Making the best of MiG-21
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From below article it appears that 21 can still hold its own in dogfight:
Try to point at and shoot well flown MiG-21!
Predrag Pavlovic, dipl.ing. and Nenad Pavlovic, dipl.ing, JAT Airways
Maneuverability of modern fighter is measured by how slow it can fly and how high
angle of attack it can sustain and still turn. During some war situations, US evaluation
and Aggressor use, MiG-21 has shown it can keep pace with modern planes in this
area. Aircraft manufacturer at one time considered this irrelevant and imposed
restrictions on angle of attack. Flying above allowed 28-33 degrees local angle of
attack at low speeds makes possible to relatively safely achieve a maneuverability once
considered privilege of modern fighters.
Couple years ago reports and testimonies appeared in the media about a dogfight during
the Israeli-Arab War '73. when the Egyptian MiG-21 pilot managed to do a Split-S
maneuver at the start altitude of 3000 feet, less than half minimum airspace the manual
says (about 6750 ft). Appropriate simulation can be found on the internet:
http://www.youtube.com/watch?v=bQMzK2WfYYM&feature=player_embedded
Figure 1.
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Initiated by this event, some American and Israeli enthusiasts (once pilots of their AF
fighters), one of which has a private squadron of various Russian fighters, attempted to
replicate that minimum altitude needed to complete Split-S figure in the two-seater MiG-
21. Previous consultation with Israeli ace, who participated in that dogfight in '73. war,
did not help test to be successful. Attempts were carried out at the higher altitude (5 km)
and the height loss during the figure was in accordance with flight manual. It remained
unclear whether ’73 event was result of "special skills or superhuman strength of the
Egyptian pilot needed to withstand the required g-loads”.
Recently disclosed files of the official MiG-21 evaluation in the U.S. revealed some
unexpected capabilities that can be correlated with the "inexplicable" ’73. maneuver.
MiGs were brought to America via Israel, in the late '60s as a result of pilot error or fled
from Iraq and Algeria. Later they were bought from Indonesia. The MiG-21 in the U.S.
Air Force is designated YF-110.
The report of a MiG-21F shows nothing particularly unusual, except for maneuvering
capabilities and behavior/handling at low speeds described as "class above competition”.
Besides that, if competitors tried to follow MiG-21F at high alpha, their engine
experienced shutdown or compressor stall. MiG could perform "hammerhead" turn (wing
over/stall turn/renversement) at 100 knots (knot = 1.853 km/h), figure where at the end of
the vertical climb pilot add rudder (with the opposite aileron and forward stick) to push
the plane in the dive. Rudder is effective from 30 knots. With the stick fully backward,
the plane flies at 210 km/h, the rolling oscillations are present, but there is no lift
breakdown or the tendency towards spin. If during the evaluation, loss of control due to
uncoordinated controls occurred, it was in the form of roll-off (usually for 180°) instead
of much more dangerous yaw-off. To put the plane back under control it was necessary
only to release controls. MiG-21 proved to be docile, safer to fly than MIG-17. During
the hundred flight tests engine compressor stall was never experienced.
U.S. of course, used MiGs in dogfight evaluation against their aircraft. Latter, they
formed "Aggressor" squadron of MiGs and other fighters for the dogfight simulation with
regular American aircraft.
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Figure 2, 3. MiG-21 on testing in the U.S.
During MiG testing, it was clear that U.S. pilots have not relied on Soviet pilot’s manuals
or they did not have one at the beginning. That is why the aircraft ability was fully
exploited. Test pilots had thousands of flight hours experience on dozens of types of
aircraft. Those who have survived the testing of U.S. supersonic fighters
F-100/101/104/4 (many of planes were called "widow makers"), learned to recognize the
pre-stall/spin signs and use rudder for rolling the aircraft at higher angles of attack.
