Read It / Do It #01: North American X-15

Read It / Do It #01: North American X-15

By @BeachAV8R - May, 2015
Originally published at: Articles - Mudspike Forums

Take a ride in a marvel of aerospace engineering that helped pave the road to space with the hypersonic North American X-15 rocket powered research aircraft.

It’s long been a desire of mine to dig up the old “Read It / Do It” format that I used to write articles many years ago at another site. We briefly resurrected a similar format with an article a couple of years ago (View It / Do It: Cactus 1549) where we took a look at the movie “Sully” and gave readers a good look at how they could recreate the conditions that the Hudson Miracle aircraft faced. We hope you enjoy the return of the series.

The North American X-15

There is no real reason I should have a fascination with the X-15 project. The final X-15 flight occurred in October of 1968, a full three years before I was even born, so it wasn’t like it was a program that was present during my upbringing. But any student of aviation usually dives into the history of the field, and something about those early X series aircraft struck that romantic chord within me, and I became fascinated by the machines that engineers and scientists created, and the men who strapped into them to soar into the stratosphere. I’ve read nearly every book about the X-15 program that I could get my hands on - from the dry and somewhat analytical X-15 The NASA Mission Reports, to X-15 pilot Milton Thompson’s excellent and humorous At the Edge of Space: The X-15 Flight Program. Recently I stumbled upon a freely downloadable PDF written in 2008 by a renowned NASA contractor and space historian, Dennis Jenkins, who wrote what is very likely the most definitive history of the X-15 program to date. Sprinkled with incredible engineering insights, and humorous stories of pilots and engineers, the 644-page X-15: Frontiers of Flight is a fascinating read for those interested in the history of the X-15 project.

In my quest to try to accurately duplicate the performance and profiles of the X-15 flights, I dove into the books and detailed official NASA mission reports and took a ton of notes. While there are excellent X-15 add-ons available for FSX and P3D, my interest mostly rested with the intriguing X-15 that is included with the default X-Plane 10/11 install. With regards to systems, it is greatly simplified, and not at all realistic. But to my great surprise, with regards to performance, the X-Plane X-15 adheres closely to what the actual aircraft was capable of. Indeed, what I hoped would be a short and easy research phase for this article dragged on into months of tweaking the aircraft, asking for assistance from those with greater knowledge of X-Plane than I have, and basically pestering my way to the light at the end of the tunnel.

Basic X-15 records

From an engineering standpoint, the X-15 was wildly successful, proving many concepts and expanding knowledge on dozens of subjects, not the least of which were the thermodynamics of hypersonic flight. Heat would be a ever present challenge to engineers and pilots and hurdling each problem that came up is what makes up the bulk of Jenkin’s excellent history of the program. For the layperson - the X-15 stands out for its incredible achievements in both speed and altitude. On October 3, 1967, USAF pilot William Knight would pilot the X-15-A2 to its maximum achieved speed on flight #188 of 4,520mph, or Mach 6.72. Four years prior to that, in August of 1963, NASA pilot (USAF retired) Joe Walker took the X-15 to an altitude of 354,200’ - 67 miles high! The story of the flight envelope expansion period leading up to those flights is fascinating to read about.

The XLR11

The default X-Plane 11 (XP11) X-15 is equipped with the 57,000 lb. thrust Reaction Motors XLR99 engine that the aircraft was originally designed for. Early teething problems and development delays of the XLR99 resulted in the first twenty-four flights of the X-15 being conducted with a pair of vertically stacked XLR11 engines - the same engine that powered the X-1, X-1A, X-1B, and D-558-2. The first four flights of the X-15 were captive flights to test systems and connectivity with the B-52 carrying aircraft. Flight #005 was a gliding flight released over Rosamond Lake. Released at 37,550’ from the drop ship, the X-15 glided for 4 minutes and 54 seconds, touching down on the Edwards Dry Lake bed. The glide flight would be the shortest duration X-15 flight of the entire program.

