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Jerry Cochran
Joined: 10 Jan 2006
Posts: 111
Location: Wilsonville, OR
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 Posted: Thu Nov 02, 2006 9:24 am Post subject: Prop: FP faster than CS? |
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Bob,
First time I've ever seen a claim that FP is 10 knots faster than CS. Would you care to elaborate?
Jerry Cochran
Time: 08:28:39 AM PST US
From: Bob <panamared3(at)brier.net>
Subject: Re: Fuel sensors
--> RV-List message posted by: Bob <panamared3(at)brier.net>
I do not fly with a CS prop. In my opinion it would only give me about 100
FPM more in climb and it would cost me 10 kts in speed, it also would cost
me 45 lbs and increased complexity and maintenance costs.
[quote][b]
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dale1rv6(at)comcast.net
Guest
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| Posted: Thu Nov 02, 2006 9:46 am Post subject: Prop: FP faster than CS? |
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Hi,
I changed from a Sensenich metal prop (mfg 2001) to a new standard Hartzell in February on a RV6a with Lyc O-360 (carb). The Sensenich was quieter and at WOT would go to 2800 rpm, yielding about 3-5 knots more than the Hartzell (which I limited to 2700 rpm). I don’t usually get noticeable speed increase when running the Hartzell 2700 vs 2600 rpm; therefore I don’t think the Hartzell would close that gap even if I raised the rpm to 2800. I am very happy with the Hartzell. I definitely get more for my money at normal cruise, and at any cruise speed. Weight increase from change was 16lbs.
Dale
RV6a 710 hours
From: owner-rv-list-server(at)matronics.com [mailto:owner-rv-list-server(at)matronics.com] On Behalf Of Jerry2DT(at)aol.com
Sent: Thursday, November 02, 2006 12:22 PM
To: rv-list(at)matronics.com
Subject: Prop: FP faster than CS?
Bob,
First time I've ever seen a claim that FP is 10 knots faster than CS. Would you care to elaborate?
Jerry Cochran
Time: 08:28:39 AM PST US
From: Bob <panamared3(at)brier.net>
Subject: Re: Fuel sensors
--> RV-List message posted by: Bob <panamared3(at)brier.net>
I do not fly with a CS prop. In my opinion it would only give me about 100
FPM more in climb and it would cost me 10 kts in speed, it also would cost
me 45 lbs and increased complexity and maintenance costs.
0123456789012345
[quote][b]
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panamared3(at)brier.net
Guest
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| Posted: Fri Nov 03, 2006 6:38 am Post subject: Prop: FP faster than CS? |
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At 11:21 AM 11/2/06, you wrote:
| Quote: | Bob,
First time I've ever seen a claim that FP is 10 knots faster than CS.
Would you care to elaborate?
|
Keeping horsepower constant, speed as I understand it is determined by the
RPM and the pitch. When you get a fixed pitch prop you can have any pitch
you want, you just can not change it. My prop was custom designed to
provide optimum climb/cruise speed for my airplane (C/S props do give a
better climb performance than my prop).
Also blade efficiency has a part to play with this. As I said my prop was
custom made, the C/S props are not, as I understand it.
My prop only weights about 11 pounds, if my memory serves me
correctly. The extra 45 pounds for a C/S prop right on the nose really
hurts in additional drag. My aircraft is tail heavy rather than nose
heavy. This tends to reduce the required downward lift of the horizontal
stab (to maintain level flight), which in turns reduces the drag produced
by lift (induced drag I think, I always forget which is which). 45 pounds
does not seem like much, but then multiply it by the moment it creates from
the center of gravity and it becomes a much larger number.
Now if I had an 11 pound C/S prop then my RV would probably go faster with
the C/S prop versus the fixed pitch.
I am not an aerodynamic engineer as are some on this list (I did major in
aerodynamics in college). They may confirm or dispute my opinions. My
opinions are not based upon actual test data, but on aeronautical
principals as I understand them. In comparison to Vans performance figures
for the RV7 (I know different airplane etc) I get about 10 kts faster
cruise speed with my fixed pitch prop than his RV7 with a C/S prop. I
realize that this is not a scientific valid comparison.
What is neat about this list you can buy into my opinion or not. I could
be wrong and if so, I am confident that many people on this list will let
me know.
Bob
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sportav8r(at)gmail.com
Guest
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| Posted: Fri Nov 03, 2006 7:29 am Post subject: Prop: FP faster than CS? |
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What the list should know is that the true secret to Bob's fast speed
is the hand-brushed olive drab latex house paint finish on his
airframe.
