Remote Vibration Measurements at a Sud Aviation Alouette III Helicopter with a CW CO2-Laser System
FYSISCH EN ELEKTRONISCH LAB TNO THE HAGUE (NETHERLANDS)
Pagination or Media Count:
This report describes an experiment with a helicopter to quantify the performance of our experimental multifunctional C02-laser heterodyne detection system 5,7 as a vibration detection instrument. The laser system emitted a beam with a diameter of 35 nun with a divergence of 0.5 mrad and a continuous output of 0.4 Watt. The purpose of our measurements was to measure the vibration spectra of a helicopter from the Dutch Air Force at distances between 0,5 to 6 km at various aspect angles. Vibration detection with the help of lasers might prove important for classification of targets. Especially helicopters are of interest because of the typical constant rotor speeds and fixed speed-ratios between the tail-and main rotor TR-ratio and other characteristics of the spectra. The obtained spectral components are compared with maintenance rotortuning frequency measurements done at the airbase with accelerometers. The results are in accordance with each other. The rotor frequencies have been determined at all positions of the helicopter. Depending of the place where the laser beam hits the target, the amplitudes of the spikes in the frequency spectrum may vary significantly. With an Advantest R9211C FFT spectrum analyser a measurement will take at least one second, yielding a fair recognisable spectrum at distances of the helicopter up to 4 km.
- Lasers and Masers