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27 MARCH 200327 MARCH 2003

ERIC HAWLEYERIC HAWLEY

Contact InformationContact InformationPhPh: (301) 744-1822: (301) 744-1822Fax: (301) 744-4410Fax: (301) 744-4410

hawleyejhawleyej@@ihih.navy.mil.navy.mil

INDIAN HEAD DIVISIONINDIAN HEAD DIVISIONNAVAL SURFACENAVAL SURFACEWARFARE CENTERWARFARE CENTER

INDIAN HEAD, MDINDIAN HEAD, MD

MK 66 ROCKET MOTOR/HELICOPTERCOMPATIBILITY PROGRAM

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Helicopter Engine Compatibility Background

• Problem description:– AH-1F downed with fatalities in 1988 while firing MK 66

Rocket Motors– Army investigation concluded that the accident was caused by

engine ingestion of high-temperature, oxygen-depleted rocketexhaust gasses

• AH-1 physical mod implemented (air scoop)

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Helicopter Engine Compatibility Background

• AH-64 testing identifies rocket exhaust ingestion intoengines still a problem

• Causes engine torque splits and torque fluctuations (surges)• Physical mod to aircraft considered not practical• Firing restrictions in effect

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• High temperature oxygen depleted rocket exhaustcaused by secondary combustion

• Secondary combustion (afterburning) occurs when COand H2 in the exhaust react with oxygen in atmosphere

Helicopter Engine Compatibility Background

Current MK 66 exhaust componentsCombustion Component Exit Composition (mole fraction)

CO2 0.1898CO 0.33007H2O 0.18146H2 0.17295N2 0.12218Pb 0.00177Cu 0.00177

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MK 66 Rocket Motor Background

Motor CaseK2SO4Salt Rod

Nozzle

Igniter

PropellantGrain

MK 66 MOD 4 ROCKET MOTOR

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Helicopter Engine Compatibility Approach

30 FEET

• Secondary combustion can be suppressed byintroducing more potassium sulfate (K2SO4) into motorexhaust– Mod 0-4 Salt Rod addresses rocket exhaust ingestion issue in

fixed wing aircraft– Helicopter ingestion situation is the same

• Ingestion timeline is different• Existing salt rod consumed in 6 feet of motion• Helicopters need salt rod effect through rotor downwash• Army Aviation Engineering specifies 30 feet as necessary

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• There is a linear relationship between salt volume andduration of afterburning suppression

• Amount and shape of salt rod modified to increaseeffectiveness for 30 feet

• Enlarged salt rod contains ~ 3x more K2SO4

Salt Rod Modification

0.33 INCH DIA X 4 INCH LONG SALT ROD

0.5 INCH DIA X 15.3 INCH LONG SALT ROD

0.5 INCH DIA X 6 INCH LONG SALT ROD

MOD 4

Modified

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• K2SO4 reactions

– Afterburning reaction:2CO + 3H2 + 2OH + 2O2 => 2CO2 + 4H2O

– Reaction with K2SO4:

– K2SO4 provides oxygen to the exhaust, which delays the overallreaction of the exhaust fuels (H2 and CO) with the atmosphericoxygen (O2)

Exhaust Chemical Analysis

Atmospheric oxygen

K2SO4 + 2CO + 3H2 + 2OH + 2O2 => 2CO2 + 3H2O + H2S + KO + K + 2O2

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Static Fire Test

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• Motor exhaust temperature found to be more than20% lower than current MK 66 motors at 77 F and150 F

Static Fire Test Results

Time (msec)0 250

Steady State Temperatures

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• Suppressed flight distance >30 ft average

Ground Launch Results

HELICOPTER COMPATIBILITY ROCKET MOTOR (150 F)

MK 66 MOD 3 ROCKET MOTOR (150 F)

Launcher

Launcher

SuppressedDistance

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• Ground launch thermal data

HELICOPTER COMPATIBILITY ROCKET MOTOR (150 F)

LAUNCHER

MK 66 MOD 3 ROCKET MOTOR (150 F)

LAUNCHER

Ground Launch Results

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• Air launch test on an instrumented AH-64A with MK66 motors w/ enlarged salt rod conducted in 1998

• Test conditions– 10 knot wind restrictions– Altitude was 150 ft– Air temperature was in upper 70s, 70-80% RH– Test pass/fail criteria:

