Dynamic tests are recommended for verification of frangibility
In the case of towers that
may be impacted by airborne aircraft, it is desirable to not only minimize the amount
of damage to the aircraft but also to not significantly impede the flight
trajectory. The impacted tower should give way to the passage of the aircraft
so that it may still achieve a successful landing or continue the take-off
procedure.
As per
International Civil Aviation Organisation (ICAO) Aerodrome Design Manual DOC
9157AN/901 Part 6- Frangibility- Chapter 5 TESTING FOR FRANGIBILITY, Dynamic
tests are recommended for verification of frangibility of navigational aids
having an overall height in excess of 1.2 m and located in positions where they
are likely to be impacted by an aircraft in flight.
The test
should be conducted at a speed of 140
km/h (75 kt). The Impactor should be mounted on the vehicle so that it
strikes the structure at a point approximately 4 m above ground level or 1 m below the top of the structure,
whichever is higher. A representative mass equivalent to the weight of the
intended aid should be mounted on the top of the tower. All required wiring and
cabling for the aid should also be mounted and secured.
The
impact should be recorded by a
high-speed camera. Due to the short time of impact, it is impossible to
visually monitor the impact sequence and the deformation. Impact speed
should remain constant during impact and should be accurately and directly recorded
from the moving vehicle at the time of impact.
Sufficient
recording capability and speed should be used to accurately record the data
from the load cells during impact tests. It is recommended that a recording
speed of at least 10 kHz be used to
capture the maximum impact force that occurs within 2 to 5 milliseconds.
Disclaimer : The testing methodology given
above is as per the International Civil Aviation Organisation (ICAO) Aerodrome
Design Manual DOC 9157AN/901 Part 6- Frangibility.