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Question for Lu Zukerman


Jesse James
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Lu and or anyone else that might be able to help. I still have some problem deciding if the cracks on the star flex on the Astar is a paint crack or a real crack. I do flex the head by pushing the blade up and down to see if a crack opens, but about a year ago we had a crack that just looked like an ordinary paint crack. The mechanics had to file it to find it. Just wondering is there a dye penetrant that a pilot could buy to use?  Thanks Jesse
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To: Jesse James

 

See if your mechanic can locate a product called "Stress Coat".  It is applied like paint and when dry and the head is placed under stress the Stress Coat will form a crack along the line of highest stress.  If it is a crack in the paint the Stress Coat should not form a crack.  (At least that is what they say on the container).

 

:unclesam:  :oops: This is Pierre.  He told his girl friend that he was flying low over a nudist colony.

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Don't fly it.  Just a ground run and pull some pitch if a manual manipulation doesn't reveal anything.

 

The problem with doing the above test is that if there is a crack it will open up but you will not be able to detect it.  When the rotor runs down the crack will close up.  If you used Stress Coat the evidence will be there when the rotor runs down.

 

:unclesam: This is Pierre.  Actually it is not Pierre as we had our first snow fall today and Pierre took off for Florida for the winter season.

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To: C J Eliassen

 

I was adding to your post.  SHEESH!

 

Make yourself clear the nest time you add to my posts.

 

However just pulling pitch might not be enough especially if the crack developed as a result of maneuvering loads.  The blades do some crazy things while maneuvering that the don't do when in a hover.

 

:unclesam:  :down: This is Pierre.  He needs an attitude adjustment.  He sent out over a hundred resumes witout a single reply.

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  • 2 months later...
A couple of items to look for are if you have a suspect crack is that when fiberglass rubs against each other as it would in a crack, you will see evidence of a black residue around the edges of the crack. The fiberglass is rubbing and creating heat and the black is smoke residue  This is usually in a more advanced crack.  Another method that works good on post flights is to use a thick liquid (OK spit) on the suspect crack and with a magnifying glass observe the area while someone moves the blade up and down.  Look at the light reflecting off of the surface of the liquid with the magnifying glass.  If there is a crack the liquid will move into the crack and when the blade is flexed up and down the surface of the liquid will pooch up and down as the liquid is pulled in and purged out of the crack.  Sounds gross but has worked every time for me up here in Alaska.  Also most cracks but not all will show up in a chevron angle on either the leading edge or trailing edge of the star.  Very few of the vertical cracks that you see on a lot of the blades have ever panned out to be a true discrepancy.  Hope his helps.  Shaboo
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  • 1 month later...

Ron, you hit the nail on the head. Deep down I always knew I could trust you and count on your verdict.

Many times, pilots would think they "found" cracks, but Shaboo's method was always the final and most accurate test method.

Like you said, most vertical or near vertical cracks are in the paint only. it is the horizontal and diagonal cracks that you have to inspect more closely. Usually, an actual crack in the starflex will manifest itself as a zig-zag pattern or curved and/or chevron pattern.

Correct me if I'm wrong, but I seem to remember more cracks on the leading edge compared to the trailing edge of the starflex.

An area I didn't know to inspect closely until much later is behind the spherical thrust bearings (or is it the frequency adapters - I always mix them up. I'm talking about the area closer to the mast) where significant cracks can develop because they are much harder to detect.

Being a pilot, I always forget the limits. Shaboo, can you elaborate on what the allowable limits are for a field repair, how many field repairs can be done per starflex, and when you have to turn the starflex into a door-stop?

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  • 2 months later...

Hi;

 

Have just joined this forum, sounds like fun.  I have a comment on the star cracking, you are all right on on about determining the cracks, there are dimensions in MM on sizes and limits, hard to memorize, only NO cracks allowed on bottom of star.

 

As a pilot I question why so many stars are cracking, having been flying Astars since 85 have only had ond crack and seen only 2 more.  Had a wise engineer tell me once that the only time he saw a cracked star was from the pilots holding the cyclic too far forward while on the ground.  I know we had one at a camp where the blades were untied and a bell 205 landed beside her.  The ecl blade tie down kit enables you to tie the blades down almost as quick as a 206, this makes it a whole lot safer to leave aircraft if windy or other helicopters landing nearby.

 

Careful not to tie the blades down too tight as is hard on the blades themselves(take slack out of rope and pull additional 10cm(4-5inches).  

 

Good luck.

 

sc

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At the overhaul level I've scrapped more than I've had to repair. We have to file down all star arms during a repair here. And I can see why no one in the field wants to try it. It's alot of filing. The ones I've scrapped are likely left too long, or not seen soon enough to save.

If you are in doubt as to whether it's a crack in the star or just the paint. don't fool around. Look at it. Find out for sure. I've yet to hear of a star arm cracking to the point of failure,( except during hard landings/ground resonance), but at the least finding a fault early can save your company $$$

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We had to change a starflex in our 355N with 1500 hours on it and we think it was due to the proximity of another helicopter taking off many times while we are parked. We see the the rotor bouncing up and down and think that would have contributed to fatigue.

Buen vuelo

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