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Posts: 99
Joined: Thu Oct 08, 2015 11:46 am
Location: 5nm West of RAF Cranwell


Post by Banananav »

Dear All

I've had my Jetmax 737 now for nearly three, very enjoyable, years. As an ex-RAF Navigator I would plan my trips using the (PMDG) FCOM tables. I quickly found that I would always land with much more fuel than planned and that the ac would not perform a Vnav Path descent without significant extra drag.

To cut a long story short, after much experimentation I found that using a Parasite Drag Scalar of 1.27 (instead of the 1.05 in the flight tuning section of the aircraft.cfg file) I was getting consistent on-speed and profile VNav descents and the cruise N1s were much more accurate. I also tweaked the engine fuel flow scalar to tune the cruise fuel flows.

Then Mark pointed out Sim-Brief which, according to FlightDeck2Sim (a current 738 captain on Youtube) is almost exactly what his operator uses. So I flew a series of trips using CI 30 with 0% factor and further tuned the fuel flow scalar.

My last trial trip today - Brisbane to Perth in nil-wind ISA conditions with a fuel flow scalar of 0.98 (originally 0.95) gave a Sim-brief planned time of 04:41 and 27436 lbs of fuel used - the actual time flown was 04:42 and 27556 lbs used (from Aivlasoft EFB flight log). This puts the Sim-Brief hourly fuel flow and the actual one within 0.3% of each other. I have had similar results with these settings on other, shorter range, trips.

In summary, I am now using the following figures to get very accurate flight performance and fuel useage:

Parasite Drag Scalar = 1.27
Fuel Flow scalar = 0.98
Cost Index = 30 (FMC & Sim-Brief)
Sim-brief fuel flow correction = 0%

I hope fellow 738 fliers find these numbers useful.


Chris Finn

Jetmax 737-800 & TQ
P3D 4.5 HotFix2
S-A 1.966
FSUIPC 5.155

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Location: Montreal

Post by jackpilot »

Thank you...will try.
Full B737-800 DSTD/Sim-Avionics P3d4
ALL FDS & OEMs (+custom TQ)

Posts: 214
Joined: Wed Feb 03, 2016 3:48 pm
Location: Buckinghamshire, UK

Post by kand »

You will never get accurate FB in any MS iteration of fsim, simply because the sim engines still burn fuel from net thrust, not gross, it has been broken for years.

You will get close for 1 particular weight/regime of flight but thats about your lot

I have rewrittrm my own 777 ER airfile to get closer RW perf but its still flawed

Posts: 1274
Joined: Fri Sep 30, 2005 2:42 pm
Location: Newmarket,Ontario

Post by Jetcos »

Thanks Chris, will give that a try.
Steve Cos
Vice President and Tech Support
Flightdeck Solutions (FDS)

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