I have only a few comments regarding the flywheel "damper" discussion:
1. The referenced EPI website is most excellent in its treatment of the subject. I'm impressed.
2. The viscous damper isn't "tuned" to a given frequency as it only responds to a change in rpm caused by the torsion inputs. A classic "torsional absorber" is tuned to a resonant frequency and reduces the amplitude. A different animal.
3. I'm a little skeptical as to whether the viscous damper reduces the torsional amplitude more than just adding a 12-pound flywheel, but I don't know.
4. I've heard good things about the viscous dampers when used with a 4-cylinder engine and wooden propeller, but I've seen no technical data to support. Heavier metal propellers seem to survive okay without the extra flywheel.
5. Yes, it's got nothing to do with the radial balance of the prop.
6. I can't see any way that adding either a flywheel, torsional absorber, or viscous damper could increase engine power ("100 rpm higher static rpm"). That just doesn't make sense.
Again, just my opinion.
Slava,
Read this to get an idea of the instantaneous torque the prop sees through its full revolution:
Many engines may have dampers to reduce power pulse effects from the drive shaft. The one we are discussing here is specifically designed to be mounted on a Lycoming starter ring. The following text was copied from the appropriate ad in the May 2010 Sport Aviation Magazine:
Grayhawk AKA Scott Krueger
PS I have been flying with this contraption on my Lyc I/O 320 for more than 12 years.
In a message dated 2/23/2011 8:11:01 A.M. Central Standard Time, slavaharlamor@sbcglobal.net writes:
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Hello All, I have been in the background studying for my build project. Grayhawk, your information about the harmonic damper is an educational point of significance. I know nothing about dampers, is there a book that I can get to learn about this subject. Does a damper have to be specific to an engine or is the design universal to any recip?
Thank you for any advice in advance,
Sincerely,
Mr. Slava Harlamor
--- On Mon, 2/21/11, Sky2high@aol.com <Sky2high@aol.com> wrote:
From: Sky2high@aol.com <Sky2high@aol.com>
Subject: [LML] Re: prop balance
To: lml@lancaironline.net
Date: Monday, February 21, 2011, 10:32 AM
Jack,
The 12 pound harmonic damper is present to reduce negative torque between power strokes. It has a steel ring suspended in silicone. It does not help balance the prop - it should be totally neutral with respect to balance but not circular momentum. On fixed-pitch prop (likely wooden or composite) driven engines, there is often a 100 rpm increase because of added momentum and a reduction in the negative torque by damping it. Constant speed prop users may find it difficult to measure the effect. Another benefit is to move the CG forward - usually a plus in the 320/360 series aircraft.
The person in Redmond is wrong. He is misinformed about the purpose of the damper.
I have such a damper and I do balance my prop. Because I am in a partnership that owns a simple balance device, I have no constraint on performing a balance or just checking the last balance to insure it has not changed (it has not).
Go balance that prop. Weights/longer bolts can be affixed where the damper is mounted to the starter ring. However, be careful that any large area washers not stick out far enough to come in contact with the cowling in dramatic + or - G maneuvers.
Geeeeze!
Grayhawk
In a message dated 2/21/2011 7:26:04 A.M. Central Standard Time, jraddison@msn.com writes:
Question?
On my LNC2-360 (BIB plus high comp pistons) there is an add-on "balancer" bolted to the face of the starter ring gear.
It is supposed to balance the engine with its internal weights that are supposed to arrange themselves to cancel or dampen our any sensed vibrations.
The "balancer" is about 2 inches in debth and almost the diameter of the ring gear; it is all self contained and you would have to take the prop off to get it off and take it apart if one was at least currious what was inside of it.
It's difficult to know if a 4 cyclynder Lycoming is as smooth as it can be, because it's not a real smooth engine under the best of conditions.
I inquired to a local experienced prop balance person in Redmond and they concluded that because of the dynamic
balancer on the ring gear, he would not attempt to balance the engine with his expensive balance work, as he thought the attached dynamic balancer would change the internal weight at will.
Does anyone have any experience with these dynamic balancers attached to the ring gear???
Cheers
Jack Addison N360JS
near Redmond, OR
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