An Accelerometer in Paradise

From:         wanttaja@chinook.halcyon.com (Ronald James Wanttaja)
Organization: Northwest Nexus, Inc. - Professional Internet Services
Date:         27 Feb 96 23:00:28 
Followups:    1 2 3
Next article
View raw article
  or MIME structure

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 occured 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.  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 occured 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 one had two peaks, dropping slightly between in
about 0.1 seconds.

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 designation-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.

                                          Ron Wanttaja
					  wanttaja@halcyon.com