Prop Condition

[skippydiesel]

Hi All,

 

I seek your advice on the following -

 

My aircraft is fitted with a European composite two blade, ground adjustable propeller.

 

The prop is 15 years old and has 750 Hobbs hours of operation.

 

Leading edges & tips are only very slightly eroded (I have seen other examples of this prop, some significantly younger/lower hours, that look like they have been "gravel" blasted). To me, the prop appears to be in remarkably good condition.

 

Until very recently I was very happy with its smooth, quiet, performance and condition.

 

While admiring my aircraft and commenting very favourably on its condition, a knowledgeable person, suggested my prop should be replaced ( Shock, horror - a $1,700 prospect).

 

The advice to replace, seemed to be focused on observation that the white front side of each blade is covered in very fine "crazing" of the gel coat. NOTE: The red tips and grey back side of each blade has no visible crazing.

 

The opinion offered was that the surface crazing is indicative of structural degradation of the prop due to engine/combustion induced vibration/pulses .

 

To the best of my knowledge(I have taken no special note), the crazing has been in existence for most of the props service life, is within the gel coat (there is minimal barely discernible surface texture & no flaking) and I am unaware of any change/progression in its appearance. I have always assumed that the crazing is due to exposure to the harsh Australian sun (UV) and has no structural significants.

 

Other than manufacturers advice to check the prop condition at initial 50 hrs, thereafter 150 hrs, I am unaware of any life limitations. (The European manufacturer speaks little English/very hard to get meaningful advice)

 

Please comment on:

 

· The advice to replace the propeller.

 

· Recommend an Australian (prefer NSW) service provider, skilled in the condition assessment of composite propellers.

 

 

[facthunter]

I can only make a general comment. The tensile stresses in a prop blade are high in service. When starting it goes into crazy shapes but it is flexing all the time, under the effect of torsional variations in the engine. It will have a safe life and shedding a blade is something you wouldn't want to contemplate. Not all engines are recommended to operate "composites" and all metal blades are inspected for cracks. It's a critical application. IF you have cause for a real doubt I'd research an alternative prop which has more to say about how long it is safe to use. Nev

 

 

[robinsm]

Get another opinion and then persist with the manufacturer. Some" KNOWLEDGABLE EXPERTS" tend to spout off regularly and, not disparaging the "expert" who spoke to you, I would be a little wary working on just one "expert" opinion. Almost got caught very expensively by an "expert" myself untill I got a 2nd and 3rd opinion from others who dealt with the day to day issues.

 

There are many so called experts out there who talk through an orifice other than their mouths. Just be carefull, and research the heck out of it before diving into the bank....just sayin

 

 

[Downunder]

I would persist with mfg. Use google to translate. Type into google "english to ****" and two boxs will appear....one for you to write english and the other for the translation.

 

Copy and paste translation into your email. I've used it several times. Russian, Korean & italian.

 

Neuform props need returning to Mfg in Germany after so many hours.

 

I know 2 people who have done so. It took a while, time wise, but they were returned looking brand new for a fraction of the replacement cost. Owners very happy.

 

 

[slb]

My aircraft is fitted with a European composite two blade, ground adjustable propeller.

You don't say who the Manufacturer is but I would contact them directly by email and send a photo to check their tolerances for wear and gain some advice. They may respond better to email than by phone.

 

 

[djpacro]

My airplane has an MT C/S composite prop which requires overhaul every 6 (from memory) years and has very specific instructions about blade condition requiring repairs. Hoffmann props are similar. TBO also based on hours too.

 

 

[rollerball]

In general I think composite props have a recommended replacement period of about 10 years in normal life. The DUC 3-blader on my Sav was older than that and had some chips on a leading edge that had been very poorly repaired, possibly with baking powder and superglue by the look of it, this being France.

 

I had been agonising over what to do - improve the repair, replace the blade, replace the whole prop - when the matter was taken totally out of my hands when I stupidly bumped into something hard with the engine running, fortunately with no damage other than to the prop itself (all 3 blades) and the spinner.

 

So I ended up buying a brand new 3 blade scimitar prop complete with spinner direct from the Ukraine (copy of Kiev) for half the price of the DUC that had been on there. Unfortunately I was then overtaken by health problems and I still haven't flown the aircraft with the prop fitted (health problems now resolved - hooray!!!) but don't foresee any problems with it. It came complete with s/s edge protectors and a purpose-built pitch gauge too, BTW.

