Meet: Robert Jercinovich
Instrumentation Engineer, 12' Wind Tunnel
Ames Research Center, Moffett Field, CA
Who am I
The performance of aircraft is defined by drag, lift, efficiency, etc.
In order to quantify these characteristics and improve efficiency we do
wind tunnel testing. These parameters cannot be measured directly but
can be calculated from other characteristics that can be measured. During
wind tunnel testing the Instrumentation Engineer is responsible for converting
physical phenomena that can be measured into electrical signals so that
they may be manipulated by a computer.
Some of the phenomena that can be measured are pressure,
force and temperature. Pressure distributions across a wing will quantify
the lift characteristics, force measurements will quantify the drag characteristics,
etc. Pressure, for example, may be measured a number of different ways,
to wit: diaphragm transducer, silicon piezoresistive element, or pressure
sensitive paint. It is the Instrument Engineer's job to determine which
type of transducer is best suited for the job in order to obtain the best
quality data. The factors that need to be considered to determine the
best type of transducer are: response time, accuracy, resolution, physical
size, signal type, etc. The Instrumentation Engineer must also interface
the transducers to the data system by specifying the gains, filters, channel
assignments, etc., on the computer. Thus the instrumentation Engineer
must be cognizant of both hardware and software.
For each test we have a pretest meeting with the
customer and the researchers. They describe what they are looking for,
their model, and what they are bringing to the test. We plan the instrumentation
requirements based on their needs. Pressure taps for instruments are built
into the model. We connect pressure sensors to these taps with tubing.
The Instrumentation engineer must specify the type of tubing to use and
must consider things like the pressure and temperature the tubing will
be used at. Also, he must consider flexibility and termination of the
tubing. Thus, a Instrumentation Engineer must be a Jack-of-all-trades.
We call a data run a sweep. For a sweep we record
the measurements at a series of angles of attack or different pitches
of the model (Alpha sweep) or angles of side slip, left to right (a Beta
sweep) for a given Mach speed or Reynolds number in the wind tunnel. The
measurements we make include the pressure distribution across the wings,
the forces through a balance on the model, and temperature to correct
for any thermal characteristics. We always measure force. But for some
tests we look for some unique data.
My Career Path
In college, at University of California at San Diego, I studied electrical
engineering. My emphasis was in Systems and Control. After college I worked
at the Naval Ocean Systems Center where I was in communications. After
that I worked at McDonnell Douglas where I worked on instrumentation for
structures and simulators. To test aircraft structures we did durability
and metal strength tests measuring the forces on the skin or substructures.
The simulator testing was for aircraft hydraulic systems and computer
What I Like About My Job
I get to play with a lot of equipment. I like that my work is objective.
The Early Influences
When I was a kid I liked to take apart cars and rebuild them. My parents
encouraged me to study science or engineering.
Take as many science and math classes as you can.
I look forward to continue working with the newly remodeled 12' wind tunnel.
It is unique in that it runs at pressure levels at up to six atmospheres.
By pressurizing the wind tunnel you can scale up the model. The 12' wind
tunnel can go from vacuum to 90 pounds per square inch. In sea water every
33' you go down is one atmosphere.