What is favorable altitude for X-C ? (It’s Not about regulation, wx…)
Asked by: Obayashi_Kenji 1857 views Aerodynamics, Aircraft Systems
Hello.
I'm a commercial pilot and currently training with multi-engine add-on course now.
It's a pretty shame for me that I'm asking these questions at commercial pilot's level.
As you guys know, as altitude increase, there's a thinner air so less drag and it increases fuel efficiency. That's why commercial air-lines usually select high altitude for high TAS.
When I was training with commercial pilot stage, I went a X-C to another airport and selected 10,000ft altitude.
In that time, IAS indicates roughly 80KTS and as far as I remember, TAS was 95KTS I think.
So It takes almost 3 hours to get there.
But When I was taking back from that airport, selected 5,000ft and IAS was 100 and TAS was 110.
Of course, It takes less hours.
My question is this.
As altitude increase, we can meet less drag, but as long as we are flying with Natural Aspiration engines, there's a thinner air are exist, so Raising the altitude unconditionally is not a right answer.
Then, Is the lower altitude good for speed? well..... That makes confusing me. cause less altitude may increase air molecules, but increases air drag as well. and TAS also less than the high altitude.
Exclude FAR(Crusing altitude), wind condition, aviation weather, How can I select most favorable altitude for X-C?
Is there any charts or diagram such as like L/D max graph?
BEST
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