Riveting Stuff

It's problems beyond the workshop that often prove the most troublesome, and today I'm driving back and forth in the rain trying to find a pop-riveter that works. The previous tool from an auto shop still pulls, but the nozzle for 5mm rivets has one jammed inside that won't dislodge.

Having graduated at Sheffield ~ a town which perfected steel ~ I decide to spend £32 on a British-made riveter that falls at the first fence. I return to the auto shop to spend five times less on a replacement riveter of the first type, which I see has a lifetime guarantee anyway. 

Plus it works admirably... was sure that pop-riveting was supposed to be fun, and so it is.

The rivets are 5mm by 50mm on the shank and I've used a 4.9mm drill bit and run five-a-side, inspired by my love of football. Thus from the far left of the bonding-plate I've punched at 6, 16, 26, 36 and 46 centimetres.

While all this is going on the first commercial spacecraft to have docked with the international space station is set to re-enter Earth's atmosphere.

If there is anything to inspire us to get out into the rain looking for rivets, it is the fact that NASA is relying on one private individual in the shape of Elon Musk to deliver astronauts.

So building a personal air vehicle in your garage can't be that difficult really, can it?

I mean, it's not rocket science.

GA's Spiral Dive

Include this as it's a thing of beauty so far as I'm concerned: six-inch PU foam infill dropped down to two using only a wire camping saw, wood-saw and hand-held sander.

Break off early for a webinar from the GoFly organisers that features the head (?) of GAMA. These talks kick off around 11:00 in the morning EST, coinciding nicely with tea and cake time in the UK.

Context: have been flying all types of fixed-wing aircraft off and on for the past four decades or more and turns out I'm a dying breed:

(a) average age of GA airframes is around 50 years old

(b) average age of pilots of above is rather older

(c) GA movements in the US practically halved in 20 years

(d) fatalities are flat-lining with over half due loss-of-control

(e) 75% of same stubbornly associated with pilot error

eVTOL will improve every count, and once I demonstrate how easily and cheaply they can be designed, built and flown then they'll be common as sparrows. Or commoner, for like most wildlife sparrows are dying out faster than general aviation.

I pose a question in the webinar, asking how the FAA plan to prevent unregulated use of piloted drones when the price falls fast like that of model drones. He's aware of the issue and compares it to electrical scooters, which have proliferated worldwide and broken both bones and fellow pedestrians in the process.

As a teenager I witnessed the circumventing of rules defining 'moped' by the Japanese, so that they could produce geared 50cc motorcycles on the same terms.

This killed so many sixteen-year olds around the globe that it showed up in mortality stats.

We have therefore to balance ~ as ever we've had to ~ the benefits and dis-benefits.

A Touch of Bias

I rescue the airframe from the garage and bring it into the snug warmth of the lounge, where I find that the badly-glued rotor-arm snaps off like a dead twig. Plastic is immune to epoxy and metal is not far behind unless prepared meticulously, and you can still see the clamps.

Next up I go for a foam in-fill, and can you see my mistake? Yes... we didn't measure twice and cut once today!

There's a fix for everything however, with the possible exception of death.

Foam meets three aims:

(1) It subdues vibration

(2) it forms a comfy collar around the waist

(3) it reinforces the central chassis

I'm designing for kit-production here and the foam inset will eventually be formed of four identical quarters formed from a single mould.

But that's for later, and being a Northerner I can't bear to see food going to waste and thus I recycle PU foam that once saw service in a hydroplane I designed, and subsequently lay in the loft where it served as insulation. It's the 'Home Guard' of foam, and no doubt delighted to receive its call-up papers once again.

It stands proud, literally, of the top of the frame and will have to be ground down to 50 mil.

We thought of every possible way of doing this, including milling, which looked like it would be finished just this side of Christmas.

Eventually I had a brainwave over tea and cake, and settled on a camping saw. This features in survival kits at outdoor leisure stores, but is unavailable in even the largest DIY outlets and I fear this is because it is equally useful for taking the heads off annoying neighbours.

Finally note that I have marked the 'forward' sense of the drone with an arrow, because if you flip it over the leading rotor-arm would be set to the right instead ~ right-handed pilots are likely to prefer a clear view on that side however, along with a side-stick controlling pitch and roll.

The choice however is yours, and this is likely the world's first universally-handed airframe.

Schedule Unstuck

Project management is as much people management as anything.

I call the fabricators to discover the parts are still lying on the office-floor where I left them, which was not what I had in mind... problem being the guy dealing is on holiday and won't be back until next week.

An issue for inventors is that everyone from patent agents to Uncle Tom Cobley will have an opinion on how things can be improved. Whilst well-intentioned it is invariably problematic and produces something like the horse designed by committee that passes for a camel.

My fault really: should have just insisted on brazing or welding, for cash on the day.

So I recover the parts and revert to epoxy and pop-rivets instead of the suggested 'rivnuts' or rivets that include a nut to allow for disassembly. Personally I prefer a chassis which, like that of the iPhone could be marked, Abandon hope all ye who enter here...

I also want everyone including Tom Cobley to be able to build this in the garage using simple techniques and materials off-the-shelf. To my mind these include adhesives and pop-rivets, which I have been using since the days as a teenager I patched up a rusting Mini with alloy.

I glue one arm at a time, making-do with two G-clamps and shuffling them as I go. Rushing rarely mixes well with aviation, and in retrospect a better idea would be to glue all four arms at once, popping the top-plate on loose with the ballast and leaving overnight, especially in view of the fact the weather has turned colder.

I do this so you don't have to.

Happy Mondays

Exciting day as we lay down the keel.

I'm big on all forms of transport and have seen from maritime museums how the greatest of ships like the Titanic were chalked out in sections on the workshop floor.

Rivets: they're my world.

These spars and base-plate are off to the fabricators, then it'll be back for foam inserts and crowning with a top-plate...

Four-Square

These are problems you face as a developer... those times when you have to go with your gut.

Persuasive factors, three-off:

Firstly, supporting the drone before flight I want it balanced around my trunk. Setting the opening farther back would mean me standing like I was selling ice-creams at the cinema.

Ditto once airborne, when I don't want any drift due to out-of-trim moments.

Finally, I've every confidence the engineer can bias the controls to allow for rotor off-set.

Talking of guts too, I have tried it on for size and it fits like a glove. I noticed the other day that the guys fixing the electricity pylons hereabouts had all-in-one coveralls that included hooks for abseiling and I've a notion I've seen commercial window-cleaners with the same.

Mental note to look into it.

That's 3mm aluminium in the pic by the way, like it says on the tin, albeit shrink-wrapped...

Cutting Metal

Returning to the sheet-metal suppliers for the material for the fixing plates top and bottom which secure the rotor-arms, I settle on a 3mm thickness to complement the wall-thickness of the alloy spars I am using for those too.

It seems also that they cut panels from sheets that measure 1000mm x 2000m, so it makes sense to enlarge the flight-deck to 500mm square so that we have a simple two-off solution.

Although I have sketched the outline of the 'hole in the drone' and made a wooden template, they are unable to use the CNC equipment as these require a .dxf file. Frankly that will have to wait, and continuing the hand-built theme for my prototype, I revert to the trusty jig-saw.

'Measure twice and cut once' they say, and in a literal last-minute change of direction I settle on aligning the pilot accommodation in the direction the drone would conventionally travel.

Of course this could be obviated in the long-term by building a bias into the control software but for now the easiest thing to do is to bias me instead toward the right side of the square.

It means that conventional programming can be adapted for one thing, and for another it means the pilot is oriented with the rotor-discs so the motion is likely to feel more natural.

Softly softly catchee monkey.