Design characteristics of canard & non canard fighters

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  1. Manticore
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    During the wing design process, eighteen parameters must be determined. They are as follows:
    1. Wing reference (or planform) area (SW or Sref or S)
    2. Number of the wings
    3. Vertical position relative to the fuselage (high, mid, or low wing)
    4. Horizontal position relative to the fuselage
    5. Cross section (or airfoil)
    6. Aspect ratio (AR)
    7. Taper ratio ()
    8. Tip chord (Ct)
    9. Root chord (Cr)
    10. Mean Aerodynamic Chord (MAC or C)
    11. Span (b)
    12. Twist angle (or washout) (t)
    13. Sweep angle ()
    14. Dihedral angle ()
    15. Incidence (iw) (or setting angle, set)
    16. High lifting devices such as flap
    17. Aileron
    18. Other wing accessories

    http://faculty.dwc.edu/sadraey/Chapter 5. Wing Design.pdf








    In aerodynamics, the lift-to-drag ratio, or L/D ratio, is the amount of lift generated by a wing or vehicle, divided by the drag it creates by moving through the air. A higher or more favorable L/D ratio is typically one of the major goals in aircraft design; since a particular aircraft's required lift is set by its weight, delivering that lift with lower drag leads directly to better fuel economy, climb performance, and glide ratio.
    The term is calculated for any particular airspeed by measuring the lift generated, then dividing by the drag at that speed. These vary with speed, so the results are typically plotted on a 2D graph. In almost all cases the graph forms a U-shape, due to the two main components of drag.
    Lift-to-drag ratios are usually found using a wind tunnel

    [​IMG][​IMG][​IMG][​IMG][​IMG][​IMG]
    MACH Aviation Magazine - på webben
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    In Europe talk was going on, with the German TKF and British EAP as starting points, for a fourth generation fighter, which in due course of time would lead to “Eurofighter 2000/Typhoon”. In France, Dassault was committed to Mirage 2000 and 4000 and was in the very early stage of Rafale-discussions. In Israel, plans for the IAI Lavi, quite similar to Gripen in fact, had set in motion, but later fell prey to the cancellation axe.

    Most of these projects had one feature in common, namely the delta canard layout.

    At Saab, then in the concept phase of a new fighter, this line of thinking was also the case, which is not surprising. As pioneers of this very aerodynamic shape in the sixties, and with some ten years of Swedish Air Force (RSAF) experience with AJ 37 Viggen at that time, this was quite natural. However, it did not mean that other configurations were neglected.

    The Americans obviously intended to stay with the aft-tailed layout, as F-14, F-15, F-16, F-17/18 and F-20 could witness. It had also been reported in the press (AW&ST) that American reconnaissance satellites had caught glimpses of new advanced Soviet fighters on the tarmac of an air base: Ram-J and Ram-L they were called in the CIA jargon and subsequently they became well known as the Su-27 and MiG-29.

    The choice of configuration, canard or tail, was far from obvious, initially. A substantial body of knowledge existed on the delta canard layout, gained from Viggen experience of course, but that was not entirely favourable for such a solution.

    The close coupled delta canard configuration’s primary feature, its stable vortex flow up to very high angles of attack, meaning high maximum lift coefficient, had lately been realized by the Americans, instead using large strakes as forward wing root extensions together with conventional tail arrangement, as found on the F-16 and F-17/18.

    The flow physics are essentially the same. The front surface, being a delta or highly swept strake, gives off a stable detached leading edge vortex that interferes with the vortex flow from the main wing and which mutually reinforces the vortex strength of each other, and therefore burst at a much higher AOA than a lone delta wing would do. This holds true for movements in the pitch plane, but generally not for the other axis, where such flow stability is more difficult to obtain, because of asymmetrical vortex bursting, so modern fighter aircraft generally “stall” first in the lateral and directional axis.


    Still the canard layout offered much, if only the weak spots could be cured. First of all a movable canard surface, higher aspect ratio wing and good cross sectional area-ruling and high slenderness ratio had to be incorporated.

    Canard layout features

    Engine air intake location is a topic of heated debate among aircraft designers. There are usually several options at the early design stage and pros and cons are easy to list for various arrangements. Many air inlet types were contemplated and some underwent both wind tunnel investigations and thorough studies at the drawing boards.

    A fixed pitot type air intake, conventionally placed on both sides of the front fuselage, was till an easy choice, because of its simplicity and favourable cost. But everything considered, this type of intake offered most versatility. The pivots for the canards found a natural bed in this structural area and the aerodynamic carry-over loads from the canards onto the upper sides of the fuselage, acting as lift contributors, are substantial. An additional pylon location on the underside of the right intake was another bonus. This is primarily a station for various sensor pods of light weight. The left bottom side is partly occupied by the internal cannon (only for the single seater).