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Figure 4. Some of the results of MiG-21 testing in the United States
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Reportedly, if Vietnamese pilots had adequate training, the U.S. fighter shot-down ratio
figures would be much worse in that war. In the hands of the well trained pilots, MiG
would always outmaneuvered Phantom. US unveils graphs depicting not only far better
instantaneous turn performance of Fishbed C compared to F-4D but also better sustained
maneuverability. MiG-21 Aggressor pilots respected only the most modern fighters
because they do not lose so much speed in turn even at low speeds. However, appearance
of all-aspect infrared missiles reduced the importance of sustained turns (M2000, F-18E,
Gripen …are not brilliant in the maintaining speed in turn). If MiG-21 had R-73 missile,
it could easily take advantage of first shoot opportunity at close range against any new
fighter.
The F-5E, fighter which does not fly above Mach 1.5, MiG-21 simulator, reportedly has
shade better subsonic sustained turn maneuverability, but inferior controllability at low
speeds. Maneuverability is the ability to change speed and direction of flight path
(velocity vector pointing) and controllability - ability of change aircraft attitude
(pitch/roll/yaw - nose pointing) and thrust (engine response - spool up time matters).
When the aircraft initial flight path in dogfight is anti-parallel flyby, combat will
inevitably develop so that someone goes in a climb with rolling scissors - turn reversals
along the opponent’s flight path to remain behind the opponent. If the F-5E does not gain
an advantage before the speed drops below 200 knots, MiG will start winning. First look
at the configuration of the aircraft, MiG – delta with the sweep near 60°, and Tiger with
nearly straight wings, would suggest the opposite, that MiG is in trouble at low speed.
Even the mighty F-15 Eagle had no solution in dogfight below 150-250 knots against
MiG-21 in US Aggressor hands. At the beginning of dogfight, at the speed of 400-500
knots MiG-21 will turn at max g loosing 70 knots per second, ending at the speed of 70
knots in less than 90º of turn (deceleration of 3.5 g, more intensive than Harrier’s VIFF
turn). Reportedly, no other aircraft can do that. This way MiG will remain behind every
opponent still having sufficient controllability for gun tracking using rudder rolls.
Opponents would think that at this speed MiG can only bring down the nose and dive, but
the MiG at less than 100 knots has sufficient pitch authority to raise the nose at enemy. If
F-15 tries to follow, ’21 should execute 'barrel-roll ' to remain behind the Eagle.
It is obvious that MiG-21 'Aggressor' pilots pulled full aft stick in turn regardless of the
lateral oscillations, roll-off and temporary loss of control.
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Figure 5. Scissors maneuver
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Latter, the F-15 pilots learned (in a hard way) not to accept maneuvering at slow speeds,
not to allow to be drown into a series of turn reversals, but to withdraw and re-attack at
higher speeds using 3D turns and it’s higher thrust/weight ratio. F-15 with 45º swept
wing and low horizontal tail, at higher angle of attack becomes longitudinally
superstable, so it can not achieve more than about 30º angle of attack.
On the example of lift and stability of the aircraft with the 45º swept wing and high-set
horizontal tail it can be seen that the lift begins to decline at 10º (buffeting starts), the
wings are stalled at the 20º (the airflow separates from the wing), and max body lift is at
35-40º after which it decreases. Delta wing of MiG-21 with sweep of 57 º retains stable
airflow to very high angles of attack.
Longitudinal stability is positive where the curve has a downward slope. In this case, the
position of the horizontal tail is causing longitudinal instability at 15º, and at 35-40º angle
of attack aircraft is trimmed without tail deflection. MiG-21 has no problem with
longitudinal stability (except with air to ground armament with low fuel) and the plane in
the example would have a limit at 15º angle of attack.
Yaw stability curve shows that the aircraft is unstable at 15º, what is not uncommon.
Few modern fighters are stable at over 20º, but it is not a problem if the aircraft maintains
lateral stability i.e. roll due to yaw. Roll stability curve is increasing as the lift increase,
so it similarly comes to the instability, in this case at about 20º angle of attack. Shall the
plane have a tendency toward spin (at no deflection of the control surfaces!) show the
curve of dynamic directional stability where factors are static yaw and roll stability along
the inertial characteristics of the aircraft. In this example, the plane is at stall just above
20º angle of attack, while MiG-21 is stable at well over 30º at low Mach numbers.
Curves correspond to a particular Mach number, at some other speed they can vary
significantly.
