fable2omg Posted October 19, 2014 Posted October 19, 2014 I was reading the emergency procedures of the Mig-21bis when I found something pretty interesting, on page 168, it says that it's possible to maintain level flight below 2000 meters will flaps and gears down, and then a couple of lines below that, there's a warning saying level flight cannot be maintained with gears down and flaps set to take-off.. ..The only conclusion I can come out of this is that when the flaps are down, the blown flaps are activated by the SPS system, now I don't want to kill myself by turning off the SPS and trying to land just to confirm my theory, but if it is true, when why don't we take-off with flaps down too? I can understand that flaps down create a large amount of drag but here's a quote from Wikipedia "In general, blown flaps can improve the lift of a wing by two to three times." Now this might be horse███ but if it is true, why?
NeilWillis Posted October 19, 2014 Posted October 19, 2014 Probably due to it accelerating the airflow over the top of the flying surface, thereby reducing air pressure, and increasing lift? Interesting to find out the technical details though. Tripled? I wonder!
fable2omg Posted October 19, 2014 Author Posted October 19, 2014 Probably due to it accelerating the airflow over the top of the flying surface, thereby reducing air pressure, and increasing lift? Yes but why don't we use this magical SPS on take-off? It could even shorten the take-off lengh thereby rendering the RATOs useless, giving space for the ASO modules even with heavy loads!
Spectrum Legacy Posted October 19, 2014 Posted October 19, 2014 (edited) Yes but why don't we use this magical SPS on take-off? It could even shorten the take-off lengh thereby rendering the RATOs useless, giving space for the ASO modules even with heavy loads! Because the increased drag from landing flaps combined with reduced thrust of your engine (as SPS-BLC is powered by bleed air and takes quite a big portion of it as it seems) would likely hamper your overall take-off performance and negate the increase of lift. Indeed SPS works only with landing flaps and has power setting threshold. Edit: Also forgot to mention, SPS will disengage shortly after exceeding 360km/h, where your aircraft should sink in 20-30m according to the manual...that itself doesn't sound like safe procedure for takeoff. P.S. Landing with SPS turned off & takeoff flaps can be quite a challenge depending on conditions, but great fun nonetheless! I think the procedure was trained in case of Konus retraction and/or airbleed system malfunction, or combat damage which could hamper the intake airflow. Approach faster than normal with lean bird (dump everything you can except for the canopy and your "throne"). :smilewink: Edited October 19, 2014 by Spectrum Legacy Sent from my pComputer using Keyboard
fable2omg Posted October 20, 2014 Author Posted October 20, 2014 Because the increased drag from landing flaps combined with reduced thrust of your engine (as SPS-BLC is powered by bleed air and takes quite a big portion of it as it seems) would likely hamper your overall take-off performance and negate the increase of lift. Indeed SPS works only with landing flaps and has power setting threshold. Edit: Also forgot to mention, SPS will disengage shortly after exceeding 360km/h, where your aircraft should sink in 20-30m according to the manual...that itself doesn't sound like safe procedure for takeoff. P.S. Landing with SPS turned off & takeoff flaps can be quite a challenge depending on conditions, but great fun nonetheless! I think the procedure was trained in case of Konus retraction and/or airbleed system malfunction, or combat damage which could hamper the intake airflow. Approach faster than normal with lean bird (dump everything you can except for the canopy and your "throne"). :smilewink: Thanks a lot for the explanation, makes sense, now I know I need to try and land with take-off flaps and SPS off!
Azrayen Posted October 20, 2014 Posted October 20, 2014 Also no afterburner with SPS (IRL). Don't know if it's implemented in DCS, though.
Flamin_Squirrel Posted October 20, 2014 Posted October 20, 2014 Flaps, while increasing lift, actually reduce your lift/drag ratio. This means that while flaps allow you to fly slower (and therefore reduce ground roll for takeoff (and landing)), as soon as your wheels leave the ground, flaps are actually hurting not helping you. Landing flaps in particular are deliberately designed to generate lots of drag too, which is why they should never be used for takeoff.
fable2omg Posted October 22, 2014 Author Posted October 22, 2014 Also no afterburner with SPS (IRL). Don't know if it's implemented in DCS, though. Oh, well thanks for the hint, I'm the kind of guy who keeps a logbook of every flight (and in the MiG-21 case, SARPP :P) so I'll be careful not to taint my records with impossibilities such as an afterburner go-around at 10 meters AGL.
Dirty Rotten Flieger Posted October 31, 2014 Posted October 31, 2014 You keep a log book! wow ! thats cool :)
ResonantCard1 Posted April 3, 2019 Posted April 3, 2019 Sorry for reviving an old thread, but is the SPS system turned on by default, or it has to be turned on? Also, in the MiG-21 the tips we get when hovering over a switch usually list the positions of the switch, if it says "Off/On" does that mean that Off is the UP position? Main: MiG-21bis, because pocket rockets are fun Si Vis Pacem, Para Bellum
Jonne Posted April 3, 2019 Posted April 3, 2019 SPS is on by default. In the MiG-21bis all on/off-switches are on if either up or forward depending on the location. [sIGPIC][/sIGPIC]
ResonantCard1 Posted April 3, 2019 Posted April 3, 2019 Okay, that makes sense. Thanks! Main: MiG-21bis, because pocket rockets are fun Si Vis Pacem, Para Bellum
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