12 SEPTEMBER 2017
landing in order to prevent excessive yaw.
With propeller placement finalized, Eviation set out to find
motors to drive them. Austrian-based Rotax, and Emrax,
a Slovenian company known for its high-performance
electric motors, powered the Orca drone. The one-third
scale Alice prototype uses a set of hyper-efficient brushless
DC electric motors from Britain-based YASA Motors.
These cutting-edge motors all have impressive power/
weight ratios, ranging from 3 to 6 kilowatts per kilogram.
For example, the YASA model 750 motor driving the scale
model’s tail prop weighs roughly 37 kilograms (81 pounds)
and turns more than 95 percent of the 200 k W (over 250
HP) it consumes at peak output into thrust. Motor selection
for the production aircraft has not been finalized with
Siemens and YASA both under consideration.
The wingtip propellers are one of the most advanced
aspects of the plane. They are in constant communication
with the onboard computer that uses them to stabilize
the plane in what Bar-Yohay calls “a complex system of
pitch control.” The fly-by-wire system can adjust the props’
pitch and rotational speed up to 400 times per second
to help the plane handle more predictably and cancel out
the unwanted effects of gusts, control inputs, and other
perturbations. The electronic controls will also eventually
be able to configure the motors and propellers as
“regenerative air brakes”, capable of partially recharging the
plane’s batteries from the energy they capture as the plane
slows or descends.
Bar-Yohay said that since all of Alice’s controls will be
fly-by-wire, they could easily be adapted for remote or
“We’re basically doing that because we can,” he said
with a chuckle in his voice. “When the plane is empty
it should come back alone. That should save an insane
amount of money, if we can do it in the existing regulatory
environment. We’re trying to be leaders in that but we have
to build the plane first.”
3D PRINTING IN FLIGHT
3D printing is playing an important role in the aircraft’s
development. “We have used a lot of 3D printing,” said Bar-Yohay. “It occurred to us because we had access to a printer
because of a company that was physically nearby.” Once
they saw how 3D printing could accelerate their development
process, they teamed with 3D printer manufacturer Stratasys
on a wide range of projects, including visualizing and creative
prototyping of aerodynamic elements. “One of the easiest
ways to validate parts such as the propeller is to build and fly
it. So we decided to use 3D printing for this,” he continued.
In another example, while the team was waiting for the final
motors to ship, Eviation printed up a set of stand-in units in a
matter of hours.
One key part of the aircraft engineered with the help of
3D printing was the wingtip motor. Engineers produced a
functional prototype in 20 hours using the Stratasys Fortus
450mc Production 3D Printer in FDM ABS material (see
Fig. 2). Eviation Eviation also used 3D printed parts to
make curved surfaces to reduce drag.
Some of the tooling for the Alice will also be 3D printed,
beginning with many of the initial molds for test articles.
Eviation is also planning printing much of the lay-up tooling
used to form the aircraft’s carbon composite hull and wings.
Figure 3. The ORCA drone helped verify much of the technology and
construction techniques that will go into the Alice Commuter.
(Image courtesy of OIDA Strategic Intelligence)
Figure 2. A functioning prototype of the 3D
printed wingtip motor (left) was produced
in 20 hours on the Stratasys Fortus 450mc
Production 3D Printer in FDM ABS material,
before the final motor (right) was available.
(Image courtesy of Eviation)