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912 with low RPM--- new vibration problem

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lgold(at)quantum-associat
Guest

Posted: Sun Mar 09, 2008 2:23 pm Post subject: 912 with low RPM--- new vibration problem

Thank you for your advice Roger, 

I followed it and lowered the pitch on my 912ULS.... but now I have a big

problem.



Although I very carefully changed the pitch of the 3-blade warp drive prop

about 3/4ths of a degree, and the maximum RPM is now within the range you

suggested, the plane now vibrated a lot more than it did at all but idle

setting. Yes I double checked the uniformity of prop pitch and made certain

that the blades were seating right.. 3 separate times. So I think the

problem is not be related to resetting the prop. I also re-sync'd the carbs,

changed the plugs, and cleaned the gas filters; which did nothing to reduce

this vibration.  There is no difference in vibration using either mag.



FYI, the engine was sitting around for over 2-years, sealed in its original

box, before I bought it and added oil to the cylinders. It ran fine for

20-hours before it the vibrating started yesterday. The engine oil analysis

that was made when the oil was changed at 10-hours, as recommended by Rotax,

showed no signs of excess wear. 



If you or anyone else has any ideas about what could be wrong, I sure would

like the information.

Thanks,

Les   



[quote] --

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun Mar 09, 2008 4:31 pm Post subject: Re: 912 with low RPM--- new vibration problem

Les,



Take a really good look at your engine mounts. Don't be gentle. Try and move them with the engine and see if they show any signs of separation or cracking.

Has the rpm ever been over 5800?

The other big item is you should really get a static and dynamic balance. Who's prop do you have and what size? This is where I would put my money right now. This could easily be the problem.  I might be willing to bet money on this one.



A static and dynamic balance's should be done by everyone. More people have this problem and don't even know it. If it is out of balance a little you may not feel it in the stick or frame. If it's out quite a bit then you really feel it. This issue is hard on gearboxes engine mounts and all the related components and this is the hardest thing to get people to do. If they can't see it it must be ok or not broken.    Wrong!

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

lgold(at)quantum-associat
Guest

Posted: Sun Mar 09, 2008 11:08 pm Post subject: 912 with low RPM--- new vibration problem

Roger,



The engine seems to be mounted properly, but I will take your advice and

recheck the mounts. (but remember, the plane only has 20 hours TT and there

was no vibration before changing the pitch).



No, I have never exceeded 5800 RPM. The highest static RPM I got yesterday

was about 5600.



Its not easy to static and dynamic balance a 3-blade Warpdrive and I

question the need to do it for a new plane that was balanced just fine

2-days ago. 



I spoke to a Rotax 912/914 mechanic today. He says he has seen Warpdrive

props that will vibrate once the pitch goes below some level. Tomorrow I am

going to set the pitch back up to where it was originally (to where I only

get 5100 static RPM) and see if the vibration goes away. If it does, I will

be having a long talk with Warpdrive.



Les   



[quote] --

jetboy

Joined: 22 Jul 2006
Posts: 233

Posted: Sun Mar 09, 2008 11:48 pm Post subject: Re: 912 with low RPM--- new vibration problem

You do need to be sure static and dynamic and pitch balance is satisfactory.



with warpdrives the piitch balance can be checked by marking each blade tip with a piece of tape, different colours  or number of strips to identify them.



Then run up to cruise or full power with an observer a safe distance viewing from the side of the disc. All blade tips should cone out equally, if one is out of line the pitch should be adjusted accordingly.



I have done this for a set of new warpdrives that were so far out static that I had to remove 1/2" of blade to match them, and increase that blade pitch around 0.2 deg. to compensate. Vibration gone.



Another tip - when setting the pitch, a very accurate way is to hold a laser pointer across the rear surface of each blade in turn, at the same chord distance position, with the blade set horizontal and laser shining onto the floor. resolution is around 1" beam displacement per degree of misalignment - more accurate than the bubble level.You may find making a special clamp to correctly locate the pointer necessary on some props.



