Archives for posts with tag: aerodynamics

The Amazing Blackbirds

November 21, 2025 //

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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Tags A-12, aerodynamics, aluminum dust, blackbird, Blended Wing Body, blended wing fuselage, boundary layer, Buick, BWB, bypass, chine, CIA, D-21, delta wing, Drone, engines, expansion, J-58, landing gear, Lockheed, M-21, NASA, nascelle, Navy, nitrogen, Radar Cross Section, ramjet, RCS, resistance, SR-71, stealth, thermal, thrust, tires, turbojet, turboramjet, USAF, V8, YF-12

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The Flying Wing Part Two – The Blended Wing Body

September 19, 2025 //

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.

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 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.

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 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 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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Tags A-12 Oxcart, aerodynamics, Airbus, B1B, Blended Fuselage Body, Blended Wing Body, Boeing, Chines, efficiency, JetZero, Maverick, McDonnell Douglas, NASA, SR-71, Tu-160, Z4

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The Evolution of the Flying Wing – Part One

September 13, 2025 //

Prologue

On June 22nd 2025 seven B-2A bombers carried out strikes in Iran. The total sortie codenamed ‘Operation Midnight Hammer’ lasted 37 hours. They dropped a total of 14 GBU-57 bunker buster bombs on Iran’s Fordow Fuel Enrichment Plant & Natanaz Nuclear Facility .

The sortie only strengthened the B-2’s formidable reputation of striking distant targets unseen & unheard..

The B-2 Spirit is a major milestone in the ongoing evolution of the flying wing.

The Pioneers

Before we get to J W Dunne (considered the father of the flying wing) , we need to first acknowledge a couple of important milestones. The first is Sir George Cayley who in 1799 put forth the concept of a fixed wing ‘machine’, one that had separate systems for creating lift, propulsion & control surfaces. He is the first person to understand the forces that act on a flying machine, weight, lift, drag & thrust. Later in 1810 he worked out the importance of having a dihedral angle at wing roots. The upward angle of wings was “the chief basis of stability in aerial navigation”. It needs to be noted Sir George Cayley was more intent on sharing his knowledge rather than patenting them, and therein lies his greatness.

The second is Alphonse Penaud , best known for his 1871 ‘Planophore’ , a rubberband powered model plane. The design achieved stable flight for 40 seconds demonstrating the stability of fixed wing aircraft designs over any others (such as ornithopters). He teamed up with mechanic Paul Gauchot in 1873 and they patented the monoplane flying wing in 1876. The structure of the ‘flying wing’ had a slight dihedral angle which provided roll stability, they had unswept wingtips and a slight arch on the leading edge with elastic trailing edges, this gave the wing better flexibility when dealing with unstable airflow. The patent contained a detailed performance analysis and is an important milestone as it integrated fixed wings, propulsion & control surfaces into a flyable machine decades before powered flight became a reality.

Alphonse Penaud’s 1876 Flying Wing. Pic Source : Wikipedia

Between 1906 – 1913 J W Dunne ran his experiments on ‘inherent stability’. From a military background, Dunne collaborated with Col. J E Capper at the British Army’s Balloon Factory to test early designs of his tailless gliders with swept wings. In 1908 his D.1b glider exhibited stable glides after the earlier D.1 crashed unceremoniously. The D.1b ‘s ‘inherent stability’ was achieved through tailless wing design alone.

The D.5 & D.8 were powered tailless biplanes (flying wing configuration) with sweeps up to 30 degrees. The wings featured a washout (a twist reducing the angle of attack at the wingtips) for enhanced stability. The D.5 demonstrated a hands-off flight while Dunne was reading a newspaper). This was a first in the early days of powered flight. The D.10 saw further refinements with a more streamlined design. Dunne’s use of Elevons (combination elevators & ailerons) is considered a first. His designs definitely helped reduce pilot work load. His work would be foreshadowed for the next ten years.

In 1910 the same year Dunne filed his patents, Hugo Junkers too filed a patent for a ‘flying wing or Nurflugel (pure wing). It was for a hollow metal airliner where passengers would sit inside the wing structure (an early blended wing). The fuel and cargo would be in the wings too. Long-term he envisioned transatlantic flights in such airplanes. His designs had structural integrity due to all metal structures with cantilevered wings and small tails for stability. The G38 was an example of his ideology. He was thrown out of his own company in 1933 as he disagreed with Nazi ideologies.

