Prop Condition

[M61A1]

I agree that there's not much to service. As far as manufacturer inspections, it's a means of ensuring that their product meets their standards. Possibly they have ultrasonic test equipment, that said, when I tried ultrasonic on a Ward Drive prop, it was useless because of the curvature around the blade root, which was the bit I was concerned about.

 

You can make a tap hammer out of aluminium or brass (depending on which works better) pictured below.

 

If the crazing is in the resin matrix, it can be sanded, as long as structural fibres are not damaged, and resin wiped to restore the finish. But I would only be paint that has crazed. You won't know until you sand it off. G ood quality epoxy resins must be used, none of that polyester rubbish.

 

 

 

[skippydiesel]

I agree that there's not much to service. As far as manufacturer inspections, it's a means of ensuring that their product meets their standards. Possibly they have ultrasonic test equipment, that said, when I tried ultrasonic on a Ward Drive prop, it was useless because of the curvature around the blade root, which was the bit I was concerned about.You can make a tap hammer out of aluminium or brass (depending on which works better) pictured below.

If the crazing is in the resin matrix, it can be sanded, as long as structural fibres are not damaged, and resin wiped to restore the finish. But I would only be paint that has crazed. You won't know until you sand it off. G ood quality epoxy resins must be used, none of that polyester rubbish.

 

[ATTACH=full]53268[/ATTACH]

Very cute hammer - I think large coin will do me for now.

 

 

[facthunter]

With metal props its nicks and cracks. In big turbo prop stuff vibration meters ( Low frequency ) pick up the vibrations and the engine is shut down. Various NDT processes may be available but the economics of it don't add up for small user low cost numbers.. You would have to establish a whole lot of reference parameters and check for variations from a "safe " condition, (whatever that is). Just off the cuff, a load /strain (deflection) comparison with a new one(.YOUR's when new) on each blade might tell you something. (Both directions) Low level load nowhere near limiting. Here you are recording a CHANGE of the blades resistance to a given load similar to what you observe with a glass or carbon fibre U/C leg. Nev

 

 

[M61A1]

Very cute hammer - I think large coin will do me for now.

A coin works well on flat (horizontal) surfaces. The idea is that you hold the coin about 1/2 inch or so off the surface and let it bounce, hard to do on a vertical surface. I prefer tap hammers.

 

 

[skippydiesel]

Had chance to check out the same prop, two years and quite a few tacho hours younger - exactly the same very fine crazing of the white front surface. Both of our aircraft have been "hangarede" all their (prop) lives. Starting to think this is a not a structural issue at all but a poor choice in finishing paint/gel coat/white epoxy??

 

 

[facthunter]

That could well be. The usual (as far as I know ) place for structural problems showing is near the hub apart from leading edge erosion IF its totally uniform all over it's probably a surface treatment issue. Nev

 

 

[skippydiesel]

That could well be. The usual (as far as I know ) place for structural problems showing is near the hub apart from leading edge erosion IF its totally uniform all over it's probably a surface treatment issue. Nev

Yes, the crazing is fairly uniform over the whole white surface (which includes the hub end) , nothing on the red tips or grey finished back.

 

At the weekend, just gone, I had the chance to discuss the matter with another pilot/maintainer of the same model & age of aircraft/prop - he informed me that he had had the same concerns, had decided to cut back the white material, using a very fine sandpaper, found the crazing did not extend to the substrate (inspected with magnifying glass) and had repainted with a more durable finish and rebalanced his prop - no further problem.

 

 

[facthunter]

Most clear cote crazes with time.. It can indicate stress, as we've discussed. . In your case I would suggest it's not doing that, but as to the safe life ??? Nev

 

 

[skippydiesel]

Most clear cote crazes with time.. It can indicate stress, as we've discussed. . In your case I would suggest it's not doing that, but as to the safe life ??? Nev

The manufacturer, Fiti, does not give any indication as to service life limit/expectancy. My prop is one of the older Fiti's around but has more hours (Hobbs) and less tip & leading edge damage than the ones I have seen.

 

 

[skippydiesel]

Great news! - Prop manufacturer confirms crazing on white painted area just surface (UV) weathering.

 

Not so great - Manufactures suggests a 6 year service life. Crazy! most of the Fiti props (other than the most recent imports) will be near double this (min is fast approaching X 3) - to the best of my knowledge no complaints from owners and no failures (not that anyone would want one).

 

 

[facthunter]

Well unfortunately, you will have to make a call. A blade coming off causes a hell of a lot of vibration. Usually the motor comes out fully or partially. I'm a wooden prop person for that reason. I did mention a yield /load assessment back in this thread you might revisit. I take no responsibility for how you use it, naturally. You don't have a new prop for comparison. You could only compare blades and you don't need to go crazy with a high load. It's a comparison with something not a limit test..Nev

 

 

[skippydiesel]

Have started checking out alternative props - so far have spoken to Bolly (very helpful) - turns out they don't have a prop similar to the Fiti (Fiti has blade, ark of 1700mm/66.93", width of 180mm compared with Bolly Optima 3, 110mm) so I might have to consider 3 blades or a slightly longer prop (comparing with the Fiti) -

 

• 3 blades, 66", slightly smaller ark, better ground clearance (less chance of prop damage), may have better acceleration (shorter TO role?), slower tip speed (quieter ?) increase cost & weight .
   
   
  
• 2 blades, 70", slightly larger ark, reduced ground clearance, greater tip speed (more noise/ less efficient), competitive cost, similar weight.
   
   
  
• Big plus for Bolly - no service life at this time, compared with 6 years for Fiti
   
   
  

 

 

Who else should I investigate ?

 

 

[skippydiesel]

Well unfortunately, you will have to make a call. A blade coming off causes a hell of a lot of vibration. Usually the motor comes out fully or partially. I'm a wooden prop person for that reason. I did mention a yield /load assessment back in this thread you might revisit. I take no responsibility for how you use it, naturally. You don't have a new prop for comparison. You could only compare blades and you don't need to go crazy with a high load. It's a comparison with something not a limit test..Nev

Agreed - the possibilities are too scary to dwell on.

 

Interesting though, I can compare my 16 year old prop to a very similar Fiti 2 blade supplied with a new just imported ATEC Fayeta (month old). The prop design has changed a little (tips are slightly more swept now), swept arc is the same, but in all other respects appears to be very similar. I could use a spring balance to apply a known force to the tips of each prop and compare the deflection ---???????

 

 

[facthunter]

Well, Why not? . You may well pick up a variation which if large enough might be an indication of something wrong. Nev