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tc1917(at)bellsouth.net
Guest

Posted: Thu Apr 09, 2009 2:35 am Post subject: vibrations

For those that have not been privy to my harmonics on my 912, here is the 

following.  The first thing I thought was wrong was the prop not being set 

"right" so I developed a laser that sits on the tip of my blades, one at a 

time, while I set them so they are near perfect.  The blades themselves were 

all different weights, one a different length and two had what looked like 

cloth bumps showing.  I sent them back and they came back better but still 

not the same.  One has a different twist at the middle and now has a smaller 

tip.  This is what WD thinks are good blades.  I believe I have a set of 

reject blades all thrown together.  My personal belief.  I sent them back 

twice but they are still basically the same.  I have been balancing large RC 

props for thirty years and have never seen blades like these.  I super 

balanced them.  Same problem.  I super tuned the carbs -- three times!  Not 

the problem.  I changed the angle of my titan exhaust outlets -- twice!  I 

added some angle sections to my pipes so the exhaust would not hit the 

blades directly -- no joy.  I have stainless tubes with holes on the ends of 

my pipes and they do reduce the noise a bunch but I still have the 

harmonics.  I have taped the wing fabric top and bottom and checked all the 

fittings, pieces and mounts for loose or dangling fabric.  I changed my gap 

seal three times.  I started with no spacer, spent $450 for a four incher, 

no help.  That changed my balance where it was not desirable, dont know why. 

I took it off and put a two inch spacer on and that seems to work good 

except the harmonics are still there.  I changed spark plug gaps and then 

spark plugs.  nothing helps.   This harmonic sound does not increase in 

beat, just intensity to the point where it actually beats on the back of my 

helmet.  My anr removes most of it so I can tolerate this noise.  It is 

noticeable from the ground as a rum rum rum sound like it out of tune.  A 

friend has a new set of WD props like mine down in Florida and I will try 

them as soon as I get down there.  If that makes it better then you can bet 

I will call WD with the 'proof' and see what they will do.  Right now I just 

live with it.  As far as changing type of prop -- well, how many of you have 

an extra grand or more to just 'try' another prop?  I dont.  I should not 

have to.  I paid my money and should have a good prop.  Like I said, I have 

not absolutely proven it is the prop yet but I will.  By the way, one blade 

really shows the cloth weaving and I believe it is the culprit.  Ever hear a 

digery do or however it is spelled?  That hum hum is what I am talking 

about.  Thought WD would replace it last time but they didnt.  Not exactly 

the service I would expect from such a reputable dealer.  Guess I dont have 

enough 'fame' to get good service from them.  My life as it is.  At least my 

rum rum is accompanied by zoom zoom and that makes it worth it.  Ted Cowan, 

Alabama, Slingshot 912 UL.   p.s. I still have a fifty buck reward for 

someone with a cure.  (something we have not already thought of or done) 

Hauck is the first one for the blades being bad.

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Thu Apr 09, 2009 5:18 am Post subject: Re: vibrations

 	  tc1917(at)bellsouth.net wrote: 	
		  For those that have not been privy to my harmonics on my 912, here is the 

following.  The first thing I thought was wrong was the prop not being set 

"right" so I developed a laser that sits on the tip of my blades, one at a 

time, while I set them so they are near perfect.  The blades themselves were 

all different weights, one a different length and two had what looked like 

cloth bumps showing.  I sent them back and they came back better but still 

not the same.  One has a different twist at the middle and now has a smaller 

tip.  This is what WD thinks are good blades.  I believe I have a set of 

reject blades all thrown together.  My personal belief.  I sent them back 

twice but they are still basically the same.  I have been balancing large RC 

props for thirty years and have never seen blades like these.  I super 

balanced them.  Same problem.  I super tuned the carbs -- three times!  Not 

the problem.  I changed the angle of my titan exhaust outlets -- twice!  I 

added some angle sections to my pipes so the exhaust would not hit the 

blades directly -- no joy.  I have stainless tubes with holes on the ends of 

my pipes and they do reduce the noise a bunch but I still have the 

harmonics.  I have taped the wing fabric top and bottom and checked all the 

fittings, pieces and mounts for loose or dangling fabric.  I changed my gap 

seal three times.  I started with no spacer, spent $450 for a four incher, 

no help.  That changed my balance where it was not desirable, dont know why. 