    The aerodynamic advantages derived from the close coupled canard configuration, foremost its good vortex flow stability up to high angles of attack (AOA), that can be translated into a very high instantaneous turn rate, and which in conjunction with pivoting canards that are automatically trimmed to give optimal lift-to-drag (L/D) ratios for all cg positions, Mach and AOA, were not technically feasible for the Viggen generation of fighters. Only full span slotted flaps on the canards were present on the Viggen, for further improvement of its already excellent Short Take Off and Landing (STOL) characteristics).

    One decisive feature in obtaining good, straight pitching moment characteristics from the type of plan-form was found to lie in the slightly aft sweep of the canard pivot. This was derived through an intensive wind tunnel effort that consisted of testing a formidable number of systematically differing plan-form shapes, both for the main wing and the front surfaces.

    In order to successfully meet the often contradictory performance requirements stipulated by the RSAF, a good balance had to be struck between the important wing geometrical parameters, such as sweep angle, thickness, aspect ratio, twist, camber and area.

    For example, a demand for high supersonic speed capability and/or low transonic buffeting levels during heavy g-loading will be eased by high wing sweep angle, but then range and manoeuvrability will be degraded accordingly. And a thin wing, good for high speed, might be a blow to rolling performance at high dynamic pressures.

    The plan-form that eventually emerged was a good balance between zero-lift, wave, and induced drag and showing a maximum L/D of 9, some 25 percent and 60 percent higher than the previous Saab fighters, the Viggen and Draken respectively. Leading edge sweep angle, actually three different angles for the main wing, is higher on the canard surface to ensure stable flow, as the up-wash there can increase the local AOA substantially.

    High angle of attack

    The topic of air combat at high angles of attack has gained much interest since the seventies, when it made reappearance, perhaps helped by the not-so-reliable air-to-air missiles of that era. Air combat seemed to end up like a classic dog-fight, with decreasing speed and subsequent high AOA. Many early supersonic fighters had a tendency to stall out of the sky when entering this region of the flight envelope, to the dismay of its pilots, as recovery was often difficult, if not impossible.

    The Viggen aircraft had gone through a program of spin testing in the late seventies, that verified the rather benign high AOA characteristics of the canard layout, a fact contrary to what was known on some contemporary aft-tailed foreign fighters. So this was also an argument favouring the Gripen canard layout. Early investigations in vertical spin tunnels and tests in different rotary rigs and subsequent simulations, also pointed to acceptable spin behaviour.

    A very substantial flight test program that recently was concluded for both the single as well as the two seat Gripen versions has also fully verified the excellent recovery capability, both in manual test mode and in the normal automatic mode. There exists a requirement in the Gripen project specification for a spin recovery capability, and if this can not be shown, a spin prevention system must not allow a departure to happen. Flight testing has also verified that the EFCS matches this additional demand. Double insurance might be said to exist.

    As remarked previously, the only externally visible “fix” to the airframe are a pair of small strakes behind the canard surfaces. This type of “flow augmentation system”, often serving the purpose of directional and lateral stability enhancement at high AOA, is not uncommon on fighters; suffice to mention the Eurofighter and the Mirage 2000.

    A spectacular Gripen aircraft departure and ensuing crash at a public air display in 1993, was the cause of modifications and revisions to the EFCS control laws in order to cure certain ailments there, one example being pilot induced oscillations (PIO). Among the changes was one pertaining to canard deflection angles at high AOA in combat mode, to increase margins for the trailing edges surfaces to run into a geometrical limitation, and thus possible longitudinal stability loss and eventual departure.

    Yaw and roll stability at high AOA is strongly dependent on canard incidence, and slightly above the MLL boundary, stability drops off rapidly, becoming unstable earlier for canard deflections in the region of minus 10 to minus 25 degrees. Obviously, this incidence range was avoided. Instead small positive values of canard deflection were used in the control law’s schedules. This was beneficial, as it meant that the trailing edge surfaces were positive, that is rear end down, thus giving more positive lift. But now it was realized that in some conditions, a physical, geometrical limitation to the elevons might be encountered, which momentarily caused loss of stability.

    A low speed wind tunnel program had immediately been instigated, and for the first time the large low speed wind tunnel model’s electrical engines, that normally were used only to provide discrete incidence changes to facilitate operations, where now deflected continually during a run.

    A bunch of “fixing devices” was tried, and success was instant with several of these. The earlier rapid drop of stability was now completely over-bridged, and the plots showed good, continuous behaviour, indicating at dramatic improvement of the flow characteristics in that a delay of separation occurred to slightly higher alphas. A new canard trim schedule could now be introduced that eliminated the risk of the control surfaces being limited in its travel.

