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The Amazing Blackbirds

November 21, 2025 //
1

SAMs , Satellites & Unseen Speed

The very first SAMs were the German V2’s from WW2. While their value was being understood they still had a long way to go as on the range & accuracy parameters.

The US began developing its missiles from the late 40s onwards and by the mid 50s had batteries of Nike Ajax missiles to guard against Soviet bomber attacks. By 1955 the Soviets themselves had the S-25 Berkut system and the famous S-75 Dvina came into being by 1957 having range, speed & accuracy.

The Soviet Sputnik launch of 1957 started off a whole new Cold War race and it was dominance from space. However satellites were still in their infancy and the CORONA & GAMBIT missions were still between 5 and 10 years away. Missile technology had a head start over satellite tech.

By 1956 the recently released U-2, Dragon Lady was already being painted regularly by Soviet defense systems, however the U2’s cruising altitude of 70,000 feet was still thought to be out of range of Soviet missile systems, even at its subsonic speed. Gary Power’s being shot down in 1960 only reinforced the need for speed, altitude and agility, the need for a Blackbird (which was already in development).

However even before the 1960 incident a fresh thought went through the US Armed services and it was speed. The recently launched B-58 Hustler had shown that Mach 2 was possible (if a little dangerous) and the various wings of the armed forces and CIA began to look at Mach 3 as the speed benchmark, stealth was not yet in the picture.

The WS-110A or what would become the XB-70 Bomber already underway was in trouble even before it got off the ground as it was believed Soviet SAMs could take down a large bomber with no stealth capabilities, the XB-70 would become an experimental aircraft as an attempt to just their cost of over $1.5 Bn for two vehicles or $750 Mn a pop! (Read here about the XB-70)

(https://theaviationevangelist.com/2025/10/10/xb-70-valkyrie-the-grand-daddy-of-supersonic/ ).

At around the same time and in parallel to the XB-70 program the CIA went to Lockheed to develop a Mach 3 capable reconnaissance aircraft that flew at over 90,000 feet (considered untouchable by SAMs) and would be difficult to detect by Radar. Lockheed with previous experience developing the U2 Dragon lady which had a service ceiling of 70,000 feet albeit at subsonic speed looked the right outfit to build such a plane.

This is the story of the Blackbird Family of aircraft and it all started with the A-12 Oxcart, an ironic name considering the A-12 was the exact opposite of an Oxcart.

A pencil sketch of the Blackbird by my Daughter from a few years ago. Hung in my office.

Project Archangel

In Apr ’58 Kelly Johnson the legendary head of Skunk Works said ‘ I recall having long discussions with (CIA Deputy Director for Plans) Richard M. Bissell Jr. over the subject of whether there should be a follow-on to the U-2 aircraft. We agreed … that there should be one more round before satellites would make aircraft reconnaissance obsolete for covert reconnaissance ‘. 

The CIA’s hunt for a U-2 successor  was called Project Gusto and by 1958 the two finalists were Convair with their Kingfish and Lockheed with their Archangel. Convair’s Kingfish had a lower cross section than Lockheed’s A-3 concept. Both companies were asked to refine their designs and here is where Lockheed pulled into the lead.

The A-11 that would be modified to become the A-12. Pic Source : Wikipedia

Following the A-3, (the A stands for Archangel) Lockheed’s iterations A-4 to A-6 used Blended Body Fuselage (BSF) designs along with turboramjet (more on this later) & rocket propellant, but they fell well short of the range requirements. Iterations A-7 to A-9 used a single J58 engine (just the turbojet) with two Marquat XPJ-59 Ramjets that used J-150 fuel, a highly classified type of fuel the JP stands for Jet Propellent and was expected to improve range, however still well short. The A-10 used two GE J93 turbojets (same as the XB-70 Valkyrie)  with underwing inlets for better range, however the iterations continued to fly short of the required parameters. Iterations on the A-11 Lockheed added twin inward canted fins that were angled inwards at 15° made of composite materials, other leading edge surfaces featured composites as well, together the improvements went a long way towards improving RCS ( Radar Cross Section) of the aircraft. To add to these design improvements  the wings were extended through chines that went right upto the cockpit and the bottom of the aircraft flattened with the wings blended into the fuselage, the improvements won Lockheed a $96.6 Mn contract to construct a dozen A-12s. The dozen airframes would extend to 18 if you include the three airframes used for the YF-12 , one trainer and two M-21 aircraft. Project Archangel / A-12 was underway.

The A-12 design: Pic Source : Wikipedia

The J-58 Engine

While the A-12 was an amazing aircraft design that is yet to be replicated almost 70 years on, it is the insane engineering that went into the engines of the aircraft that needs to be spoken of first.

