Article
Analysis of Pilot-Induced-Oscillation
and Pilot Vehicle System Stability Using
UAS Flight Experiments
Tanmay K. Mandal and Yu Gu *
Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, WV 26506, USA;
tmandal1988@gmail.com
* Correspondence: yu.gu@mail.wvu.edu; Tel.: +1-304-293-3992
Academic Editor: David Anderson
Received: 15 August 2016; Accepted: 14 November 2016; Published: 29 November 2016
Abstract:
This paper reports the results of a Pilot-Induced Oscillation (PIO) and human pilot control
characterization study performed using flight data collected with a Remotely Controlled (R/C)
unmanned research aircraft. The study was carried out on the longitudinal axis of the aircraft. Several
existing Category 1 and Category 2 PIO criteria developed for manned aircraft are first surveyed and
their effectiveness for predicting the PIO susceptibility for the R/C unmanned aircraft is evaluated
using several flight experiments. It was found that the Bandwidth/Pitch rate overshoot and open
loop onset point (OLOP) criteria prediction results matched flight test observations. However, other
criteria failed to provide accurate prediction results. To further characterize the human pilot control
behavior during these experiments, a quasi-linear pilot model is used. The parameters of the pilot
model estimated using data obtained from flight tests are then used to obtain information about the
stability of the Pilot Vehicle System (PVS) for Category 1 PIOs occurred during straight and level
flights. The batch estimation technique used to estimate the parameters of the quasi-linear pilot
model failed to completely capture the compatibility nature of the human pilot. The estimation
results however provided valuable insights into the frequency characteristics of the human pilot
commands. Additionally, stability analysis of the Category 2 PIOs for elevator actuator rate limiting
is carried out using simulations and the results are compared with actual flight results.
Keywords:
Unmanned Aerial System; PIO; pilot vehicle interaction; longitudinal dynamics;
stability analysis
1. Introduction
There has been a surge in the use of Unmanned Aircraft System (UAS) in recent years due
to their low-cost and versatility in applications such as product delivery, routine surveillance,
resource management, disaster response, agriculture, etc. However, UAS development often does
not face the same design and testing rigor that is typical of a manned aircraft. With an increase in
UAS application the question of integrating them safely into the airspace shared with manned aircraft
needs to be addressed. Due to the fact that many (although with a decreasing percentage) small UAS
today are still fully or partially controlled by a ground pilot, a poorly designed UAS with inadequate
performance characteristics or handling qualities could lead to safety concerns.
One of the serious effects of inadequate design consideration towards human–UAS interaction
is the Pilot Induced Oscillation (PIO). Military Standard Flying Qualities of Piloted Aircraft
(MIL-STD 1797A) [1]
defines PIO to be “sustained or uncontrollable oscillations resulting from efforts
of the pilot to control the aircraft”. It usually occurs when the pilot is involved in a highly demanding
task and a trigger which interrupts the task and make pilot go out of sync with respect to the aircraft.
Aerospace 2016, 3, 42; doi:10.3390/aerospace3040042 www.mdpi.com/journal/aerospace
