The Murphy Builders Site

Posted: **Fri Feb 17, 2012 11:02 pm**

I have also seen those prop tip speed calculator sites,
but they seem to go against what little that I have
learned about prop efficiency. I thought a slower
turning prop was more efficient. I am sure there is a
limit. I know fast airplanes do OK with smaller
diameters and higher RPM's but always thought for MAM
type planes, more diameter and slower prop RPM was
better. Hopefully your prop manufacturer concurs with
your choice.

Walter

-----Original Message-----
From: mike.davis@dcsol.com
[mailto:mike.davis@dcsol.com]On Behalf Of
Mike Kimball
Sent: Monday, May 19, 2003 6:28 PM
To: murphy-rebel@dcsol.com
Subject: I picked a Prop and PSRU!

Yay, I have finally made a decision! I have
decided to go ahead with the
IVO-PROP magnum 84" three bladed prop using
their electric pitch control and
electronic governor for constant speed. I
have also decided to fork out the
big bucks and go with the Firewall Forward
CAM 500 helical gear drive PSRU.
The CAM 500 will also provide a place to
mount my vacuum pump and solves
that little problem. The only thing I was
struggling with was deciding on a
1.756:1 ratio versus 2.118:1. Using the
handy prop tip speed calculator on
the web I have decided to go with the
1.756:1. It looks like I need to turn
an 84" prop about 2700 rpm to get the 0.88
mach speed (at 60 deg F) at the
tip that I need for maximum thrust. That
puts my engine at a max takeoff rpm
of 4741 rpm. That's well below the
capability of my engine but gives me the
conservative approach for reliability that I
want while still producing good
torque. I do not want to turn my engine at
5718 rpm which is what the
2.118:1 would give me, even though the
engine would be able to take it. If
I decide to fly when it's colder than 20 deg
F it will get noisy because
I'll be over 0.92 mach, but I can just back
off the power and let that dense
air lift me up. The thing that made me
decide to get into the 0.88-0.92
mach range at max power instead of being
more conservative down around 0.80
mach was the sound I hear whenever I see a
float-plane take off. There must
be a reason why float-plane operators like
those props that close to mach.
I'm inclined to believe what the prop tip
speed calculator website tells me.
If you want maximum thrust (and I do) you
need to be between 0.88 and 0.92
mach.

Mike Kimball
SR #044

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Posted: **Fri Feb 17, 2012 11:02 pm**

Yay, I have finally made a decision! I have decided to go ahead with the
IVO-PROP magnum 84" three bladed prop using their electric pitch control and
electronic governor for constant speed. I have also decided to fork out the
big bucks and go with the Firewall Forward CAM 500 helical gear drive PSRU.
The CAM 500 will also provide a place to mount my vacuum pump and solves
that little problem. The only thing I was struggling with was deciding on a
1.756:1 ratio versus 2.118:1. Using the handy prop tip speed calculator on
the web I have decided to go with the 1.756:1. It looks like I need to turn
an 84" prop about 2700 rpm to get the 0.88 mach speed (at 60 deg F) at the
tip that I need for maximum thrust. That puts my engine at a max takeoff rpm
of 4741 rpm. That's well below the capability of my engine but gives me the
conservative approach for reliability that I want while still producing good
torque. I do not want to turn my engine at 5718 rpm which is what the
2.118:1 would give me, even though the engine would be able to take it. If
I decide to fly when it's colder than 20 deg F it will get noisy because
I'll be over 0.92 mach, but I can just back off the power and let that dense
air lift me up. The thing that made me decide to get into the 0.88-0.92
mach range at max power instead of being more conservative down around 0.80
mach was the sound I hear whenever I see a float-plane take off. There must
be a reason why float-plane operators like those props that close to mach.
I'm inclined to believe what the prop tip speed calculator website tells me.
If you want maximum thrust (and I do) you need to be between 0.88 and 0.92
mach.

Mike Kimball
SR #044

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Posted: **Fri Feb 17, 2012 11:02 pm**

Unfortunately, I can't get more diameter than 84" from IVO-PROP. And I can
turn it slower than 2700 rpm. I can do that by coarsening up the pitch or
reducing power. Of course, those options for turning slower are only good
for cruise since I want max power at takeoff. Perhaps the reference to
"efficiency" refers to cruise for a plane like the Super Rebel. If that is
the case, my ability to change the prop pitch in-flight addresses that.
However, I am by no means proficient with this stuff and welcome any input.
I'm about to spend lots of money so if anyone thinks I'm paddling up the
wrong creek, don't worry about hurtin' my feelings. By all means, give me
your opinions! Thanks everyone.

