Hey guys, I've been looking for a topic for some performance calculations such as a calculated vertical speed for implementing in a VNAV code, or a calculated speed number for a VNAV code. Presently I am trying to figure out a method to solving optimum and maximum altitudes for an aircraft, any takers?

 

I'll try to contribute something here. My VNAV calculated vertical speed is something like this:

 

(L:FMC-LOAD,number) -25 * 4250 + int (L:FMC-VNAV-VS-CORRECTION,number) + 0 max 4500 min (>L:FMC-VNAV-CVS,number)

 

FMC-LOAD represents the load percentage of the aircraft as a comparison of empty weight and MTOW. VS-Correction is a variable that accounts for Cost-Index value and the difference between the desired speed and the actual speed and adjusts the VS to compensate.

Hi,

 

This is a very complicated subject!

 

Take into account MTOW (Boeing data), air-temperatures and pressures, weather, runway condition,

thrustmodes, powersettings, limits, restrictions, costindex etc. etc. etc.

Hundreds of calculations whill finally result in power, attitude and opt/max cruise-altitude with step climbs etc..

Then you will have a reasonable VNAV profile and a "cheap as possible" trip.

Quite difficult and it is hard to read my own over 8 year old code....,.

Sometimes asking myself: is it worth the effort??

Hi Jan,

 

I was hoping to model a simple solution to this. While I'm aware of the complexity of the actual FMC computations I am not a Boeing engineer and I don't see myself as being one. I want a number that is fairly on-point but not perfect. My thoughts have been to use the temperatures, pressures, weights, thrust setting, and cost index to generate a number that will give a fairly realistic imagine of where the aircraft will burn the least amount of fuel and the maximum altitude it is normally capable of climbing too.

 

I have some code now that is giving ok numbers. I have to do more testing and such and will post on my progress later on.

 

As for the VNAV I've refined my VNAV further and further. I just try to apply some common sense to the generic logical structure that I know from manuals and such. I have been getting pretty good results thus far. My VNAV code responds well to deviations from desired speed be it in mach or ias, it accounts for cost index, thrust settings, and actual performance and creates a pretty logical vertical speed profile for the most part.

 

The trouble with these things is....time. Not enough of it to be had at all! From finishing up my commercial training to finishing this semester of Calculus II, work, and chorus around the home there is absolutely not enough time to test these things and then come up with clever ideas. If this was my profession it would be much easier I feel. However it is just a hobby for us for the most part.

Best of luck, and thank you for always being very helpful! :p0504: