Vibration in aircraft can be quite serious. The aircraft industry measures vibration on a scale from 0 to 1.2 inches per second, or IPS. On the IPS scale, 0–.2 IPS gets a rating of good. Anything over .2 and under .4 IPS is considered fair. An IPS of .41–.6 is considered slightly rough. IPS measurements of .61 – .8 are considered rough. An IPS rating of 1.01 – 1.2 is considered dangerous. For helicopters, the helicopter rotor is one of the chief culprits in bearing vibration. Proper aircraft maintenance for helicopters must include dynamic propeller balance.
What Is Dynamic Propeller Balance?
The process of achieving dynamic propeller balance is done using an electric balancer which measures vibrations. When vibrations are discovered, small balance weights or added which correct for errors in the distribution of mass and thereby reduces the vibrations that come from mass imbalance.
How a Dynamic Propeller Balance Is Done A dynamic propeller balance service is provided by many shops, mechanics, repairs stations, and FBO’s. The person performing at the dynamic propeller balance will ask that the engine be put into a state ready for flight. An accelerometer is then attached to the engine in a spot where typical mass imbalance vibrations are at their maximum. A photo tach is also mounted to the cowl to produce a propeller tach signal. The engine is turned on, and the information from the accelerometer and the photo tack are processed by the propeller balancer. The processing shows the vibration level, which indicates precisely how much mass imbalance exist. The propeller balancer which processes the information coming from the photo tach and the accelerometer will also provide a phase angle to help locate the mass imbalance. Using the vibration level and the phase angle together, a balance solution is calculated which shows the weight amounts needed and the location for proper dynamic propeller balance. Trim balance weights are added to the helicopter rotor and everything is measured again. The process is repeated as often as necessary until vibration levels are acceptable.
Is it Necessary to Have Helicopter Vibration Analysis?
It’s always a wise idea to have propeller balance checked, because, on average, an aircraft that has not had a dynamic proper balance we’ll have a vibration level due to mass imbalance of about four times the levels generally considered acceptable. Often this level is noticeable to the pilot, but sometimes not, and only a proper vibration analyzer can tell for sure.
Is Mass Imbalance the Only Reason For My Vibration Problem?
Definitely not, but it is one of the most common issues. There can also be vibration when there is a misalignment of the rotor system. Vibrations also happen if the rotor blades are not able to provide equal lift. Doing a fan trim balance as well as a dynamic propeller balance is a part of smart helicopter maintenance.
How Does Mass Imbalance Happen?
because the rotor blades on a helicopter are traveling at almost supersonic speeds around a fixed point, they’re very susceptible to wear and damage, especially as they are continually called upon to pitch at different angles. When they are first attached to the helicopter, the blades are matched carefully and should provide very smooth performance. Over time, however, the blades can start to erode or sustain damage and there is no way to guarantee that this will happen evenly on the two blades. This can cause the rotor blades to become unbalanced.
Dynamic propeller balancing is a crucial part of aircraft maintenance, and rotor smoothness should be achievable for your helicopter. It was originally designed to be smooth under all conditions, but as aircraft grow older and parts begin to wear, it becomes impossible to smooth the aircraft. Doing a proper fan trim balance testing and dynamic propeller balance will fix this problem and ensure a smooth ride whenever you take your helicopter out.