Propeller Balancing

[[email protected]]

Is your airplane fitted with pneumatic wheels? The odds are, it is.
That means you probably have tools in your kit that allow you to
remove the wheel, remove the tire & tube from the rim, to re-install
them, inflate the wheel and so forth. Indeed, if you're a serious
airman you give your the same degree of attention you devote to the
engine and air-frame, which means you have the tools and fixtures
needed to maintain your wheels.

All of that also holds true for wooden propellers. Not only do you
pay careful attention to its finish, protecting it with a waterproof
sleeve when it must be parked out in the weather, you have the means
of periodically refinishing and balancing your propeller.

With regard to balancing, go here...

.....http://www.youtube.com/watch?v=uw95sC3keQs

.....and watch the video a time or two. The video shows balancing the
prop by installing a relatively massive amount of weight very near the
center of rotation. That is, he's using a very short radius.
Another common method is to use an additional coat of paint or varnish
near the TIP of the LIGHT blade. That is, using a relatively small
weight having a relatively LARGE radius. Both methods work equally
well but the small-mass/large-radius is better suited for the amateur,
in my opinion, since it calls for fewer tools and parts (ie, drill
bit, drill motor, lead slug of suitable size, wooden plugs and so
forth.).

Right now you don't have a prop to balance but I want to make you
aware of the things you WILL need, not just when making a propeller
but when MAINTAINING your propeller in the years to come.

The most important of those things is the BALANCE STAND and the
BALANCE BAR.

The Balance Stand is literally anything that can hold a pair of knife-
edges at PRECISELY the same height. Here in the States it is common
to use joiner blades as the knife edges and a section of precision-
ground oil-hardening steel for the balance bar.

There is no requirement to spin the propeller round & round on it's
balance bar; you only need to see which blade is heavier, which means
the Balance Stand may be a bench-top device, such as a pair of
accurately cut boards that have been grooved to accept the router
blades. The 'truth' of the jig is determined by placing a straight-
edge across the pair of knife edges and using a precision protractor
or level to ensure the blades are level. Nowadays, if you have the
money, you would probably use a digital protractor, most of which are
accurate to a tenth of a degree. Or you can use the old fashion
method which consists of a carpenter's framing square, a bit of thread
and a plumb-bob.

The point that needs to be made here is that your propeller balancing
tools are something you will use periodically, not just when you carve
a propeller. Just as you keep a set of tools specific to your landing
gear tires and wheels, so too must you keep a kit of tools specific to
balancing your prop.

-R.S.Hoover

[Stuart Fields]

> wrote in message
...
>
> Is your airplane fitted with pneumatic wheels? The odds are, it is.
> That means you probably have tools in your kit that allow you to
> remove the wheel, remove the tire & tube from the rim, to re-install
> them, inflate the wheel and so forth. Indeed, if you're a serious
> airman you give your the same degree of attention you devote to the
> engine and air-frame, which means you have the tools and fixtures
> needed to maintain your wheels.
>
> All of that also holds true for wooden propellers. Not only do you
> pay careful attention to its finish, protecting it with a waterproof
> sleeve when it must be parked out in the weather, you have the means
> of periodically refinishing and balancing your propeller.
>
> With regard to balancing, go here...
>
> ....http://www.youtube.com/watch?v=uw95sC3keQs
>
> ....and watch the video a time or two. The video shows balancing the
> prop by installing a relatively massive amount of weight very near the
> center of rotation. That is, he's using a very short radius.
> Another common method is to use an additional coat of paint or varnish
> near the TIP of the LIGHT blade. That is, using a relatively small
> weight having a relatively LARGE radius. Both methods work equally
> well but the small-mass/large-radius is better suited for the amateur,
> in my opinion, since it calls for fewer tools and parts (ie, drill
> bit, drill motor, lead slug of suitable size, wooden plugs and so
> forth.).
>
> Right now you don't have a prop to balance but I want to make you
> aware of the things you WILL need, not just when making a propeller
> but when MAINTAINING your propeller in the years to come.
>
> The most important of those things is the BALANCE STAND and the
> BALANCE BAR.
>
> The Balance Stand is literally anything that can hold a pair of knife-
> edges at PRECISELY the same height. Here in the States it is common
> to use joiner blades as the knife edges and a section of precision-
> ground oil-hardening steel for the balance bar.
>
> There is no requirement to spin the propeller round & round on it's
> balance bar; you only need to see which blade is heavier, which means
> the Balance Stand may be a bench-top device, such as a pair of
> accurately cut boards that have been grooved to accept the router
> blades. The 'truth' of the jig is determined by placing a straight-
> edge across the pair of knife edges and using a precision protractor
> or level to ensure the blades are level. Nowadays, if you have the
> money, you would probably use a digital protractor, most of which are
> accurate to a tenth of a degree. Or you can use the old fashion
> method which consists of a carpenter's framing square, a bit of thread
> and a plumb-bob.
>
> The point that needs to be made here is that your propeller balancing
> tools are something you will use periodically, not just when you carve
> a propeller. Just as you keep a set of tools specific to your landing
> gear tires and wheels, so too must you keep a kit of tools specific to
> balancing your prop.
>
> -R.S.Hoover

