Remos oil hoses diameter - Rotax requires 11 mm

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zaitcev
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Remos oil hoses diameter - Rotax requires 11 mm

Postby zaitcev » Thu Jan 18, 2018 2:28 pm

NTSB posted a factual report about the fatal crash of N28GX. The airplane was maintained with no expense spared, which was unusual for a rental to tell you the truth. However, the investigation found a sheared drive pin. Apparently, Rotax claims that hoses were too small and that causes pulsating oil flow, fatugue, and failure of the pin.

The engine crankcase, camshaft, oil pump shaft, and oil pump drive pin were submitted to the National Transportation Safety Board (NTSB) Materials Laboratory for additional examination. The examination indicated that the camshaft had a yoke machined into the end opposite the drive gear that drove the oil pump shaft. As designed, a drive pin passed through the body of the oil pump shaft, which engaged the camshaft yoke. The camshaft yoke did not exhibit any abnormal wear or deformation. The bearing bore in the crankcase that corresponded with the oil pump drive yoke exhibited scoring on the inner surface about mid-depth. The depth of the scoring was about 0.024 inch. The scoring was consistent with the profile of the oil pump shaft drive pin. The drive pin fractured inboard of the outer diameter of the oil pump shaft on both sides, leaving a portion of the drive pin within each side of the shaft. Examination of the fracture surfaces revealed crack arrest marks consistent with a fatigue fracture. Hardness measurements made across the diameter of the drive pin were consistent with the manufacturer's design specification. Although the drive pin had fractured, it remained engaged to the camshaft yoke and continued to rotate the oil pump shaft. Additionally, the postaccident engine disassembly revealed ample lubrication throughout the engine, and there was no evidence of oil starvation.

According to the engine manufacturer, a fractured oil shaft drive pin is indicative of an oil system with restrictive hoses and fittings that can result in a pulsating oil supply to the oil pump. The pulsating loading of the drive pin can result in a fractured drive pin. The Rotax 912 installation manual stipulates that oil hoses have an inside diameter of 11 millimeters. The oil hoses recovered with the wreckage had inside diameters that measured 9 millimeters. Additionally, the Rotax 912 installation manual stipulates full-flow angled fittings for oil hose connections. Examination of the oil cooler revealed a right-angle fitting that did not meet the engine manufacturer's full-flow fitting specification.


I know Michael Sz. would never install random hoses from AutoZone. They probably came from Remos' warehouse in Arkansas. I never heard about the hose size restriction.

Note that you can fly with a broken pin for hundreds of hours and not know that anything was wrong unless a piece of pin breaks off and jams something or starts grinding the housing.

Warmi
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Re: Remos oil hoses diameter - Rotax requires 11 mm

Postby Warmi » Thu Jan 18, 2018 3:16 pm

So was there any relation between the broken pin and the actual crash? If I remember correctly the fatal crash was basically stall/spin in the pattern due to unknown reasons..
Flying Sting S4 ( N184WA ) out of Illinois

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Jim Hardin
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Re: Remos oil hoses diameter - Rotax requires 11 mm

Postby Jim Hardin » Thu Jan 18, 2018 4:37 pm

Sounds as though it is possible that the engine failed and a stall/spin followed. The witnesses were inconsistent in their engine reporting.

Full Report: https://www.ntsb.gov/_layouts/ntsb.aviation/brief2.aspx?ev_id=20160311X11659&ntsbno=CEN16FA122&akey=1

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WDD
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Re: Remos oil hoses diameter - Rotax requires 11 mm

Postby WDD » Thu Jan 25, 2018 3:06 pm

Additionally, the postaccident engine disassembly revealed ample lubrication throughout the engine, and there was no evidence of oil starvation.


Doesn't sound like the broken pin caused oil starvation and engine failure.

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Re: Remos oil hoses diameter - Rotax requires 11 mm

Postby flightwriter » Sat Jan 27, 2018 12:32 pm

Per various communications related to the crash, it appears that Remos' position is that its Rotax 912 installation has been tested and found to be "well within" specified limits for maximum crankcase pressure and minimum suction pressure, and no changes are planned.

Seems to me that could very well be true, but that "pulsing" as described by NTSB could still exist within those limits and be detrimental to the engine. Still, it doesn't appear to have been causal in this accident.


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