Engine/Autothrottle Surge Issue

[A320driver 17]

After much trial and error, I think I have finally come up with the correct fuel_flow_gain setting for the Maddog 2006. It was originallyset at 0.003. I changed it to 0.6 and so far, thru all the testing I have done it seems to have done away with the problem. I have applied this same setting to the CLS DC-10-30F (with which I have endured the same aggravating issue) but with much less success. Will continue to test both aircraft to see how it all comes out. If anyone has any ideas on the CLS DC10 please let me know. Regards,Joe

[Bob Scott 7,720]

Which G-V add-on are you using?There can be multiple causes of A/T instability. The PID controller normally used for automatic control systems has to be flexible enough to accomodate the varied airspeed response that occurs as a function of throttle movement at different weights, altitudes etc. What works at altitude when the jet responds slowly to thrust changes may not work at all down low.The RPM change per unit of throttle travel can be (is normally) quite a bit different at the low end of the range, so A/T response can be problematic down there, because a small change in throttle setting can produce a relatively large change in RPM. But most jets don't fly with the RPM stabilized so low (including the G-V). Sounds like this could be fixed by some adjustment of the thrust factor vs throttle pos curves in the FDE (table 1506).Bob ScottATP IMEL Gulfstream II-III-IV-VSantiago de Chile

[Guest FlyinJ]

Hi Bob. The G-V (actually the G550) addon I'm using is sort of a kludge-job made up of the visual model of the AI G550 found at www.htaimodels.com (a rather nice looking model imho) and the fde and .cfg files from Mike Stone's G-V. Both of these aircraft can be found here on avsim. I've tweaked the .cfg and .air files so that she replicates (as closely as I could get) the performance of the real G550 according to specs found at www.smartcockpit.com and Gulfstream's website.I found out something interesting during the testing I did since my last post. I noticed that when the G550 engines had to work harder (thereby producing higher N1 values) the occillations stopped. So I took a ride in my Eaglesoft Ciation X and noticed that with a lightly loaded aircraft flying at 10000' and 210 kts, she was producing ~66% N1 with rock solid autothrottles. My G550 however was producing only 41% N1 (as you may recall from my last post) with occillating A/Ts. I wanted a way to increase N1 at low speeds in my G550. So I increased the induced_drag_scalar to a whopping 6.0, took the lightly loaded G550 back up to 10000' (she barely got off the ground!) and, what do you know, N1 was up around 65% and the A/T occillations were gone. Don't know what N1 value the real G550 produces under these conditions, but i'm guessing it's more than 41%. Naturally, the problem with setting such a high induced drag value is that at her MTOW of 91000 lbs, she can't get off the ground.So the question now is how do I increase N1 without setting the induced_drag_scalar so ridiculously high? I think I'll take a peek at those thrust factor and throttle pos curves you mentioned.

[Guest ThrottleUp]

----------------------------------------------------------------If wx is not the issue, I would not use the max_throttle_rate param as an adjustmentexcept as a last resort...a better solution is to try experimentally increasing the fuel_flow_gain parameter in the TurbineEngineData section of the aircraft.cfg file...a larger value makes the engine spool up/down faster. This can significantly reduce or stop A/Tspeed overshoots by damping out lag induced oscillations, thus improving A/T feedbackperformance.----------------------------------------------------------------Great tip mate, thanks will check it out. The 50N 737s are notorious for this problem!

[Guest FlyinJ]

PROBLEM SOLVED! My thanks to Bob (w6kd) and Joe (A320Driver) for the tip on setting the fuel_flow_gain parameter in the aircraft.cfg file to a value of 0.60. I had previously adjusted it from 0.002 to 0.006 with no success, but this new value works like magic. Thanks again guys!Jeff