Mr. Hoover. I watched the youtube and noticed that he balanced with the
lead slug and then added some more weight with the wood plug and then didn't
check his balance again. I've electronically balanced my helicopter tail
rotor, which BTW turns at 2700 rpm and got it down real close and then added
my cotter pin to the bolt washer system I was using for the added weight.
In my case I was also in close to the rotor center. The weight of the cotter
pin was quickly noted by the electronic balancer. I agree with you I would
rather use an additional coat of paint on the tip.

Stu Fields

[Stealth Pilot[_2_]]

On Fri, 12 Dec 2008 12:41:33 -0800 (PST), "
> wrote:


>blades. The 'truth' of the jig is determined by placing a straight-
>edge across the pair of knife edges and using a precision protractor
>or level to ensure the blades are level. Nowadays, if you have the
>money, you would probably use a digital protractor, most of which are
>accurate to a tenth of a degree. Or you can use the old fashion
>method which consists of a carpenter's framing square, a bit of thread
>and a plumb-bob.
>
>The point that needs to be made here is that your propeller balancing
>tools are something you will use periodically, not just when you carve
>a propeller. Just as you keep a set of tools specific to your landing
>gear tires and wheels, so too must you keep a kit of tools specific to
>balancing your prop.
>
>-R.S.Hoover


what I'm about to tell you is illegal in the country of origin but I
do it once or twice a year because to not do it is stupidly dangerous.

honestly you dont need planer blades.
I use two 6 or 8 inch wide hardwood plank sections that have been
dressed all round in a commercial planer.
the pivot of my balancer is a polished half inch diameter rod that was
originally a part of a photocopier.

I have machined from half inch 6061 aloooominum two tapered conical
sections that achieve a jamb fit in each side of the propeller boss
hole and are a slop free slide fit on the shaft.

The principal requirement in machining these conical sections is that
all machining is done at once without taking the workpiece out of the
lathe, that way the entire component cant help but be precisely
concentric.

in use I sit the two boards on the kitchen table after giving them a
dust off. I use a torpedo bubble level to check that the tops are
level. The rod is fed through the middle of the prop and the two
conical sections are fed over the rod and jambed into the prop's
central hole.

I sit the assembly on top of the boards, close all doors and windows
to prevent any slight breezes, and wait for the heavy blade to
descend. it is sensitive enough that a quarter of a typical 'post it'
note gummed on the end of one prop blade will make that blade descend.

I add paint or varnish from a rattle can to achieve balance. allow it
to dry a few hours then recheck.

using this technique I achieve a vibration free engine installation
for months on end.

btw there is no point in using different length screws on the spinner
and expecting the thing to remain balanced.

if you have a wooden prop and you maintain it you will have something
that can outlast the airframe.

Stealth Pilot

[[email protected]]

Dear Stealth (and you other guys, too)

Thank you for telling us how you do it. I wish more people would
share, because the truth is, you don't need a lot of stuff to detect
an imbalance in a two-bladed prop.

What's needed is some means of reducing the contact area between the
prop and its support so that a relatively small amount of imbalance
( I use cigarette papers ) will be enough to cause the heavy limb or
blade to drop. Indeed, a prop may be balanced using a support built
entirely of wood. Other successful balancers I have seen used string
( !! actually, a fairly strong twine ), safety wire, water pipe and so
on.

