HUSHKITTING NOISY old jet-powered aircraft powered by low- bypass engines, such as the Pratt & Whitney JT8D designed to meet Stage 3 noise regulations has tested the ingenuity of engineers. The few commercial hushkits available are relatively expensive, heavy and degrade engine performance .
Former Grumman test pilot Capt Thomas Friedrich claims to have designed a revolutionary new hushkit: the Retractable Ejector Duct, or RED for short. A working model has been built and tested at Cranfield University in the UK by chief research officer Richard Adkins, demonstrating a 10dB reduction in noise levels.
With a price tag of $400,000 it dramatically undercuts its nearest rival - the $700,000 FedEx/P& W hushkit for the Boeing 727. According to its inventor, it also improves performance by augmenting thrust. He is now looking for financing of around $10 million to take the idea to certification.
Technically, the RED is said to convert a low-bypass engine into a "two-cycle" engine. Fitted to the rear of the engine, the device extends during low speed (at take-off and landing) converting the "high-energy, low-bypass" engine into a "low-energy, high-bypass" engine, which reduces the shear of the core exhaust and suppresses noise. During cruise, the RED reverts to its original status which is more efficient for flying at altitude.
Engine makers are unconvinced about the claims for the hushkit, finding it hard to accept the notion of thrust augmentation.
Source: Flight International
