Abstract

Due to its strong construction, resistance to

marine environment and its projected service
life, the S-2E Tracker aircraft was chosen to
extend its operational performance through
re-engining, systems upgrading and
integration of new avionics. The aircraft was
originally designed for carrier based
antisubmarine missions and is ideally suited
for efficient and effective maritime patrol.
With the installation of rapid-response, 1645
horsepower, Garrett TPE331-15AW turbo-
propeller engines and five blade composite
reversible propellers, the S-2E/turbine
becomes a high-performance aircraft with a
greater climb rate and 50 percent reduction in
fuel consumption over the original S-2E piston
aircraft. Intensive flight tests have proven a
dramatic increase in mission capability with
increased area coverage and flight safety
improvements. lsrael Aircraft Industries (IAI) is
conducting a program to retrofit S-2E Tracker
aircraft with Federal Aviation Administration
(FAA) and MIL-STD certified, state-of-the-art
engines, avionics and sub-systems.

Introduction

The original S-2E Tracker aircraft are four-

place, twin piston engine, high-wing
monoplanes that were manufactured by
Grumman Aerospace. They were designed for
use in anti-submarine warfare (ASW) and are
capable of operating from carrier or land
bases, with or without the aid of a catapult.
Aircraft functions are to search for, detect,
track, localize and destroy submarine contacts
under all weather flight conditions. The
S-2E/turbine (see Fig. 1) is the result of an
extensive upgrade program conducted by
IAI/BEDEK Aviation Division which provides
service life extension, re-engining, avionics
modernization and maintainability
improvement.

Design Objectives

To improve flight performance with an

engine/propeller combination which will
provide a significant increase in thrust.

To improve the present standard of durability

and maintainability in operation on carrier .and
in all weather environments.

To modify the structure and systems to a

standard of safety equal to or better than that
of the original structure and systems on the
unmodified aircraft.

To demonstrate the new engines and

systems provide improved performance and
handling qualities in comparison to the
existing configuration.
 5. To extend the present flight envelope and to
establish satisfactory operating procedures and
limitations.

Figure 1: S-2E Turbine Tracker

Description
The S-2 E/turbine Tracker aircraft upgrade program
provides the following major features (see Fig. 2):

 Replace existing piston engines with two Garrett

turboprop engines TPE331-15AW. These
FAAcertified engines are light-weight, shaft rated
at 1645 HP with water/methanol injection. The
advantage this engine provides over the
"freeturbine' style engine is a rapid spool-up
response necessary for carrier operation. Major
benefits of this engine are integrated electronic
control (IEC) which provides automatic start
sequencing and power management and the
time between engine overhaul (TBO) increase
from 200 hours to 3000 hours. The turbine
engine kit (see Fig. 3) is provided by IAI/BEDEK
sub contractor Marsh Aviation Co.
 The existing fuel and hydraulic systems are
upgraded to meet the RPM and flow-rate
limitations of the new turbine engines.
 Replace existing three-blade aluminum
propellers with five-blade feathering/reversing
composite propellers.
 Redesign engine nacelle (see Fig. 4) to reduce
drag with streamlined composite cowlings.
Design features include lightning protection
and certification to meet FAA fireproof
requirements (2000° F for 5 minutes).
 Upgraded engine compartment fire detection
and suppression systems were qualified by full
scale flight testing.
 New engine mount incorporates fail-safe
design while engine isolators meet FAA
fireproof requirements (2000° F for 5
minutes).