The pipe affair was rather interesting. Until I saw it, I'd failed to
appreciate that a round section contacting another at right angles was
dealing with a relatively small area of contact -- small enough to
provide the sensitivity needed for the fellow's propeller.

The method described in my original post (above) was aimed mostly
toward the Chugger People, in that I assumed a table saw was
available. The planer blades are commonly available from Harbor
Freight, a retailer here in the States. Three-quarter inch dia bar or
tube is commonly available from a variety of sources... but they could
always use a smaller rod & cones, etc.

What really needs to be conveyed, in my opinion, is the mechanical
principles that we are working with. Once a person understands the
How behind the Why, the world becomes literally filled with 'propeller
balancers.' Or even Piston balancers... connecting rod balancers...
and so on. I see the Hat Trick as getting the message across without
losing the person's interest... adding a dose of humor to the physics
if need be.

Oddly enough, there are those who feel the only proper way to teach a
subject is to stick to the fundmentals. No humor allowed. These
people insist that the humor dilutes the message, and since 'these
people' are often professional educators, they win by default.

-R.S.Hoover

[[email protected]]

I use a balancing stand made from shelving angle. The angle is
about 1.5" x 1.5" and has slots that allow you to bolt together just
about anything. I ran a file across the critical edges, draw-file
fashion, to level and smooth them. It works fine.

I found, with the wooden prop off my Jodel, that it was out of
balance *chordwise*, not spanwise. The maker had drilled the center
hole off by about 3/32" and the bolt hole circle is radiused from
that, so the whole prop was/is orbiting the crank axis just a little.
My shelf-angle stand is tall enough that I can support a prop
vertically as well as horizontally to catch such imbalances.

Of course, we now have a Chadwick-Helmuth electronic balancer that
does the analysis with the engine running. Washers and small hardware
are attached at the specified place on the spinner backplate. Makes a
big difference. Saves instruments and radios.

Dan

[Stealth Pilot[_2_]]

On Sat, 13 Dec 2008 15:38:06 -0800 (PST),
wrote:

> I use a balancing stand made from shelving angle. The angle is
>about 1.5" x 1.5" and has slots that allow you to bolt together just
>about anything. I ran a file across the critical edges, draw-file
>fashion, to level and smooth them. It works fine.
>
> I found, with the wooden prop off my Jodel, that it was out of
>balance *chordwise*, not spanwise. The maker had drilled the center
>hole off by about 3/32" and the bolt hole circle is radiused from
>that, so the whole prop was/is orbiting the crank axis just a little.
>My shelf-angle stand is tall enough that I can support a prop
>vertically as well as horizontally to catch such imbalances.
>
> Of course, we now have a Chadwick-Helmuth electronic balancer that
>does the analysis with the engine running. Washers and small hardware
>are attached at the specified place on the spinner backplate. Makes a
>big difference. Saves instruments and radios.
>
> Dan
>

dan you've mentioned a *very* important point. when making a prop, cut
the blank to outline shape then drill the hub holes.
the hub holes and the back face of the prop then become the datums to
work from. that way you get the prop evenly disposed about the hub
hole and boss.
if you dont have a prop that is symetrical about the centre you have a
clock mount for the wall.

the chadwick-helmuth 'little finger extended while drinking tea'
balancer may have achieved static and dynamic balance for you but what
of the asymetric thrust??
it would be an interesting prop to watch you fly behind. (while
standing on the ground) must make some interesting noises.

for veedubber; the critical thing to find out with any balancer that
is home made is whether a very light weight added to a tip moves the
prop. I was amazed that mine moved with quarter of a post it note.
indeed experimentation has shown that balancing a prop in a room full
of still air is far more important than knife edges.

