Momentum - October 2019 - 6

STUDENT
GENERATION

GPS antennae
7%
Pixhawk
7%

Elevon
servos
4%

Photo credit: David Gaitan

Receiver
2%

Structure
41%

Battery
10%

Payload (ping
pong balls)
29%

Weight buildup of glider components. Total weight: 8.5 oz.

AVL and VORSTAB are both Fortran codes that were
used extensively to conduct aerodynamic and stability
& control analysis to determine if this shape of vehicle
was even possible. They necessitated adding wingtip
extensions, turning the configuration into a "cranked
delta," and making the leading edges of the triangular
wedge an acute angle to the top flat face to take
advantage of vortex lift. Elevons appended to the rear
edge of the triangle added controllability while a tall
rudder added directional stability-both essential for
controllable flight from deployment to the ground. These
elements together would create the "starship" design.
However, the unconventional design involved significant
risk to the project. Without any precedence, no one knew
whether this configuration would actually glide well, let
alone be controllable by an autopilot. Yet, this was the
exact innovative thinking that drove the team's success.
It wasn't without iteration or hard work that the final
hardware design was reached. Solidworks CAD was used
to design a lightweight balsa-wood structure, arrange
components and payload compactly, and measure center
of gravity. AutoCAD allowed for laser-cut parts to be
produced very quickly and precisely, which increased the
rate of production and subsequent speed of iteration.
Once a new design was built, it was immediately flight
tested, and the results of both the manufacturing process
and flight test were used to design a better model in an
iterative cycle. This cycle continued at least ten times
before the team settled on the final configuration.
The mothership aircraft design and assembly ran in
parallel; however, its conception to flight time was far
greater than that of the glider, necessitating innovative
testing procedures. Flight testing methods began with
a quadrotor aero tow drop and moved to powered
rc aircraft aero tow release to more closely simulate
expected flight conditions.
Flight control software design essentially centered
around programming settings into a pre-existing flight
control system, a Pixhawk running APM software. At a
6 October 2019

Glider formation flying.
high level, the control architecture utilized GPS and orientation data
in a PID control loop to actively guide the glider to the center of the
target after deployment. The decision to use a commercial-off-theshelf autopilot was due to the limited development timeframe. Even so,
finding the right settings for the autopilot to provide consistent, reliable
landings within the target zone was difficult.
The final hurdle was integration of three gliders with the mothership
aircraft. A single small rail with a hole situated near the center of
gravity provided everything needed for connection to the mothership
dropping mechanism. A simple hook attached to a servo within
the pylon of the mothership provided reliable dropping action, but
only after several failed attempts and frustrating flight tests of nondeployment. Left for the end, integration was a very difficult problem.
The forces and moments the glider experienced during flight while
attached necessitated a secure attachment that could be reliably
released. However, the team discovered that the more fixed the glider,
the more likely it would get stuck in the mechanism. There was a
careful balance struck between fixing the glider in place and preventing
excessive movement that would cause damage to the underside of the
mothership's wing. In the final week before the competition, a dropping
mechanism design prevailed, the magic software settings were found,
and the aircraft were all given competition angry eyes.
The gliders turned heads at the competition both by their
performance and their unique style. They represented an innovative
solution to a complex problem. However, this aspect of the project was
only a small part of the unique systems needed to successfully complete
the entire mission. Everyone involved worked tirelessly at all stages of
the process from conceptual design through the flight rounds at the
competition. Of the nine total gliders that successfully made it into the
target zone over the entire competition, eight of them were ours.

Frank Kozel, chief engineer of the 2019 Georgia Tech Advanced Class
competition team at SAE Aero Design, wrote this article for MOMENTUM.
He graduated from Georgia Tech and has begun a graduate program in
aeronautics and astronautics at Stanford University.

MOMENTUM

Momentum - October 2019

Table of Contents for the Digital Edition of Momentum - October 2019