Miami-based Quiet Technologies Aerospace in late January received FAA approval of its Stage 3 translating-ejector hush kit for Gulfstream IIs, IIBs and IIIs.
When Quiet Technologies announced in May 2001 it was developing a Gulfstream hush kit, it entered a market pursued by two other companies. Really Quiet of Mojave, Calif., received an STC in January last year, and its approval covers the GII, for which the company has done two installations–the initial one on its own GII for certification and a customer’s GII–at its Mojave facility. Midcoast Aviation has been contracted to do future installations, but none was scheduled at press time.
Quiet Technologies said its STC covers all Spey-powered Gulfstreams. At press time, a GII installation was under way at Total Aircraft Services in Van Nuys, Calif., and a GIII installation was completed at Quiet Technologies’ own facility in Miami. Business Jet Center’s Tulsa, Okla. shop is also a designated hush-kit installation center. Currently, seen more aircraft are scheduled to get the kit, according to the company.
Installed cost of the 234-pound Quiet Technologies system is $1.65 million. The company is quoting to customers a downtime no longer than 10 days. The converted GIII was completed in just seven days. Quiet Technologies said that customers should see less than a 2-percent range penalty.
In the words of the pilot of the first completed GIII: “At Mach 0.77 to 0.80 we were seeing a 1.5- to 1.8-percent penalty over our baseline aircraft. On the trip back we flew a constant Mach 0.79, our flight plan predicted a burn of 10,000 pounds and the actual was 10,200 pounds, two percent over.”
The 540-pound Really Quiet system costs $1.95 million installed. Downtime is currently quoted as eight to 10 weeks, but the company expects that time to drop to four to six weeks with more experience. Operators should see a maximum range penalty of 3 percent at speeds of less than Mach 0.80.
Meanwhile, Stage III Technologies of La Jolla, Calif., won’t have its GII/III hush kit ready to deliver until the third or fourth quarter. Its program was severely set back last summer when its test aircraft was grounded as part of a bankruptcy proceeding by the aircraft's owner. The company only recently obtained use of anther GII (S/N 2).
The Quiet Technologies hush kit retains the original Gulfstream acoustically treated tailpipe, but the original five-lobe mixer nozzle is replaced by a 12-lobe “fluted” mixer nozzle and includes an exhaust center bullet that serves two functions. It promotes mixing of the ambient airflow with the jet exhaust by controlling the expansion of the jet stream upon exiting the nozzle, and it reduces turbine noise through acoustic treatment.
While the nozzle and ejector reduce noise enough for compliance with Stage 3 noise levels, the ejector would obstruct the aircraft’s thrust reversers were it not for Quiet Technologies’ translating mechanism. The ejector is mounted on two carriage assemblies, one on each side, and slides on low-friction linear bearings.
The carriages are attached to the reverser’s main fittings and the ejector is mechanically linked to the reversers. When activated they deploy two “translating” links, pushing the ejector aft. This enables the reverser doors to open. Closing the reverser doors automatically pulls the ejector forward into its stowed position.
The ejector is constructed from carbon graphite with Nomex honeycomb. It creates a monocoque structure of “high strength with minimum weight.” The inner barrel is perforated and a felt metal acoustic liner is bonded to the surface. This provides, a wide-frequency band of noise absorption while also providing an aerodynamically smooth surface.
The ejector works with the 12-lobe nozzle in promoting the mixing of ambient air stream with the jet exhaust. The major reduction in noise levels is achieved through this mixing, which both cools the hot exhaust and reduces the jet flow’s exit velocity from supersonic to subsonic before leaving the ejector.
