Propeller Care & Maintenance for the Amphibian Presented by Charles “Skip” Seila

The propeller is probably the single most neglected component on an aircraft.

On takeoff, propeller tip speeds approach the speed of sound On takeoff, propeller tip speeds approach the speed of sound. The blades must absorb not only the punishing vibration of the engine’s power pulses, but also vibration caused by the oncoming airstream. Centrifugal loads – those forces that try to pull the blade out of the hub – amount to 10 to 20 tons per blade.

The blades twist and flex The blades twist and flex. The stresses imposed on the prop are more concentrated in the small areas that are nicked or cut. These nicks and scratches act as stress risers, which can weaken the blade enough to eventually cause blade failure.

TOPICS * Fixed Pitch Propellers. * Non-Feathering Constant Speed Propellers. * Full-Feathering Constant Speed Propellers. * Propeller Governors. * Proper Care and Maintenance. * Overhaul Periods. * Dynamic Balancing.

Fixed Pitch Propellers

Fixed Pitch Propellers * Pitch set for “Cruise” or “Climb”. * Can be set for other angles per the manufacturers allowable specifications. * Pitch can only be reset at an approved propeller shop. * Pitch is limited as to how many times it can be reset as it becomes “work hardened” at an unknown given time.

Non-Feathering Constant Speed Propellers McCauley

Non-Feathering Constant Speed Propellers – McCauley * Takes oil pressure to change pitch. * Lack of oil pressure or you have a fixed pitch propeller. * Only lubricated at overhaul.

Non-Feathering Constant Speed Propellers – McCauley “Threadless” * Takes oil pressure to change pitch. * If it has a large snap ring at the base of the blade as shown here – it is a “threadless”.

Non-Feathering Constant Speed Propellers – McCauley “Threadless” * To inspect. Place the blade in the vertical position and with your thumb and forefinger on the tip, check for fore & aft movement. * Movement of 1/8 “ is acceptable. * If movement exceeds 1/8”, do not remove the propeller. It is repaired right on the aircraft. * Excessive movement is not critical to flight. It diminishes at the first rotation of the propeller and is purely psychological.

Non-Feathering Constant Speed Propellers – McCauley “Threadless” * If it has a small allen screw in the middle of the hub, it probably is “oil filled”. * The oil has a red dye in it to detect early cracking in the hub. * In order to prevent unwanted red dye indications when no possibility of cracking exists, it is highly recommended to dynamically balance the aircraft.

Non-Feathering Constant Speed Propellers Hartzell

Non-Feathering Constant Speed Propellers - Hartzell Takes oil pressure to operate. Is lubricated every 100 hrs. /annual inspection.

Non-Feathering Constant Speed Propellers - Hartzell Note the 2 zerk fittings on each side. They line up perfectly with the bearings. Remove the opposite one when applying: - Aeroshell 5/6 on constant speeds. - Aeroshell 6 on turbine propellers.

Full-Feathering Constant Speed Propellers Hartzell

Full-Feathering Constant Speed Propellers - Hartzell * Lubricated at 100 hr. or annual inspection. * Attains pitch change on initial start from oil pressure from the governor. * Lack of oil pressure will result in feathering.

Full-Feathering Constant Speed Propellers - Hartzell * This view shows the propeller in the feather position. However, the spring had to be cut for us to demonstrate the actions of this propeller. Seeing this spring as it really is should remove any doubt that this propeller will feather!

Propeller Governors

Propeller Governors * Simply put – it is a high pressure oil pump. * An inertia flywheel maintains the setting that you made in the cockpit.

Proper Care and Maintenance

Proper Care and Maintenance * File the leading edges of the blades with a fine file. No rasp or coarse file! * File all blades evenly. * Do not use the shank of a screw driver for burrs. That only rolls the metal back in and does nothing to prevent further damage. * Keep in mind that to pass overhaul requirements, blades are measured on width and thickness. Blades are expensive.

Proper Care and Maintenance Burrs or nicks (stress risers) on leading or trailing edges must be repaired by using the formula of 10X the depth of the damaged area to determine the necessary area required to be repaired. Start with a file, then emery cloth and then crocus cloth to remove all file marks Do not wash your propeller. Wipe it clean and finish with a clean oily rag.

Proper Care and Maintenance

Propeller Care and Maintenance

Proper Care and Maintenance * To “store” your propeller properly after flight: 2 bladers – horizontally. 3 bladers – 2 up and 1 straight down. 4 bladers – 2 up and 2 down. - Storage in this manner prevents rain or moisture from settling in the cavity at the base eliminating the opportunity for moisture to seep in and case corrosion or destroy the affectivity of any lubrication.

Proper Care and Maintenance * Stay away from water puddles. Why? Ever notice the vortexing when running up over water? The blades are so thin that one tip may decide to go to one side while the other blade tip takes to the other side and now the prop is out of track. Avoid the vortex scenario. This can be real costly.

“___________” Overhaul Periods

What’s missing ?

The word “recommended”.