    The flow phenomenon, commonly called “dynamic lift”, perhaps more aptly called aerodynamic hysteresis, has been the object of intense interest in some countries for decades, not the least has this been the case in Russia. Its best public known, practical application may well be the awesome aerobatic display performed by test pilot V.G. Pugachev and his “cobra” turn in a Sukhoi Su-27.

    When these hysteresis effects manifested themselves during high AOA/spin tests in the specially modified second Gripen prototype, they came as no surprise. Years prior, low speed wind tunnel tests with pitching motion of the model had already demonstrated the presence of marked unsteady flow effects, hysteresis, in the post stall alpha regime. Normal force hysteresis was most evident, but all the other components, except side force, had their share.

    In the high AOA and spin tests that has taken place since 1996 and recently concluded successfully, the normal tactic was to initiate the tests with a near vertical climb with speed dropping off to near zero and a rapid increase of AOA up to extreme angles, and the aircraft could then be “parked” at 70 to 80 degrees of alpha. When giving adverse aileron input there, a flat spin with up to a maximum of 90 degrees per second of yaw rotation started and could then be stopped by pro aileron input. Recovery followed, whenever commanded.

    A very recent test performed in a specially high AOA equipped twin seat Gripen version has recorded a noticeable increase in maximum normal force coefficient over the static data base value, jumping up to 3.2, nearly doubling the static number 1.8.

    Wind tunnel and flight test data correspond reasonably well, but it must still be said that modelling these effects are difficult, so normally in high AOA simulations they are neglected. In the future, their inclusion will hopefully improve simulations of more complex behaviour, like departure entrance.


    Aerodynamic summary

    The salient points in the Gripen aerodynamics are:
    Digital fly-by-wire control system and relaxed, negative static stability in pitch (cg far aft) have made the disposition of the delta canard layout, internal as well as external, much easier, whereby:

    Optimal cros sectional area ruling, thus wave drag reduction, has been fully realized.

    Main landing gear stowed in fuselage, therefore external stores close to cg, small cg-shift that improves flying qualities.

    Wing far forward, enabling long tail cone, meaning base drag and local area distribution favourable, and efficient air brake location on tail cone with small transients when deployed.

    The direct fall-out of relaxed static stability are:

    · Higher trimmed lift.
    · Reduced lift dependent drag.
    · Reduced supersonic trim drag.

    Delta canard’s inherent good aerodynamics are:

    · Stable detached leading edge vortex flow, high maximum lift coefficient.
    · Positive trim lift on all lifting surfaces.
    · Floating canard offers stable aircraft if EFCS fails.
    · Good field performance (take off and landing), enhanced by special aerodynamic breaking mode.

    · Battle damage tolerance good, “overlapping” control surfaces.
    · Potential for future adaptations, like steep approach, fuselage aiming.
    · Low buffeting levels made even better with leading edge flaps.

    Spin recovery known to be acceptable for close coupled delta canard (not necessarily so for a long coupled canard configuration):

    · Proven spin recovery capability for complete cg and AOR range.
    · Nor risk of being trapped in a superstall, control authority exists.


    A delta wing as on the Gripen offers a light but strong and stiff structure in conjunction with the use of CFC on the outside skins and main spars, even when the relative thickness of the wing is small.

    The question of stiffness is vital, as the single-spar aluminium winged Viggen had shown years before. Not initially meeting the severe requirements on roll rate at high dynamic pressures, more hydraulic cylinders for the moving of the inner trailing edge elevons had been added. And the wings broke.

    Early into the Gripen project, the industry discussed the trouble that McDonnell Douglas faced in complying with US Navy roll rate demands for the F/A-18. Aileron reversal had occurred during testing of roll rate at high speed/low altitude. The rather high aspect ratio wing lacked enough stiffness and had to be strengthened, adding weight.

    At Saab, an intense cooperative work between the aerodynamicists and the strength department was instituted. Flight mechanics simulations had established the required minimum values for the flex-to-rigid ratio of the rolling-moment-due-to-aileron-deflection-derivative, for meeting the very stringent supersonic roll rate demands. The British Aerospace designed CFC wing was fully up to expectations, as flight tests revealed early, allowing a high rate of roll at the critical Mach/altitude/load factor values stipulated.


    A delta wing also offers a fairly large volume for fuel and has in general good static and dynamic aero-servo-elastic stability properties, even with large external stores on the wing weapons pylons.

    Careful area-ruling was adhered to during the design phase, and constant improvement suggestions flowed from the aerodynamicists to the airframe design engineers. A particular case of point was the front fuselage that was of circular shape initially, but had to yield to a complicated super-elliptical geometry. Significant gains in wave drag and also high AOA behaviour, were among the pay-offs, but the manufacturing department expressed concern over escalated costs.

