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  #11  
Old 04-21-2006, 12:36 PM
Mike S's Avatar
Mike S Mike S is offline
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Crude but simple analogy----------------imagine a car with only one forward gear in the transmission--------you have to use it for acceleration, cruse, hill climbing, and top speed. Now think how much better the 4,5,or 6 speed you drive is.

Mike
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  #12  
Old 04-21-2006, 01:38 PM
chuck chuck is offline
 
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Location: Kirland, WA
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Mel:

Thanks for the note about glide and stopped prop. I'm going to play with that this weekend. My engine out emergency proceedures have me pull to coarse pitch but not to stop the prop. Can't recall an engine out procedure on any airplane telling me to stop the windmilling.

Is the effect dramatic? If it's the area ratio of the full disk to just the prop it sounds like it would be very large.

Chuck
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  #13  
Old 04-21-2006, 01:58 PM
cobra cobra is offline
 
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"...During the same RV-4 flight we bumped the speed up to 175 mph indicated. The RPM was nudging 2600 at this point. It was obvious the airplane wanted to go faster but the engine RPM was getting into the limiting range."

Serious question: If the engine/prop were able to safely spin faster, to say 3200 rpm assuming the tips stay less than sonic speed, is your argument still valid?
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  #14  
Old 04-21-2006, 02:29 PM
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Location: Clearwater, FL
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Question What about Maint?

One thing I'm not seeing mentioned here is prop maint.

I don't know much about which prop uses more or less fuel. However the issue of a constant speed saving enough fuel in 2000 hours has too many variables. For example if the CS costs 6K more than the FP than you would have to save $3 an hour in fuel pay for the differance. This does not take into account the cost for overhaul. Most planes never make it to TBO before the prop reaches the reccomended overhaul based on age.

Lets face it a CS prop and gov overhaul is much more costly than a FP service.

Also what about insurance? I havn't checked into this and it may not even be a factor. Do insurance companies charge more or less depending on what prop?

I'm not taking either side here. Just giving some food for thought.
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  #15  
Old 04-21-2006, 02:58 PM
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The increase in glide is pretty dramatic, but stopping the prop is not usually practical. If the prop has lost some mass or is out of balance causing a lot of vibration, then yes, stop the prop if you can. Otherwise, to stop the prop usually requires almost stalling the airplane. You already have a problem. Don't push for another one.
Mel...DAR
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  #16  
Old 04-21-2006, 08:28 PM
pbesing pbesing is offline
 
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200HP RV-4, fixed pitch, 170 MPH 1700 FPM climb...the only thing a CS would benefit me is slowing this darn thing down on landing, and with aerobatics...the climb performance is fine for me.
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  #17  
Old 04-21-2006, 08:48 PM
szicree szicree is offline
 
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Fixies Unite!
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Fullerton, Ca. w/beautiful 2.5 year old son
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  #18  
Old 04-21-2006, 11:29 PM
B. Hoover B. Hoover is offline
 
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Quote:
Originally Posted by pbesing
200HP RV-4, fixed pitch, 170 MPH 1700 FPM climb...the only thing a CS would benefit me is slowing this darn thing down on landing, and with aerobatics...the climb performance is fine for me.

Assuming a limited amount of capital to invest - does anyone want to guess at the climb rates of say, a 160 HP CS vs maybe a 210 HP fixed set up for max cruise? In other words, where should I put my first "extra" $6K?

Newbee w/ -7 plans, but still thinking about the -8
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  #19  
Old 04-22-2006, 12:36 AM
Ward Johnson Ward Johnson is offline
 
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Quote:
Originally Posted by B. Hoover
Assuming a limited amount of capital to invest - does anyone want to guess at the climb rates of say, a 160 HP CS vs maybe a 210 HP fixed set up for max cruise? In other words, where should I put my first "extra" $6K?

Newbee w/ -7 plans, but still thinking about the -8
Personally I would say put in the prop. Increase in speed will be at the cube root of the added power, which is not a good return on $$, not even factoring in added weight. Increasing prop performance seems to be a good idea unless you intend to fly mostly at the optimum speed your FP is configured for (i.e. cruise). If that is the case invest the money instead, or buy snazzier avionics. From what I have read, it is a personal preference question where it would be nice to have C/S but is it worth it based on your intended flying.....
Advice from one who has never flown an RV....
You know what they say about advice!

I don't have an ore in the water on this race, so I think I am fairly objective.
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Last edited by Rosie : 04-25-2006 at 11:39 PM. Reason: Fixed quote
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  #20  
Old 04-22-2006, 06:10 AM
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RV6_flyer RV6_flyer is offline
 
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Quote:
Originally Posted by wingtime
One thing I'm not seeing mentioned here is prop maint.

I don't know much about which prop uses more or less fuel. However the issue of a constant speed saving enough fuel in 2000 hours has too many variables. For example if the CS costs 6K more than the FP than you would have to save $3 an hour in fuel pay for the differance. This does not take into account the cost for overhaul. Most planes never make it to TBO before the prop reaches the reccomended overhaul based on age.

Lets face it a CS prop and gov overhaul is much more costly than a FP service.

Also what about insurance? I havn't checked into this and it may not even be a factor. Do insurance companies charge more or less depending on what prop?

I'm not taking either side here. Just giving some food for thought.

I hit 1,842 hours last weekend. My CS prop has cost around $15 for maintenance over the 8.5 years I have been flying. I am on my second tube of grease. My insurance is $311 per year for $1 Million coverage through NationAir. Am expecting an increase this year.

I do NOT want an RV without a constant speed prop. Ken Scott once said that you can only get 85% of the performance out of an RV without the constant speed prop.

There is a fuel savings enough to more than pay for the constant speed prop. See another post that I have in the forums that show it will pay for itself and the overhaul costs over it life time.

Gary A. Sobek
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