2008 Annual Report - NASA Airborne Science Program

Figure 35
Flight Envelope with contours encompassing
90% of flight time at each flight condition
NASA Dryden built a GIII engineering simulation
for development and evaluation of the PPA. A
Monte Carlo capability was also developed in
parallel with the GIII simulation to examine the
PPA performance in the presence of vehicle
and atmospheric uncertainties. In early 2007,
flight testing of the PPA began. Cycle 1 flights
were designed to evaluate modeling of the GIII
and associated systems including the navigation
receiver, Flight Director, and factory GIII autopilot.
Cycle 2 flights were designed to map out
the flight envelope and determine the flight
conditions where the requirements are met.
Results
The five meter radius tube requirement was
met for the majority of flight conditions. Figure
35 shows results from the Cycle 2 evaluation
flights. The circles at each flight condition
represent the five meter radius tube. Generally,
there was adequate performance to keep
the GIII inside (or within a meter) of the tube
boundary over 90% of the time for each flight
segment. It was also observed as a rule that
tighter control, as reflected in more time spent
closer to the tube center, was seen at higher
Mach numbers.
The Euler rates were all within the desired
range during each flight segment for more
than 90% of the time at each flight condition.
Figure 36 shows the rates for representative
altitudes ranges, low (25k to 31k ft.), mid
(33k to 39k ft), and high (41k to 45k ft.), as
a function of Mach number. As a general,
rule roll rate was lower at higher dynamic
pressures.
Status
The PPA completed flight testing in January
2008. The precision autopilot demonstrated
the capability to provide a stable platform
that can repeatedly fly a predefined
trajectory within the tolerances prescribed
(five meter radius tube) over a 200 kilometer
track. It is currently operating on the
NASA GIII in UAVSAR flights throughout
California. Future plans for the PPA involve
deployment over Greenland to aid in ice
sheet measurements and integration into
the Stratospheric Observatory for Infrared
Astronomy (SOFIA) program.
Figure 36
Ninety percentile Euler Rates vs. Mach for low
(25k to 31k ft), mid (33k to 39k ft), and high
(41k to 45k ft) altitude ranges.
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