Spinner, aluminium or fibreglass? Safety?

I'm trying to select a suitable spinner for our Rans S6S. Besides looks,
weight and airflow I'm a bit worried about safety. There are several options
in terms of material and mechanical construction, and I'd like to hear what
experience you have with any particular type. One thing I'm wondering about
is that many spinner backplates are sandwitched between the propeller hub
and the propeller itself.

I read somewhere that the power transfer to the prop works by means of
friction between prop and hub. The prop bushings are only there to center
the prop. If that is correct then introducing an extra layer between the
prop and the hub can have profound impact on power transfer. Unfortunately
I've been unable to find any documentation on this subject at all.

Any thoughts??

Rob

On Mar 29, 3:47 am, "Rob Turk" wrote:
I'm trying to select a suitable spinner for our Rans S6S. Besides looks,
weight and airflow I'm a bit worried about safety. There are several options
in terms of material and mechanical construction, and I'd like to hear what
experience you have with any particular type. One thing I'm wondering about
is that many spinner backplates are sandwitched between the propeller hub
and the propeller itself.

I read somewhere that the power transfer to the prop works by means of
friction between prop and hub. The prop bushings are only there to center
the prop. If that is correct then introducing an extra layer between the
prop and the hub can have profound impact on power transfer. Unfortunately
I've been unable to find any documentation on this subject at all.

Any thoughts??

Rob

I've been running fiberglass spinners with carbon fiber backplates on
Rotax engines (2 and 4 cycle) for years with no problems. 2 Rans
S-6's, both with 912s had this setup. The only problem I ever had
with a spinner was an aluminum one on a 2 cycle rotax engine powered
airplane.

I am presently running a fiberglass spinner with a carbon backplate on
my Long-EZ with a 175hp engine. No problems there either.

Rick Pellicciotti
Belle Aire Aviation, Inc.
http://www.belleaireaviation.com

Sensenich addresses this matter in the installation and maintenance
instructions for their wooden propellers:

http://www.sensenichprop.com/sen_htm...stall/cf-a.pdf

(Note that it's a PDF file; make sure your browser is set to accept
PDF downloads.) In Step 2 of the installation procedure they indicate
that the rear spinner-bulkhead may be either ahead of or behind the
prop-to-engine plate. But they also specify that all contact surfaces
in the sandwich be cleaned with alcohol and a fine Scotchbrite pad.
Apparently as long as the surfaces are clean and bone-dry they'll
develop the necessary friction at all the interfaces.

On Mar 29, 2:47 am, "Rob Turk" wrote:
I'm trying to select a suitable spinner for our Rans S6S. Besides looks,
weight and airflow I'm a bit worried about safety. There are several options
in terms of material and mechanical construction, and I'd like to hear what
experience you have with any particular type. One thing I'm wondering about
is that many spinner backplates are sandwitched between the propeller hub
and the propeller itself.

I read somewhere that the power transfer to the prop works by means of
friction between prop and hub. The prop bushings are only there to center
the prop. If that is correct then introducing an extra layer between the
prop and the hub can have profound impact on power transfer. Unfortunately
I've been unable to find any documentation on this subject at all.

Any thoughts??

Rob

I have been running the spinners that Vans sells on my V-8 powered
Zenith 801. I have one cut for a two blade and the one thats on there
now is a three blade set up, The spinner is a greenish color, maybe a
kevlar material. They are very well made and reasonably priced. My
thoughts on the attach concept is this. The prop is attached to the
crank hub by six bolts, when they are torqued properly they are in
shear and tension and holding the prop tightly against the hub. That
is the friction aspect of the concept. The bushing do align the prop
to the hub, they also are in shear as they prevent the prop from
spinning on the hub. A metal prop has the abilty to absorb this as the
material is harder then say a wooden or composite prop. If those were
to rely on that only, the counterbores in those props that the bushing
sits in will quickly distort. So, my take on this is, The prop bolts
when torqued are carrying 80% of the load, the surface friction is
carrying the rest. Warning,,,,,, I didn't stay in a Holiday Inn
Express last night either so you mileage my vary....

Ben
www.haaspowerair.com

Ben Haas wrote:

Rob Turk wrote:
I read somewhere that the power transfer to the prop works by
means of friction between prop and hub. The prop bushings are
only there to center the prop. If that is correct then
introducing an extra layer between the prop and the hub can have
profound impact on power transfer.

.... So, my take on this is, The prop bolts when torqued are
carrying 80% of the load, the surface friction is carrying the
rest.

