Group dynamic balancing report

About 3 weeks ago I organized a group balancing day at Inyokern, CA. I had 4 people signed up however, only 2 showed up. I installed the sensors and started working. The results are indicated below.

First plane
Engine: O320 E2D
Prop: Catto 3-bladed (fixed pitch)
Initial Reading: 2228 rpms/0.48 IPS/ 115 deg phase angle
Number of runs req: 6
Final Reading: 2183 rpms/0.01 IPS/175 deg phase angle
Notes: Aircraft balanced at full power.

Second plane
Engine: IO360 EXP
Prop: Hart 2-bladed (constant speed)
Initial Reading: 2518 rpms/0.37 IPS/ 344 deg phase angle
Number of runs req: 7
Final Reading: 2510 rpms/0.01 IPS/024 deg phase angle
Notes: Owner selected 2500 rpms for balancing runs. Previous balancing (by me) was done at 2650 rpms.

It was a great day. I got to hang out with some RV guys, ate some good burgers, they checked out my project but most importantly they went home with a very close to perfect balancing job. Still shooting for that 0.00 reading that someone else on the board was able to obtain. Maybe the guys can give you guys a PIREP later. Pics below.

Thanks, Axel....

...I flew my -10 yesterday, for the first time since balancing it on Friday. Wow....nothing 'hums' at any RPM!

It's a very worthwhile investment, guys,

Best,

Axel.

Where did you put the weights,,,,,,,,,spinner bulkhead or the ring gear? I just di mine this weekend and settled on .04,,,,,,,,,I just could not get it dialed in any better.

what's an IPS?

HI Axel,
nice work, but what the heck did you do?
For a minute, I thought it was a seminar to help pilots get along with other 'normal' folks!
sounds like you balanced the prop, but I suppose there's more to it than that.
How different is it in flight?...can you balance with air loads?

thanks for educating us 'in the dark'.

9GT said:

Axel.

Where did you put the weights.

Click to expand...

Starter ring gear. On one airplane the unbalanced force was in-between two of the holes, so I added weight to both holes.

flyboy1963 said:

HI Axel,
nice work, but what the heck did you do?
For a minute, I thought it was a seminar to help pilots get along with other 'normal' folks!
sounds like you balanced the prop, but I suppose there's more to it than that.
How different is it in flight?...can you balance with air loads?

thanks for educating us 'in the dark'.

Click to expand...

Sorry about not being clear. An IPS is an inch-per-second. That is the way the unbalance forced that acts on the rotating components is measured. So when I say 0.20 IPS, that means that an unbalanced force is acting on all the spinning parts (engine/prop/spinner, etc..) at a specific phase angle and amplitude. The components may have been balanced individually but don?t work well together. Kind of like a balanced rim and a balance tire still have to get balanced together. At work, the bench mark for balancing our helicopters is 0.20 IPS and below.

Once you figure out the unbalance phase and amplitude you start putting weight opposite to that in order to reduce the amplitude. Kind of like the weights that are installed on car rims. Reducing that unbalance force basically improves the lifespan of your components, avionics, airframe and in some cases reduce aircrew fatigue. Hope that helps.

BTW, my wife bought me a doormat that says ?a pilot and a normal person live here". I don't think pilots and normal folks will ever get along due to stunts like that.

Our EAA chapter has been discussing buying a prop balancer for years. How hard is it to learn to use one and do you recommend the one you have. Where did you get it?

Sam Butler
Rv 7A
Chapter 983

AX-O said:

BTW, my wife bought me a doormat that says ?a pilot and a normal person live here". I don't think pilots and normal folks will ever get along due to stunts like that.

Click to expand...

Hmmmmmm, I always thought the non pilots were the abnormal ones...............

sabswbc said:

Our EAA chapter has been discussing buying a prop balancer for years. How hard is it to learn to use one and do you recommend the one you have. Where did you get it?

Sam Butler
Rv 7A
Chapter 983

Click to expand...

Sir, I bought this one. http://www.rpxtech.com/rpxweb/default.asp It works well however, you need to understand what the unit is telling you and once you make the changes, understand the results and make appropriate corrections.

I wrote an article regarding my initial impressions of the unit. I will try to find the magazine and scan it.

Mike S said:

Hmmmmmm, I always thought the non pilots were the abnormal ones...............

Click to expand...

Me too...

Found the article I wrote. I don't have any ties to this product other than buying it. Kind of long write up.

As you know, dynamically balancing propellers/rotors has always required some type of black magic, a level of experience and occasionally the luck you wish for, while you are gambling in Las Vegas. In my line of work I have seen maintenance crews chase their tails for days and sometimes weeks trying to balance tail rotors and main blades.

Although this feedback is specific to the fixed wing DynaVibe balancer, the information provided is pertinent to other platforms, including helicopters. Prior to performing these tests I had no experience with the DynaVibe balancer. My first impression upon picking up the unit was the quality and ergonomic design appeared high. It looked as if the manufacturing was of good quality and it fit on my left hand comfortably. The unit also had batteries installed so, it was only necessary to connect the sensors and quickly power up. The unit indicated zero RPMs. I fixed that by waiving a piece of reflective tape (included in the kit) in front of the infrared sensor. In a few waves of the tape, I had RPMs. Everything seemed simple enough.

