Theory Q: Cold Air, Lower Fuel Consumption?

"Peter R." wrote in message
...

My turbo Bo uses 15.5 gph in the warm summer air and 17.5 gph in the very
cold winter air.

Your Turbobo?

"Casey Wilson" wrote in message
news:7RJxh.1999$5U4.453@trnddc07...

"Matt Barrow" wrote in message


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

Your TAS increases 33%, but your Fuel Flow increases only 4%?
My fuel flow doubles between Econ Cruise and Max Cruise (9.4 gph/172kts vs
18.4gph/205kts).

Check your data.

On 2/6/2007 9:38:35 AM, "Matt Barrow" wrote:


"Peter R." wrote in message
...

My turbo Bo uses 15.5 gph in the warm summer air and 17.5 gph in the very
cold winter air.

Your Turbobo?

That be the one.

--
Peter

"Peter R." wrote in message
...

My turbo Bo uses 15.5 gph in the warm summer air and 17.5 gph in the very
cold winter air.



Temp 36 today at 4500. 190 MPH indicated on 14.5 gph in my S35 at
23/2500. Trues out to 200 mph even. Gotta love six new Milleniums.
Don't need no stinkin' turbo.

On 2/6/2007 2:33:12 PM, Newps wrote:

Temp 36 today at 4500. 190 MPH indicated on 14.5 gph in my S35 at
23/2500. Trues out to 200 mph even. Gotta love six new Milleniums.
Don't need no stinkin' turbo.

With six new Milleniums (well, OK, they now have about 300 hours on them) and
a turbo I see speeds of 220 mph at 15.5 gph (2500/WOT and LOP by 70 degrees)
in the summer months at a cruise of 15,000 feet.

Don't need no stinkin' multi.



--
Peter

I'll assume 220 mph is a true airspeed as that would be well into the
yellow. I could lean to 14 gph but my indicated goes down by 8-10 mph.
At typical summer temps I'll lose about 5-7 mph true.



Peter R. wrote:

On 2/6/2007 2:33:12 PM, Newps wrote:


Temp 36 today at 4500. 190 MPH indicated on 14.5 gph in my S35 at
23/2500. Trues out to 200 mph even. Gotta love six new Milleniums.
Don't need no stinkin' turbo.


With six new Milleniums (well, OK, they now have about 300 hours on them) and
a turbo I see speeds of 220 mph at 15.5 gph (2500/WOT and LOP by 70 degrees)
in the summer months at a cruise of 15,000 feet.

Don't need no stinkin' multi.

On 2/6/2007 3:24:46 PM, Newps wrote:

I'll assume 220 mph is a true airspeed as that would be well into the
yellow.

Sorry, yes - that is true airspeed. Indicated is usually down around 145-150
or so at that density altitude.

--
Peter

"Matt Barrow" wrote in message
...

"Casey Wilson" wrote in message
news:7RJxh.1999$5U4.453@trnddc07...


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

Your TAS increases 33%, but your Fuel Flow increases only 4%?
My fuel flow doubles between Econ Cruise and Max Cruise (9.4 gph/172kts vs
18.4gph/205kts).

Check your data.

Copied right out of the POH for the 172M, 1976 Skyhawk. Figure 5-7
Cruise Performance, pg 5-16. Got a fax number?

Peter R. wrote:

On 2/6/2007 2:33:12 PM, Newps wrote:


Temp 36 today at 4500. 190 MPH indicated on 14.5 gph in my S35 at
23/2500. Trues out to 200 mph even. Gotta love six new Milleniums.
Don't need no stinkin' turbo.


With six new Milleniums (well, OK, they now have about 300 hours on them) and
a turbo I see speeds of 220 mph at 15.5 gph (2500/WOT and LOP by 70 degrees)
in the summer months at a cruise of 15,000 feet.

Don't need no stinkin' multi.

Until the single quits. :-)

Matt

"Casey Wilson" wrote in message
newsN7yh.113034$h75.97806@trnddc01...

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

Your TAS increases 33%, but your Fuel Flow increases only 4%?
My fuel flow doubles between Econ Cruise and Max Cruise (9.4 gph/172kts
vs
18.4gph/205kts).

Check your data.

Copied right out of the POH for the 172M, 1976 Skyhawk. Figure 5-7
Cruise Performance, pg 5-16. Got a fax number?

Yeah, but I'm not going to post it on the internet. Can you scan it and send
a JPG file?

Also, I misread your numbers (in terms of measures) - you go from 5.5 GPH,
to 7.6 GPH. That's the way I'm used to calculating fuel loads.

I'd still like to see the numbers, but my example (2X fuel flow for 18%
better TAS is not too far from your 33% increase in TAS for 40% increase in
FF. Getting upwards, then over, 200kts makes a big dent in fuel use.

Another thing to look at it is this - it often doesn't pay to divert a long
way to save a few buck on gas at a cheaper FBO. AirNav has this option on
their fuel planner.