Stealth Pilot

[Peter Dohm]

"Stealth Pilot" > wrote in message
...
> On Sat, 13 Dec 2008 15:38:06 -0800 (PST),
> wrote:
>
>> I use a balancing stand made from shelving angle. The angle is
>>about 1.5" x 1.5" and has slots that allow you to bolt together just
>>about anything. I ran a file across the critical edges, draw-file
>>fashion, to level and smooth them. It works fine.
>>
>> I found, with the wooden prop off my Jodel, that it was out of
>>balance *chordwise*, not spanwise. The maker had drilled the center
>>hole off by about 3/32" and the bolt hole circle is radiused from
>>that, so the whole prop was/is orbiting the crank axis just a little.
>>My shelf-angle stand is tall enough that I can support a prop
>>vertically as well as horizontally to catch such imbalances.
>>
>> Of course, we now have a Chadwick-Helmuth electronic balancer that
>>does the analysis with the engine running. Washers and small hardware
>>are attached at the specified place on the spinner backplate. Makes a
>>big difference. Saves instruments and radios.
>>
>> Dan
>>
>
> dan you've mentioned a *very* important point. when making a prop, cut
> the blank to outline shape then drill the hub holes.
> the hub holes and the back face of the prop then become the datums to
> work from. that way you get the prop evenly disposed about the hub
> hole and boss.
> if you dont have a prop that is symetrical about the centre you have a
> clock mount for the wall.
>
> the chadwick-helmuth 'little finger extended while drinking tea'
> balancer may have achieved static and dynamic balance for you but what
> of the asymetric thrust??
> it would be an interesting prop to watch you fly behind. (while
> standing on the ground) must make some interesting noises.
>
> for veedubber; the critical thing to find out with any balancer that
> is home made is whether a very light weight added to a tip moves the
> prop. I was amazed that mine moved with quarter of a post it note.
> indeed experimentation has shown that balancing a prop in a room full
> of still air is far more important than knife edges.
>
> Stealth Pilot

I agree with you regarding the proper proceedure, and also believe that a
multi-blade propeller that is not concentric may contain additional hidden
flaws--such as voids--and likely does. Such a blatant lapse in workmanship
and inspection should clearly be viewed as a "warning shot across the bow!"

However, I also suspect that far too much can be made of the eccentric
thrust problem.

Over the decades, there have been a number of experiments with single blade
propellers--primarily on helicopters--with an opposing counterweight. While
my intuitive reaction was to question the probable bending force applied to
the crank shaft--or drive shaft--I have never actually heard of that being a
problem.

Therefore, I can only presume that the lack of popularity is due to other
factors, such as:
1) Reduced capacity for any given disk area.
2) Poor streamlining at speed in airplane propeller applications.
3) Strange appearance.

OTOH, it does make variable pitch ridiculously simple!

Peter

BTW, I still can't quite accept the idea either.

[[email protected]]

On Dec 14, 4:18 am, Stealth Pilot >
wrote:

> the chadwick-helmuth 'little finger extended while drinking tea'
> balancer may have achieved static and dynamic balance for you but what
> of the asymetric thrust??
> it would be an interesting prop to watch you fly behind. (while
> standing on the ground) must make some interesting noises.

It's not noticeable. The pitch is symmetrical, and the
chordwise offset, being as small as it is, just causes the airflow
across the blades to have a very small difference in chordwise angle.

Dan

[[email protected]]

On Dec 14, 3:18*am, Stealth Pilot >
wrote:

> for veedubber; the critical thing to find out with any balancer that
> is home made is whether a very light weight added to a tip moves the
> prop. I was amazed that mine moved with quarter of a post it note.
> indeed experimentation has shown that balancing a prop in a room full
> of still air is far more important than knife edges.
> ------------------------------------------------------------------------------------------------------------------------------------------

On my 'back bench' (ie, the bench facing the lathe) I have a
machinist's steel tool box. It contains the high precision bits &
pieces every machinist accumulates over the years, such as my ten-k
mikes (ie, accurate to .0001"), broaches, reamers and so forth. In
the top right-hand drawer is a packet of Zig-Zag cigaret papers.
These are used as a gauge when making certain set-ups. But they also
serve as my 'test mass.' When a prop has been finished, I put a
cigarette paper on one of the blades to ensure the prop not only
drops, but on that side. The blade is then leveled and the test mass
is placed on the opposite limb. Some argue that I'm merely testing
the drag of my pivot and while pivot-drag is surely a factor, the
amount of TIME the blade takes to deflect by a certain amount, such as
down to the top of the bench, tells me if the prop is properly
balanced. That is, so long as each limb takes the same amount of time
to deflect for the same amount of distance, I know the balance is
equal on both sides of the prop.