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Figure 6. Example lift and stability of aircraft
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Soviet training was based on a relatively small number of flight hours on a MiG, which is
used for training the primary purpose of aircraft, interception of fighters-bombers, under
ground control. Pilots are not encouraged to explore the flight envelope. The aircraft is
designed to fly faster and higher. Slow speeds were irrelevant, except for landing. In the
first combat manuals, the performance at altitudes only above 5 km were presented.
Later, it turned out that there are many practical constraints due to which the projected
max altitudes and speeds are rarely used.
MiG-21 wing has no camber or twist along span. The relative thickness of the higher end
of the wing than in the root. There are few prestall signs. Prestall buffet begins much
earlier (at 50-100 km/h higher speed), its intensity is light and slightly decreases at higher
α. Below Mach 0.4 buffet does not develop. Just before stall α, aircraft nose would start
wandering accompanied by more noticeable wing rocking (roll oscillations that intensify
thru the stall), symptoms of dynamic directional instability.
Stalling proceeds more vigorously with fewer signs at higher subsonic speeds.
Ailerons are ineffective in countering roll oscillations and rudder would push aircraft into
a spin. Setting control surfaces to the neutral position immediately after the onset of stall
would restore normal flight conditions. The aircraft is longitudinally stable in air combat
configuration at any internal fuel quantity.
Aircraft’s stall speed (speed at which dynamic directional stability breakdown occurs) is
function of Mach number, because directional and lateral static stability usually decreases
with speed. Stall angle of attack decreases from above 30º (far beyond indicated
α)at
So there is large margin between allowed angle of attack and stall angles of attack
especially at lower Mach numbers
.
Stall angle of attack (α)
> 30º ~ 25º ~ 23º ~ 20º
α
(~20º
α )
287 km/h 287 km/h 282 km/h
267 km/h
(stall)
Speed at 28 units local α
(~17º
α )
311 km/h 311 km/h 305 km/h 291 km/h
So, the low speed turning capabilities were not fully exploited. If situation comes, like it
happened to that Egyptian pilot during war, there is an additional lift potential.
During the Split-S fig
ure, speed should not be increased. The closer to stall α is, the lesser
the altitude loss is during figure. Below 600 km/h CAS entry speed aircraft cannot
aerodynamically reach the allowed structural load factor so there is no need for
superhuman physical stress. At higher speeds height loss in split-S at stall angle of attack
is much more than 3000 ft.
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Figure 7, 8, 9.
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Because of its very high stall angle of attack at lower Mach numbers and good pitch
control authority (large wing leading edge sweep produces strong vortical flow which
shifts aerodynamic centre forward at high alpha, reducing stability thus allowing the tail
to easily trim aircraft at more than 30° alpha), aircraft has a great point and shoot
potential with modern IR missiles.
Although it is often said that the MiG-21 looses a lot of energy in turn, the truth is also
that it has better sustained turn performance than most aircraft of its generation.
Tumansky engine proved almost stall/surge free at speeds far below minimums quoted in
conservative Soviet flight manuals. All U.S. and European contemporary designs flamed
out under same conditions. Engine has two shafts for optimized - different rotational
speeds of low and high pressure compressors stages for a compressor blade stall
resistance, feature that allows more compressors stages to be added for lowering specific
fuel consumption. But it has unusually low number of compressor stages for a two-shaft
design, contributing to reliability. Bad side of this philosophy is higher fuel consumption.
Despite the resistance of the compressor to the extreme conditions of airflow at the inlet,
if afterburner is engaged at almost zero speed (well below the conservative engine
envelope) other undesirable phenomena are possible. Distortions of the inlet airflow
causes disruption of relations of air and fuel in the AB chamber, which changes the speed
of combustion. Pressure fluctuations coupled to acoustic velocity fluctuation (AB
chamber is also exposed to sound fatigue, the noise is up to 180 decibels) associated with
combustion instability (called rumbling), can cause extreme resonant structural vibrations
of the engine with subsequent engine destruction and the loss of the aircraft.
