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  #151  
Old 09-18-2009, 05:17 AM
tinman tinman is offline
 
Join Date: Aug 2005
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I put a fixed pitch on my -8 and am very pleased. I think that the "one-gear transmission" analogy is not quite on target...it is more like a speed boat prop since it "swims" in air rather than stuck in positive traction mode on pavement. I give up a bit of climb rate since I have biased towards cruise. This isn't a problem for me because I don't fly in the mountains. If I had that mission, I would have chosen the CS prop.
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  #152  
Old 09-18-2009, 06:08 AM
RV8R999 RV8R999 is offline
 
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Doesn't surprise me the specs don't show much diff.

I switched from FP to C/S in my BD4 and honestly wasn't impressed and never really thought it was worth the money.

Climb rate for instance isn't about just the prop, it is determined by Ps (specific excess power) for a given airspeed, which is a function of the THP (thrust horse power) delivered by the prop and the Pr (power required) at that airspeed. As you know power required depends on a lot of factors. All things being equal and assuming most -8's are closely configured the biggest factors will be Gross weight and CG. Of course somebody who has gone to extreme measures to reduce the drag polar will have a better climb rate

So in a nut shell - take the same plane, under similar environmental test conditions and fly an ACCURATE performance profile in climb and cruise with both a FP and C/S I don't think you'll see significant differences in performance. But the word SIGNIFICANT means different things to different people.

If it were ALL about maximizing performance the the real discussion shouldn't be FP vs C/S but Recip vs Gas Turbine!
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  #153  
Old 09-18-2009, 06:56 AM
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Brantel Brantel is offline
 
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Quote:
Originally Posted by Toobuilder View Post
It simply boggles the mind that someone would build an RV, then hamstring its takeoff and climb performance with a fixed prop.
Because it is well proven many many times that there just ain't that much of a performance gain in an RV with a CS vs a FP and for the ~$6K delta in price, I would need to see some significant gains in performance.

Now for close formation flying, that is a different story all together....
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  #154  
Old 09-18-2009, 07:11 AM
David-aviator David-aviator is offline
 
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Quote:
Originally Posted by RV8R999 View Post
Doesn't surprise me the specs don't show much diff.

I switched from FP to C/S in my BD4 and honestly wasn't impressed and never really thought it was worth the money.

Climb rate for instance isn't about just the prop, it is determined by Ps (specific excess power) for a given airspeed, which is a function of the THP (thrust horse power) delivered by the prop and the Pr (power required) at that airspeed. As you know power required depends on a lot of factors. All things being equal and assuming most -8's are closely configured the biggest factors will be Gross weight and CG. Of course somebody who has gone to extreme measures to reduce the drag polar will have a better climb rate

So in a nut shell - take the same plane, under similar environmental test conditions and fly an ACCURATE performance profile in climb and cruise with both a FP and C/S I don't think you'll see significant differences in performance. But the word SIGNIFICANT means different things to different people.

If it were ALL about maximizing performance the the real discussion shouldn't be FP vs C/S but Recip vs Gas Turbine!
Ken,

You speak from a perspective of having a solid background on the subject, thanks.

My general perspective on this stuff is observing what is happening and drawing some conclusions from it, I do not have a formal education on it. I find that if I let my fixed pitch prop wind up to 2400 rpm at WOT after take off, the climb performance is quite satisfactory.

A few months ago, I did a brake release climb to 10,000' in 8 minutes, 27 seconds. A friend challenged someone to do likewise with a constant speed 180 HP engine just to see what the difference would be.

So far no one has taken us up on it.
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  #155  
Old 09-18-2009, 07:15 AM
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L.Adamson L.Adamson is offline
 
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Quote:
Originally Posted by Brantel View Post
Because it is well proven many many times that there just ain't that much of a performance gain in an RV with a CS vs a FP and for the ~$6K delta in price, I would need to see some significant gains in performance.
Oh really......

I know of NO one around here, who would prefer a F/P over a C/S, if it wasn't a matter of the initial cost. And we have a whole lot of RV's in this part of the world for the sake of performance comparison. All the F/P owners around here have mentioned the difference in performance when it comes to either takeoff or landing.

Personally, I'd been flying C/S props before I had the notion to build an RV. I knew the difference then, and the difference now. So being polite, I'll put it is way, ...around here................it is NOT well proven that there just isn't much of a performace gain between F/P & C/S.

If you live & fly in the flat lands at sea-level, or fly BD-4's, your thoughts may vary from mine.

