Looked good on paper (X-planes)

[Arlo]

XB-53

The project was originally designated XA-44 in 1945 under the old "attack" category. An unusual forward-swept wing-design powered by three J35-GE turbojets, the project was developed in parallel with Convair's XB-46. The original design had a wing with a 12° forward-sweep and a solid nose section, but when the Army Air Force revamped the advanced attack aircraft requirement into a light bomber requirement in 1946, the aircraft was redesignated XB-53 and the wing redesigned with a 30° forward-sweep and 8° dihedral that was borrowed from German wartime research, but also a glazed nose section. The swept-forward configuration would give the aircraft a greater climb rate and maneuverability.[2][3] It looked promising enough at one point for the Army Air Force to consider canceling the XB-46 in favor of the XA-44, since there was not enough funding for both.[1]

Classified as a medium bomber, the XB-53 would have carried up to 12,000 pounds of bombs as well as 40 High Velocity Aerial Rockets (HVAR) mounted on underwing pylons.[1]

Convair argued for completion of the XB-46 prototype as a flying testbed, without armament and other equipment, and with the substitution of two XA-44s for the other two B-46 airframes on contract. The Air Force ratified this in June 1946 but the project did not progress, nor were additional B-46s built. The XB-53 program was reinstated in February 1949 but only for a short while.

https://en.wikipedia.org/wiki/Convair_XB-53

[Arlo]

Convair XF-92

In order to gain inflight experience with the delta wing layout, Convair suggested building a smaller prototype, the Model 7002, which the USAAF accepted in November 1946.[9] The design was strongly similar to Langley's later modifications to the DM1, using the smaller vertical surface, thinner wings, and a conventional cockpit. The main difference was to the stretch the fuselage rearward to provide room for the engine, leading to a conventional fuselage shape.[10]

In order to save development time and money, many components were taken from other aircraft; the main gear was taken from a North American FJ-1 Fury, the nosewheel from a Bell P-63 Kingcobra, the engine and hydraulics were taken from a Lockheed P-80 Shooting Star, the ejection seat and cockpit canopy were taken from the cancelled Convair XP-81, and the rudder pedals were taken from a BT-13 trainer.

Construction was well underway at Vultee Field in Downey, California when North American Aviation took over the Vultee plants in summer 1947. The airframe was moved to Convair's plant in San Diego, and completed in the autumn. In December it was shipped without an engine to NACA's Ames Aeronautical Laboratory for wind tunnel testing. After testing was completed, the airframe was returned to San Diego, where it was fitted with a 4,250 lbf (18,900 N) Allison J33-A-21 engine.[8]

By the time the aircraft was ready for testing, the concept of the point-defense interceptor seemed outdated and the (now redesignated) F-92 project was cancelled. They also decided to rename the test aircraft as the XF-92A.

https://en.wikipedia.org/wiki/Convair_XF-92

[Arlo]

Republic XF-12

The Republic XF-12 Rainbow was an American four-engine, all-metal prototype reconnaissance aircraft designed by the Republic Aviation Company in the late 1940s. Like most large aircraft of the era, it used radial engines—in this case, the Pratt & Whitney R-4360 Wasp Major. The aircraft was designed with maximum aerodynamic efficiency in mind. The XF-12 was referred to as an aircraft that was "flying on all fours" meaning: four engines, 400 mph cruise, 4,000 mile range, at 40,000 feet.[1] It is still the fastest piston-engined airplane of this[clarification needed] size, exceeding by some 50 mph the Boeing XB-39 of 1944.[2] Although highly innovative, the postwar XF-12 Rainbow was made obsolete by modern jet engine technology, and did not enter production.

https://en.wikipedia.org/wiki/Republic_XF-12_Rainbow

[Arlo]

XP-79

In 1942, John K. (Jack) Northrop conceived the XP-79 as a high-speed rocket-powered flying-wing fighter aircraft. In January 1943, a contract for two prototypes (s/n's 43-52437 & 43-52438) with designation XP-79 was issued by the United States Army Air Forces (USAAF).

Originally, it was planned to use a 2,000 lbf (8,900 N) thrust XCALR-2000A-1 "rotojet" rocket motor from Aerojet that used mono-ethylaniline fuel and red fuming nitric acid (RFNA) oxidiser.[1] However, the rocket motor configuration using canted rockets to drive the turbo-pumps was unsatisfactory and the aircraft was subsequently fitted with two Westinghouse 19B (J30) turbojets and re-designated XP-79B. After the failure of the rocket motor, further development of the first two prototypes ended.

