mig25飞行员的一天
从今天开始，到精品版2正式发布，我将写一个小系列来阐述精品版苏机的战术，希望抛砖引玉，能够带动论坛上战术讨论。第二篇，mig 25飞行员的一天。
我是克里斯·赫兰特少校，隶属于民主德国国土防空军。。。 将根据下面这篇说明写出来。精品版的mig25气动很特别。
This is \"demo\", or proof-of-concept modification/WIP of MiG-25P (Foxbat-A) that can cruise over 20,000m/65,000ft.
Original model by Mig-25 package by wpnssgt, usafmtl, tomcat1974, sundowner,ghostrider, deuces and moonjumper, from the \"Foxbat\" package)
When I checked \"Foxbat\" in original form from the package, I found out that it has more/less adequate behavior for the large,heavy interceptor but its performance at altitude needs significant improvement. It suffered from too much \"Mach tuck\" that is hard to fix in the normal way, since there is no trim. Also, it was obviously hard to incorporate high-speed aerodynamics, and the \"ordinary\" shape of Foxbat airfrane can be a mislead. Truth is, Foxbat does not behave \"normally\" at high speed/altitude, having both airframe and engines in mind!
This is not the final product-this is a \"proof-of-concept\", (re)built almost solely by feel&performance understanding \"match\" and needs a lot of refinement. Basis for altitude engine perf is R-35 chart (which I took from MiG-23 to speed the things up). Many things were taken from MiG-25RB aerodynamics manual, which is basically the same airframe (performance is relaxed a little, due to competely different mission).
First-the engines. R-15B engines are, considering operational speed, ramjets augmented with turbojet core. Quite opposite of other afterburning turbojets! The role of turbine part (and first afterburner stage!!!) is to bring AB2 section in operational zone, which is +11,000m/+M1.5. AB2 switches on automatically, and is fed by air compressed by intakes, fed into turbines that are heating and further \"conditioning\" the airflow and serve it to AB2. Such powerplant produces almost 6T of thrust (each!) at peak performance (+M2.8). Maybe it does not look much, but the drag, temperature and specific fuel consumption are much lower than of \"normal\" turbojet, which would melt itself on that speed if constant, or simply \"suck\" all the fuel. Also, normal AB turbojet is on decline of performance chart when this type of poweplant just starts to \"breathe\".
I couldn\'t find the way to put these into one (i.e. two engines) so I added two more \"dummy\" engines that basically take over the propelling of \"Foxbat\" at high altitude. If you\'ve seen the charts (of MiG-25RB), it is only viable solution! ALso, R-15B is 2-stage AB engine where \"staging\" is cruical. That cannot be done, or cannot be done easily using just one set of engines.
Bigger problem was the trim. Foxbat flies straight at +20,000m not just because of engines, but because of aerodynamical qualities. The AC/CG (aerodynamic centre/centre of gravity) shift is quite huge, which is countered by large all-stab authority (-23.50/-9.15 deg total range of stabilizers, perpendicular to airstream), but even this would not be sufficient if there was no intake-fuselage lift.
Many people don\'t know that canards were ment to be installed to Foxbat during design phase. The long, heavy nose and was the main concern then. However, it was discovered that intake lips make much lift that render canards unnecessary. They shift AC forward and reduce trim drag. Some Western types have such quality, wanted or not, (like F-15 Eagle), but Foxbat really needs it. Also, huge AC shift happens when engines are \"revved\" at altitude, i.e. when aircraft accelerates/decelerates. Pilot seldom holds \"Foxbat\" straight with his muscles-there are \"autopilots\" that are common in Soviet airplanes, but with the raised priority in hi-perf aircraft like MiG-25.
I did this version with \"dummy\" lift surfaces on the nose that lift the nose at high speeds and act as intake lip lift. As the Mach increases, so does the lift of those surfaces (which is neglible at lower speeds). It is exgeratted, I know, but it has to serve the non-existant trim function as well! I made another version with \"titled\" thrust of those AB2 dummy engines for 45 deg up and roughly recalculated thrust again (c2=2a^2) so it gives the same thrust and upward vector). The result was good, but there was a little too much \"oomph\" (pitchup) when AB was lit. Maybe I wil tilt thrust a little less to get desired \"oomph\" result in final product
I had to \"shut\" braking chutes-I really got frustrated when I saw aerodynamic brakes were excluded on this model (from the \"package\") and re-instated chutes (and they are 2-part brakes on the true thing, upper used only above M1.1/7,000m). I adjusted the drag/Mach behavior to the one from the manual, and you-really-need-it now, no matter how small they are!
Flying the \"Foxbat\".
