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Propeller/engine vibration

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JohnFrance

Joined: 17 Sep 2014
Posts: 77
Location: Grenoble France

Posted: Mon Jul 13, 2015 12:29 pm Post subject: Propeller/engine vibration

Hi All,

during a recent flight I experienced (propeller!) vibration at the start of the descent when I reduced power. This was after about two hours in cruise flight. The frequency was quite high and I could feel a tingling sensation in the feet in contact with the rudder pedals which makes me think the vibration is coming from the propeller/engine combination.

Upon landing I made a close inspection of the propeller and everything seemed normal except for some flies and bugs. After cleaning, during the next flight I experienced the same problem. The vibration is at its worst at 4800 rpm and reduces slightly at 5000 but it is still noticeable.

Before I start taking everything to pieces does anyone have an idea what could cause this sudden change?

Regards,

John

_________________
Europa mono Nr 192

dg.watts(at)talktalk.net
Guest

Posted: Mon Jul 13, 2015 1:24 pm Post subject: Propeller/engine vibration

John



I have been chasing this exact problem since May 20th and finally it looks like it may be cured, but without actually finding anything wrong.



I will explain.



At 4900 rpm and 25" manifold pressure it was smooth as you could want. At 4900 rpm and 24" map down to 18" map and really severe vibration.



Over the next few weeks I checked and test flew 

Carb balance

Replaced the carb needles and jets

Changed both the carbs to a couple of spares

Flew using only one then the other mag

Checked the whole exhaust system

Replaced the whole exhaust system for an old spare setup

Checked over the whole Airmaster propeller assembly

Checked cylinder pressures

Checked the engine mounting rubbers

Checked for anything touching or loose



All of these things made absolutely no difference to the manner or severity of the vibration.



Finally after advice from a Rotax expert service agent in the UK I removed the gearbox and took it to him. He took it apart but couldn't find anything wrong.

I got him to replace the bellville washers and the front bearing as it was all apart.

Upon reassembly it now runs smooth again, so probably or maybe it was the gearbox.

I am still very wary at the moment but I am hoping the problem is solved.



Dave Watts

G-BXDY Classic MonoWheel 

2150 hrs airframe 1150 hrs 912S Rotax engine



 	  Quote: 	
		   On 13 Jul 2015, at 21:29, JohnFrance <77alembert(at)gmail.com> wrote:

 

 

 

 Hi All,

 during a recent flight I experienced (propeller!) vibration at the start of the descent when I reduced power. This was after about two hours in cruise flight. The frequency was quite high and I could feel a tingling sensation in the feet in contact with the rudder pedals which makes me think the vibration is coming from the propeller/engine combination.

 Upon landing I made a close inspection of the propeller and everything seemed normal except for some flies and bugs. After cleaning, during the next flight I experienced the same problem. The vibration is at its worst at 4800 rpm and reduces slightly at 5000 but it is still noticeable.

 Before I start taking everything to pieces does anyone have an idea what could cause this sudden change?

 Regards,

 John

 

 --------

 Europa mono Nr 192

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=444702#444702

rlborger(at)mac.com
Guest

Posted: Mon Jul 13, 2015 3:06 pm Post subject: Propeller/engine vibration

John,



I agree with Dave Watts.  First place I’d look is the gearbox.  Have a good Rotax tech go through the various checks in the maintenance manual.  I bet you need new Bellville springs.  Hopefully, nothing further needs replacing.



Blue skies & tailwinds,

Bob Borger

Europa XS Tri, Rotax 914, Airmaster C/S Prop (75 hrs).

Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP

3705 Lynchburg Dr.

Corinth, TX  76208-5331

Cel: 817-992-1117

rlborger(at)mac.com



On Jul 13, 2015, at 3:29 PM, JohnFrance <77alembert(at)gmail.com> wrote:






Hi All,

during a recent flight I experienced (propeller!) vibration at the start of the descent when I reduced power. This was after about two hours in cruise flight. The frequency was quite high and I could feel a tingling sensation in the feet in contact with the rudder pedals which makes me think the vibration is coming from the propeller/engine combination.

Upon landing I made a close inspection of the propeller and everything seemed normal except for some flies and bugs. After cleaning, during the next flight I experienced the same problem. The vibration is at its worst at 4800 rpm and reduces slightly at 5000 but it is still noticeable.

Before I start taking everything to pieces does anyone have an idea what could cause this sudden change?

Regards,

John



--------

Europa mono Nr 192

JohnFrance

Joined: 17 Sep 2014
Posts: 77
Location: Grenoble France

Posted: Mon Jul 13, 2015 11:49 pm Post subject: Re: Propeller/engine vibration

Dear Dave and Bob,

thank you for your feedback regarding the vibration problem.

