Rafale vs F-16: Aerodynamics compared. Introduction: A memory of a unique event. I first saw the Viper in 1975, competing vs Mirage F-1E M53 and Saab JAS 37 Viggen at Le Bourget (where I took my BIA successfully the same year) I could see that it was way superior to anything else in terms of maneuverability.
YF-16 second Prototype 01568 as seen at the Paris Airshow in 1975.http://www.codeonemagazine.com/archives/2007/articles/jan_07/cockpits/cockpit-views/yf16.html
We can't really write anything on the subject of F-16 without mentioning its test pilot Neil Anderson and his fabulous displays.http://www.flightglobal.com/articles/20 ... -dies.html
Thank for the dreams Neil!
A step forward: Paris Airshow 1975.
At the time I felt a little disappointed about the Mirage F1 loosing the competition but thought of F-16 as a stroke of genius, I still think it was today...
Even decades later, the Viper's still look as good as on the first days. Good designs never age. Rafale is that kind of aircraft; its aerodynamics are superior to anything I have seen so far, so Dassault-Aviation have the best platform they could wish for.
We owe Dassault designers and engineers a very loud
MERCI because it took some to pull that one of the hat, here is why...
A few pictures (Many of them courtesy of Kovy) to feed the subject of aerodynamics (we can now compare F-16 to Rafale, it is a very interesting match) and stimulate reflection...
The two aircraft are fundamentally different in their respective aerodynamic arrangements, but they still manage to have a lot in common:
Static instability, FBW/FCS, mid-fuselage mounted wing configuration, a large blended area, a single vertical fin and.....
Vortex lift.
In this view, the F-16 mid-fuselage mounted wing configuration and large blended area are visible. 
Rafale C01 showing mid-fuselage mounted wing configuration and large blended area similar to that of F-16.
These design features are known to reduce wave drag but also RCS while increasing available internal volume for fuel. Requirements and development. 1971, USAF submits LWF Request For Proposal to the industrials:
In the US, a researcher called Linwood Mc Kinney was interested in the effects of vortex on lift as used by the SAAB JAS37 Viggen and Mirage IIIS, his work demonstrated the possibility to extend the effects of integrated canards to large Leading Edge eXtention surfaces (LEX).
Comparison of vortex generation between SAAB JAS 37 and F-16.
This drawing is much simplified, in reality, canard vortexes are more numerous, the tip vortexes tends to expend straight from their sources until they merge with that of the wings, while the root vortexes follows the pressures zones along the airframe up to the fin.http://www.mach-flyg.com/utg80/80jas_uc.html
A good study of a USAF F-16, the laminar airflow and straight wingtip trails doesn't suggest a high AoA. At the same time, Northrop already had some experience in the field with the F-5 family and together with Langley, was developing designs which ultimately lead to the YF-17 Cobra.
http://oea.larc.nasa.gov/PAIS/Partners/FA_18.html The main difference here is that a delta wing produces vortex lift naturally, as opposed to a more conventional design like that of F-16, a delta doesn't need Leading Edge Extensions.
While looking for a high degree of maneuvrability, the US never took the final step of combining the delta versions of the F-16 with canard surfaces, favoring the use of Leading Edge Extension. Vortex Lift.
ONERA.
Delta at 0 AoA and high AoA 
ONERA.
Vortex from above and Combat aircraft model vortex lift.
http://www.onera.fr/conferences/mesures ... /index.php
Vortex Lift is created by a phenomena of suction, the main vortex being sucked from the intrados to the extrados, contouring the leading edge and staying traped in the zone of lower pressure above the wing.
http://ntrs.nasa.gov/search.jsp?R=80034 ... 4294964171
The F-22 is yet another aircraft making good use of vortex lift, here an intersting view showing its singular design features. Note the sharp, higly swept LEX
Vortexes increases in intensity with the sharpness and sweep angle of the leading edge, but also with angle of attack up to a break-down point;
LEX being most efficient when strongly swept back with a sharp leading edge, as seen in the F-16, F-22 and Rafale. 
With AoA increasing comes an induced increase in drag, the solution being to keep the AoA to the minimum required while maintaining a high lift coefficient using other (additional) solution for added lift. The addition of integrated canard surfaces to the delta wing, resulting in natural dynamic instability, and use of full lift control, allows for the partial resolve of the excess drag issue; the control surfaces can now be used with minimum trim drag settings, while lift coefficient remains high.
