Frederf Posted December 24, 2016 Posted December 24, 2016 The following is a comparison to demonstrated MiG-21bis takeoff unstick speeds to real world documentation (attached). The independent variables presented are: Gross weight Alpha Temperature Pressure Headwind The nomogram axes are marked in 4 scales in km/h after steps 2, 3, 4, and 5 in the calculating process. These show speeds after the various corrections (in order): uncorrected, temperature, pressure, and by headwind. By intersecting the same value for speed the values of temperature, pressure, and headwind which have no net correction can be discovered. These are: 25°C, 760mm Hg, 0 m/s. Those are the environmental variables where the step 2 speed and the step 5 speed are the same from the graph. Procedurally takeoff is an acceleration at one of three power settings to 150-200 km/h for aft stick placement, nosewheel lift at 250-270 km/h and a rotation to liftoff attitude by the UUA-1 indicator of 11-13°. The liftoff pitch is retained for the initial flyaway. Speeds were recorded by steady state flight at minimum altitude for 0 m/s climb and the appropriate UUA-1 reading. [TABLE=head]Trial|GW (kg)|Expected 11° (km/h)|Zero Climb 13° (km/h)|11° (km/h)|9°(km/h) 1|7500|323|328|349|382 2|8500|345|349|367|406 3|9500|365|367|402|427 [/TABLE]*8 alpha 3.9 AOA, 11 alpha 5.0 AOA, 13 alpha 5.9-6.0 AOA, **IAS taken from F2 readout, cockpit +10 km/h ***9500 kg used 800L external tank and 2 missiles Impression The zero-climb airspeeds are significantly in excess of those produced by the nomogram, especially if readings are taken from the cockpit gauge. It is unknown if the unstick speeds should result in no climb or a positive separate from the runway during positive pitch rate. A positive separation requirement increases the discrepancy demonstrated. Some effort was made to fly close to the surface (<10m) to reintroduce ground effect but may have been inadequate. The natural tendency of the simulation pilot is to over rotate to produce a positive liftoff before reaching tire limit speeds (370 km/h permissible, ultimate structural limit unknown). Keeping within the 11-13 alpha guidelines for takeoff is punishing especially for attempts at a non-afterburning takeoff.
zaelu Posted December 28, 2016 Posted December 28, 2016 I observed after reading your post that I use to yank the plane off the ground more lately. Definitely a lot more AoA to take off quickly after reaching 250-270Km/h. Could be because of the late modifications of FM? [sIGPIC][/sIGPIC] I5 4670k, 32GB, GTX 1070, Thrustmaster TFRP, G940 Throttle extremely modded with Bodnar 0836X and Bu0836A, Warthog Joystick with F-18 grip, Oculus Rift S - Almost all is made from gifts from friends, the most expensive parts at least
Frederf Posted December 29, 2016 Author Posted December 29, 2016 Maybe. I had always pulled more than the prescribed angle mostly because I hadn't read the book yet and as long as I didn't scrape the tail or crash who's to guess at any other way. The book mentions the gauge values so there is a chance that the true angle to gauge relationship is off or the true angle is or a mix.
RAZBAM_ELMO Posted December 29, 2016 Posted December 29, 2016 Well taking into account that LNS has simulated the slight inaccuracies of the gauges as per the real airplane I don't think we'll get it 100% perfect but I know from flying that pitching the nose up to 10° at 270kmph gives me a perfect wheels off ground action at 350-370kmph depending on external load at approx 7° AoA. Sent from my SM-G900W8 using Tapatalk Know and use all the capabilities in your airplane. If you don't, sooner or later, some guy who does use them all will kick your ass. — Dave 'Preacher' Pace, USN.
Frederf Posted December 30, 2016 Author Posted December 30, 2016 I have (for testing) turned off the pitot-shock special option. With it on the difference between F2 and gauge is nearly 50 km/h at certain speeds (near Mach) and less away from Mach. However with the option off the F2 and gauge don't disagree too much. At SL I had a small region of +2 to +6 gauge reading vs. F2 IAS from 700-1000 km/h. Anyway in all cases regardless of special option the gauge inside the cockpit will never read lower than the F2 info bar. Since the above table are numbers from the F2 info bar that means the gauge is equal or greater displayed speed. This means the issue of too fast at liftoff is at least this bad. The more the gauge overstates the speed the greater the magnitude of the problem. 10° pitch is 5° too much. 7° AOA is 15 alpha on the UUA-1. That's too much. Look at the chart in #1, the listed UUA-1 readings are 9, 10, 11, 12, and 13. Fifteen isn't in the cards. At 8300 kg and limiting yourself to 9 UUA-1 reading you should unstick at 370 km/h indicated all other factors being standard. Try it for yourself if you can do that.
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