TRACOR FLIGHT Systems has completed flight-testing of a Stage 3 hushkit for the Learjet 20-series business jet. US certification is expected in August, and marketing partner Ottendorf Aviation holds orders for 32 shipsets, at $110,00 per aircraft.
Learjet 20-series aircraft are powered by General Electric CJ610 turbojets, and sideline noise is around 104dB, compared with the Stage 3 limit of 96dB. John Ligon, director of flight test at Tracor Flight Systems, says that the hushkitted aircraft has been measured at 95.8dB -"just inside" the Stage 3 limit for sideline noise.
The Tracor-developed modification involves replacing the existing thrust-reverser and jetpipe with an eight-lobed "daisy" mixer nozzle surrounded by a similarly lobed daisy fairing.
The fairing extends 200mm aft of the nozzle, and has cutouts to increase the mixing of exhaust and freestream air, to reduce jet noise to Stage 3 levels. There is a 0.2kN (50lb) thrust loss.
Tracor estimates that some 650 20-series Learjets are still in use and the company anticipates selling 150-250 hushkit shipsets.
Source: Flight International
