Prop Balancing

[Jabawocky]

I am sure many of us know how balancing rotating components is a good thing, but how many folk dynamically balance their props regularly.

We had a pretty good resul about 6 months ago, but today after doing annual inspection tasks we balanced again.....and what a result! Smooth as the proverbial babies bottom!

http://i849.photobucket.com/albums/ab58/jaba430/balanceprop8-5-11.jpg

All I can say is that until you have done this to your aircraft, you will not believe the benefits.

Happy Jaba :)

[VH-XXX]

Glad that it worked out for you Jaba.

I went through the whole dynamic balancing rigmarole on my Continental. It didn't turn out well. Was on my 2 blade timber and fibreglass MT prop. Ran it up 2,000 on the ground and had it absolutely perfect on the dynamic balancer. Put it back together and take off.... nothing short of terrible. It was "thudding" on every RPM. Back to the drawing board and balancer back on. Got it to 2,200rpm static (we had noise issues at the LAME with the neighbours so couldn't go higher). Perfect again, until takeoff. The only thing that I could think was wrong was that one blade was dodgey and was bending forward more than the other in flight.

Arrived back home after LAME, prop damaged day after when aircraft was parked.

Fitted new Sensinich prop and new hub. Vibration no better. Swapped prop around 180, rotated prop two prop holes and she was as good as new.

It's a bit of a black art, no offence intended.

[Jabawocky]

It is a science not a black art......but application of the science is the black art :bored:.

And you really must balance in the range of your typical cruise RPM. we were using between 2300 and 2350. Regardless of noise issues thats where you should have been too. Sounds like you had a real dud.

[mootyman]

Not to be pessimistic, but whenever I have had a reading like that the accelerometer is kaput.

[rioncentu]

I had mine done once but noticed no difference:(

[Jabawocky]

Mooty
When the folk leaning on the wings verify they feel the changes and we all knew before the number came up we knew it was going to be good! Accelerometer is fine.

Rio
As XXX has pointed out there is a black art to getting it right, I am fussy with wheel balance on my cars and can pick a few grams difference, it's a curse. Maybe yours was pretty good to begin with or you are more tolerant than many.

J:ok:

[BronteExperimental]

Been meaning to at least give it a go.
Anyone know of anyone in Syd Basin or within a few hundred miles who'll do it?
Cheers

[Connaught]

i agree in my experience a reading of 0.000 means somethin is broken, either accelerometer or the box needs a cal

best i have ever seen doing a dash 8 is 0.004 and the box was chasing the measurements (moving weight hole to hole)

[Old but not bold]

Hi,
Props on horizonally opposed motors need to be fitted near to right angle to the throw of the pistons. This is known as dynamic balance. I had a Cessna 170A for many years and a new Prop was fitted, it caused terrible vibration. Upon checking the Continental Manual it stated that the Prop had to be fitted with one blade at the 11 or 1 o'clock postion when the timing was at set at Top dead centre. After arguing with the Lame he altered it and it was smooth as silk.;)

[Brian Abraham]

Anyone know of anyone in Syd Basin or within a few hundred miles who'll do it?Get hold of a LAME at a helicopter operator who is up to speed. Balancing is their bread and butter, main and tail rotors - drive shafts as well.

[T28D]

Wooden propellors are almost always out of balance and affected greatly by moisture, balancing them is a black art but well worth the effort and should be done regularly.

[Jabawocky]

Sure is....... and leaving them in certain positions has significant effects on their fluid state!

The hartzell however seems less affected, but still benefits from regular checkups.

We flew it today and I, in fact all three of us involved were stunned with how smooth it was compared to before, and we balanced it pretty well last time.

Was almost like a glider!

So T28.....your beast would benefit greatly I imagine?

[A37575]

Talking about props. There was a 500 hour pilot who regularly flew a C152 on traffic monitoring. Despite the early hours he loved the work and it got him more log book hours. He seemed unconcerned that another Cessna he flew on the job had a re-occurring significant fuel leak with fuel stains dripping down the passenger side door and in the area of the flaps.

In the C152 he said he did reduced thrust take off's. He explained that during the take off run the RPM steadily increased at full throttle until he was forced to gradually pull back the throttle to avoid exceeding the red line limit on the RPM gauge. This was during the take off run.

Questioned further, he wasn't aware of anything unusual and had never heard of the term minimum/maximum static RPM or was aware of its significance. It was suggested that he should write up his observation in the aircraft maintenance release. He declined, saying he was worried he might lose his job especially as there was no shortage of pilots lined up to get the next vacancy. In any case he thought it might be nothing more than an inaccurate RPM gauge. Other pilots flew the same aircraft and all knew about the problem but ignored it.

Some weeks later CASA looked into the matter. It was revealed that the propeller blades had been filed extensively to smooth out nicks. Apparently this placed it out of tolerance in terms of accepted wear. On take off therefore, the engine was actually overspeeding and the RPM indicator was telling the truth. Inspection of the engine revealed damage caused by regular overspeeding.

[hurlingham]

Many years ago balanced the props on a PA31 that I did a lot of hours in - bloody wonderful - actually stopped headaches I was regularly getting after 6hour flights.
Continued to have them balanced on a regular basis.

[Unhinged]

Some LAMEs do a better job of this than others. I didn't think it would be the case, but some definitely seem to have a bit of a magic touch, and/or a good dose of we-don't-give-up-until-it's-spot-on !

[Jabawocky]

Unhinged, you would be spot on there. It takes a bit of understanding, patience and all things working in your favour. Good engine mounts and rubbers for a start.:ok:

[osmosis]

Some old but interesting reading here:

http://www.ultraligero.net/Cursos/varios/helice_de_una_pala.pdf

[LeadSled]

Folks,
If you are flying anything with a Rotax, and you have anything but the standard prop., for the aircraft, and/or you think there is a balance problem, be very careful.
There seem to have been a number of engine failures ---- broken crank and severe damage to the front main bearing, as a result of prop. changes or an out of balance prop.
Tootle pip!!

PS: Winrye at YSBK have the good gear, and know how to use it.

[Jabawocky]

Leadie :ok:

Spot on old chap!

Maybe you could advise the coroner in a reopened case about exactly why a Rotax crank would have failed when clearly the owner and guy maintaining said engine knew it had a sever balance issue for a long time before he killed himself.