Simple question:The FS9 autopilot uses "trim" to hold an altitude. Real-world pilots tell me that is not the way autopilots work on real-world aircraft.Because of this, one of the problems I have with FS9 when I didengage the A/P is that the aircarft jumps up or down, sometimes on short final, which is not very nice. In a real-world aircraft, once you trim your aircraft, it will remain trimmed, the autopilot will not un-trim your plane, so when you disengage your A/P, you plane continues to fly without jumping up and down. The only FSim addon I had that replace FS9 with its own autopilot was the 767PIC, best flying FSim aircraft I had. I am considering purchasing the complete PMDG 737 package, so I'd like to know whether these aircraft use FS9's autopilot or whether they have replaced it with PMDG's own A/P?Just as a point of reference, how smooth does the PMDG 737 autopilot work compared to, say, the 767PIC autopilot?Thank you in advance,Kerke

Hi Kerke,the real AP will fly the aircraft similar to a pilot, ie first it will apply flight control pressure (moving the actual flight control, elevator or aileron) and in case the elevator was moved, it will start to trim out any control wheel force so that the aircraft is trimmed. This has a few advantages, asa) in case of an AP failure the aircraft will remain stable:( the aircraft is cleaner (aerodynamically speaking) and will therefore use less fuel(an exception to this is an autoland where the AP will artificially add nose up trim and add down elevator force...So how does PMDG function? Well, I don't know how the programming behind the scenes is, but it seems to be quite good, with the exception to some oscillations sometimes (I guess the used algorithims aren't perfect and therefore it ends up "in a mathemmatical chaos" - the real aircraft is much smoother)767PIC's autopilot was IMHO better, but the real 767's autopilot is far better than the 737's so this could be considered as realistic :-)Kind regards,Adrian

Thank you for your quick reply Adrian, I am going a post a generic FS9 A/P Trim question on AVSIM's General Discussion Forum to see how FS9 simmers manage to control FS9 aircraft (not the PMDG 737) when they disconnect their A/P.Thanks again,Kerke

The FS9 autopilot uses "trim" to hold an altitude. Well the PMDG does not use the default FS9's A/P whatsoever, this is a 100% ground built A/P.In a real-world aircraft, once you trim your aircraft, it will remain trimmed, the autopilot will not un-trim your plane, so when you disengage your A/P, you plane continues to fly without jumping up and down. Sorry I may not completely understand you here. If the A/P is in control you are not trimming anything and whatever trim you had for say a climb+speed would be retrimed to follow the FMC profile or other auto modes such as LVL CH or V/S. The A/P would not be able to fly a profile without *trimming*. A good example of autotrim would be the 400 RA trim for an autolanding. In this example, if you would gain manual control, you would certainly need to apply trim to remove the present profile for landing to perform a go-around. Just as a point of reference, how smooth does the PMDG 737 autopilot work compared to, say, the 767PIC autopilot? Well they are different. Pilots who use this NG and actually fly the RL NG tell us that this is the most realistic NG ever created for FS. How one compares this to PIC 767 is purely subjective. I love PIC but would be the first to say it's VNAV profile was not perfect in the original although the everday simmer would not know the difference. Is this aircraft as good as PIC? I would say certainly so and if we are dealing with the complextity of the A/Ps alone I would say that this A/P is more advance by nature of the systems modelled like true Contro Wheel Steering (CWS) and other modes such VNAV ALT, Speed and Altitude intervention which are unheard of in flight simulator (one freeware aircraft has a kind of CWS but not even close to the NG in complexity in RL). As our good friend Brad Marsh (pilot for Pacific Blue NGs says of the PMDG NG) "Good enough to train real world procedures on"...)Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/Animation1.gifCaution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |

Kerke,Having Adrian and Randy said the technical stuff allow me to give you an advice: Try not to compare the two products in technical matters as PIC was originally made for FS2000 which is way behind the capabilities of FS9. Another good way to get around comparisons is to try and get used to the specific needs of the newcomer. I have flown both planes as well and I certainly know that I had to make a few deals with PIC here-and-there just to make sure I USE the product the way it should be used. Now the NG should be used a whole lot differently than PIC, as they do simulate two different aeroplanes indeed. I look at it as if I had a new dog after the other one died. Both of them are dogs, may well be the same kind, but you can never say "a dog does 'X' when 'Y' happens".Just my 2 cents..Cheers,