Brackets were required to mount the photo sensor and the velocimeter. The bracket was fairly easy to make. The bracket mounts to one of the engine-case bolts, locates the velocimeter in the Y axis (up/down measurement) and locates the infrared sensor in the X axis (looking towards the back of the prop).

A friend was very glad to be the guinea pig having his prop balanced for free and quickly made a plane available. I drove down to Chino, California from this beautiful Mojave Desert. The plane was ready (no cowlings) when I arrived. We bolted the bracket with the velocimeter and infrared sensor to the engine case. Made sure all the sensors were appropriately lined up and zipped tied the sensor cables.

I lined up the aircraft after looking at the wind direction and sun angle; avoiding any sun interference with the photo sensor is important. The aircraft was chained to a full size truck and two adult males held the tail down. Hooked up the two cables to the DynaVibe balancer, put the tape on the back of the prop and moved the prop by hand to get an RPM reading. We were ?good to go?. The DynaVibe balancer instantly started to read RPMs. The engine was set to cruising RPMs and I took two averaging readings. Each average reading required two presses on the same button. The first press to take the average, the second press to reactivate the balancer. The engine was shut down and the ?black magic? began.

The screen indicated 2550 RPMs and 0.46 IPS at 356 degree phase angle. The guidance that we use at work is 0.20 IPS or below (same as with the DynaVibe balancer). The data displayed was shown in an intuitive format and was readable even in direct sun light. I started my trial, error and experience process portion of this project by changing weight and configurations. It took nine runs to get the prop/engine combo balanced on the first plane. Two runs on the second plane and three runs on the last plane. Turns out when you are doing free prop balancing, people just seem to show up out of no where and become your best friend. On my best balancing job I was able to lower the IPS to 0.09.
With limited balancing experience and very little time using the DynaVibe balancer, I leave you with some lessonslearned:

- The phase angle is measured in the direction of the prop rotation.
- Add weight at 180 degree from the phase angle reading. Or remove weight at the phase angle reading.
- Try to add the weight as close as possible to the location identified by the DynaVibe balancer. The flywheel had provisions for weight at every 30 degree. I rounded the phase angle up or down to the closest 30 degree location, then placed the weight there.
- If the phase angle changes by more than 180 degree after you added weight, then you added too much weight to that location. Remove some weight.
- If the IPS decrease and the phase angle remains in the same quadrant as your initial reading, you can continue to add weight to that location. - If the amount of weight added is the least possible due
to AN hardware limitations, try shifting the location of the weight.

All and all, the DynaVibe balancer was ergonomically pleasing, intuitive to use and had simple human interface functionality. With experience and a little black magic you should be able to balance your prop/rotor in an acceptable amount of time.

Editor?s note: The DynaVibe is the product of a designer with more than a little experience developing and fielding a dual channel balancing device used on helicopters. Based on this, the quality of the DynaVibe was expected to be high. A small pre-test was run on my bench-test set up and the DynaVibe performed quickly and accurately. This unit was designed specifically for the ?Stuck Wing? application. For helicopter work it would help to have a remote ?averaging? switch capability to allow hands on flight controls operation. Congratulations to Matt Dock on another good vibration instrument.

Axel Alvarez background:
Aerospace Engineer
Graduate of United States Naval Test Pilot School
Commercial pilot
10 yrs. Flight test engineer on numerous fixed and rotary wing aircraft

WOW!

I'm very impressed with the job Axel is doing. When I look at other prop balance entries... they have been known to say "balanced at 0.07 IPS" What a crock... I'm not going to mention names but you should be able to get it down under 0.05. Axel is doing a FANTASTIC JOB!!! I'm the one who got a 0.00 on the machine, as seen on the testimonials page for the prop balancer. http://www.rpxtech.com/rpxweb/Dynavibe-Testimonials.asp
I took a picture of it because I knew it was going to be a rare animal to see. The quote should of said 0.90 IPS instead of 0.09. It was shaking pretty good when we got a hold of it.
Kudos to Axel!

Best
Brian Wallis

I was going to post this on Brian's thread but did not want anyone to take it the wrong way.

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Just a side note regarding IPS that low. It takes time, effort, patience, know-how, luck and other factors to get IPS that low. I don?t want the VAF crowd to assume that type of solution is always possible. Sometimes due to the limitations on where you can place the weights (depending of the method being used), it is just not possible. I talked to the makers of my balancer this week and they told me most certified aircraft stop at 0.10 IPS. At work, 0.20 IPS is good enough to fly an attack helicopter. If you get your prop/engine balance and you don?t get that low of numbers, please don?t assume the person does not know what they are doing. He/she may be limited on what they can do.

One thing to consider on fixed pitch props is that they normally can only reach about 2200 RPM. A .03 IPS balance does not mean a .03 balance at 2500 RPM.