Some questions about Performance
 

Hello,

My questions are:

If a climb is done in the thrust position of Max Climb, and with C.I.=0 the airplane may climb at V_x and with a C.I. = 200 it may climb at V_y. Then if we apply the calculation of Fuel Consumption:

FuelConsumption = SpecificFuelConsumption x Thrust x Time.

Why when we are climbing at V_x (in theory less fuel consumption) we are consuming more as long as SFC is the same for V_y and V_x, thrust is the same as well, and only time changes because we climb more quickly at V_y.

There is something wrong but I don't know what :bored:

Another question is:

Which is the average angle of climb of the civil aviation airplanes ? 5 degrees ? 15 degrees ? 30 degrees ? ...

Again...

How much ground distance will fly an airplane taking-off at 0 ft and climbing to 36000 ft at a climb gradient of 4% and 250 Kt of EAS (FAA minimum all engines working) ? I calculated it and I obtained it will fly for 274Km with a climb rate of 1000 ft/min more or less but I am not sure at all :O

And finally...

If we suppose our airplane may flight with a C.I. of 200 (Minimum trip time), cannot we flight at mach maxi on the altitude where sqrt(CL)/CD (Max range lift_to_drag coefficient) is maximum, or it will not be flying at C.I. = 200 ? In this conditions, the airplane will flight at maxi range (requirement of C.I.=0) and at mach maxi (requirement of C.I.=200).

I suppose that climbing to the optimal altitude for sqrt(CL)/CD maxi and mach maxi consume extra time that implies we will not be flying at C.I.=200, may be it will be C.I.=100. I am not sure at all; I hope some of you can help me :)

Thank you very much in advance.:)

Edu

clarify
 

I'm looking at this, but what's C.I. ?

Cost Index?

Acronyms
 

Here are all acronyms I have used:

C.I. = Cost Index
V_x = Speed for best angle of climb
V_y = Speed for best rate of climb
CL = Lift coefficient
CD = Drag coefficient
SFC = Specific Fuel Consumption
EAS = Equivalent Airspeed

Thank you very much for your help :ok:

yikkes
 

Cost Index ?..., sorry I don't know anything about that :confused:

CI is the ratio of flight time cost (CT) to fuel cost (CF).
CI = CT/CF KG/MIN or 100 LB/H
The cost index is used to compute the best economic speed and Mach to be flown considering the ratio between the flight time cost and the fuel cost.
CI = 0 Corresponds to minimum fuel consumption (max range).
CI = 999 Corresponds to minimum time.

Is not the maximal value for the C.I., 200 ?

I just realize that where I write sqrt(CL)/CD it may say CL/CD.

the max number for cost index changes per company. mine has a max cost index of 200 on a honeywell pegasus fms. i have heard others on teh same system can enter values up to 999. no idea why.

On our FMS, we can put a maximum figure of 9999, however, 5000 and above you start running into VMO/MMO issues.

Cost index issues
 

Shendal,
You might found what you are looking for in some good study materials from Airbus. One is called "Getting the grips with fuel economy" and the other one is called "Getting the grips with Cost Index". Go on a search engine and type those titles.
Good luck.