The XLR11-RM-5 engines used on the first flights of the X-15 consisted of two motors with four rocket chambers in each motor for a total of eight chambers. Each chamber developed approximately 1,445 lbs. of thrust, for a total overall thrust of 11,800 lbs. On the first powered flight with the XLR11 engines, piloted by North American test pilot Scott Crossfield, the X-15 achieved Mach 2.11 and a maximum altitude of 52,341’. Over the course of the next year and twenty-four flights, the XLR11 would achieve a maximum speed of 2,196 mph (Mach 3.31) and a maximum altitude of 136,500’ - not bad for a stand-in engine setup. In November 1960, the XLR99 engine was first flown on flight #026 with a 137 second run time, pushing the X-15 to Mach 2.97 and 81,200’. Though the XLR99 was a throttleable rocket engine, the engineers and pilots, after several mishaps, agreed that by and large that the XLR99 should be run at a constant throttle setting to avoid problems encountered by altering the power setting.

In an effort to emulate the XLR11 performance, I modified the default X-15 by adding an XLR11 object graciously provided by JetManHuss. Using X-Plane’s Plane Maker, I set the eight chambers to match the performance specifications of the XLR11 - a process that took me a lot longer than a skilled aircraft modder could probably manage. Engine run times for the XLR11 ranged from 3m 45s to 4m 30s - although on one flight the engine ran for 5m 09s due to the upper engine shutting down prematurely. With that data in hand, I adjusted the X-15 XLR11 variant to carry enough fuel for 4m 20s at full power. A more talented developer could probably also make the XLR11 non-throttleable, with individual rocket chambers able to be toggled on/off, as was true for the real aircraft.

The results came out pretty good, with a believable appearance, and more importantly, close adherence to the actual performance of the XLR11 configured X-15. At 60,000’ to 70,000’, one can expect to achieve a Mach number of around 2.0 with an engine burn run that will take the X-15 from the drop location over Silver Lake, near Baker, CA to Edwards about 100 miles to the west.

The screens below show a launch from over Silver Lake dry lake bed from 37,000’. A good point of reference for that location is to simply place your aircraft at the Baker, CA airport (0O2) on a heading of 238°. With the XLR11 engines, the X-15 should burn out right over Edwards in a position for the overhead pattern and glide landing on the dry lake bed.

The XLR99

The first XLR99 engine flight in November, 1960 started to expand the X-15 performance envelope to the design goals. The flights did not go without some troubles, including a cracked airframe after a hard, overweight landing after an emergency, and the loss of X-15-3 and the tragic death of USAF pilot Michael Adams in November, 1967 when his X-15 entered a hypersonic spin, breaking apart as it reentered the atmosphere after having attained 266,000’.

The XLR99 was an amazing bit of engineering, developing 57,000 lbs. of thrust, driving the 33,000 lb. X-15 to the edge of space. Towards the end of the engine run time on flights, the X-15 weighed closer to 15,000 lbs. as all of the propellants were exhausted, giving a thrust-to-weight ratio of nearly 4:1. G-forces in the cockpit during the acceleration would range from 2 to 4G. When reflecting on the X-15, pilot Milton Thompson mused, “The X-15 was the only aircraft I ever flew where I was glad when the engine quit.”

The default X-15 with the XLR99 engine approximates the performance of the aircraft quite well. Capable of attaining Mach 6 and 350,000’, the default X-15 can be placed at the historically accurate launch locations and make either speed or altitude runs to Edwards AFB. Mission profiles were typically either speed runs with a climb to 80 to 100-thousand feet and then maintaining a relatively flat profile to build up speed, or altitude runs with a parabolic type profile where the aircraft pitched to around 45° during the 90 second engine burn. Mission profiles dictated the launch location to be used, but most of the missions were conducted over the “High Range”, a track across California and Nevada with telemetry relay stations and prepared dry lake beds that could be used in emergencies throughout the profile of the flight. Jenkin’s book goes into great detail on how the High Range was developed, constructed, and maintained, giving a fascinating insight into the process. Each X-15 flight was an incredible choreography of rescue assets, chase planes, and ground monitoring that all had to be in position to cover any eventuality. Many months of preparation went into each well rehearsed ten-minute duration X-15 flight. Launches were conducted from the B-52 (the book has an excellent section on the selection of the drop ship as well) over ten different lakes over the course of the program, but the most frequent launch sites for the 199 flights were Delamar, Mud Lake, and Hidden Hills. Many of these sites were around 80 miles north of Las Vegas, in or near what many of us are familiar with as the NTTR (Nevada Test and Training Range).