It’s history. It isn’t there anymore. It doesn’t exist. IT”S GONE ! It’s history. It isn’t there anymore. It doesn’t exist.

Overhaul Periods * Hartzell Service Letter-----HC-SL-61-61Y “Propeller – Overhaul Periods and Service Life Limits for Hartzell Propellers, Governors, and Propeller Damper Assembllies”. * McCauley Service Bulletin SB137Y----”Revised time between overhaul (TBO) specifications”.

Overhaul Periods * If you go past the TBO limits, you are all alone with no back-up or support. * If anything happens, it’s at your own risk. * It’s a gamble and it is up to you to see if it is worth it.

Dynamic Propeller Balancing

Dynamic Propeller Balancing The Basics of Vibration Definition Why it happens How it is measured How we correct it

Dynamic Propeller Balancing Definition For the purpose of Propeller Balance, vibration can be described as: “the unwanted, unproductive, cyclic oscillation of the propeller and engine assembly about its rotational axis.” For the purpose of Propeller Balance, vibration can be described as the unwanted, unproductive, cyclic oscillation of the propeller and engine assembly about its rotational axis.

Dynamic Propeller Balancing Why Does It Happen? When the weight of a rotating propeller and engine assembly is not equally distributed, the dominant or heavy point attempts to continue moving in a straight line. The resulting force attempts to pull the assembly outside its rotational axis. The assembly then orbits what would be the normal center of rotation, causing vibration.

Dynamic Propeller Balancing Understand that any imbalance at the center of rotation amplifies itself as it travels out to the tip of the propeller. The tips being thin vibrate augmenting the vibration and also show a lose in efficiency.

Dynamic Propeller Balancing How We Correct It Improve manufacturing methods Remove and replace Static Balance Static Balance + Dynamic Balance

Dynamic Propeller Balancing Vibration-Related Complaints Passenger complaints of noise in the cabin Cracked exhaust stacks and sheet metal Higher than normal occurrence of engine and prop oil leaks and light bulb failures Physical movement of airframe (buzz in the seat, yoke, rudder pedals) Malfunctioning or failed avionics

Dynamic Propeller Balancing How It Is Measured Sensor Types Displacement - Measures physical change of position. Velocity - Measures the rate of change of displacement with time. Acceleration - Measures the rate of change of velocity with time.

Dynamic Propeller Balancing Remember that dynamic balancing will prolong the life of the engine, propeller, airframe and avionics. Before dynamic balancing and right after propeller installation, it is best to put a few flight hours or good high end runs on it first. This will allow the blades to take their “set” and eliminate the need to re-do the balancing later on.

Dynamic Propeller Balancing Data Collection & Processing The vibration sensor is installed on the engine as near the front bearing as possible. The Phototach is mounted on the cowling, behind the propeller. The reflective tape is applied to the back side of the target propeller blade in line with the Phototach beam. The mass is located by the relative occurrence of tach trigger and mass passage at the radial sensor location.

Dynamic Propeller Balancing Data Collection & Processing As the heavy spot on the propeller passes the location of the vibration sensor, the sensor generates and sends an electrical pulse to the analyzer. The Reflective tape triggers a response as it passes the Phototach, which then sends an electrical signal to the analyzer.

Dynamic Propeller Balancing Data Collection & Processing The process is repeated while the analyzer averages out errors caused by momentary vibration events outside the running average.

Dynamic Propeller Balancing Data Collection & Processing A solution is then provided by the instrument based on a stored influence coefficient or a calculated test weight. If required, the process is then repeated for refinement of the solution.

Dynamic Propeller Balancing The Balancing Process Where to place the weights Test weights can be placed under the spinner retention screws. It may be necessary to use longer screws for the test weights. If doing so, account for the delta between the normal and the longer screw. Be sure you are measuring the angles in relation to the sensor or tape as you specified in the setup being used.

Fundamentals of Balancing Avoiding the Pitfalls Adjust the speed of the prop as closely as possible to the exact target RPM on EVERY run. A change in RPM will change the influence of an attached weight. Subsequent solutions will not have the same calculated results at different speeds.

Dynamic Propeller Balancing If an established influence for the engine and prop combination being balanced is not being used, the first weight the analyzer will ask you to install is a TEST weight. This weight may cause the vibration amplitude to increase. The intention of the test weight is only to induce a measurable change, not necessarily reduce the vibration.

Dynamic Propeller Balancing There is no difference in the propeller balance procedure for a radial engine, opposed engine, turboprop, geared, variable pitch, or fixed pitch propeller.

Dynamic Propeller Balancing The Balancing Process Permanent weights may be installed under the flange or on the bulkhead. If installed under the flange, offset from spinner attaching screws by four times the diameter of the spinner screws.

Dynamic Propeller Balancing Remember that when dynamic balancing you are balancing from the engine mounts forward. Dynamic balancing is not a “cure all”, as it can not compensate for gear doors that do not close properly, worn control surface rod ends, etc. It is becoming the professional opinion that all engines with propellers should be done.

Thanks so much for your time and we hope that in some way you have gained from this seminar.