LJQCN101

Now that we got NASA wind tunnel data, plus NASA flight control laws, but the flight characteristics hardly fits the description in NASA TP1538. The demo aircraft is too susceptible to spin as opposed to the study in NASA TP1538. Will check if there's something wrong with the control law, especially the automatic departure/spin prevention part. IRL: Above 35° AOA, a departure spin-prevention mode is activated which uses a yaw-rate feedback to drive the roll control surfaces and the rudder to oppose any yaw rate buildup.

Yeah, it seems that spin resistance of the aircraft has been enhanced. And that's good improvement because IRL F-15C is quite resistant to spins except above 20000Ft and with large asymmetric loads. A centerline tank will further aggravate the susceptibility to spin. Will test that later.

As for the spin recovery technique in real life F-15C. Under high AOA conditions, rudder is less effective in creating yaw moment (Cn, aka Yawing momentum) than ailerons. For example: In normal conditions, a left rudder input will make the nose of the aircraft slice to the left. However in high AOA regions, to make the nose slice to the left, rudder input is ineffective. To many people's surprise, a right stick input will make it. Yeah, in the opposite direction. And that phenomenon is called "Adverse Yaw". So in real life, the proper spin recovery technique in a F-15C is, as proposed by T.O. 1F-15A-1, full lateral stick in the direction of spin. Rudder is useless. As opposed to what is suggested in the DCS F-15C manual. And you're right, opposite roll input while in a spin does aggravate the spin.

I've been testing the F-15C PFM for a period of time, got some really strange feeling in terms of pitch short period mode, dutch roll mode, inertia-coupling, departure/spin characteristics, etc.. So I wanna start with some simple flight characteristics such as 1G stall, and compare it to the description in the real life manual. (Reference manual: T.O. 1F-15A-1) Here's the video link :http://v.youku.com/v_show/id_XNzUzMTc5MzA4 As one can see, the AOA buffet is modelled quite well. Wing rock and yaw oscillation are not observable. And the worst part, I can't pull the aircraft above 38 units AOA, let alone to stabilize at 45 units. The aircraft just went roll departure everytime when reaching 35 units AOA, which reveals a poor departure resistance. Here's a departure/spin susceptibility summary of a real life F-15. If it were me to fill in the blanks for DCS F-15C, I won't give any words similar to "Resistant". So what is called "Resistant" then? In December 1979, the NASA Langley Research Center conducted a study on stall/post-stall characteristics of a real-time simulated fighter. During the test, the control system is modified to decrease the susceptibility to departures while not degrading maneuverbility and control response. There're Basic Control System, which has least anti-departure ability; Control System B, and Control System C. Finally in Control System C, with full lateral stick input applied at 0.6Mach and an altitude of 9144m, followed by a full nose-up pitch command, the control system effectively handled the aircraft during the whole 11-sec-test so that there're no pitch/roll departure occured compared to the Basic Control System. And that is called "Resistant". With such departure susceptibility as in DCS F-15C, I wonder if it represents the real one, will it even be approved to put into production.