Best power vs economy mixture setting

[MikeOH]

1 hour ago, Shadrach said:This is why Peak EGT is a desirable engine setting if CHTs allow. It’s the theoretical intersection of what’s best about ROP and LOP. No wasted O2 or Fuel, efficient flame front characteristics with reasonable CHTs. Peak EGT is almost always my goal power setting, I only run leaner to control CHTs. That’s typically only needed on hot days or at power settings above 70%. 

 

I shoot for peak, as well, As long as CHTs are good. I’ve had many, including A&Ps tell me I’m going to destroy my engine!

[AH-1 Cobra Pilot]

18 hours ago, jaylw314 said:

(not 45 deg, where did you get that from?)

Page 7, second paragraph.

[AH-1 Cobra Pilot]

On 9/19/2022 at 11:08 AM, Shadrach said:

A unit of fuel is a unit of fuel is a unit of fuel...what it costs is not a factor.

I am quite sure people who pay for their own fuel do not subscribe to this.  Carson ignored the price of fuel, which I see as an important measure as to how fast anyone is willing to burn it, thus impacting the slope of his line determining how much extra fuel to expend to go a little faster.  If fuel were $1/gallon, you would not see so many people flying LOP, you would see more, bigger engines, and lots more twins.  The price you are willing to pay for each extra knot probably makes perfect sense to you, but is scientifically arbitrary.

[PT20J]

31 minutes ago, AH-1 Cobra Pilot said:

I am quite sure people who pay for their own fuel do not subscribe to this.  Carson ignored the price of fuel, which I see as an important measure as to how fast anyone is willing to burn it, thus impacting the slope of his line determining how much extra fuel to expend to go a little faster.  If fuel were $1/gallon, you would not see so many people flying LOP, you would see more, bigger engines, and lots more twins.  The price you are willing to pay for each extra knot probably makes perfect sense to you, but is scientifically arbitrary.

I believe Carson was simply trying to find a reasonable tradeoff between fuel burn and speed that has some analytical basis. If the primary concern is minimizing the fuel cost for a flight, as Carson points out early on, L/Dmax is the best speed. 

[Shadrach]

28 minutes ago, AH-1 Cobra Pilot said:

I am quite sure people who pay for their own fuel do not subscribe to this.  Carson ignored the price of fuel, which I see as an important measure as to how fast anyone is willing to burn it, thus impacting the slope of his line determining how much extra fuel to expend to go a little faster.  If fuel were $1/gallon, you would not see so many people flying LOP, you would see more, bigger engines, and lots more twins.  The price you are willing to pay for each extra knot probably makes perfect sense to you, but is scientifically arbitrary.

The only point of the exercise was establishing much of the surplus power available to go faster than L/D max should be used to get the most speed for the for the fuel burn. What fuel costs has no bearing on the matter. 
 

@201er put it very succinctly when called it the point at which fuel burn increases more rapidly than speed due to drag. 
 

It’s a speed per gallon calculation rather than miles per gallon calculation. It’s that simple. Does the price of gas affect your cars mileage? It might affect your driving style but the vehicle’s max efficiency is unchanged.
 

 

[AH-1 Cobra Pilot]

1 minute ago, PT20J said:

I believe Carson was simply trying to find a reasonable tradeoff between fuel burn and speed that has some analytical basis. If the primary concern is minimizing the fuel cost for a flight, as Carson points out early on, L/Dmax is the best speed. 

I take the paper to be an attempt to justify a particular speed as the "least wasteful way of wasting fuel."  I think a more valid approach to most flying would be the "least wasteful way of wasting money."  Also, that way you could include a term for what your time is worth to make the speed a determined, rather than arbitrary, number.

[jaylw314]

42 minutes ago, AH-1 Cobra Pilot said:

I am quite sure people who pay for their own fuel do not subscribe to this.  Carson ignored the price of fuel, which I see as an important measure as to how fast anyone is willing to burn it, thus impacting the slope of his line determining how much extra fuel to expend to go a little faster.  If fuel were $1/gallon, you would not see so many people flying LOP, you would see more, bigger engines, and lots more twins.  The price you are willing to pay for each extra knot probably makes perfect sense to you, but is scientifically arbitrary.

I see what you're saying, and I'd agree that cost is an important decision-making factor for people, but I think developing a psychological model of decision-making was far beyond the scope of what the article intended.  Arguing that since it fails to do so, therefore it's conceptual conclusions are arbitrary is a bit of a straw man argument.  The scope of the article seemed to be limited to "This is why you should value specific power, and if you value maximizing specific power, this is how fast you should fly."

[jaylw314]

1 hour ago, AH-1 Cobra Pilot said:

Page 7, second paragraph.

It's 45 degrees because the graph is normalized to make the line 45 degrees for visual clarity.  You could rescale the axes to make it any angle you want, the slope (in the GvK diagram in the article) is still 0.00018 in the units they used.