For WOODEN props, or wood core/composite wrap props (basically,
anything with a predominantly wooden hub), Rob is correct - the
friction between the face of the propeller and the face of the prop
extension (or hub) transmits 100% of the torque from the engine to the
propeller. The bushings do NOT transfer any force to the propeller,
and the bolts most certainly do not transfer any load to the prop and
are NOT loaded in shear.

The prop bolts are in tension (about 3000 -4000 lb on a 1/2 in. bolt),
and are there ONLY to ensure that there's enough force on the
propeller/hub interface to create the friction necessary to drive the
prop. About 600 psi is required - much less than that leads to
slippage, and more than that can crush the prop.

WRT backing plates, there are those who believe that the plate CAN
affect the transfer of torque between the hub and the prop. The
material of the backing plate may matter. From the standpoint of
friction, aluminum should be fine - that's what the hub's made of.

Personally, I think that a composite backing plate, with low
temperature epoxy, could be an issue, but ONLY if the bolts aren't
torqued correctly and/or the prop starts slipping and heats up the
backing plate, softening the epoxy more.


For visuals on what can happen when you don't torque your prop bolts
correctly on a wooden prop, see:

http://www.cozybuilders.org/Desert_Center/index.html

I need to update the web pages - I've now got all six bolts using
bellevilles.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2007

On Mar 30, 8:32 pm, "Marc J. Zeitlin"
wrote:
Ben Haas wrote:
Rob Turk wrote:
I read somewhere that the power transfer to the prop works by
means of friction between prop and hub. The prop bushings are
only there to center the prop. If that is correct then
introducing an extra layer between the prop and the hub can have
profound impact on power transfer.
.... So, my take on this is, The prop bolts when torqued are
carrying 80% of the load, the surface friction is carrying the
rest.

For WOODEN props, or wood core/composite wrap props (basically,
anything with a predominantly wooden hub), Rob is correct - the
friction between the face of the propeller and the face of the prop
extension (or hub) transmits 100% of the torque from the engine to the
propeller. The bushings do NOT transfer any force to the propeller,
and the bolts most certainly do not transfer any load to the prop and
are NOT loaded in shear.

The prop bolts are in tension (about 3000 -4000 lb on a 1/2 in. bolt),
and are there ONLY to ensure that there's enough force on the
propeller/hub interface to create the friction necessary to drive the
prop. About 600 psi is required - much less than that leads to
slippage, and more than that can crush the prop.

WRT backing plates, there are those who believe that the plate CAN
affect the transfer of torque between the hub and the prop. The
material of the backing plate may matter. From the standpoint of
friction, aluminum should be fine - that's what the hub's made of.

Personally, I think that a composite backing plate, with low
temperature epoxy, could be an issue, but ONLY if the bolts aren't
torqued correctly and/or the prop starts slipping and heats up the
backing plate, softening the epoxy more.

For visuals on what can happen when you don't torque your prop bolts
correctly on a wooden prop, see:

http://www.cozybuilders.org/Desert_Center/index.html

I need to update the web pages - I've now got all six bolts using
bellevilles.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2007

So, using your idea I can remove my 6 1/2" prop bolts and all the
bushings and replace the prop bolts with 6 3/16" or 1/4" bolts. The
total force applied with 6 of those small bolts torqued will exceed
the 600 lbs. You claim all I need 600 lbs of clamping force against
the crank hub to prevent the prop from spinning. This might work on a
model plane but I would NEVER try it on my plane. IMHO..

stol wrote:

So, using your idea I can remove my 6 1/2" prop bolts and all the
bushings and replace the prop bolts with 6 3/16" or 1/4" bolts.

Where did you get the idea that I said that?

... The
total force applied with 6 of those small bolts torqued will exceed
the 600 lbs. You claim all I need 600 lbs of clamping force against
the crank hub to prevent the prop from spinning.

Read my previous message again, please. I said, pretty explicitly,
that you need about 600 psi between the prop and the hub, not 600 lb.
PSI stands for "lb/sq. in.". For a 30 square inch area prop hub
(about the area of an SAE-2 hub), that works out to about 18,000 lb.
of force, total. That's where the 3,000 lb/bolt that I mentioned came
from.

.... This might work on a
model plane but I would NEVER try it on my plane. IMHO..

Actually, as it turns out, since each of the six bolts holding the
wooden propeller on must have about 3-4K lb of force on it (with an
SAE-2 flange), and a 1/4" AN bolt (~.036 sq-in cross section in the
threads) can withstand about 125K psi before breaking, the stress of
~110 ksi on the bolt would still put it below it's ultimate strength,
although probably higher than it's yield strength.

