I've held the opinion that we shouldn't be using multirotors but VTOLs when it comes to aerial deliveries. The multirotors are extremely energy inefficient, have very low MTBF, short-range and very low payload cap. On the other hand designing safe reliable VTOL is hard but solvable problem when thrown enough resources because you can draw a lot from existing aviation tech. However, Amazon has gone through quadrotors to VTOL and then they switched back to multirotor again, surprisingly. Unfortunately, most of the delivery vehicles are being built by relatively small limited resources startup-like groups. While multirotors are very easy to build, they have an enormous number of problems. I think if there was a well-funded group of 500 or so engineers working over ~5 years, there is a decent chance we can have safe reliable commercial-grade VTOL for autonomous point-to-point deliveries that can be adopted as standard. Unfortunately, this is a big capex project.

Google has been experimenting with tailsitters, which I think is a no-brainer.

Zipline is, imho, the real out of the box thinker. Catapault launch plus the snag line is Short takeoff, effectively-vertical landing, main downside is you need ground gear to land without damage. Main upside is weight savings for peak power (takeoff) is reduced, landing gear gone, and your engineering space is shrunk to solely the problem of steady state flight.

I foresee the paradigm of winged mothership for last-hundred-mile, plus n-rotor drones for air-to-land leg of delivery.

Zipline's system is a much lower cost, light weight implementation of what InSitu (now a Boeing subsidiary since they were acquired) designed for the defense market, for their Scaneagle. They were by no means the first to launch or recover a fixed wing drone in that manner.

As you point out it provides a lot of advantages in not needing to carry the extra weight for a VTOL, no landing gear, extra energy boost on launch. It's very close to the optimal energy usage in watts for motor, per size of craft, that can be achieved right now.

The other advantage of using a single motor fixed wing craft is ability to use lithium ion batteries which are relatively higher Wh/kg density. These are not as capable of instantaneous high amps as lithium polymer are. The best commodity, commercially available lithium ion batteries are in the range of 210 to 248Wh/kg right now. The best lithium polymer batteries are about 178Wh/kg.

FPV hobbyist fliers who build fixed wing and flying-wing craft use lithium ion for longer range.

https://www.google.com/search?q=insitu+scaneagle&client=ubun...

Zipline only works if you have a single base where you launch from land at. If you need to land at the customers site then you need VTOL capability.

I think the idea is that the full-payload drone is launched via catapult, and the takeoff from the customer's site is without payload, allowing for lower power.

Yeah I've been thinking same, possibly a UAV dirigible for the mothership. That would be cool.

Due to the very low energy storage density in Wh/kg for li-ion and li-po type batteries, VTOLs are the inevitable design decision a lot of companies are arriving at. For a big filming octo, capability to stay in the air for 45, 60 or 90 minutes is not essential and it doesn't need to travel far.

If you look at the pilot projets for drone delivery in Canberra, it's all VTOLs.

https://www.google.com/search?q=canberra+drone+delivery&clie...

The instantaneous watts required for forward flight with wings at a reasonable speed are much lower than the watts required for the same weight of craft, same general dimensions, same speed, forward flight with four, six or eight rotors.

Any insight as to why Matternet is using quads still? Just nearsightedness? Yeah, they might be a bit cheaper, but now they are grounded, that's never good for the bottom line.

Furthermore, safety critical systems are all about layers. Yeah redundant motors are good, parachute is nice, but what about passive measures?

Maybe drones should have stub wings which, in addition to lift boost, have deadman switches which cause one to spring 180° on power loss, forcing the hull to autorotate in the event the chute fails.

Ok, the gps dies, the motors fail, chute fails to deploy, and the wing ripped off, you are dropping at full speed. Well now the rapid descent causes a pressure differential (artificial eustacian tube, if you will) which trips some azide charge, inflating an airbag.

It's like they are putting in bare minimum of effort with the quad+parachute.

I actually recognize the drone body that Matternet is using there, it's a monocoque molded carbon fiber + fiberglass body from a manufacturer in China, where it's sold as an agricultural spraying drone.

Rapid descent sensors don't necessarily need to be pressure based at all. While in controlled flight there is a limitation (as governed by flight controller and ESCs) for how rapidly a quad, hex or octo can descend. Accelerometer data can be used to trigger a parachute and/or airbag system. A multiply-redundant array of small accelerometers that can detect freefall is very tiny and light weight.

Most higher end flight controllers have double or triple accelerometers onboard.

Thanks for contributing toward progress and not toward fear/restriction.

There's valid technical reasons for having a coaxial octo within a total craft body+arm size radius of 1.5 meters as well. You can generate more thrust and carry more payload for the same disc loading area.

Four large motors and four 28" CF props produce less thrust than four arms, each arm with two motors stacked, and eight props.

Octos are not a conservative, redundant, fail tolerant design decision just for the sake of protecting expensive gear. Many of them still have 1+0 non redundant power systems.