We're going to mount the motor four-square on the bolt-holes, straddling the airframe as well as a 1" angle-alloy. These angle sections come in plastic but I'll use left-overs for our build. A pain-in-the-ass feature of the U7 motor is the fact the axle appears below its base, which will need a shim or washer around the bolts to clear the frame.
Looking at the picture below I've flipped the motor over in order to trace the outline, as we'll cut the motor-mount to suit. These babies are going to run HOT according to the manufacturer's own data, which is why they're top-mounted to benefit from the downwash from each propeller. Notice that a pair of bricks prove ideal for the exercise and these were available from my local scientific instrument store ~ and always insist on PILOT marker pens for aerospace builds like this.
Note also what it says on the tin: a 280KV motor runs at 280 rpm per volt. This is the slowest running of the three U7 variants and designed to drive a big ol' lazy 22" prop at a lower speed but higher (and hotter) torque. The batteries we collected yesterday are advertised at 3.70 volts apiece and are likely to die if run down below around 3.00 volts, so you're looking at an operating range of 3.20 and 3.70 volts for commercial ops with passengers.
With the crash-test dummy (sorry, mannekin) on board however we'll be pumping iron in the form of 4.20 volts per cell... think TOGA on your Airbus with its ten minute limit. Therefore we've a total of 25.20 volts down the line, which is 1.20 volts over the 'book' figure for max thrust, our own Tmax. Thus 25.20 times by 280KV is a theoretical RPM of 7056, at which speed the propeller tips are turning at 462 m.p.h. according to back-of-the-serviette calculations: well inside the subsonic regime and the reason slower props run quieter whilst optimising thrust.