I took it off and put a two inch spacer on and that seems to work good 

except the harmonics are still there.  I changed spark plug gaps and then 

spark plugs.  nothing helps.   This harmonic sound does not increase in 

beat, just intensity to the point where it actually beats on the back of my 

helmet.  My anr removes most of it so I can tolerate this noise.  It is 

noticeable from the ground as a rum rum rum sound like it out of tune.  A 

friend has a new set of WD props like mine down in Florida and I will try 

them as soon as I get down there.  If that makes it better then you can bet 

I will call WD with the 'proof' and see what they will do.  Right now I just 

live with it.  As far as changing type of prop -- well, how many of you have 

an extra grand or more to just 'try' another prop?  I dont.  I should not 

have to.  I paid my money and should have a good prop.  Like I said, I have 

not absolutely proven it is the prop yet but I will.  By the way, one blade 

really shows the cloth weaving and I believe it is the culprit.  Ever hear a 

digery do or however it is spelled?  That hum hum is what I am talking 

about.  Thought WD would replace it last time but they didnt.  Not exactly 

the service I would expect from such a reputable dealer.  Guess I dont have 

enough 'fame' to get good service from them.  My life as it is.  At least my 

rum rum is accompanied by zoom zoom and that makes it worth it.  Ted Cowan, 

Alabama, Slingshot 912 UL.   p.s. I still have a fifty buck reward for 

someone with a cure.  (something we have not already thought of or done) 

Hauck is the first one for the blades being bad. 	




Well I do have to defend WD a little bit here. Yeah it's wierd if they're not fixing malformed blades for you, but I can't say their service has been any problem for me. 



After all, my plane does have that big ol "Experimental" sticker plastered onto the side of it. So ultimately, the plane is an experiment, so I have to keep in mind and take that responsibility. Things are just going to come up if I have to make changes. 



In my case, I'm just going to have to keep "experimenting", that's just how it is with experimental.  Its on me to do the work here and I can't expect everyone else or even WD to know exactly what's wrong with my setup. I kind of have to take the bull by the horns and get to work on things for which others might not have ready answers. That's kind of how life is in general in fact, and is no reflection on anyone else...



If this particular prop wont' work, it just wont work and that'll just be a consequence of my particular setup. 



It sure isn't the fault of the prop. I've used WD before (on my FSII) and it was a superb prop. This one I have is impeccably made and I sure can't argue with the performance.



But I am going to try different prop types. At this point I've exhausted most other things to try tho there are still a couple more things to try. But that's just how it goes with our flying machines...



LS

_________________
LS
Titan II SS

NeilsenRM(at)comcast.net
Guest

Posted: Thu Apr 09, 2009 5:34 am Post subject: vibrations

Ted



I have chased noise issues with my VW over the years and think that the 

engine mount is the area that you may want to look into. Try softer 

vibration dampers or move them around so that they isolate engine/prop 

vibrations better and still control the position of the engine/prop.



My VW high mount had the lowest noise in the cockpit and lest vibration 

transmitted to the airframe. The redrive I was using at that time would 

vibration crack engine parts quite regularly yet the noise level in the 

cockpit was so low that sometimes I could take my headphones off for short 

periods of time in flight. The engine was real loose on the mount allowing 

the engine to visibly twist away from the torque applied to the prop. After 

about a hundred hours the vibration dampers were destroyed.



When I designed the lower VW engine mount I used a damper system that placed 

the dampers further apart to better control the engine and extend the life 

of the dampers. It worked but the noise and vibration in the cockpit 

increased so much that I had to use ear plugs under my ANR headsets. Since 

then I have reduced the vibrations a bunch and the noise a bit with a 

smoother redrive. I'm now on a quest for softer damper bushings.