The J-58 Turboramjet!

The external dimensions of the engine were a length of 17.10’ a diameter of 4.9’ and weight of 6,000 pounds might feel puny by today’s standards, the engineering that went into them is unique.Pratt & Whitney JT-11 Mach 3+ jet engine (J58) . (strongly recommend a watch). The engine generated 30,000 pounds of thrust with afterburners and had 8 compressor stages.Pratt & Whitney J58 (JT11D-20) Turbojet Engine | National Air and Space Museum

Sometime between 1956-58 the US Navy approached P&W to develop a Mach 3 capable engine for their planned Martin P6M Jet Seaplane. P&W had begun testing their prototype when the Navy realized the costs involved did not justify an aircraft when their main weapons were ships, submarines & missiles. The Navy pulled out by 1958ish. The CIA, which already had Lockheed in advanced design stages of their project Archangel/A-12 had obviously heard of this engineering marvel and approached P&W to continue development on the J-58…and the rest is history.

The J-58 engine. Note the three pipes heading towards the afterburner. The plate right upfront on the side is the hydraulic computer. Pic Source : Air & Space

Coming back to the turboramjet, a couple of definitions. 

Turbojet definition : In a turbojet all the air that goes in the front is sent through the compression stages, fired up in the combustion chamber and the resulting exhaust gases generate thrust.

Ramjet definition : A ramjet is a type of engine that uses the forward motion of the aircraft to compress air and fire it up. Such an engine has no moving parts and aircraft using such engines need to be launched off another transport aircraft generally.

So why did the J-58 need both?

The J-58 was optimized for Mach 3.2 cruise and such high speed generates heat in the excess of 750°F which would melt the internals of the J-58 turbojet. A solution was required and here lies the engine’s unique feature, the frontal spike and six tubes running (three on each side) from the stage four compressor straight back to the afterburner section (a type of bypass).

The J-58’s variable geometry spike is where over 50% of the engine’s thrust is generated, but first another bit of information. At Mach 3.2 the compression at the engine’s inlet was almost as high as the thrust generated out the back, the engine would be in a neutral state of thrust, and in some cases negative (this is where the inlet management is critical). The pressure recovery on the J-58 is at 88% showing it is highly efficient at Mach 3.2.

The spike moves front and back by 26”. Right up to Mach 1.6 the spike stays in the full front position and the engine operates as a normal turbojet. At Mach 1.6 the engine begins moving back 1.6” for every increase in speed by Mach 0.1. The spike itself moves backwards into a conical receptacle and the backward movement of 1.6” for Mach 0.1 increase in speed maintains the ‘normal’ just behind the throat of the spike receptacle. The normal is the point where dynamic pressure switches to static pressure, and the movement of the normal is carefully calibrated by the spike to maintain optimal thrust across the speed Mach 1.6 – Mach 3.2 range.

At approx Mach 2.2 sensors detect that airflow and temperature are right to begin turboramjet operation by opening up the compressor bleed bypass valves, these valves are placed at the fourth compressor stage, and direct ram air through the tubes direct to the afterburners. The air is approx 400°F and helps keep the combustion chamber and turbines relatively cooler and within thermal limits. The afterburner fires more efficiently as a result of the cooler air.

A schematic showing the various engine regimes. Pic Source: Wikipedia

At Mach 3.2 the engine’s spike aligns the shockwave with the engine’s nacelle perfectly. The engine has a series of doors that maintain optimal pressure through the entire length. The cowl bleed doors is a porous strip on the inlet’s inner surface, the purpose is to bleed off excess boundary layer air and prevent an unstart at high speed.  Further back the engine has suck in doors, these doors open up at low speeds (below Mach 0.5) such as the beginning of a take off roll to feed the engine with more air and aid low speed thrust generation. Furthermore at low speeds right at the afterburners are tertiary doors that automatically open and close as per ambient pressure relative to the exhaust gases, these doors let in additional air as required. The spike itself has a porous strip that manages slow moving boundary layer air. At low speeds the engines are extremely air hungry and this creates a low pressure area at the engine nacelle, the strip pulls in the air into the centre body and vents it out through centre bleed louvres. The air reverses direction at approx Mach 1.5 the air inside the spike centrebody duct reverses. 

There is a story of a SR-71 pilot who decided to speed check his bird and got up to Mach 3.4 before he swallowed his own shockwave, flaming out both engines at 80,000 feet! He recovered one at 65,000 feet and the other at 25,000 feet. There was of course a discreet rap on the knuckles!! This story does highlight the fine balance within the engine and how it was optimized for Mach 3.2.

