A Bridge Too Far?

With motors mounted topside, in order to separate mannekin and machine I'd started to construct a 'passenger deck', or at least before discovering that an inverted Pixhawk controller looks like a flyer. As a result the electronics will be fixed to the underside of the deck which occupies the original frame, and less is more when it comes to design.

As a consequence we're still on target for initial test-flying this week, ahead of the anniversary of the previous at Llanbedr (which in turn was around a year after the first prototype flew back in 2019). Third time lucky, then?

The project has thus evolved from a passenger-booth will eight propellers overhead to a 'wheelie-bin' with four at foot- and  four at waist-level, eventually to that seen here:

https://www.teledrone.com/drone.html

Altogether simpler, but also altogether more promising as a practical kit-built craft.

Known Unknowns

A 'known unknown' connected with design and build of large drones ~ I'm informed by those who do it for a living ~ is whether or not the airframe is suitably rigid. Without this the danger is that torsional effects or those of resonance might mean the flight controller (Pixhawk, orange) cannot be tuned for stable operation. Resonance has long been a bugbear in development of rotorcraft, however, as has flutter in fixed-wings. In the long-term though there is usually no reason why each cannot be ironed out.

For the choice is to what extent people-carrying drones are designed to use what are effectively analogue control means like weight-shift for steering, or digital. Helicopters for instance are fixed in the hover by the pilot, whereas drones do so using a GPS fix. My preference at the outset however is to err on the digital side because for one thing it is going to continuously improve, and for another it is the way the world is headed.

I've just read Test Gods, the story of the development of the Virgin Galactic spaceship that is to all extents an aeroplane that isn't air-breathing. The author points out that it was effectively designed as such by Burt Rutan, whose specialism has been innovative types of aeroplane. Nonetheless the same author points out that in the race for space it is likely to be bested by both the SpaceX and Blue Origin rockets needing no human intervention and which both launch vertically and (remarkably) land vertically utilising computing power alone to do so, and all in place of pilots.

So do we have much of a choice, especially in view of the fact that the prototype at sub-scale has to be flown by remote means?

Not really.

Studies in the Quad

It is technically the centenary of the configuration next year, it having been pioneered by a Frenchman in 1922 as a diversion from inventing the stroboscope. A feature of the earliest experiments in aviation is that they were developed by polymaths like Bell, or another way of putting it would be to say that every inventor is drawn to trying their hand at a flying machine sooner or later.

What is different with electrification is how much easier it makes for inventors like me to envisage something altogether simpler. The outline you see in the previous post can be built to raise an adult using as few as a dozen structural members besides the pair of landing skids. Count the alloy tubes required by this quadcopter from 1958, and be amazed at what electricity can do.

Choice Platter

With work set to commence this week a decision has to be made as to whether, with only four propellers instead of eight as is planned at the outset, the motors should be underslung or mounted upright. I've always preferred the latter for good practical and operational reasons and instruct (plead, beg, petition) our contractor accordingly.

In order for this to work ergonomically too, that platform on which the dummy is sat is going to have to be extended to all four corners of his world. This is going to need to be done with some form of perforated sheet or grille, which is where the outside dimensions (of broadly four feet by four) prefer advantages, as most material like this comes in sheets of four feet by eight.

In the absence of stock material too there is also the option to go down the laser-cut route, which would also provide for all sorts of intriguing options like branding. In all events though the separation of the payload in this way means that the drone itself can be built and tested wholly independently, which is a rarity in this game.

Bring it on!

While We Wait

This appeared on YouTube two years ago under Heavy Lift Drone Project, and there is invaluable information on the wiring emanating from T-motor's ESCs, which like much else from China comes without documentation of any sort. The project is significant in two different ways, in that for one thing its demonstrates how the most obvious way to construct a very big drone is merely to scale up a smaller (which is not necessarily ideal); and the fact that the videos dry up prior to us ever seeing it flying. Tough game, eVTOL, and best avoided. Except like much else in life, it's discovered after the fact.

Drone Delivery

Our test-pilot Monty the mannekin remains silent on the journey South, cognisant of the fact no doubt that the next vehicle he is set to travel in is an experimental drone. Thought I was doing well too until I drew up behind a Land Rover pulling a trailered... Spitfire! And I never knew the wings came off, but there are pictures out there proving it.

The prototype's with someone who gets large drones flying for a living, whom we wish well. My friend and colleague in the US has eight broken propellers along with broken body-parts stemming from recent experiments with air vehicles of this size, and so no-one here underestimates the challenge.

Though as Anais Nin said, "Life shrinks or expands in proportion to one's courage."

We're not expecting news next week however, seeing as the same magician is involved in trials for experimental drone delivery on behalf of the National Health Service. But it is around a year since our test-flight in the hangar at Llanbedr, in whose aftermath the prototype as we know it, Jim, took on its present shape.

A recent visit to the Army Air Museum nearby was enough to convince me that early development of the helicopter was by no means smooth, which people often forget. It is a feature of technological progress that we come to imagine that everything we take for granted in the modern world was always as reliable as it now appears.

But we are, as we both agreed before leaving him to it, pioneers.

Battery Park

Have to draw a line under the construction phase and this is it, with the battery-packs arranged on the flight deck and situated beneath the seat (whose locator lugs and tie-downs can be seen around the periphery). For flexibility during flight-testing the inner packs can be removed if the flight control computer is to be fixed top-side, or with it fitted underside the inner packs or all four can be used. But I need closure, and this forms the basis of a practical air vehicle, if only for flight in ground-effect in the first instance.

True, Grit.

Proj is set back by over a week due un-forecast events viz. the monsoonal rain the drive South was subject to last Saturday meant that the spray from the road surface infiltrated every part of the machine. Beside the electricals this included the motors, which ingested the grit at the same time. The whole circus had therefore to decamp, as the chances of a motor shorting out and the disastrous effect that this might have on the batteries could not be countenanced.

Lost the battle but not the war therefore, and back at the workshop I turn the setback to advantage as ever with a few mods. Principally they involve dropping the seat lower and ~ while leaving battery-packs under the seat ~ reverting to attaching the motors and propellers to the underside of the frame. The 'bed-knobs' I leave in place so that the machine is easily inverted to accommodate this fitment (whilst also protecting the angular foot-rest during the same procedure).

The paint needs touching up, but that's the cherry on the icing. Important thing is that the finished article will look slicker. I tried suspending batteries below the flight-deck too, but decide against it. Basically anything heavy such as batteries are altogether harder to suspend than say the avionics. And whilst there are not many machines out there with underslung avionics, there's nothing quite like trying and at the same time I'd like to see if the computerised flight-controller works inverted.

The way that things are made needs constantly to be addressed so that costs are kept to a minimum. The Apple laptop I'm using was designed so that its components could be dropped into the frame from above, eliminating the detachable underside featured on every inferior device prior... and that's design for you.

Weight of what you see in the photo incidentally is just 14.80 kilos all-in.