Aerospace
In the 1980s, the Canadian Air
Force purchased a number of CL600 Challenger Aircraft
for VIP transport and electronic war fare. These aircrafts
were certified to the Federal Aviation Regulations
(FAR) part 25. Specific CF requirements made it necessary
to modify these aircrafts. Among other changes like
avionics and wiring, cut-outs were made in the tailcone
structure for an infrared sensor, a ram air intake,
as well as a chaff dispenser.
After the CF decided there was no further need to
operate the CL600 Challenger aircraft, three CL600
aircrafts were sold to a private operator who contracted
out the removal of the modifications installed by
the CF. The contractor was tasked to re-certify these
aircrafts to FAR 25. The cut-outs remaining after
removal of the tailcone modifications were considered
as damage and repair schemes had therefore been developed
to re-establish the structural integrity of the original
tailcones. Martec Limited was therefore tasked by
the contractor to analyze the proposed repair schemes
and to modify the repair schemes as required to ensure
the structural integrity and durability of the repairs.
The tailcone structure consists mainly of Kevlar
49 prepreg material for the skins and Nomex honeycomb
of variable thickness for the core material. Local
ply-build ups and changes in core thickness are used
to account for local loads in the tailcone design.
The proposed repair schemes were analyzed and modified
as required ensuring the structural integrity of the
tailcone structure for the environmental conditions
in which the aircraft operates. Technician experience
as well as inspection limitations were considered
in the repair design and analysis, providing a sufficient
margin of safety. The performed analyses were based
upon traditional classic lamina analysis theory (CLA),
basic engineering methodology, as well as lamina analysis
software. The repairs were executed by the contractor
and the aircraft has successfully been re-certified
to FAR 25.
|
