 | How does a Variable Pitch Propeller work?
Each manufacturer designs their propellers differently. However they are normally designed to operate in a single acting mode. That is one of the rotational forces to control the propeller is generated by the dynamics / aerodynamics of the rotating blade but pitch is altered by either hydraulic or electric forces. These can be aided with mass blade weights, springs and / or air pressure. Some basic designs can be purely mechanical.
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| | What are the advantages of a Variable Pitch Propeller over a Fixed Pitch Propeller ?
Fixed pitch propellers only work at their optimum in one given mode. That is they are either at their best in a certain pitch setting and these settings are usually set / designed for take off, performance and / or cruise. A variable pitch propeller allows the best performance in any given mode if operated correctly.
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| | What's the best Propeller for my Aircraft?
Unfortunately a very hard question to answer. The choice is made easier as many Aircraft O.E.M's only offer one brand of Propeller for use. However new model and designed Propellers do hit the market as replacement or upgrade items. Upgrades come mainly in the form of " STC " kits ( Supplemental Type Certification ) which are mainly sold with all the parts required for installation including the legal paper work.
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| | Aluminum verses Composite blades?
Although tricky your choices here are also limited. You do not have unlimited choice in what's available but on most occasions choice will revolve around application requirements, cost, look's and access to support. Rule of thumb is if you operate low wing Aircraft in poor airstrips the damage to composite blades can be as severe as that to the aluminum types. However repairs to composite blades may not always be easily applied in the field and may take more time to repair than the aluminum one's do. Composite blades may not wear out like metal blades do but they cost more to start with so there is much to be considered when choice is available.
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| | My propeller goes supersonic at take off and makes high pitched nosies, why?
The Propeller blade is basically a rotating wing. However Propellers can only generate thrust at subsonic speeds. If the tip nears or exceeds the design speed the blade starts to stall and the result is thrust production is reduced and the loss of energy is felt / heard via the sound it makes. This can occur for many reasons. Reasons include the low / fine angle may be set too low and / or the CSU has not been adjusted properly with regards to variable pitch units. With fixed pitches it may have the wrong pitch setting or simply be worn out.
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| | How can a propeller wear out?
The aerofoil section of the blade's wear during operation ( erosion ) and from maintenance ( dressing of the blades by your Aircraft Engineer ). There is a limit to how much material can be removed before the integrity and performance of the blade is affected. In variable pitch units all the moving parts can wear simply by doing what they are designed to do.
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| | What's a T.B.O?
The T.B.O or Time Between Overhauls is the recommended time a propeller may remain in service, interval wise, between major inspection or overhaul. This is normally listed as a calendar limit and / or operational hourly limit or both. This insures the safety of the propeller and allows a more thorough inspection of the Propeller by more specialist Engineers. This also allows a good time frame for the incorporation of A.D's, Service Bulletins, Letters, Instructions and model upgrades etc. etc..In short it keeps your propeller at it's peak, ensures safety and protects your investment.
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| | If I only fly a few hours a year, can I get a " cheap " overhaul?
Simply, the answer is NO! An overhaul is an overhaul whether a propeller has completed it's full life limit or not. Anyone who can get a cheap overhaul is either being lied to, is lying to themselves or not doing the overhaul as required, period. What you may find is the non mandatory content of the overhaul ( parts replaced due to wear and not just as instructed / required ) could be less. The same mandatory parts need replacing in a propeller that has done 30 hours as one that has done 2000 hours IF overhauled in accordance with the manufacturer's literature. ALL the processes seen at overhaul on a low time propeller are the same as for a propeller which is timex. Sometimes a low time propeller may be more problematic and more corroded than a well used one and cost more as a result of lack of use and neglect.
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| | What is done to a Propeller at Overhaul?
Overhaul is the only time your propeller is checked for dimensional and structural integrity after being manufactured. Any good shop will at this stage carry out all the dimensional inspections required of all parts ( not just the blades ), inspect all components for wear, subject all the required parts to Non Destructive Testing, replace all the mandatory parts ( not just seals ), perform all the required upgrades and processes required and re-assemble the Propeller for continued use. Naturally this whole process is more involved and not as basic as many may think.
