Squale-BAF- Posted December 3, 2014 Posted December 3, 2014 Hello happy ED testers/developpers, When I read SU 27 infos on DSC Website (product), I see: "The fly-by-wire system is a trajectory control system. In other words, if the control stick remains in the same position, the system will hold the set flight path. This is why the reduction of airspeed (for example) and resulting decreased lift and increasing angle of attack, will lead to the aircraft attempting to hold the initial flight path and prevent the aircraft from descending. This will result in the airspeed stability degradation up to neutral stability." In other words, we can understand that SU27 has some kind of "auto-trimming" feature, and whatever the airspeed, the calculator adapts AOA to keep the flight path. As a mater of fact we all figure out that our SU27 has a bad computer because we spend all time trimming............ Hopefully my trim-switch will remain reliable !!!! Thank you for your explanations !
combatace Posted December 4, 2014 Posted December 4, 2014 I had the same doubts as the plane is behaving like its a fly by steel cable thing. To support my models please donate to paypal ID: hp.2084@gmail.com https://www.turbosquid.com/Search/Artists/hero2084?referral=hero2084
nickexists Posted December 4, 2014 Posted December 4, 2014 Pretty sure it says the same thing in the manual, but that's definitely not how it behaves in DCS right now.
LJQCN101 Posted December 4, 2014 Posted December 4, 2014 Same question replied: http://forums.eagle.ru/showpost.php?p=2229658&postcount=22 EFM / FCS developer, Deka Ironwork Simulations.
Squale-BAF- Posted December 4, 2014 Author Posted December 4, 2014 Thank you for your reply. But a " trajectory control system" is not a "fly-by-cable imitator" We definitely need an official reply from ED developpement team
LJQCN101 Posted December 4, 2014 Posted December 4, 2014 Whole thread here: http://forums.eagle.ru/showthread.php?t=133600 I just concluded what Yo-Yo said. Maybe you'll find some useful info. EFM / FCS developer, Deka Ironwork Simulations.
Squale-BAF- Posted December 4, 2014 Author Posted December 4, 2014 LJQCN101 : You said in an other thread that a friend of yours knew real SU27 pilots. Is there any chance to ask them about longitudinal behaviour ?
GGTharos Posted December 4, 2014 Posted December 4, 2014 ED knows real Su-27 pilots. The Su-27SK manual is also available, and it might mention something about it there. The longitudinal control in the aircraft is as it should be. If there was 'auto-trimming', you wouldn't see degradation to neutral stability, at least within the limits of the pitch channel authority. [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
LJQCN101 Posted December 5, 2014 Posted December 5, 2014 (edited) LJQCN101 : You said in an other thread that a friend of yours knew real SU27 pilots. Is there any chance to ask them about longitudinal behaviour ? For sure. I also got hundreds of questions to ask, but first let's just trust ED of what is done and what will be done to the flight model. As for the FCS longitudinal channel, to conclude: 1. The basic pitch FCS operates as a g-command system and mainly uses normal acceleration feedback to provide constant g per stick force, and to hold the flight path if the control stick remains in the same position. But this is not the final result and should not account for the overall pitch behavior. 2. An additional control law is added to the basic pitch FCS to imitate conventional plane stability. (Pitch up when accelerating and pitch down when decelerating.) Control logic is as follows: You spend all time trimming just because of that additional control law. It is not a inherent pitch behavior, but imitated. BTW, the static stability of a Su-27 without any control system is near neutral (+ - depends on actual CoG position - fuel and payloads) and the stick balance position is constant at speeds. (Credit: Yo-Yo) Edited December 5, 2014 by LJQCN101 EFM / FCS developer, Deka Ironwork Simulations.
LJQCN101 Posted December 5, 2014 Posted December 5, 2014 Actually you can still observe neutral speed stability in Su-27 above 780 km/h. Try this: Accelerate to 800 km/h and manually trim the aircraft to 1g level flight. Then accelerate and decelerate in a speed range of 780~980 km/h. Observe pitch changes. EFM / FCS developer, Deka Ironwork Simulations.
Squale-BAF- Posted December 5, 2014 Author Posted December 5, 2014 Thank you all for these explanations. We all love so much SU27 !!! You can understand that discovering that an internal law makes this aircraft a "wild horse" for us (I only fly it for aerobatics) is very disapointing... But realism is realism, and I have to say that you made a very good job with this PFM. Last but not least : concerning roll : when ASC is on, plane goes back to horizontal situation when you release stick. Is it like real ? Thank you ED
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