SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  AF071-356 (AirForce)
Title:  Optical Ground Vibration Test
Research & Technical Areas:  Ground/Sea Vehicles

  Objective:  Improve speed, reliability, and accuracy of Ground Vibration Tests of military aircraft, wind tunnel, and micro Unmanned Arial Vehicle testing.
  Description:  Current aircraft Ground Vibration Test (GVT) technology involves instrumenting an aircraft with dozens to hundreds of accelerometers and wiring the accelerometers to a data acquisition system. The aircraft is supported by a soft support system to isolate the modes of the aircraft from the modes of the facility and the support system. Shakers are typically set up on the aircraft appendages (wingtips, edges of the stabilizer). The shakers are used to provide input forces; the accelerometers record the response. A large percentage of the test schedule is dedicated to setup and teardown of the instrumentation. There are systems that use laser technology to measure the position and velocity of a point on an aircraft on a small scale (i.e. one or two measurements on the aircraft). The intent of this research will be to develop a GVT system that uses laser technology to track the response of an aircraft at up to 500 points at frequencies of up to 200 Hz. In addition, the system should include a self contained shaker unit that can automatically (or at least remotely) position itself and provide the input forces to the aircraft at the prescribed locations. Ideally this robotic unit would be wirelessly connected to the data acquisition system. To provide for the possibility of obscured locations that need to be instrumented that the laser cannot reach (e.g. internal weapons bay points), the GVT should have wireless accelerometers that can easily be attached to these obscure locations. Finally a soft support system should be designed that is capable of accommodating a range of aircraft from a small Unmanned Aerial Vehicle to a large bomber or cargo plane. Some key issues that need to be addressed are: 1. Do the lasers need to have targets attached to the aircraft or can they be optically projected onto the surface? 2. Can one laser be used for multiple measurements or do all measurements need to be time correlated? 3. Can the laser draw the node lines for individual structural response modes on the aircraft? It would be very advantageous if the design of the laser system were such that it could also be used to measure the vibrational response of a system being tested in a high speed wind tunnel where the challenges involve a more confined space, the possibility of turbulent airflow, optical path distortion due to variations in flow density, limited access through optical ports, and obstructions to wireless technology. Finally, the capability of the design to accommodate flight testing of micro Unmanned Aerial Vehicles in a confined space, since instrumenting these aircraft with conventional accelerometers could change the response characteristics due to the influence of the mass ratio of the accelerometer to the aircraft, would be very beneficial.

  PHASE I: Produce a conceptual design for an integrated laser measurement device, shaker unit, and soft support system. Multiple measurements from one laser, indexing the laser to a point on the aircraft, and time correlation between the laser, wireless accelerometers, and the shaker should be addressed.
  
  PHASE II: Develop, test, and demonstrate a prototype system based upon the Phase I design. Additional beneficial features would include the ability of the laser to draw the node lines for individual structural response modes on the aircraft and the ease of adaptation to the wind tunnel and UAV applications.

  DUAL USE COMMERCIALIZATION: Military application: This device will be used extensively for ground vibration testing of military aircraft, wind tunnel models, and large turbine engines for ship propulsion systems throughout the development process. Commercial application: This device will find use in vibration testing of civilian aircraft, automobiles, and civil engineering structures such as bridges and high-rise buildings.

  References:  1. GROSSMAN, D. T., “An automated technique for improving modal test/analysis correlation”, AIAA-1982-640, 23rd Structures, Structural Dynamics and Materials Conference, , New Orleans, LA, May 10-12, 1982, 2. RICHARD TALMADGE, GENE MADDUX, DOUGLAS HENDERSON, Instrumentation and techniques for structural dynamics and acoustics measurements, AIAA-1988-4667, NASA, and AFWAL, Conference on Sensors and Measurement Techniques for Aeronautical Applications, Atlanta, GA, Sept. 7-9, 1988.

Keywords:  Ground Vibration Test, System Identification, structural response modes, wireless accelerometers, shaker, data acquisition system, soft support system, Unmanned Aerial Vehicle, Wind Tunnel

Questions and Answers:
Q: 1. Please clarify "key issue" No. 3, "Can the laser draw node lines... on the aircraft?" Is this a requirement to provide a visual display of vibration test results?

2. Can you provide more information on current equipment/procedures used for the soft support and shakers? Any photographs, drawings, etc. that you could provide would be helpful.
A: 1. If a scanning laser is used to measure the vibration at the measurement locations then the same scanning laser could concievably be used to draw the node lines on the aircraft once data is processed and the node lines are identified. This is not a hard requirement, but it is a useful utility.

2. There is plenty of information in the public domain regarding the equipment and proceedures used to perform GVT's.
Q: We are interested in knowing the main topic of interest for this SBIR. The RFP states interest in wireless sensors, laser measurements, soft support systems, robotic shaker positioning and mutli-scale GVT as topics of interest. Does the proposal have to address and incorporate all these topics or can a couple of the technologies be focused upon for advancement?
A: The topic of interest is expediting GVT setup, execution, and tear-down. Everything else is just enabling technology. In terms of potential gains I estimate sensor technology at about 90% (laser measurement being a big part of this, but the laser system will need to integrate with measurements where line of sight is not possible, which is where wireless sensors might come in), 8-9% excitation technology (robotic shaker units), and 1-2% isolation technology (soft support system). Multi-scale GVT would provide a
capability to support programs that are likely to develop in the future, but the main focus should be on fighter to bomber size aircraft. At the end of the day the proposals that are perceived to have the greatest potential to expedite GVT will be successful.
Q: 1. Please clarify "key issue" No. 3, "Can the laser draw node lines... on the aircraft?" Is this a requirement to provide a visual display of vibration test results?

2. Can you provide more information on current equipment/procedures used for the soft support and shakers? Any photographs, drawings, etc. that you could provide would be helpful.
A: 1. If a scanning laser is used to measure the vibration at the measurement locations then the same scanning laser could concievably be used to draw the node lines on the aircraft once data is processed and the node lines are identified. This is not a hard requirement, but it is a useful utility.

2. There is plenty of information in the public domain regarding the equipment and proceedures used to perform GVT's.
Q: We are interested in knowing the main topic of interest for this SBIR. The RFP states interest in wireless sensors, laser measurements, soft support systems, robotic shaker positioning and mutli-scale GVT as topics of interest. Does the proposal have to address and incorporate all these topics or can a couple of the technologies be focused upon for advancement?
A: The topic of interest is expediting GVT setup, execution, and tear-down. Everything else is just enabling technology. In terms of potential gains I estimate sensor technology at about 90% (laser measurement being a big part of this, but the laser system will need to integrate with measurements where line of sight is not possible, which is where wireless sensors might come in), 8-9% excitation technology (robotic shaker units), and 1-2% isolation technology (soft support system). Multi-scale GVT would provide a
capability to support programs that are likely to develop in the future, but the main focus should be on fighter to bomber size aircraft. At the end of the day the proposals that are perceived to have the greatest potential to expedite GVT will be successful.

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