Dave, did your vibration appear "out of the blue" like mine did?



My engine is a Rotax 912 UL with only 334 hours on it and according to the serial number it is one of the few fitted with a 15 degree clutch and has a TBO of 1200 hours. If I get the gearbox shaft changed at the same time it would extend TBO to 1500 as all other work has been carried out.



Not the best time to be down, right at the height of the flying season!



Regards,

John



Do not archive

_________________
Europa mono Nr 192

dg.watts(at)talktalk.net
Guest

Posted: Tue Jul 14, 2015 12:54 am Post subject: Propeller/engine vibration

John,



Yes the vibration appeared "out of the blue" on the 20th May and it got no worse and no different from the moment it started until last week, when it seems that it may now be cured.



My Rotax agent thought it may be the splines on the gearbox prop shaft and although he showed me that they still appeared to be perfect he is now of the opinion that just reassembling them on different splines may have cured my problem. (This though makes me feel that there may be some slight undetectable wear in the splines that will rear it's ugly head again in the future!!!)



Dave Watts

G-BXDY



 	  Quote: 	
		   On 14 Jul 2015, at 08:49, JohnFrance <77alembert(at)gmail.com> wrote:

 

 

 

 Dear Dave and Bob,

 thank you for your feedback regarding the vibration problem.

 Dave, did your vibration appear "out of the blue" like mine did?

 

 My engine is a Rotax 912 UL with only 334 hours on it and according to the serial number it is one of the few fitted with a 15 degree clutch and has a TBO of 1200 hours. If I get the gearbox shaft changed at the same time it would extend TBO to 1500 as all other work has been carried out.

 

 Not the best time to be down, right at the height of the flying season!

 

 Regards,

 John

 

 

 

 Do not archive

 

 --------

 Europa mono Nr 192

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=444726#444726

budyerly(at)msn.com
Guest

Posted: Tue Jul 14, 2015 3:02 am Post subject: Propeller/engine vibration

John,

During a descent especially the prop to gearbox/engine combination causes a vibration when the prop windmilling force and drive force are nearly equal.  



If the slop in the gearbox due to a worn slipper clutch or just the gear lash becomes too much you get vibration and noise all the time.  On taxi even.



To test:  If all is smooth at cruise and takeoff when the prop is pulling, simply hold your speed constant and reduce power (throttle) until the vibration starts.  On the Airmaster AC200, go to MANUAL and move the prop to a course setting.  If it stops the vibration,  as the prop begins to pull, it is just normal gear box lash.  



In a descent, my Airmaster/914 will vibrate and I either pull more power off to force the windmilling prop to compression brake, or change the pitch to a course setting to allow the prop to pull.



Common areas to feel this:  High speed descent with small power reduction or in the pattern at 4000 RPM / 17 inches turning base leg.  Either ceases with power lever movement to get the prop to fully brake, or pull.



Regards,

Bud Yerly



Sent from my iPad



 	  Quote: 	
		   On Jul 13, 2015, at 7:06 PM, Robert Borger <rlborger(at)mac.com> wrote:

 

 

 

 John,

 

 I agree with Dave Watts.  First place Iâ€™d look is the gearbox.  Have a good Rotax tech go through the various checks in the maintenance manual.  I bet you need new Bellville springs.  Hopefully, nothing further needs replacing.

 

 Blue skies & tailwinds,

 Bob Borger

 Europa XS Tri, Rotax 914, Airmaster C/S Prop (75 hrs).

 Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP

 3705 Lynchburg Dr.

 Corinth, TX  76208-5331

 Cel: 817-992-1117

 rlborger(at)mac.com

 

 On Jul 13, 2015, at 3:29 PM, JohnFrance <77alembert(at)gmail.com> wrote:

 

 

 

 Hi All,

 during a recent flight I experienced (propeller!) vibration at the start of the descent when I reduced power. This was after about two hours in cruise flight. The frequency was quite high and I could feel a tingling sensation in the feet in contact with the rudder pedals which makes me think the vibration is coming from the propeller/engine combination.

 Upon landing I made a close inspection of the propeller and everything seemed normal except for some flies and bugs. After cleaning, during the next flight I experienced the same problem. The vibration is at its worst at 4800 rpm and reduces slightly at 5000 but it is still noticeable.

 Before I start taking everything to pieces does anyone have an idea what could cause this sudden change?

