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tc1917(at)bellsouth.net
Guest

Posted: Mon Sep 08, 2008 3:33 am Post subject: resonance 912

So far some great imput on the rum rum of my 912.  By the way, my wife says 

she can hear the 'roll' quite distinctly from the ground.  Another person 

said it sounded more like a chopper coming.



to Jack Hart:  I am using a three blade warp taper tip.  Thought originally 

this was the trouble (still not proven otherwise) and checked the blades 

very carefully.  Blades were all different widths at taper and one was 

shorter.  I think one has a different twist slightely (might be the problem 

but how you gonna get warp to believe it without trying another set of 

blades?) Sent blades back twice which corrected everything but the slight 

diffence of twist and I super balanced them before installation (horizontal 

and verticle) and set the blade pitch with a lazer pointing over six feet 

away.  No decernable vibration from he blades now.  If it is gearbox, the 

blades make it louder.



Also to Mr. Hart:  Yes, I have the plastic streamlining on my struts.  Can 

reach down and feel the struts during flight.  Not the problem.  Can also 

feel under the wings and there is the harmonics there but extra padding and 

tapes have shown me it is not likely the culprit, just a residual effect of 

the 'noise'.  Also tried tapes and padding on the top side of the inboard 

wings.



Sooo, as it stands right now, it seems either the prop is producing this or 

it is originating in the gear box.  That puts Hauck and Bean in the running. 

Still has to be proven and "curred".



I am so used to the noise I just keep on truckin.  I have learned one thing 

from this and I will share it with you all.  Next time I cover the wings of 

a Kolb, I will put dampening material fixed to the cloth inside the wing 

both on the bottom and the top inside all the way to the first ribs or so. 

I believe the light weight material will dramatically reduce all vibrational 

noise from the wings.  I have been doing the same thing to the fuse insides 

for years.  Makes a hugh difference in drumming.



Thanks so far.  Lets find out what this is to benefit all that has the 

problem and for the future.  Ted Cowan, Alabama, Slingshot 912.

John Hauck

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

Posted: Mon Sep 08, 2008 4:46 am Post subject: resonance 912

> Thanks so far.  Lets find out what this is to benefit all that has the

 	  Quote: 	
		   problem and for the future.  Ted Cowan, Alabama, Slingshot 912.


	




Ted C:



I think I recommended covering the rear windows.  May or may not cure your 

problem.  Don't know.  Won't know whether it will or not if you don't try 

it.  Only takes a minute to tape on some scrap lexan to cover those two big 

holes back there.



john h

mkIII

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

slyck(at)frontiernet.net
Guest

Posted: Mon Sep 08, 2008 4:50 am Post subject: resonance 912

Ted, you gave me a thought.  -surprised that you found differences in  

the warp blades,  Im using two from

a three blade set.  I may check all three against each other to look  

for any differences.

The only balancing I've done is hanging from fish line through a  

machined center plug.

I'll check individual balance points and weights.

BB

On 8, Sep 2008, at 7:33 AM, Ted Cowan wrote:



 	  Quote: 	
		   



 So far some great imput on the rum rum of my 912.  By the way, my  

 wife says she can hear the 'roll' quite distinctly from the  

 ground.  Another person said it sounded more like a chopper coming.



 to Jack Hart:  I am using a three blade warp taper tip.  Thought  

 originally this was the trouble (still not proven otherwise) and  

 checked the blades very carefully.  Blades were all different  

 widths at taper and one was shorter.  I think one has a different  

 twist slightely (might be the problem but how you gonna get warp to  

 believe it without trying another set of blades?) Sent blades back  

 twice which corrected everything but the slight diffence of twist  

 and I super balanced them before installation (horizontal and  

 verticle) and set the blade pitch with a lazer pointing over six  

 feet away.  No decernable vibration from he blades now.  If it is  

 gearbox, the blades make it louder.



 Also to Mr. Hart:  Yes, I have the plastic streamlining on my  

 struts.  Can reach down and feel the struts during flight.  Not the  

 problem.  Can also feel under the wings and there is the harmonics  

 there but extra padding and tapes have shown me it is not likely  

 the culprit, just a residual effect of the 'noise'.  Also tried  

 tapes and padding on the top side of the inboard wings.



 Sooo, as it stands right now, it seems either the prop is producing  

 this or it is originating in the gear box.  That puts Hauck and  

 Bean in the running. Still has to be proven and "curred".