Mike Kimball
SR #044

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
Walter Klatt
Sent: Monday, May 19, 2003 5:34 PM
To: murphy-rebel@dcsol.com
Subject: RE: I picked a Prop and PSRU!

I have also seen those prop tip speed calculator sites,
but they seem to go against what little that I have
learned about prop efficiency. I thought a slower
turning prop was more efficient. I am sure there is a
limit. I know fast airplanes do OK with smaller
diameters and higher RPM's but always thought for MAM
type planes, more diameter and slower prop RPM was
better. Hopefully your prop manufacturer concurs with
your choice.

Walter

-----Original Message-----
From: mike.davis@dcsol.com
[mailto:mike.davis@dcsol.com]On Behalf Of
Mike Kimball
Sent: Monday, May 19, 2003 6:28 PM
To: murphy-rebel@dcsol.com
Subject: I picked a Prop and PSRU!

Yay, I have finally made a decision! I have
decided to go ahead with the
IVO-PROP magnum 84" three bladed prop using
their electric pitch control and
electronic governor for constant speed. I
have also decided to fork out the
big bucks and go with the Firewall Forward
CAM 500 helical gear drive PSRU.
The CAM 500 will also provide a place to
mount my vacuum pump and solves
that little problem. The only thing I was
struggling with was deciding on a
1.756:1 ratio versus 2.118:1. Using the
handy prop tip speed calculator on
the web I have decided to go with the
1.756:1. It looks like I need to turn
an 84" prop about 2700 rpm to get the 0.88
mach speed (at 60 deg F) at the
tip that I need for maximum thrust. That
puts my engine at a max takeoff rpm
of 4741 rpm. That's well below the
capability of my engine but gives me the
conservative approach for reliability that I
want while still producing good
torque. I do not want to turn my engine at
5718 rpm which is what the
2.118:1 would give me, even though the
engine would be able to take it. If
I decide to fly when it's colder than 20 deg
F it will get noisy because
I'll be over 0.92 mach, but I can just back
off the power and let that dense
air lift me up. The thing that made me
decide to get into the 0.88-0.92
mach range at max power instead of being
more conservative down around 0.80
mach was the sound I hear whenever I see a
float-plane take off. There must
be a reason why float-plane operators like
those props that close to mach.
I'm inclined to believe what the prop tip
speed calculator website tells me.
If you want maximum thrust (and I do) you
need to be between 0.88 and 0.92
mach.

Mike Kimball
SR #044

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Posted: **Fri Feb 17, 2012 11:02 pm**

Addressing Mike's comment about why the float planes typically make so much
noise; a real common plane seen on floats is the C-185. Commonly seen,
maybe not because there are more of them but because they're powered by the
Continental IO520D. When these planes take off, you're bound to look,
because of the scream of the prop. Most of the big block Continentals, as
well as the Lycomings are rated at 2700 RPM. The 'D' series, however, is
rated 300 H.P. @ 2850 RPM, for 5 minutes. So, the answer to the noise
issue is really simple; in order to make the 300 H.P. to haul that pile of
aluminum off of the water, the governor is set to bump at 2850. If the
engine doesn't turn rated RPM at WOT, then it aint producing rated
horsepower. You can tell a 185 breaking water from MILES away.

Probably not P.C. to say it, but I kinda like that sound.

Bill Delcambre

----- Original Message -----
From: <klehman@albedo.net>
To: <murphy-rebel@dcsol.com>
Sent: Tuesday, May 20, 2003 1:11 PM
Subject: Re: I picked a Prop and PSRU!

Mike FWIW I still think you are concentrating on tip speed way way too
much. Perhaps CAM will let you exchange ratios later if you need to like
Marcotte does... Anyway I maintain that you don't have the same
restrictions that spam can floatplanes have. Their engines typically
must make 2700 rpm to make the power. That tip speed and/or physical
prop diameter restrictions means losing lots of thrust and making lots
of noise. You have the opportunity to make thrust with the power they
are wasting making noise etc. If you want to make lots of takeoff thrust
and justify carrying the engine weight, you don't want to turn that prop
2700 rpm UNLESS it won't go course enough to absorb your engine power at
lower speed. That is very unlikely from what you've said.

