Helicopter data, Series J

Data Sets

Fourteen cases were collected during this excursion. All data sets were collected at a sampling rate of 10MHz, with 60dB amplification and 50kHz highpass filtering. Exactly how the data sets were obtained is described in Provenance.

Three channels were collected simultaneously for all cases, but there are potential problems with channels 3 and 4. Channel 4, while otherwise comparable to channel 1, is more susceptible to aliasing, (lowpass filter is -3dB at 5MHz, for a 10MHz sampling rate). Channel 3 remained quiescent for all cases. For these reasons, we present only channel 1 for analysis.

Some of the data sets are clipped: caveat emptor.

If you want to download any or all data sets, see Download Information.

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Table of data collected on channel 1.
Name Case Description
jac1 A Ambient, (no equipment on).
jbc1 B Ambient, (no equipment on).
j01c1 1 APU power with power to gauges only.
j02c1 2 Both engines lit, but no rotor engagement.
j03c1 3 Rotors engaged, 97.5%
j04c1 4 Rotors engaged, 100.5%, (about 265RPM).
j05c1 5 Case 4 with ARC51
j06c1 6 Case 4 with ARC51 & ARC182
j07c1 7 Case 4 with NDB.
j08c1 8 Case 4 with Tacan.
j09c1 9 Case 4 with IFF.
j10c1 10 Case 4 with RADAR Alt.
j11c1 11 Case 4 with lights on.
j12c1 12 Rotors engaged, 110%.

Table of data collected on channel 1.
Name	Case	Description
jac1	A	Ambient, (no equipment on).
jbc1	B	Ambient, (no equipment on).
j01c1	1	APU power with power to gauges only.
j02c1	2	Both engines lit, but no rotor engagement.
j03c1	3	Rotors engaged, 97.5%
j04c1	4	Rotors engaged, 100.5%, (about 265RPM).
j05c1	5	Case 4 with ARC51
j06c1	6	Case 4 with ARC51 & ARC182
j07c1	7	Case 4 with NDB.
j08c1	8	Case 4 with Tacan.
j09c1	9	Case 4 with IFF.
j10c1	10	Case 4 with RADAR Alt.
j11c1	11	Case 4 with lights on.
j12c1	12	Rotors engaged, 110%.

Provenance

We collected this data in September 1996.

Thanks

We thank Wilbur Batten, Ellick Wilson and their colleagues at The Cherry Point Naval Aviation Depot for their gracious hospitality during our visit to Cherry Point on September 12, 1996, for their efforts at coordinating our access at Cherry Point to an H-46 helicopter for data collection, and for making available helicopter rotor components for experimentation here at The University of Minnesota.

Specimen

The specimen is a H-46 marine helicopter. The engine was running and the rotors moving during some of the cases, (see table). It did not, however, leave the ground.

Equipment

Three Physical Acoustics sensors were attached to Physical Acoustics 1220A preamps, which were then connected to Mini-Circuits lowpass (anti-aliasing) filters, both via BNC cables. The Mini-Circuits lowpass filters were attached directly to the LeCroy digital oscilloscope.

Sensor Mounting

Three Physical Acoustics sensor were attached to the top of the helicopter, using putty and duct tape.

Channels 1 and 4 used Physical Acoustics S9208 broadband sensors. Channel 3 used a Physical Acoustics S9220 sensor. Note that channels 1 and 4 differ in their anti-alias filtering, and all channels differ in sensor placement.

Note that all sensors were sitting on the outside "skin" of the helicopter, not any moving part.

Preamps

Physical Acoustics 1220A preamps were used for each channel. These preamps were set for 60dB amplification, and include a 50kHz highpass characteristic.

The preamps were powered by battery packs, (3 9V batteries in series), connected in parallel with the preamp outputs.

Filters

In addition to the highpass filtering provided by the preamps, a Mini-Circuits lowpass filter was used to reduce aliasing. Channels 1 and 3 used a BLP-1.9, (-3dB at 1.9MHz), and channel 4 used a BLP-5, (-3dB at 5MHz).

Oscilloscope Settings

The LeCroy digital oscilloscope collected 1,000,002 samples/channel, (corresponding to 100msec duration at the 10MHz sampling rate). Three channels of data were captured simultaneously, for each case. The 25MHz global bandpass limiter was engaged, (to mitigate aliasing). AC coupling was used to elimiate the 27V power component.

Data Handling

Once the LeCroy digital oscilloscope triggered, we transferred the data to its removable hard disk. These were later transferred to a PC via floppy disk, converted to ASCII format 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.

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.