Sonex incident -Huebbe

[Sonex1517]

Good catch - I missed that. A very interesting part of the report...

[radfordc]

Strange that the Camshaft was also broken??

The clearance between the camshaft and the connecting rod big end is minimal. When the crank broke the connecting rod may have hit the cam.

[chris]

Materials Lab Factual Report

[kevin814]

What a senseless loss of life. :( I had no idea the crank was made from plain carbon steel.

[gammaxy]

I had no idea the crank was made from plain carbon steel.

That part was really curious to me too. The report mentions that it was a Great Plains engine, but I couldn't find a crankshaft that resembles it on their webstore. Turns out, they briefly had one listed on their website with a picture that strongly resembles the one in the report in 2010:

82mm Forged Crankshaft. Our new "Square Wave" counterweighted crankshaft is specifically made for aircraft use. German forged 1045 steel, 100% machined in the USA.

http://web.archive.org/web/201011221057 ... kshft.html

In previous years and afterwards they mention using E4340 and the photograph doesn't have the obviously welded-on counterweights.

I'm curious if "forged 1045 steel" would show up in their test as plain carbon steel or if this crankshaft simply didn't have the metallurgical properties that were claimed.

As builders, we really put a lot of faith in our suppliers.

Like everyone else, I have been heartbroken since I first learned of this accident. I only met Tom briefly during my first trip to Crossville. He let me pose for a picture with my son in front of his Sonex--only his hand and shadow appear in the picture. Seeing his airplane is what completely sold me on the idea of building one. The beautiful polish with the fun images and stripe really made what had previously seemed to be an ugly airplane into a beautiful, fun one. I watched all his videos and truly miss hearing his narration style while talking about his adventures.

[vigilant104]

Right, that crank doesn't match anything in the most recent GPAS catalog. I'm not doubting that it was sold by Great Plains, but it doesn't look like their normal product.

Do the manufacturer's marking shown on the NTSB Materials Lab photo give us an indication as to the original manufacturer of that crank (first photo, the marking is between the connecting rod journals)?

[radfordc]

http://www.steelforge.com/aisi-1045/?ex ... oCEiDw_wcB

C1045 is a medium carbon, medium tensile steel supplied as forged or normalized. This steel shows good strength, toughness and wear resistance. C1045 will through harden to 2.5” (63mm) with a tensile strength of 66 – 120 Ksi (620 – 850 MPa).

C1045 is a versatile medium carbon engineering steel that can be through hardened to about 2.5” (63mm), as well as being flame or induction hardened to Rc58. The steel can be readily welded and machined providing correct procedures are followed.

APPLICATIONS OF AISI 1045
This grade of steel is used for axles, bolts, forged connecting rods, crankshafts, torsion bars, light gears, guide rods etc.

[gammaxy]

Do the manufacturer's marking shown on the NTSB Materials Lab photo give us an indication as to the original manufacturer of that crank (first photo, the marking is between the connecting rod journals)?

The VW logo along with the text on the GPAS website lead me to believe it is a stock crankshaft manufactured in Germany, but I haven't found anything to decipher the "53 N 5". At some point a US company welded on counterweights and modified it into a stroker crankshaft. I'm not sure how the modification is performed, but I imagine they weld filler material to one side of the journal and then grind it back round.

DMS (De Mello Machine Shop) and DPR Machine shop perform this type of work, here's an example picture from DMS's website (far right crankshaft):