Friday, July 26, 2019

Final Frame

End-of-week round-up July 26 2019, and 'Houston, we are looking good'. I want you to imagine seven more power-plants affixed to the above, three more to the lower quad and four to the upper.

For the technically-inclined (and in Imperial measure) the spars are 30-inch by 2-inch by 1-inch by 1/16th, the props 32-inch, the deck 12-inch square, the aperture 9 and 1/2-inch and finally the depth 8-inch (not including the upper set of propellers).

The weight of the basic frame alone is a little under twelve pounds and still too heavy so far as I'm concerned but this will do for a proof-of-concept. The 'wearable' single-deck drone I featured months back weighed just over eighteen pounds, so I've added a further deck and four more rotor-arms and still reduced the weight by a third.

As the load is now spread too over eight arms, there remains scope for lighter alloy sections without reverting to carbon-fibre.

I've run with the simplest arrangement for test-flying though there are two variations to test longer term viz. (a) the decks could be spaced farther apart and the upper set of propellers under-slung instead of over-slung and (b) the upper frame could be inverted to provide an eight-pronged layout when viewed in planform.

The frame is modular in so far as the upper 'drone' can be detached from the lower, and in theory any number could be stacked. The principal problem with 'stretched' airframes of this kind is the increasing torsion, which requires fitting side-panels to act as shear plates.

The mannekin represents a half-scale though the frame will accommodate myself for test-flights. Realistically a commercial version would sub T-Motor U15 motors for the U13 type here (along with 40-inch propellers instead of 32-) yet still remain inside the dimensions of the GoFly competition.

For the record the axial distance between hubs is 48-inch and adding the 32-inch for the arc of each pair of propellers produces an 80-inch span. For roof-rack transport however the propellers can be stowed parallel to lie within the foot-print of an automobile.

We should be moving toward power-plant fitment and shakedown testing in the near future with tethered flights beyond that based on a 48-volt ground-power source.

Thereafter we have to return belatedly to Voltaplex with a spec on the LiPo battery-packs for free flight. My preference is for batteries to be body-worn in a back- (and/or front-) pack so that they can be tailored for the mission, as with current commercial jet-packs.

For the pilots among you the flight-control configuration is likely to call for the lower set of rotors to provide yaw plus collective with the upper set restricted to direction, and initially commanded by standard remote-control hand-sets (whether from base-station or onboard).

I am confident moving forward that the configuration as seen can be made to fly, and frankly having examined every other variation, it's going to have to as I'm betting the farm on it!

Finally to anyone thinking of designing an eVTOL, my advice is... don't.

Ever since Sikorsky helicopters have needed a big rotor on top and a smaller one on the tail, but with electrical flight nowadays that's gone the way of every other Cold War certainty.