Winds Aloft

How do the various flight planning programs determine the best altitude for a given flight? They certainly use forecast winds aloft data but do they consider aircraft performance? A turbocharged airplane can maintain the same power from sea level to above 15,000 ft and it's true airspeed will increase 15 to 20 kts at 15,000 ft. And a normal aspirated engine will lose power as it goes up in altitude. Do the planning programs consider these factors? Or do they just take the cruise airspeed that you enter as an aircraft characteristic and apply the forecast wind to that airspeed? My guess is this is what they do since they do not ask for how performance changes with altitude.

How do you determine the best altitude to fly at?

Thanks

Jim Butcher

I use weathermeister.com

Averages it out.
Very helpful tool.

I use Foreflight and Fltplan and neither one pick my altitude. I do.
I know that my plane loves altitude and flys very well @ 9-14k.
So I pick the correct altitude for the direction of flight, distance we will be flying and winds aloft. Most flight planning programs shows winds aloft for different altitudes.
Flight last week to the Bahamas 11k and 60 knot tailwind.

WingX will show best altitude but uses the TAS that you enter, unchanged for different altitudes. Nor does it consider time to climb.

Jim,

I use Weathermeister and ForeFlight for planning. Each has profiles with various parameters you fill in to get a pretty good approximation of X-C performance. Both are very good.

Weathermiester has profiles that you build, which have climb, cruise and descent parameters. You can have various profiles set up (for example for different cruise power settings). However, you choose just one profile to apply to the flight, and the selected profile applies to the entire flight...you can't designate different fuel flows for different cruise altitudes for comparison. With a little tweaking, I have found settings that fairly closely match my actual burns. The features I like in Weathermeister are that it compares various cruise altitudes based on winds, and gives you best economy and best time altitudes (yes, the fuel flows are the same, so there is a little potential error there, but its small); and it provides a lot of great weather products in one presentation?it does all the "mining" for you!

In ForeFlight, you can set up fuel flows and altitudes, and toggle between them. The presentation is good, but the side-by-side comparison of altitudes is not quite as well presented as Weathermeister. You also need to mine a little more for METARs, TAFs, etc. It all is readily accessible, but not quite as "click and view" as Weathermiester. However, FF is a great one-stop shop for planning and navigation, so it is awesome. I've played with the profiles in FF as well, to get them close to both Waethermeister and actual X-C performance.

I use them both regularly?good tools!

I fiddled with FltPlan.com, and it seems to have a very detailed flight planning aircraft profile set-up, in which (I believe) you can set up varied speeds and fuel flows for various altitudes, and have it apply them to the climbs and descents. Though it appealed to the detailed side of my brain, it got a little cumbersome, so the "let's go fly" side of my brain won, and I went with the above two products for ease of use and git-er-dun-ness!

I typically plan my X-Cs between 9,500 and 15,500, so the band is narrow enough that these products give a good SWAG of performance.

Hope this helps. and gets to the point of your Q.

Cheers,
Bob