Gloom Demon Posted January 14, 2014 Posted January 14, 2014 On numerous occasions I have noticed, that the Su-25's (both Su-25 and Su-25T) engines shut down if I am descending at high speed (above 700 km per hour). Why is this happening. The air intake speed is to high, or maybe something else? And another question - at a speed of more then 700 km per hour the Su-25s appear to loose longitudinal stability - if flying at 600 km/h I can leave the aircraft and come back in 10 minutes only to find in flying in the same orientation as I left it. However if I leave it flying at more than 700 km/h, very soon the plane gains negative pitch and tries to hit the ground. Frequently the engine stops when this happens. P.S. I understand that it is not a bug, however I would like to understand the physics of the process. AMD Ryzen 3600, Biostar Racing B850GT3, AMD Rx 580 8Gb, 16384 DDR4 2900, Hitachi 7K3000 2Tb, Samsung SM961 256Gb SSD, Thrustmaster T.Flight HOTAS X, Samsung S24F350 24'
Vedexent Posted January 14, 2014 Posted January 14, 2014 You say you are descending rapidly, but are you pulling negative gravity in your sustained decent? The fuel system isn't designed for prolonged negative G forces, and the engine often starves for fuel when under negative G forces, or flying inverted, for extended periods. I've never really noticed a long term pitch at 700Kph, but I'm usually only going that fast during attack dives, and don't often leave it for 10 minutes in that case. 1
RagnarDa Posted January 14, 2014 Posted January 14, 2014 Hmm... engine flameout because of turbulence in the intake at high speeds/altitudes/angle of attack? The pitching moment is probably related the angle of attack and when flying fast = less AoA... but then the it should nose up normally? Maybe fuel consumption makes the center of gravity move forward? It could be a bug. Edit: sniped DCS AJS37 HACKERMAN There will always be bugs. If everything is a priority nothing is.
GRUNT -Shrek- Posted January 14, 2014 Posted January 14, 2014 (edited) On numerous occasions I have noticed, that the Su-25's (both Su-25 and Su-25T) engines shut down [...] And another question - at a speed of more then 700 km per hour the Su-25s appear to loose longitudinal stability [...] P.S. I understand that it is not a bug, however I would like to understand the physics of the process. You might check these datas for your planes: http://en.wikipedia.org/wiki/VNE# http://en.wikipedia.org/wiki/VNE#VNE http://en.wikipedia.org/wiki/VNE#VO http://en.wikipedia.org/wiki/VNE#VNO edit: I did some research, too. Most likely engines shut down occur a) under the influence of continious negative G-force (fuel does not reach chamber) b) stall conditions, if the stream of air intake into the jet engine is discontinuous or in any other way disturbed. HTH Edited January 14, 2014 by GRUNT -=Shrek=-
BTTW-DratsaB Posted January 14, 2014 Posted January 14, 2014 I think the noes pitching down at speed is a phenomenon called "Mach Tuck" http://en.wikipedia.org/wiki/Mach_tuck 1 Specs: GA-Z87X-UD3H, i7-4770k, 16GB, RTX2060, SB AE-5, 750watt Corsair PSU, X52, Track IR4, Win10x64. Sim Settings: Textures: ? | Scenes: ? |Water: ? | Visibility Range: ? | Heat Blur: ? | Shadows: ? | Res: 1680x1050 | Aspect: 16:10 | Monitors: 1 Screen | MSAA: ? | Tree Visibility: ? | Vsync: On | Mirrors: ? | Civ Traffic: High | Res Of Cockpit Disp: 512 | Clutter: ? | Fullscreen: On
Gloom Demon Posted January 14, 2014 Author Posted January 14, 2014 (edited) Wow, thank You - I'd say that explains it! DCSW realism is incredible! Edited January 14, 2014 by Gloom Demon AMD Ryzen 3600, Biostar Racing B850GT3, AMD Rx 580 8Gb, 16384 DDR4 2900, Hitachi 7K3000 2Tb, Samsung SM961 256Gb SSD, Thrustmaster T.Flight HOTAS X, Samsung S24F350 24'
Revan Posted January 16, 2014 Posted January 16, 2014 Wow, thank You - I'd say that explains it! DCSW realism is incredible! yes it is DCS: F-4E really needs to be a thing!!!!!! Aircraft: A-10C, Ka-50, UH-1H, MiG-21, F-15C, Su-27, MiG-29, A-10A, Su-25, Su-25T, TF-51
Winfield_Gold Posted January 17, 2014 Posted January 17, 2014 I think the noes pitching down at speed is a phenomenon called "Mach Tuck" http://en.wikipedia.org/wiki/Mach_tuck I read this as mack truck. First though was "well that is possible considering the speeds being mentioned and if it flew past me at 50 feet at 700kms it would feel like a mack truck just blew past me
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