Helicopter data, Excursion A

Data Sets

Eight data sets were collected during this excursion. Exactly how the data sets were obtained is described in Provenance.

For each data set, the following table lists the model of sensor, the sensor's location on the helicopter, the amplification, the sampling rate, and a web link. For further information about any given data set, follow the web link.

If you want to download any or all data sets, see Download Information.
Table of collected data.
Sensor Location, (in front of...) Ampl (dB) 20 MHz 2 MHz
S9220 anti-collision light housing 0 a20mc1 a2mc1
A3 anti-collision light housing 0 a20mc2 a2mc2
S9208 anti-radar array 0 a20mc3 a2mc3
S9208 anti-radar array 0 a20mc4 a2mc4

Table of collected data.
Sensor	Location, (in front of...)	20 MHz	2 MHz
S9220	anti-collision light housing	a20mc1	a2mc1
A3	anti-collision light housing	a20mc2	a2mc2
S9208	anti-radar array	a20mc3	a2mc3
S9208	anti-radar array	a20mc4	a2mc4

Provenance

We collected this data Tuesday 22 April 1996.

Specimen

The specimen is a Cobra AH/1F, (1967). The engine was running and the rotors moving while we collected data. It did not, however, leave the ground. Estimated 6600 rev/min (engine), 324 rev/min (rotor).

Equipment

Four Physical Acoustics sensors were attached to a LeCroy digital oscilloscope, via long BNC cables. No amplifiers or filters were used during this excursion.

Sensor Mounting

The four Physical Acoustics sensors were attached to the top of the helicopter, using putty and duct tape. Two (channels 1 & 2) were mounted in front of the anti-collision light housing, and the other two (channels 3 & 4) were mounted in front of the anti-radar array. Note that all sensors were sitting on the outside "skin" of the helicopter, not any moving part.

Oscilloscope Settings

The LeCroy digital oscilloscope collected 1,000,002 samples/channel simultaneously on each of four channels, for each batch of data. We collected two batches of data, with respective sampling rates of 20MHz and 2MHz. (It has not been determined whether these data are aliased).

The vertical scales were 50 mV/div for channel 1, 0.1 V/div for channel 2, and 0.2 V/div for channels 3 & 4. (With 8-bit ADCs, the quantization step size for channel 2, for example, is (0.1 V/div)*(8 div)/(2^8)=3.125 mV).

Data Handling

Once the LeCroy digital oscilloscope triggered, we transferred the four channels of data to four, 3-1/2" floppy diskettes. These were later converted to ASCII files using LeCroy's WAVE386 utility, and finally MATLAB converted the ASCII files into its own binary (*.mat) format.

Download Information

To download any of this data, visit our ftp data archive. The data sets described in the above table are there, as compressed MATLAB files. Click on any given filename, and your web browser should download the corresponding data set to your computer. Some compressed ASCII files are also present, (distinguished by an "a" appended to the name of the corresponding data set).

If you want to download all eight data sets, in one large file, download a20m.zip, or click here. This file contains all eight MATLAB data files, compressed into one zip file.

All of the data sets have been compressed using Info-Zip's zip utility. For a description of data formats, including links to free Info-Zip utilities, see Formats.

Experience suggests that Info-Zip compresses our MATLAB files by a factor of about 20:1, and ASCII files about 40:1. Keep this in mind when downloading data.