Payload Charts for Light Aircraft

Ken Norris pixelbird at interisland.net
Sat Aug 16 13:36:00 EDT 2003


This chart generator was originally created in HyperCard on a Mac SE about
14 years ago. It was co-authored by myself and Roger Peard, Col., USMC, Rtd.
Both of us were members of the Blackhawk Sqdn (Lake Tahoe) of the Civil Air
Patrol at the time. I want to rewrite it with an entirely new UI in Rev.

It came from a concern for the safety of high Density Altitude departures at
Lake Tahoe Airport. We had seen several crashes due to high DA conditions
which resulted in the death of people we knew, and many other close calls,
even after a specially instituted policy for ATC Ground Control to say
"check density altitude" among the usual information given at first contact,
and also a lighted DA display on the taxiway.

The chart generator uses an algorithm that utilizes aircraft takeoff
performance plus Weight and Balance data derived from the Pilot's Operating
Handbook and Aircraft Log for a specific aircraft (not just Type and
Category), the Lift Formula, modified for light aircraft, Density Altitude,
and values from the Air Density Tables of the Standard Atmospheric Tables.

It makes an aircraft-specific chart which shows Horsepower and Rate Of Climb
vs. Density Altitude and Payload, i.e., it tells you how much weight in
passengers, baggage, and fuel, the aircraft can have aboard to achieve a
predetermined departure ROC at the current Density Altitude. The pilot will
still need to correctly calculate DA (note: as I mentioned before, at Lake
Tahoe, ATC gives this number routinely), and to determine a safe ROC for
clearing obstacles and terrain before using the chart.

The little chart may have saved my own life on a very hot day at an airport
in eastern Nevada. We had incorporated the use of the chart in our preflight
inspection checklists. We had had our CAP corporate bird refueled (to the
inlet collars by direction) by airport personnel. During the subsequent
preflight inspection, we determined the ROC performance we would get wasn't
adequate. Using the chart, and wanting to carry the passengers and bags, we
decided we could make it back home safely on less fuel, so we drained 25
gallons of fuel (not wasted, but used in another of the aircraft on the same
mission), about 150 lbs., which gave us a good caution-side (something more
than we needed) ROC. The departure was normal and without incident, the
guages showed the numbers we expected.

Ken N.




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