A look at the engine shows a tremendous amount of plumbing, not all of it is air, oil or fuel!. On each side of the engine nacelle is a hydraulic computer, yes hydraulic! The plumbing you observe is the computers optimizing engine operation. One of the computers is to manage the afterburner and the other is for the engine. The J-58s were created when computers were in their infancy and a solid state system was required that could withstand high temperatures and work optimally, hydraulic computers were the option.

The operating temperatures expand the engine by 6” in length and 2.5” in diameter and this sort of expansion and contraction needs exotic metals. The very front of the engine at the nacelle is titanium, the rest of the engine is made of iron nickel alloys such as Waspalloy, Inconel & Astrology. All the metal in the engine is directionally solidified so the metal expansion is directional and can be managed. The plumbing on the engine is made of steel 321 and 347 and there are over 600 pieces of plumbing on the engine.

The oil used in the engine is synthetic, made of polyphenyl ether and is stable at 650°F. The oil is maintained at 400°F by routing through a fuel oil cooler, a heat exchanger where the oil contacts with the cooler fuel heating it up and cooling itself before the fuel is routed into the engine.

The complex system was started by two V8 Buick Hellcat motors which were a petrolhead’s delight, apparently the crew blew through most of the Buick motors that salvage yards across the United States had with them. The two motors would spool up to 6000 rpm and the crank interfaced with a gearbox at the bottom of the engine and needed to retract as the aircraft engines got to 3000 rpm, the J58s fired up at 4000. The crew got so carried away with revving the Hellcats that they delayed retraction blowing their engines up! Once the Hellcat stock was run through the crew moved to Chevy 454 cu.in engines, but they were not the same.

At Mach 3.2 over 50% of the engine’s thrust was created at the inlet and an additional 28% at the afterburner. This left just about 20% of thrust needed from the turbojet! While the first A-12s flew with less effective J-75 engines, once they cutover by 1963-64 to the J-58, the blackbirds never went back to anything else.

The Design

The external dimensions of the A-12 Oxcart (the foundational Blackbird) was a length of 101.7’, wingspan of 55.7’ and a height of 18.6’. The MTOW of the aircraft was 124,600 pounds.

A front view of the aircraft showed off a flattish underbelly with blended in wings at the fuselage. A sharp angular cockpit at the very front and twin tail canted in at 15° each. The flow of the wing’s leading edge was interrupted by heavily integrated engines on each wing right in the centre.

A front view of the SR-71 note the canted fins, the flattish underbelly and the blended wing fuselage. Pic Source: Reddit User

The nose of the A-12 looks more conventional than the Blackbirds that followed. While it slopes up towards the angular cockpit windows in a more or less conical manner, the bottom is more flattened to merge with the rest of the flattish underbelly. This sort of contouring is necessary to manage shockwaves and keep the aircraft aerodynamically optimized.

While Blended Wing Bodies have existed since the early days of flight, they had never been used practically. The blackbirds are not traditional BWBs (as we know them since the 1990s) in the new sense they are what is called a Blended Wing Fuselage. Read here (https://theaviationevangelist.com/2025/09/19/the-flying-wing-part-two-the-blended-wing-body/ ).

The chines that begin on each side of the cockpit at a sharp angle of approx 70-80° and swept back towards the delta wing were an integral part of the BWF serving multiple functions. The first was stealth (yes the A-12 is the very first purpose built stealth aircraft https://theaviationevangelist.com/2025/10/22/the-theory-of-stealth/ ). The specially designed edges with their composite materials reflected radar waves away from the source and reduced the aircraft’s RCS to about 10m2 or a largish bird, a big improvement of over 90% over the RCS signatures of preceding aircraft Reducing the A-12 Blackbird’s Cross Section. The second purpose was the chines served had a critical to the aerodynamics of the aircraft and that was to generate lift. They worked to generate approx 17-20% of total aircraft lift in two ways. The first was the creation of vortices over the chines, inner wing and fuselage, delta wings with a sharp leading edge sweep, at high Angles of Attack (AoA) rely on vortex lift . The second is the blended and flattish underbelly works as a lifting body and contributes towards the 17-20% lift. This means the load is off the wings and more evenly distributed which is critical at high Mach numbers. The reason the chines were terminated at the cockpit i.s.o going right to the nose like the SR-71 was the A-12 was a single pilot aircraft and the chines terminating at the cockpit saved weight and were optimized for higher speeds at altitudes of up to 95,000 feet.

The chines blended into a delta wing with a leading edge sweep angle of 60°. The edge of the wing was interrupted in the middle by the engine nacelle.Close observation of the leading edge and the engine shows up a gap on both sides of the engine, this was to accommodate the 2.5” expansion of the diameter of the engine and boundary layer control. On the trailing edge the gap is more pronounced as this was the business end of the engine with the hot exhaust gases. Other than this the wing was fairly standard in the front view profile! A top view of the wing shows a second chime that comes off the outboard engine cowling on both wings blending back into the leading edge, these chines increase the aspect ratio of the swept back delta improving lift.