The published results of American evaluation relates to the F/PF models. BIS model has
15-20% higher ratio of inertia moments in yaw to roll. It certainly results in more sideslip
during rolls and somewhat lower stall angle of attack, angle when breakdown of dynamic
directional stability occurs. But the prevailing factor in this equation is the dihedral effect
i.e. roll stability and it is the same in all models because it depends on airflow around the
delta wing, so it can be expected good behavior of BIS model at low speeds also.
It should be borne in mind that prevailing effects at high angles of attack are dihedral and
adverse yaw due to aileron deflection. Rudder is used for rolling and if the sideslip angle
or yaw rate (induced in this way) crosses critical, result is the spin. Opposite aileron
increases the roll rate through an additional sideslip angle i.e. 'adverse yaw'. In most
modern aircraft application of such cross controls for 5-15 seconds, usually causes spin.
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Figure 10. MiG-21 derivatives J-7G and JL-9
In general, the plane that has a lower stall speed is more maneuverable. At some speed, it
will be able to achieve g-load equal to the square of the mentioned speeds quotient. The
U.S. experience from simulated dogfights during exercises indicates the importance of
the minimum speed and controllability at high angles of attack. That is why F-18 gets F-
15/16 although its performances are considerably lower. Latest F-18E has still weaker
performance, but better controllability. Angle of attack, at low speeds, of the F-16 and
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Gripen is limited to about 26º (Rafale and the Typhoon to a shade more). F-15 has max
trimmed angle of attack 30-33º with poor roll response here. Against 'stealth' fighters F-
22/35 and corresponding new Russian (whose all planform contour lines are parallel to a
few main sweep angles - cm wavelength radar return angles, in addition to other 'stealth'
measures and cost of 50 MiG-21), none of the listed has significant chances at medium
range. Analysts agree that the close combat will remain inevitable, and that each aircraft
armed with missiles cued by helmet sight has a chance, especially if it can reach high
angles of attack. Even stealth fighters do not destroy opponents with death rays. Every
component of the fire control/weapon system chain has limitations, from fighter radar to
missile fuze. Towed mini decoy (laterally separated) with monopulse deception
jammer/repeater or just simple towed corner reflector can draw away radar return signal
centroid from towing aircraft. It could help surviving medium range combat even against
stealth fighters.
The main disadvantages of MiG-21 are poor cockpit downward visibility, a
proportionally small (but inline to generation) wingspan i.e. large induced drag
(afterburner is needed for level flight at the absolute minimum speed, as at max allowed
Mach number) and relatively slow response of two-shaft engine. All this causes poor
performance on landing, especially in the case of go-around. Small fighter size means
limited mission equipment carriage capacity.
It turns out that only important is to have a reliable and economical aircraft, a platform
for carrying payload, with attack speed in the Mach 1.5+ class (that’s why a 15-20 years
younger A-10 was withdrawn prematurely). The modern nav-attack equipment
(simplified inertial system, GPS, displays…) is now relatively inexpensive to install even
in a small propeller planes. MiG-21 operators missed opportunity to realize fact that with
helmet cued, large acquisition angle R-73 missile that was available upgrade, MiG could
achieve 50:1 kill ratio in dogfight against F-18/Gripen/Typhoon class fighters just
because latter were 10-15 years late with similar weapon system. Instead of making best
of it, MiG-21 operators opted to admire newer fighters.
Because of its good characteristics, even 50 years after MiG-21 became operational,
some of its modifications are still in production in Asia.
Reference:
- Fighter Performance in Practice, Phantom versus MiG-
21, Predrag and Nenad Pavlović,
- Test and Evaluation Squadron, Nellis Air Force Base, Interviews;
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huh ?
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I agree that the MiG-21 is a very potent adversary in a dogfight. But, a trained pilot knows not to get into a fight in that kind of speed/altitude regime that the MiG-21 can excel in.
Also, most western aircraft have their AoA limiters built in. Essentially, no one except the test pilots would know what the F-16s handling without AoA limitations are. You might be surprised what the F-16 can do without AoA limiters. Unfortunately, flying without them is also very dangerous as aerodynamically unstable designs tend to end up in irrecoverable deep stalls.
