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(Off topic) Towing or being towed

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Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Sun Sep 06, 2009 11:24 pm Post subject: (Off topic) Towing or being towed

A French friend of mine was towing a glider when he got problem and had to land. Here is a photo where is is pulled to the hangar by a tractor. Why? Look carefully at the propeller. One blade is about ten centimeters shorter!



Being himself a glider pilot, Yves had no problem with a dead-stick landing; they were climbing right above the airfield. But ... how can a propeller just loose ten centimeters? I don't understand how it can happen. Split in two, yes. A blade coming entirely looose, yes. But ... loose one end?



Cheers,

Michel Verheughe

Norway

Kitfox 3 - Jabiru 2200 with 300 hours and still going strong.



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akflyer

Joined: 07 May 2007
Posts: 574
Location: Soldotna AK

Posted: Mon Sep 07, 2009 6:31 am Post subject: Re: (Off topic) Towing or being towed

two words. Manufacturing defect.

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Leonard Perry aka SNAKE
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occom

Joined: 26 Aug 2006
Posts: 404

Posted: Tue Sep 08, 2009 3:27 am Post subject: (Off topic) Towing or being towed

I noticed that it appears to have separated exactly at the paint line, could 

it have been scored at that point? I also notice the pilot is still wearing 

his headset, which I find amusing.



---

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mikeperkins

Joined: 22 May 2007
Posts: 123

Posted: Tue Sep 08, 2009 6:16 am Post subject: (Off topic) Towing or being towed

Undressed blade nicks in metal props cause stress risers that can create a crack which can progress across the blade like the one shown in the photo. Most of us with Kitfoxes use wood or composite blades that don't crack laterally like metal props. Gouges in metal props must be dressed out before being flown again but often aren't. A gouge that occurs after preflight may not be noticed until it's too late. Certain locations along the length of a propeller are more susceptible to cracks due to standing waves induced by engine vibration. Tachometers on some aircraft have a red arc (below the red-line) indicating where the engine is not to be operated for extended periods due to harmonic or resonant vibration that may lead to structural failure of the airframe or propeller (refer to "Aircraft Systems" by David A. Lombardo, p. 103).   

- Mike Perkins  

      [quote][b]

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Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Tue Sep 08, 2009 10:24 am Post subject: (Off topic) Towing or being towed

 	  Quote: 	
		   From: Dave G [occom(at)ns.sympatico.ca]

 I noticed that it appears to have separated exactly at the paint line, could 

 it have been scored at that point?


	


Yes, isn't it strange? Here is a close-up photo that shows better how it follows the paint line.



Cheers,

Michel



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akflyer

Joined: 07 May 2007
Posts: 574
Location: Soldotna AK

Posted: Tue Sep 08, 2009 11:26 am Post subject: Re: (Off topic) Towing or being towed

Looks like the leading edge is beat up pretty good, and there is some discoloration on the back side of the prop that suggests that there was a discontinuity open to the surface for awhile.  There are also some pores on the front side of the blade that look as if it could be porosity.  Kind of hard to tell from the pic, but I would say there are some manufacturing issues, as well as some bad dings on the leading edge that should have been dressed up with a file long before the tip departed.  Aluminum is funny especially if used in sand or rain.  The smallest nick in the blade will open right up if you are hitting lots of rain or the spray from floats.  Water, once allowed to get into the open grain of the metal will eat it up QUICK.  I know guys that keep a nice flat pretty smooth rock in their pocket just for dressing up blade nicks on the props of their float planes.  The old times swear that if you don't keep it smooth, the water will eat they prop in VERY short order.

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thesupe(at)hotmail.com
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Posted: Tue Sep 08, 2009 1:58 pm Post subject: (Off topic) Towing or being towed

looks like the leading edge of the prop was kind of dinged up.  Paint is wore off also.  Just my uneducated guess C but I think a crack started from a nick on the leading edge.  Take care C Jim Chuk  Avids C Kitfox  Mn.

[quote] Date: Tue C 8 Sep 2009 20:21:04 +0200

 From: michel(at)online.no

 To: kitfox-list(at)matronics.com

 Subject: Re: (Off topic) Towing or being towed

 > From: Dave G [occom(at)ns.sympatico.ca]

 > I noticed that it appears to have separated exactly at the paint line C could 

 > it have been scored at that point?

 Yes C isn't it strange? Here is a close-up photo that shows better how it follows the paint line.

 Cheers C

 Michel

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Get back to school stuff for them and cashback for you. Try Bing now.   	  Quote: 	
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Ken Potter

Joined: 18 Aug 2007
Posts: 85
Location: Lanark, Ontario

Posted: Sat Sep 12, 2009 3:52 am Post subject: Re: (Off topic) Towing or being towed

Michael,  good pic of the failure area.  In my work as a TSB Canada investigator I see a fair number of component failures.  I agree that the blade had a crack from its trailing edge, as evidenced by the dark area which is actually oxidation.   The bright area is the final fracture and judging by the leading edge it was probably a nick of some sort which propagated into a crack and then overstress failure fairly rapidly.  The trailing edge crack should have been noticeable however during a pre-flight inspection.

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Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Sun Sep 13, 2009 10:45 am Post subject: (Off topic) Towing or being towed

 	  Quote: 	
		   From: Ken Potter [kjpotter(at)sympatico.ca]

 The trailing edge crack should have been noticeable however during a

 pre-flight inspection.


	


Yes, I guess it should, Ken. Of course, this happened to a French friend who lives in south of France, where I live in Norway. I wasn't there nor have I seen the plane in real life. My friend flies gliders and, at the occasion, tow them.

I have often wondered if club's planes get the same attention as private ones. I know my Kitfox by heart and I think I would quickly discover a crack but ... if it was the club's plane, I am not so sure.



Cheers,

Michel Verheughe

Norway

Kitfox 3 - Jabiru 2200



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