The Shenyang J-50 / J-XDS
The leaked pictures of the Shenyang J-50 last week on its takeoff roll, with its sleek lines looking like something out of Star Trek raised quite a stir on Social Media.
While the J-50’s tailless design & lambda wings raised eyebrows worldwide, what really got the buzz were the all moving wingtips (AMT) .
Before we get into the evolution of Lambda Wings, let us first investigate the all moving wingtips.
The All Moving Wingtips (AMTs)
Tailless flying wings or low drag configurations have always had yaw and pitch control challenges typical only to them. The control challenges have two approaches in the flying wing ecosystem. The drag rudder (made famous by the B2- Spirit & the Ho-229) and the recently made famous all moving wingtip.
On the face of it both of them appear to do the same thing but in actuality they are different.
In AMTs the entire wingtip swivels or pivots, this gets them to act as mini wings, generating lift to create precise pitching/rolling movements with minimal drag.
Split rudders by opening to disrupt airflow create drag based yawing moments, they are effective for directional control in tailless aircraft but less agile for pitch control.
To sum up, on a fighter aircraft which has to be capable of high-alpha (high AoA) movements, AMTs are much more effective than drag rudders which are effective for stable level flight with gentler yaw moments much like a B2’s.
The evolution of AMTs
Right from J W Dunne’s early tailless flying wing designs in the early 1900s, they had high angle of attack (AoA > 15°) instability, a pitch up due to vortex formations and airflow flow separation.
Early stability was achieved through wing washout (refer part one of this series), some others such Jack Northrop’s N-1M from 1941 had manually adjustable wingtips that were adjusted preflight. These wingtips moved up and down on the vertical axis (altering the dihedral/anhedral angle relative to the main wing plane), however it was found that drooping wingtips did not contribute to lift and increased drag. Subsequently the wings were left flat inflight.
The Ho-229 used elevons, a combination of elevators and ailerons. The elevons on the wingtips leveraged the wings outer sections for a greater moment arm (the perpendicular distance from the axis of rotation to the line of action of a force), improving control authority. The Ho-229’s elevons(which either deflected together or rolled differentially) on the wingtips can be considered an early precursor to AMTs.
The Short SB.4 Sherpa is considered a milestone in the evolution of AMTs. It had an aero-isoclinic swept wing (maintaining a constant angle of incidence despite wing flexing and air loads, preventing issues like torsional instability, aileron reversal, and tip stalling). It had a 42° leading edge sweep and was designed by G.T.R.Hill who had designed the Westland Pterodactyls & BWB(detailed in parts one & two). The SB.4 Sherpa was the very first aircraft with controllable AMTs and its all moving wingtips acted as elevons (only). The AMTs were 20% of the total wing area and were hinged at 30% chord (means that the pivot point for the elevon was not at the very front of the control surface but further back. This allows the elevon to act more like an all-moving stabiliser and less like a conventional aileron, increasing its control authority).
The elevons had a symmetric rotation of ±15° and asymmetric rotation of ±10°. While the design was pathbreaking the electric actuators were slow and underpowered for larger aircraft, limiting scalability. The tests on the SB.4 that ran between 1953-64 confirmed 15% better control at high AoA vs flaps. The SB.4 Sherpa’s cancellation would only highlight the influence AMTs could have on future aircraft.
During the 1980s the concept of wingerons on RC gliders (C.R. Turbo Kit) came about. They adapted the AMT concept for lightweight, low speed gliders. It became popular in RC communities because it simplified construction and enhanced soaring efficiency. In these gliders either entire wings were pivoted or just wingtip sections around a central joiner (carbon rod). The AMTs improved glide ratios by approx 15% and the wingerons had great performance at high AoAs (greater than 20°). The wingerons were directly inspired by the Horten Brothers and the SB.4 Sherpa.