To protect the pilot if the aircraft was damaged in combat the XP-79 was built using a welded magnesium alloy monocoque structure with a 0.125 in (3.2 mm) skin thickness at the trailing edge and a 0.75 in (19 mm) thickness at the leading edge.

The pilot controlled the XP-79 through a tiller bar and rudders mounted below; intakes mounted at the wingtips supplied air for the unusual bellows-boosted split ailerons.[2]

https://en.wikipedia.org/wiki/Northrop_XP-79

[noman]

So as I am not an engineer or any where near as smart as a lot of people here I have a question. As we don't see any forward swept wing design did they finally figure that was not very efficient? I see a lot of pictures of early designs like that but not anything newer with that design.

[Arlo]

Grumman X-29

The Grumman X-29 was an American experimental aircraft that tested a forward-swept wing, canard control surfaces, and other novel aircraft technologies. The X-29 was developed by Grumman, and the two built were flown by NASA and the United States Air Force. The aerodynamic instability of the X-29's airframe required the use of computerized fly-by-wire control. Composite materials were used to control the aeroelastic divergent twisting experienced by forward-swept wings, and to reduce weight. On 13 December 1985, an X-29 became the first forward-swept wing aircraft to fly at supersonic speed in level flight. The two X-29 aircraft flew a total of 242 times from 1984 to 1991.

https://en.wikipedia.org/wiki/Grumman_X-29

[Arlo]

Rockwell XFV-12

The Rockwell XFV-12 was a prototype supersonic United States Navy fighter which was built in 1977. The XFV-12 design attempted to combine the Mach 2 speed and AIM-7 Sparrow armament of the McDonnell Douglas F-4 Phantom II in a VTOL (vertical takeoff and landing) fighter for the small Sea Control Ship which was under study at the time. On paper, it looked superior to the subsonic Hawker Siddeley Harrier attack fighter. However, its inability to meet performance requirements terminated the program.

https://en.wikipedia.org/wiki/Rockwell_XFV-12

[Volron]

So as I am not an engineer or any where near as smart as a lot of people here I have a question. As we don't see any forward swept wing design did they finally figure that was not very efficient? I see a lot of pictures of early designs like that but not anything newer with that design.

https://en.wikipedia.org/wiki/Sukhoi_Su-47

1997



https://en.wikipedia.org/wiki/KB_SAT_SR-10

2015



These are the "newest" I'm aware of, and both Russian.

[mikeWe9a]

So as I am not an engineer or any where near as smart as a lot of people here I have a question. As we don't see any forward swept wing design did they finally figure that was not very efficient? I see a lot of pictures of early designs like that but not anything newer with that design.

It wasn't efficiency which kept the forward swept wing from being adopted, but stability and material science.  The forward swept wing had a tendency for the tips to twist during high lift, increasing the angle of attack and lift (unless the angle of attack caused a stall).  At higher speeds, this tendency could cause what was known as "divergence," in which the lift would increase uncontrollably to the point of material failure of the wing.  The speed at which this occurs is known as the divergence speed.  Since the reason for a swept wing was primarily for high speed performance, this was a critical issue.  Below this speed, the tip would stall prior to failure, but the stall was not easily predicted, especially as very minor differences in the flow would cause one wing to stall before the other.  The forward swept wing also suffered from many of the same issues of conventionally swept wings, such as a tendency for the aircraft to pitch up in a stall, and yaw instability.

Later, fly by wire control systems and advanced materials would allow forward swept wings to become more practical, but by then purely aerodynamic performance was becoming less important for a fighter, as radar and missiles had moved emphasis toward low observability and fire control (radar, etc) as factors for a successful fighter.

Mike

[Arlo]

Douglas A2D Skyshark

On 25 June 1945, the Bureau of Aeronautics (BuAer) asked Douglas Aircraft for a turbine-powered, propeller-driven aircraft. Three proposals were put forth in the next year and a half: the D-557A, to use two General Electric TG-100s (T31s) in wing nacelles; the D-557B, the same engine, with counter-rotating propellers; and the D-557C, to use the Westinghouse 25D. These were canceled due to engine development difficulties, but BuAer continued to seek an answer to thirsty jets.

On 11 June 1947 Douglas received the Navy's letter of intent for a carrier-based turboprop. The need to operate from Casablanca-class escort carriers dictated the use of a turboprop instead of jet power.