Occasionally I get some guy in the shop who wants to argue that the
modern-day, all-electronic balancing is superior to my clumsy efforts,
especially with regard to TIME, in that the electronic balancers give
you an answer RIGHT NOW... and the answer is accurate to millionths of
a gram, or whatever.

Cost of such equipment is rarely mentioned :-)

This is another case of a newbie falling prey to some hi-tek
huckster. While it would be nice to have a balancer that gave such
precise results ( ie, four zeros preceding the significant digit ), in
the real world that degree of precision only applies to turbines ---
devices spinning at tens of thousands of revolutions per minute. If
you happen to have ACCESS to such a machine, you are lucky, but there
is simply no need for that degree of precision when you're dealing
with two-bladed props for Volkswagen engines.

After balancing the prop with the shiny-side out, I like to flip it
over and check the balance again. 'Shiny-side' = the prop is
finished with a good grade of VARNISH. After the varnish has cured,
the side of the prop facing the pilot [tractor installation assumed]
is given a light sprayed-on coat of FLAT BLACK paint, so as not to
reflect the sun into the cockpit.

-R.S.Hoover

[[email protected]]

On Dec 14, 7:48*am, "Peter Dohm" > wrote:
* *Reduced capacity for any given disk area.
> 2) * *Poor streamlining at speed in airplane propeller applications.
>-----------------------------------------------------------------------------

Dear Peter,

I'm not sure if the 'poor streamlining' was meant to apply to single-
bladed props or to props installed on the clutch-end of the crankshaft
but in the latter case you will find that the tranny flange of the
engine, which is about 13" in diameter, is completely submerged in the
streamline when the prop is fitted with a 12" spinner.

-R.S.Hoover

[Peter Dohm]

> wrote in message
...
On Dec 14, 7:48 am, "Peter Dohm" > wrote:
Reduced capacity for any given disk area.
> 2) Poor streamlining at speed in airplane propeller applications.
>-----------------------------------------------------------------------------

Dear Peter,

I'm not sure if the 'poor streamlining' was meant to apply to single-
bladed props or to props installed on the clutch-end of the crankshaft
but in the latter case you will find that the tranny flange of the
engine, which is about 13" in diameter, is completely submerged in the
streamline when the prop is fitted with a 12" spinner.

-R.S.Hoover

The comment was meant to apply a single bladed prop; although the "problem"
may not be significant on a relatively slow aircraft.

Peter

[Stealth Pilot[_2_]]

On Sun, 14 Dec 2008 10:48:58 -0500, "Peter Dohm"
> wrote:


>
>However, I also suspect that far too much can be made of the eccentric
>thrust problem.
>
>Over the decades, there have been a number of experiments with single blade
>propellers--primarily on helicopters--with an opposing counterweight. While
>my intuitive reaction was to question the probable bending force applied to
>the crank shaft--or drive shaft--I have never actually heard of that being a
>problem.
>
I think that that is because the eccentric thrust and load is not a
reversing load and so is not a fatigue factor on the crankshaft.

>Therefore, I can only presume that the lack of popularity is due to other
>factors, such as:
>1) Reduced capacity for any given disk area.
>2) Poor streamlining at speed in airplane propeller applications.
>3) Strange appearance.
>

it is actually easier and stronger to build a two bladed wooden prop.




>OTOH, it does make variable pitch ridiculously simple!
>
>Peter
>
>BTW, I still can't quite accept the idea either.
>
>

[Stealth Pilot[_2_]]

On Sun, 14 Dec 2008 11:45:33 -0800 (PST), "
> wrote:


>This is another case of a newbie falling prey to some hi-tek
>huckster. While it would be nice to have a balancer that gave such
>precise results ( ie, four zeros preceding the significant digit ), in
>the real world that degree of precision only applies to turbines ---
>devices spinning at tens of thousands of revolutions per minute. If
>you happen to have ACCESS to such a machine, you are lucky, but there
>is simply no need for that degree of precision when you're dealing
>with two-bladed props for Volkswagen engines.
>
>After balancing the prop with the shiny-side out, I like to flip it
>over and check the balance again. 'Shiny-side' = the prop is
>finished with a good grade of VARNISH. After the varnish has cured,
>the side of the prop facing the pilot [tractor installation assumed]
>is given a light sprayed-on coat of FLAT BLACK paint, so as not to
>reflect the sun into the cockpit.
>
>-R.S.Hoover

a balanced prop is a balanced prop is a balanced prop.
once it is balanced you cant get it any better weightwise.