The trailing edges of each wing had a pair of elevons, one inboard and one outboard of the engine. In tailless delta wings the elevons serve the purpose of the elevators and ailerons. When they move together they control pitch and when they work opposite to each other, they control roll on the aircraft.

Further back is a pair of twin fins each canted in 15° as mentioned earlier, the canting is part of the aircraft’s stealth and the original fins were made of composite (because of they non reflective properties), however most of the aircraft in the entire Blackbird fleet used titanium fins with composite accents.

The entire Blackbird was a flying fuel tank. Fuel was stored in six tanks throughout the body and wings including the chines. The fuel was burned in a specific sequence as the center gravity moved significantly rearwards at higher speed numbers. The Blackbirds famously had wet wings. That is the skin of the wings and body of the aircraft was the fuel tank itself. In the interests of saving weight and the fact the titanium skin of the aircraft was heat resistant, the fuel was stored directly. The thermal expansion in flight meant the panels had gaps on ground and there were thresholds by area of the aircraft as to the number of fuel drops falling per minute that was acceptable. The same gaps sealed in the air as the metal expanded.

Acceptable fuel leak range by zone of the aircraft. Pic Source : Reddit User

The aircraft had a tricycle landing with the main gear having three wheels in parallel. The main nose gear had a single two wheel bogie. The Goodrich tires were infused with aluminium for thermal resistance and were inflated with nitrogen, a non combustible inert gas for safety.

Most of the aircraft was constructed of titanium because of its thermal resistance, however titanium is extremely hard to work with and a specialized set of rigs and tools had to be created to work with the metal. At the time the Blackbirds were being constructed the Soviet Union was the largest exporter of titanium and the CIA procured the required titanium through a series of shell companies making the final buyers (the CIA) untraceable.

The wings of the aircraft had corrugation on the top and bottom prompting jokes that Kelly Johnson was building a Mach 3 Ford Trimotor (an early airliner). The corrugation was to aid thermal dissipation and while there was a drag penalty at lower speeds which was powered through, at Mach 3 and over 80,000 feet the drag was minimal.

The aircraft was painted black with iron ball paint. The paint helps with stealth by converting radar waves to heat and dissipating it. Furthermore according to Kirchoof’s Law of Thermal radiation a good absorber of thermal radiation is also a good emitter, means that the black iron ball paint is the right color to repel heat by emitting it!

With a first flight in April 1962 the A-12 quickly demonstrated its capabilities even with the less capable J-75 engines. The USAF which was initially part of project GUSTO quickly realized this was an aircraft that was the answer to its need for a high speed aircraft. They put out the requirements for RS-71 (Reconnaissance Strike) by approx 1963, it was President Johnson who called the aircraft SR-71 erroneously and the name stuck. Furthermore the A-12 needed to be kept classified (which it was until 1990) and the USAF’s requirements for a high speed aircraft made a great cover story in 1964 when the SR-71 and YF-12 projects were announced. The M-21 Tagboard was never officially announced during its active life. TheYF-12 and the M-21 aircraft had approx same dimensions as the A-12 Oxcart while the SR-71 was longer and bigger. The M-21 aircraft had a pylon on top between the two fins to fit a D-21 drone on it. Of the two prototypes built, one crashed in 1966 when the the D-21 drone collided with the fins after separating, the plane crashed while the pilot survived, the M-21 was cancelled immediately after this and the surviving prototype is at the Museum of Flight in Seattle. Lockheed M-21 (Blackbird) | The Museum of Flight .

The M-21 with the D-21 drone. Pic Source : Wikipedia

The YF-12 took spots 7-9 on the A-12 Oxcart assembly line and was a Mach 3 interceptor prototype. It was to be a replacement to the F-106 Delta Dart, however severe cost cuts in view of the Vietnam War resulted in the program being scrapped. The main modifications was cutting the A-12’s nose chines to accommodate radar and infrared tracking equipment. The chines of the YF-12 show a clear indentation. Today of the three aircraft constructed only one survives at the USAF Museum in Dayton Ohio, it flew with NASA until 1979 after the YF-12 program was cancelled in 1967.