For X-Plane purposes, you can launch from Mud Lake by starting your drop over Tonopah Test Range (KTNX) on a 185° heading. For an altitude flight, pitch to 35° to 45° and hold that attitude for 90 seconds until engine burnout and you should top out somewhere around 200-250 thousand feet and Mach 4.5 or so. On a typical X-15 altitude flight, you can expect engine burnout to occur around 175,000’ after which you remain on a ballistic trajectory for another two minutes until reaching peak altitude and descending to reenter the atmosphere. Through about 80,000’ the aerodynamic control will work, but above that altitude, dynamic pressures are so low that you’ll be using reaction controls. It is an interesting thing to be able to move the nose off-axis and see that it has no effect on your ballistic trajectory. Just make sure you are straight during the reentry!

As mentioned before, the default X-15 is lightly modeled, and over the last few generations of X-Plane releases, some of the features have become bugged. I owe many thanks to X-Plane developer (and fellow X-15 enthusiast) Steve Wilson for helping me out by addressing some technical issues with the default X-15. Among the items Steve fixed were the cockpit canopy function, some errant manipulators, the inertial altimeter, and the jettisonable ventral fin. His assistance and guidance were essential in bringing this article to light.


I went an additional step once I dove into this project and decided to try my hand at further modifying the default X-15 to create the X-15-A2, a variant of the X-15 that would fly later in the program, and set the ultimate speed record of Mach 6.72 (and suffering extreme heat damage during that flight). Late models of X-15-A2 were covered with a white ablative coating to help combat the extreme heating encountered during hypersonic flight. For my purposes, I borrowed some external tanks from an X-Plane 9 version of the X-15-A2 created by MeteorJ and spent an inordinate amount of time in Plane Maker trying to make them look like a good approximation of where they should fit on the X-15. I also made an attempt to cover the tanks with graphics that somewhat approximate what the X-15-A2 external tanks look like, although there were many iterations of the design over the years. I also adjusted the flame color, and finally, I decided to add a 3D pilot to the cockpit, first using Beber’s cool looking fighter pilot, but then eventually settling on the space pilot created by JetManHuss.

The addition of the external tanks to the X-15-A2 would drive the launch weight up to in excess of 52,000 lbs. and provided for an extended engine run time of 4 minutes and 20 seconds versus the original 80-90 second engine run of the standard X-15. The left tank held 793 gallons (8,920 lbs) of liquid O2 and helium bottles while the right tank contained 1,080 gallons (6,850 lbs.) of anhydrous ammonia. The tanks were normally jettisoned at Mach 2.6 during the climb. To provide for a clean separation, each tank was fitted with a small rocket engine on the nose that would fire and push the tanks away from the X-15. For X-Plane purposes, the tanks are fitted as weapons to allow for jettisoning.

[caption id=“attachment_10012” align=“aligncenter” width=“680”] A typical speed profile to 100,000’ and Mach 6 starting from Mud Lake to the overhead 360 pattern into Edwards AFB.[/caption][caption id=“attachment_10013” align=“aligncenter” width=“680”] An altitude profile flight to 300,000’ from Delamar Dry Lake with a pullout and left turn toward Edwards AFB.[/caption]

X-Plane profiles

I have to admit I was surprised at how closely the numbers put into Plane Maker resulted in the desired outcomes. As well, whoever designed the X-15 3D model and wing geometry for X-Plane must have done a good job because engine thrust is only a small part of the overall model. X-Plane uses the shape of the wings and fuselage to determine aerodynamic properties, so I was pleasantly surprised at how it all tied together nicely. Now, I don’t know if the voodoo going on under the hood is accurate or not - all I was looking for was results, so the debate can rage on the accuracy of X-Plane’s subsonic, transonic, supersonic, and hypersonic flight modeling.

What I can tell you is that according to the X-15 flight manual, aerodynamic control was usually starting to be regained during the descent at around 95,000’ with a 5G pullout, holding just shy of 15° of AOA until the aircraft starts to level out around 70,000’. This technique works well in the sim, although the critical angle of attack is right there at 15°, so holding 10° AOA or so will give you near the same results without risk of departing the aircraft. If you stall and depart the aircraft at high Mach numbers you will be in for a very wild ride until you get down into air that is thick enough to exert normal control forces. At that point, you will be very far from where you wanted to go, and is part of the reason that so many intermediate dry lake beds were prepared for X-15 emergency landings.

