[rebel-builders] Rebel Prop Diameter

Ron Shannon · Post by **Ron Shannon** » Sun Feb 19, 2012 5:46 pm

Cris,

The question can't be answered without more information. Maximum prop dia.
is a function of several things, including what engine is being used, the
prop pitch, and desired performance profile, i.e., whether emphasizing climb
vs. cruise. Maximum prop dia. will usually be limited by one or more of
those factors well before the prop is long enough to hit the ground. Of
course, at times even a taildragger will be in level attitude or less while
on or near the ground, for example, during a wheel landing or overzealous
takeoff rotation, etc.

If you specify the engine and whether you wish to emphasize climb vs. cruise
performance, or neither, I'm sure you'll get opinions about the optimal
combination of dia. and pitch. The best source of info will often be the
prop manufacturer.

Ron
254R

On Wed, Nov 18, 2009 at 3:44 AM, Karen McCaffery <cristucker@webtv.net>wrote:

Gentleman, What is the maximum two blade prop diameter one can safely
swing on a Rebel with bungee gear?
Cris #719

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Karen McCaffery · Post by **Karen McCaffery** » Sun Feb 19, 2012 5:46 pm

Hi Ron, I am using a Lyc. 0-235 C1 engine.
Craig Catto and I have had several conversations. I suggested to him that I was more interested in climb than cruise. He is wanting to sell me a 78" X 46 pitch.
composite prop. He says it should turn 2200 to 2300 rpm static and should turn 2600-2650 WOT. I would like to know if a 78 inch prop might ever strike the ground
with the bungee gear extended with std.tires.
Thanks, Cris #719

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Ron Shannon · Post by **Ron Shannon** » Sun Feb 19, 2012 5:46 pm

This question still can't be answered unless you're more specific about what
you mean by "ever". [Just kidding!! LOL]

I have spring gear which I believe sits a little higher than the bungee gear
in level attitude, so I can't even measure the radius to ground here.
Personally, I'd take Catto's advice before most others. No doubt, some other
good opinions will show up here soon though.

Ron
254R

On Wed, Nov 18, 2009 at 12:20 PM, Karen McCaffery <cristucker@webtv.net>wrote:

Hi Ron, I am using a Lyc. 0-235 C1 engine.
Craig Catto and I have had several conversations. I suggested to him that
I was more interested in climb than cruise. He is wanting to sell me a 78"
X 46 pitch.
composite prop. He says it should turn 2200 to 2300 rpm static and should
turn 2600-2650 WOT. I would like to know if a 78 inch prop might ever
strike the ground
with the bungee gear extended with std.tires.
Thanks, Cris #719

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Bob Palmer · Post by **Bob Palmer** » Sun Feb 19, 2012 5:46 pm

Cris,

I can tell you that an our Elite is approximately 48" crank center to
the ground with the tail up to roughly level attitude. That is without
wings so weight would bring that down a bit. We have 5 inches of tire
(if they were deflated -5") and minus a buffer of about 4" is pretty
close to what the prop guy is recommending. The little research that I
have done tells me that the longer the prop the more efficient up to a
tip speed close to the speed of sound. I think that is about an 80" prop
for a Lycoming @2750. However, the longer the noisier. I understand some
Super Cubs are running 80" props. Three bladed props are quieter and are
much smaller in diameter.

Unfortunately, I can't say for sure that a Rebel is the same height as
an Elite.

Bob
773E

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craig · Post by **craig** » Sun Feb 19, 2012 5:46 pm

Or...what about an 84" prop used on a radial engine radial engine with 26"
tires? Yes, I'm back in the radial/Lyc dilemma. Someone help me!! The
Lyc's a no-brainer. What about the rotec? craig

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Mike Davis · Post by **Mike Davis** » Sun Feb 19, 2012 5:46 pm

There was a guy down in Juneau that had a Borer on a Rebel, don't remember
if it was an 80" or 82" though... but he had 29" tires too. Had a picture
on the MAM website for a while labeled "One Tired Rebel".

Mike

----- Original Message -----
From: "Bob Palmer" <rtpalmer@shaw.ca>
To: <rebel-builders@dcsol.com>
Sent: Wednesday, November 18, 2009 12:18 PM
Subject: Re: [rebel-builders] Rebel Prop Diameter

Cris,

I can tell you that an our Elite is approximately 48" crank center to
the ground with the tail up to roughly level attitude. That is without
wings so weight would bring that down a bit. We have 5 inches of tire
(if they were deflated -5") and minus a buffer of about 4" is pretty
close to what the prop guy is recommending. The little research that I
have done tells me that the longer the prop the more efficient up to a
tip speed close to the speed of sound. I think that is about an 80" prop
for a Lycoming @2750. However, the longer the noisier. I understand some
Super Cubs are running 80" props. Three bladed props are quieter and are
much smaller in diameter.

Unfortunately, I can't say for sure that a Rebel is the same height as
an Elite.