The YF-12 Interceptor. Note the truncated chines. Pic Source: Wikipedia
The YF-12 with modified chines to accommodate the radar equipment. Pic Source : Wikipedia

The Lockheed SR-71 Blackbird is a fairy tale of an aircraft, it has been immortalized in movies, books, articles like this and forum across social media with a huge fan following even 60 years after its first flight. Where the A-12 was heavily classified decades after its operation, the SR-71 was heavily publicized (to cover the A-12) and this is why the SR-71 is considered the most famous of the Blackbirds. Lockheed SR-71 Blackbird | Military Wiki

The SR-71 was to have a two man crew as against the A-12 single pilot. And where the A-12 carried a high resolution camera system the SR-71 carried a sensor array that included Side Looking Radar (SLR) and Electronic Intelligence Systems (ELINT). Where the A-12 was about covert photography for the CIA (the aircraft was disguised in USAF markings) the SR-71 was more about strategic reconnaissance (SR) for the USAF. To accommodate the radar installations, the chines were extended to the nose in the manner we know so well. The chine extensions on the SR-71 had the same lifting and stealth properties of the A-12, where lifting contribution remained at the same 17-20% as the A-12, the RCS was slightly higher than the A-12 but not by much (it was the larger bulk).

In case you are wondering why the A-12 on the USS Intrepid has the chines right to the nose tip, it’s because it was used as a radar object when understanding the stealth characteristics of the SR-71.

A front view of the A-12 at the USS Intrepid. Pic Source: Wikipedia

The SR-71 was longer than the A-12 by six feet to accommodate the second crew member and had a length of 107.5’. The wingspan and height of the aircraft was identical to the A-12.The dry weight of the aircraft was 6 tons heavier than the A-12 and MTOW was 22 tons heavier than the A-12. The additional bulk and mass made the SR-71 slower than the A-12 whose max speed was Mach 3.35 vs the SR-71s Mach 3.2. The SR-71s service ceiling was 85,000 feet vs the A-12s 95,000 feet. The range of SR-71 was 3250 miles vs the A-12s range at 2500 miles.When we see a comparison of the numbers we realize the A-12 Oxcart is just not celebrated enough.

Project Nice Girl

Project Nice Girl was the face off between the A-12 & the SR-71. The costs of running multiple high cost projects for the various services was getting out of control and in the autumn of 1967 the A-12 & the SR-71 had a play off. While the A-12 had superior speed and altitude , it was hampered by cloud cover during the fly off and the high resolution panoramic cameras on the A-12 were beaten by the SR-71s sensors that could peer past the clouds and collect valuable accurate data. The dividing factor was beating the weather and the A-12 was retired in 1968, the project was only declassified in 1990 and the aircraft handed over to museums across the United States.

Summation

As satellites got better and were in a position to take over from the considerable duties the SR-71, the amazing bird saw its days numbered. Additionally astronomical sosts of keeping the birds in the air just did not make sense to keep them flying and the decision was taken to retire the program.

Over sixty years after it first flew the SR-71 and the Blackbird Family of Aircraft continue to inspire awe, several of the projects they were involved in continue to be classified and this is what contributes to their enduring legacy. Their speed and altitude records intact over 35 years after the last flight of a Blackbird.

The peak of innovation… 

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Lambda Wings & Moving Wingtips – Flying Wings Part 3

October 2, 2025 //
2

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 Shenyang J-50. Note the wingtip angle. Source: X intelligence Pic

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.

The drag rudder schematic. Pic source: screenshot from slope dudes

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 Northrop N-1M. Note the dropping wingtips set before flight. Pic Source: Northrop Grumman Corporation on FB

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 all moving wingtips set before on the SB.4 . Pic Source : Wikipedia

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 amazing B-2 Spirit. Note the split rudder on the port (left) wing. The lambda shape clearly visible on the trailing edges. Pic Source : Wikipedia

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.

The cranked lambda wings on the J-50. Note the kinks on the leading and trailing edges. The elevons & wingtips clearly visible. Pic source : China Weibo Image

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.

The Saab 35 Draken with the leading edge kink. Pic Source: Wikipedia

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.

The double delta wing on the TU-144. Pic Source : Aerospaceweb.org

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 F-16XL. Pic Source : Lockheed Martin

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 X-36 & X-45 along with other greats at the USAF Museum. Note the trailing edge kinks on both aircraft. Pic Source : USAF Museum

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.

The J-50 prepares to take off. Note the wingtips. Pic Source: X

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

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The Flying Wing Part Two – The Blended Wing Body

September 19, 2025 //
4

The BWB is Born

As J W Dunne was conducting his early flying wing tests, there were  developments happening across the Atlantic in Europe. For the very first time, engineers were thinking of using the insides of the wings. A design philosophy was born.