 I am so used to the noise I just keep on truckin.  I have learned  

 one thing from this and I will share it with you all.  Next time I  

 cover the wings of a Kolb, I will put dampening material fixed to  

 the cloth inside the wing both on the bottom and the top inside all  

 the way to the first ribs or so. I believe the light weight  

 material will dramatically reduce all vibrational noise from the  

 wings.  I have been doing the same thing to the fuse insides for  

 years.  Makes a hugh difference in drumming.



 Thanks so far.  Lets find out what this is to benefit all that has  

 the problem and for the future.  Ted Cowan, Alabama, Slingshot 912.

jbhart(at)onlyinternet.ne
Guest

Posted: Mon Sep 08, 2008 5:07 am Post subject: resonance 912

At 06:33 AM 9/8/08 -0500, you wrote:

 	  Quote: 	
		  



to Jack Hart:  I am using a three blade warp taper tip.  Thought originally 

this was the trouble (still not proven otherwise) and checked the blades 

very carefully.  Blades were all different widths at taper and one was 

shorter.  I think one has a different twist slightely (might be the problem 

but how you gonna get warp to believe it without trying another set of 

blades?) Sent blades back twice which corrected everything but the slight 

diffence of twist and I super balanced them before installation (horizontal 

and verticle) and set the blade pitch with a lazer pointing over six feet 

away.  No decernable vibration from he blades now.  If it is gearbox, the 

blades make it louder.




	


Ted,



I was more concerned about inertia.  The greater the propeller inertia, more 

and more of the engine firing impulse, must be transmitted and adsorbed by 

the mounts, cage and surrounding structure.  I believe Bob Bean has the best 

idea.  I would try the lowest inertia two blade wood propeller I could find. 

 Two blades will pretty much act as one passing the wing trailing edge, and 

so the beat frequency will be lowered from three to one.  This should make a 

noticeable change if the resonance is caused by propeller blast to the wing 

surfaces.  If that is not the case then the lowering of the propeller 

inertia should help reduce the amount of engine firing impulse to the cage 

etc.



In either case you should come out with a quieter flying machine. If it 

works out well, you can always recover most of the cost by selling your 

present propeller.



Fly safe!



Jack B. Hart FF004

Winchester, IN

Ralph B

Joined: 14 Apr 2007
Posts: 367
Location: Mound Minnesota

Posted: Mon Sep 08, 2008 5:21 am Post subject: Re: resonance 912

When I bought my 912 Kolbra, Mark took it for a test flight to make sure everything was fine. On the ground, I noticed a resonating sound and I thought it was coming from the gears. Shortly thereafter, I switched oil to Honda HP4, a semi-synthetic motorcycle oil, which has gear additives. Prior to this, Mark was using Valvoline DuraBlend which is a good engine oil but has no gear lube in it. I believe this made a difference in the drumming noise from the gears. Rotax recommends a quality motorcycle oil for the 912. Lubricating the gears is high priority.



Ralph B.

_________________
Ralph B

Kolb Kolbra 912uls
N20386
550 hours

NeilsenRM(at)comcast.net
Guest

Posted: Mon Sep 08, 2008 6:16 am Post subject: resonance 912

Ted



I have had differing levels of noise in my MKIIIC. When I had a direct drive 

VW the noise was horrible. It was primarily from the prop going supersonic. 

When I switched to a reduction drive it got much better. Then I changed to 

my new engine mount and the noise got louder. The mounting bushings are 

wider spaced which controls the engine better but allows more engine 

vibration to get to the airframe. The latest redrive smoothed out the 

engine/redrive harmonics so again I got some noise reduction. Bottom line 

make the engine as smooth as possible and use the softest bushings/vibration 

dampers you can get.



When I had my quietest engine/mount, I experimented with putting VGs on my 

cockpit windows hopping for more speed (it didn't help) but what I found was 

that it reduced the noise. The sharp break at the back edge of my cockpit 

doors causes a considerable amount of turbulence that drums the sides of 

cockpit fabric. The VGs smoothes this out a bit.



If you can't stop the noise at the source then keep it from getting to you. 

I found a product at Oshkosh that may help. Check out WWW.Soundexproducts 

It is very expensive but looks like it will block and or absorb noise and it 

is very light.



Keep us up to date on your progress.