Above around 90-thousand feet, you can bank and pull on the X-15 all you like and the only thing you will be effecting will be changing the attitude of the aircraft relative to is velocity vector, which will remain largely unchanged. The X-15 in the sim has joint aerodynamic/reaction controls simulated, so there is no need to change how you manipulate the controls. In the real aircraft, a separate “space control system” side stick was installed to provide out of atmosphere control. Using 90 lb. Reaction Motors XLR30 thrusters on the nose and wings provide pitch and roll control. A stability augmentation system was also designed for the X-15 and various mixing of controls schemes was used over the span of the project.

Of interest to both the actual pilots and simulator pilots is immediate course control and correction during the initial boost phase of the X-15, particularly on altitude flights where so much time was spent above the atmosphere. At Mach 5, a 20° heading change required a 5G turn input for 10 seconds. An azimuth (heading) error of as little as 5° at rocket burnout on an altitude flight could translate into a cross track error of as much as 45 miles! Even small pitch errors or errors in engine run times could result in significant under and overshoots. With a climb rate of 4,000’ per second, variations in the XLR99 engine thrust, and small errors that had larger results were common. 1,500 lbs. of extra thrust or just 1° of pitch excursion could result in overshoots of 7,500’. Pilot Ed White once overshot his planned altitude by 32,750’, hitting 314,750’. When he went to turn the aircraft to try to get back to Edwards, the aircraft just continued sailing past, but he was able to preserve enough energy after reentry to make it back to the dry lake bed. Famed pilot Neil Armstrong once pulled a bit too aggressively on one recovery, ballooned up and went back out of the atmosphere, passing by Edwards at Mach 3 and 100,000 with a 90° bank and full up elevator. Coming out of the atmosphere 45 miles south of Edwards, he just barely made it to the very southernmost point of Edwards dry lake, landing ten miles south on a straight-in approach to runway 35. Bill Dana once pitched to 42° instead of the planned 39° and overshot his planned altitude by 39,900’, topping out at 306,900’.

From launch to touchdown, the X-15 in X-Plane requires very steady and even movements of all of the controls. If you yank on the stick - you are going to have a bad day. Close study of the angle of attack instrument is your best guide on whether you are pulling too hard since we don’t have the seat-of-the-pants feeling of G forces (thank God!). If things get squirrelly, the speedbrakes have an excellent dampening effect (as long as you are in the atmosphere) as they help stabilize the dart that is the X-15. Just be aware that the speedbrakes will scrub off energy that you might need later during the glide portion of the flight. It is also worth mentioning a rough median L/Dmax number to keep in your mind is around 8° AOA if you are trying to stretch a glide. That AOA was obviously variable according to Mach number, but 8° would get you in the ball park for lower Mach numbers.

The bottom portion of the X-15 tail was a jettisonable ventral fin. Typically it was released at 800’ and under 300 knots inside the perimeter of Edwards and it would descend under parachute to be recovered. Interestingly, as the program progressed, it was determined that the ventral fin was not needed for most flights, and that leaving it off allowed for a steeper profile and a greater AOA capability. Of the 199 X-15 flights, 73 would use the ventral fin and 126 would fly without it. In X-Plane, the X-15 has a jettisonable ventral fin that requires a three step procedure to jettison: 1) Lift the jettison switch safety cover 2) Move the switch to jettison arm 3) Press the jettison button.

