Fighter Performance in Practice: F-4 Phantom vs MiG-21


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Book Reviews -
If you want to know who really has the better performance F-4 or MiG-21, who is more maneuverable or faster, you can find it only in this book based on official aircraft manuals.

Who is faster or more agile operationaly and who is on paper can be seen only in this book.

I'm working like performance test engineer for Airbus, after work for Lockheed Martin.
I congratulate you for your book. It's good and specially there are not another book like this in the market.
What I read is very good, with precision, you have focused in a good point of view of analysis. I would like to be so good as you to compare 2 aircraft !!! )
It's really a good job.
I hope 2012. will be the year when you will offer a new and excellent publication about aircraft !! )

Whiskey Golf

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Fighter Performance in Practice: F-4 Phantom vs MiG-21

  1. 1. Fig. 5.5 RANGE constant Mach/altitude cruise, tanks dropped 180 Fuel carried % of aircraft max 170 internal 160 150 140 130 120 110 100 90 MiG-21bis at 10-11 km 80 MiG-21bis at 5 km MiG-21bis at 0.5 km 70 MiG-21bis at 5 km with 60 warload of 20% basic weight MiG-21bis at 0.5 km with warload 20 % basic weight 50 F-4E at 11-12 km 40 0 20 40 60 80 100 120 140 160 180 200 220 240 Range % of MiG-21bis max range on internal fuelEndurance is the time an aircraft can remain in the air. It is not particularlyaltitude dependent because minimum drag is about the same at all altitudes,at the same indicated airspeed. Specific fuel consumption worsens withMach and improves with altitude so product of (L/D)max and (1 / tsfc) issimilar at all altitudes.56
  2. 2. The F-4E achieves (L/D)max at Cl=0.36 (total wetted area 194 m²,equivalent skin friction coefficient 0.00508).Maximum endurance of MiG-21bis at 500 m altitude is at lift coefficient of0.3 / Mach 0.4 / CAS 480 km/h (L/D = 8, CdO = 0.019, Oswald spanefficiency factor e = 0.7) and maximum range at Cl = 0.14 / Mach 0.58. Asin theory, at higher altitudes endurance (where drag is lowest) is at similarCAS and at 11 km altitude it is equal to Mach 0.81. 57
  3. 3. endurance minutes MiG-21 F clean true airspeed km/hendurance minutes MiG-21 F with two AAMs true airspeed km/h Fig. 5.7 MiG-21F endurance depending on cruising altitude (H meters) and true airspeed (operator’s diagram)58
  4. 4. range km MiG-21 F with 490 litre external fuel tank true airspeed Fig. 5.8 MiG-21F range depending on cruising altitude km/h (H meters) and true airspeed (operator’s diagram)Of course, best range Mach also increases with altitude, converges withendurance speed and it sooner bangs into the ‘sound barrier’ so best rangeMach stays at Mach 0,84 at 11000 m where it almost coincides with bestendurance speed. When aircraft is trimmed to best range cruise at optimumangle of attack or lift coefficient (Cl=0,3 at tropopause for MiG), as the fuelis being depleted aircraft will fly itself to new optimum higher altitude. Airtraffic control does not permit commercial planes to fly that continuouslyvariable cruise profile except in 2000 feet steps. Alternative for airliners isto cruise at a constant altitude that is optimum for some mid cruise weight. 59
  5. 5. Fig. 5.9 F-4E max range & endurance speed combat weight 18450 kg 20000 altitude meters 15000 10000 F-4E slatted 5000 F-4 w ithout afterburner m ax endurance m ax range 0 0.2 0.7 1.2 1.7 MachHeavily laden with warload after take off at max weight, the best cruisingaltitude is 5000-6000 m and in case of one engine operating (F-4), the bestrange is achieved at less than 1000 m altitude.60
  6. 6. max range constant Mach/altitude cruise, max endurance payload standard reserve with 3 with 3 external with full on on external with full tanks, internal internal internal tanks, internal tanks dropped fuel and 3 fuel fuel tanks fuel when empty external tanks droppedMiG- 1450 kg 150 kg 1250 km 1900 km 1.5 2.25 (25% of (2% of21bis M 0.84 Mach 0.83 /11 km /10 km hours hours basic basic weight) weight) 5500 kg 1100 kg 1600 km 2950 km 1.9 3.5 (38% of (8% ofF-4E Mach 0.87 Mach 0.86 /39 Kft /36 Kft hours hours basic basic weight) weight)Payload with full fuel is given as a percentage of an aircraft’s basic weightbecause a two times bigger aircraft carries two times the weight with aboutthe same effort and range percentage. 61
