Pipistrel Virus 912, Flight And Maintenance Manual

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Appendix
How fast is too fast?
Based on two recent unfortunate events, where two pilots lost their newly acquired Sinus and Virus
aircraft, the team of Pipistrel’s factory pilots decided to stress the importance of airspeed even more.
Do read this passage thoroughly as everything mentioned below affects you as the pilot directly!
The two events
Both the events took place during the first couple of hours pilots flew with their new aircrafts.
Therefore it is definite they had not become completely familiar with all the flight stages Sinus and
Virus offer. The circumstances of both the events were remarkably simmilar.
Soon after the pilots picked up their new aircraft at the distributor’s, the aircraft were severely dam-
aged aloft. One during the first home-bound cross country flight and the other during the first
flights at domestic airfield. Please note the distrubutor independently tested both mentioned air-
craft up to VNE at altitudes reaching 300 to 500 metres
(900 to 1500 feet)
with great success.
Pilots flew their machines at reasonably high altitudes but at very high speeds . One of them de-
ployed airbrakes (spoilers) at the speed of 285 km/h
(155 kts)
, the other was flying at 3000 m
(10.000 ft)
at 270 km/h
(145 kts)
IAS.
They both encountered
severe vibrations
caused by
flutter
. Because of this one aircraft’s fuselage
was shreaded and broken in half just behind the cabin (the craw saw saved thanks to the parachute
rescue system), other suffered inferior damage as only the flapperon control tubes went broken. The
pilot of the second machine then landed safely using elevator and rudder only. Fortunately both pi-
lots survived the accident without being even slightely injured.
Thanks to the Brauniger ALPHAmfd’s integrated Flight Data Recorder, we were able to reconstruct
the flights and reveal what had really happened.
What was the reason for the flutter causing both accidents?
Both pilots greatly exceeded speed which should never be exceeded, the VNE.
With the IAS to TAS correction factor taken into consideration, they were both flying
faster than 315 km/h
(170 kts)
!
You might say: “Why did they not keep their speed within safe limits? How could they be so thought-
less to afford themselves exceeding the VNE?” Speaking with the two pilots they both confessed
they went over the line unawarely. “ All just happened so suddenly! ” was what they both said.
Therefore it is of vital importance to be familiar to all factors that might influence your flying to the
point of unawarely exceeding the VNE.
Human factor and performance
The human body is not intended to be travelling at 250 km/h
(135 kts)
, nor is it built to fly. Therefore,
in flight, the human body and its signals should not be trusted at all times!
To determine the speed you are travelling at, you usually rely on two senses – the ear and the eye.
The faster the objects around are passing by, the faster you are travelling. True.
The stronger the noise caused by air circulating the airframe, the faster the airspeed. True again.
But let us confine ourselves to both events’ scenarios.
At higher altitudes, human eye loses it’s ability to determine the speed of movement precisely.
Because of that pilots, who are flying high up feel like they are flying terribly slow.