The JetZero Z4. Pic Source: JetZero Website

The Pioneers

In 1910 Hugo Junkers of Germany patented a cantilever tailless wing design. It was an all metal construction (almost all aircraft until then were fabric and wood construction). Such a design & construction would be without any external wires or braces. Furthermore the wings could be hollow and the space used to house passengers, cargo and fuel. His designs were used by the Germans in WW1 and later in WW2 (he was ousted from his company in 1933 by the Nazis). 

The G-38 of 1929 was a major innovation of his blended wing concept and was for a time the largest landbased aircraft in the World. The passengers were seated in the wings which were 5 feet 7 inches thick at the root. The leading edges of the wings had sculpted windows giving passengers a panoramic view as they flew. There were three 11 seat cabins,in addition to smoking & wash rooms. The wings had a gangway through them that allowed mechanics to work on engines while inflight, a first. There were two operating aircraft and flew through to 1941(both flew until 1936)  before the final one crashed.

The G.38 schematic . Pic Source : Wikipedia

The Mitsubishi Ki-20 was based on the Junkers G-38. Six were built as heavy bombers between 1931-35. During WW2 they saw active combat. These aircraft were considered secret and their existence only made public in 1940.

Nicolas Woyevodsky was a Russian Aerodynamicist who filed a 1911 patent called ‘Aircraft’. Here’s where the patent gets interesting. It was filed in the United States in 1911 and granted in 1921 ( how and why did a Russian file for a patent in the USA and why did it take so long?). Not much else is known about this path breaking scientist other than his name, country of origin and patent.

The patent spoke of a continuous airfoil section integrating the fuselage and wings, what we now call the BWB. The patent further described a triangular shaped body with pterygoid (triangular) aerofoil sections that enclosed the engines and passengers. Such a construction would reduce drag and weight enhancing lift. This was considered revolutionary as most aircraft were biplanes with separate fuselage and wings.

The Westland Dreadnought. Pic Source: Wikipedia

Woyevodsky’s 1921 patent led to wind tunnel tests (probably in Russia & Britain) and validated his theory which led to designer GTR Hill of Westland designing and building the dreadnought. GTR Hill was already experimenting with the Westland Pterodactyl. The Pterodactyl was a revolutionary flying wing and flew through the 1920s & 30s in the hunt for a safer aircraft. The Dreadnought unfortunately crashed on its very first flight. After an initial stable take off and stable flight the Dreadnought stalled at 100 feet altitude and crashed, seriously injuring the pilot. The design was abandoned at the time, however It is recognized and appreciated by history.

The British further tried to pursue the BWB airliner design in the late 1930s & 40s through the Miles M.26 & M.30. The data was useful, however a full scale prototype was never constructed.

The BWF (Blended Wing Fuselage)

The timeline between the 1940s & 1990s is a BWB gap (very similar to the flying wings but longer, aviation development had moved rapidly in the direction of conventional aircraft ),except for the military applications between the 1950s – 1980s when the BWF was used. The A-12 Oxcart and its successor the  SR-71 pioneered the BWF design. The BWF integrates the fuselage and wings in a smooth aerodynamic transition, however the fuselage continues to be a distinct structure. 

The SR-71 schematics. The fuselage chine clearly visible. Pic Source : Wikipedia

Such a design used the fuselage as a lifting body, and the chines around the body contribute between 15-30% of total lift generated. The design used Area ruling and mitigated parasitic & wave drag through smooth transitions.

In the 1970s the Rockwell B-1 introduced variable geometry to the BWF. The wings pivoted on 6 ton hinges which are buried inside a wide fuselage. The BWF of the B-1B contributes approx 15-20% of the total required lift. 

The B-1B Lancer & The Tu-160 Blackjack. Note their similarities. The BWF clearly visible on both. Pic Source: Wikipedia

The Tu-160 which has a very similar design to the B-1 has an even larger BWF. The BWF contributed approx 18-25% of the total lift in supersonic flight.

All the aircraft mentioned had variable geometry inlets of various types (spikes / ramps).

The BWB Evolution

The Generation 1 BWB’s commenced in the 1990s and ran through to the 2010s. They represented the ‘ High Risk High Reward’ approach to BWBs where they envisioned extra large 800 seat BWBs with maximum aerodynamic efficiency. This meant Boundary Layer Ingestion (BLI) of the engines and integrating them inside the airframe. This proved to be difficult to accomplish & certify.

The NASA/McDonnell Douglas Studies were funded by NASA between 1993-96. The studies included wind tunnel tests of tailless BWB concepts at 1-6% scale. Models tested had the centre body contributing between 31-43% of total lift and exhibited between 6-8% fuel savings. 

NASA BWB-17 was tested between 1997-2000. With a 17 foot wingspan, the 6% scale RC model was built by Stanford University for NASA. The model demonstrated low drag and had centrebody lift of between 30-40%. The model proved BWB flight handling with a tailless design. The BWB-17 had stability issues and needed artificial stabilization to correct. The model further highlighted scaling & control issues on larger aircraft.

