The Deployment Dynamics:Analysis of the 81MM Illumination Mortar Cartridges

The Deployment Dynamics:Analysis of the 81MM Illumination Mortar Cartridges

Seungeuk Han & Raymond Trohanowsky

AMSRD-AAR-MEM-A

Aeroballistics Division

Munitions Systems & Technology Directorate

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BACKGROUND

• The M853A1, 81mm Illuminating, Mortar Cartridges experienced 11 streamers during the ballistic LAT at Yuma Proving Ground on July 25, 2006.

• Nine(9) of eleven(11) streamers were reported as the non-deployment (the canopy and suspension lines still inside the bag).

• FMEA narrowed to three possible causes: frozen bag, insufficient drogue plate, or jammed main canopy.

• Pull tests and wind tunnel test had been conducted to verify the root cause.

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SYSTEM DESCRIPTION

Canister

Drogue Bag Drogue Plate

Deployed Canopy Non-Deployed (Streamer)

Main Canopy

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Drogue Plate

5

Intact Drogue Bag with/without Riser

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The deployed 9 inch Drogue Chute

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SPECULATIONS

• Frozen Bag: A bag exposed to high humidity then frozen may require more force to deploy the main canopy than the bag stored at ambient condition.

• Insufficient Drogue Plate: Drogue plate may not generate adequate drag force to deploy the main canopy.

• Jammed Main Canopy: Canopy may be jammed inside the drogue bag due to one of these phenomenon:– Chinese Finger-cuff Effect: due to the fiber orientation of the bag,

the bag may constrict as it is pulled.– Piston (Vacuum) Effect: due to the vacuum inside the bag, the

canopy may be difficult to deploy from the bag.

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PROCEDURES

• Laboratory Tests were completed to validate FMEA alternatives– Pull Tests

1. Steady Pull Test2. Dynamic Pull Test

– Wind Tunnel Tests3. Aerodynamic Characterization Test4. Drag Force Comparison Test

• This test data was evaluated to determine FMEA and propose design alternatives

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STEADY PULL TEST APPARATUS

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STEADY PULL TEST

• Alternative configurations were tested. • Ten baseline configurations were temperature conditioned

at –30°F for a minimum of 5 hours, then tested.• The drogue plate suspension line was tied to an eye bolt

connected to the 1.23” balance.TR0611: Run 0010

-16

-14

-12

-10

-8

-6

-4

-2

0

0 2 4 6 8 10 12 14 16

time, sec

Forc

e, lb

s

• The test samples were pulled at a constant rate of 1.6”/sec until the main chute is fully deployed from the drogue bag. The data acquisition system tracks the force history.

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DYNAMIC PULL TEST APPARATUS

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0

1

2

3

4

5

6

7

8

9

10

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

time, sec

Forc

e, lb

s

DYNAMIC PULL TEST

• A balance was mounted to an A-frame in a high bay area.• The safety to protect the balance was 80 lbs.• A ballast of 4 lbs was dropped at two predetermined heights

(29 inches and 78 inches from the ground).• The data acquisition system tracks the force history

transmitted through the balance during the entire testing.

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• Three configurations were tested: drogue bag without the riser, the drogue bag with riser, and the drogue plate.

• The 0.88B strain gage balance was used.• Mach numbers tested include 0.21, 0.30, 0.50, and 0.61

with the angles-of-attack of -4 to +15 degrees.

DRAG FORCE COMPARISON TEST

Axial Force Coefficient

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65

Mach number

Axi

al F

orce

Coe

ffic

ient

Drogue Plate Drogue Bag w/o Riser Drogue Bag w/ Riser

• The aerodynamic test conditions, axial force, pitching moment, and normal force were recorded.

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• The drogue chutes were attached to an eyebolt, which was attached to the 0.88B strain gage balance inside the bomb strut assembly located upstream of the test section.

• Mach numbers tested include 0.21, 0.30, 0.50, and 0.61 at zero angle-of-attack.

AERODYNAMIC CHARACTERIZATION TEST

Drag Force of 9"x9" Drogue Chute

-15

-14

-13

-12

-11

-10

-9

-8

-7

-6

-50.05 0.07 0.09 0.11 0.13 0.15 0.17 0.19 0.21 0.23

Mach number

Dra

g Fo

rce,

lbs

• The aerodynamic test conditions, and axial force were recorded.

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RESULTS

• Steady Pull Tests:– Required pull force (2 -4 lbs) agreed with historical data,

without any abnormality.

• Dynamic Pull Tests:– The required pull force increases as the snatching force

increases.– The required pull force is not linear over snatching

velocity.

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AERODYNAMIC CHARACTERIZATION

– No significant differences in drag among the three configurations (the intact bag with/without riser, the drogue plate).

– Due to similar drag and weight between the drogue plate and drogue bag, there is no momentum difference between the two.

– Inversely, this finding raises a question about the successful deployments.

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DROGUE CHUTE DEPLOYMENT TESTS

– The 9 inch drogue chute performance is insensitive to the tested suspension line lengths.

– The drag of the 9 inch drogue chute exhibited around 30 lbs (about 8 - 9 times of the drogue plate) at Mach 0.2.

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CONCLUSIONS

• The results of the pull test came out as expected and agreed with the previously reported data (no new findings).

• The dynamic pull test showed an increase in the mean pull force but inconclusive due to a trend of nonlinearity.

• The wind tunnel test showed no drag difference between the drogue bag and the drogue plate.

• The successful deployment in the past might be done mechanically and accidentally (by swing motion of the aluminum drogue plate) rather than aerodynamically.

• In order to make the function aerodynamically, the 9” square drogue chute is highly recommended.

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RECOMMENDATIONS

• Conduct a horizontal ballistic test to characterize the ADS of the 81mm, M853A1.

• A lab test to simulate and understand the steel cable bending phenomenon.

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POCs

• Seungeuk Han– US Army, RDECOM-ARDEC– seungeuk.han@us.army.mil– 973 – 724 – 2978

• Raymond Trohanowsky– US Army, RDECOM-ARDEC– trohanowsky.raymond@us.army.mil– 973 – 724 - 7865