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  #51  
Old 04-27-2011, 07:30 AM
hevansrv7a's Avatar
hevansrv7a hevansrv7a is offline
 
Join Date: Jul 2005
Location: Detroit, MI
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Default Sorry, this is wrong.

Quote:
Originally Posted by Chris Hill View Post
L/D max is not best range airspeed. It is best endurance.

Wind does affect best range airspeed. With a tail wind you want to fly best range airspeed.

Those are facts of life in airplanes
Please refer to my chart above or numerous other publications. Best endurance is about 76% of best range and best range in a zero wind is equal to best or max L/D. Comparing best endurance to L/D max you will use approximately 14% more BHP and get about 32% more speed.

With a moderate head wind or a moderate tail wind, you would want to adjust the airspeed. Also see the link I posted above. In a mild wind, the correction is pretty small.
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  #52  
Old 04-27-2011, 08:34 AM
Chris Hill Chris Hill is offline
 
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Location: Del Rio
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Default

Yes, I hate being wrong and thats what happens when you blab before youre 100% sure.

Edit
What's I said earlier applies to jets incase anyone is wondering.

Last edited by Chris Hill : 04-28-2011 at 09:51 PM.
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  #53  
Old 04-27-2011, 08:46 AM
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hevansrv7a hevansrv7a is offline
 
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Location: Detroit, MI
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Default Welcome to the club

Quote:
Originally Posted by Chris Hill View Post
Yes, I hate being wrong and thats what happens when you blab before youre 100% sure.
I've been there, done that, probably will do it again, soon.
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H. Evan's RV-7A N17HH 240+ hours
"
We can lift ourselves out of ignorance, we can find ourselves as creatures of excellence and intelligence and skill. We can be free! We can learn to fly!" -J.L. Seagull
Paid $25.00 "dues" net of PayPal cost for 2015, 2016, 2017 and 2018 (December).
This airplane is for sale: see website. my website

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  #54  
Old 04-27-2011, 10:10 AM
Bavafa Bavafa is offline
 
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Default

Does any one know if GRT calculates the MPG based on ground speed or TAS?
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  #55  
Old 04-27-2011, 10:22 AM
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RVbySDI RVbySDI is offline
 
Join Date: May 2005
Location: Tuttle, Oklahoma
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Default

Quote:
Originally Posted by Mike S View Post
O.K., so I read this, and went "WOW" another goodie I have yet to discover.

Immediately went to the GRT manuals, and while it is mentioned, there is nothing I can find detailing how to activate this option.

How about a hint???
Mike I have a pic from my flight to Sun N Fun that shows the upper left hand corner of the Engine screen on the GRT HX. There is also a user configurable box on the bottom left corner of the Eng display just above the D ALT box I set up. If you zoom into the right side of the picture you can see the MPG showing 21.2 MPG on the Eng screen. I did not set anything up on my GRT to see the top left display but did for the box on the bottom left. Hope this helps.

The pic below can also be found in this photo album of my trip to Sun N Fun 2011:
https://picasaweb.google.com/1140831...XV5rzlxJy9kAE#



I can't help but comment on a few things displayed on this picture. I thought the read outs on this picture were very interesting in regards to the discussion on this thread.

This picture captured just about everything important to discuss concerning fuel burn and flight characteristics except the airspeed and the EGT's. The ground speed can be seen on the top left corner of the 695 GPS. It is showing a ground speed of 219 MPH (that is statute miles not knots) but the picture does not show True airspeed. The true airspeed when this picture was taken was 180 MPH.

Here are the specifics of this particular flight:
Altitude - 9500 MSL
TAS - 180 MPH
Ground Speed - 219 MPH
RPM - 2780
MP - 21.7
Fuel Flow - 10.1 GPH
Fuel MPG - 21.2
CHT TEMPS
Cyl 1 - 350
Cyl 2 - 354
Cyl 3 - 353
Cyl 4 - 352
Hottest CHT - 354 (Notice how close the temps are to each other. The EGT's are also very close, within 10 degrees of each other.)
Hottest EGT - 1386 (Wish I could have captured the EGT's but was cut off on the pic)

Although I was burning 10.1 GPH I was still getting 21.2 MPG flying 219 MPH across the ground. In my opinion that is pretty good.
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  #56  
Old 04-27-2011, 10:58 AM
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Experimental Chaos Experimental Chaos is offline
 
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Location: Fairfield, CA
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Default But how fast can you go?

Yes, head wind / tail wind absolutely make a difference as to what speed you should fly to obtain best miles per gallon, you need to push the power up into a head wind, and pull it back with a tail wind. But come on, how many of us when blessed with a good tail wind don?t push the power forward, just to see how high we can get the ground speed to read?
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  #57  
Old 04-27-2011, 11:07 AM
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erich weaver erich weaver is offline
 
Join Date: Aug 2006
Location: santa barbara, CA
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Default

Quote:
Originally Posted by DeltaRomeo View Post
What MP/RPM (not leaning) settings gets others the highest MPG?
So, am trying to sum this discussion up with respect to the original question for all us lower life forms. If I understand things right, for no wind conditions, you want to fly at best L/D airspeed (about 110 mph for a 6 or 7), adding some speed for headwinds, subtracting some for tailwinds. To achieve these speeds, RPMs should be minimized and MP should be maximized, at least to the extent allowed by prop restrictions and your personal comfort zone.

Do I have it right?

Im thinking most of us would be pretty bored staying at these speeds for any length of time.

erich
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  #58  
Old 04-27-2011, 11:27 AM
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pierre smith pierre smith is offline
 
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
Default More than likely groundspeed...

Quote:
Originally Posted by Bavafa View Post
Does any one know if GRT calculates the MPG based on ground speed or TAS?
....because TAS wouldn't include tailwind/headwind info.

I've seen under 10 MPG in a strong headwind and as high as 20 MPG with a very strong tailwind, using the same power settings each way.

Best,
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  #59  
Old 04-27-2011, 11:55 AM
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Toobuilder Toobuilder is offline
 
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Location: Mojave
Posts: 4,652
Default

Got to be ground... It's telling you how much fuel is being consumed getting from point A to point B - that's MPG.
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  #60  
Old 04-27-2011, 12:17 PM
Experimental Chaos's Avatar
Experimental Chaos Experimental Chaos is offline
 
Join Date: Mar 2008
Location: Fairfield, CA
Posts: 120
Default what tail winds

Quote:
Originally Posted by erich weaver View Post
So, am trying to sum this discussion up with respect to the original question for all us lower life forms. If I understand things right, for no wind conditions, you want to fly at best L/D airspeed (about 110 mph for a 6 or 7), adding some speed for headwinds, subtracting some for tailwinds. To achieve these speeds, RPMs should be minimized and MP should be maximized, at least to the extent allowed by prop restrictions and your personal comfort zone.

Do I have it right?

Im thinking most of us would be pretty bored staying at these speeds for any length of time.

erich
Just about, for all practical purposes you would want to fly at best endurance airspeed with a tail wind, with a head wind you want to go faster. How much? How much head wind? How long is the flight? How much time, and fuel to climb to what altitude? Is it worth the fuel to climb to an altitude where leaning pays bigger dividends? Higher altitude, better true airspeed, better fuel flows, but probably worse head wind. Ugh, why can?t this be easy? Ah, but if it was easy, it wouldn?t be as much fun!
As an aside, it?s worth noting, that most winds aloft hurt, they?ve got to be on the tail within about 45 to do much good. Doesn?t hardly seem fair.
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