the remaining factors on a balanced prop are mounting it square to the
shaft and having the aerofoil distributions symmetrical.

what we are describing is *not* a deficient process.
Stealth Pilot

[[email protected]]

On Dec 15, 1:31 am, Stealth Pilot >
wrote:

> a balanced prop is a balanced prop is a balanced prop.
> once it is balanced you cant get it any better weightwise.
>
> the remaining factors on a balanced prop are mounting it square to the
> shaft and having the aerofoil distributions symmetrical.
>
> what we are describing is *not* a deficient process.

I wish it was a simple as that. Most props are built with their blade
mass a little ahead of the hub/root so that centrifugal force will try
to flex them back in line with the hub's plane of rotation. This is to
fight the forward flexing caused by thrust loads. If you lay a prop on
a flat surface, trailing edges down, you'll see lots of clearance
between the TE and the surface on most of them. Turn it over and the
leading edges will be against the table, and on some metal props
they'll lift the hub's front face clear of the table.

So, if the heaviness we want to remove is due to a thicker section of
blade near the hub, or maybe just a denser area of wood, and we add
weight to the opposite tip to counter it, we balance it statically but
not dynamically. The heavier blade tip will flex back more than the
lighter one, putting the prop's tips out of track and screwing up its
dynamic balance. It'll shake. Only the electronic device will find
that.

I'm fortunate to work is an aircraft shop where we have such stuff
available. I couldn't justify owning a $5000 machine myself. Heck, I
could build a small airplane with that $5k.

Dan

[[email protected]]

Good discussion. Of course, most of it does not apply to Joe Newbie
hacking out his first prop :-)

But it does a good job of explaining what goes in to a well engineered
propeller. What it DOESN'T do is tell the newbie that the efficiency
of his prop will be within a few percentage points of a professionally-
made wooden propeller. Which means Joe Newbie's efforts WILL fly the
plane. And that's the message I'd like to get across.

The propeller's job is to convert torque into thrust. To do that
efficiently the propeller must be perfectly balanced. After mass
balance is dealt with the next most important factor is dynamic
balance, which is beyond the skills of the amateur. But the
homebuilder CAN ensure the propeller is perfectly SMOOTH so that it
presents the least possible amount of drag as it rotates. The amateur
is also capable of ensuring a uniform air foil, especially with a
computer to take care of the lay-out chores... you must still make the
patterns from old beer cans will do for the material... in fact, stiff
cardboard would do well enough.

Wood is a forgiving material. And so is AIR. A propeller that is
nice and smooth, properly balanced and of the required diameter and
pitch, will typically produce within 90% of the thrust produced by a
professionally carved prop.
---------------------------------------------------------------------------

If you've taken advantage of YouTube and the archives devoted to
various homebuilts, you will have seen a number of propeller
duplicators in action. You would also have seen that these machines
are quite simple in both concept and construction. If the homebuilder
is building a wooden aircraft it's fair to assume they are well versed
in building from that material. It is a relatively small step between
the spar of a Jodel and a profiler -- or duplicator -- capable of
producing a propeller.

Which raises a very interesting point: If you have a propeller
duplicator you only need to produce ONE BLADE of the prop... and you
may produce it from a variety of materials as well as wood, including
foam-fiberglas composite, cast aluminum, cast zinc and so on.

--------------------------------------------------------------------------

The next most common question that arises is 'Why do I need all that
stuff if I'm only making ONE PROPELLER?'

The most correct answer is that you will probably need THREE
propellers to find the one that most closely matched YOUR combination
of engine and air frame. Yeah, I know: It's built EXACTLY according
to the plans. Good for you (seriously). But there are variations
even among commercially built airplanes. With commercially built
engines such as an O-200, driving a commercially built METAL
propeller, these variations are quite small: One Cub was virtually
identical to another. But there ARE variations and it doesn't matter
if your name is Boeing, Douglas or Lockheed ( indeed, there are some
heroic examples which, unbelievable as they might appear, are flying
the world's skies ). If you had to BUY two -- or more -- commercially
built props it can cost you up to $500 to nail down the 'perfect'
prop.