Bob's night-fighter is so fast, when he comes by to visit me, he's
gone before I know he's even been here, which explains why I never see
him - maybe. It couldn't be that he's forgotten where I live and
never comes over anymore 
Where ya been, buddy?
-Stormy
On 11/3/06, Bob <panamared3(at)brier.net> wrote:
| Quote: |
At 11:21 AM 11/2/06, you wrote:
>Bob,
>
>First time I've ever seen a claim that FP is 10 knots faster than CS.
>Would you care to elaborate?
>
Keeping horsepower constant, speed as I understand it is determined by the
RPM and the pitch. When you get a fixed pitch prop you can have any pitch
you want, you just can not change it. My prop was custom designed to
provide optimum climb/cruise speed for my airplane (C/S props do give a
better climb performance than my prop).
Also blade efficiency has a part to play with this. As I said my prop was
custom made, the C/S props are not, as I understand it.
My prop only weights about 11 pounds, if my memory serves me
correctly. The extra 45 pounds for a C/S prop right on the nose really
hurts in additional drag. My aircraft is tail heavy rather than nose
heavy. This tends to reduce the required downward lift of the horizontal
stab (to maintain level flight), which in turns reduces the drag produced
by lift (induced drag I think, I always forget which is which). 45 pounds
does not seem like much, but then multiply it by the moment it creates from
the center of gravity and it becomes a much larger number.
Now if I had an 11 pound C/S prop then my RV would probably go faster with
the C/S prop versus the fixed pitch.
I am not an aerodynamic engineer as are some on this list (I did major in
aerodynamics in college). They may confirm or dispute my opinions. My
opinions are not based upon actual test data, but on aeronautical
principals as I understand them. In comparison to Vans performance figures
for the RV7 (I know different airplane etc) I get about 10 kts faster
cruise speed with my fixed pitch prop than his RV7 with a C/S prop. I
realize that this is not a scientific valid comparison.
What is neat about this list you can buy into my opinion or not. I could
be wrong and if so, I am confident that many people on this list will let
me know.
Bob
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khorton01(at)rogers.com
Guest
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| Posted: Fri Nov 03, 2006 7:43 am Post subject: Prop: FP faster than CS? |
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On 3 Nov 2006, at 10:33, Bob wrote:
| Quote: |
At 11:21 AM 11/2/06, you wrote:
> Bob,
>
> First time I've ever seen a claim that FP is 10 knots faster than
> CS. Would you care to elaborate?
>
Keeping horsepower constant, speed as I understand it is determined
by the RPM and the pitch. When you get a fixed pitch prop you can
have any pitch you want, you just can not change it. My prop was
custom designed to provide optimum climb/cruise speed for my
airplane (C/S props do give a better climb performance than my prop).
|
The propulsive horsepower is equal to the horsepower delivered by the
engine times the propeller efficiency. You were turning the FP prop
up to 2800 rpm, but only running at 2700 with the CS prop, so the
engine was making more power when with the FP prop. I don't recall
you said which FP prop you had, but I have seen several reports that
indicate the Sensenich has slightly higher prop efficiency than the
old Hartzell, as the old Hartzell was not optimized for RV speeds.
The newer blended airfoil Hartzell is apparently more efficient than
the older Hartzell, and it may have finally equalled or exceeded the
Sensenich.
Of course at lower speed conditions, and engine with a FP prop is
turning at lower rpm, and thus makes lower power than if it had a CS
prop. But in cruise, it is possible for a FP prop to be faster, if
it is optimized for RVs, and the CS prop isn't.
| Quote: |
Also blade efficiency has a part to play with this. As I said my
prop was custom made, the C/S props are not, as I understand it.
My prop only weights about 11 pounds, if my memory serves me
correctly. The extra 45 pounds for a C/S prop right on the nose
really hurts in additional drag. My aircraft is tail heavy rather
than nose heavy. This tends to reduce the required downward lift
of the horizontal stab (to maintain level flight), which in turns
reduces the drag produced by lift (induced drag I think, I always
forget which is which). 45 pounds does not seem like much, but
then multiply it by the moment it creates from the center of
gravity and it becomes a much larger number.
|
The drag penalty at cruise from 34 lb on the nose would likely be
small, in my opinion. It would be overshadowed by the differences in
engine power and prop efficiency. If you kept the engine and prop
the same, and added the 34 lb on the nose, you might be able to
measure a very, very small difference in speed.