L.Adamson --- RV6A Lyc 0360, Hartzell C/S
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  #156  
Old 09-18-2009, 07:18 AM
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Brantel Brantel is offline
 
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Quote:
Originally Posted by David-aviator View Post
A few months ago, I did a brake release climb to 10,000' in 8 minutes, 27 seconds.
A Friend of mine did the same from KMOR with similar results. 1000fpm average to 10K is pretty sweet if you ask me....
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  #157  
Old 09-18-2009, 07:30 AM
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Brantel Brantel is offline
 
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Quote:
Originally Posted by L.Adamson View Post
it is NOT well proven that there just isn't much of a performance gain between F/P & C/S.
Subjective....Show the apples to apples data that prove that there is a huge difference in TO/Climb/Landing performance as an average across the board at an average density altitude....

Quote:
Originally Posted by L.Adamson View Post
If you live & fly in the flat lands at sea-level, or fly BD-4's, your thoughts may vary from mine.

L.Adamson --- RV6A Lyc 0360, Hartzell C/S
Fly in and around the mountains of East TN....no sea-level here.

To each their own, You guys with C/S have fun squeezing the last drop of power from your craft, if money was no object, I would have one as well just to have another knob to adjust. Since I am on the budget plan for owning an airplane, I will put the extra $6k in avgas and still have a blast! I can fly along with a C/S RV with ease, yeah it might pull away slightly in the climb but I will never loose sight of it. Slowing a F/P RV down is easy if you use the correct technique and all the tools at your disposal.
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RV-10, #41942, N?????, Project Sold
---------------------------------------------------------------------
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
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Last edited by brianwallis : 09-18-2009 at 08:47 PM.
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  #158  
Old 09-18-2009, 07:39 AM
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Rick6a Rick6a is offline
 
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Quote:
Originally Posted by L.Adamson View Post
...if you live & fly in the flat lands at sea-level, or fly BD-4's, your thoughts may vary from mine......L.Adamson --- RV6A Lyc 0360, Hartzell C/S
Your oft-repeated partisan bias is well known among members of this forum. At long last Larry, you finally seem willing to concede at least one highly significant point. Good on you. Not everybody flies out of a high altitude environment. Around much, if not most of the country elevations are not nearly as extreme as the environment you operate from. But when anyone is given to issuing blanket statements, in this case a C/S is superior to a F/P without qualifying it in any way, they are bound to be challenged. One more thing, at my airport with its pattern altitude of 1400' MSL, I have ZERO trouble slowing down my Sensenich equipped RV from cruise speed to landing speed while in the pattern. Those RV'ers who operate out of a similar environment yet *think* one has to start slowing down a F/P equipped RV some miles from the airport may benefit from some additional dual instruction.
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  #159  
Old 09-18-2009, 08:39 AM
zav6a zav6a is offline
 
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Location: Sedalia, Colorado (KAPA)
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Default Fixed v. CS

I'll try to do this without joining the argument but to provide my experience for those that are at the point of making a decision about which way to go.

I fly in high DA enviroment (my second home airport conisistantly has 10,000+ foot DAs for 3 months of the year), with turbulence and downdrafts because of the surrounding mountains, and rough short runways that, because of mountainous terrain, are quite often poorly aligned with the wind. To exit the valley, I need to be at 12,500 (15,000 DA) within 10 miles of the airport to clear the mountains in practically any direction.

In this environement, getting off the ground and away from it quickly are tatamount to comfort and safety, not just fun.

IFR flying with an RV in this enviroment not advisable if not suicidal. There is great turbulence, ice, and rocks in the clouds up here!

So, if you are building for a high mountain environment, and you intend to use your plane often, the above argument begs for more investment firewall forward. You can put less in the panel though because it is unlikly that you are going anywhere in IFC. Pretty easy to save the cost of CS prop by dropping the instruments you will never look at if you are going to give clouds the berth they deserve.

A mountain plane, and all the tradeoffs that you have to make when deciding how to outfit it, rightfully looks a little different than one intended for lower, flatter operations.

And my WW 151 is lighter than metal my Sensinich was!
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  #160  
Old 09-18-2009, 01:19 PM
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dedgemon dedgemon is offline
 
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Default Partisan bias

seems to be a 2 way street Rick!

This whole discussion really is about what we want. Not necessarily what we need.

I WANT all of the climb rate I can get. If all I wanted was 1000'/minute I could fly a spam can.

Quote:
Originally Posted by Rick6a View Post
Your oft-repeated partisan bias is well known among members of this forum. At long last Larry, you finally seem willing to concede at least one highly significant point. Good on you. Not everybody flies out of a high altitude environment. Around much, if not most of the country elevations are not nearly as extreme as the environment you operate from. But when anyone is given to issuing blanket statements, in this case a C/S is superior to a F/P without qualifying it in any way, they are bound to be challenged. One more thing, at my airport with its pattern altitude of 1400' MSL, I have ZERO trouble slowing down my Sensenich equipped RV from cruise speed to landing speed while in the pattern. Those RV'ers who operate out of a similar environment yet *think* one has to start slowing down a F/P equipped RV some miles from the airport may benefit from some additional dual instruction.
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