Ralph

_________________
Ralph - CH701 / 2200a

rampil

Joined: 04 May 2007
Posts: 870

Posted: Mon Mar 10, 2008 4:42 am Post subject: Re: 912 with low RPM--- new vibration problem

The other possibility is simply that changing pitch and thus the RPM

simply plopped you right into an engine-airframe resonance.  This

scenario wold imply nothing wrong with your engine. Did you try other

RPM settings and find that the vibration reduced on either side of 5100?

_________________
Ira N224XS

daveaustin2(at)primus.ca
Guest

Posted: Mon Mar 10, 2008 5:38 am Post subject: 912 with low RPM--- new vibration problem

You didn't mention if you had checked the tracking of the prop.

Dave Austin  601HDS - 912, Spitfire Mk VIII

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Mon Mar 10, 2008 7:13 am Post subject: Re: 912 with low RPM--- new vibration problem

Les,



A few things here. 

Changing the prop pitch can indeed change a vibration from a fine frequency vibration into either a rougher one or a finer frequency vibration. The fact of the matter is it is there and still is.

Setting the Warp Drive or any prop should give you no vibration in the normal rpm ranges. Go fly your plane where the pitch is at and see if you can get 5500rpm or there about. If you have a vibration correct that. It isn't the rpm's fault. Changing the pitch to give a finer vibration will still cause you problems in the future. That vibration goes right into your gearbox and engine. It just shouldn't be there at all, fix the cause and don't mask it.

One item the guys are talking about is blade tracking, making sure each blade is flying in the same plane of reference. This can be done by putting something like a cardboard box up under the tip of the low blade pointing down and drawing a line at exactly where it crosses. the box should be only 1/4" away from the tip. Each blade there after should cross the line when turned by hand across that line. 

The next item is to do a static balance. This is done with the prop off the plane and to make sure when put on a balancer of some type that no side of the prop is heavier than the other. This should be done with all hardware attached. The blades may be equal from the factory, but all the nuts, bolts and washers are not.

Third is a dynamic balance. This is done on the plane and tested at cruise rpm with a balancer.

I have a 3 blade Warp Drive. With the hardware it was out of balance on static. The Warp Drive factory claimed each blade was within a few grams of each other. I put it on my Flight Design CT for a static balance and it was out by .33 IPS a third of an inch.That's alot. I couldn't feel it in the stick, but I new I should balance my prop. I had to ad 24 grams of weight (washers) to the prop hub to bring it back down with in spec. Everyone wants one that will read out at.000, but mine got as close as .02, a whole lot better.

Unless you do a track, static balance and a dynamic balance you may just chase you tail and make the vibration a fine vibration over a courser vibration, but it will still be there. 



None of these items are hard to do and you could do it all in 2-3 hours. The dynamic balance will probably take the longest at 1-2 hours with a tech and his tester.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Mon Mar 10, 2008 2:48 pm Post subject: 912 with low RPM--- new vibration problem

Actually I think the installation instructions that come with Warp props

specify to use the tip for setting pitch.  Yes, it goes against convention

but the convention is only with the OEM specs which is not the case with

Warp.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

williamtsullivan(at)att.n
Guest

Posted: Tue Mar 11, 2008 10:46 am Post subject: 912 with low RPM--- new vibration problem

Just an idea- Can you borrow a prop? That would be one way to check it.

                                            Bill Sullivan

                                            Kolb Firestar

                                            447 with 2 blade Warp Drive



Roger Lee <ssadiver1(at)yahoo.com> wrote:

   [quote]--> RotaxEngines-List message posted by: "Roger Lee" 



Is your gearbox within the group for recall? Probably not, but I had to ask.

If it were me I would do a dynamic balance. Anything else at this point is guessing and chasing your tail. The balance guy can probably help you on finding the vibration if it's not the prop. Remember the prop blades may weigh very close to the same, but all the hardware to fasten it down doesn't.



Do you have a mag rpm drop when you do a mag check?



Check your gearbox magnetic plug and look you debris. If something has started to wear badly or chipped inside you will start to see it at the plug.



I know this is very frustrating.



--------

Roger Lee

Tucson, Az.





Read this topic online [quote][b]

lgold(at)quantum-associat
Guest

Posted: Wed Mar 12, 2008 9:32 am Post subject: 912 with low RPM--- new vibration problem

Roger, Guy, Bob, and William.



