39
Environmental testing
3 // The full-size prototype
of Lilium’s air taxi flew for
the first time in May 2019
4 // The four co-founders of
Lilium started the company
in 2015 after meeting while
studying at the Technical
NO FAULTS FOUND
As processing speeds increase, small
perturbations in a signal that once could
be ignored, now can lead to No Fault
Founds (NFFs), where a Line Replaceable
Unit (LRU) does not work in the aircraft
but does work when tested separately. NFFs are
frustrating and time consuming to remedy. Often this is
caused when a signal is fine on a test stand but becomes
corrupted when on the aircraft.
Copernicus Technology in Elgin, Scotland has
developed Intermittent Fault Detection (IFD) equipment
able to trace out the source of a faulty signal. Jim
Cockram, technical director of Copernicus Technology
says, “The testing confirms the integrity of the unit
under test rather than the functionality, which is verified
separately using the automatic test equipment relevant to
the unit under test.”
IFD technology enables circuits under-test to be
tested continuously and simultaneously without gaps,
digital averaging or scanning – there are no testing blind
spots. This allows the user to have a high level of
confidence that there are no intermittent faults on the
item under test. During a stress test, IFD equipment
monitors all the circuits and detects disturbances in
the interconnects.
“In the case of LRUs, testing of the entire range of
interconnects in rogue LRUs reveals a wide range of
AEROSPACETESTINGINTERNATIONAL.COM // JUNE
THE NEXT GENERATION
German on-demand air taxi developer
Lilium has been flight-testing a two-seater
prototype since 2017 and last month
celebrated the maiden flight of a full-sized,
five-seater prototype. The aircraft features
ducted electric jet engines built into the
wing flaps, which shift position to transition
flight from vertical to horizontal flight, a
maneuver which has been key to prove as
viable during testing.
The sleek five-seat design is powered
by 36 all-electric jet engines. The airframe
has no tail, rudder, propellers, or gearbox,
reducing mechanical complexity and weight
and increasing reliability, says Lilium. The
engines themselves only have one moving
part. The design of the aircraft has been
driven by the aim of maximizing redundancy.
“We believe in ultra-redundancy. As well as
36 independent engines, we have 12 flaps,
a triple redundant flight control computer
and many other redundant systems in the
current prototype,” the company says.
The battery-powered aircraft has a top
speed of 300km/h and a range of 300km
according to the company. By transitioning
to fixed wings for horizontal flight after the
vertical takeoff the aircraft uses less than
10% of the maximum 2000hp available from
the power plant.
Existing testing regimes for VTOL drones
show they tend to be structurally resilient
and that most failures occur in electronics
and cabling, such as cracked solder joints
and connections, that were not designed
for repeated takeoffs and landings. These
challenges have always existed for any
safety critical electronics application in
aviation. Lilium sees no difference between
designing and testing electronics for
drones and conventional aircraft. “There
is no difference – they are managed and
regulated by EASA to the same standards,”
says the company, “the aircraft is designed
to the strictest aviation safety standards”.
integrity faults that contribute to poor
reliability, disconnects and transient
performance,” says Cockram.
CABLES ARE NOT EASY
While cabling may look simplistic, this is
often one of the more susceptible areas of
electronic design. Simply described, a
cable is a long strand of conductive
material running from one component to
another. Hayes from Element says, “Cables
act as both good radiators of RF energy
and also receptors to RF signals and are
therefore a critical aspect of assessing the
EMI performance of fitted equipment
and systems.”
Design methods such as shielding and
grounding have long proven effective in
keeping a cable from becoming an
antenna, but even here, the advance of
aircraft structural changes have an
impact. “Radiation from and to cables is
University of Munich
4
3
/AEROSPACETESTINGINTERNATIONAL.COM