Thursday, November 24, 2022

Cost Benefit Analysis

The mannekin of choice is container-bound like so much else in the modern world and not expected before the end of February. Common traits entrepreneurs share are impatience ~ Elon Musk at the end of the spectrum ~ and a reluctance to compromise which was best expressed by Steve Jobs. Human progress stemming, as Bernard Shaw observed, from those least reasonable.

For our unenlightened selves however this requires a decision, and there is a firm out there who'll rent the same mannekin for measuring up purposes and PR shots, so it need not hold us back. As it is I've viewed so many child mannequins online that I fear a knock from the vice-squad any day.

Meanwhile it's clear that the U7 motor will provide not nearly enough power as a quad, especially as said mannekin comes in wood and fibreglass. It will be struggling to lift the payload at max chat and therefore we need to look at an upgrade. In the long history of aircraft design to-and-fro between airframe and power-plant is a perennial issue, and as often as not it's the airframes that depend on the engine manufacturers moreso than the other way round.

We can up the motor-count like the designers of the Avro 146 had to do when two jets were not sufficient, else fit larger power-plants in the way aerospace evolves toward: so we can maintain our 36" airframe and add four more motors and 22" propellers as on the right, or up the frame to a metre and fit larger U11 motors and 27'' propellers.

Surprisingly the octocopter produces much the same thrust at 60% throttle, not least because it sweeps 50% more disc area (although you could probably reduce its performance by upto 10% due overlap)... 18kg. The quad delivers 21kg at that setting, or 20kg with 20" propellers.

The differences between the two arrangements however lies in:

(a)    price
(b)    practicality
(c)    plausibility

The quad costs around $2500 to motorise whilst the octo costs around $3300. It also has motors and rotors on one side and is more easily transported without damage. For PR purposes too it has cleaner lines and is the more relatable for experts and public alike, who can see that four more motors might coincide for engine-out capability.

Construction to date will therefore be used as a look-and-feel representation of the working model, which will incorporate all of the lessons learned to date.