188
Chapter 4
equipment is also costly, the components (tubes, transistors, resistors, etc.)
are comparatively inexpensive and can be tested individually under a variety
of controlled conditions. A study of the mathematical principles of
reliability has many useful concepts to offer the designer, despite the lack
of extensive quantitative design data on mechanical systems.
Attempts at establishing quantitative statements concerning reliability
were initiated
during World War II and were mainly concerned with
developing good vacuum tubes and reliable radio communication.
Between 1945 and 1950 studies [4.29] revealed that:
1. A navy study made during maneuvers showed that the electronic
equipment was operative only 30% of the time.
2. An army study revealed that between 2/3 and 3/4 of their equipment was out of commission or under repairs.
3. An Air Force study over a 5-year period disclosed that repair and
maintenance costs were about 10 times the original cost.
4. A study uncovered the fact that for every tube in use there was
one on the shelf and seven in transit.
5. Approximately one electronics technician was required for every
250 tubes.
6. In 1937 a destroyer had 60 tubes, by 1952 the number had risen to
3200 tubes.
It must be remembered that these studies were based on equipment
produced during World War II by anyone able to walk to a production
line. The engineering design work for many of these items was based
on pre-World War II design concepts. The analytical techniques coming
from design work on Korean and World War II weapon systems may
have contributed as much to improvement of systems reliability
as
the mathematical concepts of reliability.
Also note that airplanes in
World War II were designed by using slide rules and desk calculators,
where as the advent of analog and digital
computers has allowed
designers to simulate performance before committing themselves to a
fixed design. In other words, more variations and parameters can be considered in the analyses today.
What the concept of reliability has done is to bring to engineering the
benefits of statistics and probability for use in design. This in itself gives
the engineer additional tools to use while designing.
Missile projects [4.29] such as the "Sparrow," "Regulus" and
"Redstone" missiles and those since 1950 have used reliability concepts.
The 10% reliability
of the early Vanguard program increased to virtually
100% in the Minuteman. (The engineering design capabilities during this
time period were also increasing by leaps and bounds.)
Chapter 4
equipment is also costly, the components (tubes, transistors, resistors, etc.)
are comparatively inexpensive and can be tested individually under a variety
of controlled conditions. A study of the mathematical principles of
reliability has many useful concepts to offer the designer, despite the lack
of extensive quantitative design data on mechanical systems.
Attempts at establishing quantitative statements concerning reliability
were initiated
during World War II and were mainly concerned with
developing good vacuum tubes and reliable radio communication.
Between 1945 and 1950 studies [4.29] revealed that:
1. A navy study made during maneuvers showed that the electronic
equipment was operative only 30% of the time.
2. An army study revealed that between 2/3 and 3/4 of their equipment was out of commission or under repairs.
3. An Air Force study over a 5-year period disclosed that repair and
maintenance costs were about 10 times the original cost.
4. A study uncovered the fact that for every tube in use there was
one on the shelf and seven in transit.
5. Approximately one electronics technician was required for every
250 tubes.
6. In 1937 a destroyer had 60 tubes, by 1952 the number had risen to
3200 tubes.
It must be remembered that these studies were based on equipment
produced during World War II by anyone able to walk to a production
line. The engineering design work for many of these items was based
on pre-World War II design concepts. The analytical techniques coming
from design work on Korean and World War II weapon systems may
have contributed as much to improvement of systems reliability
as
the mathematical concepts of reliability.
Also note that airplanes in
World War II were designed by using slide rules and desk calculators,
where as the advent of analog and digital
computers has allowed
designers to simulate performance before committing themselves to a
fixed design. In other words, more variations and parameters can be considered in the analyses today.
What the concept of reliability has done is to bring to engineering the
benefits of statistics and probability for use in design. This in itself gives
the engineer additional tools to use while designing.
Missile projects [4.29] such as the "Sparrow," "Regulus" and
"Redstone" missiles and those since 1950 have used reliability concepts.
The 10% reliability
of the early Vanguard program increased to virtually
100% in the Minuteman. (The engineering design capabilities during this
time period were also increasing by leaps and bounds.)