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| | Why rework my Propeller blade's? Can't you just paint over them?
The Propeller blade MUST be reworked at overhaul. In general the blade is more dynamic than most people consider and is under considerable load when in use. Operating the propeller induces fatigue to the propeller and the blade even when operating in ideal conditions. In order to make sure this blade stays airworthy and efficient the aerofoil section need's to be re-established and that all stress risers and the fatigued layers of material is removed from the blade surface. However the more damaged the blade is from service the more metal removal takes place.
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| | Who sets the limits for the minimum dimension a blade can be?
The Propeller manufacturer controls this data. They provide, via their manuals, the MINIMUM dimension a blade can be released to. The minimum dimension of the blades chord and width have to be met AFTER all blade rework has been completed. These dimensions should also be referred to in the field should any major rework be required on wing. The manufacturers also controls the face alignment, twist and edge alignment criteria too. These items are checked at overhaul or repair by any decent propeller shop. Undersize blades can cause blade flutter and will not work efficiently to absorb the horse power produced by your aircraft engine.
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| | What do I do in the event of a Propeller / ground strike?
There is only one answer to this, that is the propeller needs to be fully overhauled PRIOR to further flight. In general if the propeller is that badly damaged that removal is required the engine may also be subject to a bulk strip. The propeller is overhauled after a " strike " as some minor external damage could relate to a more serious condition within the propeller itself if left uncorrected. Manufacturers do prefer a more conservative approach in light of safety issue's and past historical data.
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| | Can bent Propeller blades be straightened?
In many cases yes they can. They can be repaired by Propeller shops with this knowledge and experience. The blades must meet a number of criteria and are fully overhauled at the same time. Please note bend repair's in the field must NOT be attempted and any field tampered blades should be rejected if presented to a decent propeller shop. General rule again, if the blades are rejected due to the bend limits being exceeded then the hub unit should also be rejected.
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| | Why should we service propellers anyway?
Apart from the fact the propeller is not just a rotating mass it is also the most highly stressed component on any propeller driven aircraft. The load propellers endure is staggering when researched and therefore monitoring and preventative action and care during it's life not only promotes safety but also reduces the operating costs long term.
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| | Manufacturer Approved Shops verses Non Approved Shop's?
All shops performing work on propellers should be approved by the local and regional Airworthiness Authorities as a basic minimum. Work done by just any person or organisation cannot be legally released. However some shop's, like WCP, are also Approved by the Manufacturer. Shops with such approvals and distinction are audited on a much stricter basis and are generally much better shops to deal with. Manufacturers demand that their approved shops have staff attend regular training sessions, that these shops carry spares, change all the mandatory parts required, incorporate all the latest service data, stick to laid down procedures and generally conduct their business dealings in an open and honest way. In short such shops are 99 / 100 the better shops for customers to deal with for such things as warranty and in service issues. Such shops ( approved shops ) have basically been vetted for you by the manufacturer assuring quality control and that the required and correct procedures are being followed. Non approved facilities do not always meet the required controls or quality requirements necessary.
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| | Why do shops vary so much?
In truth in a perfect world they shouldn't. However there are BIG differences when one considers each shops level of experience, commercial exposure, stock holdings, geographic location, the tooling they have, whether the shop has O.E.M Approval or has just a basic local authority approval, the level of service they provide and quite simply as the whether the shop is actually doing work in accordance with what is required. In short, it's like getting a 100 hourly done, each maintenance organization interprets the manuals to what they want to see. Not many organizations service aircraft the same way as each other yet they employ the same literature ! Another reason manufacturer approved shops should be a better deal for the end user as some of the quality research has been done for you. In short it pays to see " what " you are getting for your money and make sure apples and being compared with apples. Sometimes the cheapest job's done are cheap for some very odd, dangerous or outright commercial reasons.
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