The 2023 paper ‘Numerical analysis of pitch-break and all moving wingtip aileron of lambda wing configuration’ (https://www.sciencedirect.com/science/article/abs/pii/S1270963823004054) reflects on decades of tailless aircraft research (ex: SACCON(Stability And Control CONfiguration), 1303 UAV(lambda wing unmanned combat aerial vehicle UCAV, configuration used for extensive aerodynamic and stability studies, notably its low-speed characteristics) and advances in computational fluid dynamics (CFD). It further proposes AMTs on aircraft such as the B-2 & X-47B. The reason for this is pitch break (cites the B-2 crash of 2008) over lambda winged aircraft. Pitch break on a lambda wing aircraft is a sudden and unstable pitch up motion that occurs at high AoA . This aerodynamic instability is caused by the complex flow patterns over the wing at high AoA, particularly flow separation over the outboard portion of the wing. The paper further suggested that Pitch-break on lambda wings is attributed to the combined effects of the leading edge vortex and the trailing edge pressure gradient at high angles of attack. A numerical analysis suggests that an all-moving wingtip (AMT) auxiliary aileron could provide more stable pitch control during the pitch-break zone compared to conventional ailerons, demonstrating engineering feasibility.
The paper’s AMTs or pivoting wingtip sections suggested them to be approx 10-15% of the wingspan, rotated symmetrically for a pitch of ± 10°. The differential rotation for roll of ±8°. To achieve precise control fly by wire is a must and the leveraged wingtips influence spanwise flow by adjusting lift and manipulating wingtip vortices, thereby enhancing aerodynamic stability. The paper references A. Schutte ( German Aerospace Centre (DLR)) & Sedat Yayla (Kocaeli University) among many others who researched aerodynamic challenges in tailless lambda wing configurations.
The Shenyang J-50 is a synthesis of all the knowledge gained over 70+ years and applied on a sixth generation fighter. The J-50 likely has its AMTs working in a similar manner as suggested above. The hydraulic actuators driven by fly by wire should have responses of <0.5s with composite hinges. The weight of each wingtip should be <100kg (speculation).
In summation the AMTs on the Shenyang J-50 overcame the challenges the tailless Horten Ho-229 & Sherpa SB.4 elevons faced. It takes the RC community idea of wingerons for low drag rotation and further synthesizes it with the 2000s research to deliver unmatched agility on a tailless lambda wing.
The Evolution of Lambda Wings
Without doubt the most famous lambda ( ƛ )wing is the legendary B-2 Spirit. Lambda wings get their name from the lambda shaped kink on their trailing edges. Almost 40 years after her first flight, she continues to inspire awe and respect. The B-2’s lambda wing design emerged from a combination of Jack Northrop’s (considered one of the fathers of the flying wing) flying wings from the 1940s, the need for stealth and desire for superior aerodynamics. To truly understand the lambda wing, let’s go back to the beginning.
The basic supersonic shape of a wing is the Delta wing, it shaped like a ⍙ . Triangular in shape with a continuous wing sweep of between 35-60°. Double delta wings have kink on the leading edge a 50-60° sweep (vortex lift) and the outer wing (planar lift) has a sweep of approx 30-40°. The moderate kink blends delta and straight wing traits, improving low speed handling without really compromising high speed performance while maintaining aspect ratio.
The J-50 is a Cranked Lambda(Arrow) Wing which has a sharp kink on the leading edge. The inner wing has a sweep of between 60-70° and the outer wing has a sweep of between 30-40°. Furthermore the trailing edge has a kink (ƛ shaped) on it too and contributes to the J-50s stealth performance.
To fully understand Lambda Wings let’s go back to the beginning. Post WW2 early deltas such as Convair XF-92 (1948) and Dassault Mirage I (1955) had excellent high speed characteristics, but poor low speed handling. Engineers looked at hybrids to balance the two, the cold war dictated fighters capable of Mach 2 intercepts and be agile dog fighters. The answer was the double delta.
The Saab 35 Draken is considered a major milestone as the first operational double delta winged aircraft. It had an inner wing sweep of 80° and an outer wing sweep of 60°, this gave it excellent transonic performance and high maneuverability. The draken had only a vertical stabilizer. The kink improved lift to drag ratio by 10-15% at subsonic speeds compared to pure deltas. The Saab 37 Viggen had canards coupled close to the double delta wing, this boosted low speed agility even more and reduced the incidence of stall by generating additional vortices that interacted with the main wing flow.
