amalahama Posted July 19, 2018 Share Posted July 19, 2018 (edited) It would definately not hit a "wall" as described in this very thread. Yes, the top speed is OK. But it accelerates like a SR-71 on steroids even from 1.8 to 1.85 and then suddenly the acceleration is gone completely. No real airplane would do that, 'cause physics. It should gradually accelerate until it won't do so anymore roughly at ~ 1.85 - 1.86 in ISA conditions. So the real problem is just in acceleration, it should decrease and going from 1.8 to 1.85 shouldn't last just like half a second, but rather a minute or even minutes. If the aircraft had complex adaptative inlets to manage inbound shock waves then yes, but Viggen has fixed ones that can choke, so it might be possible that the Viggen experiments such a wall IRL Regards Edited July 19, 2018 by amalahama Link to comment Share on other sites More sharing options...
TLTeo Posted July 19, 2018 Share Posted July 19, 2018 It would definately not hit a "wall" as described in this very thread. Yes, the top speed is OK. But it accelerates like a SR-71 on steroids even from 1.8 to 1.85 and then suddenly the acceleration is gone completely. No real airplane would do that, 'cause physics. It should gradually accelerate until it won't do so anymore roughly at ~ 1.85 - 1.86 in ISA conditions. So the real problem is just in acceleration, it should decrease and going from 1.8 to 1.85 shouldn't last just like half a second, but rather a minute or even minutes. As I posted above, the physics of supersonic flight are too complicated to just use "cause physics" as a justification for whether something behaves correctly or not. Link to comment Share on other sites More sharing options...
TOViper Posted December 6, 2018 Author Share Posted December 6, 2018 (edited) Now I cannot fly faster than M1.715 :( Edited December 6, 2018 by TOViper Visit https://www.viggen.training ...Viggen... what more can you ask for? my computer: AMD Ryzen 5600G | NVIDIA GTX 1080 Ti OC 11GB | 32 GB 3200 MHz DDR4 DUAL | SSD 980 256 GB SYS + SSD 2TB DCS | TM Warthog Stick + Throttle + TPR | Rift CV1 Link to comment Share on other sites More sharing options...
Vitormouraa Posted December 7, 2018 Share Posted December 7, 2018 Now I cannot fly faster than M1.715 :( Try colder temperatures? SplashOneGaming Discord https://splashonegaming.com Link to comment Share on other sites More sharing options...
TOViper Posted December 7, 2018 Author Share Posted December 7, 2018 Try colder temperatures? I was on ISA. Try it out, the "wall" now occours on M1.715, not on 1.85 as before. Visit https://www.viggen.training ...Viggen... what more can you ask for? my computer: AMD Ryzen 5600G | NVIDIA GTX 1080 Ti OC 11GB | 32 GB 3200 MHz DDR4 DUAL | SSD 980 256 GB SYS + SSD 2TB DCS | TM Warthog Stick + Throttle + TPR | Rift CV1 Link to comment Share on other sites More sharing options...
HWasp Posted December 7, 2018 Share Posted December 7, 2018 If the aircraft had complex adaptative inlets to manage inbound shock waves then yes, but Viggen has fixed ones that can choke, so it might be possible that the Viggen experiments such a wall IRL Regards That is quite possible, but my problem is, that if the engine inlet parameters would change as rapidly as the thrust change suggests, then there would be an engine surge or stall. Or the very least there would be a visible fluctuation of engine parameters. I've seen none of those. Link to comment Share on other sites More sharing options...
TOViper Posted December 7, 2018 Author Share Posted December 7, 2018 That is quite possible, but my problem is, that if the engine inlet parameters would change as rapidly as the thrust change suggests, then there would be an engine surge or stall. Or the very least there would be a visible fluctuation of engine parameters. I've seen none of those. true Visit https://www.viggen.training ...Viggen... what more can you ask for? my computer: AMD Ryzen 5600G | NVIDIA GTX 1080 Ti OC 11GB | 32 GB 3200 MHz DDR4 DUAL | SSD 980 256 GB SYS + SSD 2TB DCS | TM Warthog Stick + Throttle + TPR | Rift CV1 Link to comment Share on other sites More sharing options...
