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Gearbox dog wear (pockets) and Warpdrive props?

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peterz(at)zutrasoft.com
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Posted: Tue May 17, 2022 12:10 pm Post subject: Gearbox dog wear (pockets) and Warpdrive props?

So, my resonance issue at cruise (5krpm) has been narrowed down to the gearbox dogs, and a worn spot at either end of the dog as felt during a recent friction test. Thx to Chris on this list for the heads up!  I verified the torsional resonance issue using the very well engineered SmartAvionics PB40 dynamic balancer with multiple axis measurement.

Rotax is suggesting that this pocket-wear can be induced from low friction torque (which I have since my box rebuild by the certified rotax depot :-/  not impressed) and/or the warp drive having too high a rotating mass.  The latter brings up the obvious question: since the warp-drive has been the default for the europa prior to the more recent blade choices, how many others in the fleet (or any other fleet for that matter), have had similar gearbox issues with the short 65" three blade WD's?

It's looking like I may now have to dish out $5000 in gearbox parts to replace the dogs (gear-set + clutch I'm told).  What a waste of $$ - was planning on an autopilot and airmaster...... ain't gonna happen now.

Cheers and thx for any data,

Pete

C-GNPZ

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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Tue May 17, 2022 12:59 pm Post subject: Re: Gearbox dog wear (pockets) and Warpdrive props?

Pete, Sorry to hear about the possible expense (I know the feeling). You can thank Phil Lockwood for that hint. He told me it is a very common issue if the gearbox is old, and not properly rebuilt. Low friction torque? Dunno. I was always told that if your gearbox has low friction you can easily tell (very noisy).

Chris

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peterz(at)zutrasoft.com
Guest

Posted: Tue May 17, 2022 1:15 pm Post subject: Gearbox dog wear (pockets) and Warpdrive props?

Hi Chris,

My FT is at the lower limit, but isn't noisy fwiw.

Such is life when buying a used aircraft - one never knows the true service history - always full of unanticipated surprises    For a personality type such as mine, it's killer.  More motivation to get my 20+year old kit bits finally into formation with new bits (and cross my fingers lol).... it's gonna happen. really. 



Thanks again!

Pete

PS - WD couldn't tell me their moment of inertia, but I just tripped on a rotax service bulletin which lays out a simple hanging string test to determine.... guess what I'll be doing tomorrow morning 



On Tue, May 17, 2022 at 5:06 PM n7188u <chmgarb(at)gmail.com (chmgarb(at)gmail.com)> wrote:



 	  Quote: 	
		  --> Europa-List message posted by: "n7188u" <chmgarb(at)gmail.com (chmgarb(at)gmail.com)>

 

 Pete, Sorry to hear about the possible expense (I know the feeling). You can thank Phil Lockwood for that hint. He told me it is a very common issue if the gearbox is old, and not properly rebuilt. Low friction torque? Dunno. I was always told that if your gearbox has low friction you can easily tell (very noisy).

 Chris

 

 

 

 

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Area-51

Joined: 03 May 2021
Posts: 391

Posted: Tue May 17, 2022 6:53 pm Post subject: Re: Gearbox dog wear (pockets) and Warpdrive props?

The warpdrive blades work great and are the heaviest of all composites; (they are did composite, heavy) Bolly blades on the other hand are one of the lightest and share the same shaft profile; so interchangeable and your easiest solution.



If you want to read more there's a great write up on stolspeed website

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Jon Smith

Joined: 12 Dec 2021
Posts: 2

Posted: Wed May 18, 2022 11:12 pm Post subject: Re: Gearbox dog wear (pockets) and Warpdrive props?

Hi Pete,   Don’t know if this is of any relevance to your issues but I too had some vibration issues a few years back (912ULS/ Ground Adjustable Warp Drive).    My symptoms were a horrid, high frequency, grinding vibration after start for a few seconds which tended to crack the rear exhaust down pipes - I later found I could usually avoid the vibration by getting the starter motor up to speed before turning the ignition on.   This was not the dreaded kick back - I’ve never had that.   Also the same horrid vibration could occur inflight, specifically when throttling back for descent from a normal fast cruise, ie when the prop was changing from loaded to unloaded.   Again I found a way to avoid it by slowing the airspeed right down (by a small climb), then throttling back to descend, increasing airspeed as required.   I (unwisely) lived with it for a couple of years with no issues, avoiding the vibration as described above.



Eventually I got it sorted.   Kevin Dilks (UK Rotax genius and top chap) immediately diagnosed it (over the phone) to be worn prop shaft splines, he’d come across it many times.   The main cause being low idling RPM causing the wear.    My engine was second hand and had come off a weight shift microlight - he said this issue can be very common on those as they often use foot operated throttles which makes the RPM control very imprecise and they can often allow them to idle very slowly on the ground.



So I took the box off and took it to Kevin who replaced the prop shaft - and while he had it fitted a slipper clutch which mine didn’t have then.   He said that not having a slipper clutch can accentuate the development of the prop shaft spline wear.    The labour cost was minimal - I think he had the job done within half an hour while I watched him.    The parts were eye-wateringly expensive though…!



The good news is that it has completely cured the problem and touch wood it has been completely perfect ever since - Thanks Kevin!  The difference, even in normal running was unbelievable - I would never have believed that an engine could run so smooth.    Whilst very expensive (£1,700 GBP for prop shaft & slipper clutch)  - and that was with me minimising the cost by removing and refitting the gearbox myself and taking it to him -  it was the best single financial investment I’ve made on the aircraft since I bought it and the moral of the story is I should have done it straight away rather than keep putting it off…!    

Cheers!

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