Historical Birdstrike

Developing and Tailoring Aircraft Design Requirements: A Case Study for the F-16 Risk-based Bird Strike Requirement Tailoring Methodology 

SYNOPSIS

A bird strike on aircraft flying at low altitude is an ever-present danger. The aircraft designers, both for military and civilian aircraft are well aware of the potential hazard of bird strike and take precautions to protect the aircraft and the crew and passengers. The conundrum arises when the requirement of the design rigidity is chosen. Also a consideration is the area most likely to be struck by a bird and the appropriate precautions to take for adequate protection and safety but not at the excessive sacrifice of aircraft performance.

During the design and development of the F-16 Fighting Falcon aircraft, the design requirements for the lightweight fighter competition was chosen as a 4-pound bird at 350 knots, the popular requirement of the structures Mil Spec, Mil S-8860 in the 1970’s when the competition was conducted. However, when bird strike testing was conducted, the canopy, a 3/8” thick polycarbonate design, the canopy deflected inward significantly, causing a depressed bubble to travel the length of the canopy, striking the pilot on the top of the head with potentially fatal force.

A redesign of the canopy commenced, along with an assessment of the requirement. Perhaps the bird weight was too low, or too high, or the speed was not correct. The mission analysis was conducted and was combined with an assessment of bird weights and past experience with bird strike on aircraft. The bird strike experience included all parts of the aircraft, including the canopy, engine inlet and the leading edges.

The Air Force concluded that the design requirement should be developed based on the weight distribution of birds, along with the aircraft mission, the time at low altitude, the expected speeds at low altitude, the number of aircraft and the hours spent at low altitude.

The history of the F-16 and the testing and the analysis conducted during the development of the aircraft will be assessed and the progress of testing and analysis methodologies will be studied. A case for a process to develop specific deterministic design criteria  from a probabilistic assessment will be presented. 

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Developing and Tailoring Aircraft Design Requirements: A Case Study for the F-16 Risk-based Birdstrike Requirement Tailoring Methodology Discussion

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