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Guest Racer

FDE Philosophy

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Hello guys, so I have fallen down the very slippery slope of panel/ aircraft design and am having great fun with it. I am currently reworking the FDE for Veneavione's Citation II. My question for all you guru FDE makers out there is this: once you have some hard numbers on the aircraft like lbs. static thrust, empty weight, payload capacity, MTOW, max initial climb, etc. how much do you set those numbers and leave them alone? Right now I have accurate figures on the wing area, static thrust, empty weight and MTOW input into the flight model. My dad used to fly citations and says that at MTOW they could mainted approx. 3000 fpm initial climb (@210knt). At MTOW my citation is chomping at the bit and the airspeed only stabilizes at a little over +4000 fpm. It then decays so that at 20k feet I can barely maintain +500 fpm. Even reducing fuel to 15% only gives me another 500 fpm. I won't even start on the cruise performance, let's just say, at this stage, it won't. :)Should I just work the drag & fuel side, and leave thrust alone (since I know it's an accurate number) or not?What do you think??thanks,Ryanp.s. -I've read most of the tutorials, haven't seen "fuel flow gain". What is it?

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What I have found is you need to do things logically, and they wont always be real world numbers in order to get real world performance. If the jet wont cruise at altitude, then you need to tweak things like static thrust/ drag numbers and things like wing and tail area. They might not be realistic but could yield realistic flight characteristics. The big problem with working FDE's is if you fix one area others might get dorked up so it requires a good bit of testing. With 2004 you can do some changes to the aircraft geometry and flight tuning sections of the aircraft.cfg file that can have pretty big affects on the handling and performance. Go slow and try not to change too much at one time. having some knowledge of aerodynamics is kind of important also, for instance you need to know what induced drag is to change it. Or how changing things like span/chord/and area will affect diferent surfaces and the flight model.Hornit

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------- Setting "Static_thrust". --------p.s. -I've read most of the tutorials, haven't seen "fuel flow gain". What is it?RyanSetting "static_thrust = 5000" doesn't mean you get 5000 lb thrust at SL. Typically Thrust goes quite a bit higher at full throttle. One has to use a test gauge, such as AFSD, to see what thrust really is. The static_thrust value should be set to what gives RATED TO Thrust at a given N1. For example, the AIR file turbine table 1506 may set 100% of the 'static thrust' setting at CN1 = 100.0 %, or perhaps at N1 = 95.0 %. But, the throttle may drive CN1 to 106%. If TBL 1506 sets 100% thrust at CN1 = 100.0, but you need SSLT at 95.0%, then the value in aircraft.cfg has to be set higher than the rated SSLT. Note CN1 = N1 (panel gauge value) at standard 15C. ------------------ It took me years to figure out what 'fuel_flow_gain' refers to. Apparently, it relates to the GAIN of the turbine fuel controller. Higher "Gain" results in a faster spoolup. Ron

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Ron & Hornit, thanks very much for your replies. I have taken your advice and have worked on it over the weekend, now the Citation matches the performance information that I have. Now I'm just looking for more detailed information (no POH here...)...........thanks again!Racer

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