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Propellers - 101

Propellers - 101. Presented by Skip Seila FAASTeam Lead Rep. The propeller, though most reliable, is still probably the single most neglected component on an aircraft. What is really unusual?. Nope, not this. Not this, either. Hmmm. Give up?.

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Propellers - 101

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  1. Propellers - 101 Presented by Skip Seila FAASTeam Lead Rep.

  2. The propeller, though most reliable, is still probably the single most neglected component on an aircraft.

  3. What is really unusual? Nope, not this Not this, either Hmmm. Give up?

  4. What is highly unusual is the fact that the engine is still in the aircraft. In the majority of cases, this scenario will result in fatalities!

  5. 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 20tons per blade.

  6. 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.

  7. 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 – it is a “threadless”. * Only lubricated at overhaul.

  8. Non-Feathering Constant Speed Propellers – McCauley “Threadless” * The retainer (2 ea.) on the left are put in place on the blade and the blade is then allowed to drop down in place. The blade “play” is then removed by installing shims under the large snap ring.

  9. 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.

  10. 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.

  11. Full-Feathering Constant Speed Propellers Hartzell

  12. Full-Feathering Constant Speed Propellers - Hartzell * Lubricated at 100 hr. or annual inspection with Aeroshell 5. * Attains pitch change on initial start from oil pressure from the governor. * Lack of oil pressure will result in feathering.

  13. Full-Feathering Constant SpeedPropeller - Hartzell * This shows the propeller reaching the low pitch stop.

  14. Full-Feathering Constant Speed Propeller - Hartzell * This shows the propeller at the feathering stop.

  15. Full-Feathering Constant Speed Propellers - Hartzell * Here’s a close up view of the feathering stop that shows the elongated slots and the spring that from inertia allows the propeller to feather.

  16. 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!

  17. Propellers for Turbine Aircraft Hartzell

  18. Hartzell Turbine Propeller * Lubricated at 100 hr./annual inspections with Aeroshell 6. * Lack of oil press. will result in feathering.

  19. Turbo Propellers

  20. Lightweight Turbine – 2nd Generation * Hartzell Compact Aluminum Hub off a Piaggio Aircraft. * Raysbeck Aircraft STC’s

  21. The M-TPropeller

  22. M-T Care & Maintenance * Do not file leading edge. It’s stainless steel. If it is damaged, have it replaced. If discolored or stained, use a scotch brite pad. * Do not wash it but keep it well waxed. Auto wax is fine. * Note that these bearings are lubricated at time of O/H only.

  23. Propeller Governors

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

  25. Propeller Governors * Notice that the tear-drop arm has moved allowing the flywheel arms to come into play and regulate the oil pressure flow to the propeller and thus regulating the pitch of the propeller. * IT’S AN OIL PUMP !

  26. Propeller Care and Maintenance

  27. Proper Care and Maintenance * File the leading edges of the blades with a fine file. No rasp or coarse file! * 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. * Do not wash propeller. Wipe it clean and finish with a clean oily rag. • Keep in mind that to pass overhaul requirements, blades are measured on width and thickness. Blades are expensive.

  28. 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

  29. Proper Care and Maintenance * Check to assure that the spinner is not touching the blades. * Check that the flyweights (if installed) are not touching and damaging the spinner. * Check for blade play at the tip by fore and aft movement, in and out movement and twist movement. Slight play is okay if the blade returns to it’s original position. * Check for grease leaks.

  30. Proper Care and Maintenance

  31. Propeller Care and Maintenance

  32. 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.

  33. Proper Care and Maintenance * Stay out of tall grass. It’s not a lawnmower. * It’s not to be used as a tow bar. Do not use the propeller tip to move the aircraft! * 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.

  34. Proper Care and Maintenance * Note: A.D. 2004-10-14 Lycoming Engines Change in definition of propeller strike or sudden stoppage. “(3) A sudden RPM drop while impacting water, tall grass, or similar yielding medium where propeller damage is not normally incurred.”

  35. 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”.

  36. Overhaul Periods * Notice there is no “recommended” in there anywhere. * If you exceed or go past the TBO limits, you are all alone with no back-up or support.

  37. Dynamic Propeller Balancing

  38. Dynamic Propeller Balancing * Understand Basics of Vibration * Understand the Benefits of Balancing * Understand Fundamentals of Dynamic Propeller Balancing

  39. Dynamic Propeller BalancingDefinition 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.”

  40. Dynamic Propeller Balancing * Understand that anyimbalance 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.

  41. Dynamic Propeller BalancingVibration-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

  42. Dynamic Propeller BalancingHow It Is Measured * The vibration sensor generates a small voltage when the mass compresses the piezoelectric element. That voltage is proportional to the force being exerted on the element.

  43. Dynamic Propeller BalancingHow It Is Measured * Engineering Units • Mils (0.001 inches) - displacement • IPS (Inches Per Second) - velocity • gs (equivalent gravities) - acceleration

  44. Dynamic Propeller BalancingEquipment Required * A device to collect vibration and phase data. * A phase angle /speed sensing device * A vibration sensing device * Accessories: Cables, balance weights, hand tools.

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