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  #21  
Old 02-04-2009, 10:58 AM
Jerry Cochran's Avatar
Jerry Cochran Jerry Cochran is offline
 
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Location: Sherwood, Oregon
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Quote:
Originally Posted by Andy Hill View Post
We have a C/S... and run a Formation School with FP and C/S.

One aspect that has not been mentioned above is aerobatics... I'm doing some Formation Aerobatics and potentially Display stuff, and the carefree handling in these areas of the C/S, particularly approaching VNE, is a bonus

Andy & Ellie Hill
RV-8 G-HILZ
Andy,

Could you elaborate on the above, for instance in loops., both up and downhill? What are the main differences?

Jerry
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  #22  
Old 02-04-2009, 11:09 AM
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n5lp n5lp is offline
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Location: Carlsbad, NM
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Quote:
Originally Posted by Jerry Cochran View Post
Andy,

Could you elaborate on the above, for instance in loops., both up and downhill? What are the main differences?

Jerry
The main difference is that with a fixed pitch prop, on the downside of a loop, it may be necessary to retard the throttle to prevent the engine from exceeding RPM redline.
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Carlsbad, NM

RV-6 N441LP Flying
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  #23  
Old 02-04-2009, 11:30 AM
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Andy Hill Andy Hill is offline
 
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Jerry... Larry's given the quick answer

A FP will have an IAS at full power at Max RPM. For a "Cruise" Prop this will be quite a high speed (150K+?) especially at cruise altitudes... Doing gentle aerobatics at height (say 3000'+), with moderate entry/exit speeds (~140KIAS), it might not trouble you...

Increase the IAS to ~195KIAS, drop the altitude to not a lot, and now do your aeros on someone's wing, and keeping the RPM in your scan becomes a See this Link

Andy & Ellie Hill
RV-8 G-HILZ
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  #24  
Old 02-04-2009, 04:36 PM
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miyu1975 miyu1975 is offline
 
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Location: Indianapolis, IN
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"You won't lose anything on top end speed if you choose the right fixed pitch prop."

Can you elaborate on the right fixed pitch prop?. I have always said I am going to put a CS prop up front, but dollar for dollar I may end up with an FP prop. Seems like it is about 7k to 8k$$$ less upfront too. I only know of the Sensenich f/p..what are others?.. other than wood.
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  #25  
Old 02-04-2009, 04:54 PM
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Chino Tom Chino Tom is offline
 
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Location: Chino, CA
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Default eat beans......

Which ever way you choose you will have a great airplane. But IMHO the C/S makes a great airplane even better. For me the ability to turn max rpm
at takeoff at airports in the west where the Density Altitude in the summer is
7k+ is real nice.... Rosie should chime in here...he has had both. A wise
man once told me...."eat beans for a year if you have to....but buy a C/S prop!"
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RV-8A,180/CS/Carb, AFS 4500 EFIS/EMS
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  #26  
Old 02-04-2009, 05:41 PM
N62XS N62XS is offline
 
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Location: Hazlehurst, GA
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Default Had both, FP from now on.

I have had a CS on a Lancair, a Mooney and a RV. I have owned a FP on a Mooney and part owner of another. On every CS(Hartzell and WW), ADs, SBs, governor issues and most recently major issues with the prop company have soured me on the benefits of a CS prop in the future. A FP cruise prop will not cost me enough takeoff or climb out performance to justify repeating my past CS experiences. Simplicity, cost and maintenance are the primary reasons my nearly complete RV-6A will have a FP prop. Future project like a RV-10, HRII and Ercoupe, all already in house, will have FP props. A guy like Craig Catto is the reason all of them but the Ercoupe will have a Catto prop.
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  #27  
Old 02-04-2009, 06:11 PM
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hevansrv7a hevansrv7a is offline
 
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Location: Detroit, MI
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Default CS better on Fuel in Theory

Quote:
Originally Posted by lsu-rv View Post
ok, i'm leaning CS, but this thread is interesting. I plan on IO so i can run lean of peak easier. If i cruise 6K - 11K will a CS allow me to burn less fuel?

I have never flown behind fixed pitch in something faster than a 172 or citabria. My rv6a had io320 and CS and my bonanza is CS.

I don't want to start an argument, just some of you who have flow both please enlighten me on fuel burn at same speed and LOP with each?
jeff h
I fly FP only. However, at lower power settings, the ability to reduce RPM's and thus fully open the throttle plate (yes, FI engines have them, too) and reduce pumping losses should mean that the CS can operate more economically. However, if you want to cruise at 75% at 8,000' then the CS has run out of advantage because even the FP is wide open up there. Same goes for higher, of course. I have no idea how big the advantage is at, say, 65%, but in theory it is there.
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  #28  
Old 02-04-2009, 06:35 PM
Andy_RR Andy_RR is offline
 
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Location: Melbourne, Australia
Posts: 427
Default Climb rate and take-off acceleration only...

I thought that having a CS prop would allow one to bring the engine speed right back to save some fuel in the cruise.

Taking at look at the data in the Superior O-360 installation manual it appears in reality a 60% cruise at 5000', if you're going to run LOP, demands at least 2300rpm - probably much closer to 2400 if you really lean it properly. At this point, you're already on the fixed-pitch prop load curve in the manual. I don't see where you could go with a CS prop that would improve fuel burn significantly.

Actually, I can begin to see why an O-390 could produce a significant improvement in fuel burn over an O-320 if you were to run a CS, especially if you could re-tune it to lower the peak torque speed allowing you to run higher power levels at lower engine speeds. You'd have to sacrifice some maximum power to do it though.
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  #29  
Old 02-04-2009, 06:48 PM
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L.Adamson L.Adamson is offline
 
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We were hanging a unit heater at a large hangar today. I brought up this subject, since I knew that all RV pilots present, wouldn't dream of being stuck with a "half baked" fixed pitch. Of course I was still correct in my assessment. No one had any desire for an F/P.

L.Adamson --- Just telling it... like it is...
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  #30  
Old 02-04-2009, 08:12 PM
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Webb Webb is offline
 
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Location: Jackson, MS
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Default Define your mission

You need to decide what your needs are.......ie: Define your mission.

Both have advantages and disadvantages. Cost, performance, fuel economy, do you fly IFR, acrobatics, and the list goes on.

I recommend you close your eyes to cost and look at how you will use your plane. VFR pleasure flying would suggest FP since 95% of your time is spent in cruise. Gonna fly into heavy IFR, then a CS is a much better choice.

Make your list and then decide. Good luck.....
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