3 Day Open Conference

Wind envelope expansion testing of the JAS 39 Gripen single and dual-seat aircraft
Wednesday 19th November 2008
10.00 - 10.30
Auditorium 3

All a/c must be able to operate in windy conditions, at least to somedegree. The most requiring task is often landing in turbulence and/or crosswind.Customer or authority requirements are often stated as allowed crosswind fortake-off and landing and flight test of some sort is regularly required to verify ordemonstrate the characteristics in those conditions.

The verification of the cross wind landing requirement for the JAS39 Gripensingle and dual seater a/c was performed as a build-up in turbulence and crosswind. Turbulence testing had the “lead” over cross wind testing, as had testingof the single seater over the dual seater.

A number of criteria to abort a landing or stop continued testing were stipulated.On-line calculations of turbulence and control surface activity, together withother things such as CHR, are examples of parameters used in those criteria.Testing was mainly performed at local airfields but to increase the possibilitiesto get the right wind conditions, the testing also involved a dual seater JAS 39Gripen stationed in South Africa. This required some extra liaison and logisticactivities in cooperation with the local test facilities.

Result wise, it was clearly noted that a single moderate disturbance at the“wrong time”, can trigger events and affect the landing performance more thanlarger disturbances at less critical altitudes or stages in a landing.Wind envelope expansion can be hard to achieve, giving the need for the rightconditions. An early preparation for alternate locations and extra high alert fordeployment should therefore definitely be considered.

A number of lessons were learned along the way, spanning from landingtechniques and wind reading to geographical turbulence profiles and tire wear.

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