Required specification vs Aerodynamic design goals: The Viper have a fairly conventional (but advanced) arrangement, with the elevators situated behind the main wings, the design resulting from the 1972 USAF Light Weight Fighter required specification and from studies made by John Boyle and Pierre Sprey on the subject of Energy management.
http://www.aviation-history.com/airmen/boyd.htmhttp://www.codeonemagazine.com/archives/1997/articles/jul_97/july2a_97.html These requirements were:
. Turning performances at Mach 1.2 (demanding low wave drag).
. Turning performances at Mach 0.90 (requiring minimal wave drag).
. Maximum lift at Mach 0.8/40.000 ft (requiring optimum drag-lift coefficient or induced drag).
To achieve the requiered performances, Lockheed-Martin designers chosed the following solutions:
. Single engine with ventraly mounted normal shock inlet.
. A 40* leading edge swept wing.
. Aspect ratio of 3.0.
. Leading edge and trailing edge flaps for variable camber.
. Large Leading Edge Extention.
. Blended-wing body with vertical booms suporting the elevators and airbrakes.
. Single fin.
http://oea.larc.nasa.gov/PAIS/Partners/F_16.html This resulted in very good subsonic and good supersonic turn rates, YF-16 won the LWF because it achieved all USAF requirements, showing better transient performances than its competitor, the Northrop YF-17 Cobra.
Simulated F-16 drag polar. Source: Air Force Flight Test Center Edward Air Force Base: The F-16 have a flight envelop matching that imposed by the LWF requirements, making of it a high transonic/mid-supersonic optimized design with turning performances only equaled at the time by the Mirage 2000.
Turning performances of the F-16A compared to that of a Mig-21 Bis. NASA/DRYDEN were always heavily involved in the F-16 programe, conducting flight-tests on behalf of both manufacturers competing for the LWF and helping solving a few problems.
Researcher William A. Newsom, Jr. with the free-flight model of the YF-16 used in tests in the Full-Scale Tunnel.http://oea.larc.nasa.gov/PAIS/Partners/F_16.html France flair for the element Air: Rafale is an advanced evolutive integrated canard delta solution designed for a higher Critical Mach than the Viper.
http://www.adl.gatech.edu/classes/ae3021/ae3021_f06_6.pdf AdA ACT (Avion de Combat Tactique) and Marine Nationale ACM (Avion de Combat Marine) requierement started to emerge at Dassault-Aviation end of 1980.
ACX was to be the technology demonstrator for both AdA and the proposed MN programes but Marine Nationale wasn't really interested until 1988, having planned to acquier F-18s in replacement of its F-8 FNs.
http://www.flightglobal.com/pdfarchive/%20...%2002068.html Born from the ACX programe, Rafale A was primarily designed with high maneuverability in mind, at least four out of six ACX specific requirements were for Air Combat, including against helicopters.
At the 1986 Farnborough Airshow, Rafale A, flown by Guy Mitaux-Maurouard, routinely demonstrated angle of attack of 45* and a sustained turn rate of 24*/sec at slow speeds.
Guy Mitaux-Maurouard with the Rafale A. Note the main wings positioned higher on the airframe where it would have been more difficult to add the LEX seen in the series aircraft.
YF-16 and YF-17 flying together, the differences between them and Rafale are interesting to note, the Cobra especially, as its descendents are the unconditional US champions of high AoAs. In the Air-to-ground role, ACX basic requirement was to be able to carry 3.5 ton of armament 300-350 nm from base, including advanced stand-off weapons.
The aircraft was also required to be able to take-off within 500 m at Maximum TOW, with two F-404, Rafale A take-off roll time in reheat was about 9 seconds.
The RB-199 was turned down in favour of the GE F404, while the future M88 was qualified of "Dogfight engine" by the then (1983) Dassault-Aviation President Benno Claude Valliere.
After studies, weighting required specs versus design goals, designers felt that the achieved Mirage 2000 turning performances were situated too high in its flight envelop.
Experience had shown that combat was more likely to take place at lower Mach, 1.6 to 1.8 Maximum, instead of M 2.0 and M 2.2.
The delta planform saw an evolution on its design and a reduction of its leading edge sweep angle from the Mirage 2000 58* to the series Rafale 48*, aspect ratio was increased from 2.0 to 2.2.
One fundamental difference with F-16 is the use of leading edge SLATS instead of flaps.
Leading edge flaps proved too dragy for the 40* swept wing of the YF-16, their drag penalty being lower when combined with a delta wing, this solution offered the best lift/drag ratio compromise and was retained.
Both aircrafts make use of variable camber but the progress in the case of Rafale comes from the full use of variable lift.