So, 3/16" bolts wouldn't work, but 1/4" bolts could possibly work, in
certain circumstances, like on SAE-1 flanges, which require less force
(being smaller) to create the same 600 psi.

In fact, Jabiru uses 1/4" bolts to hold their props on some of their
engines, and also uses belleville washers.

Learn something new every day, huh?

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2007

On Mar 31, 12:24 am, "Marc J. Zeitlin"
wrote:
stol wrote:
So, using your idea I can remove my 6 1/2" prop bolts and all the
bushings and replace the prop bolts with 6 3/16" or 1/4" bolts.

Where did you get the idea that I said that?

... The
total force applied with 6 of those small bolts torqued will exceed
the 600 lbs. You claim all I need 600 lbs of clamping force against
the crank hub to prevent the prop from spinning.

Read my previous message again, please. I said, pretty explicitly,
that you need about 600 psi between the prop and the hub, not 600 lb.
PSI stands for "lb/sq. in.". For a 30 square inch area prop hub
(about the area of an SAE-2 hub), that works out to about 18,000 lb.
of force, total. That's where the 3,000 lb/bolt that I mentioned came
from.

.... This might work on a
model plane but I would NEVER try it on my plane. IMHO..

Actually, as it turns out, since each of the six bolts holding the
wooden propeller on must have about 3-4K lb of force on it (with an
SAE-2 flange), and a 1/4" AN bolt (~.036 sq-in cross section in the
threads) can withstand about 125K psi before breaking, the stress of
~110 ksi on the bolt would still put it below it's ultimate strength,
although probably higher than it's yield strength.

So, 3/16" bolts wouldn't work, but 1/4" bolts could possibly work, in
certain circumstances, like on SAE-1 flanges, which require less force
(being smaller) to create the same 600 psi.

In fact, Jabiru uses 1/4" bolts to hold their props on some of their
engines, and also uses belleville washers.

Learn something new every day, huh?

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2007

I see you have the .edu in your email address so you must be a teacher
or professor. Now tell me how you came up with 30 square inches of
surface area on a a SAE-2 crank hub...Thanks in advance.

Ben

Is there any particular reason for using six bellevilles? Are they stacked
parallel? I read the whole story about the Cozy that threw a prop and
checked out the graphical data piece and think I understand why the
bellevilles are better than conventional. Due to the fact that a belleville
is a spring, if the prop hub shrinks or expands, the belleville acts as a
buffer. Yes?

I have a wooden prop, not yet installed and a sudden departure due to
improper torque is not a pleasant thought. If possible I'd like more
specific installation recommendations.

Ebby


"Marc J. Zeitlin" wrote in message
...
stol wrote:

So, using your idea I can remove my 6 1/2" prop bolts and all the
bushings and replace the prop bolts with 6 3/16" or 1/4" bolts.

Where did you get the idea that I said that?

... The
total force applied with 6 of those small bolts torqued will exceed
the 600 lbs. You claim all I need 600 lbs of clamping force against
the crank hub to prevent the prop from spinning.

Read my previous message again, please. I said, pretty explicitly, that
you need about 600 psi between the prop and the hub, not 600 lb. PSI
stands for "lb/sq. in.". For a 30 square inch area prop hub (about the
area of an SAE-2 hub), that works out to about 18,000 lb. of force, total.
That's where the 3,000 lb/bolt that I mentioned came from.

.... This might work on a
model plane but I would NEVER try it on my plane. IMHO..

Actually, as it turns out, since each of the six bolts holding the wooden
propeller on must have about 3-4K lb of force on it (with an SAE-2
flange), and a 1/4" AN bolt (~.036 sq-in cross section in the threads) can
withstand about 125K psi before breaking, the stress of ~110 ksi on the
bolt would still put it below it's ultimate strength, although probably
higher than it's yield strength.

So, 3/16" bolts wouldn't work, but 1/4" bolts could possibly work, in
certain circumstances, like on SAE-1 flanges, which require less force
(being smaller) to create the same 600 psi.

In fact, Jabiru uses 1/4" bolts to hold their props on some of their
engines, and also uses belleville washers.

Learn something new every day, huh?

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2007

stol wrote:

I see you have the .edu in your email address so you must be a teacher
or professor.

Nope. I'm an aeronautical engineer, and I work for Scaled Composites.
Does that somehow change the facts of the matter?

... Now tell me how you came up with 30 square inches of
surface area on a a SAE-2 crank hub...Thanks in advance.

Math. My prop extension is about 7" in diameter. If I subtract the
area of the large hole in the center and the small holes for the
bolts, I get about 30 square inches.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2007