The BWB-17 by NASA. Pic Source : NASA

Boeing Phantom Works BWB studies ran between 2000-2007. Post the McDonnell Douglas acquisition of 1997, Boeing continued to build on the earlier program that ran between 1993-96. 

Part of the program was to construct the 35 foot wingspan X-48A demonstrator in 2004, however the program was cancelled before construction began. In 2005 a 12 foot wingspan BWB model was constructed to study transonic aerodynamics in a wind tunnel. This model exhibited a 15-20% drag reduction and lift to drag ratio of 20-23. As the project was for 450 seat passenger airliners it highlighted manufacturing complexity & airport compatibility issues.

The Boeing X-48B program ran between 2007-2010. It was a 8.5% scale 21 foot wingspan model that was powered by three jet engines and flew between Mach 0.3-0.7. The centrebody contributed 35% of the lift and had L/D improvements of approx 20% over conventional designs. The X-48B continued to have challenges with yaw handling and full size scaling. Furthermore engine out control and stall characteristics were tested and needed improvement. The aircraft needed artificial stability management.

The X-48B. Pic Source : NASA

The Generation 2 BWBs run from approx 2010 to date. Gen 2 highlights a safety first approach to design and has podded engines mounted above the airframe. The realistic path sacrificed potential efficiencies for safety with the approach. The Gen 2 BWBs also explored different propulsion types.

NASA N2A/B/C BWB concepts ran between 2010-2015. The concept was for a 300-450 passenger aircraft. Conducted in partnership with Boeing the N2A had two podded engines mounted on top of the upper surface of the aircraft. Wind tunnel testing was done to study its aerodynamic and acoustic performance at low speeds. The N2B used BLI and had embedded engines. While the N2B showed improvements over the performance of the N2A, the embedded engines increased manufacturing complexity. The N2C was a supersonic concept. The data gleaned from these concepts was to inform the future aviation industry on future design areas.

The Boeing X-48C first flew in 2012. With a wingspan of 21 feet it was a 8.5% scale of a large transporter. The C was focussed on noise reduction and featured vertical surfaces adjacent to the engines.The Modified X-48B had an extended aft fuselage on which the engines were mounted. It completed its 30th and final flight in 2013.

 

The X-48C. Pic Source : NASA

NASA N3-X Hybrid Wing Body that ran between 2013-2018 is a concept design. NASA tests such concepts through computer simulations and & wind tunnels. The research was on advanced technologies and propulsion. Some of the concepts explored included Turbo Electric Distributed Propulsion where instead of large engines, smaller electric fans distributed propulsion across the aircraft. Another concept explored was the Superconducting Power System, where superconducting technology allows for high power density with minimum energy loss. Others included wingtip generators and liquid hydrogen cooling. 

The N3-X can achieve a 70% reduction in fuel burn, significantly lower emissions and noise levels while maintaining performance at the same time.

The Airbus Maverick began development in 2017. With a wingspan of 10.6 feet and a length of 6.7 feet, the Maverick had two engines to the rear with each having a vertical fin on it. The model explored aerodynamic and technical specifications and results were encouraging .

The Airbus Maverick. Pic Source : Airbus

Airbus has further built on its BWB program by targeting 2035 as the first year for a zero emission aircraft. Such an aircraft would use hydrogen combustion or cells for propulsion. Storing Hydrogen is a big challenge in aviation and the BWB is considered an excellent test design. Airbus is further  studying conventional aircraft for its zero emission program. 

JetZero 

JetZero is founded by Mark Page a BWB pioneer. He was part of the seminal NASA / McDonnell Douglas collaboration on the BWB program as technical program manager. NASA concieved the program as a challenge to rethink aircraft design for greater efficiency. The program (although Mark was not part of it after 1996) culminated in the BWB-17(spoken of earlier) the very first BWB of the modern era. It was inspired By Northrop’s flying wings of the 1940s but was a completely fresh approach to aircraft design. The BWB design was co-created with Robert Liebeck & Blaine Rawdon and offered 20-30% better L/D ratios than conventional aircraft. The three of them authored ‘Beyond Tube and Wing’ in 2020 in which they charted the path to the BWB design.

The philosophy was Multidiciplanry Optimization (MDO) integrationg aerodynamics, engines, stability and internal structures to minimize drag and maximize efficiency. Page virewed the BWB as the fundamental reimagining of an aircraft blending wing and body into a seamless flowing structure. In one presentation Page mentioned imagine a Boeing 777 fuselage cut up into three parts and placed side by side. You then stick wings on the first and last sections, the middle one being the longest (with the cockpit) and place the engines on top of the stacked side by side fuselage, and lastly smooth them all together into one fused structure.

