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North American X-15
Here is my interpretation of the North American X-15 hypersonic aircraft. It is built to minifig scale and has many articulating features. In the images that follow, I’ve represented the variants of the three production aircraft. As always, leave a comment if you wish. The LDD model of the X-15 variants is available on my Etsy site: <a href="http://www.etsy.com/ca/shop/KurtsMOCs" rel="nofollow">www.etsy.com/ca/shop/KurtsMOCs</a>.
About this creation

The North American X-15 is a hypersonic rocket-powered aircraft operated by the United States Air Force (USAF) and the National Aeronautics and Space Administration (NASA) as part of the X-plane series of experimental aircraft. The X-15 set speed and altitude records in the 1960s, reaching the edge of outer space and returning with valuable data used in aircraft and spacecraft design. The X-15’s official world record for the highest speed ever recorded by a manned, powered aircraft, set in October 1967 when Willian J. Knight flew Mach 6.72 at 102,100 feet (31,120 m), a speed of 4,520 mph (7,274 km/h), has remained unchallenged today.

This image shows the first X-15 produced (serial 56-6670) as it undergoes initial testing with North American Aviation (NAA) Inc. The early X-15 aircraft are distinguishable by the extended fuselage coverings for the XLR11 liquid-propellant rocket engines and the nose air data probe. The first two X-15s (serials 56-6670 and 56-6671) were equipped with the interim XLR11 rocket motor, the same used on the earlier Bell X-1, and grouped into two clusters of four motors providing a total of 16,000 pounds-force (71 kN) of thrust. The XLR11 engine was not throttleable but each chamber could be turned on and off individually. The XLR11-powered X-15s made 24 powered flights before being replaced by the more powerful and fully throttleable XLR99 rocket engine, which produced 57,000 pounds-force (250 kN) of thrust.


The X-15 was based on a concept study from Walter Dornberger for the National Advisory Committee for Aeronautics (NACA) for a hypersonic research aircraft. The requests for proposal were published on 30 December 1954 for the airframe and on 4 February 1955 for the rocket engine. Two manufacturers built the X-15: North American Aviation was contracted for the airframe in November 1955, and Reaction Motors was contracted for building the engines in 1956.

The X-15 fuselage was long and cylindrical, with rear fairings that flattened its appearance, and thick, dorsal and ventral wedge-fin stabilizers. Parts of the fuselage were heat-resistant nickel alloy (Iconel-X 750). The retractable landing gear comprised a nose-wheel carriage and two rear skids. The skids did not extend beyond the ventral fin, which required the pilot to jettison the lower fin just before landing. The lower fin was recovered by parachute.

The X-15 had a thick wedge tail to enable it to fly in a steady manner at hypersonic speeds. This produced a significant amount of drag at lower speeds; the blunt end at the rear of the X-15 could produce as much drag as an entire F-104 Starfighter. Side panels that could be extended from the tail to increase the overall surface area aided stability at hypersonic speeds, while also doubling as air brakes on landing.

In this image, the X-15 undergoes Phase 1 testing with NAA’s own test pilot Scott Crossfield at the controls. The X-15 test program was divided into nine phases. Phase 1 of the X-15 program schedule involved basic aircraft system and XLR-11 engine demonstrations by North American Aviation and its test pilot Scott Crossfield. Phase 2 was a series of customer flights by government test pilots would evaluate the aircraft with the interim XLR-11 engines. Phase 3 ran parallel to Phase 2 and would qualify back-up pilots (Peterson, McKay, Rushworth, and Armstrong). Phase 4 was a manufacturer demonstration of the capabilities of the more powerful XLR-99 rocket motor. Phase 5 was the government demonstration of flight capabilities with the new engine, taking over flight activities from the contractor. Phase 6 was the demonstration of the MH-96 flight control system to check it out on the X-15-3 for further capabilities within the flight envelope of the aircraft. Phase 7 ran the research program that would take the aircraft to its limits and present the X-15 to the high-altitude and high-speed flight regimes for which it had been designed. This phase would stretch its performance to provide a predictable set of flight capabilities for Phase 8. Phase 8 applied the aircraft to a series of scientific experiments, using the X-15 as a carrier and as a platform rather than as an experimental tool in its own right. Phase 9 was unplanned at the beginning of the program and resulted from the near catastrophic accident involving X-15-2, after which it was returned to NAA for a rebuild. During that time, and at the behest of the Air Force, it was extended in length and given extended burn duration for an attempt to get close to Mach 8.


