I can't tell if this is sarcasm or a new kind of cope.
Tailless flying wing aircraft has been attracting tremendous attention due to their remarkable advantages in terms of aerodynamic efficiency, large flying range, and stealth property [1], [2], [3], [4]. Up to now, several advanced tailless aircraft have been developed such as B-2 (US), X-47B(US), Neuron (FRA), etc.
There are several challenges to controlling tailless aircraft. The first is the absence of the vertical tail and rudder, leading to the lost stability of course and poor stability of longitudinal. Second, tailless aircraft typically adopt redundant control surfaces configuration to generate three-axis torque, which means if the yaw moment is generated, the pitch and roll moment will be produced simultaneously. Such a design causes the new issue that the deflections of the redundant control surfaces will inevitably result in a serious coupling between longitude and lateral dynamics. Third, how to coordinate multiple control surfaces in ways that optimize performance and minimize energy consumption, minimize additional drags and minimize total control surface deflections. All those cause difficulties in the design and implementation of tailless aircraft controllers. In addition, some crucial problems remain open for tailless aircraft including convergence time, fault-tolerant, and input saturation, whose importance is explained hereafter.
https://www.sciencedirect.com/science/article/abs/pii/S1270963823003693
T
he stability decrease for increased Mach number is greatest for the tailless configuration and least for the canard configuration. A destabilizing break in the pitching-moment curve at constant Mach number is most pronounced for the tailless configuration,while the canard configuration is least affected. A given 44° trapezoidal wing configuration has a greater lift-curve slope and zero-lift drag and a lower maximum lift-drag ratio than its 60° delta wing counterpart. The effect of the strake on the 44° tailless and aft-tail configurations is to increase the lift-curve slope, maximum lift-drag ratio, trimmed drag performance, and pitching-moment curve nonlinearity.
https://ntrs.nasa.gov/api/citations/19850019510/downloads/19850019510.pdf
No configurations offers everything, each one loses something while retaining something.
Flat nozzle design advantages
Since about the 80s of the last century, aircraft designers have discovered a number of advantages for military aircraft engines, which can bring the use of a nozzle with a flat cross-sectional shape.
On the one hand, such a design feature improves the take-off and landing performance (CV) of the aircraft and makes it more maneuverable.
And on the other, it allows the combat vehicle to become less noticeable to the enemy radar. This is because the contours of an axisymmetric nozzle of circular cross-section are very difficult to coordinate with other structural elements of the aircraft to make the aircraft not so noticeable to radars. This is much easier to achieve if you use a flat "jet" nozzle. In addition, in order to further reduce the radio sensitivity, in the manufacture of such a nozzle, materials capable of absorbing radiation are used.
Additionally, the infrared radiation of an aircraft using this nozzle shape is also reduced. This is achieved by the height-to-width ratio of the nozzle, significantly reducing the temperature of the outgoing jet.
Of course, this nozzle shape has its drawbacks. Firstly, when switching from a round engine cross-section to a rectangular nozzle shape,
there is some pressure loss. At best, about five percent is lost. The second drawback is the need to increase the rigidity and strength of the nozzle, since the design of this shape experiences a greater load than a round nozzle.
But all these disadvantages more than overlap with the benefits
https://en.topwar.ru/171233-nuzhno-li-rossijskim-voennym-samoletam-ploskoe-soplo.html
The thrust-vectoring in particular “Fluid” type is of increasing interest for the maneuverability and the agility of combat and fighter aircraft. This has been employed for different nozzles mainly axisymmetric
and 2-dimensional. For the latter, the aspect ratio, i.e. the ratio of the long-to-short side of the nozzle has significant influence upon the exhaust and thrust-vectoring performance. The effectiveness of a high aspect-ratio nozzle in order to deflect the jet engine’s thrust has been demonstrated {Hiley, 1975} but, such large aspect ratios often causes increasing of the structure weight and internal pressure losses.
Here, the design of a two-dimensional nozzle with respect to the thrust-loss factor of a small jet-engine is presented. Computational Fluid Dynamics (CFD) techniques were used in order to simulate the nozzle’s flow characteristics under various engine’s operating settings as well as different aspect-ratio designs. Computations results were obtained from the “Fluent” program. All developed models are 3-D and meshed by using “Gridgen” code. Moreover, the boundary conditions were obtained by using of the engine’s performance model developed in TURBOMATCH program. Also, the paper describes an experiment in order to predict the engine’s performance for a test case that has aspect ratio of 8.5. The CFD results were compared with experimental measurements.
The results showed that nozzle with higher aspect-ratio results in larger pressure losses, while, its thrust discharge coefficient is not far from the moderate aspect-ratio nozzle
https://www.researchgate.net/public...of_a_Planar_2-D_Nozzle_for_a_Small_Jet-Engine
The "flat" nozzle will reduce the Su-57's thrust somewhat, but it will improve the rear fuselage stealth characteristics that are so essential for this type of aircraft.
https://en.topwar.ru/255577-snizit-...ijskij-istrebitel-su-57-s-ploskim-soplom.html
A serpentine nozzle directs the jet engine exhaust through bends, to improve flow characteristics and reduce thermal signature, incurring a slight thrust penalty. This property of serpentine nozzles is beneficial for military aircraft operating in hostile airspace, as it improves stealth characteristics. The present work aims to develop a serpentine nozzle model and simulate the flow characteristics using a computational tool. The computational model has been validated against literature data. Four different inlet and outlet geometries have been investigated at Mach 0.9 at 2000 m AMSL. The effect of changing these geometrical parameters on pressure contours and velocities has been analyzed. Based on this study, a cambered rectangular inlet serpentine nozzle is optimal for the target application. Computational results indicate that, for serpentine nozzles, increasing the exhaust velocity after a certain threshold, based on nozzle geometry, leads to unfavorable pressure characteristics. Furthermore, reducing the exit area 0.5 times when compared to the inlet area allows for the best possible expansion characteristics.
https://www.researchgate.net/publication/377434104_Computational_Analysis_of_Serpentine_NozzlesThe serpentine convergent-divergent nozzle represents an optimal configuration for next-generation fighter aircraft characterized by low detectability and high thrust-to-weight ratio. In contrast to the serpentine convergent nozzle, such configuration offers increased design flexibility with additional parameters, leading to heightened interactions among these parameters. As such, it is crucial to reveal the influence of design parameters on the aerodynamic performance of the serpentine convergent-divergent nozzle and the multifactor interaction, as well as its mechanism. Therefore, the influence, interaction and sensitivity of parameters on the aerodynamic performance of the nozzle were numerically investigated using the orthogonal test method. Additionally, the influence mechanism of the convergence angle, throat aspect ratio, and axial length to inlet diameter on the flow characteristics of the nozzle was investigated in detail.
The results show that the convergence angle is identified as the main factor affecting the aerodynamic parameters of the nozzle. As the convergence angle increases,
the thrust coefficient, total pressure recovery coefficient and discharge coefficient
gradually decrease. The interaction between throat aspect ratio and other parameters is obvious. Different design parameters affect the local loss and the friction loss by affecting the curvature and wetted perimeter area, resulting in different aerodynamic characteristics of serpentine convergent-divergent nozzle.
https://www.sciopen.com/article/10.1016/j.cja.2024.07.017
is not sarcasm