Sim-A 737 not holding airspeed

[Kennair]

A call to Sim-Avionics NG drivers out there.

Got a problem I can't seem to sort. The Sim-A 737 doesn't seem to want to hold airspeed in cruise. Each time I reach cruise Alt, say FL370, the airspeed very slowly drops until reaching the stall buffet warning. I have to disengage autothrottle to speed up then set about 91% N1 in order to maintain speed. Cruise N1 setting on the EICAS is 86% which seems to be insufficient and it won't chase the speed bug at all. I've tried tweaking the autopilot settings in the server but no joy. I've also replaced the entire Sim-A aircraft model and rebuilt config files. The aircraft is usually loaded to about 80% but I've also tried it lightly loaded.  The Sim-A 777 on the other hand nails the airspeed as expected so its not to do with FSX (I don't think?). This has been happening through the last few updates, I'm currently using v1.48 but my home sim has only been up and running recently so I can't say if earlier versions were any better.

Can anyone offer any other suggestions or directions to take?

Cheers,

Ken.

[rs3tier]

Hi Ken

Sorry, I am not going to be any help here, but just FYI - I installed 1.48 a few days ago and noticed this problem started happening.  Prior to that I had been on 1.46 and had not seen it.

If it had only just been introduced, it might be easier to roll back a version I suppose - but if you have seen it happening in for a few versions then a job for the SA guys I suppose.

Rob

[sagrada737]

Hi Ken,

This is an interesting post...   I have seen issues with the airspeed slowly bleeding off in earlier versions.  However, I am currently running Sim-Avionics version 1.40 and I do not have this problem.   I don't know about higher versions of Sim-Avionics.

It seems you have done everything that needs to be checked, eg. re-loading the Sim-A 737 aircraft, creating new configuration files, then saving the aircraft.  I can't think of any reason for this behavior.  Has it behaved this way from the beginning of this version, or have you installed or changed anything new (hardware/software) since installing this version?  I think Fred and Sam are running the newer versions, so it may be good to check in with them.

One thing I have done that really has helped to keep my Sim running smoothly and reliably, is to always begin each and every flight from a Cold & Dark start up - then always doing a full shutdown to a Cold & Dark condition.  This seems to have a way of helping to keep interfaceIT better in sync with the physical switch settings.   Also, I will regularly run CCleaner on both the FSX and Sim-A computers after each flight.  I also run anti-virus and malware checks "quick scans" once a day, and full scans once a week.  This is what has worked well for my Sim setup and I now find Sim-Avionics to be very stable.

As always, check in with Steve at FDS to get some guidance on these kind of issues.

Best wishes in getting this resolved soon, and please report in as to any resolution you find.

Best Regards,
Mike

[Jetcos]

I flew 2 flights last week. Toronto-Florida then back to Toronto. All at FL350 and FL360.  No issues. I am running 1.48 with the Sim-A B737 and new config files. Been flying our JetMax Demo set-up. Next is VatSim for some online flying or even Pilotedge one day.

Running solid.

We have a B777 ready to pack for it's new home in Europe. Running great as well. A380 out the door this week, off to Dubai.

[Kennair]

Thanks Mike and Steve for you replies.  I've done further test flights and discovered this could well be a weight issue.  Even though I had reduced the weight before I tried today with a virtually unladen aircraft.  Gross take off weight was 49.2 tons and takeoff was swift as you'd expect.  My flightplan had me cruise at FL410 but I leveled off at FL390 and lo and behold the aircraft cruised as expected without a significant drop in airspeed using an N1 of 87%.  I then climbed to FL410 and after leveling off my airspeed began to drop ever so slowly with no attempt by the engines to speed up.  So the issue remains.

I wonder what other users have for payload on regular flights?  Mine is usually about 13 tons with a GTOW of about 58 tons on a flight such as todays.  Given the max weight is about 78 tons I am surprised if weight is the issue.

Another issue on a similar line is that of taxiing, I am using the DynamicFriction lua file for more accurate taxiing and while this works perfectly on my laptop sim running the PMDG 737, my Sim-A setup seems to taxi very heavily pretty much like default FSX.  When I lightly loaded the sim this morning it tended to taxi much better, increasing speed on idle rather than stopping.  This tends to point toward an over weight issue however I still wouldn't expect this to be the case with the regular weights I'm using.  What else could I be doing wrong?

Any thoughts anyone?

Ken.

[Sam Llorca]

Hi folks,

Running version 1.48 and is running solid! Very stable!

[Jetcos]

Cruising right now at FL410, very steady and holds speed accurately.

YYZ-LAS

Entered 16.5 for Total Fuel (KG's) and set everything up in Pre-flight.

[Kennair]

Thanks Steve,

What was your GTOW?

Ken.

[Jetcos]

ZFW was 57.1 and I loaded 16.5 Kg's of fuel.

[FredK]

Normally I fly no higher than FL370 but I tried one last night at FL410 and all was fine.....

KEWR-KORD
16,600 lbs fuel
Above FL360 V/S was sluggish but steady at 1000-1100 using LVL CHG flying into a steady headwind of 50 knots.
Airspeed steady all the way at 0.79 mach, N1 88

Descent using LVL CHG worked perfectly all the way down (have had problems with fluctuating V/S descents in previous SimA versions).

Currently using Version 1.45.

Fred K

[Kennair]

Thanks guys, all that helps a lot.  More investigations required.

Ken.