Carbon props

[Guest raccoon]

DETAILS OF INCIDENT/ACCIDENT/DEFECT

 

On the 9th of November 2009, a new Bolly Duralite propeller and hub was fitted (as per manufacturers’ recommendations & specifications) to the my Jabiru J170, this was followed by the recommended run up, flight times as well as bolt tension checks. All post prop instillation checks and flight times had been performed, incident free. After the initial flight period and checks, I decided to go on a 2.5hr cross country to give the prop a decent run.

 

Approximately 30 minutes into the flight whilst cruising at 3500’, a loud bang followed by a severe vibration, which lasted approximately a second or so, was experienced. My hand was already on the throttle which I proceeded to pull shut almost immediately. I am certain the engine had already stopped by this stage.

 

As luck would have it there was an unused airstrip about 1 mile away, so after re-assuring my 12yr old passenger that everything was ok I showed him where we planned to land. An uneventful circuit and landing was carried out.

 

Upon removal of the top cowling it became pretty obvious why the engine had stopped so quickly. The carby had been knocked off the back of the engine along with 4-5 plug leads (lucky that). The muffler had also been spat off the header pipes and several scat hoses torn off, the lower right engine mount rubber had also been shredded. One entire prop blade, apart from the aluminium retaining collar and a small amount of composite material was all that remained of one side of the prop. Apart from some scuffing on the cowls where the spinner had made contact, no other obvious damage had occurred.

 

The next 3-4 hrs was spent putting the engine back together and checking engine mounts and associated bolts. A thorough checking of the airframe revealed a loose front wing mount bush on the left wing, but everything else seemed okay. The remaining propeller blade and hub was removed and the engine tested to see if it was serviceable. The engine seemed okay so some calls were made to arrange for my old prop to be delivered so that the aircraft could be flown home for more inspections.

 

Once the original prop had been fitted the engine was run up to full power with everything looking and sounding quite normal. My passenger and baggage were loaded into the car for the trip home and I proceeded to fly home. The flight home was uneventful and with the aircraft back in its hangar, an inspection by RAAus Technical Manager, Stephen Bell was carried out. No major problems were found so following the replacement of the left front wing bush and the prop hub, the aircraft was returned to service.

 

The reason i am forwarding this article is that an incident report was lodged with CASA and RAAuS but there has been no mention of it in the RAAus magazine. Since my incident i discovered that another unfortunate Jabiru pilot suffered the same fate but he wrote his aircraft off during the outlanding. The company has apparently been told not to sell these props to 4cyl jabbi owners, so if there is anyone out there considering using a carbon prop, make sure your life insurance is up to date.

 

Regards

 

Tom O'Donnell

 

 

[Guest check-in]

Thanks for the heads-up. I have been running one of Rob Patroney's very nicely finished props on my Jab 2200 powered Sonex. About 12 hours so far. It seems very smooth and delivers better performance than the earlier wood prop, but I will certainly be on the lookout for anything unusual.

 

Presumably all the damage resulted from the Bolly throwing a blade and not as a result of the engine doing a dummy spit 1st?

 

 

[Captain]

DETAILS OF INCIDENT/ACCIDENT/DEFECTso if there is anyone out there considering using a carbon prop, make sure your life insurance is up to date.

 

Regards

 

Tom O'Donnell

Tom,

 

I think you are going too far damning all carbon fibre props on 2200's. Because you report a failure with one brand doesn't mean that the others are faulty.

 

Regards Geoff

 

 

[Guest Maj Millard]

I recently sent in a defect report in respect to corrosion found during normal inspection on two carbon props. One was a Bolly Alum hub which had severe exfoliation corrosion. The hub was returned, and a new one was given to the owner gratus.

 

Corrosion was also found on the blade alum base-rings on an Airplast 3 blade prop. If left unattended this would have caused an unsafe condition down the road. Have not seen either report in the Magazine yet...................................................................................Maj..

 

 

[Captain]

I recently sent in a defect report in respect to corrosion found during normal inspection on two carbon props. One was a Bolly Alum hub which had severe exfoliation corrosion. The hub was returned, and a new one was given to the owner gratus.Corrosion was also found on the blade alum base-rings on an Airplast 3 blade prop. If left unattended this would have caused an unsafe condition down the road. Have not seen either report in the Magazine yet...................................................................................Maj..

Where was that corrosion Maj? Between the hub and the prop flange of between the hub and the blades?

 

 

[Guest Maj Millard]

On the Bolly (2 blade), the whole hub was affected. It may have been an early model. I was offered the plane for a fly ( I had ferried it some years ago) but refused the offer due to the condition of the hub as I considered it to be quite unsafe. The owner sent it in to the factory the following week. The corrosion was well embeded and completly throughout the hub.

 

On the Airplast (3 blade), there is about 6-7 ml of expossed alum at the base of the blade where it enterers the hub. There was a lot of large corrosion pitts starting. This particular Magni gyro had spent sometime flying up in the Kimberly area. I believe the red dust has a lot of iron oxide in it, and may have kicked off the corrosion. In another six months (or less) the blades would have required replacement IMOP.....................................................Maj..

 

 

[Captain]

Thanks Maj.

 

 

[Guest Maj Millard]

Now that I give it some further thought, you are bolting a piece of alloy to a piece of steel (engine prop boss), so galvanic corrosion kicked off by two disimiliar metals is quite possible, especially where moisture is present.

 

The best way to stop this effect is to separate or isolate each from the other. A light film of grease or other suitable medium on the prop boss might do the trick..................Maj..

 

 

[Captain]

Now that I give it some further thought, you are bolting a piece of alloy to a piece of steel (engine prop boss), so galvanic corrosion kicked off by two disimiliar metals is quite possible, especially where moisture is present.The best way to stop this effect is to separate or isolate each from the other. A light film of grease or other suitable medium on the prop boss might do the trick..................Maj..

Galvanic action was my initial thought too Maj, for the reasons that you have stated, except on mine there is also a SS backing plate and a chrome covered aluminium spinner to add to the galvanic soup.

 

I doubt that your grease fix would be enough as the steel bolts that connect it all together are contacting the steel prop flange and the alloy boss.

 

Attached FYI is a pic of my Sensenich boss, looks lovely now but should not be too hard to keep an eye on through the spinner and when checking bolt torques.

 

Regards Geoff

 

[ATTACH]10170.vB[/ATTACH] [ATTACH]10171.vB[/ATTACH]

 

 

 

 

[Guest ozzie]

Duralac works quite well on alloys.

 

 

[Guest Maj Millard]

Captain, have not seen one of those in the flesh, but from your photos it appears to be a well engineered item, and from the finish may have been alodined ?...which will help guard against corrosion.

 

Ozzie, Yes works very well for isolating two metals..........................Maj..