ENERGENCY FUEL DUMP SYSTEM
RELIABILITY ANALYSYS
PREPARED BY
Young Kim
Javier Molina
E419 Spring 2013
Professor Joseph Berk
1.0 SCOPE:
The following report is a Reliability Analysis detailing mathematical models
and reliability predictions for the Emergency Fuel Dump System, abbreviated as
EFDS, presented in IE419. The system reliability is calculated and determined
to be
2.0 REFERENCE DOCUMENTS:
A. MIL-HDBK-217F
B. RIAC AUTOMATED DATABOOK(NPRD-2011)
C. LECTURE SLIDES
3.0 OVERVIEW:
The design of EFDS is broken into two major sections. These sections are
Relay-Actuated Barrier, which is blocking the piston from penetrating fuel tank
in case of malfunctioning of system when idle. Another main section is Piston
with Pressure Cartridge, responsible for penetrating fuel tank when powered by
power supply. These two main sections operate independent to each other, but,
both of them have to work simultaneously in order for the system to successfully
work.
4.0 ASSUMPTIONS:
The following assumptions were made for the calculation of reliability:
a. Electrical parts of system were modeled after MIL-HDBK-217F
b. The aircraft is a fixed wing military aircraft
c. Calculated Time (Hours) = 3 hours
d. Temperature = 35°C
e. Relay Cycle Time ≤ 1 Hour
f. Contact form of the Relay = SPST
g. Parts for the fuel tank do not affect the reliability of the system
h. Only two bolts and O-ring are necessary for the pressurized cartridge system
to work properly
i. Aircraft is operating in environment that is ¼ hazard than that of operating
in AA environment
5.0 Rationale for failure rate prediction:
For the parts that are not list on either NPRD-2011 or MIL-HDBK-217F,
rationales made were that it is going to
have same failure rate or twice of that of the parts that are essentially
performing similar jobs.
Such Parts includes: Gland, Tank, Barrier, and Piston.
6.0 Block diagram
7.0 Calculation and prediction of reliability for electrical
parts:
Equation: λp=λb*πL*πC*πCYC*πF*πQ*πE
λb(10^-6)
|
πL
|
πC
|
πCYC
|
πF
|
πQ
|
πE
|
λp(10^-6)
|
|
Relay
|
0.0063
|
1
|
1
|
0.1
|
9
|
0.1
|
9
|
0.005103
|
Switch
|
0.00045
|
1
|
1
|
1
|
18
|
0.0081
|
8.0 Butterfield Calculation:
Equation: Ƞs = (Rs‐1)/((RsVc)^2 +Vp^2)^1/2
Characteristic
|
Influence Factor
|
Characteristic Variabiltiy
|
V^2*i
|
Initial Internal Volume
|
1.000000
|
0.030000
|
0.002500
|
Target(tank)
|
8.000000
|
0.080000
|
0.021600
|
O-Ring/Cylinder Friction
|
0.500000
|
0.010000
|
0.000100
|
Unknown/Unassessable
|
0.005000
|
||
Total
|
0.029200
|
Variable N N*
Mean SE Mean StDev
Minimum Q1 Median
Q3
|
|||
C1 20 0
8549.8 6.29 28.1
8507.0 8530.3 8543.0
8576.8
|
|||
Square root(v_p)
|
0.170880
|
||
V_c=std/avg
|
0.003287
|
||
Available pressure
|
510.000000
|
||
Actual Output Pressure
|
270.000000
|
||
R_s
|
1.888889
|
||
Ƞs = (Rs‐1)/((RsVc)^2 +Vp^2)^1/2
|
5.198399
|
||
Normdist(reliability)
|
0.99999989949401100
|
||
Failure Rate
|
3.3502E-08
|
||
9.0 Complete list of parts with failure rate and
reliability(NPRD-2011):
Quantity
|
Part Name
|
Part Number
|
Failure Rate(10^-6)
|
MBTF
|
Reliability
|
Source
|
1
|
Gland
|
38507
|
0.05
|
2.00E+07
|
0.99999985
|
|
8
|
Bolt
|
MS20995C
|
0.005523
|
1.81E+08
|
0.999999983
|
NPRD-2011
|
8
|
Bolt
|
MS20998C
|
0.005523
|
1.81E+08
|
0.999999983
|
NPRD-2011
|
2
|
O‐Ring
|
7010MR954T
|
0.097487
|
1.03E+07
|
0.999999708
|
NPRD-2011
|
1
|
Tank
|
80920
|
0.236298
|
4.23E+06
|
0.999999291
|
|
2
|
Barrier
|
81021
|
0.1
|
1.00E+07
|
0.9999997
|
|
1
|
Gasket
|
NAS1612‐6A
|
0.5
|
2.00E+06
|
0.9999985
|
NPRD-2011
|
2
|
Cylinder
|
81121
|
0.118149
|
8.46E+06
|
0.999999646
|
NPRD-2011
|
4
|
O‐Ring
|
7008MR954T
|
0.097487
|
1.03E+07
|
0.999999708
|
NPRD-2011
|
2
|
Closure
|
81026
|
0.05
|
2.00E+07
|
0.99999985
|
|
2
|
Harness
|
EA7689
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
1
|
Harness
|
EA7690
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
2
|
Piston
|
80934
|
0.1
|
1.00E+07
|
0.9999997
|
|
2
|
Harness
|
EA7691
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
2
|
Link
|
80935
|
0.098074
|
1.02E+07
|
0.999999706
|
NPRD-2011
|
1
|
Harness
|
EA7692
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
1
|
Harness
|
ES7693
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
1
|
Harness
|
EA7694
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
1
|
Harness
|
EA7695
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
1
|
Harness
|
EA7696
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
1
|
Battery Power supply
|
PS3457
|
15.574868
|
6.42E+04
|
0.999953276
|
NPRD-2011
|
1
|
Harness
|
EA7697
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
1
|
Battery Power supply
|
PS3458
|
15.574868
|
6.42E+04
|
0.999953276
|
NPRD-2011
|
1
|
Harness
|
EA7698
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
1
|
Battery Power supply
|
PS3460
|
15.574868
|
6.42E+04
|
0.999953276
|
NPRD-2011
|
1
|
Harness
|
EA7699
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
1
|
Harness
|
EA7699A
|
1.312255
|
7.62E+05
|
0.999996063
|
NPRD-2011
|
Total Failure rate(Mechanical + Electrical) = 67.488*10^-6
MTBF = 1/λ
= 14817 hours
10.0
System Reliability,
Failure Rate, and MTBF
Failure Rate:
|
67.488*10^-6
|
MTBF(system):
|
14817 hours
|
System Reliability:
11.0
Recommendation:
Due to small mission time, the calculated reliability of the system is
relatively high. However, in consideration that this system will operate in a
situation where people’s lives are involved, we would want it to be reliable as
possible. The highest failure rate happens at the power supply. Hence, we
should modify the design so that chance of system failing due to power supply
becomes 0. What we can do is to make the power supply a parallel circuit with a
diode installed. When switch is closed, both power supplies will provide a
power while diode will permit only one power supply to provide a power
preventing from over powered system and allow it to pass when other one fails.
Correct implementation of this method will decrease the chance of system
failing due to power supply hence increases the system’s reliability.
12.0 System Schematic:
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