Friday, August 23, 2019

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.

Wednesday, August 21, 2019

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?

Tuesday, August 20, 2019

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.

Monday, August 19, 2019

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.

Sunday, August 4, 2019

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.

Friday, July 26, 2019

Final Frame


End-of-week round-up July 26 2019, and 'Houston, we are looking good'. I want you to imagine seven more power-plants affixed to the above, three more to the lower quad and four to the upper.

For the technically-inclined (and in Imperial measure) the spars are 30-inch by 2-inch by 1-inch by 1/16th, the props 32-inch, the deck 12-inch square, the aperture 9 and 1/2-inch and finally the depth 8-inch (not including the upper set of propellers).

The weight of the basic frame alone is a little under twelve pounds and still too heavy so far as I'm concerned but this will do for a proof-of-concept. The 'wearable' single-deck drone I featured months back weighed just over eighteen pounds, so I've added a further deck and four more rotor-arms and still reduced the weight by a third.

As the load is now spread too over eight arms, there remains scope for lighter alloy sections without reverting to carbon-fibre.

I've run with the simplest arrangement for test-flying though there are two variations to test longer term viz. (a) the decks could be spaced farther apart and the upper set of propellers under-slung instead of over-slung and (b) the upper frame could be inverted to provide an eight-pronged layout when viewed in planform.

The frame is modular in so far as the upper 'drone' can be detached from the lower, and in theory any number could be stacked. The principal problem with 'stretched' airframes of this kind is the increasing torsion, which requires fitting side-panels to act as shear plates.

The mannekin represents a half-scale though the frame will accommodate myself for test-flights. Realistically a commercial version would sub T-Motor U15 motors for the U13 type here (along with 40-inch propellers instead of 32-) yet still remain inside the dimensions of the GoFly competition.

For the record the axial distance between hubs is 48-inch and adding the 32-inch for the arc of each pair of propellers produces an 80-inch span. For roof-rack transport however the propellers can be stowed parallel to lie within the foot-print of an automobile.

We should be moving toward power-plant fitment and shakedown testing in the near future with tethered flights beyond that based on a 48-volt ground-power source.

Thereafter we have to return belatedly to Voltaplex with a spec on the LiPo battery-packs for free flight. My preference is for batteries to be body-worn in a back- (and/or front-) pack so that they can be tailored for the mission, as with current commercial jet-packs.

For the pilots among you the flight-control configuration is likely to call for the lower set of rotors to provide yaw plus collective with the upper set restricted to direction, and initially commanded by standard remote-control hand-sets (whether from base-station or onboard).

I am confident moving forward that the configuration as seen can be made to fly, and frankly having examined every other variation, it's going to have to as I'm betting the farm on it!

Finally to anyone thinking of designing an eVTOL, my advice is... don't.

Ever since Sikorsky helicopters have needed a big rotor on top and a smaller one on the tail, but with electrical flight nowadays that's gone the way of every other Cold War certainty.