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You have the point. Also....I can not put jpg so I will cite excerpt from other article:
"Despite the obvious breakthroughs afforded by its stealth and supercruise capabilities, the Air Force chose not to have a fast, high-flying fighter that couldn't maneuver. "We learned in Vietnam that all you have to do is get a small maneuvering fighter inside the 'fast flyer's' turn circle, and it will eat him up", says Hodge...Thrust vectoring "makes for phenomenal maneuverability", particularly at low speeds and at high angles of attack, he adds. Maneuverability in a modern fighter is measured by how much angle of attack it can sustain and still turn."You are right for F-16. A lot more lift would be extracted from its aerodynamics without limiter. Unfortunately F-16 is longitudinaly unstable. If you rolls at high alpha, pitch up moment develops that in concert with low longit.stability makes pitch-down problematic ie deep stall. Thay could make stabilizers bigger or LERX shorter to pitch down unstable ac.
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I always tot that one of the reason for the AoA limiter is that at some point above 30 deg AoA, the fuselage blocks the tail and there goes the use of your rudder ie can't control the direction of the aircraft.
As to longitudinal instability, that's what FBW is meant to cover. Relaxed static stability = controlled flight.
btw, did they ever put fbw in a mig-21...the answer would probably explain a large part of the 340+ non combat mig-21s were lost out of 793 in the IAF to date.
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Unfortunately even Mig-29 or Su-27 are unstable directionaly even at 15 deg alpha at high subsonic speeds. But lateral stability compensates. Whether ac will yaw-off depends on dynamic directional stability. But who am I to talk about that. It can be seen in above and other books.
FBW has its limits. F-16 was longitudinaly 6% unstable (subsonicaly, it is stable at ss speeds) and F-22 is I think 40%. Depends on computer and actuator speed. At high alpha ARI [(t)aileron-rudder interconnect] helps control in roll. I thing only F-18C/E, Su-35 and F-22 have kind of FBW in lateral-directional axis and stability augmentation depends on control surface area and distance from cg.
I do not any test FBW MIG-21. I think that most IAF 21 loses are because of its high landing speed (270 to 300+ km/h), poor cockpit visibility, relatively slow engine response in case of go-around (one must quite early at landing select AB in order to produce thrust needed to climb)..you know better.. I do not think IAF ever fly its 21 above 17-20 deg alpha.
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The degree of stability of the aircraft shouldn't affect the fbw ops (except in its calculations) and the fbw should work even at low alpha. Its basically to maintain stable flight based on the hotas control. The higher degree of instability requires greater offsets from the aircraft controls but that means greater reaction as well.
fbw doesn't work only on the longitude axis but also lateral (pitch, roll and yaw). If a plane pitches (ie lateral axis) which ironically means high or low aoa, fbw kicks in. The fbw does cover elevators as well. The limits of the fbw are dependent on software configuration and the actual flight limits of the aircraft (ie control surface as you have mentioned) ie if the rudder can go x deg, ýou can't do x+1.
As to ARI, I tot this is to manage cornering force...
As to reason for mig crashes (the official response)...
http://pib.nic.in/archieve/lreleng/lyr2003/rmay2003/09052003/r0905200330.html"Majority of human error accidents are caused due to error of skill, error of judgement, poor airmanship, non-compliance of instructions, lack of situational awareness etc." - India defence minister...
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If aircraft is more unstable longitudinaly , it generates more pitch-up when rolling and more taileron power is required for pitch control.
There is airspeed limit below which aero surfaces cannot arrest adverse yaw durring rolling, say 150 kt for F-16. Bigger control surfaces are needed or thrust vector control below that speed.
I believe if IAF had only MiG-21 fighters, they would fall from the sky in much less extent.
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Most of the 110 pilots lost in these MiG-21 accidents were new pilots, which pointed out another problem. India has long put off buying jet trainers. New pilots go straight from propeller driven trainer aircraft, to high performance jets like the MiG-21.
MiG-21 is not wonder, it is just useful and it has some surprising abilities that are not exploited..
There is one aphorism: It does not matter how big dog is in the fight, but how big 'fight' is in the dog. Remember Vietnam, Afghanistan.. No hi-tech weapon is good against decisive defender.
