Stage III now ready to install Gulfstream II, III hush kits

 - October 9, 2006, 12:32 PM

After some six years of development, Stage III Technologies is ready to start installing its FAR Part 36 Stage 3 combined hush kit/thrust reverser for the Gulfstream II, IIB and III. The La Jolla, Calif.-based company received FAA certification of the hush kit in November and an STC for the complete hush kit/reverser system in mid-May.

Stage III is seeking orders for installations to begin late this summer. The first four kits are priced at $1.5 million. Subsequent orders booked before July 31 are priced at $1.795 million, after which the full retail price of $2 million applies. (Painting is not included.) Western Jet Aviation, a long-time Gulfstream maintenance center at Van Nuys Airport in California, will perform the initial installations. Typical downtime after the company has progressed along the learning curve of initial installations is estimated to be two to three weeks.

Stage III anticipates a “5-percent range penalty–about 130 nm or 18 minutes–due to additional drag.” The company expects lower interior cabin noise, but it has not yet taken any measurements in its test aircraft to provide a definitive number. Verification of the drag penalty and noise reduction will have to wait until customers have logged some time in the airplane with the hush kit. Stage III said engine overhaul facilities Rolls-Royce and Dallas Airmotive have provided assurances that the hush kit won’t affect their warranties. Spokesmen for Dallas Airmotive and Rolls-Royce confirmed that statement.

While the new reverser has no effect on noise, Stage III said its cascade-type system is lighter and “more efficient” than Gulfstream’s original clamshell reverser. “We provide the same stopping power at a reduced power setting, which means less wear and tear on the engines.” No scheduled maintenance is required, according to the company. “This eliminates the 1,000-hour lubrication and 4,000-cycle heavy inspection” required on the original system.

No Moving Parts

Stage III’s hush kit differs from that of its competitor–Quiet Technology Aerospace (QTA) of Opa Locka, Fla.–in several ways, most visibly in its ejector design. The Stage III ejector is a fixed system, while QTA’s ejector is mounted on a slide or rail and translates aft when the aircraft’s original-equipment reversers are deployed. When the thrust reversers are stowed, the ejector is pulled forward automatically into its stow position. The hush kit is the same design as the system QTA certified in 2000 on the BAC 111. The QTA hush kit also consists of a 12-lobe mixer nozzle and an engine inlet bullet.

A (fixed) ejector and mixing nozzle are also the key components of the Stage III system. The inner dimensions of the ejector are approximately 36 inches in diameter by 72 inches long.

The Stage III ejector is attached directly to the fuselage with its pylon structure separate from the engine pylon “to eliminate any added stress on the engine.” The inner surface of the ejector is treated with acoustical lining to absorb high-frequency jet noise. The mixer has 10 lobes around its circumference to allow “deep penetration of the high-velocity jet exhaust, effectively mixing the hot exhaust with ambient air to lower the temperature and velocity without thrust loss,” the company said. “Engine operating characteristics are also unaffected by the installation of the mixer,” it added.

There is no required maintenance for the Stage III ejector or mixer. The QTA kit requires periodic cleaning of the ejector translating rails, greasing of the bearings and visual inspections during A, B and C checks. Although QTA’s system is more complex than Stage III’s, the Opa Locka company said its hush kit allows access to all engine systems, “creating no change in normal maintenance procedures.”

Stage III said that its hush kit “does not change the standard takeoff power settings or required power for climb. “Our dBA ratings permit maximum- thrust takeoffs at max takeoff weight.” According to the flight manual supplements, there are no changes to any of the GII or GIII limitations or procedures due to installation of the hush kit and reverser, except that the maximum N2 speed during reverse thrust is reduced.

On the other hand, thrust settings and gross weight limitations apply with the QTA system to maintain Part 36 noise levels, according to that company’s flight manual supplements.