Landing the X-15 was always a tricky affair given its high speed, high descent rate approach. If energy allowed for it, pilots were trained to fly an overhead 360° pattern that started at around 38,500 (all altitudes MSL) and 300 knots. At this point you are only 145 seconds from touchdown. A spiraling, descending 360° turn was made at 45° of bank while maintaining 300 knots. At around 3,500’ (MSL) you should be rolled out on final at 300 knots, with flaps down (I recommend only one notch in X-Plane) and about 20 seconds from touchdown. At about 3,000’ (800 AGL) drop the landing gear, begin the flare, and shoot for a touchdown speed of 200 knots. The rear skids of the X-15 were designed for simplicity, reliability, and resistance to the high heat environment of hypersonic flight. If you watch pretty much any X-15 film footage, it is easy to see how the high drag skids caused the nose to slam down pretty aggressively upon touchdown. Indeed, one fuselage was cracked in half due to a heavy weight emergency landing at Mud Lake early in the program. The tendency for pilots to attempt to cushion the nose slamming down by adding more back pressure to the stick would actually exacerbate the problem as it loaded the aft skids up even more, increasing friction, and causing the nose to slam down even harder. It was found that a slight forward push on the stick with the SAS off at about .4 second prior to touchdown was a good technique for taking pressure off the main skids and making for a lighter nosewheel touchdown.

I’ve probably flown the X-15 from drop to landing at least a hundred times now, so I’ve become very familiar with the geography across the High Range and northeast towards Arizona, Nevada, and Las Vegas. From a couple hundred thousand feet, everything looks pretty similar, so you should get familiar with what Edwards and the other dry lake beds look like along the route. Edwards becomes fairly easy to spot even at ranges of a couple hundred miles as a distinct shadow with a lighter patch on the northwestern edge of the lake bed. With X-Plane, we have to wait for the higher detail textures to load as we get closer, so it is helpful to have your graphics pushed out to the maximum rendering distance.

No two speed or altitude flights are exactly the same. Due to the aforementioned pitch, speed, and engine run factors, each flight will dump you out at a variable distance from Edwards. I screwed up enough flights that I also managed to come up short and long a few times and had the excitement of setting up approaches to intermediate dry lake beds. I pored over Google maps and satellite imagery for hours while researching this article and it was neat to see that some of the old dry lake beds (like Silver Lake) still have the faintest traces of the marked emergency runway layouts on them.

If you use satellite imagery overlays (ortho), it becomes quite easy to recognize landmarks and reference points on the approach into Edwards. A particular favorite of mine is the Honda Proving Center racetrack about 20 miles north of Edwards. If you are at 10,000’ MSL abeam the racetrack at 280 knots or better - you can stretch a glide to Edwards.

X-Plane tips

While you can launch the X-15 from the NASA B-52 included with X-Plane, I found it is easier to just start at an airport near my launch location (Tonopah, NV or Baker, CA) and then use the map feature to set a “drop” altitude of around 45,000 and a speed of Mach .8 (450 knots) with about -3 degrees of nose pitch down on the desired flight path heading. Alternatively, you can set the X-15 to drop from the NASA B-52, slew the B-52 to the launch location, and hit the spacebar to drop. Whatever the case, the initial twenty seconds of your X-15 are probably the most delicate and important to achieving a successful profile. NASA originally planned to have the X-15 dropped from 38,000 to 40,000’ - from which the X-15 generally needed about 3,000’ to recover. When NASA upped the launch altitude to 45,000’, the X-15 needed 4,000’ - 9,000’ of recovery altitude, negating the value of the higher launch altitude.

Immediately after the drop, your best bet is to go to the 3-pack of instruments on the panel and pull on the stick smoothly to maintain about 10-12° of AOA while steadily increasing pitch to the desired attitude (probably 30-45°). Don’t worry about airspeed - if you don’t exceed the critical angle of attack (15°-ish) you won’t stall the aircraft. Remember, your displayed/indicated airspeed will drop rapidly as you climb due to falling dynamic pressure while your Mach number will steadily increase. Rapid stick and/or trim movements below 85,000’ or so can result in a sharp snap stall and complete degradation of speed, so be gentle. Once the X-15 is above 85,000’ you start to rapidly lose aerodynamic control forces and the reaction control system takes over, and is much more forgiving, however your velocity vector will be very difficult to change, so you need to reach your desired velocity vector pitch attitude prior to 100,000’.

Flying from the profiles from the 3D cockpit is very immersive since the cockpit is so cramped and visibility is relatively poor. The actual X-Plane pilots practiced the mission profiles many times in a ground simulator that featured breakthrough technology in its own right. One of the pilots commented that flying an X-15 mission was very much like the simulator since they very rarely looked out the window, instead focusing on the instruments and flying the profiles that the scientists and data collection engineers wanted. When you do look out the window, you can see the coastline from San Francisco to Tijuana.

