Control Interval - an experiment

[Richard McDonald Woods 168]

On a trip EGLL to WSSS, I decided to experiment with varying CI settings. The results are quite interesting.On a leg with constant heading and wind vector, 4400 nms to run, at FL310, and a gross weight of 345.4 tonnes, I got the following results:CI Fuel at Destn/tonnes Commanded speed/Mach Time at Destn00 1.3 .782 00:2210 3.2 .828 23:4920 3.2 .829 23:4830 3.3 .830 23:4640 3.3 .832 23:4550 3.3 .833 23:4460 3.3 .835 23:4370 3.3 .836 23:4280 3.3 .838 23:4190 3.3 .839 23:40100 3.3 .841 23:39150 3.3 .848 23:33200 3.2 .856 23:27It would seem that, in PMDG,- changing CI has relatively little effect on fuel consumption,- there is a big jump from CI 00 to 10 in both commanded speed and time at destination,- a difference of only 1 minute in each CI increase up to CI 100,- use of CI 150 and 200 made little difference to fuel at destination, but continued to decrease time at destinationYes, I know that my fuel forecast is way too low, but hoping for better winds later in trip.What comments do you have re these findings?Cheers, Richard

[cavaricooper 2,615]

Richard:Not to belabour the obvious, but did you allow sufficient time between each recalculation (assuming this was in pause)?The time relationship seems ok, the fuel burn differences are surprising. I learned a long time ago that the PMDG engine burn and RR RB211 data is not synchronous- but I am still surprised from time to time- such as now. Perhaps when separated engine thrust/burn models are implemented that will improve? As you know, there is only the GE engine model dataset across all 3 variants despite the differing instrumentation.I never use above CI90 so I do not have operational data to share with you. I would suggest however, that entering all cruise waypoint winds will give you insurance against that sort of FUEL REM preds. I love how accurate the FMC is (within the sim- not RW), and once flight planning methodology includes all cruise wp wind information (and of course DESC FORECAST winds later on, it becomes child's-play to arrive with 12-13T REM (here's where we all beg for ACARS winds ;) ). That indication holds for the entire flight- so then a significant drop in FUEL REM is a further alert for fuel/engine system issues.LOVE THAT BANNER!Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png| XP Pro SP3 with FS-GS System Unification | 2 x APC UPS | Coolermaster Stacker 830 SE | Asus P5E-Deluxe (X48) | e8500 @ 4gHz | Tuniq Tower 120 | EVGA 8800GT 512MB | Sony 40" Bravia XBR | 2 x 1 GB Corsair XMS2 | 500GB Seagate Barracuda 32MB SATA2 x2 (Acronis) | Corsair HX620W PS | CH Products Yoke-Pedals-Throttle Quadrant | Aerosoft 747MCP-EFIS-EICAS |