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rv7a(at)cox.net
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 Posted: Wed Mar 15, 2006 11:11 am Post subject: Blended Airfoil 72" vs. 74" |
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Does anyone have any information on pros and cons on choosing a 72" vs. 74" Hartzell blended airfoil prop? Have searched archives and was unable to find any specific information relative to propeller diameter.
Jim Thorne
7A-QB CHD
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lance553(at)comcast.net
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| Posted: Wed Mar 15, 2006 3:01 pm Post subject: Blended Airfoil 72" vs. 74" |
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-------------- Original message ----------------------
From: "Jim Thorne" <rv7a(at)cox.net>
| Quote: |
Does anyone have any information on pros and cons on choosing a 72" vs. 74"
Hartzell blended airfoil prop? Have searched archives and was unable to find
any specific information relative to propeller diameter.
Jim Thorne
7A-QB CHD
I asked this of one of Van's engineers and he advised me to go with the 74 for more thrust. I have 127 hours now on my Aerosport 0-360/74" combo. The airplane jumps off the ground and moves out smartly.
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Lance Johnson
RV-8A
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flyboy.bob(at)gmail.com
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| Posted: Wed Mar 15, 2006 6:53 pm Post subject: Blended Airfoil 72" vs. 74" |
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I also asked Van's the same question re: my RV-8 with O-360 clone . . . the
person I talked to recommended the 72" version . . . I really don't think
there is a world of difference?!
Bob in SE-Iowa
RV-8 - Finishing Slowly!!
On 3/15/06, Jim Thorne <rv7a(at)cox.net> wrote:
| Quote: |
Does anyone have any information on pros and cons on choosing a 72" vs.
74" Hartzell blended airfoil prop? Have searched archives and was unable to
find any specific information relative to propeller diameter.
Jim Thorne
7A-QB CHD
|
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LessDragProd(at)aol.com
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| Posted: Thu Mar 16, 2006 7:53 am Post subject: Blended Airfoil 72" vs. 74" |
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The difference may be more than performance.
The 72" diameter is the minimum diameter of the Hartzell propeller. Damage
the tips on a 72" diameter Hartzell, and the complete propeller is scrap.
If the 74" diameter blades are damaged, and can be trimmed to a 72"
diameter, or greater, then the blades would be useable. Unfortunately, the hub is
still scrapped.
Regards,
Jim Ayers
In a message dated 03/15/2006 6:53:42 PM Pacific Standard Time,
flyboy.bob(at)gmail.com writes:
I also asked Van's the same question re: my RV-8 with O-360 clone . . . the
person I talked to recommended the 72" version . . . I really don't think
there is a world of difference?!
Bob in SE-Iowa
RV-8 - Finishing Slowly!!
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luckymacy(at)comcast.net
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| Posted: Thu Mar 16, 2006 11:42 am Post subject: Blended Airfoil 72" vs. 74" |
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That's what Hartzell told me when I called them directly and so I ordered a 74" prop as well.
-------------- Original message --------------
From: LessDragProd(at)aol.com
| Quote: |
The difference may be more than performance.
The 72" diameter is the minimum diameter of the Hartzell propeller. Damage
the tips on a 72" diameter Hartzell, and the complete propeller is scrap.
If the 74" diameter blades are damaged, and can be trimmed to a 72"
diameter, or greater, then the blades would be useable. Unfortunately, the hub
is
still scrapped.
Regards,
Jim Ayers
In a message dated 03/15/2006 6:53:42 PM Pacific Standard Time,
flyboy.bob(at)gmail.com writes:
I also asked Van's the same question re: my RV-8 with O-360 clone . . . the
person I talked to recommended the 72" version . . . I really don't think
there is a world of difference?!
Bob in SE-Iowa
RV-8 - Finishing Slowly!!
|
That's what Hartzell told me when I called them directly and so I ordered a 74" prop as well.
-------------- Original message --------------
From: LessDragProd(at)aol.com
-- RV-List message posted by: LessDragProd(at)aol.com
The difference may be more than performance.
The 72" diameter is the minimum diameter of the Hartzell propeller. Damage
the tips on a 72" diameter Hartzell, and the complete propeller is scrap.
If the 74" diameter blades are damaged, and can be trimmed to a 72"
diameter, or greater, then the blades would be useable. Unfortunately, the hub
is
still scrapped.
Regards,
Jim Ayers
In a message dated 03/15/2006 6:53:42 PM Pacific Standard Time,
flyboy.bob(at)gmail.com writes:
-- RV-List message posted by: "Bob C. " <FLYBOY.BOB(at)GMAIL.COM>
I also asked Van's the same q
uestion re: my RV-8 with O-360 clone . . . the
person I talked to recommended the 72" version . . . I really don't think
there is a world of difference?!
Bob in SE-Iowa
RV-8 - Finishing Slowly!!
onics.com/contribution
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czechsix(at)juno.com
Guest
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| Posted: Thu Mar 16, 2006 12:58 pm Post subject: Blended Airfoil 72" vs. 74" |
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Hi Jim,
The general laws of aerodynamics say that the larger diameter will give
better low speed thrust and the smaller diameter will be better for high
speed flight. This may not hold true depending on how Hartzell shaped
the blades, but all other things being equal it should work this way.
Whether there's a measurable difference between these two diameters is
arguable. I got the 74" in part because it allows you to cut off 1" of
each tip in case of damage and still be airworthy. Of course it might be
more likely to get damaged if it's longer to begin with so this may be a
toss-up.
If I had to do it over, I'd be inclined to go with the smaller diameter
because during full power runups to set the low-pitch stop, my 74" prop
sucked up a lot of sand and now the paint looks like crap on the leading
edges. It's pretty close to the ground on the nosedraggers and 1" might
make a measurable difference in how much trash your prop picks up on the
ground.
Or just flip a coin and pick one : )
--Mark Navratil
Cedar Rapids, Iowa
RV-8A N2D 11.3 hours flying...
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Time: 11:11:54 AM PST US
From: "Jim Thorne" <rv7a(at)cox.net>
Subject: Blended Airfoil 72" vs. 74"
Does anyone have any information on pros and cons on choosing a 72" vs.
74" Hartzell
blended airfoil prop? Have searched archives and was unable to find any
specific information relative to propeller diameter.
Jim Thorne
7A-QB CHD
| | - The Matronics RV-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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gmcjetpilot(at)yahoo.com
Guest
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| Posted: Sat Mar 18, 2006 2:39 am Post subject: Blended Airfoil 72" vs. 74" |
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Mark:
Is actually not arguable it is just small. I have actual Hartzell data
as I mentioned, but not for the BA, for the C2YK.
Granted analytical data and actual performance on a plane may very,
but if comparing diameter on the same plane there will be real diffences,
they are just small. We are talking about 0.1% to 2.0% diffence, real
but small. The 74" has a real advantage at Vx or Vy speed in climb.
The 72" has a real but smaller advantage in high speed curise. For
most flyers the 74" is the way to go.
George
***************************************************************************************
Subject: Re: Blended Airfoil 72" vs. 74"
From: Mark E Navratil <czechsix(at)juno.com>
Hi Jim,
The general laws of aerodynamics say that the larger diameter will
give better low speed thrust and the smaller diameter will be better
for high speed flight. This may not hold true depending on how
Hartzell shaped the blades, but all other things being equal it should
work this way. Whether there's a measurable difference between
these two diameters is arguable.
---------------------------------
Use Photomail to share photos without annoying attachments.
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