Weigh-In

20 kilos on the spring balance, with the weight of the eight speed-controllers added. At 44 pounds that's around half of my original estimate for the mass of a competition airframe.

With jet-packs and parameters weighing in anywhere between 25 and 30 kilos that leaves us around a further fifty percent or 10 kilos to dedicate to battery-packs.

My guess is that isn't going to get us far, but getting us safely airborne represents first base.

Build it and they will come.

Step Away From The Vehicle

There was a French philosopher who once said that anything looked at for long enough appeared absurd... might have been Marcel Duchamp?

When designing though I always think it's wise to step away from the vehicle overnight and look at it with fresh eyes in the morning. Paid off here because returning to the garage today I've grown used used to those eight legs and trying it on it's comfortable to walk around in.

In other words, it works ergonomically. What I've had to devise today is its ground-handling routines, because (a) those carbon-fibre propellers are sensitive as shins and (b) there's enough weight in the airframe to put your back out if you lift it without the right technique.

In that vein it is altogether easier to mount it on the tailgate for transport instead of the roof-rack. Having adapted the spare wheel mounting (an idea I've returned to a few months on) it's good to see that only the lowest pair of propellers require ties because the others rotate freely within the road-legal span of eight feet.

The airframe span with the rotors stowed as above is just 4 feet and 8.5 inches, whilst with the propellers freely-rotating their farthest tips span only 7 feet and 4 inches.

Four Legs Good, Eight Legs Bad?

Learned a lot here about airframe geometry and the mounting of motors, beside the practicalities of ground-handling.

Looking at it now though I could go yet smaller and lighter, but that might be deferred until after power-testing with this one here.

Hard to say whether these eight legs offer any thrust-advantage over four mounted with paired propellers, but without setting both up on a test-rig then it's anyone's guess.

Certainly light enough to wander around in, and the ESCs are unlikely to add much weight.

Batteries will be something else though, but they're a job for another day.

Motor-vation

For reasons too tiresome to enunciate I've had to modify the engine-mounts to my liking and this has involved reducing the rotor-arms by four inches along with the associated clearance, although the tips still stop short of the flight-deck (which has yet to be armoured).

It reduces the airframe span to four foot eight and a half inches, which spookily matches the railway gauge on which the original passenger rail network was based (starting right here between Liverpool and Manchester).

Happily the potato-and-paint template method for centring the drill-holes has worked a treat, or at least on this first motor to have been mounted. I shall hold it there however on this fine evening which marks the start of the August holiday weekend in the UK. Experience has taught me to tackle precision jobs with a fresh head.

I have chosen too to modify the geometry with which each set of rotors is to be mounted viz. those on the lower quad will remain upright as seen here, while those on the upper rig will be inverted.

This creates a mirror image that minimises the depth of the airframe whilst maximising the vertical spread between propellers, obviating any chance of their blades colliding no matter under what duress.

Engine-uity

Inspiration comes from the unlikeliest sources.

With the engine-mounts affixed, the thorny question of how to mark up the centres of the holes for the retaining bolts?

I achieve this by the simple expedient of dipping the base of a motor in a coat of paint and embossing a piece of paper with it, as seen at the ends of the rotor-arms here.

Something I last did around fifty-five years ago shortly after starting school, except with half of a potato.

Didn't imagine back then that I'd be using the same technique to build a flying machine.

And there was me thinking my education was wasted?

Alloyed Joy

Gives us a better idea of the layout, but basically two quads one of which is inverted and stuck to the bottom of the other to provide eight arms on which to mount motors and rotors.

Been fairly plain sailing as indeed it should have been in view of the fact this is the sixth frame of its kind that I've assembled. As a result each iteration has got altogether lighter and faster to build.

The central aperture is such a tight fit that ~ as it stands ~ it is too tight a fit, which is a variation on building the boat that's too big to get out of the workshop doors.

I'm confident it'll fit by tomorrow however as I think the issue is friction, with the foam filling in this sandwich construction being somewhat rough prior to a lick of resin.

It ought to fit anyhow because it's based on a template I tried on for size repeatedly only yesterday (although admittedly I dined handsomely last night).

I've designed aeroplanes in the past so small that you needed measuring for, but this may yet be the world's first 'bespoke' helicopter.

Third Time Lucky?

Been preoccupied by life's preoccupations, which I recall one of the webinistas warned against in the pursuit of projects such as this.

I keep coming back to the wearable, which is telling because most inventors succeed at whatever it is they keep returning to, guided by gut feeling.

With eight rotors to mount on the airframe the only question is as to whether the beast is to be four-legged or eight i.e. do we colocate the eight motors in pairs one atop the other or else provide eight separate cantilevers?

The airframe is made up of two identical modules like the one pictured above, with the proviso that the lower is inverted to produce that extra set of legs.

I mock that second set up in part as seen so as to convince myself that the tips of the upper four propellers rotate clear of the motors belonging to the lower set, which they do by about a half-inch. Clearance between those tips and the edge of the flight deck however is nearer five inches... a big improvement on the minimal clearance offered by the the larger diameter propellers considered at the outset.

Been a good day in the workshop although it didn't really kick off until mid-day. The hardest part of all such enterprises is ~ as with much else in life ~ merely getting started.

Zee-Day Landing

The great French novelist Marcel Proust tells in his masterpiece A La Recherche de Temps Perdu of how he was moved to tears whilst walking along the coast of Normandy by the sight of an aeroplane, then a form of transport in its infancy. Reporters tell a century on of how Franky Zapata was moved to tears after accomplishing this ~ the first crossing of the English Channel by a jet-powered personal air vehicle.

There is probably no more significant stretch of water in the world to establish historic feats of aviation. After the Wright Brothers first flew, it was on this side of the Atlantic between the efforts of Germany, Great Britain and above all France that the aeroplane saw the most rapid development. This was accompanied one hundred and ten years ago by Louis Bleriot being the first to pilot one across this twenty-two mile stretch of water.

So this changes everything, and were we to replicate the crossing by electrical rotorcraft we'd be standing on the shoulders of a giant in the shape of this man; for buried among the press reports came the revelation that he lost two fingers to a turbine while flying the prototype.

Which brings to mind Otto Lilienthal's final words, of how "Sacrifices have to be made."

Part 103

"When a man knows he is to be hanged in a fortnight, it concentrates his mind wonderfully."

Or so said the celebrated Dr. Johnson. News from the organisers of the GoFly challenge that they have a pair of FAA retirees on board in order to guide entrants through the maze that is aircraft certification.

Actually the United States' Federal Aviation Authority is more liberal than most when it comes to defining 'ultralight vehicles', which fall into Part 103 of the regulations.

For it now appears (with a submission required by the middle of the month) that I must definitively specify the location of this airframe around my own frame. Fortunately after arranging it like this on a Saturday evening, the mental mist began to clear.

That's one benefit of the rules and timelines of a competition: they focus the attention.

Another quote from Leonardo Da Vinci, in this context: "A small room concentrates the mind."

I've always been impressed by designs that minimise the outline of a product, and I see now how the means of getting airborne could be reduced to a cipher.

Watch this space.