Three X-15s were built, flying 199 test flights, the last on 24 October 1968. The first X-15 flight was a captive-carry unpowered test by Scott Crossfield on 8 June 1959. Crossfield also piloted the first powered flight on 17 September 1959 and his first flight with the XLR-99 rocket engine on 15 November 1960. Twelve test pilots flew the X-15, among them were Neil Armstrong, later a NASA astronaut and first man to set foot on the Moon, and Joe Engle, later a commander of NASA Space Shuttle test flights.

There would be three kinds of flights: speed, altitude, and heating. For speed flights, it was NACA practice to increase speed by one half Mach number for each successive flight. For altitude flights, the pilots continued upward at a fairly steep angle and wither continued to engine burnout or shut the engine down at a predetermined speed or altitude. They would spend two to five minutes out of the atmosphere in a weightless condition and when above 200,000 feet, the aerodynamic controls had no effect. Pilots had to use the reaction control system for attitude control. Heating flights to test the effects of aerodynamic heating in hypersonic flight demanded the most piloting precision, especially in holding a precise angle of attack. These flights would be done at altitudes around 80,000 to 90,000 feet, at high speeds, and usually continued until engine burnout.

Each flight of the X-15 lasted around ten minutes but the flight would cross three states: Utah, Nevada, and California. NACA and the Air Force selected a test range beginning in Wendover, Utah and ending at Rogers Dry Lake that overflew a series of dry lakebeds that could be used for emergency landings. If the X-15 were able to reach maximum speed or maximum altitude, it would be able to glide 400 miles to Edwards for landing.

In this image, Neil Armstrong brings the X-15-1 back to Edwards after completing Flight 064 where he took the X-15 to Mach 5.74 and an altitude of 98,900 feet. Landing the unpowered X-15 involved entering a spiral descent from 28,000 feet at either a 30-45 degree bank. Here you can see the new XLR99 engine in place. X-15-1 was refitted with the new engine and was back for testing on June 10, 1961.


Scott Crossfield made the first powered flight of the program, reaching a tentative Mach 2.11. On his third flight on 5 November 1959, Crossfield dropped away from the B-52 and began the ignition sequence at which point one of the XLR-11 chambers exploded. Having to make an emergency landing, the aircraft was still heavy with propellant and came down hard, breaking the fuselage just behind the cockpit. The aircraft was sent back to NAA and repaired in 30 days, Back at Edwards on 11 February 1960, the aircraft flew several more flights before being sent back to NAA in September that same year for an engine upgrade to the XLR99.

Designing and building this model was challenging. There are several excellent Lego X-15 models out there and I didn’t want mine to be derivative. I strove to keep the proportions as close to the original design as possible, but to have functional landing gear, flaps, etc. meant sacrificing some aspects of the design, especially the nose and cockpit. In this image, you can see the slender lines of the aircraft as it streaks into the upper atmosphere.


The third aircraft arrived at Edwards on 29 June 1959 with no engine. Delays in the XLR99’s development meant the aircraft would not begin test flights until the “Million-Horsepower Engine” was installed and tested. By 2 June 1960, Crossfield began ground testing. On 6 June 1960, a frozen regulator caused the motor to explode, which sent the forward section of the aircraft 30 feet further along the test area and left the smouldering motor section secured to the stand. Dazed but unhurt, Crossfield was pulled from the cockpit and the fuselage remains were sent back to Downey for repairs. The first flight was on 20 December 1961, with Neil Armstrong at the controls.

In this image, US Air Force test pilot Major William “Pete” White takes the X-15-3 to 314,750 feet and a speed of Mach 5.45 on Flight 062 on 27 July 1962. In July and August 1963, pilot Joseph A Walker exceeded 100 km in altitude, joining NASA astronauts and Soviet cosmonauts as the first human beings to cross that line on their way to outer space. The USAF awarded astronaut wings to anyone achieving an altitude of 50 miles (80 Km), while the Federation Aeronautique Internationale (FAI) set the limit of space at 100 km (62.1 miles).


