Dynamic Propeller Balancing

Glenn, I tell this story. I dealt with a shop that offered this dynamic balance with a Chadworth system. I did all there SAT checks and one day they offered a free to me prop balance. This was on my Cherokee that I owned for 20 yrs. First we removed the cowl and mounted a transducer on the nose of the engine. They then put a reflector on the prop blade. Start the engine run it up to static power ie full blast with brakes locked and chocked. There was a reading of 3 volts from the transducer and a chart with the light gun said add 10 grams at this blade position. Ok we added three washers to the inside of prop spinner and did the test again. Super the transducer reads less than a 1/2 volt. Problem solved. Now I fly the plane home and for the life of me I notice absolutely NO difference in operation, noise or vibration. This was normal nothing changed until next Annual you guessed it my spinner backplate had cracked right where the added washers are installed. Moral to my story is the only thing that really matters is the engine mounts. Fast forward to the crate -2 what a difference when I replaced the Lord mounts. End of story. Lynn the crate locked in the dead of winter like the Germans in Stalingrad! :!:
 
With N8533R, there was a strong vibration @ 2300 RPM. This was dissapointing for a freshly rebuilt engine and prop. After talking to the engine rebuilder, the prop rebuilder and comments from McCauley, the motor mount bolts were checked for being bottomed out. There were bottomed out, so washers were added to cure that, and at the next flight, half the vibration was gone.
Next, the prop shop, the engine shop, and McCauley reccomended taking off the prop, rotate it 180 degrees and reinstall, which cured the rest of the vibration.
EAA326, which I'm a memeber, has bought a Dyna Vibe. Those that have used it, like it, but I think you should check the mounts and other mechanical sources first.
 
Thanks for the replies - my engine is running smoth. Someone recommended it for the "intangable differences" to engine life over time. I had great luck on my last engine. Engines have done just fine without this. Never really saw the need for this but thought I'd ask.
 
I had it done once to a Navion I had and it did make a difference. My Frankin has always been incredibly smooth. I had a non-standard straight three into one exhaust on each side and just put on and original exhaust looking for more cabin heat and it is not near as smooth now with the original exhaust.

Kevin
 
glennhake said:
Does this serve any real purpose? Does anyone have any experience with it?
Is it worth it?
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With a Dynamic Balance the crankshaft, bulkhead, spinner, nuts and bolts are balanced as one unit and it makes a real difference. Cuts down on stress caused by vibration though out the airframe. It pretty cheap and only takes about 2 hours. Find a shop that does a lot of balancing. Ask if they have the correct weights. If they plan to drill holes in your bulkhead and attached bolts for weights run and run fast! In SoCal we have a guy who does NOTHING but balance props. He comes to us for about $150.

Watch the video on this page. http://160knots.com/prop%20balance.htm

balance2b.JPG
 
lwford said:
This was normal nothing changed until next Annual you guessed it my spinner backplate had cracked right where the added washers are installed.
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And that's why I say ask if they have the correct weights. Drilling holes in the bulkhead is amateur hour at best and you'll be buying a new bulkhead pretty soon.
 
Thanks for the info on the weights. I had my Pitts balanced with washers and a bolt in the prop bulkhead, I will need to keep an eye on it for cracks. Anyone know a good contact for dynamic balancing with weights in the Kansas City area?
 
I own an ACES 2020ProBalancer & have dynamically balanced the props of over 100 planes. Vibration is measured in IPS (inches of second of acceleration) not volts. The accepted method of eliminating vibration is to add TEMPORARY weight to the spinner screws until the vibration is reduced to acceptable levels. The FAA suggests .15 IPS or less, my equipment uses a maximum allowable vibration of .07 IPS. Most of the props that I have balanced have a final vibration of .03 or .02 IPS. The entire rotating assembly is balanced during the process.
Permanent weight is usually attached to the rear spinner bulkhead in the form of bolts, nuts & washers. There is a proper way to drill a hole and limits on the amount of weight per hole. I have never had a spinner bulkhead crack from a properly installed weight. The flat weights on the hub of a variable pitch prop are for static balancing at the prop shop and are not to be tampered with as part of a dynamic balance procedure. Dymanic balancing is beneficial to the longevity of aircraft components and the cumfort of the aircrafts occupants.
 
If you drill a hole in the bulkhead that's where the crack often starts. Ask someone who does a lot of annuals. The bulkhead on a Viking is $1000 before paint.

How do you get a good balance if all the weight is at one station? If you put the weight on the spinner then move the weight to the bulkhead is it the same? My guy removes and reattaches the spinner two or three times during the balance.

The guy most use in SoCal is an IA who does nothing but balance props. Three days a week he's under contract with a defense contractor. Was one of three people who wrote the standards for the FAA. .02 or .03 is pretty much what one should expect unless it was made in Russia.
 
I'll try to answer some questions. Temporary weight is first attached to a spinner screw at the location closest to the location that was specified by the balance system computer. The location & amount of the temporary weight is then input into the computer. Once the vibration is reduced to the desired level, the amount of permanent weight can be calculated by the computer once the spinner diameter & the amount of offset to the location of the permanent weight on the rear spinner bulkhead is input into the computer. The amount of the permanent weight will be greater than the temporary weight due to the distance from the crank centerline being less (moment). A verification runup is then performed to ensure that the reduced vibration level was maintained. Weight can also be attached to the holes in the starter ring gear on Lycoming engines. My equipment alows for the input of the location of existing holes available for the attachment of weight.

Good equipment will calculate the correct solution to counter vibration with one weight location. My equipment will calculate a solution using split weight locations if needed.

I perform an average of 2 annual inspections per week & have never encountered a crack in a spinner bulkhead that was caused by the correct installation of balance weights.

Just trying to give you guys some insight from one who balances a lot of props including some of the planes that race at Reno.

Regards

Ray
 
My experience is most guys drill holes in bulkheads adding nuts, bolts and washers because they don't have to stock a large selection of propeller weights. For me, I want the factory weights, not something from home depot. My airplane, my money, my choice.
 
Here is a link to a propeller balancing guide which may be enlightening to some. http://www.acessystems.com/downloads/manual-gpb/gpb.pdf By the way, all weights that I use in the balancing process are aircraft grade. It may be possible to dynamically balance a prop by manipulating the static balance weights which are used by the prop shop to counter a heavy blade but it is not the normal procedure when dynamically balancing the entire rotating assembly at cruise RPM. To each his own, the end result is what is important.

Ray N33GM
 
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