I phones Lockwood and the tech there told me that on new engines they have

seen this vibration when the idle jet gets clogged from installation crud.

So I immediately drove the 50 miles to the Petaluma Airport and cleaned all

the jets... There wasn't any dirt in them (although there were a few specs

in the bowl) and this did not stop the vibration. I also checked the

cylinder pressures (all running 1790-180#)... so I'm back to square one! 



To answer your question, there is only a normal (100RPM) drop when doing mag

checks.



I still can't believe the prop is out of balance since it only has 20 hours

on it, was fine up to Saturday, and Warpdrive says they have not seen this

type of problem and I did everything right regarding the adjustment (the

prop tracks within 1/64th of an inch and the pitch of each of the 3-blades

does not vary by more than a 1/5th of a degree). I will call Lockwood again

and may give up and get a local tech to look at the engine... Maybe I'll

sync the carbs again... 

Out of ideas,

Les

   

 



[quote] --

lgold(at)quantum-associat
Guest

Posted: Wed Mar 12, 2008 8:26 pm Post subject: 912 with low RPM--- new vibration problem

Thanks Thilo, 

I'll check the check as soon as I can get time.

Les 



[quote] --

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Mar 13, 2008 4:37 am Post subject: 912 with low RPM--- new vibration problem

Les,



A couple other ideas:

1) Have you checked the spark plugs to see if one (or more) of the  

cylinders is running richer or leaner than the rest? If this is the  

case, let us know and I'll tell you about the solution that took me  

months to finally find and fix. It was nothing anyone could think of,  

including the experts at Lockwood. If not, then no need to go into the  

long story.

2) When you disassembled the carbs for jet cleaning etc. did you get  

the cylinder and diaphragm back in the right direction? I didn't once  

and the result was rough running in the mid range.



Thom in Buffalo

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

bear_creek_lsa(at)bellsou
Guest

Posted: Thu Mar 13, 2008 5:34 am Post subject: 912 with low RPM--- new vibration problem

We had a problem with a 582 that was similar. Two things, first there 

was crud way up in the jet almost impossible to see without looking thru 

it at a bright light, secondly the gas was "decomposing" and no sooner 

had we cleaned it out it had started compacting some sort of white 

material  back into the idle jets. Incidentally, I would never eliminate 

any variable, prop, engine, motormount etc, until it was proven 

serviceable regardless of it's age/hours



Good luck,



Terry.

lgold(at)quantum-associat
Guest

Posted: Thu Mar 13, 2008 9:06 am Post subject: 912 with low RPM--- new vibration problem

Thom,

I changed the plugs at 20-hours after "feeling" the problem. They all looked

the same. I also pulled the new plugs once to check cylinder pressure..

Again, they were all the same.



I never attempted to pull apart the tops of the carbs, so I didn't run into

problems putting back cylinders & diaphragms. I just pulled the bowls and

the jets for cleaning (which they didn't need).



Thanks for trying to help,

Les  



[quote] --

TheSchultzFamily(at)comca
Guest

Posted: Thu Mar 13, 2008 2:50 pm Post subject: 912 with low RPM--- new vibration problem

Did you check the spark gap on each plug?



Is the vibration the same with each mag alone? Worse together?



--

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Thu Mar 13, 2008 5:02 pm Post subject: 912 with low RPM--- new vibration problem

As soon as I saw the reference to white material the questions came to mind

1. what are your tanks made of??  2. Are you flying with ethanol fuel?  3.

Do you premix?



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Thu Mar 13, 2008 9:23 pm Post subject: Re: 912 with low RPM--- new vibration problem

Hi Les,



Doesn't sound like a carb issue anymore since you checked that. You checked the mags (ignition coils), balanced the carb and checked for clean carbs. It kind of only leaves one thing. When you rule out everything else then what ever is left is probably the culprit.  My Warp Drive was out of balance since day one. Has any little nut, bolt or part been changed from the prop hub forward? You still need to rule out static and dynamic balance. Until the last two things are done you could chase a ghost for ever. I know you don't want to hear that, but what else is left.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

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