High MPG: a.k.a. Thrifty Flying

[hevansrv7a]

Sorry, this is wrong.

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.

 

[Chris Hill]

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.

 

[hevansrv7a]

Welcome to the club

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.

 

[Bavafa]

Does any one know if GRT calculates the MPG based on ground speed or TAS?

 

[RVbySDI]

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/114083177287781041474/SunNFun?authkey=Gv1sRgCMXV5rzlxJy9kAE#



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.

 

[Experimental Chaos]

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?

 

[erich weaver]

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

 

[pierre smith]

More than likely groundspeed...

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,

 

[Toobuilder]

Got to be ground... It's telling you how much fuel is being consumed getting from point A to point B - that's MPG.

 

[Experimental Chaos]

what tail winds

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 45⁰ to do much good. Doesn?t hardly seem fair.

 

[6 Gun]

cheap speed

read this in dec 2010 aopa by dave hirschman its called the carson # for b.h. carson the aerodynamicist who identified it
accepting that fuel is to be traded for airspeed during normal operations this is the method of operation which represents the least wastful way of wasting fuel carson wrote in 1980
the l/d max in the pilot handbook is Vg a typical piston airplanes max range is about 10% above l/d thats the most miles per gal out of our airframes
sadly l/d nd max range are small numbers carson determined that a 32 percent increase in speed over l/d max is available for a mere 16% in added fuel consumption (excluding variables such as wind and propeller efficiency) add a gain in true airspeed by flying high at 10k feet and add a 20% gain and pilots can travel an impressive 52% for that 16% rise in fuel comsumption
thats some cheap speed
so how do we find this optimum place at which we get the biggest increase in airspeed for the smallest fuel penalty
simply multiply your airplanes best glide speed by 1.316 or add 32% and thats the carson #
bob willis

 

[gasman]

You can also use that same speed (1.31 times VY=target IAS) to cruse climb as high as possible with the throttle wide open. When you've reached the maximum altitude at which you can maintain your target IAS with mixture properly leaned, you're done. That will be your best cruse altitude.

by Dave Hirschman also

 

[sailvi767]

Here is a excellent article on the subject. You have to take the short quiz to get to the article.

George

http://www.db.erau.edu/research/cruise/

 

[hevansrv7a]

Jack Norris wrote the book

Jack sells two books for $15 plus postage at www.propellersexplained.com.
The book that's relevant here is The Logic of Flight - The Thinking Man's Way to Fly. They are back to back in the same volume. Jack was the technical director for the Rutan Voyager flight around the world. He knows his stuff.