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Whirlwind Prop Balance

Walt

Well Known Member
Whirlwind recommends dynamic prop balancing before first flight in their installation manual. Based on the this one and a few other whirlwinds I've done, I would definately agree that this is not something you should ignore!

This one started out quite high (a bit of an understatement) at 0.747 IPS (the little red circle represents the upper limit), 4 runs later I had it at 0.023 IPS after adding 61 grams of weight.

prop%2520bal%2520whirlwind.jpg
 
I'm getting mine done next week. I have about 55 hours on the prop, no balance yet. I hope I haven't damaged anything already. :eek:
 
Walt can you tell by feel when balance is needed? I guess if is far out of balance but to what extent can you depend on your senses to tell if you need balancing. I have a Catto 3 blade that feels good at some rpms and less so at others but overall feels OK
 
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Walt can you tell by feel when balanci is needed? I guess if is far out of balance but to what extent can you depend on your senses to tell if you need balancing. I have a Cargo 3 blade that feels good at some rpms and less so at others but overall feels OK

Most folks have no frame of reference to compare it to, so unless you know what "smooth" feels like in an RV, you'll have no way of knowing what excessive vibration is.

In something like the one above there was a very obvious and noticable reduction in vibration. If the vibration is around 0.2 IPS to start the decrease to lets say 0.03 will be much less noticeable by the average person and some folks may not feel it at all. However, even though you can't feel it, the airframe/engine/avionics 'feels' it, less vibration means less fatigue on these componets which equates to a longer life.
 
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What is the average cost for a two and a three blade?

I still do experimental aircraft for $175 (owner RR's his upper cowl) and most certified AC for $225. Same price for 2 or 3 blades.

Boy, you'd think they could get a better static balance to start off with....

My guess would be the prop itself is static balanced, but the spinner and associated attachments which on the whirlwind are quite substancial, may be more difficult to effectively balance.
 
Hey Walt, what is the proper sequence on a newly overhauled (no test cell time) engine and a new Whirlwind? A new engine is supposed to get minimum ground run time so I ASSume the balance should take place after engine break in?
 
Hey Walt, what is the proper sequence on a newly overhauled (no test cell time) engine and a new Whirlwind? A new engine is supposed to get minimum ground run time so I ASSume the balance should take place after engine break in?

The one above was done at 25 hrs (new engine/prop), for a whirlwind I would do it asap after break-in which for most engines probably could be done around 5-10 hrs (after you see the typical drop in CHT's during break-in).
 
One note of caution for WW owners: the spinner and backplate are both marked with a "1" and a "2" so if the spinner comes off you can clock it the same way when it goes back on, however there is no indication of clocking the backplate to the actual blades. I have had my prop off and when reinstalling it didn't know how to clock the back plate to the prop blades. Once you have balanced your prop, mark the back plate with the blade number stamped at the base of the blades. That way, if the prop comes off, you can clock it correctly when it goes back on.

All that said, if it comes off for reseal or overhaul, you're going to be re-balancing anyway:rolleyes:
 
Hmm, the front of the hub on my whirlwind is marked 1 and 2. I don't have a 200rv so not sure if they mark the front of the hub on it. Might want to double check.

Walt, your exactly right on the static balance. I was thinking along the terms of rotor blades. We don't have spinners for them. :)
 
I just had my Whirl Wind 200RV balanced today. It went from .24 to .01 using 9.2 grams at 120 degrees and 19.3 grams at 150 degrees. It took five runs to get it perfect--what a difference! Bob (Bob4Rv4 here at VAF) and Kurt over at the "Area 51" hangar at KFFZ did a great job!
 
PROP BALANCING

Hello Flight:

Many companies recommend doing Dynamic Prop Balancing, Whirlwind, McCauley, Sensenich and even Power Flow Exhaust Systems. When it comes to Power Fly, the time length of their warrantee is cut in half if you do not do a dynamic prop balance.

The next question was: How do I know if I need prop balancing? If you haven?t done prop balancing - Then you need it. Do you put tires on your car without balancing them? Same is true for a prop. They both spin and the slightest unbalanced weight becomes more and more of an unbalanced force the faster they spin.

There are two types of balancing that should be done to props ? Static and Dynamic.

Static balancing: Is, or should be done by the prop manufacture or overhaul shop. Let?s talk fixed pitch and constant speed props here? Fixed Pitch: This is done by placing a precision arbor through the center hole of the prop. Then the prop and arbor are placed on a low friction balance known as ?knives?. The prop is dresses so no mater what position the blades are places the prop does not move. At this point the prop is Statically Balanced. Constant Speed: This is a bit trickier, since there is no through hole to put an arbor through. A flange mounted arbor with a counter weight length is bolted to the prop. Then the prop is placed on a different design set of ?knives?, the prop is dressed until the same balance results are obtained as with the fixed pitch prop. At this point the static balancing is done.

Dynamic balancing: Is done on the plane, the engine is run to the very top speed that it can achieve while on the ground. So, if you have a constant speed prop you do it at the flattest pitch, you also lean to achieve the highest RPM. Why? The slightest amount of static imbalance it amplified as the rotational speed increases. When on the ground you can only reach what is called a Static RPM; in the air the plane moves forward and the ?Air Load? on the prop decreases, this is know as unloading the prop and then you will see the higher RPM?s 2400, 2500, 2600 and 2700 RPM.

Balancing: Or the lack thereof, is the displacement of a rotating device (PROP and ENGINE) off the proposed circular track. This displacement is measured in units known as IPS (Inches Per Second). A small, a very small amount of weight being swung around at speed can create a very large displacement. And as the RPM increases so does the IPS; even though the weight has not changed. The effect of the weight has changed due to RPM.

How much vibration is too much? Whether you feel the vibration or not is NOT the way you determine if you should or need balancing, you must use the equipment. How sensitive are your toes or your fingers? Not sensitive enough to replace the equipment! Your plane will feel it, your instruments will feel it and you will feel the effects of it with Noise, Stress, lack of Concentration and Irritability. Just like sitting next to a crying baby on a long road trip. Solid-state instruments will take longer to show the effects but they do. The needle type instruments will show vibration with the needle bouncing around and in a fairly short period of time the jeweled bearings will fail. These instruments are: Attitude Indicator, Directional Gyro, Altimeter, VSI and the VOR needle; all expensive equipment.

A question was brought up: I put on about 55 hours on my plane and prop without dynamic balancing, did I do any damage? No, not yet. But my answer is considering what I have seen as normal or average amounts of vibration. Should you get it balanced? You bet ya! And you are playing a betting game? You are betting that no damage will be done. I?m betting it will be. Vibration Wins! You loo$e.

When balancing the prop, a reading of 0.07 IPS is considered EXCELLENT.
On the last job I did we started off with a reading of 0.35 IPS and finished with a reading of 0.02 IPS. Sometimes you can reach 0.00 other times you cannot. There are quite a few variables in balancing? Prop, Engine and all the associate attached equipment to the engine and plane. One job drove me crazy, I just could not get the vibration down. Then I LQQKed at the Starter Ring Gear? It was wobbling? It was 0.043? out of flat. And that was while it was still on the engine. I pulled the starter ring gear and put it on a surface plate, there it was 0.067? out of flat. The fellow had a real good friend with a spare starter ring gear and as if a genie granted a wish, the wobble and most of the vibration went away.

So, Flight, if you have any question, please ask. And if you are interested in getting a Dynamic Balance, I am located in NJ.

Clean side up, dirty side down,

Barry
[email protected]

Test Engineer, Mechanical Engineer & Electrical Engineer.
 
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