Pressure transducers are housed in tubes on the inlet rake of NASA's F-18 High Alpha Research Vehicle (HARV) to test pressure distortion patterns at different angles of attack. Located at the engine face, these probes provide information on how to adjust the engine to accomodate the distortions. The highly modified F-18 airplane flew 383 flights at NASA's Dryden Flight Research Center, over a nine year period and demonstrated concepts that greatly increase fighter maneuverability. Among concepts proven in the aircraft is the use of paddles to direct jet engine exhaust in cases of extreme altitudes where conventional control surfaces lose effectiveness. Another concept, developed by NASA Langley Research Center, is a deployable wing-like surface installed on the nose of the aircraft for increased right and left (yaw) control on nose-high flight angles.