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://www.kilohotel.com/rv8
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aerokinetic(at)sbcglobal.
Guest
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| Posted: Fri Nov 03, 2006 8:31 am Post subject: Prop: FP faster than CS? |
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RPM is horsepower...
most fixed-pitch guys (with wood props anyway) overwind their engines and see more speed than a similar constant-speed equipped plane. This speed comes at the price of higher fuel burns though. Pretty common knowledge in racing circles...
Scott
N4ZW
3 years racing my -4 in the Airventure Cup...
[quote][b]
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panamared3(at)brier.net
Guest
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| Posted: Fri Nov 03, 2006 1:49 pm Post subject: Prop: FP faster than CS? |
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| Quote: |
What the list should know is that the true secret to Bob's fast speed
is the hand-brushed olive drab latex house paint finish on his
airframe.
Bob's night-fighter is so fast, when he comes by to visit me, he's
gone before I know he's even been here, which explains why I never see
him - maybe.
|
Bill
Boy are you in trouble now. Releasing classified National Security Secrets
on the internet are we? I would sure hate to be in your shoes when the
Homeland Security, FBI, ATF, Fincastle Police Department and the worst of
all the Dreaded RV List Police get a hold of you!
Unfortunately, the NightFighter is no more. It will soon emerge as
something else. When one of the locals asked what I was doing, I told him
it would be a surprise. He asked if I was going to paint my aircraft and I
told him that truly would be a surprise. You can't beat that house paint
finish (actually it is not that good) nor can you see it.
Bob
RV6 the former NightFighter
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gmcjetpilot(at)yahoo.com
Guest
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| Posted: Sat Nov 04, 2006 8:02 am Post subject: Prop: FP faster than CS? |
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Yes RPM means more HP, about 3-5 HP per 100 RPM. FP, turning faster makes more HP, than a C/S governed to maintain a max RPM, usually 2,700 RPM. Of course this works in the C/S props advantage on takeoff and climb, because you can (gear down or go to low pitch) and turn more RPM's than a FP, which is stuck in high gear, (high pitch).
Metal Fixed Pitch props like the Sensenich tend to be more efficient than wood fixed pitch because of the airfoil thickness. That means they have potential to also be faster. However the RENO racers are running 12" long prop extensions and a light weight WOOD prop is safer for them, especially at the high RPMs they run at. It is not that METAL props can't be safe, only that you have to test every installation and RPM to assure it is safe. Wood is much more forgiving. However it is not ideal for performance.
Vans Last PROP test compared C/S props and one Sensenich prop. (here is a photo copy of results.)
http://img82.imageshack.us/my.php?image=prop200415me.jpg
The Sensenich actually was faster than all, but the new Hartzell BA prop. However as was mentioned at the cost of higher RPM and of course fuel burn. The BA was 208.9 mph and the Sensenich was estimated to be 207.9 at equal 2,500 RPM. My est is the Sensenich throttled back to maintain 2,500 rpm would actually be slower than 207.9 MPH because of, pumping loss, or induction drag or restriction from a partially closed throttle. Never the less the Sensenich is a good performer and value. That is another reason or advantage of C/S props, they're more efficient, you can run WOT and adjust the RPM with out moving the throttle.
A fixed pitch prop is optimal at only one speed power setting. A constant speed is more efficient at a wide range of air speeds and power settings. Its like a car with one gear or one with 6 gears. EFFICIENCY means the power at the crank shaft is turned into thrust. Props max efficiency run around 80% plus/minus. Wood props tend to be thicker and not as efficient, turning engine HP into thrust and thinner metal props. As mentioned metal is harder to design and test, which is critical.
Prop weight HAS little to do with top speed. A light Prop does affect payload, CG, yes! A lighter prop can help or hurt. A RV-7 like mine with a O360 needs the nose weight to get full use of the baggage area.
Bottom LINE the FP is a compromise and efficient at ONE POINT, a C/S is more efficient at a wide range of conditions but cost and weighs more. It is possible a well designed FP metal prop can be almost as efficient or as efficient as a C/S prop at one point, but the FP prop sacrifices performance in other flight regimes. Also from Van's test the Sensenich Rocks. Wood props do have the advantage of being smoother.
Cheers George RV-7, RV-4, B757
Access over 1 million songs - Yahoo! Music Unlimited [url=http://pa.yahoo.com/*http://us.rd.yahoo.com/evt=36035/*http://music.yahoo.com/unlimited/]Try it today.[/url] [quote][b]
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