VR immersion

The reason this article finally came to light was me obtaining an Oculus Rift last year and finally getting to experience the X-15 cockpit as it is meant to be experienced. Cramped, tight, claustrophobic, with limited visibility - the X-15 is a VR pilot’s dream and nightmare. With the simplified systems of the X-Plane X-15, there really isn’t much need to throw switches unless you want to go through a few steps to turn the battery on and get the engine going, but the visual experience of the ride is just fantastic. It isn’t hard to imagine how insane the profiles were to fly for the real X-15 pilots. I guess one could simulate it by putting your sim in a freezing vacuum chamber and having a cow sit on your chest to simulate the 4Gs of acceleration. I don’t know how you’d simulate the two to five minutes or so of weightlessness at the top of the parabola, but that’s a challenge I’ll leave up to you guys.

Flying the altitude profile, seeing the landscape unfold below and the curvature of the Earth, the black sky and twinkle of stars above is an awesome experience. Keeping your eyes glued to the AOA gauge and hoping you have the energy to make Edwards, flying the overhead 360, and managing your energy as you line up for a landing are just a ton of fun. I can’t thank Steve Wilson enough for fixing the inertial altimeter, tweaking the landing drag, fixing the jettisonable fin, and a bunch of other little (and big) things he’s assisted on during this extended project.

## Fun X-15 trivia

So I have copious notes, and this article is definitely a self-indulgent romp through my aviation fetish, so rather than draw it out any further, I’ll leave them here:

  • Flights were divided roughly 1/3 for speed, 2/3 for altitude
  • Neil Armstrong said the X-15 was “the most successful research plane in history”
  • Goals of the X-15 included discovery and validation of wind tunnel techniques, exploring high dynamic pressures and heating, stability and control engineering, and biomedical research into weightlessness and high G forces
  • Sensors recorded temperatures of up to 1,350°F and pressure of 2,200 psf
  • Max theoretical altitude of the X-15 was 1,130,000’, but even a 770,000’ / 84° ballistic profile would require a 10G pullout
  • There was some consideration of implementing some sort of retro/braking thrust
  • Landing speed was 213 mph, stall speed 177 mph
  • A simple stopwatch was used to record burn time and predict top out altitude
  • The revolutionary “Ball Nose” used to measure dynamic pressure, provide inertial inputs, and other measurement was an Inconel X sphere able to measure AOA to -10 to +40° and slip within 20°
  • The Ball Nose was tested to withstand heat to 1,200°F by subjecting it to the flame from an F-100 afterburner
  • The XLR99 was throttleable from 30-100% but limited to 40% minimum
  • The XLR99 had a mean time between overhaul of 1 hour of engine run time or 100 starts.
  • There were only 8 propulsion problems over 199 flights
  • The XLR99 flew on 169 flights - 165 flights were a success for a 97.6% reliability
  • Muroc AFB was renamed to Edwards AFB in 1948 in honor of Captain Glen Edwards, killed flying the Northrop YB-49 Flying Wing
  • 1948 was an incredibly tough year for the Flight Test Center with 13 fatalities
  • Chuck Yeager once flew 27 different types of aircraft at Edwards in a single month
  • Brig. General Albert Boyd said the California and Nevada dry lakes were “God’s gift to the U.S. Air Force”
  • X-15 pilot Milton Thompson said of Edwards “Rogers (dry lake bed) was where God intended man to land rocket planes”
  • The High Altitude Continuous Tracking Range was 400 miles long, 50 miles wide, 500,000’ high, and stretched from Wendover, Utah to Edwards
  • Groom Lake was a desired X-15 launch and emergency recovery lake, but the CIA and Lockheed were concerned about access
  • Each dry lake was continuously monitored for suitability by dropping an 18 lb. steel ball from a height of six feet to measure the resulting depression
  • Markings on the launch, emergency, and recovery lake beds were a tar like compound laid on top of the lakebed surface. All runways were 300’ wide and at least two miles long. The tar strips marking the edges of the runway were a standard 8’ wide. Each year, new tar had to be laid, eventually building up to (in some cases) 3 or 4" in height!
  • X-15 external tanks would freefall to 15,000’ then descend under a deployed chute at 20-25’ FPS.
  • To simulate X-15 flights, F-104s in a high drag configuration were used, as were F-100A aircraft outfitted with drag chutes that would deploy in flight
  • A specialized NT-33A with variable SAS programming allowed for simulated X-15 flights in a hooded environment that simulated the 5G pullout by banking 75 degrees while a safety pilot monitored the system.
  • Neil Armstrong once broke the side stick controller of the NT-33A clean off, went into a hangar, engineered another one, an replaced the one he broke
  • The B-36 and B-58 were both considered as launch platforms before NASA secured new B-52s for the job
  • In 1966 there was a study in which the XB-70 was considered as a launch platform
  • C-130s, H-21 helos, and F-104s were arrayed along the flight corridor to come to the rescue of X-15s that encountered emergency landings - it was quite the ballet of resources
  • Upon launch, there was time enough for two engine light attempts (10 seconds) before commencing fuel dumping and setting up for an emergency landing
  • USAF Major Bob White was the first man to fly Mach 3, 4, 5, 6 and the first man to fly higher than 200,000 and 300,000’ - I doubt he had to buy many drinks at the bar
  • Eventually, X-15-3 was revamped with a more modern looking Leer Siegler panel that featured vertical scale gauges
  • Major Michael Adams, killed in 1967, was using an incorrect instrumentation mode on his attitude indicator cross pointers that resulted in a 15° sideslip during reentry. The plane weathervaned at 120,000’ and Mach 4.7 inverted, but the SAS dampers blocked the pilot inputs that might have allowed recovery. The plane broke up at 62,000’ and Mach 3.9.
  • X-15-1 is located at the National Air & Space Museum, Washington DC.
  • X-15-2 is located at the National Museum of the USAF, Wright Patterson AFB, Dayton, OH
  • X-15-3 (destroyed in 1967, killing pilot Major Michael Adams) is buried at an undisclosed location on Edwards AFB.
  • Launch platform NB-52A “The High & Mighty One” is located at Pima Air Museum, AZ
  • Launch platform NB-52B “Balls 8” only retired in 2004, is located at Wings Over the Rockies Air & Space Museum, Denver, CO

