1033. An Oleo Settling Weight and Balance System

Paper

Abstract

The development of a high reliability pressure type Weight and Balance system, with accurate static reading capability,
is the result of four years of intensive investigation by Canadian Marconi Company into the general problem of on-board
weighing systems for aircraft. Beginning with the installation of a simple pressure system on a Canadian Air Force
Fanjet Falcon in 1972, the program has now advanced to an accumulation of measured data on almost all major aircraft
types, including the Lockheed C-130 and L-1011, McDonnel Douglas DC-8 and DC-9 and Boeing 707, 727, and 747 aircraft,
using the olea pressure curve technique.
The simple pressure type Weight and Balance system operates on the principle of measuring the static pressure of each
of the aircraft oleos, and electronically multiplying by the known oleo piston areas to determine the force acting on
each of the landing gear. The system thus consists of a set of pressure sensors and a computer/display unit. Take-off
Gross WEight (TOGW) and Center of Gravity (% MAC) are automatically computed from aircraft constants.
The two main advantages of this type of system are:
(1) ease of installation
(2) low maintenance
The first advantage derives from the fact that the sensor can be installed via the existing charge valve opening and can
therefore be easily retrofitted on all aircraft types. The second advantage derives from the fact that pressure sensors
have been proven to be much more stable than strain gauge sensors* thus requiring little maintenance.
The major disadvantage of the simple pressure system is that it is subject to large and unpredictable errors due to oleo
friction.
Accordingly, Canadian Marconi Company has developed an advanced pressure system which can measure, and electronically
cancel friction force error while the aircraft is in static condition,
*Comments on strain gauge instability errors in the C-7A and on the 747 and DC-10 aircraft can be found in SAWE Paper No 881
by Lieutenant Colonel Edward Low, and in Kit No. 8 of the 1973 Avionics Maintenance Conference report.