    Airframe summary
    Delta wing, multi spar, carbon fibre composite, offering large fuel volume and low weight.

    Strong and stiff wing with good aeroelastic properties. High flex-to-rigid ratios for aerodynamic control derivatives.

    Fuselage mounted main landing gear means good external stores capability and small cg-shift, thus easier to meet Flying Qalities requirements.

    Optimal cross sectional area distribution and mid winged blended body with low drag.

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  2. Manticore
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    http://www.defence.pk/forums/milita...ts-designs-index-2nd-post-28.html#post1590554
    http://www.defence.pk/forums/milita...ts-designs-index-2nd-post-26.html#post1562188


    CANARDS

    Modern high-speed aircraft, especially military, are very often equipped with single or compound delta wings. When such aircraft operate at high angles-of-attack, the major portion of the lift is sustained by streamwise vortices generated at the leading edges of the wing. This vortex-dominated flow field can breakdown, leading not only to loss of lift but also to adverse interactions with other airframe components such as the fin or horizontal tail

    The performance of a canard design depends strongly on the amount of lift that the canard must carry. This is set by stability and trim requirements.
    An analysis of the effects of canard shape, position, and deflection on the aerodynamic characteristics of two general research models having leading edge sweep angles of 25 and 50 degrees is presented. The analysis summarizes findings of three experimental transonic wind-tunnel programs and one supersonic wind-tunnel program conducted at this Center between 1970 and 1974. The analysis is based on four canard geometries varying in planform from a 60-degree delta to a 25-degree swept wing, high aspect ratio canard. The canards were tested at several positions and deflected from -10 to +10 degrees. In addition, configurations consisting of a horizontal tail and a canard with horizontal tails are analyzed. Results of the analysis indicate that the canard is effective in increasing lift and decreasing drag at Mach numbers from subsonic to high transonic speeds by delaying wing separation. The effectiveness of the canard is, however, decreased with increasing Mach number. At supersonic speeds the canard has little or no favorable effects on lift or drag. It is further shown that the horizontal tail is a superior trimming device than the close- coupled canard at low-to-moderate angles of attack and that a configuration consisting of canard, wing, and horizontal tail is superior in performance, to either canard or horizontal tail at high angles of attack.

    [​IMG]


    The Canards in the Lavi have also dihedral but also they are far too close to the wings in fact over them-- The Eurofighter`s are not as close to the wings as those on the Lavi, the position has to do with drag/lift ratio, the best combination is high aspect canards low aspect wings check the Eurofighter has also strakes -- chinese J-10 also the canards are not too far from the wing, however are not so close as those in the Lavi and Rafale, both the Eurofighter and J-10 have the least drag canard delta wing configuration specially good for a fast aircraft -- the Viggen has low aspect wings and canards, these low aspect canards and wing are best configured for high lift



    long-coupled canard and close-coupled canards= The two approaches to canard fighter design are more different than the names imply.
    In a close-coupled design, the developers were trying to optimize the aerodynamic interaction between the wing and canard, with the objective of improving aircraft lift-to-drag and high angle-of-attack performance. For the Lavi , this means that these airplanes can fly further on less fuel than their conventional counterparts.
    In a long-coupled design like the Eurofighter Typhoon or X-31, the developers were trying to minimize the canard-wing interactions, and simplify their aerodynamic design process. They still gain the benefits of improved aerodynamic control at high angles of attack, but they do not see an appreciable improvement in the airplane's lift to drag ratio.
    You can tell the difference between the two approaches to canard fighter design, based on how close the canard is positioned to the airplane's wing (measured in mean chord lengths), and also by whether the canard is positioned above or below the wing. On the Lavi, J-10, Kfir, Gripen and Rafale, the canard is positioned just ahead of, and above the wing, to maximize the aerodynamic interaction between the two. On the Typhoon and X-31, the tips of the canard are canted downwards, to ensure that the canard tip vortices are swept below the wing.


    Novi Avion
    [​IMG]







    What does mean LERX ?

    It is an English abbreviation of Leading Edge Root Extension who wants literally to say : Extension of the root of the leading edges.
    Word corresponding in French is: APEX.


    Where are they on the plane ?

    LERX are the natural prolongations of the wings towards the nose of the plane. In some kind, they make the joint between wings and fuselage.

    The F-18 has LERX of very great dimensions so much so that his manufacturer, Northrop (absorbed since by Boeing), had baptized "Cobra " the preliminary projetct due to the fact that this airplane seen on top resembled the reptile with these two surfaces behind the head.

    All aerodynamic surface forming an angle higher than 30˚ with the axis of relative wind passing around it stalls, because the air passing on the upper face of this part changes from a laminar flow to a turbulent flow. The turbulet airflow create a fall of lift power. The wing takes down and the
    plane falls!

