Air Force Research
Laboratory scientists are working on a novel unmanned air vehicle
called SkyTote that will take off and land vertically like a
helicopter, but also transition into horizontal flight like a
SkyTote's primary mission is to deliver a payload to a specific
point within a tactically relevant range and time. It is a Small
Business Innovative Research Phase II effort orchestrated by
AeroVironment Inc of Monrovia, Calif., for AFRL's Air Vehicles
Directorate. According to AFRL's Tom Cord, SkyTote program manager,
the aircraft is a concept demonstrator and not a working
"We are not trying to reach a certain performance and
capability; we are trying to show that a hovering UAV with a fast,
forward speed is a likelihood. It's something we can do in a simple
way," he said.
Researchers are hopeful that after careful analysis and testing,
SkyTote will become a safe, inexpensive and reliable choice for
assessing bomb damage and conducting resupply missions or helping
with emergency troop evacuations. The SkyTote combines the vertical
takeoff, and landing and hover capabilities of helicopters with the
high-speed cruise capability of a fixed-wing aircraft.
Counter-rotating rotors with individual cyclic control provide
propulsion. Propulsion and transition from wing to propeller flight
are some of the major technical challenges in this effort.
Because of the cyclic
control, SkyTote looks like a helicopter when it is flying in
helicopter mode. When it is flying like an airplane, the helicopter
propeller-rotor system functions more like a propeller.
"It's not a great rotor or propeller; it's a good compromise
between a helicopter rotor system and an airplane propeller, and
that's part of what we are trying to show is that this system will
work well for this type of airplane,” Mr. Cord said.
“When you look at the design parameters, you either go one
way or the other. When you start to blend the two systems together,
it becomes challenging. That is one of the big areas we have
addressed during the past few years."
Researchers have been working on various versions of the SkyTote
since 1998. It was smaller then with a design meant to deliver a
400-pound payload to a point within a 300-mile range in less than
two hours. During the initial design phase, the vehicle was
redesigned from the original 2-foot to an 8-foot vehicle to make it
more realistic and usable for customers.
The new test vehicle was altered to carry a 50-pound payload
within 150 nautical miles because researchers believed a
medium-sized vehicle would be a more representative test of
technology and would be directly useful to customers. Mr. Cord said
these characteristics cannot be met by conventional helicopters and
Conventional helicopters with the same payload characteristics
can only attain speeds between 100 and 105 knots, while the
SkyTote, equipped with hover capabilities, can attain speeds of 200
The change in payload capabilities created a more realistic,
mechanical system, rather than a simplified concept demonstrator.
It also created more challenges for developers.
"We had to choose a different type of engine, a 52-horsepower
engine from UAV Engines, Ltd., a real engine that could be seen in
a car almost," Mr. Cord said. "Our vehicle is 208 pounds, so we've
grown significantly. We added a more complex transmission,
A more complex, heavier mechanical system also meant that
developers had to look closely at the control aspects of the
"The reason for this is that excess power reduces the need for a
carefully conceived flight control system and helps avoid several
problem areas, such as loss of control. With less thrust-to-weight,
we have to rely on the flight control system and the pilot to keep
us out of dangerous flight conditions. Autonomous control gives us
an advantage during testing because it provides safer, more
efficient tests," Mr. Cord said. During testing, SkyTote is
expected to operate in hover and conventional wing-borne flight
while also transitioning from hover to wing-borne and back. A pilot
will be standing by to take control of the plane, if needed.
However, most of the testing will be controlled autonomously.
Developers say these transitions have to be done at least five
times to demonstrate that SkyTote and its characteristics are a
good concept and should be considered for future applications.
The next cycle of SkyTote testing will be conducted in June at
Camp Roberts in California. [ANN Salutes Karen Y. Jackson, Air
Force Research Laboratory Public Affairs]