Drag/lift ratio is optimized at all time responding to pilot inputs (gas, controls, aircraft attitude and speed etc) instead of a few configuration pre-sets.
The final design was also the result of numerous configuration studies: 265 from 1979 up to the final Rafale A prototype design in 1983.
More than a few were conceived specifically to achieve hyper-maneuverability, some of which resembled the HIMAT project were tested at the wind tunnel of Saint Cyr.
A comparative of some wind tunnel models studied in the frame of the ACX programe (right), with the configuration used in the DRYDEN HIMAT programe (left).
All were designed to achieve a certain degree of hyper-maneuverability.http://oea.larc.nasa.gov/PAIS/Partners/X_31.html Rafale was therefore designed to achieve a much wider board of performances than F-16 with a significantly higher Critical Mach and better low-speed/High AoA characteristics.
The demands for low speed capabilities came from the AdA 70's requirements for shorter take-off and landing distances (Mirage g variable sweep and Mirage F-1 etc).
That of Marine Nationale for Carrier landing were later added, when plans to acquire F-18 in replacement of F-8 FN Crusaders were all but dropped, and as for all Dassault-Aviation designs, the evolutive philosophy was applied.
Consequently, the original Rafale A design also saw a few changes:
. The original ACX cranked delta was changed for a straight delta.
. The wing was lowered in view of a higher degree of integration of the ensemble wing/canard surfaces to the front fuselage and inlets.
. The canard surfaces saw their size increased (from the Rafale A 5% of the wing surface).
. Small, sharp LEX could be then added, running from the inlet leading edge.
. The nose was redesigned to offer better visibility forward at higher AoA for Carrier operations.
. The control surfaces were reduced from six to only two elevons and two elevators, two of the actuators and their fairing were also eliminated.
. The airbrakes were replaced by a combination of canards-upward and elevons-downward breaking solution (involving an fair amount of AoA).
A beautiful view: Rafale A in its prime. The design afiliation to the ACX conceipt are obvious.
A similar view of Rafale A and C01 make a comparison easier. Controls and FCS: F-16 had some unique characteristics; for the first time designers were able of using the elevator surface as an additional lifting surface.
As an instable aircraft its elevators have to counter a natural nose-up moment at subsonic speed and doesn't have to be deflected to induce pitch-up.
This also meant that the elevator could be designed with a profile similar to that of the main wing, lifting positively instead of negatively as is the case for a stable configuration, this is obviously reversed by the shift of cg in supersonic.
F-16 innovative lifting elevators allows for a reduction of wing size and weight, as well as control response time compared to non-instable aircraft. This have for effect of adding to the total amount of available lift, which in turn allows for a reduction of the total main lifting surface, reducing structural weight and wing drag.
This also reduced response time, as the amount of elevator deflection needed for pitch-up is far lower than in the case of a stable configuration, the pitch-up moment having just to be relaxed with minimal surface movement.
So the two aircrafts have really different design goals and achieve their high level of maneuverability using different aerodynamic arrangements, resulting in different sets of performances and flight envelops.
Apart for the specific landing configuration at 16* AoA where the canard surfaces have a fixed incidence of 30*, Rafale control surfaces are programmed to be used with minimum drag in mind.
Rafale doesn't use its canard surfaces for direct lift at 1 g like F-16 uses its elevators, most of the time these surfaces are used for acquiring/controlling an attitude in pitch.
The automatic launch control sequences of the Rafale M are particularly illustrative of the full use of lift control.http://www.dailymotion.com/video/x73l84_rafale-marine_creationHere is an excellent video on the subject by Marine Nationale. Observe the positionment of the control surfaces before, during and after catapult firing. After acquiring the desired attitude (g or AoA) lift control then kicks-in to participate to the drag reduction and changes the overall configuration.
The canard are then used in conjunction with the trailing edge surfaces (Elevons and Ailerons) and leading edge slats, to obtain the desired amount of lift and minimize drag accordingly.
Visual clues for the enthusiats: To illustrate the results of these solutions we can use a few good photographs.
This one is particularly striking: Reason is that paint ware is showing exactly the way the canard root vortex is spreading outward and feeding the airflow above the wing in the region of the elevons.
Compare to this Belgian F-16 and the pair of main vortexes generated by the large LEX. The presence of small sized LEX on Rafale increases the effects of the canards while limiting their drag coefficient which is higher than that of the canards at high AoA, as their incidence cannot be adjusted to reduce drag...
Optimization of the chosen design goals and solutions: Aircrafts performances are the results of compromised solutions.