Rick Neilsen

Redrive VW powered MKIIIC

slyck(at)frontiernet.net
Guest

Posted: Mon Sep 08, 2008 6:46 am Post subject: resonance 912

-or you can start a propeller collection.  My "office" here now  

sports a nice shiny powerfin 3 blade on the wall.

Next will be the warpdrive.  The ceiling has a four blade fan to  

accompany the motif .

BB



On 8, Sep 2008, at 10:05 AM, Jack B. Hart wrote:



 	  Quote: 	
		   

 <jbhart(at)onlyinternet.net>



 At 06:33 AM 9/8/08 -0500, you wrote:

> 

>

> to Jack Hart:  I am using a three blade warp taper tip.  Thought  

> originally

> this was the trouble (still not proven otherwise) and checked the  

> blades

> very carefully.  Blades were all different widths at taper and one  

> was

> shorter.  I think one has a different twist slightely (might be  

> the problem

> but how you gonna get warp to believe it without trying another  

> set of

> blades?) Sent blades back twice which corrected everything but the  

> slight

> diffence of twist and I super balanced them before installation  

> (horizontal

> and verticle) and set the blade pitch with a lazer pointing over  

> six feet

> away.  No decernable vibration from he blades now.  If it is  

> gearbox, the

> blades make it louder.

>



 Ted,



 I was more concerned about inertia.  The greater the propeller  

 inertia, more

 and more of the engine firing impulse, must be transmitted and  

 adsorbed by

 the mounts, cage and surrounding structure.  I believe Bob Bean has  

 the best

 idea.  I would try the lowest inertia two blade wood propeller I  

 could find.

  Two blades will pretty much act as one passing the wing trailing  

 edge, and

 so the beat frequency will be lowered from three to one.  This  

 should make a

 noticeable change if the resonance is caused by propeller blast to  

 the wing

 surfaces.  If that is not the case then the lowering of the propeller

 inertia should help reduce the amount of engine firing impulse to  

 the cage

 etc.



 In either case you should come out with a quieter flying machine.  

 If it

 works out well, you can always recover most of the cost by selling  

 your

 present propeller.



 Fly safe!



 Jack B. Hart FF004

 Winchester, IN

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Mon Sep 08, 2008 9:31 am Post subject: Re: resonance 912

 	  jbhart(at)onlyinternet.ne wrote: 	
		  

I was more concerned about inertia.  The greater the propeller inertia, more 

and more of the engine firing impulse, must be transmitted and adsorbed by 

the mounts, cage and surrounding structure.  I believe Bob Bean has the best 

idea.  I would try the lowest inertia two blade wood propeller I could find. 

	




I would never use a wood propeller on a Kolb with a 912-S.   Wooden propellers are so fragile, the first time you have something go through the prop it will likely come apart with disastrous results.  Not to mention the tendency of wood to change balance over time, and the problems with keeping it torqued properly to the hub with changing humidity.



There are lots of Kolbs with 912-S engines that use Warp Drive and other composite props with no problems like you are having.   As a matter of fact, most Kolbs with 912-S engines, including my use a composite prop, including mine with no evidence of the problems you are having.   There is no reason you should be forced to use a substandard wooden prop.  Its just a matter of finding out what is causing this problem on your particular plane.



Mike

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

Kolb MK-III Xtra, 912-S

Ricochet

Joined: 29 May 2008
Posts: 36
Location: Fresno, CA

Posted: Mon Sep 08, 2008 1:39 pm Post subject: resonance 912

Yeh, it's great...and exciting...if not expensive to start a  

propeller collection.  Got a few meself, some remnants from having  

turned a few into toothpicks.  Had a 3-blade Warp on an 618-powered  

Avid that turned a gearbox shim into little pieces.  Made a hell of a  

racket at idle/taxi speeds, but not the rum rum discussed here.  The  

prop looked great, especially with the striped white tips I painted  

on it.  What I didn't know that it was way too heavy for the C-box.   

That was something at the time we didn't know about or understand.



Jerry

Fresno

On Sep 8, 2008, at 7:44 AM, robert bean wrote:



 	  Quote: 	
		   



 -or you can start a propeller collection.  My "office" here now  

 sports a nice shiny powerfin 3 blade on the wall.

 Next will be the warpdrive.  The ceiling has a four blade fan to  

 accompany the motif .

