Comparison of Lockheed Martin F-35C and
Aurduplane UAS Firmware
The Lockheed Martin F-35C Lightning II is
a fifth-generation Joint Strike Fighter aircraft designed for operation from
aircraft carriers. The C model differs from the A model (delivered to the U.S.
Air Force) and the B model (the short-takeoff vertical landing version used by
the U.S. Marine Corps) by adding avionics that assist the pilot with approaches
to a pitching and rolling carrier deck.
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| Figure 1. F-35C Lightning II sea trials. |
Additionally, the F-35C is constructed
with titanium-reinforced airframe components, making the aircraft 5,500 pounds
heavier than the F-35A (Lockheed Martin, 2015). The catapult-launched takeoff
roll is automated, because the extremely high acceleration and short runway
distance are too short for a pilot to react to any changes that might occur.
The violent acceleration is also very physically demanding for the pilot. The
F-35C (and many other Naval aircraft) utilize heading hold and auto-throttle
during the catapult launch. The landing is a different story. There are several
technological advances that have made carrier landings easier for pilots, but
have not removed the human from the loop entirely. The Automatic Carrier
Landing System (ACLS) uses a ship-based radar and aircraft datalink to guide an
aircraft autopilot to a very small spot on the carrier deck. The pilot’s job is
to monitor the approach and adjust throttle as necessary to maintain the glide
slope. However, this system is only used by very experienced pilots, as
conducting a manual approach is much more difficult, and is a perishable skill
(Hibbetts, 2016).
However, a new feature of the F-35C is a
system known as Delta Flight Path, an automated glide path tracking system that
greatly reduces the amount of pilot input to maintain an approach path. Early
test results show that land-based practice approaches can be reduced from as
many as 18 approaches to just 6. Current carrier landing qualification requires
ten good traps, but could be reduced to six in the future (Seck, 2016).
The limitations of the F-35C automated
takeoff and landing systems are primarily due to integration and operability
issues that are often common to newly-fielded equipment. In a recent F-35A
exercise, five out of six aircraft were unable to launch due to software
stability issues on the ground (Dillow, 2016). Another issue with the nose gear
has led to oscillations during the takeoff roll resulting in pilot discomfort
and autopilot control issues (LaGrone, 2017).
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| Figure 2. Example fixed-wing aircraft utilizing Ardupilot flight controller firmware. |
The open-source Arduplane firmware is a
popular platform for integration in hobby and commercial UAS applications. The
Pixhawk autopilot is one of many compatible flight control systems, and can be
configured to operate an airplane, rotorcraft, or rover using branches of the
Ardupilot program. Arduplane is designed for fixed-wing propeller-driven
electric aircraft and features options for automatic takeoff and landing.
During automatic takeoff, the autopilot will command full throttle and pitch up
at a set angle, maintain a bank angle within a set angle, and climb to a
pre-set altitude before continuing on an automatic flight plan. Several
parameters must be set to account for different launch methods, in particular a
parameter called TKOFF_THR_DELAY that will delay starting an electric motor for
a set time after an acceleration is detected. This will prevent injury when hand
launching, or aircraft damage when bungee or catapult launching. There are also
options for ground steering during a takeoff roll for aircraft with landing
gear (Ardupilot, 2016).
An automatic landing may also be
incorporated into an automated flight plan for Arduplane. A NAV_LAND command
must be added to the end of the mission, indicating the GPS coordinates and
altitude of the touchdown point relative to the takeoff point. The autopilot
uses inputs from an airspeed sensor to calculate a glideslope that will provide
the necessary touchdown speed and altitude. Additional parameters can be
modified to provide an extended flare, or a pre-flare airspeed target that
leads to a deep-stall or reverse-thrust landing. The autopilot will fly the
approach while navigating to the touchdown waypoint, then enter a “flare” mode
that maintains a set pitch angle and wings less than 5 degree bank angle.
Several landing abort modes are available that permit autonomous go-arounds or
pilot-on-the-loop-controlled landings using the same pitch and bank limits as
the automated landing (Ardupilot, 2016).
Automatic takeoff and landing may both be
interrupted and continued manually by a pilot with an RC transmitter. The main
limitation of the automatic landing mode is that it is susceptible to
barometric altimeter errors due to changes in atmospheric pressure during the
flight, errors due to increased temperature of the autopilot electronics, or
errors due to local pressure changes from airflow around the altimeter sensor.
All of these can be mitigated through the use of a low-cost laser rangefinder,
which is an additional plug-and-play sensor that can be easily incorporated
into the aircraft systems (Ardupilot, 2016). There is no specific training
required to operate the Arduplane firmware, although a background in remote
control aircraft flight is highly recommended.
References:
Ardupilot.
(2016). Automatic takeoff. Retrieved
from http://ardupilot.org/plane/docs/automatic-takeoff.html
Ardupilot.
(2016). Automatic landing. Retrieved
from http://ardupilot.org/plane/docs/automatic-landing.html
Dillow,
C. (2016, August). Only one of six Air
Force F-35s could actually take off during testing. Retrieved from
http://fortune.com/2016/04/28/f-35-fails-testing-air-force/
Hibbetts,
T. (2016, March). How effective is the
automatic carrier landing system? Retrieved from
https://www.quora.com/How-effective-is-the-Automatic-Carrier-Landing-System-ACLS-Do-pilots-use-it-or-do-they-prefer-manual-landings
LaGrone,
S. (2017, February). Navy to test fix for
F-35C catapult problem next week. Retrieved from
https://news.usni.org/2017/02/16/f-35c-catapult-problem-next-week
Lockheed
Martin. (2015, October). The C at sea:
the F-35 aboard the USS Dwight D. Eisenhower. Retrieved from
https://www.f35.com/in-depth/detail/the-c-at-sea-the-f-35-aboard-the-uss-dwight-d.-eisenhower
Seck,
H.H. (2016, August). F-35’s new landing
technology may simplify carrier operations. Retrieved from
http://www.military.com/daily-news/2016/08/17/f-35s-new-landing-technology-may-simplify-carrier-operations.html
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