The Junkers G-38 of 1929. Pic Sour : Wikipedia

Between the wars Germany was not allowed to build powered aircraft and this gave rise to a number of glider clubs . Alexander Lippisch worked at Junkers between 1925-27 and this inspired him to take up the ‘nurflugel’ torch. His Storch series of gliders were tailless with swept wings. His Delta series of gliders explored low aspect ratio wings for better roll control. His gliders featured wingtip rudders and elevons. By the early 1930s he had contracted with DFS (Deutsche Forschungsanstalt für Segelflug a.k.a German Institute of Glider Research, a Nazi front) for powered prototypes such as the 1931 DFS 40, a rocket powered tailless plane. Lippisch directly inspired two young brothers who would go on to create one of the most fabled aircraft of all time, enter Reimar & Walter Horten and the aircraft they would create the Ho-229.

The Lippisch, Storch & Delta gliders. Pic source Wikipedia

Mentions: The powered Cheyranovskii BICh-3 Tailless research aircraft of 1926 & G T R Hill’s Westland Pterodactyl series of tailless gliders between 1926-32. Hill would go on to design and construct the Westland Dreadnought, the very first purpose built Blended Wing Body.

The sequence of events mentioned above illustrates the evolution of wings over an almost 200 year period starting with Sir George Cayley. The unveiling of the B-2 Spirit in 1988 was 112 years after Alphonse Penaud’s patent of 1876. During the early years of aviation, patents filed in different countries could be viewed or accessed through scientific journals, world fairs & patent translating offices. Percolation of ideas was slow and the timespan mentioned above makes the point.

The Horten Brothers

Between the wars in Germany several ‘civil clubs’ sprung up where students trained on gliders under the supervision of WW1 veterans. By the mid-late 1920s, the young brothers, heavily influenced by Alexander Lippisch began experimenting with tailless gliders. Their recollections in later life mention they turned their bedroom, attic & basement at home into a workshop, cluttering their family home in Bonn with airplane models. The home based experimentation was important to their later productions. Their gliders were simple tailless constructions with a cocoon for a pilot integrated into the design. The models focussed on keeping parasitic drag (all objects experience drag through the air) down and had better performance than conventional designs.

By 1931 the brothers had moved their activities to Bonn-Hangelar Field, a gliding club where they had access to mentoring, tools & materials from more experienced aviators. Their first full scale glider was the Horten H-I from 1931 and had a 40 foot wingspan, it was constructed of wood and fabric. The design integrated swept wings & elevons.

By the mid 1930s (1933-1937) the Hortens were further refining their designs at Wassekrupp, Germany’s Mecca of gliding. They too had support from the DFS and constructed their subsequent designs (Horten H-II – H-IV).

Each model kept growing in size. The H-II had a 52 foot wingspan while the H-III & H-IV each had a 80 foot wingspan. The materials used got better with funding from DFS, for example they began using plywood i.s.o fabric. The internal structure moved from wood on the initial models to steel and aluminum in later ones.

H-III was a motorized version which had a 32hp VW engine driving a foldable propeller. Model H-IV was a high performance pure glider.

The models exhibited a bell shaped lift distribution curve across the wing. It is higher near the wing root and tapers off near the wingtips with a smooth non linear profile. This sort of lift balances efficiency & stability and is essential for gliders with no engine to compensate for inefficiencies. The non-linear curve is important as the bell has a flatter peak and falls off at the tips, meaning optimal lift is maintained for longer.

The gliders achieved this with swept wings of up to 30 degrees, the wingtips had washout built into them and had variable chord, meaning they tapered toward the wingtips from the wing roots. An example of this lift efficiency is when the H-III achieved flights as long as 300 km.

Reimar Horten’s focus on lift distribution gave their designs a glide ratio of 30:1 i.e they could glide thirty times their height in distance. The focus on lift distribution is also one of the possibilities of the Ho-229’s ‘ stealth properties’ which we speak of later. Ludwig Prandtl was the scientist credited with presenting the concept of spanwise lift distribution in 1919 , Reimar Horten adapted Prandtl’s insights fifteen years later.