You have thrust numbers for a 76" IVO. What ratio was that using? You
NEED to know. Do you have numbers for the 84" prop? With an 84" prop you
are really going to need a higher ratio than what was optimum for the
76" prop. Static thrust is only another small part of this but it's a
start and it's more significant than tip speed.

I really think you should look into this a little more based on what
you've said here. If this was for a high speed aircraft like a Lancair I
would not be near as concerned. I have never looked at LS1 torque curves
but a lot of this applies to all auto engines and some guys go through
several props and still end up changing to a higher ratio.

Ken

Mike Kimball wrote:
Yay, I have finally made a decision! I have decided to go ahead with

the

IVO-PROP magnum 84" three bladed prop using their electric pitch control

and

electronic governor for constant speed. I have also decided to fork out

the

big bucks and go with the Firewall Forward CAM 500 helical gear drive

PSRU.

The CAM 500 will also provide a place to mount my vacuum pump and solves
that little problem. The only thing I was struggling with was deciding

on a

1.756:1 ratio versus 2.118:1. Using the handy prop tip speed calculator

on

the web I have decided to go with the 1.756:1. It looks like I need to

turn

an 84" prop about 2700 rpm to get the 0.88 mach speed (at 60 deg F) at

the

tip that I need for maximum thrust. That puts my engine at a max takeoff

rpm

of 4741 rpm. That's well below the capability of my engine but gives me

the

conservative approach for reliability that I want while still producing

good

torque. I do not want to turn my engine at 5718 rpm which is what the
2.118:1 would give me, even though the engine would be able to take it.

If

I decide to fly when it's colder than 20 deg F it will get noisy because
I'll be over 0.92 mach, but I can just back off the power and let that

dense

air lift me up. The thing that made me decide to get into the 0.88-0.92
mach range at max power instead of being more conservative down around

0.80

mach was the sound I hear whenever I see a float-plane take off. There

must

be a reason why float-plane operators like those props that close to

mach.

I'm inclined to believe what the prop tip speed calculator website tells

me.

If you want maximum thrust (and I do) you need to be between 0.88 and

0.92

mach.

Mike Kimball
SR #044

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Posted: **Fri Feb 17, 2012 11:02 pm**

Mike - FWIW - I called Chris Opperman to confirm the thrust numbers and ask
about the gear ratio. He was getting the 1483 Lbs thrust with the 76" 3
bladed 45-105 pitch Ivo spinning the prop at 2850, the engine at 4400 using
a 1.53 Stinger gearbox.
His mission is different than ours as he is trying to optimize the RV7 to go
327 MPH with 70% power at 15000 feet (wow) so he needs that extra pitch.

I mentioned that I was thinking that you needed to be at 4800 RPM on the LS1
because that was where the max torque is on the curves. Chris believes that
(and I agree - I just don't know to what degree) the curves are built on a
"whole car" dyno so they include the drivetrain exhaust/cat and all
associated losses so it is hard to predict.

Britt

-----Original Message-----
From: Bill Delcambre [mailto:bdelcambre@cox-internet.com]
Sent: Tuesday, May 20, 2003 11:33 AM
To: murphy-rebel@dcsol.com
Subject: Re: I picked a Prop and PSRU!

Addressing Mike's comment about why the float planes typically make so much
noise; a real common plane seen on floats is the C-185. Commonly seen,
maybe not because there are more of them but because they're powered by the
Continental IO520D. When these planes take off, you're bound to look,
because of the scream of the prop. Most of the big block Continentals, as
well as the Lycomings are rated at 2700 RPM. The 'D' series, however, is
rated 300 H.P. @ 2850 RPM, for 5 minutes. So, the answer to the noise
issue is really simple; in order to make the 300 H.P. to haul that pile of
aluminum off of the water, the governor is set to bump at 2850. If the
engine doesn't turn rated RPM at WOT, then it aint producing rated
horsepower. You can tell a 185 breaking water from MILES away.

Probably not P.C. to say it, but I kinda like that sound.

Bill Delcambre

----- Original Message -----
From: <klehman@albedo.net>
To: <murphy-rebel@dcsol.com>
Sent: Tuesday, May 20, 2003 1:11 PM
Subject: Re: I picked a Prop and PSRU!

