An Accelerometer in Paradise

By Ron Wanttaja (

(Posted to rec.aviation.misc February 1995)

Recently, I completed some business travel to a remote location.  For my return trip, I was to transport two Environmental Data Recorders (EDRs).  These contain three accelerometers, an electric thermometer and hygrometer, and 1 Meg of memory for storing the collected data.  It's a surprisingly  small device, about 3/4ths the size of a thick paperback novel.

My trip back included flying on a commuterliner as well as on a common twin-engine jet airliner.  Like any engineer, I couldn't resist the temptation:  I activated the EDRs for the trip home.  The following posting is a report of the results.

I carried two EDRs in my checked suitcase, a large hard-sided older model American Tourister.  One was in a metal foam-lined case specifically designed for the job; the other was placed between layers of clothing (isolated from the sides of the suitcase).  I'm going to use the results of the loose EDR as more representative of ordinary belongings inside the suitcase.

Axial orientation was as follows:  Imagine the suitcase lying flat.  The EDR Y-Axis was parallel to the hinge line of the suitcase, and the X axis was parallel to the ground from the back to the front of the suitcase.  The Z-Axis was "up" in this orientation, in the direction the top would open.

Note the axial directions change while the suitcase is carried:   The Y axis is in the direction of travel, the X axis is "up", and the Z axis points to the side.

The EDR stored the 70 highest impacts.  The threshold was set to 1G, but enough events occurred to fill the buffer, at which point the lower impacts were rewritten by the higher.

The EDR was activated at 7:03 AM.  A near-continuous series of 23 shocks is recorded from 07:13:04 to 07:13:32. X axis predominated, ranging from 1.85 to 3.75 Gs.  During this period, the suitcase was being towed on its wheels over a rough asphalt parking lot.  In this attitude, X axis was vertical. A look at the event spectrum revealed that the environment was quite sine-wave like, rather than a series of individual impacts.  Frequency was approximately 25 Hz.

40 seconds after the cessation of the series, a single impact was detected, with the Z axis predominating (2.24Gs Z, 1.85Gs X, 1.05Y).  At this time, I had opened the car trunk and hoisted the suitcase inside.  I loaded it flat, hence the primary shock in the Z axis.

After completing some other business, I arrived at the airport at 09:09.  Here, another series of X-axis shocks occur as I tow the bag into the terminal.  These are lower than the first set; the airport sidewalks were smoother than the earlier parking lot.

Nothing occurred until about ten minutes prior to departure of the small turboprop commuterliner.  Then seven shocks with different axes predominating, maximum 5.6G... obviously when the baggage was being loaded onto the aircraft.

No shocks are recorded from that time until the plane arrived at the hub airport... this arrival time was approximately 90 minutes prior to departure of the major carrier for the next leg.  Twenty shocks occur in this period, with 14 of them over one five-minute period (probably transhipment from one baggage carrier to another).  Various axes, maximum 5.26Gs, most in the 2-3G range.

I suspect the last shock of this series (~45 min prior to scheduled departure) was the suitcase being loaded on the aircraft, as no shocks were recorded until after takeoff.  It gets interesting about a half-hour after the plane got airborne.  Three shocks, a minute or so apart, with maximum values of 10.1, 9.13, and 5.429Gs!  I recall nothing but ordinary turbulence in that period.  Luggage shifting in the bay, I suspect.  The 10.1 G event lasted about 0.1 seconds with a short period of damping afterwards.

Other than that... two ~3.5G hits during descent (undoubtedly baggage shifting again) and a 6.167G impact at landing (rough landing).  There didn't seem to be any destination-airport baggage-handling events, just another Z-axis hit when I dropped the suitcase into the trunk of my own car.

For the entire travel period, the maximum G level was:
   X = 6.167
   Y = 6.889
   Z = 10.10

These sound high, but remember, most of them are short-lived events with not much energy in them.  It should be noted that I carried a china teapot in  the same suitcase as the EDR (wrapped in bubble wrap); it arrived unbroken.

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