 Regards,

 John

 

 --------

 Europa mono Nr 192

ptag.dev(at)tiscali.co.uk
Guest

Posted: Tue Jul 14, 2015 3:17 am Post subject: Propeller/engine vibration

Hi! John /David /All ,

If your engine/gearbox set up includes a  propeller strike engine protection

drive clutch(Slipper Clutch) you may find that the peaks of the drive lobes

have eroded spots of the flame hardening on the mating surfaces in the

valleys  which is part of the gear pinion machining. (Entire gear and pinion

pair replacement usually needed about £1Kfor parts alone!) I believe that

the mating surface loading of this device when under light loading, with the

lobe peaks centred has too  small surface contact, is not getting adequate

high pressure lubrication from the approved engine oils.

For instance under heavy thrust loading in normal flight the lobe surface

has a much larger contact surface having moved up the drive slopes from out

of the valley's . On throttling back the lobes move back to the limited

surface area contact position giving the intense surface pressure loading

where the erosion is happening . ( This has all been reported to the LAA

with photographs with no response .) I had the services of the ROTAX service

engineer in dismantling and reassembling but chose to carefully dremel the

offending places of erosion before reassembly and torque setting. 

On any engine oil change I am now adding a full can of Holts STP high

contact pressure additive by carefully mixing it hot with the new engine oil

before pouring it into the oil tank . All sign of metal contaminant on the

magnetic plug have now stopped(Multiple checks and also at EVERY oil change)

and the vibration is now minimal .  The engine has completed in excess of

200 hours with this set up but the vibration (although very much minimised

and probably un-noticeable by anyone else!)  is slightly there in a very

light load condition (just above idle). No further contamination has been

detected on the magnetic plug.

Flight engine RPM landing control is the key to keeping away from the very

light loading position and an full idle setting to lose speed on approach

rather than a low power setting is in my opinion the answer. 

My first notice of vibration prompted me to check the magnetic plug and

conduct an investigation since it failed the visual check.

Best regards to all

Bob Harrison G-PTAG Rotax 914

 



--

dg.watts(at)talktalk.net
Guest

Posted: Tue Jul 14, 2015 4:43 am Post subject: Propeller/engine vibration

Hi Bob



The parts you seem to be describing are not the slipper clutch, although I

and everyone I have spoken to during the period of my vibration problem,

assumed that it was.



These parts are the dog drive system and are present on all the 912UL and

912ULS and 914 engines. They are held in contact by the Bellville washers

and incorporate the 15 or 30 degrees of movement that we have to regularly

check for in the Friction Torque Test.



On engines with a slipper clutch the output part of the dog drive system is

much larger and incorporates a clutch drive system within it, a bit like a

motorcycle clutch. This output dog drive is splined on to the Propeller

Drive Shaft.



When I had my gearbox at the Rotax Service Agent I asked him to show me how

it all worked and with the parts on the bench it all became very clear.



Dave Watts

G-BXDY



--

ptag.dev(at)tiscali.co.uk
Guest

Posted: Tue Jul 14, 2015 5:44 am Post subject: Propeller/engine vibration

Hi! David,

You may be right, except the torque loading to which you refer as well as

loading the clutch also contains the lobes of the dogs within their working

range and it is this resultant surface contact  pressure which in my opinion

is too high for the PEAKS of the lobes giving a concentrated surface point

load when in the valley much reduced when up the driving slope.

Really antiquated principles .....my 1936 Vellocette OHC has a similar drive

between engine sprocket and gear box drive sprocket, protecting shock of the

cylinder power stroke through the primary drive chain.

For the many, the understanding of what I wrote was more intended as a guide

where to look for surface erosion and a remedy. 

Without my dogged refusal to put my hand in my pocket the agent was content

to order a pair set of gears and Rotax would be £1000 in pocket as a result

!

Regards

Bob H  G-PTAG. 



--

paul.the.aviator(at)gmail
Guest

Posted: Tue Jul 14, 2015 7:33 am Post subject: Propeller/engine vibration

Hi John,

I had something similar happen. Out of the blue I started getting vibrations when I throttled back and it turned out to be the carbs being out of balance.Â  I don't know why it suddenly turned up but I balanced them and life was good.

Paul



  [quote][b]

JohnFrance

Joined: 17 Sep 2014
Posts: 77
Location: Grenoble France

Posted: Sun Jul 19, 2015 2:00 am Post subject: Re: Propeller/engine vibration

Here is an update on my vibration problem. I checked balance of the carburettors they were perfect, checked all engine mounts, carburettor mounts  electrical connections on ignition circuit  including ht leads and air box and everything looks fine. I cleaned the propeller (again) very thoroughly and went for a flight. The vibration has disappeared! Just the normal area where it is not so smooth at 4800 rpm. The vibration through the rudder pedals has also disappeared.

I must admit I am confused as I have not identified a cause. Regards John

_________________
Europa mono Nr 192

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