Mike FWIW I still think you are concentrating on tip speed way way too
much. Perhaps CAM will let you exchange ratios later if you need to like
Marcotte does... Anyway I maintain that you don't have the same
restrictions that spam can floatplanes have. Their engines typically
must make 2700 rpm to make the power. That tip speed and/or physical
prop diameter restrictions means losing lots of thrust and making lots
of noise. You have the opportunity to make thrust with the power they
are wasting making noise etc. If you want to make lots of takeoff thrust
and justify carrying the engine weight, you don't want to turn that prop
2700 rpm UNLESS it won't go course enough to absorb your engine power at
lower speed. That is very unlikely from what you've said.

You have thrust numbers for a 76" IVO. What ratio was that using? You
NEED to know. Do you have numbers for the 84" prop? With an 84" prop you
are really going to need a higher ratio than what was optimum for the
76" prop. Static thrust is only another small part of this but it's a
start and it's more significant than tip speed.

I really think you should look into this a little more based on what
you've said here. If this was for a high speed aircraft like a Lancair I
would not be near as concerned. I have never looked at LS1 torque curves
but a lot of this applies to all auto engines and some guys go through
several props and still end up changing to a higher ratio.

Ken

Mike Kimball wrote:
Yay, I have finally made a decision! I have decided to go ahead with

the

IVO-PROP magnum 84" three bladed prop using their electric pitch control

and

electronic governor for constant speed. I have also decided to fork out

the

big bucks and go with the Firewall Forward CAM 500 helical gear drive

PSRU.

The CAM 500 will also provide a place to mount my vacuum pump and solves
that little problem. The only thing I was struggling with was deciding

on a

1.756:1 ratio versus 2.118:1. Using the handy prop tip speed calculator

on

the web I have decided to go with the 1.756:1. It looks like I need to

turn

an 84" prop about 2700 rpm to get the 0.88 mach speed (at 60 deg F) at

the

tip that I need for maximum thrust. That puts my engine at a max takeoff

rpm

of 4741 rpm. That's well below the capability of my engine but gives me

the

conservative approach for reliability that I want while still producing

good

torque. I do not want to turn my engine at 5718 rpm which is what the
2.118:1 would give me, even though the engine would be able to take it.

If

I decide to fly when it's colder than 20 deg F it will get noisy because
I'll be over 0.92 mach, but I can just back off the power and let that

dense

air lift me up. The thing that made me decide to get into the 0.88-0.92
mach range at max power instead of being more conservative down around

0.80

mach was the sound I hear whenever I see a float-plane take off. There

must

be a reason why float-plane operators like those props that close to

mach.

I'm inclined to believe what the prop tip speed calculator website tells

me.

If you want maximum thrust (and I do) you need to be between 0.88 and

0.92

mach.

Mike Kimball
SR #044

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Posted: **Fri Feb 17, 2012 11:02 pm**

Mike FWIW I still think you are concentrating on tip speed way way too
much. Perhaps CAM will let you exchange ratios later if you need to like
Marcotte does... Anyway I maintain that you don't have the same
restrictions that spam can floatplanes have. Their engines typically
must make 2700 rpm to make the power. That tip speed and/or physical
prop diameter restrictions means losing lots of thrust and making lots
of noise. You have the opportunity to make thrust with the power they
are wasting making noise etc. If you want to make lots of takeoff thrust
and justify carrying the engine weight, you don't want to turn that prop
2700 rpm UNLESS it won't go course enough to absorb your engine power at
lower speed. That is very unlikely from what you've said.

You have thrust numbers for a 76" IVO. What ratio was that using? You
NEED to know. Do you have numbers for the 84" prop? With an 84" prop you
are really going to need a higher ratio than what was optimum for the
76" prop. Static thrust is only another small part of this but it's a
start and it's more significant than tip speed.

I really think you should look into this a little more based on what
you've said here. If this was for a high speed aircraft like a Lancair I
would not be near as concerned. I have never looked at LS1 torque curves
but a lot of this applies to all auto engines and some guys go through
several props and still end up changing to a higher ratio.