Like many X-series aircraft, the X-15 was designed to be carried aloft and drop-launched by a carrier aircraft. Several large planes were considered, such as the Convair B-36 Peacemaker and the Convair B-58 Hustler, but it was the Boeing B-52 that was coveted because of its lifting capacity and high airspeed. Unable to secure the X-15 in its bomb bay, the rocket-powered plane was hung from a pylon under the B-52’s massive wing. NACA secured two early B-52A production aircraft from the Air Force: NB-52A, “The High and Mighty One” (serial 52-0003, or “Balls 3”), and NB-52B, “The Challenger” (serial 52-0008, or “Balls 8”) served as carrier planes for all X-15 flights. The B-52s would climb to altitude in large circles. The release took place at an altitude of about 8.5 miles (13.7 km) and a speed of about 500 mph (805 km/h).

The X-15 pilot would enter the aircraft while it was on the ground with no other means of egress to the mother ship. The pilot would have to wait one and a half hours to reach altitude. While most flights went as planned, any malfunction would cause the mother ship to return to Edwards, making for a very long trip in a very small cockpit for the test pilot. Test pilots could also eject from the X-15 while it was attached to the B-52 in an emergency.

In this image, X-15-1 is carried to its drop point by NB-52B “Balls 8.” In order to fit the X-15 under the wing, a small trailing edge cutout was required to the starboard inboard flap and part of the wing. During the drop, the X-15 pilot had to keep the aircraft within a 20-degree roll to prevent the vertical stabilizer contacting the starboard wing.


The X-15 used a series of chase planes to monitor the X-15 during all phases of its flight. These aircraft would monitor the X-15 while attached to the B-52, monitor as much of the powered flight as possible, help coach the X-15 pilot to an emergency landing site, and coach the pilot during normal landing at Edwards. Chase 1, usually an F-100, would stay with the B-52 during prelaunch of the X-15. An F-104 was used for all other flights. Chase 2 would try to keep up with the X-15 upon launch and stay with it in the event of an emergency landing. Chase 3 would cover emergency landings at intermediate emergency landing sites. Chase 4 provided landing assistance at Edwards and Chase 5 was a second intermediate chase aircraft for long high altitude flights.

The Starfighter was favoured because of its speed and flight characteristics. Test pilots trained in the F-104 because of its similar handling characteristics. They would normally make 75-100 landings in the F-104 before each X-15 flight. These landings would be accomplished with flaps down and the engine at idle. This would closely simulate the X-15’s performance on landing.

X-15-3 glides in for a perfect landing at Edwards under the watchful eye of an accompanying F-104N. This F-104N is based on Henrik Jensen’s marvellous F-104; he graciously allowed me to use it for this image (thanks, Henrik!). The X-15 used a nose wheel and rear ski strut landing gear configuration. Getting the nose gear to function at this scale was a real challenge. Also, just seconds before landing, the X-15 would jettison the bottom section of the lower ventral stabilizer to make clearance for the ski struts. This section would parachute to the ground and recovered for future use. After 1962, the lower ventral fin was removed for good as it improved the handling characteristics of the aircraft during high altitude/high angle of attack re-entry flights.


The first serious crash of the program occurred on 9 November 1962. After dropping from the B-52 over Mud Lake, Nevada, NASA pilot Jack McKay advanced the XLR99’s throttle but found it unresponsive beyond 30% power. Unsure he could make it back to Edwards, McKay elected to make an emergency landing at the launch lake and although he jettisoned some propellant, the X-15 was still heavy as he lined up for landing. To compound the situation, the flaps failed to deploy and the aircraft came in faster and heavier than usual. After touching down, one of the aircraft’s main gear struts failed, causing the wing tip to dig into the lakebed and send the aircraft rolling. McKay had jettisoned the canopy knowing he may need to get out quickly, but as the aircraft rolled to a stop inverted, his head impacted the lakebed causing serious injuries and complicating attempts to get him out of the stricken vehicle. The remains of X-15-2 were returned to North American Aviation.

The aircraft was rebuilt as the X-15A-2 and became the fastest X-15 flown. The aircraft was lengthened by 2.4 feet (73 cm), had a pair of auxiliary fuel tanks attached beneath its fuselage and wings, and a complete heat-resistant ablative coating was added. The plane took flight for the first time on 28 June 1964 with Bob Rushworth at the controls. It reached its maximum speed of Mach 6.7, or 4,520 mph (7,274 km/h) on 3 October 1967 with pilot Major William “Pete” Knight on the U.S. Air Force in control. In this image, Knight takes the X-15A-2 to an altitude of over 100,000 feet. The large propellant tanks would be jettisoned after the propellant had been expended and parachute to the ground.


