What is a propeller?
The propeller is a twisted airfoil that converts the rotating power of the engine into thrust, which propels the aeroplane through the air. Sections of the propeller near the centre are moving at a slower rate of speed than those near the tip, which is why the blades are twisted. Modern propellers are fabricated from high strength, heat-treated, aluminium alloy forgings. Some are made up from fibreglass resins into composite materials.
How does a propeller work?
Think of it as a spinning wing. Like a wing, it produces lift, but in a forward direction. A force we refer to as Thrust. Its Rotary Motion through the air creates a difference in air pressure between the camber and face surfaces of its blades.
What are the different types of propellers?
Fixed Pitch – one piece prop with a single fixed blade angle. The pitch must be high enough to offer good cruising performance and yet low enough to achieve acceptable takeoff and climb characteristics. Constant Speed – A governor is used in conjunction with the propeller to automatically provide constant RPM as the pilot selects the proper setting. The governor controls the forces acting on the propeller to automatically change the blade angle within a preset range. Full Feathering – Blades can be rotated to a high positive angle to stop rotation (windmilling). This feature is common on multi-engine aircraft, because it allows an engine to be shut down and the prop stopped to reduce drag and asymmetric control forces. Reversing – Blades can be rotated to a “negative” blade angle where they will provide a rearward thrust to slow down, stop or move the aircraft backward. This capability is normally provided for turbine installations.
What are the correct terms for various parts of a propeller?
Blade – One arm of a propeller from hub to tip. Hub – Center section of the propeller that carries the blades and is attached to the engine shaft. Blade Tip – That part of the blade furthest from the hub. Prop Diameter – The diameter of the circle circumscribed by the blade tips. Blade Root – Section of a detachable blade nearest the hub. Blade Shank – The thick portion of a blade near the hub. Blade Station – One of the designated distances along the blade as measured from the center of the hub. Blade Camber Surface – The cambered or most cambered side of a blade (as seen from in front of the aircraft). Blade Face or Thrust Surface – The flat or least cambered side of the blade (as seen from in back of the aircraft). Blade Thickness – the maximum thickness between the cambered surface and the face or thrust surface at a given blade station. Blade Leading Edge – The forward full “cutting” edge of the blade that leads in the direction of rotation. Blade Trailing Edge – The continuous edge of the blade that trails the leading edge in the direction of the rotation. Blade Width – The measurement between the leading edge and the trailing edge at a given station. Blade Angle – An angle (less than 90o) between the chord line of a propeller blade section and a plane perpendicular to the axis of propeller rotation. The chord line is a theoretical straight line drawn between the leading and trailing edges of the blade. Blade Angle Settings – Low and high angle settings of a controllable pitch prop, as determined by built-in stops, for feather, reverse, latch and start locks.
Why is propeller overhaul needed?
A fixed pitch prop does not need overhaul. It requires blade reconditioning only, as necessary. Constant speed and full feathering props do require periodic overhaul. Overhaul of the propeller is needed to increase safety, prolong the propeller life, and improve function or operation. Overhaul is the periodic disassembly, inspection, reconditioning, and reassembly of the propeller. The overhaul interval is generally based on hours of service (operating time) but a calendar limit also applies. After being disassembled, the propeller is inspected for wear, cracks, corrosion or other abnormal conditions. Certain parts are replaced, while other parts are reconditioned and refinished. Reassembly and balancing complete the job.
Where do I find allowable repair procedures?
Most minor damage found in propeller blades can be repaired locally. If in doubt always consult one of our team members who will be happy to assist in your inquiry. All repair procedures for propeller blades will be found in relevant propeller Owner’s manual. Please use the link in the Technical Data to obtain this information.
Where do I find general maintenance answers?
The Propeller Owner’s Manual is a great source of information, not only does it give you repair procedures but it will also give you tolerances to check for blade movement, lubrication, air charge and so much more. Please Click on the applicable Propeller Manufacturer for direct links to there resource library containing Owner’s Manuals : Hartzell McCauley MT – Propeller
Where do I find installation torque?
All propeller mounting torques can be found in the Propeller Owner’s Manuals. Be aware that some torque figures can be wet torque. Always consult the Owner’s Manuals for the correct torque value to be applied and whether it is a wet or dry torque value.
Where should I send my propeller?
You should always send your propeller to a shop that is approved by the O.E.M. Shops with OEM approval are subject to strict audits to ensure that they adhere to all overhaul requirements as well as attending Manufacture’s training courses to maintain an up to date knowledge of all product improvements. Just because a propeller shop is approved by the local authority does not necessarily mean that they comply with all overhaul procedures and processes or adapt the same quality control measures that an Authorised shop does. You can always be guaranteed that dealing with an authorised shop gives you the satisfaction that you get what you pay for. By this, I mean NO SHORT CUTS, GENUINE OEM PARTS and ALL MANDATORY REPLACEMENT PARTS as specified in the respected manufacturer’s Illustrated Parts List.
I have had a propeller strike, do I need to overhaul the propeller?
The criteria applicable to any propeller involved in any ground / impact requires the propeller to be inspected at the very least. Propeller strikes can be as major as ground impact damage and can be as minor as striking a tow bar or a tie down peg. We have seen instances where a propeller has come to our shop for inspection following a Kangaroo strike where there was no external damage evident. Upon dismantling one blade was found cracked, approximately fifty percent around the shank. Certain inspections need to be carried out to determine if the propeller requires overhaul. In most instances it will. There are not short cuts in this as minor blade damage may have more serious internal damage which in can result in a catastrophic failure. Our recommendation is always to eer on the side of caution and a full complete overhaul is required.
My propeller only has 100 hours of ttsn, why do I need to overhaul my propeller?
Irrespective of the hours on a propeller, it must be completely overhauled regardless. The propeller is subject to the same process of that which has completed 2000 Hrs. All components are inspected per the manual, full NDT check are carried out and mandatory replacement parts per the OEM are fitted. If it is a cheap overhaul then it is a very good chance that what should be done is not.
What is the difference between 'anti-ice' and 'DE-ICE'?
With anti-ice equipment, alcohol is permitted to flow over the propeller blades to prevent ice formation. It is not effective after ice has formed. A de-ice system applies electric heat to the blades after ice has formed so that it is melted near the surface and centrifugal force will cause the ice to “shed”.
My governor is being overhauled and I need a new drive gear, what are my options?
It may be a cheaper alternative to purchase a brand new governor, being brand new no parts will be previously reworked which in turn can help you save money down the track. All tolerances and measurements will be at new specifications.