  7. 7. 6. Turn performanceAs said, maneuverability is the ability to quickly change velocity vector,in other words, direction of flight and magnitude of aircraft speed.Most missiles, having cruciform configuration (two pairs of wings and tailsor without wings at all) can equally maneuver in any plane, without anybank angle. Since airplanes have wings in one plane, they can makesignificant turns only in one plane. Lateral turns with fuselage lift ispossible but with not more than about 1.5 (g) load factor because of limitedrudder (and aileron) control power and tail structural strength to trim thatsideforce. Some of the most maneuverable missiles depend just on fuselagelift to turn at 30 g at high speed. At very high angle of attack body lift issignificant as is vertical component of thrust which augments lift. bank angle 81,0° º aircr pla aft g ne of sy (nor mme ma try lift l load fac 6,5 * to vertical weig r) 6 ,5 ht component of lift = (-) weight horizontal componenet of lift = (-) centrifugal force of turn plane of turn radial g √ (n² -1) = 6,42 Fig. 6.1 Sample steady horizontal turn62
  8. 8. During a steady horizontal coordinated turn, the lift is inclined to produce ahorizontal component of force to equal the centrifugal force of the turn.Vertical component of lift must equal the weight of the aircraft.Coordinated means without sideslip.load factor (normal acceleration g) = lift / weightload factor = 1 / cosine bank angle (radial acceleration (g) = [√ (load factor² - 1)] * gSteady, coordinated turn requires certain relationship between load factorand bank angle, as seen in the equation. For example, bank angle of 80ºrequires load factor of 5.76 for steady turn (bank angle of 89º requires57.3 g). Of course, perfectly horizontal turn is irrelevant in combat. Onlymaximum and sustained load factors at any bank angle counts.Turn performance is defined by  structural,  control surface actuator power,  lift (aerodynamic) and  thrust limits. 63
  9. 9. Fig. 6.2 F-4E max available load factor at H = 3 km combat weight 18450 kg 13 12 structural 11 load 10 lift factor, thrust & "g" 9 drag 8 7 6 5 4 3 2 1 0 0,5 1 1,5 MachStructure strength limit defines maneuvering load factor that will notdamage primary structure or shorten aircraft’s service life. The utmostimportance in aircraft design is to keep structure weight to minimum, just tofulfill requirements.A short look at aircraft structure material characteristics should helpunderstand structural limit of the aircraft.64
  10. 10. 65
  11. 11. Figure 6.3 shows the mechanical behavior of a material under a load anddefines the strength. The stress is the ratio of the applied load divided bythe cross sectional area of the material. The strain is the non dimensionalelongation of the material to the applied tensile load. The portion of thestress-strain curve that is linear is known as the elastic range. The slopeof the stress-strain curve in this elastic range is called the Modulus ofElasticity and denotes the stiffness of the material – ability to resistdeformation within the elastic range.Important material properties are strength (ultimate stress) and stiffness,both divided by material density or simply strength/weight and E/weightratio, besides impact resistance (toughness) – the area under the stress-strain curve, property where graphite composites are weak. Ultimate Yield Modulus Temperature tensile tensile of Density RelativeMaterial limit ºC*** strength, strength Elasticity kg/dm³** cost Hi alt Mach bar* bar 10³ barAluminum 125 ºC 5200 4400 730 2.80 1alloy 7075 2.1 MachSteel 540 ºC 18200 15400 2100 7.75 15Cr-Mo-V 3.7 MachTitanium 410 ºC 11200 10150 1120 4.45 10Ti-6Al-4V 3.3 MachGraphite 125 ºC 6200 6200 1170 2.60 15Epoxy 2.1 Mach* kilo psi (pressure) = 70 bar (bar ≈ atmospheric pressure = 10^5 Pa (N/m²))** lb/in³ (density) = 27.68 kg/dm³*** ºF (temperature) = ºC * 1.8 + 32Materials should be safe if stressed below their yield strength and notsubjected to impact loading, but the fact is that failure may still occur if theload is applied, removed and repeated many times. This type of failure iscalled fatigue. This cyclic loading is an every day occurrence for an aircraftas it is parked, takes off, maneuvers and then lands. Fatigue is one of themost important causes of material failure. If aircraft is designed for 3000hours service life and limit load factor 8 with load factor spectrum 8 g oncein hundred flight hours, 6 g on every flight hour and 4 g ten times per hourand if in actual conditions aircraft is subjected to an 8 g load on every flighthour, decreased service life or premature structural failure can be expected.66
