Vibration Identification & Minimization - Rotor & Wing International
Excessive vibration of main and tail rotors can cause the tail section of Gearbox or drive train vibrations can be harmful to a pilot. Phase is the relationship between peak signal and a reference on the rotor. “They are integral in the analysis of systems like helicopters and other aircraft,” Menon says. Understanding the relationship of these systems allows the .. The tail rotor driveshaft is connected to both the main transmission and the tail rotor transmission. extreme for a system with tail rotor rotating top-forward than top-aft. Differences are advance ratio in lateral direction; positive to right. ˜μy lateral advance . trim condition of zero tilt of the main rotor disk, measured with respect to its shaft.
Feathering is accomplished by the feathering hinge, which changes the pitch angle of the blade. Rigid Rotor System[ edit ] The rigid rotor system is mechanically simple, but structurally complex because operating loads must be absorbed in bending rather than through hinges.
Rotorcraft Fundamentals/Introduction to the Helicopter - Wikibooks, open books for an open world
In this system, the blades cannot flap or lead and lag, but they can be feathered. Anti-torque Systems[ edit ] Figure The anti-torque rotor produces thrust to oppose torque preventing the helicopter from turning in the opposite direction of the main rotor.
Tail Rotor[ edit ] Most helicopters with a single, main rotor system require a separate rotor to overcome torque. This is accomplished through a variable pitch, antitorque rotor or tail rotor.
You will need to vary the thrust of the antitorque system to maintain directional control whenever the main rotor torque changes, or to make heading changes while hovering. The fenestron antitorque system provides improved safety during ground operations. This system uses a series of rotating blades shrouded within a vertical tail. Because the blades are located within a circular duct, they are less likely to come into contact with people or objects. This type of sensor can be big enough to not require signal conditioning, and can have a sensitivity that is accurate down to lower frequencies than a typical accelerometer.
The primary disadvantage can be mechanical wear since there are moving parts involved. Spectral Analysis With advances in sensor technologies, spectral analysis of helicopter components is now possible.
Similar to ultrasound monitoring in medicine, these new digital mechanical microsensors convert vibrations across a spectrum of frequencies into a signal that can be remotely monitored using wireless transmitters.
Tail rotor - Wikipedia
An individual gear set will generate a specific vibration profile teeth x RPM. It may help detect if a premature failure is about to occur.
These failures can include cracks, loose attachments or bearing failures. This wireless system assists the crew in making critical decisions about continuing flight before a catastrophic in-flight failure occurs. If a sinusoidal force acts on an undamped mass-spring system and the forcing frequency equals the natural frequency of the mass-spring system, the response is infinite.
This is called resonance, and it can cause vibration and other severe problems helicopters. Eurocopter has experimented with anti-slap trailing edges in rotor blades that are electrically activated to reduce flight noise in different flight configurations. The first are those that cancel by applying an equal force opposite the offending vibration, typically sprung masses that are tuned to the helicopters N-per rev at its operating frequency. The second are those absorbers that accumulate energy and return it later in the operating cycle: Similar to absorption techniques, isolation removes the transmission path for vibration energy, so if the main rotor and transmission are isolated from the airframe the airframe will not be susceptible to vibration from these components.
Predictive maintenance can prevent breakdowns, unscheduled shutdowns, operational instabilities and expensive repairs. These types of programs are available commercially and have features that simplify the data comparison effort.
Predictive maintenance can be handled in-house or by external consultants. Menon believes internal analysis teams should complete these programs because of knowledge of equipment, regular and frequent access to equipment and regular dialog with equipment operators and pilots.
Fackler believes it takes both. Both have vested interests. If you are looking for a company or person to administer a vibration program, look for someone that has a track record in finding the problem before it is torn down and found.
Many analysts point to how their systems identified a problem only after finding the problem post mortem then going back through the data to prove the data. For this reason, tail rotors are painted with stripes of alternating colors to increase their visibility to ground crews while the tail rotor is spinning. Eurocopter ECwith a fantail assembly tail rotor.
- Vibration Identification & Minimization
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There have been three major alternative designs which attempt to solve the shortcomings of the tail rotor system. The first is to use a ducted fan rather than an un-ducted fan. This design is referred to as a fantail, or by the trade name Fenestrona trademark of Eurocopter. Placing the fan within a duct reduces tip vortex lossesshields the tail rotor from damage, shields ground crews from the hazard of a spinning rotor, and is much quieter than a conventional tail rotor.
The ducted fan uses shorter and more numerous blades, but otherwise it is very similar to a conventional tail rotor. The NOTAR system uses a variable pitch ducted fan driven by the helicopter's powerplant, but the ducted fan is mounted inside the fuselage ahead of the tail boom, and the exhaust passes through the tail boom to the end, where it is expelled out one side.
Helicopter Antitorque System
This creates a force which cancels out the main rotor torque and provides directional control. The advantages of the system are similar to the Fenestron system discussed above. There are at least four ways to eliminate the necessity of a tail rotor altogether: Such a design is commonly seen on heavy lift helicopters like the tandem rotored CH Chinook and effectively with the tiltrotor configuration V Osprey. Other designs such as the Kamov Ka and Sikorsky X2 use coaxial counter-rotating main rotorswhich means that both rotors spin around the same axis but in opposite directions.