Erratic A/P behavior
Moderators:fsafranek, DBushell, admin
I'm struggling to get the A/P to operate properly. I get to 30k, accelerate to the appropriate speed to begin the 450KEAS, set the A/P altitude to 80k, speed hold mode to 450KEAS, then I to ry put the switch into speed hold mode and engage the A/P. Now any other A/P I've encountered with speed hold mode, the A/P will control pitch to maintain said speed and you as the pilot can modulate this by manipulating the throttles, but for some reason this aircraft comes with a autothrottle which A.0 wasn't even on the real Cygnus, and B.) doesn't really work all that well, for when I try to engage the AP along with speed hold, the plane pitches up all the way to 90 degrees, going way below the KEAS setting I have entered. According to the interview with a A-12 pilot here, https://www.youtube.com/watch?v=SSTRXGP0nWM&t=1s the climb was done in KEAS hold and the pilot could control the rate of climb with the throttles, and also they cruised in Mach hold mode and again if they didn't want to climb they would control it with the throttle. The manual for this mentions a Autothrottle on off switch but I have yet to find it.
Re: Erratic A/P behavior
Hi,
Sounds like something else is going on there. Are you accelerating to Mach 1.1 in a gentle dive from 35,000 feet? This speed hold only holds the speed, it doesn't control the pitch to maintain speed only the throttles. The logic behind that is way beyond my capability. I welcome you to try. The autopilot provided is more than adequate to get to speed and altitude so long as you follow the climb profile set out in the manual.
In real life the pilots would cruise climb from 70,000ft at 100ft per minute so by the end of the Mach 3 cruise they would be several thousand feet higher. So set the autopilot altitude lower eg 70k, and then cruise climb. But really the key to this is performing the dipsy doodle maneuver to get to Mach 1.1, set the vertical speed at say 6k, keas hold to 450 and ride it on up to 60k then start reducing the climb, set the speed hold to mach 3 and you should be fine. If she still pitches up, check the CG, because it climbs flawlessly if you follow the profile.
David.
Sounds like something else is going on there. Are you accelerating to Mach 1.1 in a gentle dive from 35,000 feet? This speed hold only holds the speed, it doesn't control the pitch to maintain speed only the throttles. The logic behind that is way beyond my capability. I welcome you to try. The autopilot provided is more than adequate to get to speed and altitude so long as you follow the climb profile set out in the manual.
In real life the pilots would cruise climb from 70,000ft at 100ft per minute so by the end of the Mach 3 cruise they would be several thousand feet higher. So set the autopilot altitude lower eg 70k, and then cruise climb. But really the key to this is performing the dipsy doodle maneuver to get to Mach 1.1, set the vertical speed at say 6k, keas hold to 450 and ride it on up to 60k then start reducing the climb, set the speed hold to mach 3 and you should be fine. If she still pitches up, check the CG, because it climbs flawlessly if you follow the profile.
David.
Re: Erratic A/P behavior
Getting to M1.1 isn't an issue, nor is getting into a stable climb of 450KEAS, it's when I turn the AP on that I start having issues. Knowing now that the AP in this addon isn't designed to adjust pitch of the aircraft as a means to control speed answers my question. Seeing as how the worst thing to do in this scenario is reduce power, which the AT is doing, I'll just leave that mode off and fly the climb with the V/S controls. Thanks.
Re: Erratic A/P behavior
Hi,
I still believe there is something else going on there. Is this in P3D or FSX? Are you using a default flight, or creating a new one each time? If it's a default flight you're loading the aircraft into, it could be unbalanced. Possibly worth checking trim to make sure that is level.
I can climb using autothrottle and v/s control all the way to cruise speed and altitude with no pitching at all.
David.
I still believe there is something else going on there. Is this in P3D or FSX? Are you using a default flight, or creating a new one each time? If it's a default flight you're loading the aircraft into, it could be unbalanced. Possibly worth checking trim to make sure that is level.
I can climb using autothrottle and v/s control all the way to cruise speed and altitude with no pitching at all.
David.