    This phenomenon is even more delicate at low speed due to the fact that the speed of the air moving on the top surface of the wing decreases
    with the proper speed of the plane. Lift obtained by the wings being directly in relation with the speed of the airflow of the upper surface of
    the wings, when the plane slows down, the lift power decreases.

    It is possible to counter this phenomenon by 3 main ways:

    - To increase speed obviously, but it's not what one seeks at the time of the landing for example...
    - To increase the angle which the wing and the airflow are forming, this one being limited to 30˚ as we saw above.
    - To increase camber of the wing. It is what we do when the plane extends the flaps and the mobile leading edges at the time
    of landing or takeoff.

    Militarily speaking, it is interesting for a fighter, involved in a dogfight for example, to decrease its speed as much as possible in order to let
    a faster airplane go ahead. By this manoeuvre, the fastest plane of both go ahead of its adversary and then allows the slower airplane
    stay behind him in position of shooting.

    It is vital for the fighters to fly fast to be able to reach a zone of intervention as soon as possible, but it is critical too to be able to fly as slow
    as possible while keeping the plane control in order to be able to ensure itself to remain behind the adversary and therefore in offensive
    position.

    In that way, the LERX provide a considerable supplement of lift at raised angles of attack, i.e. when the angle formed by the wings and the
    relative wind direction due to the displacement of the plane increases.
    Indeed, the LERX generate powerful swirls of air or Vortex which increase the air velocity on the roots of wings and around tails. This makes
    it possible to keep the control of the plane at angles superiors of 30˚. These Vortices when are intenses are particularly visible,
    materialized by the condensation of the moisture of air.

    LERX also allow the correct air feeding of the engines during those flights at high angles.
    Lerx

    http://dc185.***********/img/eWV16wOM/0.9003554746114637/check1.JPGhttp://dc185.***********/img/MfX6oRPR/0.44802734121847665/check2.jpghttp://dc185.***********/img/tAXxr7qS/0.45726369516279997/check3.JPG[​IMG][​IMG]
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  3. Manticore
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    [​IMG][​IMG]
    CFD visualization of vortices created by leading edge extensions on the F-18
    [​IMG]
    Vortex bursting observed during smoke flow visualization tests on NASA's F-18 HARV
    Aerospaceweb.org | Ask Us - F-18 Leading Edge Extension Fences


    [​IMG][​IMG]


    Condensation vortex flows along an F/A-18's LERX
    Leading edge root extensions (LERX) are small fillets, typically roughly triangular in shape, running forward from the leading edge of the wing root to a point along the fuselage. These are often called simply leading edge extensions (LEX), although they are not the only kind. To avoid ambiguity, this article uses the term LERX.

    On a modern fighter aircraft they provide usable airflow over the wing at high angles of attack, so delaying the stall and consequent loss of lift. In cruising flight the effect of the LERX is minimal. However at high angles of attack, as often encountered in a dog fight, the LERX generates a high-speed vortex that attaches to the top of the wing. The vortex action maintains a smooth airflow over the wing surface well past the normal stall point at which the airflow would otherwise break up, thus sustaining lift at very high angles.

    LERX were first used on the Northrop F-5 "Freedom fighter" which flew in 1959,[1] and have since become commonplace on many combat aircraft. The F/A-18 Hornet has especially large examples, as does the Sukhoi Su-27. The Su-27 LERX help to make some advanced maneuvers possible, such as the Pugachev's Cobra, the Cobra Turn and the Kulbit.
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    Manticore SENIOR MODERATOR

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    [​IMG]
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    http://www.mig-21.de/english/technicaldataversions.htm
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    Two very different area wings can provide the same lift by flying at different angles of attack (and hence different lift coefficients). This is a big reason why aerodynamicists tend to work in coefficients rather than absolute forces.
    Since weight is usually an input, the lift is constant. So more area means less lift coefficient (same lift), and lower drag.
    Sweep, span, and area are all totally independent.
    Wingspan
    [​IMG]

    Wing loading
    In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing.[1] The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly, the landing and take-off speeds will be higher. The high wing loading also decreases maneuverability. The same constraints apply to birds and bats.

    Wing loading is a useful measure of the general maneuvering performance of an aircraft. Wings generate lift owing to the motion of air over the wing surface. Larger wings move more air, so an aircraft with a large wing area relative to its mass (i.e., low wing loading) will have more lift at any given speed. Therefore, an aircraft with lower wing loading will be able to take-off and land at a lower speed (or be able to take off with a greater load). It will also be able to turn faster.


