Thursday, April 4, 2019

Slim Air of the Year


It's clear from the Phase Two awards that I can count in months what the competition have expended in years on their own eVTOL projects, but then I doubt anyone else can construct an airframe in an hour or two... whether the real deal in alloy like the one on the left or else a mockup in timber off-cuts like that one on the right, which in practical terms differs little.

Fact is I'm up against well-financed teams with ample facilities, reserves of cash from lives well led and who don't need to idle a Suzuki Jimny to keep the place warm. In contrast I've a garage and a tool-box available to me, but as we're not trying to split the atom I figure that's enough (although admittedly my electrical contractor has a barn too).

I figure I may as well enter the fly-off time-trials too beside anything and strip the frame to a minimum the way they build F1 cars from carbon-fibre. The chassis of such cars, stripped of wheels, gear-box and engine is negligible and I intend my own airframe to be the same: the gross weight at lift-off will practically consist of me, motors, rotors and battery.

The frame at right is a fraction of the weight of that on left, which was only nineteen pounds anyhow. Nonetheless it is actually the more capable, swinging a 40-inch rotor in place of a 36-inch. When it comes to disk-area I'm a dog with a bone and this restores my thirty-five square feet and pops the disk-loading back beneath that of the Chinook.

For those intending to copy ~ and fill your boots ~ the flight-deck has been reduced to twelve by sixteen inches and the rotor axes are fixed at three inches from the spar-ends, which means that the motor housings (at six inches diameter) fit flush. The motor axes have been fixed at 30 inches from the centre-point of the pilot accommodation.

A design ponderable (in view of the renewed geometry of the flight-deck) was whether to maintain the rotors full-square or else distributed around a circular outline in a rectangular layout. I chose the latter, foreshortening two of the spars to under one metre. It sets the pilot centrally between the propellers, but sets them in a rectangular layout instead of a square.

This offset is easily overcome by (a) the pilot's brain or else (b) software, and from the outset the vehicle never advanced full-square anyway: in view of its layout it 'tracked' normal to the pilot, but tangentially to its planform.

Shall colour it in red this time to remind us it's destined to fly us around in phone-boxes.