Vitormouraa Posted December 7, 2018 Share Posted December 7, 2018 I was on ISA. Try it out, the "wall" now occours on M1.715, not on 1.85 as before. I did some tests today, OATC was -3.1, and yep, maximum Mach number I was able to reach was 1.72, regardless of the altitude. It's quite interesting how the aircraft accelerates extremely quickly but all of the sudden stops at M 1.72. But I agree on the statement above, something is choking the engine. (It's been a few months since I flew the Viggen, so much fun flying it!) SplashOneGaming Discord https://splashonegaming.com Link to comment Share on other sites More sharing options...
TOViper Posted December 7, 2018 Author Share Posted December 7, 2018 (edited) "Chocked" is a term used in compressible aerodynamics when talking about convergent ducts in the exhaust. Chocked names the effect that supersonic speed is reached, but whatever we do before the narrowest diameter (e.g. increase p, T, mass flow) there is no acceleration beyond M1 possible, unless we attach a divergent duct (Laval) to accelerate the air further beyond M1. IMHO the inlet might be the limiting factor. According to my thinking about programming (I might be wrong), the code could take the inlet geometry into considerations. The inlet appears as a normal Pitot super sonic inlet, thus the re-compression after the normal shock is not as efficient than it would be when using ramps and braking it down stepwise. Also, the shock might move at different speeds, leading to complex airflows along the inlet lip and the duct behind the lips. What happened in the recent one is unknown to me, maybe Cobra has some news on this issue to bring light into darkness. Edited December 7, 2018 by TOViper Visit https://www.viggen.training ...Viggen... what more can you ask for? my computer: AMD Ryzen 5600G | NVIDIA GTX 1080 Ti OC 11GB | 32 GB 3200 MHz DDR4 DUAL | SSD 980 256 GB SYS + SSD 2TB DCS | TM Warthog Stick + Throttle + TPR | Rift CV1 Link to comment Share on other sites More sharing options...
Vitormouraa Posted December 7, 2018 Share Posted December 7, 2018 @TOViper Thanks, I am aware of its meaning in the fluid dynamics. I was using the 'choke' as a typical/general term, not the one explained by the physics. Choke in the sense of "choke, stifle, asphyxiate, suffocate...", i.e; something is preventing the engine from doing its natural work of propelling the aircraft forward at Y or X speeds. Perhaps I shouldn't have used that word in this discussion unless I was using its technical meaning... :D SplashOneGaming Discord https://splashonegaming.com Link to comment Share on other sites More sharing options...
TOViper Posted December 7, 2018 Author Share Posted December 7, 2018 (edited) @TOViper Thanks, I am aware of its meaning in the fluid dynamics. I was using the 'choke' as a typical/general term, not the one explained by the physics. Choke in the sense of "choke, stifle, asphyxiate, suffocate...", i.e; something is preventing the engine from doing its natural work of propelling the aircraft forward at Y or X speeds. Perhaps I shouldn't have used that word in this discussion unless I was using its technical meaning... :D talking on a higher level is fun, isn't it :) Anyway, we are thinking, approximating, believing, assuming, guessing ... Nothing a technician likes to do :smartass: Mathematically speaking, we are approaching M0.0. Not tomorrow, not the day after tomorrow ... but ... who knows how many updates will follow. The gradient is negative ... what will happen when we arrive at M-0.8? Ok, that one was really bad ... ;) We should go flying instead of this, and Cobra is invited to polish our inlet ducts. :P Edited December 7, 2018 by TOViper Visit https://www.viggen.training ...Viggen... what more can you ask for? my computer: AMD Ryzen 5600G | NVIDIA GTX 1080 Ti OC 11GB | 32 GB 3200 MHz DDR4 DUAL | SSD 980 256 GB SYS + SSD 2TB DCS | TM Warthog Stick + Throttle + TPR | Rift CV1 Link to comment Share on other sites More sharing options...
Goblin Posted December 10, 2018 Share Posted December 10, 2018 Looks like there’s some mixing of ”choked” and ”shocked” flow here... https://en.m.wikipedia.org/wiki/Choked_flow A shock wave can choke a duct, since supersonic flow causes a shockwave, where local airflow is reduced to subsonic speed, thus choking the duct. Link to comment Share on other sites More sharing options...