 BB



 On 8, Sep 2008, at 10:05 AM, Jack B. Hart wrote:



>

Ricochet

Joined: 29 May 2008
Posts: 36
Location: Fresno, CA

Posted: Mon Sep 08, 2008 1:46 pm Post subject: resonance 912

 	  Quote: 	
		  

Not that he needs it, but I endorse Mike's thinking on NOT using a  
	


wooden prop on a Kolb...or any pusher for that matter.  I and several  

others hereabouts have spent a fair amount of money replacing or  

repairing props when things come loose and/or break (exhaust spring  

hangars for example).  Sometimes you even get to land earlier and not  

where you would like when a big chunk of blade takes off on its own.



Jerry

Hangar 2



 	  Quote: 	
		   I would never use a wood propeller on a Kolb with a 912-S.   Wooden  

 propellers are so fragile, the first time you have something go  

 through the prop it will likely come apart with disastrous  

 results.  Not to mention the tendency of wood to change balance  

 over time, and the problems with keeping it torqued properly to the  

 hub with changing humidity.



 There are lots of Kolbs with 912-S engines that use Warp Drive and  

 other composite props with no problems like you are having.   As a  

 matter of fact, most Kolbs with 912-S engines, including my use a  

 composite prop, including mine with no evidence of the problems you  

 are having.   There is no reason you should be forced to use a  

 substandard wooden prop.  Its just a matter of finding out what is  

 causing this problem on your particular plane.



 Mike



 --------

 &quot;NO FEAR&quot; -  If you have no fear you did not go as fast  

 as you could have !!!



 Kolb MK-III Xtra, 912-S





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p 3223#203223

pj.ladd(at)btinternet.com
Guest

Posted: Tue Sep 09, 2008 1:41 am Post subject: resonance 912

use a  > substandard wooden prop. >>



Thats a bit of a sweeping statement. Why should you assume that a wooden 

prop is substandard



Time was when all aircraft had wooden props from Sopwith Pups to Vickers 

Vimy etc and they managed to go to war and fly the Atlantic.

You may have a situation where a badly matched prop and engine is giving 

trouble but that is no reason for such an intemperate statement.. Kolbs are 

flying here with 582`s, Jabiru`s with wooden props and  there are many light 

aircraft flying happily with wooden props.



Pat

tkrolfe(at)toast.net
Guest

Posted: Tue Sep 09, 2008 7:22 am Post subject: resonance 912

pj.ladd wrote:  	  Quote: 	
		  --> Kolb-List message posted by: "pj.ladd" <pj.ladd(at)btinternet.com> (pj.ladd(at)btinternet.com)   

   

 use a  > substandard wooden prop. >>   

   

 Thats a bit of a sweeping statement. Why should you assume that a wooden prop is substandard   

   

 Time was when all aircraft had wooden props from Sopwith Pups to Vickers Vimy etc and they managed to go to war and fly the Atlantic.   

 You may have a situation where a badly matched prop and engine is giving trouble but that is no reason for such an intemperate statement.. Kolbs are flying here with 582`s, Jabiru`s with wooden props and  there are many light aircraft flying happily with wooden props.   

   

 Pat 

   

 	
 Pat,

 

 Because that is the only kind of statement he seems capable of!  

 

 During college I worked for Sensenich Aircraft Propeller Co. building wood props.  One of their tests was to put a propeller on a test stand and the throw objects through the spinning propeller to demonstrate, that even though chunks of wood would be torn off, the prop was still able to provide thrust and give the pilot a chance to land safely.  You can imagine the excitement of that demo!!!!  Do that with an aluminum prop and it will immediately fold back making flight impossible.  There weren't any composite props back then, but it would have been an interesting test also!!  Believe it or not, they would actually repair wood props that had the ends sheared off.

 

 I have also seen what a piece of hard candy will do to a carbon fiber prop when striking it.  Causes major damage that is not easy to repair, but repairable.  Metal hardware would do more damage.

 

 Again, we have someone talking that doesn't know what he is talking about!!

 

 Wood props are not fragile, do not have problems with moisture if kept in good repair and the hub does not keep on compressing after the first couple of times of torquing it up.  I have 925 hr.s in front of my Tennessee wood prop and get great performance from it.  Meets the published numbers for climb and cruise and I burn 2 gallons per hour consistently.  It survived a major strike from my left wheel when my leg strut broke over a year ago upon landing.   The brake cable held on and swung the wheel assembly back up into the prop.  Sent the prop back to Tennessee Propeller and they spliced and repaired the tips and did a great job.  Been flying it ever since with total confidence!!

