Fsbuild-2 Flight Planner

I've got VNAV up and running using the SMITHS FMS. I'm now trying to optimise the VNAV performance.

I've read all the posts on the forum, and found these two helpful pointers from Ernie in November last year:

1. "If you enter an FPA value, then the DescentRate is calculated from the FPA and DescentIas values."

2. "You'd have to create a performance file (.prf) and use the 'PerformanceData=' option to specify the name of the performance file to use. It would then calculate the climb FPA based on the fuel burns listed in the .prf file."

I assume that the same logic would apply equally to VNAV climbs and descents.

My conclusion from the above is that in order to establish VNAV climbs and descents at (reasonably) controlled airspeeds for a particular aircraft, and with vertical speed being changed as necessary by the FMS in order to maintain this speed throughout the climb and descent, it is only necessary to define 'ClimbIas=' 'DescentIas=' and 'PerformanceData=' in the .cfg file .

I have a couple of questions related particularly to using the SMITHS FMS:

The cfg options allow you to set 'ClimbIas' ClimbIasMax' and 'ClimbIasMin'. For best results with the Smiths, should I set all 3, or just 'ClimbIas' or just 'ClimbIasMax' and 'ClimbIasMin'? Same goes for cruise and descent.

I assume the cfg options 'MaxVnavClimbRate' 'MaxVnavDescRate' and 'MinVnavIas' are just limits, and don't influence performance provided the limits are not reached. Is this correct?

If a 'PerformanceData' file is specified then I shouldn't set an 'FPA="?

'ClimbRate' and 'DescentRate' should not be specified, because these will be calculated by the FMS from the data in the PerformanceData file.

Have I got this right?

Steve Hutchison

Thanks again Ernie. Great support!

I'll make a few tweaks based on your reply.

Concerning the .prf files:

I'm aware of the "commonality" between the .prf files in the Aircraft folder of FSBuild2 and those which the flight logging feature of ISG creates. I also remember reading that you had some issues with direct interchangeability of those files, and that this was on the back burner.

I can understand that the fuel burn tables are required in the FSBuild2 .prf files for fuel planning purposes. However, it now seems to me from your answer that the ISG SMITHS FMS only reads the ROC (or ROD) and TAS (not fuel burns) values at various levels from the [CLIMB], [CRUISE] and [DESCENT] sections of the specified PerformanceData= .prf file.

Is this correct, and are the fuel burn tables in the ISG .prf files just ignored by ISG, or should they be deleted from the file?

Steve Hutchison