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02-09-2009, 05:23 AM
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Join Date: Jan 2005
Location: NC25
Posts: 3,507
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Quote:
Originally Posted by David-aviator
Gary,
Gary Hertzler won the CAFE 400 in 1990 with his VEZ and a FP prop. Klaus Savier has recorded 100 mpg with his VEZ, also with a FP prop. The efficiency gurus can not afford the weight of the CS system. For all out speed, the CS wins. For efficiency it loses.
If you'd rather walk than fly behind a fixed pitch prop, have at it. I'd rather fly anything than walk. 
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We are talkng about RVs not EZs. Lets compare RVs to RVs and EZs to EZs. Show me links to the RESULTS I do not want to take your WORD for it.
How may RV PIC flying hours do you have to backup your statement: "I'd rather fly anything than walk." ?
__________________
Gary A. Sobek
NC25 RV-6 Flying
3,400+ hours
Where is N157GS
Building RV-8 S/N: 80012
To most people, the sky is the limit.
To those who love aviation, the sky is home.
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02-09-2009, 05:59 AM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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Hi Todd....
Quote:
Originally Posted by Pallet
Maybe this has already been dicussed, but with a fixed prop set up for cruise, I'm wondering how much longer ground roll this would take.
Anyone with experience that has kept track?
I'm thinking possible grass strip.
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....I have over 440 hours on my 0-360 powered -6A and its Catto. I've flown quite a few other RV's with 360's and CS props and the acceleration is phenomenal compared to my airplane and climb is much better. That said, however, the weight on the nose is definitely notable, as is the reduced glide at idle. FWIW, a FP RV anything is no slouch considering that I still climb at near 2000 FPM solo and use around 650 feet takeoff roll. The CS airplanes get off in about half that.
Regards,
__________________
Pierre Smith
RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15 Sold
Air Tractor 402 PT-6-20 Sold
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga
It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132
Dues gladly paid!
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02-09-2009, 06:29 AM
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Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514
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Quote:
Originally Posted by RV6_flyer
We are talkng about RVs not EZs. Lets compare RVs to RVs and EZs to EZs. Show me links to the RESULTS I do not want to take your WORD for it.
How may RV PIC flying hours do you have to backup your statement: "I'd rather fly anything than walk." ?
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You win with more RV PIC time, but I'd still rather fly anything than walk.
The CAFE 400 results are on their web site. Do a search on Klaus Savier, that's how I found the 100 mpg effort. He is also mentioned at CAFE with his Lightspeed stuff when they did the ignition testing. I've sat in on one of his lectures at OSH and he is one of my favorite guys in this business. Very interesting mountain of data on electronic ignition at CAFE, in fact more than my mind can absorb in one sitting. One conclusion was clear with regard to magnetos, they are OK up to about 8500', I liked that.
Gary, the CS speed prop is good. The FP prop is also very good for those on a short budget and/or a fetish about weight. My NG weight has been reduced from 364 to 244 pounds, I love it notwithstanding the slightly reduced take off performance. The RV is a delight to fly with either prop system.
(This thread should have died a week ago - every square inch of ground has been plowed on the subject at least one time)
__________________
RV-12 Build Helper
RV-7A...Sold #70374
The RV-8...Sold #83261
I'm in, dues paid 2019 This place is worth it!
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02-09-2009, 06:57 AM
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Join Date: Apr 2005
Location: KSLC
Posts: 4,021
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Quote:
Originally Posted by David-aviator
The FP prop is also very good for those on a short budget and/or a fetish about weight.
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Regarding weight..........
I seen the words "light & nimble" used. Yes a lightweight RV is kind of like a Cub, and a heavier RV, thanks to a larger displacement engine and C/S prop is more comparible to a P-51 fighter. And the F1/Rockets are even closer!
And BTW, I have been in both Cub's and Mustangs for comparison sake...
L.Adamson
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02-09-2009, 09:43 AM
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Join Date: Oct 2007
Location: Alviso, CA
Posts: 405
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Hours don't equate to being right
Quote:
Originally Posted by RV6_flyer
.................
MY OPINION:
"I would rather walk than own an RV that does not have a Constant Speed prop." I have over 2,000 PIC hours in RVs when I make that statement. How many RV hours do you have to backup your opinion?
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Except in being clear on what you like to fly behind. I'm not questioning your choice. These decisions, like everything else in an airplane, are about trades between one feature or another. The extra few hundred FPM are not worth it to me, they are to you. No problemo.
I don't need empirical data to know that it takes less energy to lift a lighter airplane. That is immutable fact. Likewise that it takes more energy to cruise in a heavier airplane.
That CS will outperform FP in takeoff and climb is not being disputed. However, it cannot have greater fuel efficiency when doing so because it weighs more. Unless you have found a way to violate the laws of physics, that is fact not opinion.