 

 

 

[Raytol]

Gelcoat is such a brittle surface treament. The flexure of the structure of the blades may deflect more than the gelcoat can handle.

 

 

[Charlie Tango]

Definitely would look into a prop overhaul. 750 hours, 15 years, it sounds like a good candidate anyway.

 

 

[skippydiesel]

Gelcoat is such a brittle surface treament. The flexure of the structure of the blades may deflect more than the gelcoat can handle.

I am calling it "gelcoat" because that's what it looks like - it may be something else entirely.

 

 

[skippydiesel]

Definitely would look into a prop overhaul. 750 hours, 15 years, it sounds like a good candidate anyway.

Fair comment, howevr my prop looks to be in very good condition in every respect other than the front side "gelcoat" - hence my hesitation to go out a cough up nearly 2,000 big ones.

 

The hairline "crazing" seems (to me) to be cosmetic rather than structural and yes I do understand that this surface appearance could/may be an indicator of deeper issues within the fabric of the blades.

 

l approached Bolly to see if they would do an assessment for me - they politely declined citing some restriction by CASA regarding commenting on other props than their own.

 

 

[Head in the clouds]

I don't know whether it's already been said here, but composites (and that includes timber) don't fatigue, so they don't have a limited life due to fatigue unless they have been overstressed which is unlikely for an airscrew.

 

The main issues with composite props would be physical damage, usually to the leading edge which would normally be simply repairable, and UV damage which results in breakdown of the resin matrix, and isn't repairable, but is easily determined by inspection.

 

 

[djpacro]

Composites do suffer from fatigue eg see http://journals.sfu.ca/ts/index.php/ts/article/download/276/259

 

Note references #3 by Gary Esson and Alan Patching, #15 by Alan plus other Melbournians such as Nick Mileshkin. Alan spent much of his life working on fatigue: starting with Mustang airframes after WW2 to the composite glider work that he did at RMIT.

 

(I recall Alan also telling us that wood also has some behaviour which could be characterised as fatigue but really only of slight academic interest.)

 

 

[skippydiesel]

I don't know whether it's already been said here, but composites (and that includes timber) don't fatigue.I am sure this is what I have also been told

 

................. UV damage which results in breakdown of the resin matrix, and isn't repairable, but is easily determined by inspection.

In your opinion - what would be the inspection procedure ???

 

 

[skippydiesel]

Composites do suffer from fatigue eg see http://journals.sfu.ca/ts/index.php/ts/article/download/276/259Note references #3 by Gary Esson and Alan Patching, #15 by Alan plus other Melbournians such as Nick Mileshkin. Alan spent much of his life working on fatigue: starting with Mustang airframes after WW2 to the composite glider work that he did at RMIT.

(I recall Alan also telling us that wood also has some behaviour which could be characterised as fatigue but really only of slight academic interest.)

Had a quick glance - all to far above my poor head. What I did take away (possibly wrong) is that a fatigue life had yet to be determined (in wings) and as yet a suitable testing regime had not been found/implemented.

 

 

[Head in the clouds]

In your opinion - what would be the inspection procedure ???

I'm glad you asked, and I also respect everything that DJP says - I really was talking the more simplistic version, perhaps that applies to sport aviation more than the far more demanding rigours of competition aerobatics where you may well be 'exercising' the composite toward its upper limit, or, indeed, unwittingly exceeding it occasionally.

 

However, in normal use our composite props operate well below their overstress limit and for all practical purposes, IN MY OPINION, will never reach anywhere near any perceived fatigue life, or issues thereof.

 

In specific response to your question, perhaps you're a fisherman? If so it would help you in your inspection. Some really keen fishermen, like me, have rods that cost up to a grand each, and would never leave them in the sun except when in use, consequently they look like new even when ... well some of mine are forty years old. After any use they get a good rinsing in fresh water, towelled dry, wiped with Armorall as a UV protector and which also helps to prevent the degradation of the plasticisers in the resin matrix ... and that is the crux of the matter.

 

The plasticisers are both good and bad, they keep the matrix as flexible as the fibres they bond together, but they also reduce the efficacy of the bonding itself.

