REFLECTOR: Fuel Consumption Performance

Tue Aug 4 18:47:43 CDT 2009

Al,

Hey thanks for that.  Can I do anything to help fill in the matrix any
better?  I could get you some 165 TAS numbers on my next long trip.  It
seems like runs at similar altitudes and TAS would make for the easiest
comparisons.  But,  I could fly at whatever altitude or fuel flow, etc you
wanted to know about.  

Here is a log of my cruz numbers to date.   A couple of months before we
lost him, Mac Murphree sent me a performance chapter he had scrounged up
from a Cirrus or a Lanair or something.  I forget which.  He said he though
these numbers would be close enuf for a  LY 540 Velo XL.  It had climb
charts and the like.  The plan was that he and I could cobble together a
performance guide for the group.  I am sorry to say, I never got back to it,
and then I went through three hangar moves and things get lost.  I cannot
find it here in Chicago, so when I get back to PA in November I will look
around for it there.   

It may be we have too many variables out there, but it would be nice to have
a set of fleet numbers and aprox offsets factors we could create based on
model, FG/RG, and powerplant, etc.  We could, as we just did here on a small
scale, collect  and interpolate some actual numbers.  Thanks for what you
have done here.  I'll get back to this in the fall.  

Terry

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Al Gietzen
Sent: Tuesday, August 04, 2009 11:15
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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