 

 But, then what do I know compared to someone who knows it all,

 

 Terry -  FireFly #95

 

    [quote][b]

Ricochet

Joined: 29 May 2008
Posts: 36
Location: Fresno, CA

Posted: Tue Sep 09, 2008 9:02 am Post subject: resonance 912

Terry,



...to clarify on my earlier comment on wood props on pushers, lemme say although I'm not high on wood props on pushers, prolly not aluminum either, after what you said, I do have a wood Sensenich on my Jab-powered Skyranger, and in fact love their props.  Wish I'd known about the tests you describe.  I'd have felt more comfortable flying with one of their props after a loose bolt went through one on takeoff (A&P screwup--me) on my Titan.  Didn't know it at the time, except the Titan went into a brief stall at its usual extreme takeoff angle (had a 3300 on it giving me incredible climb, even when well above Vy).  Discovered the problem when I landed--prop was split lengthwise and a small chunk was missing.  Wrapped the amazing invention, duct tape, on it and flew it home--praying all the way, of course.  Couldn't save the prop.  Fixed a lot of others though with baking soda and super glue after things went through them.  Simple and easy fix.

Jerry (aka Ricochet--story there too)

Hangar 2 

[quote] 	  Quote: 	
		  



 	
 Pat,

 

 Because that is the only kind of statement he seems capable of!  

 

 During college I worked for Sensenich Aircraft Propeller Co. building wood props.  One of their tests was to put a propeller on a test stand and the throw objects through the spinning propeller to demonstrate, that even though chunks of wood would be torn off, the prop was still able to provide thrust and give the pilot a chance to land safely.  You can imagine the excitement of that demo!!!!  Do that with an aluminum prop and it will immediately fold back making flight impossible.  There weren't any composite props back then, but it would have been an interesting test also!!  Believe it or not, they would actually repair wood props that had the ends sheared off.

 

 I have also seen what a piece of hard candy will do to a carbon fiber prop when striking it.  Causes major damage that is not easy to repair, but repairable.  Metal hardware would do more damage.

 

 Again, we have someone talking that doesn't know what he is talking about!!

 

 Wood props are not fragile, do not have problems with moisture if kept in good repair and the hub does not keep on compressing after the first couple of times of torquing it up.  I have 925 hr.s in front of my Tennessee wood prop and get great performance from it.  Meets the published numbers for climb and cruise and I burn 2 gallons per hour consistently.  It survived a major strike from my left wheel when my leg strut broke over a year ago upon landing.   The brake cable held on and swung the wheel assembly back up into the prop.  Sent the prop back to Tennessee Propeller and they spliced and repaired the tips and did a great job.  Been flying it ever since with total confidence!!

 

 But, then what do I know compared to someone who knows it all,

 

 Terry -  FireFly #95

 

  	  Quote: 	
		  

href="http://www.matronics.com/Navigator?Kolb-List">http://www.matronics.com/Navigator?Kolb-List

href="http://forums.matronics.com">http://forums.matronics.com

href="http://www.matronics.com/contribution">http://www.matronics.com/contribution



	
[b]

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Tue Sep 09, 2008 10:23 am Post subject: Re: resonance 912

 	  tkrolfe(at)toast.net wrote: 	
		   

 

 Again, we have someone talking that doesn't know what he is talking about!!

 

 Wood props are not fragile,  



	




Terry,



Despite all Terry wrote about working and having knowledge of all these propeller tests,  Terry is JUST PLAIN WRONG.



Wood props are very fragile, and are very likely to be broken by something coming off a pusher plane like a Kolb.   This is a very well known fact.



If anyone out there is starting to wonder after reading Terrys very misleading post, read this:



http://www.associatedcontent.com/article/418892/four_disadvantages_of_aircraft_propellers.html



http://users.hunterlink.net.au/~dddj/Powershift.htm



Terry claims that "Again, we have someone talking that doesn't know what he is talking about!!  "



Its pretty sad that a guy that likes to make this claim is the one that is posting bad information.



Mike

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

Kolb MK-III Xtra, 912-S

John Bickham

Joined: 10 Jan 2006
Posts: 170
Location: St. Francisville, LA

Posted: Tue Sep 09, 2008 7:58 pm Post subject: Re: resonance 912

Ted,



Sorry for late response.  Using Internet at work.  Still without power from Gustav (day .