The H-V (1937-1943) was an exception to the materials the Horten brothers used for their gliders. They used experimental plastics. The H-V is considered the very first composite materials aircraft, however the first prototype crashed on its very first flight and Hortens reverted to wood as their material of choice. The H-V had a 46 foot wingspan and was powered by two 79 hp Hirth HM 60 R engines from the mid 1920s, powering pusher propellers. Specs gleaned from wikipedia showed the H-Vb(the second of three built) had a cruise speed of 230 km/h and a landing speed of 70 km/h.

It is just about here we observe the iterative design approach the Hortens took. They alternated each glider model with a motorized version, the H-III had a motor as did the H-V, H-VII & H-IX.

The H-VI (1944) reverted back to pure glider form after the learnings from the H-V and had significant design improvements such as a very high aspect ratio of 32.4 and a 80 foot wingspan. The wings had a sweep back of 20 degrees. The refined control surfaces were drawn from H-V data. The model had extensive stall behavior examination using tuft tests done on it. A tuft test is where strings of yarn (tufts) are attached to the entire wing surface and the aircraft is tested either in a wind tunnel (or in the Hortens case in flight). Attached airflow shows the tufts align smoothly with the laminar airflow. Separated flow is when the tufts begin to flutter erratically. Using this test is important to identify stall onset, control effectiveness, drag data & tip stall mitigation.

The H-VII(1944) was once again the H-V under a new guise. It was powered by two 240 hp Argus AS 10C engines. The V8s powered propellers once again in pusher configuration. The pilot seating was side by side vs the H-Vs semi prone position. Key increments included better control surfaces (elevons, spoilers & drag rudders) and in general a more robust internal structure for longer operations.The H-VII had a cruise speed of 300 km/h and service ceiling of over 21,000 feet. (source wikipedia).

The H-VIII(1945) was an upscaled version of the H-VII. It was sold incomplete to the RLM (ReichsLuftahrtMinisterium a.k.a Ministry of Aviation). It had a 131 foot wingspan and was powered by six pusher propeller engines. Each Argus 10 engine developed 236 hp. It represented a clear step in the direction of military applications and was expected to have a 1000 km bombing radius. The incomplete aircraft was destroyed by the Allies.

The H-IX v3 or the Ho-229 was the aircraft that is responsible for the Horten legend. When the allies got to the Gotha factory they found an aircraft unlike any other they had seen. It had bat-like wings and jets for engines (largely unknown then). The H-IX was a direct evolution of the H-V & H-VII designs. It was powered by two Junkers Jumo 004 turbojet engines buried inside the wings. Each of the engines generated 1990 lbs of thrust. The H-IX had a 55 foot wing span and the wings had a 32 degree sweep. It could fly at 977 kmph and had a service ceiling of 49,000 feet. This aircraft was beyond anything the Allies had to offer in terms of speed and agility.

The tailless wing at such speeds did throw up control related challenges, and in the era before fly by wire computers the aircraft had as many as eight control surfaces for the pilot to manage. The aircraft had a total of four elevons (two per wing), two drag rudders (one per wing) to induce yaw, and two speed brakes to control dives (also known as dive rudders). The v3 was the third in the series after the v1 & v2 and is the only surviving example of the H-IX/Ho-229.

Jack Northrop

Northrop began his aviation journey as a young man in 1916 with the Loughead Aircraft Manufacturing Company. As a mechanical draftsman & engineer, during his first stint there (1916-17) he worked on multiple aspects of the F-1 flying boat. Importantly his work focussed on light weight and high strength structures which would further fuel his focus on efficiency.

By 1917 he was drafted into the US Army where he served as an infantryman, however he quickly transferred to the Signal Corps to analyse Curtiss flying boats. In 1918 Loughead secured his return from the army where he continued his aviation career co-designing the Loughead S-1 a small sports plane that used moulded plywood construction and was known for its drag reducing streamlined fuselage.

Between 1926-28 after stints with Douglas Aircraft, Jack Northrop rejoined Loughead Aircraft (soon to be Lockheed) as chief engineer and designed the Lockheed Vega made famous by Amelia Earhart and her 1932 Transatlantic solo flight. The Vega was known for its low drag coefficient of 0.02. His work on the Vega further refined his expertise and focus on lightweight aerodynamic airframes, contributing to his future work on flying wings.