In fact... ( now, you KNEW that was coming, right? ) In fact, a
manually operated profiler ( ie, 'duplicator,' et al ) is exactly
the sort of thing you want to consider as a chapter project. With the
cutting element removed (ie, the portable saw or the ) the frame of
the profiler is flat enough to be hung up for storage, tucked in the
rafters and so on. You must provide the MASTER -- one blade of your
propeller, the practical limits of which are for a prop having a
diameter of about 72" and a depth of about 6". Of the examples you
will find on YouTube and other video sources, the one using a portable
saw as the cutting element is probably the most practical for the
homebuilder, since those using a router have quite an appetite for
cutters.

The 'manually operated' means that YOU are the motive force shoving
the profiler back & forth, advancing an eighth of an inch or so for
each pass -- BOTH back and forth. The tracer/tracker/profiler what-
have-you is a disk of steel or aluminum having EXACTLY the same
diameter as the BLADE of the portable circular saw. The WIDTH of the
tracer must be APPROXIMATELY the same as that of the saw blade --
indeed, it may be considerably WIDER, so long as the advancing edge
(ie, the edge nearest the tip of the pattern) is exactly the same as
that edge of the saw-blade.

The thing you are shoving back & forth whist advancing down the length
of the pattern is a hinged plate or table to which the tracer disk and
the portable saw are attached. This table is attached to a pair of
rods or bars so that it slides back & forth with very little
friction. The weight of the saw is borne by nylon blocks which serve
as bearings. A counter poise or weight
is used as a mass-balance, allowing the tracer to easily follow the
contours of the MASTER PATTERN, which has a very durable finish.

The pattern and the prop-blank are drilled to EXACTLY match, typically
using a master drill guide.

It takes FOUR PASSES through the profiler to produce a near-perfect
propeller. The MASTER PATTERN as well as the blank must be
dismounted, turned over (or reversed) for each new cut, If you are
only doing one propeller, the set-up time makes up an appreciable
amount of the whole, whih is why it makes good sense to produce a
NUMBER of identical props at the same time, Of course, that isn't
practical for our situation but it IS practical for a GROUP of
builders using the same power-plant in the same air frame.

Even when the prop-blank has been run through the band saw (or other
means, such as a saber-saw with a long blade.. [go slow, give it a
chance to cut] ) to remove most of the wood, the tip must be dealt
with manually and the prop will require finish-sanding. But the
process is straight-forward.

-R. S. Hoover

[Stealth Pilot[_2_]]

On Mon, 15 Dec 2008 18:35:28 -0800 (PST), "
> wrote:

>
>
>Good discussion. Of course, most of it does not apply to Joe Newbie
>hacking out his first prop :-)
>
>But it does a good job of explaining what goes in to a well engineered
>propeller. What it DOESN'T do is tell the newbie that the efficiency
>of his prop will be within a few percentage points of a professionally-
>made wooden propeller. Which means Joe Newbie's efforts WILL fly the
>plane. And that's the message I'd like to get across.
>
<snip>
>
>The most correct answer is that you will probably need THREE
>propellers to find the one that most closely matched YOUR combination
>of engine and air frame. Yeah, I know: It's built EXACTLY according
>to the plans. Good for you (seriously). But there are variations
>even among commercially built airplanes. With commercially built
>engines such as an O-200, driving a commercially built METAL
>propeller, these variations are quite small: One Cub was virtually
>identical to another. But there ARE variations and it doesn't matter
>if your name is Boeing, Douglas or Lockheed ( indeed, there are some
>heroic examples which, unbelievable as they might appear, are flying
>the world's skies ). If you had to BUY two -- or more -- commercially
>built props it can cost you up to $500 to nail down the 'perfect'
>prop.
>

snipped so that I can comment on these points.

a well made newbie prop can deliver exactly the same performance as a
professionally carved prop. after all they were newbies once
themselves.

my experience relates to a wooden prop on an O-200 powered tailwind,
but it is still relevant to a vw prop although it turns the opposite
way.

