MustangFan

O.K. .... you win .... I'll balance ..... your correct.

I hope this ends the attack.

Flyboy Dave

My Feedback: (21)

Yo, Fellas....

....why mess up a good wood prop trying to sand some weight
off the heavy end....? Try the FBD method....

....take some medium sand paper, and sand some of the shellac
off the backside of the "light side" of the prop....right in the middle.
Smear some epoxy into the sanded surface with you finger,
get it down nice and tight. You have to be kinda quick if your
using 5 min epoxy.

Leave the prop right in the stand....when the epoxied side gets too
heavy....quickly start removing just a touch at a time with your
finger until it balances level in the stand.

I balance ALL my props to within a gnats rear end....as well as the
spinners and backplates. Next time you use a new inexpensive
metal spinner....put the parts on the balancer....your gonna be in for
a big suprise....[X(]

Dave.

JWN

My Feedback: (42)

Good point on the spinner Dave. I used to fly with a guy who had an old CB Associates aluminum spinner that was so out of balance, he could not remove enough material without making the spinner unusable.

John

Flyboy Dave

My Feedback: (21)

Here's another slightly out of balance backplate....[X(]

pe reivers

I balance all my props. Not because an out of balance prop will destroy bearings, but it sure will destroy planes and equipment.
I balance the following items, and in this sequence in the larger props:
Blade angle
Blade geometry
Tip to tip weight
Hub cross weight

In Mejzliks, I only need to slightly adjust hub cross weight. With Menz-S I had to do all four items.

In support of Dar and Hobbsy,
Prop unbalance always is a rotary force, so it will never completely cancel out reciprocal and highly unlinear piston mass motion. The prop being in a different plane makes it next to useless to compensate for lacking engine balance.
Chances are, you'll make things worse with unbalanced props. The chance to make things better are the same like the uncle who smoked a few packs a day and lived to be 90.

Motorboy

Never thrust all propeller are well balanced from factory! Well balanced propeller will engine and plane last longer.

Hobbsy

My Feedback: (102)

Thanks Pe, I was a fairly young man when this thread was started.

pe reivers

yep! My beard has grown white since. The thread is worth keeping alive though. Prop balancing is a much neglected item. With growing engine sizes it becomes even more important. My props of 20" and over balance so that a small snippet of paper will offset it.

RaceCity

CB = "Can't Balance".

Balance everything, and leave the junk spinners in the hobby shop.

JollyPopper

My Feedback: (6)

How do you know they're junk spinners unless you take them out of the hobby shop and try them?[&o][]

rambler53

My Feedback: (494)

I've talked to guys that race nelsons (24000 rpm on the ground) and naturally with rpm like that, they religiously balance props that are 8". There is a mark on the drive washer indicating a point of reference for mounting the prop I was told, if I heard right. A single cylinder engine doesn't sound to me like you can get it dynamically balanced on a 2 stroke, plus with the energy from the combustion stroke. Am I wrong? Twin cylinder engines aren't evenly firing either. I balance my props and take material off the tip, but a pylon racer told me he removes material from the prop on the face so he doesn't alter the arc line. I think the arc line is not nearly as important as maintaining integrity to the airfoil and how can you possibly sand the face of the prop by hand and accomplish that integrity? I guess I'm asking questions more than giving answers. I note hardly any vibration I can detect on smaller props, and if I forget to balance a 14" prop on my Saito, the whole plane looks like it's going to hover from all the shaking. I can tell when I miss one real fast on the bigger props, and who knows which are balanced on my 10" props, can't tell until I put them on the balancer. Love that magnetic one Tower sells by the way. I had a Robart one and was able to get it further balanced or more precisely using the magnetic one. Frictionless. Is balance done by removing material on the tip the best way to go?

http://www3.towerhobbies.com/cgi-bin...&I=LXHY61&P=ML

onewasp

Just 'happened' to drop by this thread------------Hard to believe anyone is debating it------------Had they come from reed days you were a dead man without a balanced prop.

Back then we had to build our own balancers and then balance the props.
You should see how an unbalanced prop would make a reed bank 'dance' ----- and with each 'dance' an uncalled for control movement.