TOViper Posted December 10, 2018 Author Share Posted December 10, 2018 Looks like there’s some mixing of ”choked” and ”shocked” flow here... https://en.m.wikipedia.org/wiki/Choked_flow A shock wave can choke a duct, since supersonic flow causes a shockwave, where local airflow is reduced to subsonic speed, thus choking the duct. Yeah, that was my understanding. I think chocolate is something that we should consider "using" when reading the books about chocked nozzles due to their normal shocks ... :D What do you think of it? Visit https://www.viggen.training ...Viggen... what more can you ask for? my computer: AMD Ryzen 5600G | NVIDIA GTX 1080 Ti OC 11GB | 32 GB 3200 MHz DDR4 DUAL | SSD 980 256 GB SYS + SSD 2TB DCS | TM Warthog Stick + Throttle + TPR | Rift CV1 Link to comment Share on other sites More sharing options...
Goblin Posted December 10, 2018 Share Posted December 10, 2018 What do you think of it? That you are contributing to the confusion by spelling ”shocked” as ”chocked”. :) I hope you don’t choke on my reply ;) Link to comment Share on other sites More sharing options...
Vitormouraa Posted January 20, 2019 Share Posted January 20, 2019 I was testing this out again and I noticed the Viggen doesn't have RPM lockup, this isn't simulated apparently, any idea how this works in the RL Viggen? SplashOneGaming Discord https://splashonegaming.com Link to comment Share on other sites More sharing options...
some1 Posted February 10, 2019 Share Posted February 10, 2019 Kinda relevant to the topic. I measured the acceleration of various aircraft in DCS at 40'000 ft from Mach 1 to Mach 1.5, clean, 60% fuel: [b]Viggen: 26 seconds[/b] M2000: 55 seconds F-15: 67 seconds MiG-29: 72 seconds Hornet: 93 secods Su-27: 96 seconds MiG-21: 108 seconds Low altitude performance seems believable, and Viggen is one of the slowest of the bunch at sea level, but at high altitude it's way off. Hardware: VPForce Rhino, FSSB R3 Ultra, Virpil T-50CM, Hotas Warthog, Winwing F15EX, Slaw Rudder, GVL224 Trio Throttle, Thrustmaster MFDs, Saitek Trim wheel, Trackir 5, Quest Pro Link to comment Share on other sites More sharing options...
Vitormouraa Posted February 10, 2019 Share Posted February 10, 2019 A bit too fast... :) SplashOneGaming Discord https://splashonegaming.com Link to comment Share on other sites More sharing options...
Svend_Dellepude Posted February 10, 2019 Share Posted February 10, 2019 A little derail i know, but try dogfighting an AI viggen. most surprising. He will fly circles around any A/C. [sIGPIC][/sIGPIC] Win10 64, Asus Maximus VIII Formula, i5 6600K, Geforce 980 GTX Ti, 32 GB Ram, Samsung EVO SSD. Link to comment Share on other sites More sharing options...
amalahama Posted February 12, 2019 Share Posted February 12, 2019 Yes, high speed-high altitude performances are weird. HB should have a look at it Link to comment Share on other sites More sharing options...
QuiGon Posted February 12, 2019 Share Posted February 12, 2019 Kinda relevant to the topic. I measured the acceleration of various aircraft in DCS at 40'000 ft from Mach 1 to Mach 1.5, clean, 60% fuel: [b]Viggen: 26 seconds[/b] M2000: 55 seconds F-15: 67 seconds MiG-29: 72 seconds Hornet: 93 secods Su-27: 96 seconds MiG-21: 108 seconds Low altitude performance seems believable, and Viggen is one of the slowest of the bunch at sea level, but at high altitude it's way off. :shocking: There's definitely something at odds! Intel i7-12700K @ 8x5GHz+4x3.8GHz + 32 GB DDR5 RAM + Nvidia Geforce RTX 2080 (8 GB VRAM) + M.2 SSD + Windows 10 64Bit DCS Panavia Tornado (IDS) really needs to be a thing! Link to comment Share on other sites More sharing options...