Do not know if this will be helpful.  I had a drumming problem when I first built my Mark IIIC w/ 912.  It was my one and only attempt at plane building. I opted for the full enclosure.  Problem was that the cage was fabricated with a slight bow outward at the bulkhead at shoulder level.  This resulted in a small gap (less than 1/8") between the fabric and a couple of the long tubes on the side of the cage.  I couldn't see it with a string line.  With some speed and a big prop, the drumming would start.



On the rebuild/modification, I used John Williamson's method.  Started with fabric on bottom and rolled over each tube and glued.  Overlapped and taped a joint to start for the next section.  I'm not a fabric stitcher.



Made a big difference.  Much quieter and a bit faster.  Not sure how much the fabric drumming affected speed. My plane is faster after the rebuild and I'm leaning to that as a big contributor.  That or I knocked it into trim with that high/hard landing.



Long shot but may help.  I remember looking at your plane's instrument panel but did not pay attention to the rear area.  Do not know if this will apply.



best wishes!

_________________
Thanks too much,

John Bickham
Mark III-C w/ 912UL
St. Francisville, LA

I know many pilots and a few true aviators. There is a distinct difference that I have the greatest respect for.

tc1917(at)bellsouth.net
Guest

Posted: Wed Sep 10, 2008 3:22 am Post subject: resonance 912

Firstly, let me say to these two guys (men?), both of you shut up, nobody 

wants to hear it.  Take it to personal mail and not on the list.  This is a 

great list for information and experiences, not for arguing.  One mans idea 

is another mans folly.  One size dont fit all.  You have to pick and chose 

what you want to do and how to do it.  This list and its wonderful 

participants only SUGGEST things based on their own experience.  Nobody HAS 

to do anything.  If you dont like the advice, dont take it!!!  Saying nasty 

things to each other on this list is terrible.  Shows your intelligence 

level.  Thats it.



Now, on to the resonance on my slingshot with a 912.  Have tested out many 

of the theories mentioned so far by several great guys.  One that I have not 

tested out so far is by John Hauck about putting my windows in.  May not 

have time before homecoming to try it but hope I do.  Lots of humidity out 

there now.  Just about everything has been checked and double checked.  I am 

going to pull the filters off my carbs and watch them while tied down under 

power enough to create the rum rum.  Might be one of the slides are moving 

up and down slightly.  Might be the boot leaking.  Gotta check it out. 

Called Miss. Lite and talked to Ronny Smith and he says his experience has 

shown -- guess he knows of an instance -- that its the prop.  Warp makes its 

own troubles.  He suggested the pulses from the exhaust of the titan exhaust 

system hits the prop and causes the whop whop which is amplified by the warp 

drive prop.  He suggested I go to a Kiev Prop, about the same length. 

States it is quiet and very efficient and less mass to spin.  Has had very 

good luck with them and are very much quieter and more efficient. He stated 

it is NOT the gear box.  I would have a lot of crap on the magnet in the 

gear box and a chatter if it was loose.   Great, another thousand bucks!  I 

just bought the spinner for my warp.  I may have a whole warp system up for 

sale soon.  havent enough time to get the prop and test it before the 

homecoming.  That is no place to be testing something new on your plane.



Just wanted to let you all know of the updates on the rum rum problem.  I 

have what I would call a perfect aircraft (for myself) except for the rum 

rum.  If I can get that fixed, almost no matter what it cost, I will be a 

very happy man.  Thanks to all who have helped.  Oh, yeah, Bean is the one 

who was strongest in the suggestion about the props.  We might end up with a 

winner.  Thanks Again, Ted Cowan, Alabama, Slingshot 912

John Hauck

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

Posted: Wed Sep 10, 2008 5:30 am Post subject: resonance 912

Ted C:



Daryl, at Warp Drive, has always had a 100% satisfaction guarantee on his 

props.



I'd call him and see if he will send you another Warp Drive to try.  There 

may be some problem with your particular Warp Drive.  More mysterious things 

have happened when it comes to home built airplanes.



I never had a problem with prop blades and Titan exhaust noises, but the 

first thing I noticed when Erich Weaver showed up at MV with his new STE 

exhaust system.  It made a terrible noise as the exhaust pulses 

intermittently smacked the advancing blade on the right silencer exhaust 

pulses.