In 1928 Jack Northrop founded the Avion Corporation focussed on developing all metal aircraft with tailless designs and by 1929 he built the Avion Experimental No 1 (Northrop Flying Wing a.k.a X-216H). While it was a flying wing, Northrop retained a twin tail boom, this was for added safety during testing (wings were still being understood). The wing was made of aluminium and was of stressed skin multi cellular construction. Such constructions distribute loads across the entire wing while reducing weight and maintaining structural integrity. The wing demonstrated low Cd of 0.015 but suffered from pitch and yaw instability. Aircraft company consolidation meant that Avion Corporation was acquired by William Boeing as part of UATC (United Aircraft Transport Corporation) and was renamed Northrop Aircraft. At the time Jack Northrop designed the Alpha, a conventional low wing monoplane mail carrier.

Around 1931 the depression played a major role with Jack Northrop and UATC merged Northrop Aircraft with Stearman in Wichita, Jack Northrop refused to relocate and quit. In 1932 with the backing of Donald Douglas, Jack Northrop founded the new Northrop Corporation as a Douglas subsidiary. He developed the Beta, a faster variant of the Alpha and Gamma between (1932-34). The Gamma was a 700 hp mail & research plane. The most famous was the ‘Polar Star” that was transported via ship to Antarctica. This was followed by the Delta which was intended for passengers, however regulations prohibiting single engined aircraft from carrying passengers at night or over rough terrain curtailed this aircraft. Technically it was a success.

Further to these aircraft Northrop’s multicellular wing design greatly influenced the legendary DC-3. By 1937 Douglas was acquired once again and Northrop who yearned freedom to chase his wing designs quit once again and founded the Northrop Aircraft Inc in Hawthorne California.

The N-1M(1940-41) made its first flight in 1940 as Northrop’s first flying wing. It had a 38 foot wingspan and two 65hp Lycoming O-145 pusher prop engines. The skin was laminated wood around a tubular steel frame. It had an adjustable wingtip with a 15 & 30 degree vertical sweep. Its glide ratio was 15:1 and it proved tailless flight stability.

In 1941 the USAF was looking for a new bomber and authorized Northrop to develop the YB-35 flying wing bomber. As a first step Northrop developed the N-9M(1942-45) a one third scale flying wing with a wingspan of 60 feet and two 400 hp O-540 engines. The aircraft had automatic trim, split flaps & drag rudders which were an improvement over the N-1Ms manual controls. The first airframe crashed in 1943 killing the pilot, the reason being pitch control failure, which prompted redundancies to be built into later aircraft. The aircraft had a cruising speed of 320 km/h and a service ceiling of over 21,000 feet with a glide ratio of 18:1. The numbers validated full scale construction of the XB/YB-35.

The YB-35 Dimensions. Pic source : Wikipedia.

With a wingspan of 172 feet and four contra rotating pusher props the X/YB-35 was a majestic sight. The aircraft used four Pratt & Whitney R-4360 radial engines. The contra rotating gear boxes caused excessive vibrations leading to mechanical failure and stress. The engines & propellers were owned by AAF ( United States Army Air Force) . None in the supply chain had checked the engines for compatibility with the Hamilton Standard propellers, furthermore nobody took responsibility for the shortcomings either. The XB-35 flew a total of 27 flights between the two aircraft and only one flight was deemed satisfactory. Of the 14 YB-35s built only one was completed and that flew a total of seven flights for a total of less than ten hours. The YB-35 continued to be plagued by the same engine problems that plagued the XB-35. Reverting the engines to single propellers resulted in the aircraft being underpowered resulting in low speed handling issues.

Jack Northrop grew frustrated with the engines and attempted corrections, however he had severe limitations as the engines and propellers were owned by the AAF. In the meantime the AAF had turned its attention to jets and ordered two of the YB-35s converted to the jet engined YB-49. By 1948 the troubled YB-35 was terminated, never reaching fruition for reasons beyond its control.

The YB-49 had eight Allison J-35-A-15 turbojet engines, each developing 4000 pounds of thrust.The aircraft immediately hit 40,000 feet and cruised at 587 km/h (wikipedia), however with eight engines instead of four the range effectively dropped to half the YB-35. While the specifications were the same, the YB-49 did have four small passive vertical fins on the wings to help with yaw control. The two wings completed approx 25 flights between them, however both crashed in 1948 & 1950 the first killing all its crew including Captain Glen Edwards after whom Edwards AFB is named.