    Fuselage lift
    The F-15E Strike Eagle has a large relatively lightly loaded wing

    A blended wing-fuselage design such as that found on the F-16 Fighting Falcon or MiG-29 Fulcrum helps to reduce wing loading; in such a design the fuselage generates aerodynamic lift, thus improving wing loading while maintaining high performance.
    [edit] Variable-sweep wing

    Aircraft like the F-14 Tomcat and the Panavia Tornado employ variable-sweep wings. As their wing area varies in flight so does the wing loading (although this is not the only benefit). In the forward position takeoff and landing performance is greatly improved.[11]
    [edit] Fowler flaps

    The use of Fowler flaps increases the wing area, decreasing the wing loading which allows slower landing approach speeds.



    http://dc306.***********/img/s8-jwhsT/0.6235182629976099/gra6.PNGhttp://dc317.***********/img/gyg_jEpA/wing_configurations.PNG

    [​IMG]

    Aerodynamic Characteristics

    Perfection in airframe performance can give the pilot battle-winning edge, providing that airframe is part of the Eurofighter Typhoon Weapon System.

    Eurofighter Typhoon has a foreplane/delta configuration which is, by nature, aerodynamically unstable.

    The instability of the aircraft is derived from the position of a theoretical “pressure point” on the longitudinal axis of the aircraft. This is calculated from the contribution to lift from each of the aircraft components (the wings, the canards, fuselage etc). If the pressure point is in front of the centre of gravity on the longitudinal axis, the aircraft is aerodynamically unstable and it is impossible for a human to control it.

    With the Eurofighter Typhoon, in subsonic flight the pressure point lies in front of the centre of gravity, therefore making the aircraft aerodynamically unstable, and is why Eurofighter Typhoon has such a complex Flight Control System – computers react quicker than a pilot.

    When Eurofighter Typhoon crosses into supersonic flight, the pressure point moves behind the centre of gravity, giving a stable aircraft.

    The advantages of an intentionally unstable design over that of a stable arrangement include greater agility – particularly at subsonic speeds - reduced drag, and an overall increase in lift (also enhancing STOL performance).
    http://www.eurofighter.com/capabilities/performance/aerodynamic-characteristics.html


    http://books.google.com.pk/books?id...sign and centre of gravity of fighter&f=false

    Fundamentals of Airplane Flight Mechanics
    *By David G. Hull






    detailed diagrams / comparative pics of different fighter programmes are posted here
    http://www.defence.pk/forums/air-warfare/75408-combat-aircraft-projects-designs-index-2nd-post.html
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  6. Manticore
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    I wasnt planning to start a thread... was just surfing for info on lift-to-drag ratio --- ended up starting a thread on it...from lift-to-drag ratio of different fighters , this thread is growing out to be a designs & aerodynamics thread... maybe will change title

    trying to make an informative thread... will appreciate input
    :cheers:
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    Wing loading
    In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing.[1] The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly, the landing and take-off speeds will be higher. The high wing loading also decreases maneuverability. The same constraints apply to winged biological organisms


    Aspect ratio (wing)
    In aerodynamics, the aspect ratio of a wing is essentially the ratio of its length to its breadth (chord). A high aspect ratio indicates long, narrow wings, whereas a low aspect ratio indicates short, stubby wings ----Maneuverability: a high aspect-ratio wing will have a lower roll rate than one of low aspect ratio, because in a high-aspect-ratio wing, an equal amount of wing movement due to aileron deflection (at the aileron) will result in less rolling action on the fuselage due to the greater length between the aileron and the fuselage. A higher aspect ratio wing will also have a higher moment of inertia to overcome. Due to the lower roll rates, high aspect ratio wings are usually not used on fighter aircraft.
    Geometry Definitions


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  8. Fulcrum15
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    Wing Dihedral

    Large aircraft such as An-225 and C-5 Galaxy (high wing aircraft) have anhedral to reduce maneuverability, and to stabilize the aircraft. While Harrier has anhedral to increase maneuverability .

    For low wing aircraft, such as commercial jets, dihedral is used to increase stability of the aircraft. As seen in the A380 image below.

    [​IMG]

    So, in military aircraft zero dihedral or negative dihedral (anhedral) is used, to increase maneuverability, while positive dihedral is used in large aircraft to decrease maneuverability.
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  9. sandy_3126
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    sandy_3126 PDF THINK TANK: ANALYST

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    F-15B Active- With Carnards and Thrust vectoring

    [​IMG]

    In 1993 Dryden Flight Research Center acquired the first F-15B (two-seat) aircraft built, following it’s career with McDonnell Douglas and the U.S. Air Force. By that time the aircraft had already undergone considerable modification, including the addition of canards and a pair of “pitch-yaw balance beam nozzles” (PYBBN) for thrust vectoring. The exhaust nozzles deflected as much as 20 degrees in a 360 degree arc.
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  10. Manticore
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    Manticore SENIOR MODERATOR