I wonder is there any recent-fighter comparison paper like "Fighter Performance in Practice" book.
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Well, if the IAF had F-16s, they'd be having less maintenance and engine problems too. Overall, there would be a higher rate of readiness.
The thing about the F-16 is that its not designed for high-AoA type of turning fights. The Hornet has that capability, but not the F-16. The F-16 is pretty much a product of Col Boyd's energy manuever theory.
http://en.wikipedia.org/wiki/Energy-Maneuverability_theory
Its different from the type of ham-fisting, pull all you can to get the nose in front type of BFM that the Hornet is capable of. Instead, its more like a "graceful" ballerina that uses the momentum to retain its ability move around the sky into an offensive BFM position.
The thing is this, even if I had no limiters and threw all my energy into a pull into the target, I would bleed off so much airspeed that I would be in trouble if I don't kill him in that turn, or if he has an unseen wingman waiting for me to squander my energy like that. No energy = equal no manueverability. No way to get out of trouble.
However, if the aircraft is flown such that the energy is managed properly, the pilot will retain sufficient KE or PE to get out of trouble. So in its domain, the F-16 can out turn a MiG-21 easily, if the pilot keeps his corner airspeed and watch his energy state carefully. The MiG-21, without those high AoA turns, which also violates what it was designed for, will find itself lose its energy state really quickly, essentially sinking and losing the fight.
Having high AoA controllability may be good, but it comes at the expense of increased drag and as a result, loss of airspeed. If a hornet doesn't get his high-aspect kill on an F-16 as it tries to winch his nose across it, chances are, the F-16s gonna go around and turn the tables on him.
In short, high AoA turning capabilities is not necessarily a good thing. There will be trade offs as laws of physics still apply.
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I think maintaining F-16 in tech less advanced countries would be expensive. Especially if you need to call manufacturer for any repair. We see that now with French aircraft.
You are absolutely right. In guns only fight, in the Boyd's world, F-16 would be unbeatable. But, imagine, now with head cued AAMs, you just need to pass by furball and lose off AAMs to foes you see. As I remember, in US close combat simulations F-15 with AIM-9E vs MiG-21 with generation older AAMs kill ratio was ~ 20:1. When F-15 was armed with hypothetical head cued large off-boresight angle IC AAMs (like R-73 Shlem) kill ratio went to almost 1000:1.
Hornet differs from all previous planes in hi-alpha handling. But F-16 is also very nice. Spin free with crisp and easy handling to some 25 deg or 15 deg at 9g. Very effective ARI.
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Originally posted by Shotgun:
Well, if the IAF had F-16s, they'd be having less maintenance and engine problems too. Overall, there would be a higher rate of readiness.
The thing about the F-16 is that its not designed for high-AoA type of turning fights. The Hornet has that capability, but not the F-16. The F-16 is pretty much a product of Col Boyd's energy manuever theory.
http://en.wikipedia.org/wiki/Energy-Maneuverability_theory
Its different from the type of ham-fisting, pull all you can to get the nose in front type of BFM that the Hornet is capable of. Instead, its more like a "graceful" ballerina that uses the momentum to retain its ability move around the sky into an offensive BFM position.
The thing is this, even if I had no limiters and threw all my energy into a pull into the target, I would bleed off so much airspeed that I would be in trouble if I don't kill him in that turn, or if he has an unseen wingman waiting for me to squander my energy like that. No energy = equal no manueverability. No way to get out of trouble.
However, if the aircraft is flown such that the energy is managed properly, the pilot will retain sufficient KE or PE to get out of trouble. So in its domain, the F-16 can out turn a MiG-21 easily, if the pilot keeps his corner airspeed and watch his energy state carefully. The MiG-21, without those high AoA turns, which also violates what it was designed for, will find itself lose its energy state really quickly, essentially sinking and losing the fight.
Having high AoA controllability may be good, but it comes at the expense of increased drag and as a result, loss of airspeed. If a hornet doesn't get his high-aspect kill on an F-16 as it tries to winch his nose across it, chances are, the F-16s gonna go around and turn the tables on him.
