DEFENSE - Abdonline

program at Beale Air Force Base in California,
explains that the aircraft is largely automated and
occasionally does the unexpected. When that
happens, Northrop Grumman technicians have
been able to go back and determine why the
aircraft did what it did from reviewing the data
logs.
For example, early on in the program, it was
discovered that taxiing a Global Hawk presented
problems. The RQ-4 is designed to turn short of its
programmed waypoints to provide a smooth taxi
line. Taxiing around a curved taxiway is achieved by
plotting a series of points on the intended track.
The first time that technicians attempted to taxi an
RQ-4 around a curve, they found that the result of
the turn-short feature was that the radius on the
curve the aircraft actually followed was substantially
less than the radius on the mission plan. The
solution to this problem was to plot additional
points and use a wider radius circle than the
intended taxi path. That way, when the aircraft
turned short, it was where it was supposed to be.
Long-endurance unmanned aerial vehicle (UAV)
design puts a premium on light weight. RQ-4
aircraft use integrated fuel tanks, as opposed to
fuel bladders, to cut down on weight and increase
fuel capacity.
To further minimize weight, the fuel system on
the first RQ-4s, the Block 10s, is very rudimentary.
These aircraft are refueled using the over-the-wing
method (to refuel, the maintainer must hold a fuel
hose nozzle in an opening on the wing), as
opposed to having a single-point receptacle. This
technique results in uncertainty about the quantity
of fuel loaded, so the aircraft must be weighed
after each refueling to determine if it has received
the full amount of fuel needed for its mission.
In the beginning, maintenance crews used the
same type of scales utilized to weigh cargo pallets
for this task. This approach was problematic,
however, because maintainers had to find and
attach ramps to the scales, and then tow the
aircraft up these ramps to get them onto the
scales. Since then, a variety of lower profile scales
have been used that have smaller ramps built into
them, thus making the process much easier. The
scales currently in use at Beale Air Force Base are
made by the Intercomp Company, of Medina,
Minnesota.
In Block 10 aircraft, fuel inevitably flows to the
lower wing during the refueling process, resulting
in the need to elevate this heavier wing section
with a jack to ensure that fuel gets out to the
farthest fuel tanks in both wings. Newer Block 20
RQ-4s have been equipped with single-point
refueling capabilities, a feature that was strongly
advocated for by maintenance personnel, mainly
for ease of refueling and de-fueling.
In addition to the single-point capability,
Northrop Grumman added capacitance probes to
replace the float switches used in the earlier Block
10s. Unfortunately, it was discovered during testing
that not enough probes were added to give
KEEPING THE RQ-4 IN THE AIR
Airman Todd, refuels
the Global Hawk on
the flightline at Beale
Air Force Base in
California.
WWW.ABDONLINE.COM AVIATION AFTERMARKET DEFENSE | SPRING 2010
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Photo by Airman 1st Class Krista Rose