One more YB-35 was converted to a YB-49A reconnaissance aircraft (with podded engines) however this was never completed either.

Jack Northrop’s dream project was abruptly cancelled in 1950. Northrop himself was deeply anguished to see his dream cancelled and retired in 1952. In 1979 Northrop mentioned the Flying Wing contracts were cancelled because he refused to merge with Convair. Hindsight shows the flying wing program was way behind execution deadlines and over budget, hindsight also shows there was always a place for the flying wing. Alas that was not to be and all the wings were scrapped and none exist today.

The Story of WW2 Stealth Myth vs Reality

The Indiana Jones style discovery of the Ho-229 v3 deep in the German countryside inside a dark deserted hangar created the myth. The fact it looked like no other plane before and was referred to as the batwing only added to the myth, the jet engines solidified it.

The aerodynamic properties of flying wings naturally make them stealthy. The glide ratios of all the powered wings (including the YB-35 & 49) had ratios in the range of 20-28:1 . This compares favorably with the B-2 which has a similar ratio. Physics dictates that all flying wings will look similar and flying wings through the decades attest to this.

The wings were built for speed, their aerodynamics being the enabler. This meant the speed of the Ho-229 was over 75% faster than convention fighters of the time.

The controversial 2009 Nat Geo documentary with Northrop Grumman where a representative replica was made and subjected to RCS tests, showed a 20% decrease in the RCS (Radar Cross Section) properties over conventional aircraft of the time. This combined with the speed of the Ho-229 / H-IX v3 is what would have made the aircraft difficult to counter. Point to note in the documentary was the Northrop Grumman team had difficulty replicating the complex aerodynamic surfaces of the original wing.

A step back from the Horten story tells you this was incomplete. The incomplete H-VIII which was delivered to the Ministry of Aviation highlights the state Germany was in and the increased pace of aircraft iterations (1943-45) along with the H-XVIII Amerika Bomber being just plans on paper point to the incomplete story (much like Northrop’s).

Reimar Horten’s 1983 claim in the book ‘ Nurflugel” about planning for the v3’s successors to be stealthy by mixing carbon in the binding elements & painting the aircraft with graphite sounds opportunistic in view that no hard evidence or documentation was ever found. The Ho-229 did not exhibit any carbon in its adhesives conclusively. The timing of the claim ties in well with the announcement of the B-2 Stealth bomber, and Reimar who for all his achievements was fading into insignificance perhaps wanted to make the best of the reflected glory and renewed interest in the Ho-229. This is the reality.

History finds stories like the Ho-229 irresistible, and there lies the fable.

The B-2 Spirit

By the 1970s military designers were chasing the concept of Stealth. Low RCS is achieved by a cross section of materials, aerodynamic design, electronics & of course masking engine thermal signatures & sound.

By 1979 Northrop’s Tacit Blue program had already proved that stealth was possible and the technology was incorporated in the B-2.

During the 1981 presidential race Ronald Reagan repeatedly dug into Jimmy Carter and his cancellation of the B-1A bomber. In response to this Carter on August 22nd 1980 disclosed the Department of Defence was working on the B-2.

While the development was a black program, the B-2 was less closely guarded than the Lockheed F-117 stealth fighter. The unveiling of the B-2 in 1988 was highly restricted. At least two Northrop employees went to prison for espionage during and after its development.

The B-2 dimensions. Pic source : Wikipedia.

That the wingspan of the B-2 is 172 feet, the same as the YB-35/49 is perhaps a happy co-incidence, however its capabilities are entirely intentional. Its cruise speed is 1010 km/h, range is 11,000 km, and service ceiling of 50,000 feet the numbers are very similar to the Ho-229/YB-49 (except range).

The control issues all the flying wings faced dissipated as computers took over the pilot’s work load and made continuous split second corrections for stable flight.

A very old Jack Northrop was shown a model of the B-2 a few months before his passing in 1981 and he poignantly commented “ I now know why God kept me alive for the last 25 years”.

The B-21 Raider had its first flight in Nov ’23. While it is smaller than the B-2 , it remains just as exciting.

Epilogue

In the centre of the Udvar- Hazy hall at Smithsonian sits the H-IX / Ho-229 v3. Everyday hundreds of spectators file past its still figure as if paying homage. The aircraft that launched a thousand dreams continues to do so.