On Mon, 05 Feb 2007 17:30:43 GMT, "Casey Wilson"
wrote:


"Matt Barrow" wrote in message
...

"Doug" wrote in message
ups.com...
The higher the density altitude, you get better gas mileage for a give
TAS. So colder means lower density altitude and WORSE gas mileage
(everything else being equal, which it probably isn't). There may be
some other things going on, I am not sure about them.

You will be able to climb better and go faster at full throttle when
it is cold.

This last part is more correct/to the point.

In colder weather, your engine CAN develop more power. Power = Fuel.

In cold weather you can go FASTER because your engine can develop more
POWER. For a given engine, faster means less MPG.
Let's beat this dog some more. Going faster also means less time
required to get to the destination. Considering that as pilots we are more
interested in fuel consumption, gallons per hour, than MPG is it more
economical to fly faster/higher?
Let's presume a 250NM trip at 10Kft [for the nitpickers, the wind is
nil both ways]. According to the POH for the C-172M that I fly the trip will
take 2.8 hours and burn 15.4 gallons at 89 KTAS. Shove the throttle to the

but at 10,000 feet you probably will not be able to get more than 55
to 60% power full throttle in a normally aspirated engine. In the Deb
I find maximum true speed comes some where between 6000 and 8000 feet
depending on temperature.


firewall and the trip will take 2.1 hours and burn 15.9 gallons at 119 KTAS.

almost 16 in a 172 just doesn't sound right even at maximum crusise at
lower altitudes let alone 10,000
I only burn 14 at 75% in the Deb witha 260 HP, 6-cylinder IO-470N
engine. At 10,000 the fule burn is down to about 12.5.

To steal a line from Paul Harvey; "And now, the rest of the story."
At first glance, it is going to cost more to fly faster. But the
analysis isn't quite over, yet. Let's pay $4/Gal for the fuel, that means I
paid $2 more for fuel to go the distance. But the airplane is also costing
me an hourly rate of about $85. By flying faster, I shaved off 0.7 hours. or
$59.5. We could extend this into other cost advantages, such as extending
the miles flown between overhauls, but I think I've made my point.
My point is, you may get more miles per gallon at the penalty of other
expenses. When you are cruising, push the throttle to the firewall and screw
the friction lock down -- but by all means keep the engine properly leaned.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com