Aircraft Motion

A Trimble 2000 GPS unit provides aircraft position and an accurate time. Position is updated each second when a sufficient number of satellites are in contact. Latitude, longitude, and altitude are recorded. The GPS position data are recorded with the T-28 data stream. The GPS time, groundspeed, and ground track angle are also recorded.

Airspeed is computed using dynamic pressure obtained from a pitot-static probe under the right wing, and static pressure obtained from a side-facing pressure port on the rear fuselage. The pressure transducers, two dynamic and two static, are all mounted in the rear fuselage. The two dynamic pressure transducers perform similarly. The two static pressure transducers do not. The parameter we call "Static Pressure 2" (data tag number 104) is generally much noisier than "Static Pressure 1" (data tag number 103).

T-28 armored research airplaneThe aircraft carries two accelerometers. One is a Humphrey vertically-stabilized accelerometer, and the other a Crossbow Technologies 3-axis accelerometer, fixed to the aircraft frame of reference. Both were mounted as close as possible to the aircraft center of gravity, behind the pilotís seat. Comparison of the readings from these instruments showed very good agreement in straight-and-level flight.

Engine manifold pressure is also recorded and can be used as a proxy for power generation by the engine. Pitch and roll are obtained from the vertically-stabilized Humphrey accelerometer. There is no probe for angle-of-attack. Heading was not recorded during STEPS, although GPS ground track angle can be used as a crude proxy for heading.