Bob
773E

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Richard Wampach · Post by **Richard Wampach** » Sun Feb 19, 2012 5:46 pm

There is information in the FAR's. No I have not looked it up. As memory
serves. With everything that can go wrong, such as flat nose strut and nose
tire for trikes, or flat mains for tail wheel. A prop clearance of 1 1/2"
to the ground is required. That is if you choose to use FAA approved data
on your project. You should look that up That should be in part 23 under
design requirements.

Dick

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]
Sent: Wednesday, November 18, 2009 1:41 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] Rebel Prop Diameter

There was a guy down in Juneau that had a Borer on a Rebel, don't remember
if it was an 80" or 82" though... but he had 29" tires too. Had a picture
on the MAM website for a while labeled "One Tired Rebel".

Mike

----- Original Message -----
From: "Bob Palmer" <rtpalmer@shaw.ca>
To: <rebel-builders@dcsol.com>
Sent: Wednesday, November 18, 2009 12:18 PM
Subject: Re: [rebel-builders] Rebel Prop Diameter

Cris,

I can tell you that an our Elite is approximately 48" crank center to
the ground with the tail up to roughly level attitude. That is
without wings so weight would bring that down a bit. We have 5 inches
of tire (if they were deflated -5") and minus a buffer of about 4" is
pretty close to what the prop guy is recommending. The little research
that I have done tells me that the longer the prop the more efficient
up to a tip speed close to the speed of sound. I think that is about
an 80" prop for a Lycoming @2750. However, the longer the noisier. I
understand some Super Cubs are running 80" props. Three bladed props
are quieter and are much smaller in diameter.

Unfortunately, I can't say for sure that a Rebel is the same height as
an Elite.

Bob
773E

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Walter Klatt · Post by **Walter Klatt** » Sun Feb 19, 2012 5:46 pm

I am sure the Borer would give you great climb, but how much would you
sacrifice in cruise. I know the Supercubs don't go fast with these, but not
sure if that is because of the plane or the prop.

Walter

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]
Sent: November 18, 2009 1:41 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] Rebel Prop Diameter

There was a guy down in Juneau that had a Borer on a Rebel, don't remember
if it was an 80" or 82" though... but he had 29" tires too. Had a picture
on the MAM website for a while labeled "One Tired Rebel".

Mike

----- Original Message -----
From: "Bob Palmer" <rtpalmer@shaw.ca>
To: <rebel-builders@dcsol.com>
Sent: Wednesday, November 18, 2009 12:18 PM
Subject: Re: [rebel-builders] Rebel Prop Diameter

Cris,

I can tell you that an our Elite is approximately 48" crank center to
the ground with the tail up to roughly level attitude. That is without
wings so weight would bring that down a bit. We have 5 inches of tire
(if they were deflated -5") and minus a buffer of about 4" is pretty
close to what the prop guy is recommending. The little research that I
have done tells me that the longer the prop the more efficient up to a
tip speed close to the speed of sound. I think that is about an 80" prop
for a Lycoming @2750. However, the longer the noisier. I understand some
Super Cubs are running 80" props. Three bladed props are quieter and are
much smaller in diameter.

Unfortunately, I can't say for sure that a Rebel is the same height as
an Elite.

Bob
773E

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Mike Davis · Post by **Mike Davis** » Sun Feb 19, 2012 5:46 pm

I seem to recall him saying that he cruised about 90, so definitely slow...
but he didn't build it for cross country flying and was perfectly happy with
it. I have a climb prop & big tires on my Cessna and usually find the
scenery here in Alaska more than enough to keep me happy with my slower
cruise.

Mike

----- Original Message -----
From: "Walter Klatt" <Walter.Klatt@shaw.ca>
To: <rebel-builders@dcsol.com>
Sent: Wednesday, November 18, 2009 4:30 PM
Subject: RE: [rebel-builders] Rebel Prop Diameter

I am sure the Borer would give you great climb, but how much would you
sacrifice in cruise. I know the Supercubs don't go fast with these, but
not
sure if that is because of the plane or the prop.

Walter

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]
Sent: November 18, 2009 1:41 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] Rebel Prop Diameter

There was a guy down in Juneau that had a Borer on a Rebel, don't remember
if it was an 80" or 82" though... but he had 29" tires too. Had a picture
on the MAM website for a while labeled "One Tired Rebel".

Mike

----- Original Message -----
From: "Bob Palmer" <rtpalmer@shaw.ca>
To: <rebel-builders@dcsol.com>
Sent: Wednesday, November 18, 2009 12:18 PM
Subject: Re: [rebel-builders] Rebel Prop Diameter

Cris,

I can tell you that an our Elite is approximately 48" crank center to
the ground with the tail up to roughly level attitude. That is without
wings so weight would bring that down a bit. We have 5 inches of tire
(if they were deflated -5") and minus a buffer of about 4" is pretty
close to what the prop guy is recommending. The little research that I
have done tells me that the longer the prop the more efficient up to a
tip speed close to the speed of sound. I think that is about an 80" prop
for a Lycoming @2750. However, the longer the noisier. I understand some
Super Cubs are running 80" props. Three bladed props are quieter and are
much smaller in diameter.

Unfortunately, I can't say for sure that a Rebel is the same height as
an Elite.

Bob
773E

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