No! It isn’t required to be approved by the FAA. The analyzer you use, ACES Systems or otherwise, is only a tool much as a wrench or screwdriver. As such, the equipment itself needs no approval. The FAA approval is required for the hardware and associated methods of application needed to accomplish the dynamic balance. To say ACES Systems’ equipment (or any other equipment) is FAA approved is misleading. To say a balance job done with ACES equipment (or any other equipment) is FAA approved is also misleading. The only portion of the job that requires an FAA approval is the actual hardware and associated methods of application used to accomplish the task. ACES published an FAA-approved document which spells out these requirements of hardware and methods. The “ACES Systems Guide to Propeller Balancing” is provided with each propeller balancing kit sold by ACES Systems. You may also download a copy from this web site. You may use the guide with any balancing equipment and be assured that the balance job is then FAA-approved.
Ensure the surface of the propeller blade has been cleaned and is dry prior to installing the reflective tape. make sure the edges of the reflective tape are flat and not raised. Flatten out any bubbles in the reflective tape. It should be flat against the propeller blade. If these steps do not fix your problem you may apply a thin layer of clear finger nail polish to the edges of the reflective tape. Take care to apply a thin and even coat and not the cover the reflective tape more than necessary.
Purchase Reflective tape here
The Tacoma Narrows Bridge collapse is an excellent example of what could happen if vibration is not counteracted.
The original Tacoma Narrows Bridge was opened to traffic on July 1, 1940. It was located in Washington State, near Puget Sound.
Prior to this time, most bridge designs were based on trusses, arches, and cantilevers to support heavy freight trains. Automobiles were obviously much lighter. Suspension bridges were both more elegant and economical than railway bridges. Thus the suspension design became favored for automobile traffic. Unfortunately, engineers did not fully understand the forces acting upon bridges. Neither did they understand the response of the suspension bridge design to these poorly understood forces.
Furthermore, the Tacoma Narrows Bridge was built with shallow plate girders instead of the deep stiffening trusses of railway bridges. Note that the wind can pass through trusses. Plate girders, on the other hand, present an obstacle to the wind.
As a result of its design, the Tacoma Narrows Bridge experienced rolling undulations which were driven by the wind.
Strong winds caused the bridge to collapse on November 7, 1940. Initially, 35 mile per hour winds excited the bridge’s resonant vibration frequencies, with amplitude of 1.5 feet. This motion lasted 3 hours.
The wind then increased to 42 miles per hour. In addition, a support cable at mid-span snapped, resulting in an unbalanced loading condition. The bridge response thus changed to a 0.2 Hz resonant vibration frequency, with amplitude up to 28 feet.
The torsional shape was such that the bridge was effectively divided into two halves. The two halves vibrated out-of-phase with one another. In other words, one half rotated clockwise, while the other rotated counter-clockwise. The two half spans then alternate polarities.
A 600 foot length of the center span broke loose from the suspenders and fell a distance of 190 feet into the cold waters below.
The fundamental weakness of the Tacoma Narrows Bridge was its extreme flexibility, both vertically and in torsion. This weakness was due to the shallowness of the stiffening girders and the narrowness of the roadway, relative to its span length.
Engineers still debate the exact cause of its collapse, however. The prevailing explanation is called the “Aerodynamic Instability” theory.
Aerodynamic instability is a self-excited vibration. In this case, the alternating force that sustains the motion is created or controlled by the motion itself. The alternating force disappears when the motion disappears. This phenomenon is also modeled as free vibration with negative damping.
Airfoil flutter and transmission line galloping are related examples of this instability.
The wind did not strike the bridge perpendicularly, thus the bridge is initially at an angle-of-attack with respect to the wind. Aerodynamic lift was generated because the pressure below the span was greater than the pressure above. This lift force effectively placed a torque, or moment, on the bridge. The span then began to twist clockwise. Specifically, the windward edge rotated upward while the leeward edge rotated downward.
The span had rotational stiffness, however. Thus, elastic strain energy built up as the span rotated. Eventually, the stiffness moment overcame the moment from the lift force. The span then reversed its course, rotating counter-clockwise.
The span’s angular momentum did not allow it to simply return to its initial rest position, however. The reason is that there was little or no energy dissipation mechanism. Thus, the span overshot its initial rest position. In fact, it overshot to the extent that the wind struck the span from above. The wind’s lift force effectively placed a counter-clockwise moment on the span.
Once again, strain energy built up in the span material. Eventually, the stiffness moment exceeded the moment from the wind’s lift force. The span thus reverse course, rotating clockwise. Again, it overshot its rest position. The cycle of oscillation repeated, except that the span then had rotational velocity as it passed through the original rest position.
The cycles of oscillation continued in a repetitive manner.
Eventually, one of two failure modes occurred. The span experienced fatigue failure due to an excessive number of stress reversals, or the angular displacement increased in an unstable manner until the material is stressed beyond its yield point, and then beyond its ultimate stress limit.
These two failure modes are interrelated. Accumulated fatigue effectively lowered the yield and ultimate stress limits.
Effectively the wind excited the bridge to the point where it vibrated itself into two pieces. The Tacoma Narrows Bridge’s collapse remains the most well-know structural failure due to vibration.
|Minimum Tape Required|
- The balancer was exposed to the elements for a prolonged period of time.
- The balancer experienced a large electrical power surge for an external source.
- The balancer was dropped repeatedly or from a height over three feet.
- A component in the balancer’s hardware failed.
