Weighing everything up ~ quite literally ~ I settle on the final build. For every prototype there is a point where a spec has to be frozen so as not to be chasing a moving target. Accordingly I decided to replace alloy sections with plastic to bring the gross weight to within the range that smaller motors (the U7) can be used instead of larger. This in turn lowers the operating voltage and allows for lighter batteries within a virtual circle.
The plastic is supplied in metre lengths or three; the latter requiring a bulk purchase. Accordingly the columns around the phone-box are reduced again to the former dimension. At this height either mannekin will fit and so I revert to the lighter. An impromptu X-ray reveals a severe neck-fracture, however, which needs repairing with a gauze dressing set with resin of the sort sold at auto shops... a simple procedure that need not require a suspension of flying duties.
Meanwhile beside plastic another order has gone out for equipment to motorise the prototype i.e. four U7s and 80A ESCs, plus two pairs of 22x6.6" propellers. A perusal of the performance on the manufacturer's site shows that this largest of the available propellers for the motor in question rotates slowest and draws the lowest amperage, whilst producing much the same thrust.
Larger diameter propellers provide disproportionate improvements in performance ~ a helicopter being around twenty times more efficient in the hover than a Harrier jet for instance. Nonetheless the U7 motor clearly struggles with the torque required to turn the 22" prop and while operating temperatures are quoted for smaller sizes, this one is recorded in the table as simply being HOT.
Nonetheless we'll be pushing those babies to the max, for as the late Colin Chapman was prone to say at Lotus, the ideal Formula One racing car is one which falls apart when the race is finished.
Now if you'll excuse me I must get scrubbed up for an operation...