Stage III Is Quietest Hush Kit

While the hush kits from both Stage III and QTA meet Stage 3 (both kits include a tradeoff for exceeding the Part 36 Stage 3 sideline noise limit) a comparison of the hushed GII and GIII noise levels as published in the FAA-approved flight manual supplements from each of the hush kit manufacturers shows that the Stage III system is quieter in all three measuring parameters, as well as in aggregate total, than QTA’s system (see table above).

Additionally, extensive data obtained from Stage III and its contracted engineering firm, J. R. Engineering of Everett, Wash., indicate that in a back-to-back fly-off between aircraft equipped with both manufacturers’ hush kits last year at Van Nuys Airport the noise monitors at the airport showed that the Stage III system was quieter.

While conceding that the Stage III system is “marginally” quieter, QTA officials claimed that the demonstration flight was “not scientific” and, therefore, not accurate. “It was geared to make them look good and us look bad,” said a spokesman. Stage III disputes that allegation.

Regardless, a noise official at Van Nuys Airport told AIN that Gulfstreams with Stage III hush kits should be able to meet the airport’s tough curfew requirements but that QTA-equipped Gulfstreams, for all practical purposes, would not because they would have to be limited to a mtow of 62,000 pounds to remain within the curfew’s 74-dBA threshold (as listed in Advisory Circular 36-3H or by demonstration). QTA told AIN it is working with the airport authority to establish compliance.

Part of the QTA hush kit includes an acoustic treatment to the engine inlet bullet that results in “substantial reduction” in interior cabin noise levels, according to the company. “Testing of several customer aircraft shows the aft cabin noise level to be reduced by more than 5 dB. A GII operator said in a June letter to QTA that his “boss is very happy. He has claimed a 25- to 30-percent reduction in cabin noise.”

The QTA hush kit weighs 234 pounds and moves the cg aft. “This has the effect of keeping the nose up in cruise, resulting in less horizontal trim drag,” the company said. “This drag reduction offsets the drag from the hush kit and results in no [performance] loss on long flights.” Engine overhaul warranties are not an issue, according to the spokesmen at Dallas Airmotive and Rolls-Royce.

Stage III, of course, does not yet have the benefit of any customer experience–good or bad–by which to evaluate the quality and effectiveness of its hush kit. But QTA does, with some 30 installations since it received certification in January 2003. Based on monitoring of performance by customers, QTA reports that on a flight of two hours or less there is an increase in fuel burn of 1 to 1.5 percent. On longer flights, “operators have reported no penalty,” said the hush kit maker. The director of aviation of the company that sent the letter lauding interior noise reduction said he was “unable to notice any fuel penalty with the QTA hush kit.”

An operator who has close to 600 hours on two GIIIs equipped with QTA hush kits described them as “low maintenance.” However, the operator also told AIN that an aircraft polisher inadvertently unbent a cotter pin, which subsequently slipped out of a castellated nut at a critical attachment point of the hush kit, allowing the nut to unscrew and the bolt to back out. That caused the hush kit ejector to be pulled off its rail when the reversers were being stowed. This operator found another pin on the same engine that also had been bent out, apparently also from the polisher. QTA started using both a self-locking, castellated nut and cotter pin since that incident.

Early in the program, painting adhesion problems prompted QTA to discontinue using a painting contractor and install its own paint booth. “Operators that were affected were covered under warranty,” the company said. To resolve an early issue with accelerated wear of the translating rails, QTA said it introduced a rail that has a hard chrome surface. “All customer aircraft have been upgraded free of charge, with zero wear on the new rails.”

Installations 30 and 31 of the $1.25 million QTA hush kit were to have been completed last month at Jet Aviation in Geneva. Two more installations are scheduled for this month.

After Stage III Technologies has a few hush kits installed on customer aircraft and those customers log some time, the company should be able to obtain feedback on actual operations, performance and durability. Meanwhile, the company has already embarked on a program to reduce the installed weight of the hush kit/reverser from the current 120 pounds per side to about 80 pounds per side.