• Torque split exceeds 15%,• Main engine torque fluctuations of ±15%,• Tail rotor torque fluctuations of ±500 ft-lbs

Air Launch Verification

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• All engine surge conditions eliminated except one– Hover: All surge conditions eliminated– 40 kts forward flight: All conditions but one eliminated

Air Launch Results

CONDITION L E F T O U T B O A R D LEFT INBOARD RIGHT INBOARD RIGHT OUTBOARD MK 66 MOD 3 HELICOPTER COMP

ROCKET ROCKETS ROCKET ROCKETS ROCKET ROCKETS ROCKET ROCKETS ROCKET MOTOR ROCKET MOTOR

DENSITY FIRED DENSITY FIRED DENSITY FIRED DENSITY FIRED

10 28 8

12 1219 1919 19 19 19

HOVER 14 2 1 TESTED TWICE12 4 1 TESTED TWICE8 8

19 2

17 2

15 2

16 4

12 12

19 19

19 2/1 1 1, 1 (NOTE 1)17 2/1 1 1 (NOTE 2)

40 KTAS 15 2

FORWARD 2 2

19 2 1 TESTED TWICE17 2 1 TESTED TWICE15 2 1 TESTED TWICE

12 4 12 4 1 TESTED TWICE8 8 8 8 5

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• Worst condition: 40 kts forward flight, one or tworockets fired from left inboard launcher

Air Launch Results (cont.)

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• Enlarged salt rod causes ignition pressure spikes– Enlarged salt rod known to increase pressure, and therefore

thrust during ~ 0.10 second of burn– Measured thrust values near MK 66 specification limit of 2100

lbf

Internal Pressure Concerns

Thrust Curve Comparison

-500

0

500

1000

1500

2000

2500

3000

0

0.05

0.11

0.16

0.21

0.26

0.32

0.37

0.42

0.47

0.53

0.58

0.63

0.68

0.74

0.79

0.84

0.89

0.95 1

1.05 1.1

1.16

Time (sec)

Thru

st (l

bf)

MOD 4Modified

Thrust Limit = 2100 lbf

Thrust Limit = 2350 lbf Thrust Limit = 2900 lbf

0.5 s0.7 s

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• Thrust requirement derived from internal forward endmeasured pressures

• Aft end known to be weakest point on motor (lockwirejoint)

• Efforts made to measure pressure at aft end

Pressure Differential Test

Lockwire joint

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• Pressure differential test performed at Indian Head inJune 2002– Previous analysis predicted a 350 - 500 psi drop at 150oF– Aft pressures measured ~400 psi lower than forward end

during first 0.10 seconds at 150oF

Pressure Differential Test

Pressure Comparison

-500

0

500

1000

1500

2000

2500

0

0.06

0.11

0.17

0.22

0.28

0.33

0.39

0.44 0.5

0.55

0.61

0.66

0.72

0.77

0.83

0.88

0.94

0.99

1.05 1.1

1.16

Time (sec)

Pre

ssu

re (

psi

)

Head Pressure

Lockwire Pressure

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• Thrust limit redefined based on aft end pressures– Recommended a new thrust limit of 2500 lbf for the first 0.10

seconds of burn• Maintains motor tube factor of safety of 1.5• Verified by analysis and historical data• Approved by sponsor

Pressure Differential Test Results

Thrust Curve Comparison

-500

0

500

1000

1500

2000

2500

3000

0

0.05

0.11

0.16

0.21

0.26

0.32

0.37

0.42

0.47

0.53

0.58

0.63

0.68

0.74

0.79

0.84

0.89

0.95 1

1.05 1.1

1.16

Time (sec)

Thru

st (l

bf)

MOD 4Modified

Thrust Limit = 2500 lbf

Thrust Limit = 2100 lbf

Thrust Limit = 2350 lbf

Thrust Limit = 2900 lbf

0.1 s 0.5 s 0.7 s

New Thrust Limit

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• Enlarged salt rod design will be incorporated into theMK 66 MOD 6

• Qualification of MOD 6 scheduled to begin in thisspring– Qualification includes:

• Environmental Tests• Ground Launch• Air Launch

• Due to enter production midway through FY04

Future Work

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Contact InformationContact Information

ERIC HAWLEYERIC HAWLEY

PhPh: (301) 744-1822: (301) 744-1822Fax: (301) 744-4410Fax: (301) 744-4410

hawleyejhawleyej@@ihih.navy.mil.navy.mil

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