  12. 12. Aircraft structure should experience no objectionable permanentdeformation when subjected to limit load factor (say 8). Above limit loadfactor, the yield stress may be exceeded and permanent deformation canresult. Metals used in aircraft structures are ductile – they do not breakimmediately when deformations becomes plastic. Famous duraluminumalloy (2024) has ultimate tensile strength to yield strength ratio 1.5(4410/2940 bar). It means that 50 % more load (say 12 g) is needed forfailure in relation to one needed to start permanent deformation. Aircraftwould be capable to withstand a load factor which is 1.5 times the designlimit load. That became the usual safety factor. Now when many structuralmaterials have ultimate to yield strength ratio ≤ 1.2 and when aircraft haveelectronic load factor limiters, safety factor might be less (e.g. limit loadfactor 9, ultimate 11), structure weight lighter or service life multiplied. limit structural load factor “g” at combat weight * MiG-21bis F-4E combat weight 7550 kg 18450 kg subsonic limit 7,8 8 fuselage AIM-7s has (< M 0.8/0.72) a/c limit 80 % of g rolling maneuver limit not recognized without rolling 2 IC missile 8 6.5 carriage limit limit at Mach 0.9 6.5 6.8 supersonic limit** 6.5 6* Load factor at design weight (7100/17000 kg) is 8.5. Allowed load factorat other weights is in proportion to design weight.** Because of bigger static margin at supersonic speeds, both wing and tailmust generate more lift (bigger bending moment) for the same resultingload factor. Tail lift is negative. 67
  13. 13. In many aircraft, flight controls despite being hydraulically powered, athigh dynamic pressures cannot move aerodynamic surfaces enough to turnthe aircraft to structural or even thrust ‘g’ limit. If elevator hinge is far fromelevator aerodynamic centre, hinge moment can be bigger than hydraulicactuator power and that could limit the available load factor.Aerodynamic limit is defined by the ability of aircraft to generate lift (theproduct of wing area and maximum lift coefficient in respect to aircraftweight). Turns reaching the aerodynamic limit are called instantaneous.Dominator of aerodynamic turning performance is the wing level stallspeed. When F-4E flies at stall α, at 265 km/h (143 kt) lift will be equal toweight of 18450 kg i.e. aircraft will fly at 1 g.Remember that:Lift = ½ (true airspeed)² * air density * wing area * lift coefficient CLBasic wing area is used as reference area because it is most important liftgenerator and the easiest area to calculate, although most of aircraftplanform surface produces lift.68
  14. 14. where:q – dynamic pressure = ρ*V²/2 CDo – zero lift drag coefficientD – drag AR – wing aspect ratioT – thrust ¶ = 3.1416…W – weight = m*g e – Oswald span efficiency factorρ – air density V – true airspeedS – wing areaIt is often said that MiG-21 loses energy in turn. MiG-21F has bettersustained maneuverability than most fighters of its generation. If it turns tothe stall speed of 220 km/h, of course that it will lose energy faster than F-4C at say 270 km/h, because load factor would be much higher. If MiGholds it’s allowed angle of attack (28 units), that will give similarinstantaneous turns as F-4 but with only slight buffet as opposed to a heavyone in unslatted F-4. Lower aspect ratio of MiG wing does not give thewhole picture of sustained turns.There are various official performance comparisons of F-4 and MiG-21,both western and eastern which all differ. US claims that MiG is better andeast side draws graphs that F-4 is better. The reason behind most claims ismyth or politics.80
  15. 15. With the advent of all-aspect missiles turns are usually maximum(instantaneous) with thrust and drag (SEP at high g) determining whetherspeed will be preserved.If one aircraft has better sustained turn capability that does not mean that itwill dissipate less speed during maximum turns. A high thrust to weightfighter may, during e.g. 8 g turn lose energy much faster than jet trainer,although fighter may sustain e.g. 6 g and trainer 5 g. 81