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    credits to the great crobato
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    Pak47 FULL MEMBER

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    Amazing information.. Once again Thanks Ab! :-)
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  12. Manticore
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    Manticore SENIOR MODERATOR

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    http://www.defence.pk/forums/chines...rcraft-updates-discussions-2.html#post1824495
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  13. Manticore
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    [​IMG][​IMG]



    vortex will generate lift , high AoA --

    twin tails might give stability [directional control?]...Having two vertical stabilizers allow each of them to be smaller than a single one, would decrease height in hangers-->reduction of the load at the root

    The LERX were designed in to keep airflow attached at high alpha .Strakes wereadded to the LERX to stabilise the vortex

    I read somewhere that twin tails reduced supersonic drag and saved structural weight -- at subsonic Mach the two fins interfere with each other, which reduces their effectiveness as lifting surfaces--At a supersonic speed, the 2 surfaces begin to work independently --twin tail fins helps the airplane benefit from this vortex and retain yaw control in high AoA--- if one engine fails , 2 vertical tails would be better in controlling the fighter --shedding vortices from the wing root , vortices being shed by the strakes are used to energise airflow over twin fins thus retaining control

    my understanding [layman] is high vortex--high aoa but high drag ----> this drag can be reduced by twin tails

    Drag reduction, combine the tasks of the elevators and rudder,increase surface area without increasing aspect ratio are other things that ive read regarding Vtails like on f117


    the two vertical stabilizers on the F-22 Raptor angled sort of like a V-Tail as opposed to being completely vertical 90 degrees-- i guess due to stealth issue aswell as stability
    [​IMG][​IMG]
    [​IMG]

    NASA SR-71 Blackbird Challenges and Lessons Learned 2009
    NASA's Lessons Learned from the SR-71 program. page 36 RCS reduction





    [​IMG]
    F-15 Silent Eagle with canted vertical tails?

    [​IMG][​IMG][​IMG]
    again i am a layman and might be completely wrong .. sir pshamim would be able to correct my assumptions








    ---------
    wiki
    Types of vertical stabilizers

    Conventional tail
    The conventional tail of an Airbus A380, with the vertical stabiliser exactly vertical
    The vertical stabilizer is mounted exactly vertically, and the horizontal stabilizer is directly mounted to the empennage (the rear fuselage). This is the most common vertical stabilizer configuration.
    T-tail
    A T-tail has the horizontal stabilizer mounted at the top of the vertical stabilizer. It is commonly seen on rear-engine aircraft, such as the Bombardier CRJ200, the Boeing 727 and Douglas DC-9, as well as the Silver Arrow small airplane, and most high performance gliders.

    T-tails are often incorporated on configurations with fuselage mounted engines to keep the horizontal stabilizer away from the engine exhaust plume.
    T-tail aircraft are more susceptible to pitch-up at high angles of attack. This pitch-up results from a reduction in the horizontal stabilizer's lifting capability as it passes through the wake of the wing at moderate angles of attack. This can also result in a deep stall condition.
    T-tails present structural challenges since loads on the horizontal stabilizer must be transmitted through the vertical tail.


    Cruciform tail
    The cruciform tail is arranged like a cross, the most common configuration has the horizontal stabilizer intersecting the vertical tail somewhere near the middle. The PBY Catalina uses this configuration. The "push-pull" twin engined Dornier Do 335 World War II German fighter used a cruciform tail consisting of four separate surfaces, arranged in dorsal, ventral, and both horizontal locations, to form its cruciform tail, just forward of the rear propeller.
    Falconjets from Dassault always have cruciform tail.



    Multiple stabilizers

    Main article: Twin tail


    The twin tail of a Chrislea Super Ace, built in 1948
    Rather than a single vertical stabilizer, a twin tail has two. These are vertically arranged, and intersect or are mounted to the ends of the horizontal stabilizer. The Beechcraft Model 18 and many modern military aircraft such as the American F-14, F-15, and F/A-18 use this configuration. The F/A-18, F-22 Raptor, and F-35 Lightning II have tailfins that are canted outward, to the point that they have some authority as horizontal control surfaces; both aircraft are designed to deflect their rudders inward during takeoff to increase pitching moment. A twin tail may be either H-tail, twin fin/rudder construction attached to a single fuselage such as North American B-25 Mitchell or Avro Lancaster, or twin boom tail, the rear airframe consisting of two separate fuselages each sporting one single fin/rudder, such as Lockheed P-38 Lightning or C-119 Boxcar.


    Triple tail

    A variation on the twin tail, it has three vertical stabilizers. An example of this configuration is the Lockheed Constellation. On the Constellation it was done to give the airplane maximum vertical stabilizer area, but keep the overall height low enough so that it could fit into maintenance hangars.


