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Engine Vibration
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Thom Riddle

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

Posted: Mon Jan 14, 2008 2:27 pm Post subject: Re: Engine Vibration

Hugh,



I think you are getting a run-around. Its not like Type Certificated aircraft have never had gearbox PSRUs. The Cessna 175 comes to mind. The center of rotating mass asymmetry with respect to the rotational center of the prop shaft, which what dynamic balancing is supposed to correct, has nothing to do with the fact that there is a gearbox between the prop shaft and the crankshaft, at least to my way of thinking, but I could be wrong.



do not archive

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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Roger Lee

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

Posted: Mon Jan 14, 2008 2:34 pm Post subject: Re: Engine Vibration

Hi Hugh,



I don't know why a Rotax gearbox would scare anyone away. You balance it just like any other prop. They are just uneducated. The gearbox wouldn't make any difference. The prop will balance or it won't.



You attach balance weights (washers) to the hub bolts.

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

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Mon Jan 14, 2008 3:22 pm Post subject: Engine Vibration

At 02:14 PM 1/14/2008, you wrote:

 	  Quote: 	
		  1. They do not balance props that have a gearbox between the engine

propeller drive.

2. There is no place on the WoodComp aluminum hub to attach balance weight.


	


Polite BS. I've had my Rotax 582 / Warp 3-blade dynamically balanced. 

They attached weight to the spinner backing plate. You could do the 

prop bolts as well.

Guy Buchanan

San Diego, CA

K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.

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Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Mon Jan 14, 2008 6:41 pm Post subject: Engine Vibration

Tom, Roger, Guy: 

Thanks for your feedback! I suspected the very same thing. I am going to

continue to seek out some one to do the Dyn. Balancing. At least I'm going

to follow up with the firm that was willing to look at my plane. Thanks

again to all of you.



Hugh



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Roger Lee

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

Posted: Tue Jan 15, 2008 7:46 am Post subject: Re: Engine Vibration

Hi Hugh,



The Flight Design CT people are having another Fly-In May 15-18, 2008. We are going to have a prop balancing person there at the fly-in for everyone and at a reduced rate. We are in the middle of lining that up right now. We have a number of other planes fly in and spend time with us and have a lot of fun flying out to the coast and for breakfast and BBQ's. You are more than welcome to come and have a good time plus get your prop balanced.

The Fly-In is in Mcminnville, Or. Right across the street form the big air museum with the Spruce Goose. We at dinner under the Spruce Goose wing last year.

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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
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Mark Burton

Joined: 10 Jan 2006
Posts: 74

Posted: Tue Jan 15, 2008 12:22 pm Post subject: Re: Engine Vibration

Hi Hugh,



Speaking as someone who:



1 - manufactures dynamic prop balancing equipment



2 - owns a 912 powered aircraft (with a Woodcomp prop)



I know something about how gearboxes affect the dynamic balancing process.



The balancers I manufacture make use of the gearbox ratio to optimise the removal of engine vibration (1/2 crank) from the prop vibration signal. But it's an optimisation to get a better result, not a requirement. I don't know if other manufacturers have such a feature in their equipment.



So to say the gearbox has no effect is not quite right but, in practice, it makes little difference. You can balance a prop on a 912 as easily (or as difficult!) as on any other engine.



Anyone who balances props will tell you that there are a lot of factors that affect the quality of balance achieved. Factors such as: carb balance, ignition performance, engine mounts, airframe resonance, prop blade pitch balance, wind speed and direction, RPM used, and so on. Most of these factors will have more of an influence on the balancing process than whether the engine has a PSRU or not.



I think the people you asked are either ill informed or they really didn't want the job.



Cheers,



Mark

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hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Tue Jan 15, 2008 7:05 pm Post subject: Engine Vibration

Mark: 



Thanks for your input and knowledge. From your note I assume you have

dynamically balanced your 912 and WoodComp prop together. If so, I would

like to know where and how you added mass, if mass was needed to get every

thing (engine and prop)in balance. Since the spinner and spinner flange are

fiberglass, the firm near here (H&H Propellers)

www.hhtriad.com/hhpropellers.asp that I am talking with (who hopefully will

do the job) seem to be concerned that there may be no place to add mass

except on the aluminum hub, and if that is so, where is that mass to be

added? If it is to be added at one of the six 8mm thru bolts, is it added by

using thin washers on the backside of the gearbox flange before the final

safety wiring is attached through the bolt heads?



Hugh



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hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Tue Jan 15, 2008 7:14 pm Post subject: Engine Vibration

Roger:



Thanks for the information and the invite to Oregon. I lived in Oregon

(Salem) for two years back in the 60's and loved it. However, I hope to get

my prop done closer to home at H&H Propellers

www.hhtriad.com/hhpropellers.asp and before May. North Carolina to Oregon is

a long haul in an Allegro 2000 for just a prop balance. My rear end might

not make it!! Thanks again though. I'll keep you informed as to the outcome

here in NC.



Hugh



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