These are dictated by advances made in aerodynamics and materials technologies, in the case of F-16, it is obvious that those retained for its design reflects this perfectly.
For this part of the comparative, we should start by the Rafale to give examples of advances in the field of aerodynamics, illustrating the benefits of evolutionary designs.
Boundary layer control or the advantages of evolutionary design: The Rafale inlet arrangement allows for the boundary layer from the frontal area of the fuselage to be more controlled, and contribute to energizing the airflow over the wing and around the fins at much higher AoA than is possible with the F-16.
The now famous V-shaped inlet of Rafale have many hidden secrets to the novice, and they are typical of the design philosophy maintained by Dassault designers over the years.
This trend seems to have started with the Mirage 4000 which already had some degree of V shaping in its inlet design, compared to the straight-lined inlet diffusers seen on previous Mirages.
The few degrees of V shaping in the inlet leading edge area of the Mirage 4000 were apparently meant to reduce supersonic wave drag. In conjunction with slightly larger nose cone than the area situated directly behind it, it did work as a "coke bottle" or area shape, reducing the airflow pressure and altering the efficiency of the "Souris" near Mach 2.0".
Dassault engineers were then able to determine the optimum front fuselage/inlet design for best boundary layer control at the Mach they were looking to optimize their design.
Dassault had the advantage of practical experience with the formula delta canard, this Atar 9K-50 Mirage III NG was a fixed-canard, instable FBW/CCV equiped modified Mirage V. Note the crancked delta wing typical of the solutions favoured at the time. http://www.aviastar.org/air/france/dassault_mirage-3ng.php ON the Rafale, this solution was pushed further as to make best use of the airflow by separating the boundary layer around the wing roots, this way it was also possible to further increase the dynamic effect of the canards above the wings.
Boundary layer control optimized. Note how at 30* incidence, the canard surface deflects the ambient airflow directly on the extrados. At point A, the airflow slows (compression), part of it enters the secondary inlet behind the diffuser, to aliment both the avionic bay (when not in flight) and the engine cooling channels.
It then is channeled to accelerate (expension) at point B, just behind the canard trailing edge, and E and acts on the upper fuselage as if strakes were used (without the additional drag and radar return) as is the case with the Mirage 2000 and Typhoon designs.
A primary vortex is created at the LEX root (C) and another at the juntion with the wing (D), turning it into a two cornets delta.
Note the sharpness of the LEX leading edge, meant to augment its effects, one solution which on F-16 was suggested by Langley to the F-16 team in order to increase the strength of the LEX vortexes.
http://oea.larc.nasa.gov/PAIS/Partners/F_16.html This have for effect of energizing the boundary layer and sustain the airflow around the fin at high AoA when the rear fuselage becomes shielded from ambient air and the fin looses efficiency...
As seen on the Rafale, this phenomenon increases in strength with speed and is particularly noticeable in supersonic regime where expensive shockwaves are created.
In conjunction with the canards and small LEX, this helps maintaining a higher level of control on the YAW axis but also PITCH control (canard and LEX root vortexes) and ROLL control (Canard tip vortexes) at AoA where other design features are already out of efficiency...
While it was demonstrated by Langley that the LEX did play a role in increasing directional stability at high angles of attack, the boundary layer on the F-16 airframe is not controlled to the same extend.
It is possible that an inlet and diffuser arrangement similar to that of Rafale would have avoided the problems encountered by the YF-16 during flight-testing, when it was realized that it was necessary to limit the AoA in order to avoid a near-unrecoverable nose-up attitude.
http://www.codeonemagazine.com/archives/1986/articles/july_86/deep_stalls/index.html
Paint ware in an aerodynamically hot area.
Where both canard root vortexes and expending boundary layer coming from the front fuselage combines to energize the airflow around the fuselage/wing junction, the same feature, (without the canards) is replicated on the underside. Such design features explains the capability of Rafale to stay fully controlable at extreme AoAs, the picture above is also showing the effects of the boundary layer channels coming from behind the inlet diffusers.
By comparison, F-16 is AoA limited because of the risks of super stall, at high AoA the elevator "parks" themselves in the low pressure area behind the wing and become irresponsive, making it impossible to recover a normal (horizontal) attitude...
http://oea.larc.nasa.gov/PAIS/Partners/F_16.html This of course is due to the overall arrangement, the conventional design lending itself for such a problem, which is also seen on different configurations such as some T-tail.
But the issue on F-16 MIGHT have been sorted with a higher level of boundary layer control, in view of the LWF competition, the F-16 design team might just have ran out of time...