John W got an STE system and hit did the same thing.  The system was 

designed for the Pulsar, a tractor aircraft.  Not for pushers like our 

Kolbs.



About the same time my Titan exhaust system had multiple tube failures over 

a very short period of time.  I had to have something I could rely on.  I 

got the STE knowing it had the exhaust pulse, prop blade smacking problem. 

Yes, it did the same thing.  Sounded like it was coming apart.  My idea was 

to weld some 45 degree elbows on the outlets, but could not find anyone to 

do it for me before time to depart on a long flight.  Got another idea.  Cut 

the tips off perpendicular to the ground with the aircraft sitting in the 3 

point position.  Cranked it up and the smack was gone.



John W trimmed his similar to mine and that fixed his problem.



If, by chance the Titan exhaust is creating your resonance problem, then it 

is easy to change the silencer outlets to point in any one of three 

different positions.



Yours is the only problem I have heard of with a 912/Warp Drive/Sling Shot 

(or any model Kolb) resonance problem.



Ronny Collins had the similar resonance problem with Sling Shot/582 caused 

by loose fabric on the top of the right wing.  Two stroke turns opposite the 

four stroke, so the top of the right wing was getting drummed by the fabric. 

It had been rib stitched, stitches pulled loose, and Ronny's SS sounded like 

a twin engine airplane with the props out of synch.  Popped the fabric back 

to the ribs and the resonance went away.



I really don't think you have a prop problem, but a prop drumming problem 

associated with fabric and air flow.  You can take 10 minutes, tape up the 

back windows, go fly, and see if that changes anything.



Check to insure fabric is affixed tightly to all fuselage tubes and wing 

ribs and tubes.



Something is causing this problem.  Just gonna have to keep looking until 

you find and fix it.  There are too many Kolbs with 912's, Warps, and Titan 

exhaust out there flying without resonance to blame it on an engine, prop, 

or airframe design problem.



john h

mkIII

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

vicsv(at)verizon.net
Guest

Posted: Wed Sep 10, 2008 6:56 am Post subject: resonance 912

Hey John,

 Did you mean to say perpendicular or parallel to  the ground concerning Titan exhaust.

 Mine, used, came perpendicular and I thought of  cutting the tips because of prop noise.

  

 Vic

 MIII Exrra 912ul

  

   [quote][b]

John Hauck

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

Posted: Wed Sep 10, 2008 7:12 am Post subject: resonance 912

Vic:

  

 A Titan exhaust can be tried with the outlets  pointed left, right, or straight up.

  

 I never had a noise problem with the Titan systems,  only the STE.

  

 john h

 mkIII

  	  Quote: 	
		      

   Hey John,

   Did you mean to say perpendicular or parallel to    the ground concerning Titan exhaust.

   Mine, used, came perpendicular and I thought of    cutting the tips because of prop noise.

    

   Vic

   MIII Exrra 912ul

    

	
   [quote][b]

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

tc1917(at)bellsouth.net
Guest

Posted: Sun Sep 14, 2008 3:36 am Post subject: resonance 912

Well, thanks to you all with your wonderful suggestions concerning the hum 

hum of my little 912.  I want to report that I still have it live and strong 

as ever.  I built two 60 degree elbows for the exhaust flanges of my titan 

exhaust system -- did not help.  actually it made the exhaust louder.  did 

not affect the resonance.  I already went from none to four inch spacer and 

back to two inch which I have today.  I was told it was not the gear box 

because there was no scrap in the oil.  (I still believe it is the spacers 

in the box or an elliptical gear or something that is not actually tearing 

it apart.  I dont seem to be able to get the 'AUTHORIZED DEALERS AND REPAIR 

CENTERS' to care or want to do anything about it.  I even offered to pay 

them out of my pocket.)   I have padded just about everything padable.  I 

put my windows in - Haucks suggestion - wow, was that hot inside.  I like 

free air while I am flying.  No joy, still there.  I was told by a prop 

person, Kiev Props that their prop would help in a lot of ways but the prop 

was probably not the producer of the sound, just the amplifier.  So, there I 

am.  When we get to the Homecoming, you all can hear it from the ground and 

while I am in the air and solve this mystery for me.  Looking forward to 

seeing you all again.  Ted Cowan, Alabama, Slingshot, 912 UL

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