Food for thought and as always worth what you paid for it.



Rick Neilsen

Redrive VW powered MKIIIC



---

robcannon

Joined: 22 Jun 2008
Posts: 39
Location: British Columbia

Posted: Thu Apr 09, 2009 5:34 am Post subject: Re: vibrations

Ted - I took some training last summer in a Rans S 12 in preparation for my Kolb first flight. (it was the only high thrust line pusher around).  It has the same harmonics you describe (annoying in the cockpit, and annoying on the ground) It has a Rotax 912 with a three blade "kool"prop. They have over 1700 hours on this plane and motor, and they have accepted this thrum thrum thrum and part of the package. When I flew it I just chose a throttle setting that minimized it the most.

  Don't get me wrong here, if I were in your shoes I would not give up untill I had a explanation/solution, but it may not be the warp drive that is the culprit.  

good luck, Rob Cannon

ps: Rans has probably sold more 912 pushers than most - I would call up their tech support guy and see what he says.

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Thu Apr 09, 2009 5:50 am Post subject: vibrations

That hum hum is what I am talking

 	  Quote: 	
		   about.  Thought WD would replace it last time but they didnt.  Not exactly 

 the service I would expect from such a reputable dealer.  Guess I dont 

 have enough 'fame' to get good service from them.  My life as it is.  At 

 least my rum rum is accompanied by zoom zoom and that makes it worth it. 

 Ted Cowan, Alabama, Slingshot 912 UL.   p.s. I still have a fifty buck 

 reward for someone with a cure.  (something we have not already thought of 

 or done) Hauck is the first one for the blades being bad.


	


I've offered several suggestions since Ted C has had the harmonic problem. 

Guess none of them worked.



Also offered to try my WD off my airplane.



I believe the place to start is remove the suspect prop and hub.  Put 

another WD prop on from a setup that has no problem.  Test it.  If it 

developes the same problem, then it is not the prop.  If the problem 

disappears, then you have more ammunition to go back to WD and get a 

replacement prop.



I also recommended contacting Daryl to request another prop and hub to use 

for a test.  I have a good feeling he would do that to see that his 

customers are satisfied.



I don't think 'fame' has a thing to do with getting good service from WD. 

This company has been in business for many years, and not because they 

mistreated their customers or because they sold inferior products.



While I am recommending, highly recommend you give Daryl a call at 

1-800-833-9357.  I reminded him of your problem.  He would be glad to 

discuss it with you.



john h

mkIII - 60 west of Ted Cowan's airstrip.

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

slyck(at)frontiernet.net
Guest

Posted: Thu Apr 09, 2009 6:10 am Post subject: vibrations

Ted, borrowing other props for comparison would be my first choice  

too.  I know I wouldn't

be happy if I had paid for new blades and got blades that didn't even  

look cosmetically perfect.

The "proof" approach is the way to go.



I also have a rum rum but I have noticed that some of it may be my  

hearing.  I hear it just walking up the driveway, in time with my  

heartbeat.

Something to go along with my tinnitus.



If you have a two blade WD hub that would be a good thing to try.   

That reminds me

to order a two blade hub for my powerfin.  I sure would like to be  

able to keep the

70" two blade WD on my suzuki because it gives me what seems like 10  

hp  better performance than the

3 blade 65" powerfin I had on before.



Mix match and compare.

BB

 	  Quote:

The BaronVonEvil

Joined: 23 Jun 2006
Posts: 76
Location: Walla Walla, WA.

Posted: Thu Apr 09, 2009 12:46 pm Post subject: vibrations

Hi Ted,



While I dont have any personal experience with a 912, I do have a few 

suggestions of a general nature.



Check the gearbox oil of your engine to see if every thing is okay. Perhaps 

there is a bearing or gear that is causing your grief. Any metal in the gear 

oil is not a good sign and warrants a tear down of the gearbox.