Simply can't imagine anyone actually debating the issue-----

DarZeelon

Quote:

Twin cylinder engines aren't evenly firing either.

Horizontally-opposed twin cylinder engines (with one exception that I know of, the early '80s Taiwanese G-mark) are either even-firing four-stokes, or simultaneous-firing two-strokes. That G-mark was an even-firing two-stroke... Very off-balance.
The vast majority of model twins are horizontally-opposed.

Most in-line and V twins really are not even-firing.

The vibration levels of horizontally-opposed twin cylinder engines, are usually the result of the pistons not moving within the same plane; with one being situated slightly to the rear of the other.
So, even though both pistons reach TDC and BDC at the same instance and have identical acceleration levels at all points in their cycle, the engine in whole will still vibrates around its vertical axis.

This cannot be 'canceled' by a non-balanced prop, so a good level of prop balance is important, but I believe any finger-tip balancer will achieve sufficiently good results. No need for 'an investment' in a magnetic balancer.

blw

My Feedback: (3)

Dar, I've used a finger balancer carefully while set on top of two drinking glasses. It will only get you somewhat in the ballpark. I later bought an inexpensive Dubro balancer, and found that my props balanced with the finger balancer were off by a good margin. It is a good investment when considering the power losses and vibrations without one.

DarZeelon

Barry,


If a finger-tip balancer has its threaded 'shaft' and both cones; all straight and completely concentric, there is no reason it should be off by anything...

I balance all my props with the one I bought from Tower Hobbies, some some 10 years ago.

The Bolly props I had sent to you and to Dave Hobbs were all checked using this balancer.

None of them needed any actual balancing work done; after just de-slagging the leading and the trailing edges of both blades.


Dave had remarked in the past that their balance was perfect.

rambler53

My Feedback: (494)

$19.99 isn't a big investment for a good balancer. To each his own.

DarZeelon

Quote:

Saito 100 twin, didn't fire 180 degrees.

True, that is another exception to the rule that I did not recall...

I added nothing to the issue of where to trim from the prop, because from where I'm looking, the prop may increase vibrations, from 'trying' to spin in its own dynamic balance plane.

...Just another 'degree of freedom' to tend to... I don't need that!

I just do what I feel is best, around the prop's theoretical rotation axis, using the balancer of my choice; and consider all else too minor to care about.

With the 'natural imbalance' of all single-cylinder engines that I use, a minute prop imbalance, to the scale of less than one milligram, really is not worth loosing any sleep over... Even at 30K... I am not racing against anyone.

HighPlains

My Feedback: (1)

The drive washer/spinner backplate for racing Nelsons and Jetts are made out of balance to augment the counter balance on the crank. It has to be positioned correctly to run smoothly. In the past, some racers would balance the prop with a measured piece of tape on one blade and then remove the tape after balancing to operate with an unbalanced prop. Due to the fairly small light wood blades, you could actually run with a very unbalanced prop with the heavy prop on the counterbalance side quite smoothly on a racing 40.

rambler53

My Feedback: (494)

Thank you for an experienced reply! Adding tape to the light side would make good sense rather than sand off the heavy side then for us 14000 rpm sport engine users? Ima never tink of dat.

HighPlains

My Feedback: (1)

No, you misunderstood what I said. They would put the tape on and then balance the prop by sanding. When it balanced with the tape, they took the tape off. It was used to establish a fixed imbalance.

However, some of the price tags stick so well to the props, that stuff would work to balance a prop.

blw

My Feedback: (3)

Dar-

The best thing is to use what you like to use. I have only flown one of the Bollys, and I can't remember any details on balancing it. I just looked and found scrub marks on one blade where I always shave them if needed.

Balancing is something I've always done since almost losing an engine with a 3 bladed prop way out of balance. Also must be from all of the balancing that had to be done on helicopters. 8^)

rainedave

My Feedback: (1)

I can't think of a single reason not to balance every prop I use. It takes about two to five minutes. It can reduce the risks of several things happening to your plane such as fuel foaming, radio equipment failure, structural weakening, premature engine wear and noise. There are others.

Other than saving a few minutes what could possibly be the advantages to not balancing props? What could one gain by not doing it?

David