[caption id=“attachment_10075” align=“aligncenter” width=“680”] The current version of Edwards AFB for X-Plane was created by BedaNo1 and is a gorgeous recreation.[/caption]


If you can’t tell - I’m a fan of the X-15. I’m in awe of the engineering, the construction, the problem solving, the piloting, the analysis, and the constant quest for knowledge that the X-15 program represented. Dennis Jenkins, author of “X-15: Frontiers of Flight” makes the observation that the X-15 program probably would not be approved today. The well managed risks and thoughtful application of obtained data to expand the X-15 flight envelope and test engineering concepts would probably never fly in today’s risk averse society. It was a different time for sure, and one that can’t always be looked at through rose colored glasses. The loss of so many men and machines was a steep price to pay to expand our knowledge and pave our way to space and provide for other modern aviation and aerospace breakthroughs. I feel it is important that, generations later, we remember those that participated in these programs - engineers, pilots, (and some who were both!), managers, and support staff who risked everything to field a successful hypersonic aircraft.

Chris “BeachAV8R” Frishmuth

Required reading:

“X-15 Frontiers of Flight” by Dennis R. Jenkins

“At the Edge of Space: The X-15 Flight Program” by Milton Thompson

X-15 with SASL Enhancements modified by Steve Wilson: DOWNLOAD*

  • The X-15 Enhanced was originally created for XP10 - further modifications by Steve Wilson, myself, and the expansion to the X-15-A2 and the LR11 X-15 provided by JetManHuss will have to be submitted to Laminar Research for permission to be released since they contain Laminar assets.


Extremely nice write-up! And some fantastic screens and background info as well :slight_smile:

I think rocket-029.jpg was supposed to be an image :slight_smile:
The actual X-Plane pilots practiced the mission profiles many times in a ground simulator that featured…” I think that’s supposed to be the X-15 pilots :smiley:


You’ve been busy!
Great article!
I too have a thing for the X-15. We used to have a really good icecream with that name, and because of all the cool things I read about it (the aircraft, not the icecream) when I grew up.


Thanks…I think I fixed that image…!

