Optimal cruise altitude with a headwind?

[rookie1255]

So the higher the altitude the higher the TAS as well as improved fuel economy. However, if the wind will also tend to increase with altitude which is bad if there's a headwind.

How much TAS/fuel economy is gained with altitude increase and how much of a headwind would negate the benefits? Could it make sense to travel at lower altitudes where the headwind is less? How does the math work out?

 

[genna]

So the higher the altitude the higher the TAS as well as improved fuel economy.

Not exactly. Depends on the plane, or rather the engine. You lose power with altitude. For normally aspirated engines the sweet spot for speed is around 6-9000ft(Edit: after that you gain economy but lose speed). Edit: For turbo that altitude is a lot higher, but particulars depend highly on the turbo configuration.

You can make your calculations based on weather reports or you can have EFB -- FF does it -- do it for you. It's all estimates and usually do not matter as much as you think, unless there is a considerable wind change. The higher you go, the longer you have to fly slower in the climb..

 

[Caramon13]

Also, your POH, or the POH for the plane you are flying should already HAVE the sweet spot/optimal altitude for cruise efficiency.

@genna is right though, 6 - 9 K is the sweet spot for a lot of single engine/non-turbo aircraft.

 

[steingar]

Usually with headwinds I fly as low and temperatures and bumps allow.

 

[BigBadLou]

Usually with headwinds I fly as low and temperatures and bumps allow.

^^^^ THAT

Comfort is #1. Time is #2. Fuel is #3. At least for my wife.

 

[Goofy]

Good flight planning software figures it for you?

 

[RudyP]

What genna said. For my NA SR22, the TAS was pretty constant (168-173 KTAS) but fuel flow decreased as you climbed so flying high on tailwind legs gave more GS and more range, while being low on headwind legs preserved speed and generally neutral-ish range.

With my turbo SR22, I gain 2 kts of TAS for every 1000 ft of altitude while fuel flow remains constant. Typically, even into a direct headwind, the wind gradient is at or below 2 kts/ 1000 ft so it tends to be neutral to slightly beneficial to be in the 8000-12,000 ft range into a headwind and as high as practical with a tailwind. Of course, there are some nasty headwind days where my GS will be faster at 6000 than any higher but practically speaking I don't fly below 5000 AGL unless it is a really short hop.

There are a lot of factors besides speed and efficiency that come into play for altitude selection in a non pressurized, limited WX capability airplane as well.