    V-tail
    Main article: V-tail
    A V-tail has no distinct vertical or horizontal stabilizers. Rather, they are merged into control surfaces known as ruddervators which control both pitch and yaw. The arrangement looks like the letter V, and is also known as a butterfly tail. The Beechcraft Bonanza Model 35 uses this configuration, as does the F-117 Nighthawk, and many of Richard Schreder's HP series of homebuilt gliders.

    Winglet
    Winglets served double duty on Burt Rutan's rear wing forward canard pusher configuration VariEze and Long-EZ, acting as both a wingtip device and a vertical stabilizer. Several other derivatives of these and other similar aircraft use this design element.
  14. Manticore
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    founds some info-- will make some deductions in next post
    http://www.defence.pk/forums/air-wa...ts-designs-index-2nd-post-30.html#post1615644


  15. Manticore
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    Manticore SENIOR MODERATOR

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    some pointers that i am collecting


    Low aspect delta wing and High aspect canard configuration obtains the less drag and good lift

    Stealth aircraft with canards have low aspect canards at the same level of the wing

    LERXes are low aspect delta wings (forebody strake) with a high aspect main wing,with medium to low swept wings

    LREX provides a sustained Lift during High AoA maneuvers which otherwise would result in stall

    LERXs & Canards, both basicly both generate vortices and add lift ahead of the center of gravity , in the case of the LERX this is due to wing fuselage blending that starts at the apex of the LERX

    There are two distinct LERX designs, one has an inward curve like the F-16, and the other has an outward cobra like curve, like the F-18.*

    planes that have a ground attack role is better to have a higher wing loading to get a smoother flight in low altitudes.*



    low wing loading is a necessity for planes performing at higher altitudes.*






    Leading edge root extensions (LERX) are also sometimes referred to as wing strakes.F-5,F-16,F-18
    The F-18 has a very low swept wing which gives excellent lift at low speeds and requires less pitch , AoA to achieve lift.The best wing for low speed is not highly swept, most combat is in that region e.g f-18


    Fifth gen fighters t traded off performance over stealth as canards & wing are at same level

    Gripen stealth demostrator the Canards are above wing level, to improve performance even at the expense of RCS
    The LEVCON is a LEADING EDGE VORTICE CONTROL system so it does all what a canard does but can be planformed well without any drag or downwash. LEVCON *is a LERX with a slat

    Tight Turns =LIFT + THRUST

    [​IMG]
    http://www.acsol.net/~nmasters/vortex-lift/delta.html





    Any idea about the JF 17 wingloading?. been looking for it for 2 years... a ground attack role is better to have a higher wing loading -
    low wing loading is for performing at higher altitudes---multirole aircraft has to find a proper balance... would be interesting to know jft's



    I was under the wrong impression that the jft design is actually a 2nd gen design , which was slightly updated , but having severe aerodynamic deficienies ...... this aspect had started to plague the thoughts of meny pdf members aswell

    i was concentrating on the design evolution or lets say different schools of thought to stabilize the wing at high alpha , vortex generation/ fuselage lift---e.g double delta, lerx, levcon, canard fixed/movable



    Slats/Leading edge Flaps increase the coefficient of lift-increase the maximum AOA during low speed

    LERXes improve AoA handling

    based on the design of wings the jft aoa seems better than f16 and closer to the f18 [prominent lerx/strakes---> upto 50% increase in max lift + low/moderate swept wing --> spin resistance] -- which is famous for its aoa


    LERXs & Canards, both basicly both generate vortices and add lift ahead of the center of gravity

    Low aspect delta wing and High aspect canard configuration obtains the less drag and good lift-- thus used mostly in such designs , primarily for flight performance


    The tailplane serves three purposes: equilibrium, stability and control.

    F-16 / f14 use ventral fins to improve lateral stability whereas in F-15/ F-18 dorsal and vertical fins are enough



    long-coupled canard
    Eurofighter Typhoon or X-31, the developers were trying to minimize the canard-wing interactions,



    close-coupled canards
    Lavi ,
    improving aircraft lift-to-drag and high angle-of-attack performance.


    chinese J-10 also the canards are not too far from the wing, however are not so close as those in the Lavi and Rafale, both the Eurofighter and J-10 have the least drag canard delta wing configuration specially good for a fast aircraft




    On the Typhoon and X-31, the tips of the canard are canted downwards, to ensure that the canard tip vortices are swept below the wing.

    On the Lavi, J-10, Kfir, Gripen and Rafale, the canard is positioned just ahead of, and above the wing, to maximize the aerodynamic interaction between the two.




    ---
    I am in the process of reading the effects of canards and 3d nozzels .. are these an undisputed evolution or another school of thought to address the same issues -- keeping in mind u.s didnt go e canards even after experimenting