Trace matching for indicated airspeed and altitude

A significant test limitation during a recent check climb test was the lack of indicated airspeed and pressure altitude in the data stream, as well as the lack of outside air temperature (OAT) indication. These limitations were surpassed using a trace matching technique between the GPS altitude and GPS airspeed and the recorded Hp and IAS from the cameras, and meteorological predictions in the test area.
Initially the available GPS/INS data were synchronized with the video of the instrument panel using the popular flight debriefing tool Cloudahoy and data were extracted for 10sec intervals.

Trace_matching_cloudahoy

Considering the monotonous altitude nature of the check climb, the approximate constant heading and the wings level parts of the flight, trace matching using the synchronized data and video was performed as shown in the figure below.

Trace_matching_data

The benefit of this method was twofold: (i) The resulting altitude relation between tapeline and pressure altitude confirmed the OAT obtained by the test area weather forecast within 1deg C and the resulting ΔV to altitude relation confirmed the forecasted wind profile over the test altitude (ii) From the resulting relations the indicated airspeed and altitude traces could be generated along the stabilized parts of the climb with an airspeed accuracy of 1kt.

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