The Viper's elevators have a hard time to get out of a high nose-up attitude, through the area of unsteady airflow behind the trainling edge of the wing, should the pilot go over 25* AoA; this picture show us why.
The Viper's inlet arrangement limits the efficiency of the airflow recovered from the diffuser area, as it is channeled under the wing.
On the Viper, the airflow exhausting from under the inlet diffuser does little for the area above the wing where it would be more efficient, energizing the upper airframe boundary layer at high angle of attack, and perhaps helping sorting out the issue encountered with the elevators deep stall. Note that such a solution was adopted on the F/A-18, and that this sort of "transfer" of boundary layer was already used in the YF-17 which had a few narrow openings at its LEX roots ahead of the diffusers.
This solution increased the speed of the boundary layer above the wing but created extra drag, it was not retained in the design of F-18 but made a curious return with the Super Hornet.
YF-17 had the particularity to have LEX with longitudinal opening allowing for a certain amount of airflow transfer from the intrados to the extrados at high AoA. While it proved most efficient in increasing lift, this solution was also cause of excessive drag at zero degree angle of attack and was dropped in the final F-18 design in an effort to retain a sufficient range which on the Hornet, was marginal.
Conclusion: When more becomes less. Langley's FIX to F-16 Deep Stall issue.
The relative lack of available (energized) airflow behind the wing at high angle of attack was responsible for what turned out to be the F-16 only Achilles heal; its AoA limits.
http://oea.larc.nasa.gov/PAIS/Partners/F_16.html
Following Langley extensive flight-testing and analysis, the F-16 elevator was modified with a 30% increases in area in 1981 (5% more than suggested). Introduced from the Block 15, this modification allowed for more pith authority and prevented (together with FCS AoA limiter) the out-of control attitudes early F-16 had encountered.
F-16 would probably be capable of pulling more g if this wasn't generally associated with an increase in AoA, in particular at low speeds or during violent maneuvers with high g onset where inertia makes precise pitch control more difficult to achieve.
So the Viper is, de-facto, limited by less developed aerodynamics from design stage, although already quiet advanced, they show limitations which are unknown from the more aerodynamicaly evolved Rafale design.
The solutions which won YF-16 the LWF conpetion, based on the chase for low drag, also meant that the aircraft became AoA limited at a later stage, it was a compromise at the time which perhaps could have been avoided with further conceiptual studies.
The newer, more developed aerodynamic solutions used on Rafale explains why it can reach extreme AoA in fully controlled flight, the F/A-18 and F-16 pilots can testify for themselves of this demonstrated capability...
Note the compression area under the wing at the level of ailerons/wing junction, the air is slowing down, becomes denser and hotter, this like vortexes creates vapor...
Under somce conditions, vortexes stay quasy invisible to the nacked eye. 
More examples of vortex generation, on the picture above, the high number of g can be guessed at the way the airflow becomes more unsteady.
The Viper can get "all dirty" as well, just pull a little on this stick! F-16 Flight Control System is known for giving priority to g load vs AoA as the aircraft looses speed quiet fast as AoA increases, and as a normal AoA limit of 25* due to the risks of super stall inherited from its conventional tail configuration.
http://www.codeonemagazine.com/archives/1994/articles/jul_94/jula_94.html
Rafale generally shows a very clean and steady airflow during high AoA maneuvers, more laminary than most, mainly due to the good level of boundary layer control around the airframe, results of its design optimization. When it starts got get unsteady, you can be sure that AoA and g beggins to get high...
No doubts aerodynamic have also progressed since F-16 was conceived, the good thing about this is that what we see here, is just the SIMPLE version of it, there is a lot more to it, in the field of Drag coefficient due to Critical Mach and the associated drag polars for example...
Recommended:
http://www.youtube.com/watch?v=aIwNMmIP20c A very impressive display by this Dutch F-16, its pilot equals the prestation of Cpt Ruet in that he also pulls a -3 g turn...
Congrats!
Some useful links...
http://www.aviastar.org/air/france/a_dassault.htmlhttp://www.codeonemagazine.com/archives/1986/articles/jan_86/f16_control/index.htmlhttp://www.codeonemagazine.com/archives/1986/articles/apr_86/f16_aero/index.htmlhttp://www.dfrc.nasa.gov/gallery/photo/F-16AFTI/index.htmllhttp://www.dailymotion.com/video/x9xhmj_preparation-du-pilote-pour-la-demo_techhttp://www.codeonemagazine.com/photos/gallery/f16_gallery/index.html