 

So, if you're a fisherman who doesn't care much about your gear (or maybe you have a friend like that?) you'll have a few rods which are starting to look a little opaque, whitish and are starting to develop a matt surface instead of a shiny, glossy finish. Also, as any good braggardly fisherman you will have regularly bent your favourite rod from tip to butt, to show your best buddies how good it is ...? Well, if you do that after ten years of neglect and UV exposure it will likely snap and embarrass you. On the other hand, if you stored it in a bag, in the dark, and bathed it in protectant regularly then you might find that it'll bend just as well on your hundredth birthday. And, of course, still look nice and glossy.

 

So, do all you composite prop owners have blade covers that you install as soon as you land? Do you have a small container of Armorall or 303 UV protectant that you apply regularly?

 

I made my blade covers as soon as I opened the box from Bolly ...

 

 

[skippydiesel]

........................................................................................................is easily determined by inspection.

You are the first respondent to hint at an inspection procedure.

 

I enjoyed your interesting advice on the protection of fishing rods and I am sure it can be applied to composite props but doesn't actually answer my question regarding the inspection of a prop (cant bend the tip of my prop around to the hub).

 

If you have an inspection procedure, I would be very grateful to hear it.

 

All the best for the New Year

 

 

[facthunter]

There probably is not reliable inspection procedure for composites at this level of the market in a general sense. The error should be on the conservative side as the consequences of a blade failure can be quite dire especially with a pusher and close clearance boom. A pusher also operates in more disturbed airflow and this plus engine vibrations don't use rpm ranges (often not known) do affect the LIFE of a prop.. Most aircraft parts are built as light as possible for obvious reasons. Things don't stay reliable for ever. Metals change and all other materials as well.. Nev

 

 

[Head in the clouds]

You are the first respondent to hint at an inspection procedure.I enjoyed your interesting advice on the protection of fishing rods and I am sure it can be applied to composite props but doesn't actually answer my question regarding the inspection of a prop (cant bend the tip of my prop around to the hub).

 

If you have an inspection procedure, I would be very grateful to hear it.

 

All the best for the New Year

Thanks for the New Year wishes - and to you too!

 

No, I don't have a specific inspection procedure as such but what we'd be looking for is the condition of the resin matrix i.e. how good the resin part of the whole is, and how good the bond between the fibres and the resin is.

 

Assuming no knowledge at all of fibre re-inforced composites, one would want to start with knowing what a composite part in good condition looks like. We want something transparent, not covered in gelcoat, obviously. I'd start with a brand new fishing rod and a 10x, 15x and 30x multi-element (triplet) loupe which can be bought on ebay for about $10. Then have a good look at the rod and see how the resin and fibres seem to be 'as one'. That new rod needs to be a cheap one ($10 kids rod from BCF or similar), and fibreglass rather than carbon fibre, boron etc.

 

Next call all your mates and ask them to dig out the oldest and ugliest things made of fibreglass that they have, preferably things that have been left outside for years - some golf clubs had fibreglass shafts, some garden furniture etc, even old fishing rods ...

 

Now start breaking things, start with the new fishing rod, see how it eventually snaps and usually leaving long spears of glass fibres still encased in quite intact resin. Put your loupes to work and study the fracture points, see how little powderiness of the attached but fractured resin there is. Wear gloves and eye protection when you snap things ...

 

Next examine the surface of the old fibreglass and see how porous the surface is, under magnification it resembles a sponge. Note the powdery surface and particularly note the visible fibres where resin has decomposed away leaving the fibres exposed. Next scrape the surface of the fibreglass to see how brittle the surface is, how soft/chalky it is and how deep the decomposition is. Next start breaking up the old fibreglass and compare the fracture points under magnification with the fractures in the new fibreglass, you will see that whereas the new glass snapped leaving very little exposed fibres, because the resin stayed bonded to the fibres until they broke, the old resin crumbled before the glass fibres broke, so longer strands of glass are left exposed after it breaks.

 

Armed with this new understanding of the visual appearance of new and ageing fibre-reinforced resin matrices you should find that you will be better qualified and more confident to make a judgement about the actual state of your prop blades.

 

Also - if you are anywhere near a fibreglass boatbuilder/repairer they may be able to help too.

