REFLECTOR: Fuel Consumption Performance

[Al Gietzen]

Tom;

Fuel burn is directly proportional to power produced; and speed increases by
the cube root of power; so it's very dependant on speed.  But 6.2 gph at 125
is very good.

 

Here's a tabulation of what people have reported.  Numbers given for fuel
consumption are hard to compare because of different conditions, and degree
of leaning, so everything below is approximate.  Comparing at TAS helps as
it eliminates some variables on air density.

 

Just computing in nautical miles per gallon (nm/g)

 

Jim - - - - - - - - - - - - 20.4    @ 143

Tom's friend  - - - - - - 20.2   @ 125

Terry  - - - - - - - - - -  16.8   @ 193

John  - - - - - - - - - - - 15.5   @ 165

Dave - - - - - - - - - - - 12.9   @ 185

 

My SE RG with 20B rotary does roughly as follows: speed, burn, nm/g.


120

6.2

19.4


140

7.3

19.2


160

9.0

17.8


180

11.4

15.8

 

In an effort to compare at the same speed, I assumed then relationship with
speed would be about the same as my plane (using least squares fir to data).
So translating to 165 KTAS, the nm/g comes out as follows:

 

Terry  - - - - - - - - - -  20.4   

Jim - - - - - - - - - - - - 18.8    

Tom's friend  - - - - - - 18.1   

Al - - - - - - - - - - - -- - 17.4

John  - - - - - - - - - - - 15.5   

Dave - - - - - - - - - - - 12.9  

 

Terry's look very good (too good?); Dave's are not leaned, but may have more
drag; and of course, the 173 FG with 200 hp could probably not go 165 KTAS.


 

It is interesting to note that, for my plane, the nm/g flattens goes pretty
flat as the speed goes below 140 KTAS, but does peak at about 130 - 135.  So
if you are looking for minimum cost per mile; somewhere about that speed may
be it; but you'd have to run the numbers for your aircraft.

 

Hopefully this doesn't lose its formatting when transmitted.

 

FWIW,

 

Al

 

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Tom Tolton
Sent: Monday, August 03, 2009 3:29 PM
To: reflector at tvbf.org
Subject: REFLECTOR: Fuel Consumption Performance

 

I recently traveled to Oshkosh with a friend who owns a Velocity 173 with
fixed gear and a 200 HP fuel injected Lycoming.  He was able to reduce gas
consumption to 6.2 gallons per hour at 10500 feet and maintain a speed of
about 125 nm/hr using LOP techniques.  

 

I am building a XLFG -5 with constant speed propeller.  I am looking for
what one might expect in minimum gas consumption using LOP techniques at a
density altitude of 10000  feet.  I am considering the Lycoming IO540 260
and 300 HP, as well as, the 310 HP Continental 550N.  It has been suggested
that if I buy one of the more powerful 300 HP engines  I will just be able
to run with less throttle and bring the fuel consumption to a reasonable
level.

 

I would appreciate any comments / experience of the builders and owners with
a similar XLFG configuration.    

 

 

 

Tom Tolton

989-835-5828 (Home)

989-750-8567 (Cell)

 

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