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  #21  
Old 04-26-2011, 11:36 AM
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Kahuna Kahuna is offline
 
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Quote:
Originally Posted by DeltaRomeo View Post
Question #2: What MP/RPM (not leaning) settings gets others the highest MPG?
The RV is VERY linear in speed and fuel flow. Its not a bell curve.
What that means is that there really is no best mpg. The ratio of FF to speed is pretty constant.
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  #22  
Old 04-26-2011, 11:49 AM
BillFear BillFear is offline
 
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Default MPG in GRT

Mike look at the very bottom of page 5.3 in the setup guide. Looks like it is called performance/fuel box 2. You can select MPG there.
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  #23  
Old 04-26-2011, 12:24 PM
DeltaRomeo DeltaRomeo is offline
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Default 4_26_11 PIREP: 27.7mpg

.3hr lunch flight. Just in the door.

OAT 58°F. 1,300 MSL.
15.6" MP 2290 RPM 4.9 gph fuel flow
118.5 kts IAS (TAS and GS within 1kt of each other)
124 kts ground speed. Agressively leaned.
Hottest CHT 335°F. Hottest EGT 1410°F.
14kt wind from 90 degrees right. Autopilot on holding altitude and heading.
Image below photoshoped to get screens closer together.

27.7 MPG was the best I could get varying MP and RPM. Fun to play with.


Over $130 to fill up my RV last time.....I might be doing the 'Best ECO' settings a lot more in the future!
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Last edited by DeltaRomeo : 04-26-2011 at 06:58 PM.
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  #24  
Old 04-26-2011, 01:30 PM
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Nice bunch of numbers, really shows the ability to conserve if need be.

It also reminds me of something my Bonanza friend said when I ask him about fuel burn while running LOP: I didn't buy a fast airplane to fly it slow.
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  #25  
Old 04-26-2011, 01:32 PM
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Quote:
Originally Posted by BillFear View Post
Mike look at the very bottom of page 5.3 in the setup guide. Looks like it is called performance/fuel box 2. You can select MPG there.
Thanks Bill, I will try that-------it does state it is a "upper left" display box, but then it also says MPG
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  #26  
Old 04-26-2011, 01:41 PM
steve91t steve91t is offline
 
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If you have a tailwind, best MPG, or range, will be to pull the power back.

If you have a headwind, it's best to fly a higher power setting.


Some of you guys should try it and see what happens. I've really on heard about this, but have never actually seen the numbers.

Steve
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  #27  
Old 04-26-2011, 01:47 PM
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hevansrv7a hevansrv7a is offline
 
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Default How can this be?

Quote:
Originally Posted by Kahuna View Post
The RV is VERY linear in speed and fuel flow. Its not a bell curve.
What that means is that there really is no best mpg. The ratio of FF to speed is pretty constant.
The drag curve is the same shape for RV's as any other GA aircraft (not laminar flow). Prop efficiency varies, but not a huge amount. Engine efficiency likewise. If you fly at your best L/D (for example, around 106-110 for a 6 or 7) you will get (no wind) best mpg. And if you fly at max velocity you will get poorer mpg.

I have never seen any evidence that an RV has a different shape drag curve than other airplanes. Do you have any?

This is an idealized illustration of the point, not specific to RV's. The green line for THP should be roughly proportional to fuel flow. Velocity is the x axis. It is not a bell curve but it is curved, not straight.

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  #28  
Old 04-26-2011, 01:49 PM
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Kahuna Kahuna is offline
 
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Quote:
Originally Posted by steve91t View Post
If you have a tailwind, best MPG, or range, will be to pull the power back.

If you have a headwind, it's best to fly a higher power setting.


Some of you guys should try it and see what happens. I've really on heard about this, but have never actually seen the numbers.

Steve
huh?
Headwind and tail wind has nothing to do with the effeciency of the plane.
It also has no place in discussions of trying to determine power settings and MPG discussions.
Plotting your TAS against FF is the way to get it. It wont matter if your readings are accurate as long as they are relative to themselves.
We have a gazillion of these plots running around.
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  #29  
Old 04-26-2011, 01:51 PM
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rv7boy rv7boy is offline
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Quote:
Originally Posted by steve91t View Post
If you have a tailwind, best MPG, or range, will be to pull the power back.

If you have a headwind, it's best to fly a higher power setting.


Some of you guys should try it and see what happens. I've really on heard about this, but have never actually seen the numbers.

Steve
Steve, I agree with you based on my non-RV experience. I'd like to see some real world data though.
P.S. to Mike. Slow down and think about this: We're talking about efficiency across the ground not efficiency through the air. The iPhone is slow right now so I'm out.
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Last edited by rv7boy : 04-26-2011 at 02:00 PM. Reason: Added ps
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  #30  
Old 04-26-2011, 01:59 PM
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Flyfalcons Flyfalcons is offline
 
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Quote:
Originally Posted by Kahuna View Post
huh?
Headwind and tail wind has nothing to do with the effeciency of the plane.
It also has no place in discussions of trying to determine power settings and MPG discussions.
Plotting your TAS against FF is the way to get it. It wont matter if your readings are accurate as long as they are relative to themselves.
We have a gazillion of these plots running around.
that is not quite correct. A plane's best efficiency over the ground is dependant on the relative headwind or tailwind. The higher the headwind, the plane needs to fly faster for best MPG.
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