After the propeller was balanced, I could still feel the vibration from inside the cabin on ground runs. This condition is likely caused by resonant vibrations being transmitted through the airframe and aircraft skin paneling. Vibrations may also be cause by prop wash reflecting off the ground and striking the aircraft sheet metal. Harmonic vibrations may also be exciting the resonant (natural) frequencies of the airframe components. These vibrations are normal and should be lowered, if not eliminated entirely, during flight.
Your balancer uses filters to remove all vibration readings that do not correspond to the propeller’s rotation frequency. Vibrations that do not occur in the RPM you indicated, to the balancer, cannot be eliminated by the Model 1015 ProBalancer Sport.
If you suspect a mechanical problem or another components is causing the vibrations, a vibration survey should accomplished to verify the source.
After the propeller was balanced, I/the pilot can still feel the vibration inside the cabin during takeoff.
The propeller and engine are rotating at a higher speed than normal, during takeoff. Vibrations caused at these higher RPM’s can only be reduced by balancing at takeoff power. Balancing at these higher RPM’s can increase vibrations at idle and cruise.
Since takeoff power is the shortest power band used for flight, balancing at this RPM is not efficient.
Vibration should be viewed as a bowl of jello. As you push the vibration jello down in one area, the vibration jello in one or more areas will go up to compensate.
The best solution is to balance at cruise RPM. During flight, this is the most widely used RPM and will show the greatest results to the customer and passengers.
After the propeller was balanced, I/the pilot can still feel the vibration inside the cabin during flight.
Some airframes transmit resonant frequencies throughout their frames and paneling. If these resonant vibrations were not prevalent prior to balancing the propeller, they were likely masked by the vibrations from the propeller.
They may have also become excited by shifting the balance from the previous RPM or frequency to the new balance RPM or frequency. Vibrations excited by these means will only be prevalent at the RPM’s or frequencies that were taken out of balance.
As an example, they may be present during cruise, but not at takeoff, if the propeller was balanced at cruise. In this example the vibrations were likely covered up by the preexisting vibrations from the propeller.
To eliminate resonant frequency vibrations, a vibration spectrum survey should be accomplished. The survey should include all RPM’s in question and the manufacturer’s balancing recommendation.
During the vibration survey, a vibration sensor may be installed on the cabin floor (or any non-dampened structure) to measure the actual vibration felt in the cabin. Measuring the vibration felt in the cabin will assist you in locating its source by locating the frequency at which the vibration occurs.
Balancing at the RPM’s (indicated in the vibration survey), that have high vibration peaks will assist in eliminating the vibration felt in the cabin.
Was this the first weight installation?
This is a normal condition. The first weight solution the balancer gives is a test weight. THIS WEIGHT IS NOT INTENDED TO BALANCE THE PROPELLER. It is intended to create a change in the vibration level of the propeller. The balancer learns from the changes incurred by the test weight and uses the information acquired to accurately calculate a balance solution.
The balancer requires reliable input from its user to accurately calculate balance solutions. This is imperative to the success of your balance.
- High winds or wind gusts
- Mechanical problems in the engine or propeller assembly.
- You should check your cable connections to ensure the connectors are properly installed.
- Check your vibration sensor and cable for visible damage.
- Ensure your vibration sensor is properly installed and the connector has the proper orientation.
- If no discrepancies are found, you may have a damaged vibration sensor.
Nothing! When you balance the propeller you are balancing at a specified frequency, the RPM you selected as a balance speed. In doing so your balancer displayed the once-per-rev synchronous vibration associated with that frequency. Anything vibrating outside that frequency isn’t displayed in the propeller balancing program. Other components may be vibrating at different frequencies. You may also be feeling a resonate vibration in the airframe structure that has been excited by the propeller or other fundamental frequency. If you perform a vibration or acoustic survey and read the overall vibration you may see a level (IPS) higher than that being read from the propeller assembly. Having an operating frequency chart of common components for the aircraft will greatly simplify the task of pinpointing the source of the vibration. A full graphics spectrum survey can be accomplished using an ACES Systems Model 2020 ProBalancer, Analyzer or Model 4040 VIPER Analyzer.
Yes! The Model 1015 Probalancer Sport Analyzer use an IMI 608AII accelerometer. The analyzer can only recognize this sensor. This configuration was engineered to give our customers an economic balancer with the highest accuracy possible.
- First, measure the distance from the center of the propeller shaft to the location you intend to place the reflective tape.
- In the chart below, select from the RPM column the first speed greater than the speed at which you intend to balance.
- From this RPM number, proceed across the chart to the right until you come to the first number larger than the distance measured in Step 1 above.
- From this point, follow the column up to the top to the minimum tape width required for your application. As an example, use the following parameters the distance from the propeller shaft to the intended tape location measures 25 Inches and the balance speed IS 2300 RPM. Select 2400 from the RPM column since this is the first speed greater than your intended balance speed of 2300. From this number, follow the row across to 26.5,which is the first number higher than your intended tape location of 25 inches. From 26.5 folow the column straight up to the top–2 inches. This is the width of tape required for accurate readings at the intended distance and RPM level. (If your reflective tape is only 1-inch wide, place two 1-inch strips of tape side-by-side to create 2 inches.)
|Diamter of Spinner||14.0″|
|Divide by 2||/2|
|Equals Radius of Spinner||=7.0″|
|Minus Distance from Test Weight to Permanent Weight||-1.5″|
|Equals Permanent Weight Radius||=5.5″|
|Required Weight to Balance||25.0 Grams|
|Times Radius of Spinner||x 7.0″|
|Equals Net Effect||175 Gram Inches|
|Divided by Permanent Weight Radius||/5.5″|
|Equals Permanent Weight||31.8 Grams|