Page’s contributions influenced the X-48B/C programs as well. These programs validated the theory of BWBs with subscale models and wind tunnel testing. They sorted out  issues such as space by moving the main landing gear to the rear of the aircraft from the centre, saving space and increasing passenger numbers another example is sorting out pitch stability control issues with belly flaps, every thought had to be out of the box.

Later in 2012 Page co-founded DZYNE Technologies as chief scientist & VP and here he continued to focus on aircraft with high lifting efficiency , but the BWB bug was always there, first as a business jet and later as an airliner. In 2021 Page along with Tom O’Leary founded JetZero to take forward the BWB vision.

Page has mentioned that startups like JetZero are ideally placed to revolutionize the aircraft manufacturing space as they do not have massive legacy businesses that need to transition ex : Boeing & Airbus.

So far it has walked the talk with Alaska & United Airlines investing in JetZero through their investment arms. Delta Airlines is a strategic partner sharing expertize from a customer engagement perspective. In addition JetZero are talking to 14 other airlines and the USAF has awarded a $235 million contract to JetZero to build a full scale demonstrator, but we are getting ahead of ourselves.

The 12.5% scale JetZero pathfinder with its 21 foot wingspan first flew in 2023 and received FAA clearance in 2024. The USAF found the Pathfinder to exhibit similar characteristics to the X-48 program and has given the go ahead to JetZero to create a full scale demonstrator which is to be ready by the first quarter of 2027. The demonstrator is being constructed by Scaled Composites founded by the legendary Burt Rutan who has aircraft/spacecraft such as Spaceship One (won the Ansari X Prize) and Stratolaunch to his credit. Scaled Composites is now part of Northrop Grumman (its amazing the name Northrop is involved here, a doff of the hat to Jack Northrop).

The Z4 is a multirole platform and can be used for both passengers & military applications such as a sky tanker (the USAF is looking at the KC-Z4 as a replacement to its aging KC-135 tanker). To cut down the development & certification runway JetZero will be using Commercial off the shelf (COTS) parts where possible. 

The KC-Z4. Pic Source : JetZero Website

The engine choice is Pratt & Whitney PW2040 each generating approx 43,000 pounds of thrust. These are the very engines that powered the Boeing 757 & the Boeing C-17 Globemaster. While the design of the engines might be almost 50 years old, they are tried and tested and have a solid track record. Delta have provided three engines for the demonstrator. These engines are more than capable of managing the Z4s 5,000 nm range and cruise altitude of 45,000 feet. They will obviously be modernized for the production models. In future the Z4 might be offered with newer engines. Mark Page did note they were not looking for perfect tech, but are more interested in proving the airframe.

The JetZero Z4. Pic Source : JetZero Website

The fuselage ( after the demonstrator)will be made of composites and be manufactured at their Greensboro facility. Some of the other innovations it will have are shorter landing gear to enhance low speed handling, cargo door matching the KC-10 size (USAF applications). The passenger experience stresses comfort & efficiency (the 3D renderings on the JetZero website look stunning).

The personal passenger experience aims to revolutionized by offering larger seats, flexible cabin layout and dedicated overhead bin space (have forgotten what this feels like!). Instead of physical windows JetZero plans on high definition exterior cameras that provide a live view on digital windows. There is a possibility of overhead windows as well in addition to mood lighting.

While the overall exterior design of the aircraft is very sculpted, Page and his colleagues came up with a ‘ T ‘ shaped plug solution to scaling up the aircraft to either smaller or larger capacities, this means the aircraft construction has to be modular in nature almost like ‘LEGO’ !! They did this back in the 90s and the 25 year limit on the patent has expired, in Page’s own words “ I am happy to have it back” !

Page giving a DZYNE Technologies presentation in 2018 where describes the T shaped plugs that sum up the scalability of the BWB. Note their similarities plugs next to the engines. Pic Source : Page presentation off YT

Mark Page emphasizes pragmitism over perfection and this is achieved by delivering on the USAF contract, using milestones to attact fresh funding (the Z4 is expected to cost approx $5-7bn to develop as per Jon Ostrower of TAC) and target the largest market segment for aircraft the 200-250 passenger aircraft market worth over $2.5 Bn per annum. With projected savings of 50%, this will be a no-brainer for airlines future fleet decision making.

BWBs have promises to keep…..

Please be sure to read Part 1 of the two part series which details the evolution of the flying wing in detail at http://theaviationevangelist.com/2025/09/13/the-evolution-of-the-flying-wing-part-one/

End of Part 2

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