[David Paule]

Had the prop balanced yesterday. The FBO used a device made by ACES. We found out during the balancing that the device is hard-limited to stop when it gets to .07 ips. It simply refuses to go past that.

This is a relatively high value. You can probably feel the difference between that and something below .05 ips.

Check with the FBO before starting, and if they are using ACES equipment, find another place to do it.

I called ACES and was told that one of their devices and future devices will not have that limit. So in a few years this situation might resolve. But right now don't waste your money like I did.

Dave

 

[Walt]

Dave,
Even though everyone would like to see 0.000 IPS vibration, the fact of the matter is it's impossible to get there (you merely reach the machine limits) and anything below about .07 is not likely to be felt by pilot or passengers, which is probably why ACES did it that way (saves the tech time).

So if you balanced yours and you were over the limit and got it down to .07 that's not bad (and better than many shops will do, some will stop when they get to .1 IPS and call it good).

I strive to get them all at least in the .040 -.050 range or less. The Microvib system that I use goes out 3 digits and is not limited to any specific value (even though I've never gotten one to .000 this one was close at .016 IPS.

The customer below noted an immediate huge improvement, he was over twice the upper limit before balancing at .414 IPS

 

[Flybuddy2]

We purchased an ACES probalancer sport 2 years back. It does go below .07. Most of the a/c we've done (mainly RVs) come up from .01 to .05. When using it, it lists .00 to .07 as good and will stop at that point unless you punch in for it to continue. The manual states that you will not be able to feel any diff below .07 but it has the capability to go lower if desired.

 

[BJohnson]

OK dumb question time

Why is prop balance (vibration) measured in velocity units of inches per minute, instead of an amplitude (frequency comes from the RPM) or an acceleration term of i/s^2?

 

[DennisRhodes]

Vibration units

When comparing Vibration values in IPS ( inches per second) or Velocity units, You are able to compare apples to apples regardless of RPM. When you measure and indicate mills or another amplitude displacement valve you have to indicate at what RPM to be able to evaluate the seriousness of the imbalance. IPS or the velocity values seems to be the accepted units for talking vibration or unbalance. Get it below .07 or lower and your good to go at any RPM. And Yes the ACES equipment will go below .07 if you want to "continue"

 

[douglassmt]

NW Prop balancing

Anybody know where I can get my prop balanced in the Northwest?

 

[Walt]

Why is prop balance (vibration) measured in velocity units of inches per minute, instead of an amplitude (frequency comes from the RPM) or an acceleration term of i/s^2?

Dennis already nailed this but here's basically the same info worded differently, copied and pasted from someone smarter than me

IPS is just an acronym for "inches per second". When measuring a vibration, the velocity is the speed the object reaches as it passes through the center of the range of displacement. Similar to the highest speed a pendulum reaches at the center of its swing.
Velocity is arrived at by simply integrating the signal that an accelerometer produces. If you integrate a second time, you get displacement.

It has been found through experience that velocity is a better unit of measurement to use if you want the numbers to track with how severe a vibration is independent of RPM. In other words, a 1 IPS vibration is pretty severe no matter if the object is turning at 200 RPM or 200,000 RPM. This is not true for units of acceleration or displacement.

Now, for harmonic oscillation, the acceleration is just omega times the velocity; for, say 2400 rpm (fundamental frequency of 40 Hz), your vibration of 1 IPS corresponds to an acceleration of 20.9 ft per sec^2 or about 0.7 Gs. That does seem a fairly healthy vibration for the front end of an engine with propeller.

It takes on average 65 grams to correct for a 1 IPS vibration. But this value varies greatly from ship to ship. From a low of 20 to a high of 130