Flitetest X-57. Take 2.

...a long time between drinks

After a long hiatus the X-57 is back in the air and flying OK.

The issue I'd had initially with unbalanced thrust turned out to be only an over-tightened motor mount - backing off a couple of screws was all it took to get the slow motor spinning up to speed.

However, the wings still seem to be generating too much lift, with the X-57 soaring with even modest throttle settings and fairly wanting to loop with anything more than that.

In fact, I had to fly it with negative elevator trim just to try and get it flying level-ish. For my next try I'll use a heavier 4S 3000 to try and even things out a bit.

This may help it fly level and so help to eliminate the problem of the big disparity between power on and power off flight and allow it to glide properly with a bit of airspeed. At the moment when you cut the throttle it stalls which makes trying to land it, well trying...

FT Cruiser X-57. First Flight.

...hey I made an X-plane. sort of...

Having seen NASA's intriguing X-57 Electric Research Plane, I decided to converted Flitetest's twin-engined FT Cruiser into an RC version of NASA's experimental plane, featuring twin electric motors mounted in the wingtips.

The X-57 actually features 14 motors, twelve small motors with folding props mounted in the leading edge of the wings providing supplementary power for takeoff. The two larger motors installed in the wingtips provide the high-speed cruise propulsion.

I wasn't going to be wiring up fourteen motors, so I dispatched with the dozen leading edge units favouring the simpler hand-launch solution. I used small 89W quad motors (1806 2300kv) running at on a 3S 2200 battery. The propellors are 5x3 props, swinging inwards sweeping air onto the top of the wing to counteracting the wingtip vortex.

This is one of the main benefits of the wingtip design, a second being that the concentrated wingtip flow feeds into the propellor, increasing the dynamic thrust. Finally, additional thrust is generated by virtue of the outside sweep of the prop being unimpeded by the presence of a wing; the prop wash goes into free air.

The modified FT Cruiser with weighs 940g all up, or 749g without battery compared to the spec mass of 766g. The 17g difference is due to reduced wing size, one less servo (rudder servo ditched in favour of differential thrust) and smaller motors. However, 7g ballast had to be added to the nose for CoG correction due to the motors being set rearwards compared to the standard Cruiser configuration.

The motors generate a combined 710g of thrust as installed, sufficient for cruise but certainly not 3D flight. Static thrust of a commercial aircraft is a quarter of its loaded weight and around half of its empty weight. In the case of the xCruiser this would equate to 235g to 470g respectively. So it's comfortably powered in aircraft terms although less so in RC terms where closer to 100% is nice-to-have...