outbaxx Posted February 13, 2019 Share Posted February 13, 2019 Kinda relevant to the topic. I measured the acceleration of various aircraft in DCS at 40'000 ft from Mach 1 to Mach 1.5, clean, 60% fuel: [b]Viggen: 26 seconds[/b] M2000: 55 seconds F-15: 67 seconds MiG-29: 72 seconds Hornet: 93 secods Su-27: 96 seconds MiG-21: 108 seconds Low altitude performance seems believable, and Viggen is one of the slowest of the bunch at sea level, but at high altitude it's way off. There is data for 20k feet for the Viggen and a clean ac will accelerate from 1.0 to 1.5 in approximately 80sec. Link to comment Share on other sites More sharing options...
Airhunter Posted February 13, 2019 Share Posted February 13, 2019 The Viggen can go up to mach 1.34-1.35 when clean down on the deck in stage 3 burner. It wasnt really designed for high altitudes and going high mach's (at least the AJS variant). Link to comment Share on other sites More sharing options...
Vitormouraa Posted April 4, 2019 Share Posted April 4, 2019 Kinda relevant to the topic. I measured the acceleration of various aircraft in DCS at 40'000 ft from Mach 1 to Mach 1.5, clean, 60% fuel: [b]Viggen: 26 seconds[/b] M2000: 55 seconds F-15: 67 seconds MiG-29: 72 seconds Hornet: 93 secods Su-27: 96 seconds MiG-21: 108 seconds Low altitude performance seems believable, and Viggen is one of the slowest of the bunch at sea level, but at high altitude it's way off. F-14 takes 68,4 seconds by the way. :) Looks like HB got it right this time. SplashOneGaming Discord https://splashonegaming.com Link to comment Share on other sites More sharing options...
QuiGon Posted October 7, 2019 Share Posted October 7, 2019 (edited) So, where are we at with this issue? How does this Kinda relevant to the topic. I measured the acceleration of various aircraft in DCS at 40'000 ft from Mach 1 to Mach 1.5, clean, 60% fuel: [b]Viggen: 26 seconds[/b] M2000: 55 seconds F-15: 67 seconds MiG-29: 72 seconds Hornet: 93 secods Su-27: 96 seconds MiG-21: 108 seconds Low altitude performance seems believable, and Viggen is one of the slowest of the bunch at sea level, but at high altitude it's way off. fit to this: Heatblur? Anyone? :dunno: Also, why does the Viggen's acceleration gets faster with increasing ambient temperature? Put together some numbers, after testing I think the F14-B might the fastest Jet in DCS on the deck. Please feel free to double check and correct. Alt under 1kft clean air frames speed taken from F10 map (knots ground speed) Temps @ -12c/10F below, F14B- 956 Viggen (rb24 glitch)- 924 F18C- 885 SU27- 851 Viggen- 830 F16C- 829 F15C- 827 MIG29A- 798 M2000C- 751 AV8- 560 SU25T- 545 A10C- 360 TFP51-318 UH1- 124 Temps @ 15c/59f below, Viggen (rb24 glitch)-970 F14B- 895 F16C- 878 Viggen- 866 MIG29A- 825 F15C- 822 SU27- 813 M2000C- 797 F18C- 780 AV8- 560 SU25T- 558 A10C- 350 TFP51= 326 UH1 =131 Temps @ 50c/122f below, Viggen (rb24 glitch)- 1017 Viggen- 905 F-16C- 863 M2000C- 853 F15C- 815 F14B- 813 SU27- 752 MIG29A- 718 F18C- 706 F86F- 622 AV8- 593 SU25T- 574 A10C- 317 TFP51- 309 UH1- 118 Edited October 7, 2019 by QuiGon Intel i7-12700K @ 8x5GHz+4x3.8GHz + 32 GB DDR5 RAM + Nvidia Geforce RTX 2080 (8 GB VRAM) + M.2 SSD + Windows 10 64Bit DCS Panavia Tornado (IDS) really needs to be a thing! Link to comment Share on other sites More sharing options...
F900EX Posted October 8, 2019 Share Posted October 8, 2019 Clean, stage 3 A/B 46000ft straight and level, I can only get to M1.71 2-3months ago I was doing M1.81 What happened? Link to comment Share on other sites More sharing options...
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