Prop Balance and Murphy

wrote:
On Mar 17, 6:52 pm, nrp wrote:
On Mar 15, 8:32 am, Peter wrote:

What also suprises me is how bad brand new props can be, despite
having been statically balanced *supposedly* very accurately.
In my life I've purchased two brand new McCauley fixed pitch props.
Both were substantially out-of-balance as they came out of the box,
and both were fixed by a local prop shop. I am amazed the prop shop
(Maxwell) could do better given their comparatively crude tools. Must
just be skill & attention to detail.

This flys in the face of the "FAA certified parts are perfect" theory.
One would think after spending several thousand dollars on a piece of
forged aluminum that might cost 200 bucks in raw materials that the
remaining costs are for the manufacturer to deliver a high quality
product. The fact that a local prop shop with crud tools can balance
it better then the manufatcturer is laughable......... JMHO..

Ben

The same goes for the engine manufacturers. I put six new Millenium
cylinders on about a year and a half ago, all the pistons within 1 gram.
On a typical Continental they don't really care how much the pistons
weigh.

The same goes for the engine manufacturers. I put six new Millenium
cylinders on about a year and a half ago, all the pistons within 1 gram.
On a typical Continental they don't really care how much the pistons
weigh.

I don't have any love for Continental....But.....It is MUCH more important
to balance rotating parts than reciprocating.

"It is MUCH more important
to balance rotating parts than reciprocating."


I challenge that. Acceleration of a mass (or mass error) creates the
same dynamic force whether in a rotating motion or in moving in only a
translational motion. The only difference is that the force direction
is changing vs just reciprocating.

One gram may be overly accurate but it is something that is easily
achieved. I recall a Continental paper that said though that they
deliberately built up an engine with one pound (!) heavier piston & it
ran "satisfactorily".

Yeah, I'll bet......!

On Mar 18, 1:58 pm, nrp wrote:
"It is MUCH more important
to balance rotating parts than reciprocating."

I challenge that. Acceleration of a mass (or mass error) creates the
same dynamic force whether in a rotating motion or in moving in only a
translational motion. The only difference is that the force direction
is changing vs just reciprocating.

One gram may be overly accurate but it is something that is easily
achieved. I recall a Continental paper that said though that they
deliberately built up an engine with one pound (!) heavier piston & it
ran "satisfactorily".

Yeah, I'll bet......!

If one cylinder is oversized by .010" , the opposing cylinder
gets it, too. The heavier .010" oversize piston will throw everything
out of whack otherwise.
A one-pound heavier piston would run satisfactorily to someone
else, not to most of us. It would shake pretty good. Might get you
home, but that's about it.

Dan

If one cylinder is oversized by .010" , the opposing cylinder
gets it, too. The heavier .010" oversize piston will throw everything
out of whack otherwise.
A one-pound heavier piston would run satisfactorily to someone
else, not to most of us. It would shake pretty good. Might get you
home, but that's about it.

A .010 inch oversize piston doesn't necessarily have to weigh more.
And the piston area is less than 1 percent larger than standard. I
don't think that would cause a rough engine, as typical ignition
timing and mixture distribution variances will be much greater than
that.

But, a single 1 pound piston mass imbalance would give a typical
engine crankcase vibration of about 3 ips, which would obviously be
pretty rough to most of us.

wrote:
On Mar 17, 6:52 pm, nrp wrote:
On Mar 15, 8:32 am, Peter wrote:

What also suprises me is how bad brand new props can be, despite
having been statically balanced *supposedly* very accurately.
In my life I've purchased two brand new McCauley fixed pitch props.
Both were substantially out-of-balance as they came out of the box,
and both were fixed by a local prop shop. I am amazed the prop shop
(Maxwell) could do better given their comparatively crude tools. Must
just be skill & attention to detail.

This flys in the face of the "FAA certified parts are perfect" theory.

That's a new theory to me. I thought FAA certified was
more about initial testing, documentation and accountability.

I'm a serious woodworker

Dang. You can afford to fly AND do wood work? I've got a basement full of
serious power equipment that has nary been touched since I learned to fly 14
years ago. With the price of cherry, building a dresser works out to way
too many AMUs for me to justify doing both.

You must be one of dem "rich playboy pilots"...

;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"