Certification of Raytheon's Premier I has again been delayed, with tyre burst and rudder centring issues pushing US approval of the entry-level business jet into the first quarter of next year.
Already over two years behind its original schedule, Raytheon had hoped to certificate the Premier I and begin deliveries by the end of this year. The latest setbacks, however, have resulted in a further delay of "seven to eight weeks", says vice-president development Jack Hulsey.
Certification rules require that the aircraft can withstand a tyre burst inside the wheel well, and Hulsey says Raytheon underestimated the amount of energy released. Pressures in the well reach 14bar (200lb/in²) when a tyre bursts, he says, and this required relocation of some components.
A fuel filter has been moved out of the well, while a fuel shut-off valve has been moved to a corner where it is better protected. Raytheon has also incorporated a shroud around the tyre to redirect burst energy.
The company has agreed a certification test configuration with the US Federal Aviation Administration and plans to conduct a series of 12 tyre-burst tests in a ground rig between late December and mid-January, Hulsey says.
The rudder centring issue is a result of airflow over the vertical stabiliser holding the control surface at maximum deflection in high sideslip conditions. For certification, pedal forces are required to increase as rudder deflection increases. Premier rudder forces increase up to 12° deflection, then begin to reduce until the rudder reaches its full 25° travel and will not return, Hulsey says.
The fix involves adding a rudder centring spring and a small ventral fin, similar to those used on the Raytheon Beechjet 400A. After initial tests using the centring spring from the Beechjet, "which got very close", the spring rate was changed and the Premier I is now flying well, says Hulsey.
Raytheon has logged around 2,200h flight testing and only 240 test conditions remain to be accomplished, he says. These include ground handling tests in crosswinds with the rudder fix in place. Hulsey believes the risk of further delays to the Premier I programme are "minimal".
Source: Flight International
