737-800 Simulator and Mars Rover

Position Measurement & Control - Issue 33

APPLICATION FOCUS

737-800 Flight Simulator Feedback Sensing

The Operator Performance Laboratory (OPL) at the University of Iowa has developed a 737-800 flight simulator that incorporates fully functional, highly realistic controls and switches. Their simulator is state of the art in that it can simulate an array of sensors such as Forward Looking Infrared (FLIR), mm-Wave, and weather radar (WXR) used on physics-based models. The simulator is used for research in Synthetic Vision Systems (SVS) and Enhanced Vision Systems (EVS) for commercial and military applications. The OPL uses other sophisticated equipment such as eye-tracking devices to determine pilot performance and to allow design optimization of the advanced display avionics. A key objective of the development was to emulate the high-workload environment of an actual aircraft.

Figures A1 and A2 - Roll and pitch position transducers and throttle quadrant position transducer.

A part of the Center for Computer Aided Design (CCAD), the OPL chose seven Firstmark Controls position transducers to measure a variety of deflections and rotations on the simulator hardware. Three transducers measure the position of the aileron, elevator, and rudder axes. The rudder transducer is inside the cockpit behind the pedals, while the aileron and elevator transducers are underneath the simulator. In the throttle quadrant, transducers measure throttle positions, flap setting, speed brake setting, and deployment of the thrust reversers. The transducers are connected to a bank of programmable microcontrollers (PIC16F87) to perform voltage measurements. The analog values are then sent via a serial connection to the flight model as control inputs.

The simulator is used for research conducted for a variety of users including Rockwell Collins, NASA, and the U.S. Air Force. For more information on the project, visit http://opl.ecn.uiowa.edu/new_2/facilities/737-800home.htm.

Figures A3 and A4 - Rudder position transducers.

Figure A5 - The OPL 737-800 Flight Simulator with, back to front and left to right, Tom Schnell (Director OPL), Frank Gutierrez (graduate student), Mike Keller, Carl Richey, and Fuat Aktan (Research Engineers at OPL).

CUSTOMER FOCUS

Displacement Sensors Measure Mars Exploration Rover Airbag Performance

Airbags used in the Mars Exploration Rover mission are the same type that Mars Pathfinder used in 1997. Airbags must be strong enough to cushion the spacecraft if it lands on rocks or rough terrain and allow it to bounce across Mars' surface at freeway speeds after landing. To add to the complexity, the airbags must be inflated seconds before touchdown and deflated once safely on the ground.

Firstmark Controls Series 160 displacement sensors were used to test the airbag performance to ensure the airbag compressive stroke did not exceed its design requirements. The flexible displacement cable made for easy installation with no special fixturing.

Each Rover uses four airbags with six lobes each, which are all connected. Connection is important, since it helps abate some of the landing forces by providing a damping mechanism to dissipate the impact energy. The fabric of the airbags is not attached directly to the rover; ropes that crisscross the bags hold the fabric to the Lander, which in turn holds the Rover. While in flight, the bags are stowed along with three gas generators that are used for inflation.

To learn more about the Rover, head to the NASA Mars Exploration Rover Mission Home Page.

APPLICATION CORNER

Adapting Displacement Sensors to Harsh Environments

A recent poll at Firstmark Controls's Web site asked visitors "Which environmental hazard causes your position transducers the most problems?" The summary results of this poll are presented below. Keep in mind that the answers reflected the use of all types of position transducers and not necessarily Firstmark Controls cable-type position transducers.

As a follow-on to this poll let's answer the question: "What can be done to overcome these environmental hazards?" A somewhat obvious answer is to specify and purchase a position transducer designed for the environment into which it will be placed. But what if you don't have that luxury due to budget, time, legacy, or other constraints? What else can be done? Below are our thoughts on the subject based on over 35 years of experience. Let us know if you have ideas on the subject.

• Shock - cushion the sensor to change the resonant frequency; re-orient the sensor to see if the shock axis contributes to the failure
• Vibration - as with shock, cushion the sensor to change the resonant frequency, isolate the sensor from the vibration using mechanical fixtures
• High Temperature - cool the sensor area; insulate the sensor area; locate the sensor away from the heat source
• Low Temperature - heat the sensor area; insulate the sensor area
• Dust/Debris - apply positive pressure to the sensor cavity to keep out foreign agents; cover damage-sensitive areas with appropriate plates, screws, and other solutions
• Moisture - enclose the sensor with an appropriate enclosure; apply suitable adhesive-lined shrink tubing or similar measures; apply positive pressure to the sensor cavity to keep out foreign agents
• Fluids - enclose the sensor with an appropriate enclosure; apply suitable adhesive-lined shrink tubing or similar measures; apply positive pressure to the sensor cavity to keep out foreign agents
• Corrosion - coat the sensor with corrosion-inhibiting coatings; enclose the sensor with an appropriate enclosure; wash down the sensor periodically
• Low or High Pressure - provide passages that will allow pressures to equalize
• Magnetism - re-orient the sensor to make it less susceptible to magnetic influences; mechanically isolate the sensor from the magnetic field using fixtures
• Humans - to err is human . . .

NEWS YOU CAN USE

• Wright Flyer Displacement and Air Data Measurement
• Feeling Some Heat and Need Fast Shipment?
• Get a REMOVE BEFORE FLIGHT Keychain, Stainless Steel Ruler, and Technical Reference CD
• Have a Crazy Requirement? Maybe It Isn't So Crazy . . .
• Poll Update: Which environmental hazard causes your position transducers the most problems?

ISSN 1527-5108 • Document Number S050S(040121)