One of the major redesign considerations of the X-15A-2 was that it would become a test bed for the experimental hydrogen-fueled, air-breathing scramjet engine that would push the aircraft to Mach 8. The 28-inch fuselage extension allowed for the inclusion of the scramjet’s liquid hydrogen tank. The external drop tanks carried 1,800 gallons of propellant that would extend the burn duration of the XLR99 from 90 seconds to 150 seconds.

Flights to Mach 8 necessitated a very different form of heat insulation that after considerable deliberation was a special ablative coating that would ‘burn’ away and remove the heated material. The MA-25S ablative coating was applied to a scrubbed down and extensively cleaned fuselage and then covered in a protective coating of white Dow DC90-090 aerospace sealant. The new, all-white aircraft was devoid of any national markings.

Also, a new elliptical cockpit window was installed. The ablative coating caused a problem for the pilot as residue would collect on the canopy windshield and obscure his vision. To combat this, the left-hand pane was fitted with a mechanical “eyelid” which could remain closed until the speed run had been completed. At this point, it would be opened and provide the pilot at least one clear window to use for approach and landing. The eyelid caused its own problems as when open, it generated a small canard effect, causing the aircraft to roll slightly.

In this image, X-15A-2 powers up for a high-speed run. Tests were conducted with a dummy scramjet in place to test handling characteristics.


Phase 9 of the X-15 program pushed the X-15A-2 beyond what it was designed to achieve. The structure needed heat protection and the addition of the external tanks and scramjet altered the flight characteristics of the aircraft. During deceleration on Knight’s fastest flight on 3 October 1967, he made a number of stability and control evaluation pulses to test the dynamics of the airplane/scramjet combination. Heating was so severe on the ventral fin from shock waves from the scramjet that much of the fin’s leading edge was burned away and the explosive bolts fastening the scramjet overheated and voluntarily fired, jettisoning the dummy engine. If any more of the fin had burned away, it would have made the aircraft uncontrollable. The ventral fin was repaired but the aircraft never flew again.

For the X-15A-2 variant, I changed the design of the canopy. This design is more faithful to the original design but lacks the correct profile. I thought it might be interesting to see the differences and highlight the design decisions Lego builders are confronted with. I usually go through several iterations and revisions before settling on the final design. Sometimes, I choose function over form and at other times the reverse it true. These are the choices that make one’s work unique.


In the late 1960s, the X-15 program was reaching its end. With most of the high speed/high altitude testing completed, the X-15 was now being used for high altitude scientific research, as part of its Phase 8 commitment.

Sadly, on 15 November 1967, U.S. Air Force test pilot Major Michael J. Adams was killed during X-15 Flight 191 when X-15-3 (serial 56-6672) entered a hypersonic spin while descending, then oscillated violently as aerodynamic forces increased after re-entry. As his aircraft’s flight control system operated the control surfaces to their limits, acceleration built to 15 g (150 m/s2) vertical and 8.0 g (78 m/s2) lateral. The airframe broke apart at 60,000 feet (18 km) altitude, scattering the X-15’s wreckage for 50 square miles (130 km2). Major Adams was posthumously awarded Air Force astronaut wings for his final flight in X-15-3, which had reached an altitude of 50.4 miles (81.1 km).

In this image, X-15-1 returns from a scientific experiment flight. Note the wingtip pod designed to carry a variety of scientific experiments. X-15-1 and X-15A-2 were also modified to carry onboard telescopes and sensory devices. The pick-up truck is based on one of Makaleves excellent Lego vehicles.


The 200th flight over Nevada was first scheduled for 21 November 1968, to be flown by Willian “Pete” Knight. Numerous technical problems and outbreaks of bad weather delayed this proposed flight six times, and it was permanently cancelled on 20 December 1968. This X-15 was detached from the B-52 and then put into indefinite storage. The aircraft was later donated to the Air Force Museum at Wright-Patterson Air Force Base for display.

This is a cutaway image showing the internal structure of my X-15 design. Unfortunately, I wasn’t able to get a functioning cockpit for a minifig into the design. Perhaps in the future, I’ll be able to remedy this issue!


Thanks to Wikipedia, David Baker’s “North American X-15 Owner’s Workshop Manual,” and David Boslaugh’s excellent and thorough account of the X-plane program website “First-Hand: The Experimental Research Airplanes and Sound Barrier.”