Check the runout of the propeller drive flange to see that it is running 

true. Also check  to see if there is any  play or slop in the drive that 

shouldn't be there. In general terms, some gearboxes have preloads and no 

play while others require a small amount to operate properly. The Rotax 

manuals may call out the details for your gearbox.



Have you checked the compression of the cylinders to see if they are okay? 

Uneven compression maybe causing harmonics in your engine.



A fixed pitch wood prop would be less costly alternative to a composite if 

you have to purchase one for testing.



Again these are a few general items I would look at  if I was having your 

troubles.



Good Luck and let us know when you have found the problem.



Best Regards

Carlos G

AKA

BaronVonEvil.



---

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Thu Apr 09, 2009 1:34 pm Post subject: Re: vibrations

We have a couple MK III's here at my field, and both of us have had to do a mod to reduce the noise inside the cockpit.  Built by the plans, there is an open space from the prop that makes the cockpit act like a resonant bell, the noise was HUGE !   My " Neighbor " put a piece of clear lexan behind the seats, where a headrest would be if he had one.  This simple, one piece of flat lexan made a huge difference in making his cockpit noise tolerable.  His noise reduction worked so well, that I went a lot of steps further and enclosed the entire cabin of my plane, above and rear, and put sound dampening in the lower fabric in the cage behind the seats where it faces the prop. I also have sound dampening on the rear lexan windows.  In other words, I put sound dampening in any part of my cage on my plane that " Sees " or faces towards the the prop at anything less than a 90 degree angle.  John Haucks MK III is pretty much like this, with all rear areas enclosed.  This made a huge reduction in the noise level.  I use ANR headsets, but don't need any earplugs.  I wonder if you have a typical loud hum hum that would be hardly noticeable with some noise prevention measures.  Its hard to tell how severe this is, or if its typical without hearing it first hand and comparing it to other Kolbs with a similar setup.



My warp drive prop is perfect.  Did you check the tracking on the tips of your prop, all three blades should be within 1/16 of an inch or so.  My Rotax 912-S / prop is as smooth as silk, smoother than any other piston engine I have flown behind.  I can barely feel it running if I place my hand on the cage tubing.  I have had several occasions to deal with Warp Drive, and they have always been more than fair, and gone the extra mile as far as I am concerned.  There are lots of warp drive props on experimental airplanes, it is very rare to hear anything bad about them.  It is possible to get a combination of equipment that will not work well together, but there are such a huge number of Warp Drive / 912-S combos flying, that I don't believe this should be problematic combo.  Maybe time to look more at the airframe ??



P.S.   Going from a 4 inch spacer to the two inch spacer you have now is a such very small change of CG, I don't see how this could possibly have any meaningful impact on the flying qualities of the airplane.  You must have miscalculated something or not have a full understanding of effect this has on CG.   Anyways, the 4 inch spacer on the prop is far better than a two inch spacer, for a number of reasons.  I would most definitely use the 4 inch spacer...  Just off the top of my head, I think two extra inches on the prop spacer would equal less than one pound of weight added to the nose IF you wanted to keep the same CG..  Thats a rough guess off the top of my head, it would be easy to calculate given your WB information and prop weight.  In other words, its negligible and I would not even bother with such a small change.  The longer spacer is much better for a pusher setup like found on our Kolbs.



Gook luck chasing this down, like Lucien said, we did sign up for Experimental aviation, and it can make you want to beat your head against a wall sometimes.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Thu Apr 09, 2009 3:18 pm Post subject: Re: vibrations

 	  JetPilot wrote: 	
		  We have a couple MK III's here at my field, and both of us have had to do a mod to reduce the noise inside the cockpit.  Built by the plans, there is an open space from the prop that makes the cockpit act like a resonant bell, the noise was HUGE !   My " Neighbor " put a piece of clear lexan behind the seats, where a headrest would be if he had one.  This simple, one piece of flat lexan made a huge difference in making his cockpit noise tolerable.  His noise reduction worked so well, that I went a lot of steps further and enclosed the entire cabin of my plane, above and rear, and put sound dampening in the lower fabric in the cage behind the seats where it faces the prop. I also have sound dampening on the rear lexan windows.  In other words, I put sound dampening in any part of my cage on my plane that " Sees " or faces towards the the prop at anything less than a 90 degree angle.  John Haucks MK III is pretty much like this, with all rear areas enclosed.  This made a huge reduction in the noise level.  I use ANR headsets, but don't need any earplugs.  I wonder if you have a typical loud hum hum that would be hardly noticeable with some noise prevention measures.  Its hard to tell how severe this is, or if its typical without hearing it first hand and comparing it to other Kolbs with a similar setup.