Through the 1960s & 70s various aircraft experimented with variations of the double delta wings, and some of the notable examples were the XB-70 Valkyrie(1964, please read the detailed piece on it), the Tu-144(1969). These examples highlight design progression toward multi role versatility.
Other examples of evolution of the double delta (kink of leading edge) handling include the General Dynamics F-16XL (1982), developed under NASAs high speed research program. It modified a F-16s cropped delta into a cranked double delta with an inner sweep of 70° and an outer wing sweep of 50° and incorporated an S curve on the leading edge for a smooth flow transition. This design experiment improved fuel efficiency by 25% at subsonic speeds , increased range and had enhanced payload (weapons / fuel). The F-16XL had a vertical stabilizer, but proved double delta wing efficiencies. Through the 80s there were several experimental delta wings such as the Grumman X-29, a forward swept wing with close coupled canards that tested aerodynamic efficiencies.
The 1997 McDonnell Douglas/Boeing – NASA X-36 was a sub-scale tailless demonstrator with lambda wings and close coupled canards. The X-36 would directly influence UACV designs moving ahead.
In the early 2000s a generic lambda wing was used in transonic research to study complex vortical phenomena that occur at subsonic speeds (Mach 0.5-0.8) on lambda wings. The SACCON was used as a research test bed.
The 2002 Boeing X-45 was a tailless UCAV demonstrator featuring a cranked lambda wing with a 65° inner wing sweep and a 30° outer wing sweep. The trailing edge kink was in the range of 30°.The wing’s leading edge had a sharp kink and swept back planform aligned edges aided RCS (Radar Cross Section) reduction. The design exhibited improved lift coefficients by 15% at transonic speeds, with vortex lift sustaining high-alpha (high AoA) maneuvers. The X- 45 proved autonomous technology along with lambda wing maneuverability.
The Northrop Grumman X-47B program that ran between 2011-2015 is another example of lambda wings. The X-47B was a lambda wing UAV to test carrier operations. The program was cancelled in 2015 as engineers struggled to balance stealth, aerodynamics & propulsion. The 2023 paper mentioned earlier recommended AMTs. The program validated the concept of unmanned carrier aviation.
Summation
The cranked lambda wings (a.k.a cranked arrow) represents a move forward and an evolution of the double delta wing design. The design features a more pronounced leading edge kink in the range of an inner sweep of between 60-70° and an outer wing sweep of 20-40° to optimize transonic efficiency and stealth. The crank enhances lift by between 5-10% in the transonic regime and improves vortex sustainability for better longitudinal stability. The lambda shaped kink (approximately 30°)on the trailing edge improves aerodynamic efficiency across the speed regime in addition to contributing to stealth properties.
The Shenyang J-50 a sixth generation Chinese fighter with it’s cranked lambda wing balances subsonic agility , transonic efficiency and supersonic dashes, with its wingtips enhancing high-alpha control by over 15% over traditional elevons. The wing further aid reduced RCS.
The fly by wire J-50 represents the next step in lambda wing evolution and it combines stealth, autonomy & adaptive surfaces and is definitely up there as far as sixth gen fighters go.
Please do read parts 1 & 2 of this series:
http://theaviationevangelist.com/2025/09/13/the-evolution-of-the-flying-wing-part-one/
http://theaviationevangelist.com/2025/09/19/the-flying-wing-part-two-the-blended-wing-body/ do keep scrolling down, and do share
Follow me:
LinkedIn : https://www.linkedin.com/company/the-aviation-evangelist/
X : @ManiRayaprolu
Reddit : r/theaviationevangelist
Facebook : https://www.facebook.com/profile.php?id=61583497868441#
https://www.instagram.com/theaviationevangelist?igsh=ZjA5YXI3MWd3OGZs&utm_source=qr