I have been refinishing my prop and balancing it for years so I have
experience with paint layer variations in the shape of the one prop.
Over the polyurethane varnish I use the cheapest aerosol paint can
lacquer that I can find. it dries quickly, is easy to apply smoothly
and .... when it is all chipped and scuffed it wipes of with a rag
soaked in either MEK or Acetone.

tiny variations in the paint surface can have noticeable effects on
cruise speed.
when I inherited the prop as a new owner it was all daggy and glass
resin runs. straight and level cruise was 110knots.
when I cleaned off all the dags and sanded the surfaces smooth the
straight and level cruise was 115knots.
with some other fuselage changes I now cruise at 120knots reliably.

on one repaint I used lots of coats of paint around the leading edge.
about 65 coats on one blade I recall.
the paint didnt last too long before chips were eroding the finish but
while it was pristine I achieved 124knots cruise.

try as I might I cant get the shape again. best I can get usually is
121 knots in pristine condition.

the point here is that making a family of props all subtly varied from
each other can find you the crackerjack best prop for your aircraft.
in australia a prop is typically $3200 so making them yourself can
make the exotic quite affordable.

here is a trick for sizing the prop. make it an inch overlength.
in straight and level flight you should not be able to hit redline
with full throttle.
trim 5mm from each end and rebalance and refinish.
fly it again and the top rpm will be slightly higher.
when the revs come just up to redline rpm with full throttle your prop
is the correct size.

Stealth Pilot

[[email protected]]

On Dec 16, 4:16 am, Stealth Pilot >
wrote:
> a well made newbie prop can deliver exactly the same performance as a
> professionally carved prop. after all they were newbies once themselves.

I'd be willing to bet that the prop I have--a Colin Walker
unit, uncertified, built by a guy who probably got his start building
one for himself, is MORE efficient than, say, a Sensenich. The builder
of my prop used a more cambered airfoil that pulls better than a
Sensenich, he milled off the leading edge and built it up with hard
urethane and shaped it so that it's a seamless, lightweight abrasion
protection much better than Sensenich's crude riveted-on brass leading
edge that disrupts airflow and can harbor moisture under it, and so
on.

> here is a trick for sizing the prop. make it an inch overlength.
> in straight and level flight you should not be able to hit redline
> with full throttle.
> trim 5mm from each end and rebalance and refinish.
> fly it again and the top rpm will be slightly higher.
> when the revs come just up to redline rpm with full throttle your prop
> is the correct size.

I shortened mine from 76" to 72" to get more RPM on takeoff,
and lost performance in all regimes. I wish I could put those tips
back on. It used to cruise at a speed and RPM that indicated zero or
slightly negative slip, believe it or not. Not anymore. Now it slips a
little. Don Downie, an old homebuilder of note, said that long props
would do that.

Dan

[Jan Carlsson]

Hi

I tryed to replay to this when I was in Thailand but it did not get here.

Cutting 4 inch off is like reduce pitch by 8" when come to power needed.

if diameter is right (depending of what you want) the relative pitch and propeller pitch at 75% r. is about the same, for a standard purpose pitched prop. at the flat botom that is.

A little negative alpha on a CLIMB prop, and little positive alpha on a CRUISE prop.

A speed prop will have maybe 2 degree of positive alpha.

this also depends on the thickness of blade, a thinner/ less camber will need more alpha, and a thicker less alpha. and it also depends on the blade aspect ratio.

You can trade diameter for pitch, in most cases 1 inch diameter for 2 inch pitch.

and it differ 2" in pitch between each of the 4 purpose props, CLIMB, STANDARD, CRUISE and SPEED.

Jan Carlsson
www.jcpropellerdesign.com



here is a trick for sizing the prop. make it an inch overlength.
in straight and level flight you should not be able to hit redline
with full throttle.
trim 5mm from each end and rebalance and refinish.
fly it again and the top rpm will be slightly higher.
when the revs come just up to redline rpm with full throttle your prop
is the correct size.

I shortened mine from 76" to 72" to get more RPM on takeoff,
and lost performance in all regimes. I wish I could put those tips
back on. It used to cruise at a speed and RPM that indicated zero or
slightly negative slip, believe it or not. Not anymore. Now it slips a
little. Don Downie, an old homebuilder of note, said that long props
would do that.

Dan[/QUOTE]