In short, high AoA turning capabilities is not necessarily a good thing. There will be trade offs as laws of physics still apply.
Boyd's more evident with the F-15..... minimise drag/wing loading + increased twr isn't exactly rocket science to maintaining energy/airspeed in a turn.
Interesting to note that the fbw/cas could be switched off in early versions. Now everything is digitalised.
And as to mishanbgd's post of 23 Jul at 4pm, doesn't that depend (ceteris paribus which may include things like flaps position) on whether the cg is in front or behind the neutral point.
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It seems that nobody agrees on these a/c abilities, agencies, air forces...not even Israelis
Has anyone else had a look on it at eBay and would offer a comment ?
http://cgi.ebay.com/Fighter-Performance-in-Practice-F-4-Phantom-vs-MIG-21_W0QQitemZ290477872650QQcategoryZ378QQcmdZViewItemQQ_trksidZp4340.m263QQ_trkparmsZalgo%3DSIC%26its%3DI%252BC%26itu%3DMRU-267%252BUCI%252BIA%252BUA%252BFICS%252BUFI%252BDDSIC%26otn%3D10%26pmod%3D290463351336%26ps%3D63%26clkid%3D5551890937250223520
Thanks !!! -
Haha, I always thought the F-4 vs MiG-21 performance comparison was pointless. The F-4 was dubbed the Rhino for a reason. Its ugly and flies like a brick.
http://www.sci.fi/~fta/JohnBoyd.htm
Weasel, i think the both of you were talking about the same thing. If I don't get my "feel" of physics wrong, the CG is part of longitudinal stability in relation to where the wing is or where the lift is generated. Somewhere along there, the distance from thrust to CG as well as how much thrust is factored in as well. I'm no aerospace engineer, but thats my impression of it.
How much pitch from rolling about can be compensated from modern flight control systems by manipulating the elevators, ailerons, rudder and canards (if any). "Clean" pilot inputs help too.
I think its not that nobody agrees on abilities etc. Its that each aircraft has its own merits. I liked the F-16's acceleration, crisp turning and sustained turn rates. Its a relatively easy plane to fly, and a terrible one to land. The F-18 on the other hand has very good nose pointing ability, and is able to pull its nose inside the turn circle on the merge. It holds its altitude and airspeed well, though at lower airspeed regimes. Doesn't accelerate as fast the the -16, but handles low speeds well, thus lands well. I like that its very controllable at sub 200kts albeit with generous rudder inputs. The cockpit instrumentations are also more well organized too.
There lots of subtleties and nuances that makes comparing similar aircraft difficult. More importantly, different pilots will experience each differently as well. A guy whose more sensitive and graceful with his inputs might find an aircraft more agile or easy to handle than guy who hamfists the control surfaces. Very subjective stuff.
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Yeah but aircraft can be compared, how else one can differentiate between F-15 and F-4. Turns without/with loosing speed, acceleration/climb thruout the envelope, envelope itself, limits, even handling/aircraft response can be defined thru derivatives..
What about F-4 vs MiG-21 in these matters ?
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Yes they can, but you have to know what you're comparing. The MiG-21 might trump the F-4 in a dogfight, but try getting the -21 to haul the same load of iron that the Rhino does. Or even just bringing it out for a SEAD mission like what the F-4Gs did.
Yes, a MiG-21 can take on an F-15/16 in a low and slow fight. But can it take on an A-10 in a low and slow fight? Even a Cessna 172 can turn as sharp as hell, but whats the use of having no power?
The jet that can't fight low and slow, will fight high and fast. Theres really a lot more to BFM than I can describe here.
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It is question whether 21 is better than F-4 in turns...
Of course it can not be compared to A-10 or Cessnas because 21 has high drag at slow speeds and in the same time it has SEP 0 at Mach 0.5 higher speeds than many most modern fighters.. Also it can try to take F-15/16 when low and slow, but very few AForces is trained to do so.
You are right for BFM, it is getting more and more importance...as recent US wars shows, but need for dogfight will stay.
Here's one graph, below, depicting roll rate at hi alpha vs longitudinal stability...