Fixed, Multi-Rotor or both?
A lot of writing has gone in to what kind of drone will be used for drone deliveries.
My TL;DR answer. It is most definitely going to be VTOL
I am kind of going over some ground that many other writers have gone over before but bare with me.
There are pretty much 3 types of drones.
Fixed wing,
Rotary wing,
and VTOL (a mix of both).
Fixed wing is like the plane you probably have flown on before. The wings are fixed in place on the side of the plane...hence the name.
Positives - efficient and has long endurance
Negatives - requires runway for take off and landing.
Rotary wing is a helicopter. The wing is rotating around creating lift as it moves through the air. Multi rotors fall in to this category.
Positives - requires only a small place to take off and land
Negatives - not as efficient and does not go as far as fixed wing when flying straight and level.
VTOL stands for Vertical Take Off and Landing. It is a combination of fixed wing and rotary wing.
Positives - take off and landing in a small place. Does not require a runway.
Negatives - not as good as the fixed wing with regard to endurance and efficiency. Also not as good as rotary wing when it comes to hovering, but the difference is marginal.
VTOL typically look like a fixed wing but the rotors will pivot to allow for both hovering and fixed wing flying
So as you already know I firmly believe that drone deliveries are going to come in the form of VTOL. When you properly think about how drone deliveries are going to happen in reality. Where you extrapolate out each step of the drone delivery process. The only answer I can come up with is VTOL. You only need to hover at take off, delivery and then landing. All the rest of the time you can fly in the economical fixed wing form
Let me explain why
The short answer is that the other two options are not fit for the job.
Multi rotors
They are fine and could do the job however, multi rotors do not have the endurance that a fixed wing can provide. They are great if you are only flying a short distance.
I will agree that some of the deliveries in the future will be short distance. However, multi rotor is inefficient. They will need to be recharged more often. If the drone is sitting around getting charged more often, then it is not available for deliveries.
You want your hardware up and running as much as possible otherwise it is wasted resources sitting there not earning money. This is true for the airline industry. The turn around time for an aircraft has to be a minimum because for every minute that it is not in the air is a minute that it is not making money. It is the same for any industry really. You want the money that you poured in to that resource to pay you back as quickly as possible and the only way for that to happen is to have it working.
Battery swapping tech is available. However, the same arguments arise. Are you going to have spare batteries sitting around? It is much better if they are being used.
Multi rotors have more endurance with alternative power sources like liquid fuels (Hydrogen and petrol) there are advances in hydrogen that look very promising. Up to 4 hours flight time. However if you put that same motor (hydrogen or petrol) in a fixed wing you would get far more distance. Or in other words far more hours of use.
Fixed wing
Without a runway at each house, how is a fixed wing drone going to land and deliver your package?
Drop it by parachute! maybe but I honestly don't think so. Gusts of wind are a factor to consider. Your package could drift next door or in to a pool or get stuck on the roof. If you have a large area in which to receive the delivery this could work.
Steerable parachutes might work but I really don't think so. The tech for steering the parachute would have to be cheap enough to be disposable or robust enough to be sent back and used again. To me it seems a little bit to difficult. I will agree that it could work, I just don't think it is viable.
Amazon have already patented parachute delivery
https://www.theverge.com/2017/5/31/15717432/amazon-patent-drone-parachute-label-prime-air-delivery
They have also filed a patent for controlling the packages as they descend
https://www.businessinsider.com.au/amazon-patents-way-to-control-how-drone-parcels-fly-to-the-ground-2017-2?r=UK&IR=T
We'll see how they go with that.
That only leaves VTOL
Google and Amazon have already shown that they intend on using VTOL. Googles first attempt at drone delivery was a VTOL. They could see early on that this is the way to go for all the reasons I have given above. Amazon have said that they will use different drones for different deliveries but a common fleet will be easier for maintenance and infrastructure. I think they will choose one type eventually
VTOL has all the benefits of each type of platform with none of the flaws.
It is not going to be as good as a fixed wing at endurance or as good as a multi rotor at hovering but it is a happy medium.