 

 

[M61A1]

Are the blades finished in the resin, or are they painted? Are they solid composite (monolithic) of foam/wood filled (sandwich) construction?

 

Are you familiar with Tap Testing? It works quite well.

 

 

[M61A1]

A quick search shows the Atec Zephyr fitted with a FITI prop. The manufacturer's servicing schedule requires 50 hr servicing , which is just a retorque, but the required 150 hr servicing requires inspection by the manufacturer.

 

Assuming your aircraft is LSA, this will unfortunately be mandatory.

 

 

[skippydiesel]

Are the blades finished in the resin, or are they painted? Are they solid composite (monolithic) of foam/wood filled (sandwich) construction?Are you familiar with Tap Testing? It works quite well.

Hi M6,

 

My poor answers are:

 

• "finished in the resin", - I think the dark grey back of each blade may be a resin finish (no crazing)
   
   
  
• "are they painted" - tips are hard red gloss (no crazing) and appear to be a either a two pack or similar. Front of blade, white material (crazed) gives the appearance of being thinner & less substantial than either the red tip or grey back - could be a thinner two pack or gel coat,
   
   
  
• "solid composite/ foam/wood filled" - I believe these are solid composite (base is hollow for a short distance)
   
   
  

 

 

I do remember Tap Testing now that you have caused me to do so - Promoted as a method of determining the structural integrity of a cured/finished composite lay up - 20 cent coin or similar "taped" over a surface while you listen for inconsistencies (bit like primitive sonar). Inconsistencies could be voids, changes in material density, etc etc. Problem would be in interpretation of sound. An experienced "operator" having found many inconsistencies that are then "deconstructed" would have a memory/library of sound interpretation - I start from scratch & have no intention of deconstructing my only prop but I guess it wouldn't hurt to compare the tap sound of each prop (if they are same what do I make of it ??. If they differ there could be a serious problem).

 

Thank you for your thought provoking response.

 

 

[skippydiesel]

....................Assuming your aircraft is LSA, this will unfortunately be mandatory.

To the best of my knowledge all Australian registered ATEC Zephyrs are 19. There are two ATEC Fayeta's that are both 24.

 

Again to the best of my knowledge the FITI inspection intervals you refer to are advisory (ie not mandatory) for the ground adjustable range - there is no mention of service life and further inspections after the initial 150 hr. The FITI inflight adjust/CS range may be mandatory due to the additional moving parts and wider range of stresses imposed on an inflight adjustable system.

 

 

[M61A1]

Usually when a maintenance schedule says retorque at 50 hrs, it means every 50 hrs and if it must have an inspection at 150 hrs , it means every 150 hrs. The fact that it’s 19 reg will help a lot if you choose to do your own inspection or replace with another type.

 

Tap testing is not difficult. I find often that a defect will not only sound “dead”, but will also feel “dead” and won’t bounce the same.

 

Gel coat is not often used on props, so I would suggest that the white bit with crazing is probably ( but not certainly) just paint.

 

 

[skippydiesel]

Usually when a maintenance schedule says retorque at 50 hrs, it means every 50 hrs and if it must have an inspection at 150 hrs , it means every 150 hrs. The fact that it’s 19 reg will help a lot if you choose to do your own inspection or replace with another type.Tap testing is not difficult. I find often that a defect will not only sound “dead”, but will also feel “dead” and won’t bounce the same.

Gel coat is not often used on props, so I would suggest that the white bit with crazing is probably ( but not certainly) just paint.

I will certainly try the Tap Test.

 

Regarding the service/inspection intervals - What's to service??

 

There are no moving parts and subject to no damage to the blades nothing to repair. Sure the torque settings for the prop assembly and prop to engine need to be checked (I do this every 50 hrs) but this is a no brainer requiring only a reasonably accurate (calibrated) torque wrench.

 

As long as the screws bolts & nuts are secure, there is no apparent damage, each prop is firm(no movement) in its "socket" what more can be done??

 

The big question in my mind is what is involved in the inspection - how is it done and what are the "check" points/features.

 

As I said earlier in this conversation - I am very happy with the performance and condition of my prop - it was but the unexpected & unsolicited advice from a virtual stranger (but an acknowledged expert) that has caused me to worry about the integrity of my prop. As FactHunter said " the consequences of a blade failure can be quite dire"