flight testing
things like that we buy. The process of instrumenting
the aircraft with thousands of load cells, accelerometers,
and temperature sensors and beaming it back is a whole
industry in itself. It’s something we feel we’re good at.”
The off-site team included Bell’s mobile telemetry
group. “You have real-time monitoring being beamed
back to the engineers on the ground in flight and
being recorded on-board on a hard drive. It’s
thousands of parameters, especially for Ship
3.” The sensor suite extends to the twin
CT7-2F1 engines on each helicopter.
“We had full telemetry for both aircraft,”
says O’Neil. “It takes quite a bit of logistics to get
that capability up there.” The comprehensive
instrument suite on Relentless FTV 3 measures
more than 3,000 parameters constantly for airground
downlink or on-board recorders. O’Neil says,
“You’re talking about hundreds of data codes available to
you live and thousands being encoded on the aircraft for
post-flight examination.” He adds, “Taking care of all
that instrumentation is another part of that team. The
expense of a broken sensor keeping a test aircraft on the
ground is unacceptable”.
The two helicopters flew about 100 sorties at
Yellowknife, pushing out to 175kt Vne (never exceed
speed) and 35kt in sideward and rearward flight. “It’s not
really the maximum speed that sets your limitations,”
says O’Neil. “It’s margins with control surfaces showing
you have all the travel you need and all the power you
need coming out of the engine and rotors to operate as
expected.” He notes, “We really investigated every
combination in cold weather. We had very good
agreement with our analytical predictions and our
previous experience with the aircraft.”
34 SEPTEMBER 2019 \\ AEROSPACETESTINGINTERNATIONAL.COM
109
Bell employees
involved in cold
weather testing
of the 525
The two FTVs had slightly different objectives
gaining certification data.
“We did divvy up the testing,” explains O’Neil. “Ship
3 in particular was gathering a lot of data for calculating
loads and stresses. It flew all over the sky, at all kinds of
altitudes, all in cold weather. It was really doing
everything. . . Ship 2 was really more focused on
compliance flyability – handling qualities, performance
under cold weather conditions.”
Part of the Yellowknife test plan was starting the
engines after soaking outdoors overnight in extreme
cold. “Engines will start up a good bit more slowly when
they’re very cold,” acknowledged O’Neil. The Model 525 is
powered by twin General Electric CT7-2F1 turboshafts,
each rated 1,879 shp for takeoff and 2,129 shp in
emergencies. The engine maker noted the
baseline CT7 was designed to provide greater
torque for cold-weather starts.
Significant cold weather testing information
for the new CT7-2F1 was derived from the -2E1
engine previously certified for the Agusta
Westland AW149 and AW189 helicopters. The -2E1
fuel system also carries an extra anti-icing
certification. With safety and durability
enhancements, the -2F1 turboshaft in the Relentless
also integrates an Engine Electronic Control Unit as well
as a Health and Usage Monitoring System. It is cleared
for operating temperatures from -40 to +58°C (-40 to
+135°F) and received its FAA Type Certificate Data Sheet
in March. \\
7
6
6 // Bell 525 FTV 2 was
used to document handling
qualifies for certification
7 // The FirstAir Hangar at
Yellowknife gave testers
space for both Relentless
Flight Test Vehicles
8 // Photo: Bell rented
hangar space for the Model
525 test team at the
Yellowknife Airport
(Photos: Yellowknife Cold
Weather Testing Group)
8
/AEROSPACETESTINGINTERNATIONAL.COM