  16. 16. Diagrams which present longitudinal acceleration vs. load factor and speedhelp visualizing what happens with speed in turns. But when aircraft makes,for example 360º max turn neither instantaneous nor sustained turn plotstell end speed or total turn time. Computers must be used for a preciseanalysis.Without aerodynamic force, moment and stability derivatives, it is difficultto compare other fighter measures of merit such as control surfaceseffectiveness at high angle of attack or departure resistance ataileron/rudder application.82
  17. 17. Book Reviews - The Aeronautical Journal (May 2010) :Naucna KMD, Belgrade, Serbia. 2009.(Contact/order e-mail: Illustrated. €25 including postage/packing.ISBN 978-86-6021-017-5.This book, written by two aeronautical engineers from the former Yugoslavia, sets out to provide acomparison of the performance of the F4 Phantom II and the MIG 21. Early chapters are devoted todescriptions of both aircraft together with relevant weights, dimensions and configurations.Data on the F-4C, F-4E, F-4J, MiG-21bis, MiG-21-MF and MiG-21-F-13 and their General Electric andTumansky engines are provided for reference throughout the volume. The sources of data are notstated but simply described as ‘official and already available to the public’.This is followed by chapters devoted to the comparison of the aircrafts’ flight envelopes andperformance during take-off, acceleration, climb, cruise, descent, landing and maneuvering. Eachelement includes the statement, but generally not the derivation, of the basic well-establishedperformance equations and many diagrams comparing the performances of the two aircraft types.In essence the book leads the reader through the processes normally carried out by engineers workingon competitor aircraft analysis for marketing purposes and tactical evaluations by air arms. It does notcover the more difficult areas such as the determination of aerodynamic characteristics andengine installation effects, for example, which are essential to accurate comparisons without access tomanufacturers’ configuration and performance data.In comparing the two aircraft types, the authors present many flight performance charts and flightenvelopes and offer a number of reasons for the flight limitations included in them. For example, thelimitation of the maximum speed of the MiG-21 to Mach 2⋅05 above an altitude of 11,000m isattributed to reduced directional stability rather than a lack of engine thrust.Particular emphasis is given to instantaneous and sustained turning performance culminatingin the authors’ view as to how a MiG-21 could be observed to perform a split-S manoeuvre below3,000ft a.g.l during combat when published data stated that 6,750ft were required this.The final chapter records the authors’ conclusions as to how the two aircraft compare and provides anumber of photographs that illustrate their general features.The editorial style of the book could be improved for western readers. Commas are used instead ofdecimal points, figures are not generally referenced in the text, there is no single list of symbols andequations are presented in a format foreign to UK practice.In conclusion, the book gives an interesting insight into the quantitative comparison offighter aircraft and the interpretation of the significance of the differences presented inthe performance curves and flight limitation boundaries. It makes informative andentertaining reading for anyone interested in the assessment of the merits ofcompeting fighter aircraft.Dick Poole CEng, MRAeSIm working like performance test engineer for Airbus, after work for Lockheed Martin.I congratulate you for your book. Its good and specially there are not another book like this in themarket.What I read is very good, with precision, you have focused in a good point of view of analysis. I wouldlike to be so good as you to compare 2 aircraft !!! )Its really a good job.I hope 2012. will be the year when you will offer a new and excellent publication about aircraft !! )Whiskey GolfE-books: Aircraft MiG-21 UM (US) Pilots Manual (in English),Manual on the Techniques of Piloting and Military Use of the MiG-21F-13and Capt. Boyd: Aerial Attack Study are sent as a gift.