While it resembled the AD Skyraider, the A2D was different in a number of unseen ways. The 5,100-equivalent shaft horsepower (3,800 kW) Allison XT-40-A2 had more than double the horsepower of the Skyraider's R-3350. The XT40 installation on the Skyshark used contra-rotating propellers to harness all the available power. Wing root thickness decreased, from 17% to 12%, while both the height of the tail and its area grew.

Engine-development problems delayed the first flight until 26 May 1950, made at Edwards Air Force Base by George Jansen.

Navy test pilot Cdr. Hugh Wood was killed attempting to land the first prototype XA2D-1, BuNo 122988, on 19 December 1950, on its 15th flight. He was unable to check the rate of descent, resulting in a high-impact crash on the runway. The investigation found the starboard power section of the coupled Allison XT40A turboprop engine had failed and did not declutch. This meant the surviving engine was powering the failed engine's compressor, using up much of its available power. Additionally, the propellers failed to feather. As the wings' lift disappeared, a fatal sink rate was induced.

Additional instrumentation and an automatic decoupler was added to the second prototype, but by the time it was ready to fly on 3 April 1952, sixteen months had passed, and with all-jet designs being developed, the A2D program was essentially dead. Total flight time on the lost airframe was barely 20 hours.

Allison failed to deliver a "production" engine until 1953, and while testing an XA2D with that engine, test pilot C. G. "Doc" Livingston pulled out of a dive and was surprised by a loud noise and pitch up. His windscreen was covered with oil and the chase pilot told Livingston that the propellers were gone. The gearbox had failed, but Livingston successfully landed the airplane. The A4D was ready to fly by the summer of 1954, and the escort carriers were being mothballed, so that time had run out for the troubled A2D program.

Twelve Skysharks were built, two prototypes and ten pre-production aircraft. Most were scrapped or destroyed in accidents, and only one has survived.

https://en.wikipedia.org/wiki/Douglas_A2D_Skyshark

[Arlo]

RB-1/C-93

Built by the Budd Company (which built railroad passenger cars) as a transport, the RB-1 Conestoga. Constructed from stainless steel and by shotwelding, in order to save on aluminum. With an innovative cargo ramp under a raised tail, it could takeoff with a full load in under 1,000 feet. The Navy ordered 200 in 1943, and the Army wanted 600, designated the C-93. Delays in building, though, allowed the C-46 and C-47 production to catch up, and the Army cancelled its orders while the Navy only took 17. It never entered an operational squadron, and the 17 were retired from service in 1945. The War Assets Administration sold 12 to the National Skyway Freight Corp for scheduled air cargo flights. Three of them crashed, and the remainder were sold when the outfit, now called the Flying Tiger Line, sold them for C-47s.

posted on 'U.S. Naval Aircraft FB group':

https://www.facebook.com/photo?fbid=4928183860555578&set=gm.1230617663991734

[Arlo]

Tacit Blue

Built in the early 1980s in great secrecy, the revolutionary Tacit Blue aircraft tested advanced radar sensors and new ideas in stealth technology.

Tacit Blue proved that a stealthy aircraft could have curved surfaces -- unlike the faceted surfaces of the F-117 Nighthawk -- which greatly influenced later aircraft like the B-2. Tacit Blue’s design also minimized the heat signature emitted from the engines, further masking its presence. Tacit Blue was aerodynamically unstable, but it had a digital fly-by-wire system to help control it.

With its low, “all-aspect” radar signature, Tacit Blue demonstrated that such an aircraft could loiter over -- and behind -- the battlefield without fear of being discovered by enemy radar. Using advanced sensors, it could also continuously monitor enemy forces (even through clouds) and provide timely information through data links to a ground command center. Moreover, these sensors functioned without giving away the location of the aircraft.

The Tacit Blue aircraft flew 135 times before the program ended in 1985. The aircraft was declassified and placed on display at the museum in 1996.

A plaque mounted in the cockpit recognizes these Tacit Blue pilots:

Mr. Richard Thomas
Col. (Select) Don Cornell
Lt. Col. Russ Easter
Lt. Col. Ken Dyson
Maj. Dan Vanderhorst

TECHNICAL NOTES:
Crew: One
Engines: Two Garrett ATF3-6 high-bypass turbofan engines
Design operational speed: 287 mph/250 knots
Operating altitude: 25-30,000 feet
Weight: 30,000 lbs.

NATIONAL MUSEUM OF THE UNITED STATES AIR FORCE™

https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/195769/northrop-tacit-blue/fbclid/IwAR1EaCe-O41poNZGiZTVzKf4ygU4RvrL__KOysnp0C4MH11EDPqDl436Q3g/