Does the 360 have greater fuel efficiency than the 320? If so, fine, but it is not relevant to FP verses CS, since either can use either. In fact, I can fly FP and 360 with less weight than CS and 320.
__________________
Steve Brown
N598SD - RV9A second owner
O-320, 9:1 pistons, Catto 3 blade
KRHV - Reid Hillview airport, San Jose, CA
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02-09-2009, 10:12 AM
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Join Date: Nov 2007
Location: Keller, TX
Posts: 151
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The big question is - What kind of primer did you use on your prop? 
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02-09-2009, 03:20 PM
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Join Date: Jan 2005
Location: England
Posts: 1,087
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Quote:
Originally Posted by Steve Brown
Raising the extra weight of a heavier engine and prop to the same altitude takes more energy.
In this case the tables have turned on CS verses FP because in climb the FP will typically be turning lower RPM than CS, reducing friction & prop drag. The CS pilot could decrease the RPMs even further, but then would definitely NOT out climb the FP pilot since he will be using less power to raise more weight.
Assuming: - Equivalent aerodynamic & propulsive efficiency
- CS somewhat more efficient at cruise power settings because of running at lower RPM
- CS somewhat less efficient at cruise power settings due to extra weight resulting in greater angle of attack, resulting in more drag.
- CS takes more energy in climb due to greater weight
- FP somewhat more efficient in climb due to turning lower RPMs
Those more knowledgeable than me could probably put numbers on those relationships. Which would win overall would depend on the time in climb, verses time in cruise, specific weight differences, specific prop efficiency differences, and possibly the phase of the moon.
I would not want to bet on the outcome, but if I had to bet, I would go with the FP prop.
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I think you have convinced yourself that an FP would win out over a CS when all of the data this is available suggests otherwise. The weight difference between a FP O-320 and a CS IO-360 is probably around 50lb, or about 3%, if all other factors are equal. If you can measure the increased fuel burn due to that 3% then that's really good data collection! The CS is more efficient in the cruise because the pilot can set the engine to operate at the rpm where the prop is most efficient, the FP cannot. Assuming the FP is optimised for the cruise, any advantage in the climb through lower revs may be negated due running at sub-optimum conditions.
All I can tell you is that in my experience CS is more ecomomic than FP, and bigger engines are more economic than smaller engines, when flying at the same speed, (which is as fast as the slowest airplane will go).
Pete
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02-09-2009, 05:27 PM
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Join Date: May 2007
Location: Pinedale, WY
Posts: 118
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shows how much I know...
I saw the original post when it was new. I figured this subject had been beat up enough that someone would just refer the poster to a previous thread, and it would fade away. But, danged if it hasn't turned into quite the soap opera! And all over whether, on a scale of 1-10, an RV with a FP only rates a 9.6 and the CS is a 9.8  . Or is it the other way around?
I read somewhere about a guy, years ago, with an RV-3 with something like a dinky little O-290/wood prop. I guess there were some uninformed folks around that thought even that was pretty cool.
BTW, I don't think we've heard from the original poster lately. He probably ran for cover. 
__________________
David Daniel
RV-6, flying
Rans S7S, building ('cause Van's doesn't have one!)
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02-09-2009, 06:22 PM
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Join Date: Jan 2005
Posts: 848
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Anybody remember Lindbergh?
Gary,
I did a quick search for Lindbergh and oversquare and came up with this, as well as many other links. There didn't seem to be a reason to read any farther, but then you convinced me years ago and my Hartzell was planned into the budget.
http://www.experimentalaircraft.info...aft-engine.php
Oh good Lord, here's another. I love this stuff. Here Deakin goes into the friction thing as well as tons of other info, but on his IO-550 he claims a 20 horsepower loss to friction by spinning the prop up from 2,100 to 2,700 rpm's. For those unfamiliar he has done extensive dyno testing and puts on seminars on engine management.
http://www.avweb.com/news/pelican/182583-1.html
__________________
Bryan 9A Sold
Beech S35, and daydreams of a Super 8 or a Rocket starting to take over my brain.
Last edited by Bryan Wood : 02-09-2009 at 06:45 PM.
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02-10-2009, 07:20 AM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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Hi Dave....
....I'm 63 and built a Cassutt in '73 when a dollar was....sho 'nuff, a dollar and fresh out of the Army poor but I wanted a) a fast airplane, or b) aerobatic, if not fast. Fortunately, my 12 G airplane was both.
Van came along then and offered a super deal, near 200 MPH airplane, aerobatic for a bargain price, cheap engines and a wood prop. Nowadays, high tech has radically changed everything and steam is out, glass is in...albeit at a price. It stands to reason then, a $75-$100,000 airplane must have a CS prop, no?
An RV can still be built in the $30's but that wouldn't include a CS prop, would it?
My .02c
__________________
Pierre Smith
RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15 Sold
Air Tractor 402 PT-6-20 Sold
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga
It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132
Dues gladly paid!
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