First, the climbout; it has to be done properly: roughly, best way is to press throttle to full Ab, release the brakes, and switch on the autopilot. Once gear and flaps are up, you can take over and point it into general desired direction, -but- keeping the altitude below 1,000m and airspeed under 1,100kph. MiG-25 has a \"hard limit\" of 1,100 level/1,150KPH climb IAS at low altitude, due to adverse aileron effect on earlier machines, and it was kept on newer models with differential stabilator to prevent pilots to have too much \"jollies\" and keep engine life up (air is dense, and it easily goes outside temp limits).
Achieving \"on\" speed, pull to 30 deg pitch. It is a steady pull. Your goal is 5,000m+ deck, where you level out and wait it to hit M1.2 or close to 1,000kph IAS. Then pull 25 deg and keep that Mach number (or with tendency to go little higher) to 12,000m, where you level out again and aim again to 1,000kph. You will notice the speed rise significantly over M1.5 (AB2 on!), pull 20 deg , and watch MiG Mach-accelerate through the climb! Passing 14,000m start level-out and ease throttle to cca. 80% at 17-18km alt. It is easy to overshoot or \"undershoot\" 20-21,000m (which is atmospherical change in \"TK\'s world\") so you will have to practice.
Once you are level at cca. 20,500m (wing leveler on&steady), when speed is M2.35 you can chop thrust to 68-69 percent (still AB!) that will keep the speed up (more/less, real Foxbat also either accelerates or decelerates, since the smooth regulation of AB2 is not possible).
Performance&fighting
Maybe some of you have read about Iraqi Foxbats, and that the elite fighter unit of Iraqi dictatorship was not Fulcrum unit-but Foxbat unit. There is a reason-flying Foxbat needs alot of competence, not because the type itself is (overly) unforgiving, but because -keeping- it within usable envelope requires more than party ties! Pilot has to think ahead -waay ahead- and to remember that if speed and altitude goes down it is just a big, clumsy target. The general rule is that it is outperformed by virtually everything under 5,000m (limited to subsonic speeds), about equal to \"Phantom\" between 7-12,000m and M 1.2-1.3 and absolutely superior in performance to everything in range +12,000m and over M1.5, including the mighty Eagle!!! SR-71 flies outside the range of \"ordinary\" airplanes and overlaps \"the curve\" only with \"Foxbat\". Cca. 3g allowed turn at those altitudes is extremely fast, and there is simply no target that can get outside the \"g\" envelope of \"Acrid\" missiles (because there is simply no air dense enough to allow any conteporary fighter more than 3.5-4g turn).
Stay above 6,000m and M1.2. Whenever you get close to these numbers, level out and pick up speed and altitude. You will get into controlability problems once speed around 1,100kph-\"Foxbat\" wings flexes a lot! It is easy to over-g the real aircraft, though, newer models have coupled alpha and g-limiter that prevent this. To get down from 20km altitude, the procedure is to go max dry thrust (2nd, \"supersonic\" dry thrust), slow down to M2.2, and descent keeping the IAS the same. You can zoom the fighter up to cca. 27km altitude, but it is too sensitive and lazy on controls up there. Brakes are effective, but at too high speeds they mess up the airflow around the aircraft too much (not forbidden, but not recommended either). After firing two missiles from the same wing, you will get quite of bank which has to be (smoothly!) countered or you will make an unintentional roll. Before introduction of differential stabilator, \"Foxbat\" exibited uncouterable auto-roll after firing \"Acrid\" at high IAS (called \"Kazaran effect\", after the pilot who \"discovered\" that flaw).
\"Smerch\" radar is jam-proof but not too much range and with much clutter under 1,000m alt, no \"lookdown-shootdown\". Missiles are all-aspect (IR, too!), but IR model is very sensitive to the \"heat clutter\" (real thing is restricted 30 deg sun/moon), so no \"shootdown\" with it either. Missile is designed in \'60es and was, actually, quite a performer. Snap-up is normal procedure. The true \"Foxbat\" has a unique digital targeting computer (for its time) that analyzes target speed, altitude and trajectory, \"Foxbat\" relative position, altitude and speed compared to the built-in missile speed/turn performance aerodynamic ability (calculates PK) and will not give firing solution unless those parameters are satisfied and PK is viable, regerdless that target is acquired by seeker... former \"Foxbat\" pilots write in forums that they had quite a number such \"guaranteed lock-ons\" on SR-71\'s!
Enjoy-and I will try to get the rest of series soon!
Zip file containing modified ini attached, backup your existing MiG-25P_DATA.INI and replace it with the one in this file. Note that \"Foxbat\" entered service in 1971-72, so you may have problem with the missiles (due the date). The model can \"act\" as early export \"Foxbat\" to Lybia, too, as they were equipped with \"Smerch\" radars, but they can carry R-60\'s. MIG-25好像有很多版本的，各种性能不同啊。。。。。。。
页:
[1]