Copyright of RotorSport UK Ltd
Document number RSUK0060
Page 28 of 101 Page issue 2, dated 12.09.11
normal manoeuvres, the rotor will quickly slow to a level to match the reduced load – and
similarly speed up to match increased loads.
If the load is reduced to a point where the centripetal load can no longer support the
bending load, then the blades will fold up, and the aircraft will enter an uncontrolled
terminal descent.
The point of blade fold is significantly below any operational flight speed, provided G is not
significantly reduced. Attempts to fly manoeuvres that induce negative or low G are
extremely dangerous. Manoeuvres such as highly banked slow turns or those where a
sudden engine failure would lead to significant loss of rotor loading may result in a fatal
accident!
If in doubt, smoothly close the throttle whilst maintaining a level flight attitude. This will
return the aircraft to a stable, slow speed condition very quickly, from which the pilot can
recover to normal flight.
3.11 VIBRATION
A gyroplane is subject to a number of out of balance forces which will generate different
levels of vibration depending on the engine and rotor rpms, and on loading conditions.
Rotors are normally balanced two seated, so a reduction in occupant loading will naturally
change the rotor response.
1. Engine and propeller. Vibration in this area will change with engine rpm, and can
therefore be affected and isolated by the pilot. The propeller is normally balanced to less
than 0.1ips, meaning low vibration. Vibration will increase as the propeller gets dirty, and
will also increase if damaged. A sudden change in flight will indicate a fault has
developed, either through an impact (loose luggage, bird strike etc passing through the
propeller) or by some mechanical failure. In the event the pilot should make a
precautionary landing for evaluation. Propeller damage may also be evident from a
change in noise level.
Upon landing, carefully check the propeller for damage, loose bolts or evidence of
mechanical failure within the prop or engine. Especially check the engine to engine bearer
connections, and the engine bearer to airframe connections.
2. Rotor.
Rotors will vibrate in flight due to tracking errors (side to side stick shake), rotor CG
misalignment with the axis of the bearing in the flat plane (oscillatory stick shake), and
also in the vertical plane (two per rev shake). The amount of shake will not suddenly
change in flight or between flights unless there has been mechanical failure, external
influence or rotor strike.
Vibration will increase (and performance decrease dramatically) with dirt build up on the
rotor blades, so before any analysis make sure they are clean.
If there is a change in vibration in flight make a precautionary landing and investigate. If
on rotor startup, stop and investigate.
Things to check:
Rotor impact with tail of aircraft.
Hanger damage eg twist or distortion of trailing edge.
Blade bent from ground handling.
If after re assembling the rotor, that the blades and hubs are serial no matched, and that
the shim washers are correctly matched to the hub bar and rotor tower.
A reduction in vibration may be caused by increased flexibility between the rotor head and
the occupant. This may be control system looseness, so check all system joints for
tightness, and also for cracks at the base of the mast. Check security of all fastenings
between the rotor and the pilot.
If a cause cannot be found, remove on ground to a suitable repair facility for analysis.