Ken

Mike Kimball wrote:

Yay, I have finally made a decision! I have decided to go ahead with the
IVO-PROP magnum 84" three bladed prop using their electric pitch control and
electronic governor for constant speed. I have also decided to fork out the
big bucks and go with the Firewall Forward CAM 500 helical gear drive PSRU.
The CAM 500 will also provide a place to mount my vacuum pump and solves
that little problem. The only thing I was struggling with was deciding on a
1.756:1 ratio versus 2.118:1. Using the handy prop tip speed calculator on
the web I have decided to go with the 1.756:1. It looks like I need to turn
an 84" prop about 2700 rpm to get the 0.88 mach speed (at 60 deg F) at the
tip that I need for maximum thrust. That puts my engine at a max takeoff rpm
of 4741 rpm. That's well below the capability of my engine but gives me the
conservative approach for reliability that I want while still producing good
torque. I do not want to turn my engine at 5718 rpm which is what the
2.118:1 would give me, even though the engine would be able to take it. If
I decide to fly when it's colder than 20 deg F it will get noisy because
I'll be over 0.92 mach, but I can just back off the power and let that dense
air lift me up. The thing that made me decide to get into the 0.88-0.92
mach range at max power instead of being more conservative down around 0.80
mach was the sound I hear whenever I see a float-plane take off. There must
be a reason why float-plane operators like those props that close to mach.
I'm inclined to believe what the prop tip speed calculator website tells me.
If you want maximum thrust (and I do) you need to be between 0.88 and 0.92
mach.

Mike Kimball
SR #044

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Posted: **Fri Feb 17, 2012 11:08 pm**

I think you're right. I need to look into this a bit more. The
manufacturer of the PSRU suggests that I would be happier with the 2.118:1
ratio as well. Thanks very much!

Mike Kimball
SR #044

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
klehman@albedo.net
Sent: Tuesday, May 20, 2003 10:11 AM
To: murphy-rebel@dcsol.com
Subject: Re: I picked a Prop and PSRU!

Mike FWIW I still think you are concentrating on tip speed way way too
much. Perhaps CAM will let you exchange ratios later if you need to like
Marcotte does... Anyway I maintain that you don't have the same
restrictions that spam can floatplanes have. Their engines typically
must make 2700 rpm to make the power. That tip speed and/or physical
prop diameter restrictions means losing lots of thrust and making lots
of noise. You have the opportunity to make thrust with the power they
are wasting making noise etc. If you want to make lots of takeoff thrust
and justify carrying the engine weight, you don't want to turn that prop
2700 rpm UNLESS it won't go course enough to absorb your engine power at
lower speed. That is very unlikely from what you've said.

You have thrust numbers for a 76" IVO. What ratio was that using? You
NEED to know. Do you have numbers for the 84" prop? With an 84" prop you
are really going to need a higher ratio than what was optimum for the
76" prop. Static thrust is only another small part of this but it's a
start and it's more significant than tip speed.

I really think you should look into this a little more based on what
you've said here. If this was for a high speed aircraft like a Lancair I
would not be near as concerned. I have never looked at LS1 torque curves
but a lot of this applies to all auto engines and some guys go through
several props and still end up changing to a higher ratio.

Ken

Mike Kimball wrote:

Yay, I have finally made a decision! I have decided to go ahead with the
IVO-PROP magnum 84" three bladed prop using their electric pitch control

and

electronic governor for constant speed. I have also decided to fork out

the

big bucks and go with the Firewall Forward CAM 500 helical gear drive

PSRU.

The CAM 500 will also provide a place to mount my vacuum pump and solves
that little problem. The only thing I was struggling with was deciding on

a

1.756:1 ratio versus 2.118:1. Using the handy prop tip speed calculator

on

the web I have decided to go with the 1.756:1. It looks like I need to

turn

an 84" prop about 2700 rpm to get the 0.88 mach speed (at 60 deg F) at the
tip that I need for maximum thrust. That puts my engine at a max takeoff

rpm

of 4741 rpm. That's well below the capability of my engine but gives me

the

conservative approach for reliability that I want while still producing

good

torque. I do not want to turn my engine at 5718 rpm which is what the
2.118:1 would give me, even though the engine would be able to take it.

If

I decide to fly when it's colder than 20 deg F it will get noisy because
I'll be over 0.92 mach, but I can just back off the power and let that

dense

air lift me up. The thing that made me decide to get into the 0.88-0.92
mach range at max power instead of being more conservative down around

0.80

mach was the sound I hear whenever I see a float-plane take off. There

must

be a reason why float-plane operators like those props that close to mach.
I'm inclined to believe what the prop tip speed calculator website tells

me.

If you want maximum thrust (and I do) you need to be between 0.88 and 0.92
mach.

Mike Kimball
SR #044

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