Friday, April 16, 2021

Turner Prize

Width of the lower quadcopter's body has been depressing me, in turn a function of the fact that fibreglass mannequins are incapable of squeezing into smaller spaces, so that the accommodation needed to be much wider than it was long (15" by 10" even at half-scale)... as if I don't have enough to do with building an electrical aircraft.

This cost me half a day of staring at the ceiling wondering what to do about it ~ if not give up altogether ~ but God or providence supplied a solution in the form of an about face on the part of the mannequin. Turning it through ninety degrees meant the sides had to be raised by an inch or two, though you'll see it comes together in due course. Be fair to say there are periods when I never want to look a drone win the face again, but with a pandemic restricting practically all else it's that or self-immolation.

(It does also mean that the box is now much longer than it is wide, but this does at least allow for a reduction in the outline of the drone it sits upon, whilst providing the protection for the lower limb's that would inevitably have been raised as an issue at some stage along the way.)

Wednesday, April 14, 2021

Re: Purposed

Benefit of working with metal instead of exotic materials like carbon fibre is the fact they can be used many times over, which is ideal for prototyping. This might look like something from months past, but there's a significant difference that stems from the practical experience of flight testing. The outline mocked up here will benefit from its modularity, in so far as the lower quad is separate from the accommodation, which in turn can be separated from the upper quad.

This allows the uppermost drone tasked with the steering to be tested independent from the lowermost, which will be tasked with lift alone. This means that the various regimes for testing laid down by the aviation authority are more easily navigated, while at the same time we can progress toward an operational reliability of the independent units. There's a whole lot more to designing an eVTOL capable of lifting you or I than you would imagine...

Sunday, April 4, 2021

"Over Exposed"

It's years since I'd cross the Pennine hills on a motorbike, back and forth to university in Sheffield, but I figured I'd try to find one of the few relatively distinct aircraft crash-sites, just a mile or two beyond the road. Ferrying between RAF Scampton in the East of England and the USAF base at Burtonwood near the West coast nearly seventy-five years ago, the crew needed sufficient altitude to cross the peaks forming the 'spine' of  the country. I've flown hundreds of approaches to Manchester's airport nearby, which even now involves a series of stepped descents under radar control.

Back in 1948 however, aircraft like this B-29 would be flown by old-school navigation (and there's a memorial from a course of navigators at nearby RAF Finningley, which is where I first took to the skies). This would involve dead reckoning and timing, with the crew 'letting down' after a passage of time considered sufficient for a safe transit. On the day it proved not to be, although as ever it appears from the location that an extra hundred foot or so might have made the difference. In the event however all thirteen onboard the aircraft ~ named OVER EXPOSED after the graphic 'nose art' of the time ~ died following the impact and fire.

The tail-section was all that remained intact, but has long since been removed along with much else. What is surprising however (and a tribute to human nature) is how much remains: amongst the recognisable parts the engines, undercarriage and what must have been rubber-lined centre tanks, which still bear evidence of the floor and seat-rails fixed to their upper side. Many years after the crash a fell-walker found the captain's wedding ring (though there were two such crew-members onboard), and this would eventually be returned to his daughter in the US.

The site is sign-posted at least initially from the route of the cross-country Pennine Way, although this appears to lapse at a crucial juncture when you need to strike west for the nearby trig point. Beside this the mobile phone coverage is patchy, so that there's an element of personal dead reckoning involved that in some ways sets the scene.

Thursday, April 1, 2021

Runway Model

If it proves a point at all, it is only that technically speaking it is possible to build an eVTOL in three separate parts viz. a lower and upper quad, with a box in between. The outline of the box is only a question of ergonomics and I've tried standing varieties at half- and full-height, beside seated types that confine the pilot wholly or partially like this. Every iteration is built on lessons from the previous and time itself will prove the most plausible, along with consumer preference. Should one work it is likely that all will, to the extent that whichever form of box might be substituted within the vehicle.

In the meantime, may the best box win...

Wednesday, March 31, 2021

Movie Trailer

After some Springtime spit-and-polish I return to the former RNAS Ringtail for a few PR shots to take the campaign forward. People who build VTOLs are very aware of the challenge of logistics when it comes to transporting air vehicles and in fact the outline of the drone here is adapted somewhat to the one by two metre flatbed trailer itself.

Electrical flight is the first technology to permit the deployment of aircraft practically single-handedly, so long as you discount powered parachutes or individual jet-packs. Only recently the US Army issued a tender for just that ~ a means of air mobility which can be deployed by a single soldier for transient operations.

Monday, March 29, 2021

Skid Row

Without a doubt the undercarriage has always been ~ quite literally ~ the Achilles heel when it comes to the design, but the one thing we learned from the test-flights back in December at Llanbedr was that cross-bars (or lateral stabilisers) proved to be quite unnecessary. In fact it was they that broke free during one heavy landing and took out all four of the lower props... precisely what they were supposed to be there to prevent.

Short story long however I've gone for a relatively conventional pair of skids and left them aligned with the arms of the drone. There are operational reasons for doing so in so far as it makes carrying the vehicle altogether easier, and looking ahead to a scaled up version, altogether easier to get in and out of whilst providing for the best possible view. At the same time, raising the lower quad has improved the propeller clearance over the previous prototype, which again removes the need for lateral stabilisers.

For the techies out there the diagonal measure between the motor axes is 1.40 metres and the weight including the lower battery set is around 35 kilos or 78 pounds without the dummy onboard ~ he weighing a further four kilos. The accommodation is two feet tall, such that the model is the best part of two-thirds scale.

The lower quad will provide the greater portion of the lift ~ for which Phil already has an Arduino program to suit ~ and the motors are addressed directly by an associated battery-pack. The upper quad will be conventionally wired and you see from the wing-nuts that it is removable such that it can be tested independently as a regular drone that falls within the regulatory weight-limit.

Remains to be seen whether it all works to spec... but it's the taking part that counts.

Friday, March 19, 2021

Please Be Seated

For a variety of reasons that you'd only appreciate if you'd spent two years of your life designing and building eVTOL variants, I have elected to go for a half-scale model in the most compact format possible. As such I have reverted to flying perpendicular to that direction you'd expect from an 'H' quad, as it allows for a reduction in the vertical extent of the accommodation. I've also reverted to seating in lieu of standing for the same reason.

I'm also avoiding the complexity of multiple levels of redundancy because at this stage of the game ~ and the project is not alone in this regard ~ it's a case of walking before you can run. As a consequence the lower quad supplies lift alone at a constant RPM across all motors, and these are individually addressed by a battery-pack each to keep life simple from the electrical point of view.

A by-product of this is that even at full-scale the height reduction brings the vehicle back within the remit of the GoFly challenge in terms of size, although larger motors, propellers and batteries would nonetheless be required.

Weight-wise what you see here (without speed controllers, avionics and skids) tips the scales at 35 kgs (77 lbs) with dummy and 31 kgs (68 lbs) without. Having put several such airframes together I can say with confidence that in order to bring the vehicle in below the CAA's official drone classification of under 25 kgs (55 lbs), smaller motors and batteries would certainly be required.

This one will be registered here for testing as a large radio-controlled model, on which basis it will also be devoted to the display circuit in perpetuity, which should do no harm to the prospect of scaling it for human flight. Also you'll notice the upper quad is removable so that it can be tested independently AS a regular drone, prior to fitting to the remainder in order to provide the steering beside a portion of the lift.

This division of 'brains and brawn' will simplify testing altogether, which is ultimately the key to success in such endeavours.