Comments

 I made it 
  October 20, 2018
Quoting Szilard Pauler Hi!That's all very fine and gratulations.
Thanks, Szilard!
 I made it 
  October 20, 2018
Quoting Michael Cichonsky Perfect! I've been looking for a bigger plane to build, working on a B-17 now! Just did a microscale B52 but would love to do a larger version!
Thanks, Michael. I’m glad you like the model. The BUFF is on its way. Stay tuned!
 I like it 
  October 20, 2018
Hi!That's all very fine and gratulations.
 I like it 
  October 18, 2018
Perfect! I've been looking for a bigger plane to build, working on a B-17 now! Just did a microscale B52 but would love to do a larger version!
 I made it 
  October 15, 2018
Quoting Michael Cichonsky Where is the MOC for the B-52?! Thats the one I'm looking for! Great job on the X-15, even with some of the small variations to add in the working gear.
The BUFF is on its way, Michael! Stay tuned for that one because it will be a big post and is taking a long time to prepare.
 I made it 
  October 15, 2018
Quoting Marty Fields Brilliant work again, Kurt. Great write-up and attention to detail.
Thanks, Marty. I appreciate the continued support and I'm glad you like the model.
 I like it 
  October 15, 2018
Where is the MOC for the B-52?! Thats the one I'm looking for! Great job on the X-15, even with some of the small variations to add in the working gear.
 I like it 
  October 15, 2018
Brilliant work again, Kurt. Great write-up and attention to detail.
 I made it 
  October 14, 2018
Quoting Gabor Pauler I can see that it was big battle with the scaling to match it with your B-52. Still you could solve wings and engine part marvelously.
Thanks, Gabor. The X-15 model emerged from my work on the BUFF (coming soon). I thought about using someone else's design but I decided to take on the challenge myself. I'm glad you like the model.
 I like it 
  October 14, 2018
I can see that it was big battle with the scaling to match it with your B-52. Still you could solve wings and engine part marvelously.
 I made it 
  October 14, 2018
Quoting BATOH rossi great job Kurt! as always, the presentation and documentation would be the envy of Wikipedia!
Thanks, BATOH. I'm glad you like the model.
 I like it 
  October 13, 2018
great job Kurt! as always, the presentation and documentation would be the envy of Wikipedia!
 I made it 
  October 13, 2018
Quoting killswitch95 (Last Name is Dank AF) The best plane we ever made. Make American Planes Great Again...
Thanks, killswitch!
 I like it 
  October 13, 2018
The best plane we ever made. Make American Planes Great Again...
 I made it 
  October 13, 2018
Quoting Clayton Marchetti I’ve always loved this x plane since my first visit to the Air and Space musume in DC. Funny I built a model of this, but not in Lego. Maybe one of these days. This is fantastic. Love the internal view too. And as always all the background information you provide along with it. Magnificent!
Thanks, Clayton! I'm glad you like the model and the narrative.
 I like it 
  October 13, 2018
I’ve always loved this x plane since my first visit to the Air and Space musume in DC. Funny I built a model of this, but not in Lego. Maybe one of these days. This is fantastic. Love the internal view too. And as always all the background information you provide along with it. Magnificent!
 I made it 
  October 13, 2018
Quoting Tom's MOCs Another excellent product, Kurt. Thanks for including so many interesting details of plane's history. I would enjoy a few close-up pix of certain features in your MOCs such as the cockpits, landing gear, and similar dynamic features, because they help others like me with ideas for building techniques. I wonder if you can point to a reference on how to superimpose letters/numbers on the Lego elements, because they retain a real-life orientation as the pieces are viewed from different perspectives. Again: well done.
Thanks, Tom. I'm glad you like the model. I'll look into featuring some details of the design work in later posts. As for the livery, I add them all in Photoshop after taking a snapshot in LDD. I found some USAF-style fonts online and use them for the text; the rest of the imagery (rescue notices, warnings, ejection seat triangles) I create myself. I'm sure you can print these off and affix them to real models, as other builders have. Good luck with your building!
 I like it 
  October 13, 2018
Another excellent product, Kurt. Thanks for including so many interesting details of plane's history. I would enjoy a few close-up pix of certain features in your MOCs such as the cockpits, landing gear, and similar dynamic features, because they help others like me with ideas for building techniques. I wonder if you can point to a reference on how to superimpose letters/numbers on the Lego elements, because they retain a real-life orientation as the pieces are viewed from different perspectives. Again: well done.
 
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