REFLECTOR: Fuel Consumption Performance

Tue Aug 11 22:23:34 CDT 2009

Got back from vacation today-- Texas to Seattle and back. My fuel filter clogged up at 10,500 feet between Butte and Missoula in the Rockies. Pretty exciting. Ask me about that story some time.

Last two legs were Laramie, WY to Denver FTG, then FTG to Dallas.  Had to divert around some thunderstorm activity, so those two legs were 765 nm on 38 gallons of fuel. 5.9 hrs on the hobbs. That's 20.1 nm/gal including two take offs and landings. Average TAS around 140-145 kts at 9500 feet, 2400 RPMs, 50 degrees LOP. IOX-360 with electronic ignition. FG with a retractable nose gear. Fixed pitch, 2-blade prop. Standard fuselage. Hauling about 475 lbs of people and baggage.

Doug Holub
N2980W, 95 hrs
  ----- Original Message ----- 
  From: Tom Tolton 
  To: 'Velocity Aircraft Owners and Builders list' 
  Sent: Thursday, August 06, 2009 8:08 AM
  Subject: Re: REFLECTOR: Fuel Consumption Performance

  Thank you all for the data on my fuel consumption question.  I especially appreciate the time spent to help me better understand what is involved.  It is a pleasure to be part of a group so interested in building and flying.  

  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Al Gietzen
  Sent: Tuesday, August 04, 2009 12:15 PM
  To: 'Velocity Aircraft Owners and Builders list'
  Subject: Re: REFLECTOR: Fuel Consumption Performance

  Corrected data below - I made an error on the number for Dave's plane; it should be 15.2 nm/g at 165KTAS.  So you can delete the previous message and look at this one.

  Al

  -----Original Message-----
  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Al Gietzen
  Sent: Tuesday, August 04, 2009 7:54 AM
  To: 'Velocity Aircraft Owners and Builders list'
  Subject: Re: REFLECTOR: Fuel Consumption Performance

  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 fit 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 - - - - - - - - - - - 15.2  

  Terry's look very good (too good?); Dave's are not leaned; 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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