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SinusoidDelta

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    FAQ for F-15 AFM Development

    in F-15C for DCS World

    Posted · Edited by SinusoidDelta

    Sounds like every plane out there!

     

    It's really not. We're seeing 200dps at low AoA. Very NOT like the Bitburg roll.

     

    Yes, a lot of research has been done, and every time it's done the CAS gets an upgrade to stop it from happening.

    The Bitburg roll is an interesting example, but the end it is said to 'not be well understood', and in any case if you do read the research you'll find that the eagle doesn't enter what they call a 'true departure' too often, even when they're trying for it.

     

    In hindsight I agree, they are dissimilar. I didn't know the roll rate in DCS was 200dps. I actually have read the research on uncommanded roll and departure in the F-15, quite extensively. The Bitburg Roll had multiple contributing factors. These factors result in lateral asymmetries, producing transient yaw acceleration, yaw and wing rock. This is amplified with low fuel and carrying stores. In this sense I think the AFM issue is quite similar.

     

    My gut says yes, but I'm not sure it's really testable (or at least easily testable). You could turn the CAS off, but in theory the horizontal stabilizers can still be physically rigged to deal with it.

     

    As you're aware, AFCS is not modeled properly in the AFM. CAS off flight is wildly inaccurate compared to the real data I've seen.

     

    Some of these things you can log with lua. Frankly unless you're an F-15 pilot though or you're trying to match public empirical research, you're probably not doing anything that's very useful. That's not to say it can't happen, just that it's rare. There's also a lot of data that's simply not available.

     

    I'm not a test pilot :( I'm just an engineer who looks for problems to solve, sometimes I end up creating them:lol: I did come up with a solution for data logging (Not involving Tacview). That being said, there is a plethora of useful empirical data, it only needs sorted through and correlated to DCS flight test data.

     

    I still see people coming around complaining that 'this FM sucks, the F-15 can't climb straight up!' Usually they don't even know what the -1 is :)

     

    I think the FM is very, very good. It just needs refinement and I'm excited for future developments. Furthermore, most people don't realize the -1 isn't the only manual. ;)

    F-117

    in Military and Aviation

    Posted

    It's just a track for streaming. RCS is already modeled in the game, it always was (factors into countermeasure rejection probability).

     

    As for the real F-117, it had nothing to do with 'long wave radar', 'open bomb bay doors' or any other funny business.

     

    What happened is simply this: Those SAM sites are mobile, and the Serbs did not keep them in one place, and wisely so.

     

    Thus the probably SAM defense drawn on NATO maps was basically a shape/circle surrounding Belgrade; anywhere within that line you were in danger of running into a SAM.

     

    And that's exactly what happened with that (And another) F-117: They found themselves too close to those SAMs when the radar started operating, and they were legitimately detected and launched on at close range (around 30km or less, engagement was IIRC at around 17km).

     

    Stealth is there to help you sneak between the radar ... but it really helps if you know where they are.

     

    Perhaps the source is inaccurate but here's where I got that information:

    http://m.liveleak.com/view?i=a43_1429013746

     

    "

    Unknown to NATO, Yugoslav air defenses operators had found they could detect F-117s with their obsolete Soviet radars after some modifications. In 2005, Colonel Zoltán Dani confirmed in an interview suggested that those modifications involved using long wavelengths, allowing them to detect the aircraft when the wheel well or bomb bay doors were open. In addition, the Serbs had also intercepted and deciphered some NATO communications, and thus were able to deploy their anti-air batteries at positions best suited to intercept NATO planes.

     

    On March 27, 1999, the 3rd Battalion of the 250th Air Defence Missile Brigade of the Army of Yugoslavia , under the command of Colonel Dani , downed F-117 Air Force serial number 82-0806 , callsign "Vega 31".

     

    The Army of Yugoslavia unit was equipped with a Yugoslav version of the Soviet Isayev S-125 "Neva" missile system ( NATO reporting name , SA-3 "Goa" ).

     

    At about 8:15 pm local time, with a range of about 8 miles (13 km) several missiles were launched. According to Sergeant Dragan Matić, who was identified in 2009 as the soldier who fired the missiles, they detected the F-117 at a range of about 50 to 60 kilometres (31 to 37 mi), operating their equipment for no more than 17 seconds to avoid being locked on to by NATO anti-air suppression. According to Dani in a 2007 interview, his troops spotted the aircraft on radar when its bomb-bay doors opened, raising its radar signature. "

    - See more at: http://m.liveleak.com/view?i=a43_1429013746#sthash.Sd3vlqHz.dpuf

    F-117

    in Military and Aviation

    Posted

    I remember reading the F-117 had an RCS the size of a bird and B-2 has an RCS the size of a marble. The only F-117 shot down was allegedly due Serbians using long wave radar to detect when the bomb bay doors opened.