Figure 2: S-2E Turbine Tracker Upgrade Areas

Figure 3: S-2E Marsh Aviation Turbine Kit

 New exhaust/eductor system provides

nacelle ventilation and waste heat for
existing sonobuoy heating system.
 Replace existing mixture, throttle, and
propeller controls with new power and
speed levers with friction controls to
provide accurate ground and flight
handling.
 Replace existing flight control system
(FCS) with modern FCS integrated with
new ADI/HSI, vertical gyro, compass and
existing TACAN system (see Fig. 5) The
FCS is a 3-axis flight director and
autopilot. It consists of a flight
computer, air data computer, mode
controller and annunciator panel. The
FCS uses digital signal processing for
mode selec1ion, annunciator and
command computation. It incorporates
radio navigation, navigation and
localizer coupIing, plus manual/auto trim
as well as half-bank and turbulence
modes.
 Other options include:
o -yaw axis control
o -airspeed gain scheduling
o -go-around mode
o -dual manual electric trim system
with pilot
o -long range navigation system
 compatibility
 Electrical system upgraded to meet
turboprop engine specifications. New
400A DC starter/generators replace
existing transformerrectifiers providing
increased capability to add new ASW
equipment not previously possible (see
Fig. 6 ).
 Cockpit redesigned to accommodate
new systems, engine control panels,
warning and caution/advisory panels
and new avionics displays.
 Existing heating and ventilation system
is replaced by a new environmental
control system (ECS). The air cycle
machine (ACM) utilizes engine bleed air
to provide cooling, heating, and
ventilation to the crew and equipment
compartments. The ECS is designed to
meet the requirements of an
unpressurized aircraft while providing
capacity for additional ASW equipment.
The ECS bleed supply ducts incorporate
leakage detection to improve system
reliability.
 New gaseous oxygen system is designed
to meet the requirements of an
unpressurized aircraft and the typical
mission profile. Four diluter demand
regulators for crew extends the flight
envelope beyond original limitations.
 Replace existing carbon arc searchlight
with continuous duty, high intensity,
80,000,000 candlepower xenon arc
searchlight.
  Add 150-gallon auxiliary fuel tank in the
weapon bay to extend the aircraft range
for maritime reconnaissance missions.
 Stall improvement modifications include
vortex generators placed between the
ailerons and leading-edge slate and 18-
inch stall strips placed between fuselage
and nacelles (see Fig. 7).
 New propeller synchrophaser system
minimizes cockpit noise levels.
 Existing airframe de-ice system
modified to operate from low pressure
engine bleed air.

Design Qualifications

In order to certify the aircraft and meet

design objectives the following were
considered:

 Engine tests and analyses to

demonstrate compliance for carrier use
which resulted in:
o oil tank and tank mounting
modifications.
 Engine marinization (see Fig. 8) which
provides enhanced corrosion
resistance including:
o -improved aluminide-type turbine
coatings on the first and second
stage bIades and vanes.
o -use of aluminum material in
gearbox housings in place of
magnesium.
 Propeller development in accordance with
FAR Part 33 pending MIL-SPEC endurance
test requirements. Propeller testing
included ground and in-flight strain
 surveys conducted by Hartzell, the
propeller manufacturer.
 Conducting failure modes and effects
analysis (FMEA) and maintenance
analysis with compliance to military
specifications for the engine and utility
systems.
 Using the subcontractor (Marsh Aviation
Co.) demonstrator aircraft to conduct full-
scale ground, flight and field-carrier
landing practice (FCLP). Tests
demonstrated flight and propulsion
performance, flying qualities, systems
and equipment performance, structure
loading and carrier suitability. In
addition, the aircraft was shown to be
flutter-free up to Vd=322 ktas.
 Analyze wing bending moment, shear
force and torsion to establish new
maximum flying weight and
maneuvering envelope.

Summary of Results

 The demonstrator aircraft has

completed over 200 hours ol flight tests
and has proven the S-2E/turbine is
capable of speeds in excess of 250 ktas
and can reach an altitude of 25,000 feet.
 With the new engines, the S-2E has 45
ktas higher cruising speed with 50 percent
reduction in fuel consumption and 30
percent reduction in the take-off and
landing distances. The aircraft rate of
climb is improved by 50 percent. Single
engine rate of climb is improved by 3 0
percent. With the auxiliary fuel tank, the
range is extended approximately 180
 Nm and the endurance is prolonged by
1.3 hours (see Fig. 9). Note: Recent flight
test data demonstrate considerable
performance improvements over the
conservative performance predictions
presented in Fig. 9.
 Under supervision of the U.S. Navy,
catapult launches and arrested landings
were successfully performed.
 New flying weight limitation reflects
weight reduction in the engine nacelles
due to the new turboprop engines,
additional fuselage equipment and nose
ballast installed to retain the aircraft
center of gravity within established
limits (payload remains unchanged).
 The existing permissible indicated
airspeeds remain unchanged.
 The modified aircraft experienced
increased control about the roll axes as
well as improved aerodynamic warning
with the stall devices installed.
 The reduction of weight in the nacelles
and the modification of the thrust vector
caused by the turbine conversion
effectively lowers the vertical center of
gravity which also helps to improve the
pitch up tendency found in the
S2-E/piston engine version.

Business Opportunity

In today's world of restricted budgets and

reduced manpower levels, some operators are
currently considering converting their S-2 E
Trackers to the turboprop configuration with
or without upgrading the ASW systems.
 Others are considering converting their S-2E
Trackers for use as fire fighting aircraft
utilizing the turboprop configuration with 800-
1000-gallon retardant tank installation.

Figure 4: S-2E Streamlined Nacelle

Figure 5: Block Diagram of the S-2E/Turbo Autopilot
System
Figure 6: Electrical System Block Diagram