe weighs from that figure yields a theoretical payload.

Budgeting for development ~ again a novelty for me ~ is key to progress, however, and so it pays to build the airframe prior to shelling out on the motors etc. Happily we can now do this, because having the diameter of the propellers we can refer to the post of 28th October so as to draft an outline of the drone itself.

Above us only sky?

Let's explain the rationale behind this.

Prior to the introduction of the jet-turbine, helicopters did not have the option to mount the motor on the roof, where with the exception of the Robison R66 it has remained ever since. The object lesson of helicopter design throughout its evolution is therefore that (a) the ideal place for rotors is the overhead and (b) the ideal place for motors is the overhead.

People-carrying drones, however, don't come awfully light. This is principally because what you have gained in terms of weight-savings from the power of electric motors, you have generally lost in replacing high-density fuel i.e. kerosene, with battery-packs.

To support a sizeable drone at two metres you would therefore need a substantial structure (phone-box as originally conceived), besides an extensive undercarriage to stop it from toppling.

The 'method and means' above solves each problem at a stroke.

At the same time it preserves a unique selling point ~ ours a flat-pack flying machine and yours not ~ because the columns can be inserted individually into the base from above, through the four channels in the drone included in its centre-section with that in view.

Expert UAV builders caution that the drone will be insufficient manoeuvrable in view of its low-pitched centre of gravity ~ but by and large we have progressed more often with expert advice having been ignored, than with it having been acknowledged.

Let's start building.

Re-Boot

As personal air vehicles go as distinct from flying taxis, there's currently only one game in town and that's Jetson, who've done for Sweden what Spotify did earlier and proven that everything need not necessarily emerge from California... just most of it.

After a four-month break whilst I needed to step away from the vehicle, I've had to ask myself what counts? What's in the DNA?

And the conclusion I've come to is that it has to be about moving people a shortish distance in three dimensions in the simplest superstructure possible, by using wholly unique home-grown means. I don't believe that you succeed by copying everyone else in the longer term, and that goes for products as well as it does for personalities.

So we'll take it from the top ~ literally ~ and draw upon the rich inventory that is the WIPO patent specification and in particular, this configuration for eight or more rotors.

Electrical air vehicles have been something of a fool's errand, as they looked like they could replace the main-rotor of helicopters at a stroke. They did so on the shoulders of drones, which got away with as few as four maintenance-free means of lift at each corner.

What distinguished the develop of drones and subsequently eVTOLs was the fact that the majority of people involved had never been (nor intended to be) pilots. And when it comes to life-or-death scenarios like engine failures, it's the gladiator in the arena that counts and not the spectators.

As a consequence, the number of motors on practical multicopters has proliferated, and as things stand eight is the minimum for entry to the ball.

Why though abandon the X-8 configuration of over-and-under power units used by most commercial drones and current eVTOLs? Well the estimates for the losses of aerodynamic efficiency involved I have heard range from an eerily precise 14% to T-motor's own estimate (or warning) of as much as 25%.

And that's far too much power to trade at the outset.

The advantage of the outline above however is that it continues as a simple four-point proposition, with pairs of motors addressed as modules that I'd describe as cassettes as they relate to two rotors, or bogeys where they are attached (over-and-under) in a set of four.

The only addition to the configuration as originally conceived are those torsion bars around the perimeter, pictured in black.

The dots featured at each corner of the centre-section we'll investigate anon.

I had intended to discontinue this blog ~ Jetson thriving without one ~ but relented as the stats disclosed a consistent readership. If you're reading this, then rest assured you make a difference.

60" Build Step #40

And take a picture. Whether it would be anything either you or I need let alone anyone else, given the parlous state of the world, is moot, for few of us after all are anything like Richard Branson and his need to flit between one of his Caribbean islands and the next.

But then it is what it is, and I'm proud to have brought it this far.

60" Build Step #39

Mounted this on the flat-bed at four points, not unlike the twist-lock system on your freight container, and lifted on inverted from off to one side. Could do with rails so as to slide it into place and save my back, particularly once there's the weight of motors to consider. Also an argument for the 36" props and a frame nearer 52" than 60", but this will have to do for starters.

60" Build Step #38

Here's the power installation, and for the final cut I've made a facsimile of a Fullymax 12S pack of 5600 mAh that is normally used for RC helis, but which we may just get away with here. It is the type that includes a pair of six-cell packs sealed end to end, so that the cables would appear from the right in the picture.

From thence they power the ESC, which in this case is a facsimile of the Flame 180A that we've used before in test-flying. From the right-most end of the ESC, therefore, the batteries connect to the underslung motor.

Am pleased with the (wooden) mock-up battery-packs, as they represent a first foray into shrink-wrapping.

60" Build Step #37

I re-fit the looky-likey motors and take the opportunity to correct the fact the props all appeared to have been running in the same direction.

The control logic we're using was likely the very first applied to quadcopters, it being most straightforward. It is no longer in common use among model drones, it being aerodynamically sub-optimal as speeds increase... racing drones therefore invariably feature 'X' frames instead of '+' types like that here. Nonetheless design of people-carrying drones is invariably a compromise, so I've pursued operational practicality and cost-efficiency over speed.

What you see in the picture is still not entirely correct as the clock-anti-clock-anti sequence seen in the inset is generally viewed from above, and this is the underside of our drone. Yet something else you learn quickly in this game is that the perfect is the enemy of the good.

We've just the look-and-feel of the electronic speed controllers (ESCs) to contrive and then this baby's good to go, for PR purposes if nothing else.