     

    I am curious how detailed the RCS of aircraft is modeled in the game. Perhaps modeling a real life stealth technology demonstrator like the F-117 help create a better radar model.

    list of corner speed for DCS world aircraft?

    in DCS World 1.x (read only)

    Posted · Edited by SinusoidDelta

    To all those saying to 'read the manual': You are being very unhelpful and should probably refrain from posting.

     

     

     

    For a start, the answers to this question are not in the manuals. A much better response would be the actual location of the information in the manuals, or a quote from them. However, because you yourselves haven't read them, you don't know that the answers aren't actually there. The best we get from the SU27 manual is on page 106/107 where we get an EM diagram of a typical modern fighter. Great.

     

    Additionally, there is no guarantee that the flight model of DCS aircraft really simulates this aspect accurately so using 'real world' information probably isn't that good either. Finally, maintaining a constant speed in a dogfight is pretty tricky so precise numbers aren't terribly useful anyway.

     

    The numbers that I use for the max-energy high-rate-of-turn 'corner speed' are 650-750km/h in the SU27 or 375-425kts with the F15. YMMV.

     

    I think the issue is a misunderstanding of what corner speed is; it is not a static airspeed. Saying "maximum energy point" is misleading with regards to EM theory as the energy height actually dips negative at corner. It is an intersection that where turn rate goes to maximum and turn radius goes to minimum on a constant altitude path. If you would look at the document I referenced you would see a concise explanation using actual F-15 performance data.

     

    From this example, the following points concerning sustained turns can be noted: 1-Mn^occursbetween0.87and0.96Mach(maximumsustainedloadfactorequals

    7.33 g)

    2. M_ occurs at 0.87 Mach (maximum sustained turn rate equals 13.0 deg/sec).

    HMUC

    3. Mr, occurs at 0.34 Mach (minimum sustained turn radius of 2200 feet). "min

     

    In Addition,the turn rate-radius versus Mach plot shows the maneuver "corner"point. It is denned as the wmi«mm speed at which the maximum aircraft load factor (n) can be achieved. On the V-n diagram (Figure 9.29) it is located at the intersection of the lift boundary (line A) and structural limit boundary (line B). In Figure 9.35, it occurs at the intersection of the max lift line and the maximum load factor line. In this case, the corner point is at 0.55 Mach, pulling 7.33g and achieving approximately 23 deg/sec turn rate. Notice that this equates to a P. value of less than -2000 ft/sec. To the pilot this means a loss of Mach at constant altitude pr a loss of altitude at constant Mach to hold 7.33g. Hence this is often noted as the mayiirmm instantaneous turn capability of the aircraft and the term

    "quietest, tightest turn" is used in the fighter community to describe the aircraft performance at that point.

    By «"^mining the P, = 0 plot in Figure 9.35, it can be seen that for each level of load factor there are two Mach values where the aircraft can stabilize. This may be better visualized

    byanalyzingFigure9.36,whichshowsthatbyincreasing -^ foragiven,thespeedat

    which these stable points occur come closer together. And, at some point, there is a load factor that can be sustained at only one speed.

     

    I'm not implying this data will match DCS performance data. The theory needs to be understood first.

    • Like 1

    F-117

    in Military and Aviation

    Posted

    I'm just speculating from a systems modeling point of view. The F-117 was a relaxed static stability aircraft and not flyable without the extremely resilient FBW system that was developed. I think AOA was limited to 17deg, it's ceiling was like 25,000 ft. @ Mach 0.8 and it was G-limited to +3/-1 G. I suppose a flight envelope that small would be easy to model but outside of that envelope it would almost be guess work.

    F-117

    in Military and Aviation

    Posted

    Regardless of being classified, CFD analysis of the F-117 would be a nightmare in addition to modeling the flight control system. It's a jet that did not want to fly. I'd rather have a bomber like the B1

    Belsimtek F-15C

    in Chit-Chat

    Posted

    It is termed "semi" because the flight control system is triple redundant using mechanical linkage and stick force input. Should the hydromechanical system fail the control surfaces can still be deflected by the CAS system alone and vice versa. I still maintain the augmentation system itself is far different in the A/B/C/D vs E models in that it is digital and supplied by Lear/BAE Astronics.

    Belsimtek F-15C

    in Chit-Chat

    Posted

    The F-15C control augmentation is analog. The F-15E's controls are digitally augmented and thus are easily reprogrammed. Pilot inputs are determined via strain gauges on the flight stick.

    Belsimtek F-15C

    in Chit-Chat

    Posted

    Depends on what you're talking about. Avionics, yes night and day. Fuel, hydraulics, flight control, and ECS systems basically mirror images.

     

    The F-15E Flight control system is semi fly-by-wire. It is quite different and far more advanced than the F-15C CAS system. Some F-15E's also have the pw229 engines which have more max thrust than the 220's overall,and significant gains in the supersonic and high altitude regimes. The 229's also eliminated the need for a vmax switch and have improved advanced DEEC with Assymmetric Thrust Departure Prevention System.

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