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What is the most economic fligth profile for an jet aircraft?
Most of our captains say that a parable is the most economic profil on a short flight, but I think it's not because climb thrust is set for a longer time than in a profile with a level-off at a cruise altitude where cruise thrust will be set!!??
hawk37
25th Dec 2005, 21:41
Perhaps you'd best define what you mean by most economic. Least fuel? Use of Cost Index?
I'm not familiar with parable. Parabola yes, but don't see how that could fit in unless the climb flight path speeds chosen are made to approximate a parabola
Hawk
XPMorten
26th Dec 2005, 11:37
This (http://www.xplanefreeware.net/morten/DOCS/Airbus_Fuel_Economy_Material.pdf) should give you a few hints..
Cheers,
M
Miles Magister
26th Dec 2005, 14:44
As said above it depends on how your company work out their cost profile.
Lowest fuel use on a short trip is generally straight up and striaght down without a cruise.
Lowest fuel on a long leg is as high as you can get.
However I believe that the largest cost per hour is still servicing so the height that gives you the highest groundspeed for the day is the cheapest. Generally around highest TAS depending on winds.
Some flight planning programmes help with this. A particularly good one (I am not connected with the company) is PPS by Air Support of Denmark which uses your own specific airframe with the winds of the day. It may give you different routes and heights for the same trip on different days. It also prints a table on your PLOG to show how costs change by going up or down slightly or by changing payload.
MM
GlueBall
26th Dec 2005, 16:02
In the real world, on short sectors, especially in crowded airspace, the "economic" cost profile is not something that any pilot has control over, nor does he have time to be dabbling with such matters...because he is too busy with ATC communications, flying SIDS and STARS or otherwise comply with "unplanned" altitude assignments and vectors, airspeed adjustments for in-trail spacing that are hardly "textbook" profile. For openers, in many instances you don't get your "economic" altitude; you're made to descent early [burn more fuel] or late [with speed brakes], ...saturated ATC traffic flows that make a mess of your optimum planned flight profile. :{