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.

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.

Bleri... Oh!

One hundred and ten years to the day since Louis Bleriot flew the English Channel, the remarkable Frank Zapata tries on his jet-powered 'flyboard' but sadly ditches during a refuelling event.

It's only good news however because (a) it IS going to happen and (b) he has a military contract already.

Thus inspired I re-examine the prospects for using what we have in hand to test-fly a foot-mounted drone, seeing as they're all the rage.

Actually a mock-up in the lounge here suggests the prospects are pretty good. It'd be a whole lot easier to build as a simple quad, but lacking redundancy would suit it only to ground-effect operations (for which I've always been convinced there's a market).

The upper-deck is hollowed out ~ because I can ~ and the pair of decks will be separated by tie-rods again just sufficient to provide clearance to the lower set of propellers.

Ideally the upper set of propellers are better under-slung for reasons of safety, but for the test-flights at least we might as well run with the simplest configuration and mount on top.

First time as well that the motor's been anywhere near the frame, and there's nothing like arranging parts in this way to accelerate progress... and this is beginning to look like a flyer.

And although modelled here with the half-scale mannekin, this same airframe fits me too.

Umpteenth Build, Half-Scale #3

This is going to be the end of me.

Too much torsion and looking at it am not at all surprised. The classical way to build a fuselage is using stringers, longerons and a stressed skin and this is missing the latter.

Strength in compression however is remarkable and mainly thanks to that stay at waist-level that is slid into place like a pair of trousers... there's around twenty-seven kilos up top and barely a bend in eight millimetres of tie-rod.

There may yet be an argument to say that the torsion might not matter when it comes to flight. Anyone who's sat at the back of a 757 will have noticed the twisting along the length of the fuselage, or seen the belly of an overly-stretched DC-9 buckling under the load over bumps on the taxi-way.

Or indeed wings, which are able to flex in the case of the 747 over an arc of thirty-five feet.

Problem is, lacking the software the only way to find out is to get it airborne and that's a long way to go down what might be a dead-end.

Umpteenth Build, Half-Scale #2

Tie rods in place. These are M6 threads and they run through the depth of the lower-deck or 'landing module' as I like to call it. I've drilled these without a power pillar, so am pleased that they run generally true.

In a perfect world all those surfaces that they penetrate would have been drilled en-bloc so as to line them up precisely, but then hindsight is a wonderful thing.

These rods will support the upper quadcopter or my 'command module' and enroute they will pass through a stay worn around the pilot's waist that stops them from bowing unduly.

Umpteenth Build, Half-Scale #1

I've gone for a mannekin a little under a metre, which (like the motors, propellers and ESCs) has travelled all the way from China.

Its steel pediment will do fine 'as is' measuring as it does ten inches square.

The tie-rods I bought locally are too short so I've ordered 2000mm M6 rods online.

Never thought I'd ever be ordering clothes for a mannekin online, but I've gone for an olive green flying-suit instead of the red, along with a full-face helmet.

(At least it won't be needing the school fees.)

I need to take him/her with me to a shoe-shop for a pair of boots, which will doubtless label me in perpetuity as the local crank.

"One Small Step for a Mannekin...

One... giant leap for mannekind."

For this is our moon-shot. And not many people know this, but the first man to orbit the moon was not Michael Collins but a Russian mannekin accompanied by two tortoises. The latter were dissected upon return to Earth to see how well they had survived travelling a half-million miles through space. Very well, apparently, or at least until the dissection.

In ways that Neil Armstrong was to benefit from turns of fortune in being the final selection for commanding the first lunar landing, the mannekin here passed the albeit more hurried selection by dint of the fact that our engineer's wife had run out of the 1.20 metre models. The one here therefore represents say a five-year-old child rather than a seven-year-old.

The mannekin commented at the press-conference: "I'm delighted to have been selected for the UK's effort to get people airborne in a flying phone-box and although my own piloting skills will not be called upon as were Neil Armstrong's when 3000 feet above the lunar surface, I have every confidence in the automatics."

And with this he/she was escorted off the podium in order to get suited and booted.