Prop Balance and Murphy

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.

*Must
just be skill & attention to detail.

Exactly... Look at the fine cabinetry for the nobility made in the
1700-1800's.... No rulers, no micrometers, no lasers, no power tools,
only crude hand tools and skill...


denny

Denny wrote:
Must
just be skill & attention to detail.

Exactly... Look at the fine cabinetry for the nobility made in the
1700-1800's.... No rulers, no micrometers, no lasers, no power tools,
only crude hand tools and skill...

Waaaaait a minute! G

I'm a serious woodworker, and the guys who made stuff for nobility back
then most certainly did have good tools!

1.) Wooden hand planes, some with metal mechanisms, go back to the
Greeks and Romans, as does metallurgy for making cutting tools. There
were many fine tool examples made in the 17 and 1800's. Basic tools,
like squares, go back thousands of years, and are easily made by the
user and calibrated to themselves.

2.) They had rulers back then, but they weren't made by Starrett or
Brown & Sharpe. G A ruler is simply an arbitrary measuring device.
If you use the same measuring tool to make an item, the tool doesn't
need to be accurate to a specific standard.

Furniture fits people, items made for specific people (the King), were
made to that person's preferences. Parts like doors and drawers are
made slightly oversize and hand fitted to specific openings. This is
still done today, with fine, very high-quality work.

Specific measurements are not important until interchangeability of
parts (factory production) becomes a requirement. Much furniture and
cabinetry is built with a measuring device called a "story stick". A
modern example of a simple story stick are the red 16" and black 19.2"
stud spacing markers printed on measuring tapes for framing buildings.

3.) You don't need micrometers for woodworking. They get used for
setting up precision machinery, not for measuring the wood.

4.) Water powered machines were available at that time for such tasks as
heavy sawing.

5.) Low cost apprentices, and sometimes slaves, were plentiful. Who
needs machines when you have 100 helpers?

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"

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

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.