My warp drive prop is perfect.  Did you check the tracking on the tips of your prop, all three blades should be within 1/16 of an inch or so.  My Rotax 912-S / prop is as smooth as silk, smoother than any other piston engine I have flown behind.  I can barely feel it running if I place my hand on the cage tubing.  I have had several occasions to deal with Warp Drive, and they have always been more than fair, and gone the extra mile as far as I am concerned.  There are lots of warp drive props on experimental airplanes, it is very rare to hear anything bad about them.  It is possible to get a combination of equipment that will not work well together, but there are such a huge number of Warp Drive / 912-S combos flying, that I don't believe this should be problematic combo.  Maybe time to look more at the airframe ??



P.S.   Going from a 4 inch spacer to the two inch spacer you have now is a such very small change of CG, I don't see how this could possibly have any meaningful impact on the flying qualities of the airplane.  You must have miscalculated something or not have a full understanding of effect this has on CG.   Anyways, the 4 inch spacer on the prop is far better than a two inch spacer, for a number of reasons.  I would most definitely use the 4 inch spacer...  Just off the top of my head, I think two extra inches on the prop spacer would equal less than one pound of weight added to the nose IF you wanted to keep the same CG..  Thats a rough guess off the top of my head, it would be easy to calculate given your WB information and prop weight.  In other words, its negligible and I would not even bother with such a small change.  The longer spacer is much better for a pusher setup like found on our Kolbs.



Gook luck chasing this down, like Lucien said, we did sign up for Experimental aviation, and it can make you want to beat your head against a wall sometimes.



Mike 	




For what it's worth, according to Daryl, the tracking need only be within about 5/16" max. 1/4" is typical, my current one and the one I had on my FS II were about 1/4" off (the one on my FS II was smooth as glass).



I'd personally try to keep the spacer as short as possible. A long spacer adds a signficant amount of arm to the Coriolis forces the prop imposes on the prop shaft. Every little bit helps to preserve our gearboxes even tho they're still strong as stink.....



My FSII was unbelievably loud in the cockpit and sure enough it was open at the rear. Wish I'd had my telex ANR headset back when I had that plane......



LS

_________________
LS
Titan II SS

lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Thu Apr 09, 2009 4:03 pm Post subject: vibrations

[quote]   My FSII was unbelievably loud in the cockpit and sure enough it was open    at the rear. Wish I'd had my telex ANR headset back when I had that    plane......



LS



--------

LS

Titan II    SS





For what its worth, on my trip to Texas    with Arty, I used the full enclosure on my Firestar. That is the full    windshield and the fabric with the convertible type window in it. It cut my    maximum speed to 60 MPH. Without it and using the full windshield I gained 7    MPH. It might be quieter, but I am not willing to take the cut in top    speed.

   Larry C

[b]

_________________
do not archive

zeprep251(at)aol.com
Guest

Posted: Fri Apr 10, 2009 1:53 am Post subject: vibrations

Larry,

     I ran into the same speed problem with my FS2 full enclosure.When I tried to pick up speed by lowering the nose a little,the enclosure tore loose from the right side of the windshield former  tube and entered the propeller arc.I was lucky enough to drag it back into the cabin and continue to my field.It put 1 big gash in the clear vinyl part of the enclosure but it was repairable and a lesson was learned.I have no idea why it did not wad up in the prop and create the scenario that is going thru your mind right now,I really don't.

                      G Aman former FS2 driver.It's still my favorite Kolb.

 

   

 

   

 

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