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What a great article! I expected it to wrap up after each section but it just kept on coming. Thanks a lot!

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Me too… :rofl:

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Really enjoyable read @BeachAV8R - thanks!

This really got my attention. “stall speed 177 mph”.

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Excellent article @BeachAV8R - and it’s uncanny how you always manage to get your screens to look so good.

I do have one comment to make though:

“The well managed risks and thoughtful application of obtained data to expand the X-15 flight envelope and test engineering concepts would probably never fly in today’s risk averse society.”

This seems a little unfair. Today’s risk assessments factor in the ability to solve most design problems in risk free ways using computer simulation and / or robotic technologies. For the X programme the only way to collect data was to build something and try it out, and unmanned technologies were not up to the job. The choice was between doing it whilst minimising the risk to the extent possible or not doing it at all.

Today’s choice, however, would be between doing it manned with the associated risk to life, or doing it unmanned just as effectively (or maybe even more so) with technology taking the brunt of the risk. Not as gung ho I agree, but I know which method I would choose. Just ask Elon Musk.


Not sure if you came across this book in your research, @BeachAV8R, but NASA actually has a pretty detailed and modern review of the problems that culminated in Michael Adam’s demise.

^ See Chapter 4, Section 1 of the book (Screening Versus Design), Page 71 of the PDF. The rest of the book is good content too, if… a little dry. It is NASA after all. :slight_smile:

Yep! Add to that a lot of introspection and discussion on the psychology of the Cold War and how society worked at the time and you’ve got one complicated issue.

It used to be you had no hope of figuring out what a vehicle was going to do in certain flight regimes- the theory was there, but the numerical methods were limited by the computational power of a bunch of people sitting in a room cranking out the results with slide rules. If you wanted certainty you needed a good test plan, a whole lot of observers, and a handful of brave and razor-sharp pilots capable of executing it to the letter.

There’s more to this as well- pilot workload as a concept was frequently ignored or sneered away as the vocabulary of some lesser bugsmasher that needed to stand aside and let a legend show the world his Righteous Stuff.

In retrospect it’s a very sexy, hairy-chested vision of the past and there’s certainly something to be taken from their intrepid approach. You don’t learn a whole lot from trying out things you know are going to work. The brutal truth though is that this approach can and will kill a lot of pilots. Society has decided today that we want to keep our heroes around and not throw money away when we can predict results with a lot more certainty, and I’m okay with that.

(Oh gosh that was more than I intended to write)

ANYWAY, excellent read Beach. The X-15’s one of my favorite programs too and it’s encouraging the sim world’s keeping them alive in some virtual sense. Hopping into the cockpit and taking it for a spin is one thing, but you truly did your homework! Fingers crossed for an article like this on the NF-104 next? :slight_smile:


I agree it is partially unfair. I do think society (in general) has a much more CYA attitude that can sometimes overshoot the target of safety. I’ve had a long enough career in aviation already (25 years) to have seen and experienced this. Risk Assessments and briefings that eat up valuable time that could be better used doing the real meat of preflight actions that actually DO have an effect on flight safety. But if there is a record of all of the things that could go wrong with one of my flights, the lawyers and corporate entities will have something to trot out to pin me to the wall.

I think I mention at the end of the article that it isn’t really a good idea to over-romanticize the projects in the 50s, 60s, and 70s, but it’s hard not to. I feel that my statement about risk aversion is legit and doesn’t have much to do with engineering or how much we value life, but is rather just the result of a slow evolution over the decades into a more litigious (and safety conscious I would think) society.

My example of Neil Armstrong fashioning his own side-stick controller is a good example. He would have been brought up on charges by a union for using their tools, circumventing OSHA requirements, and not providing an environmental impact survey for what he was doing… :wink:

I hadn’t - I’ll check that out. The whole Michael Adams thing could be the subject of an entire article in itself. The short gist I got from the Jenkins book was that engineers realized they should (generally) not provide multiple modes to critical instrumentation that could be switched and misinterpreted. The reality of that is probably not workable in a lot of cases, but I’m sure a lot of thought goes into how to display and annunciate what modes things are in to avoid confusing and “red flag” when something is not set right.

Yes. I think there is a lot of that that makes the 40s and 50s different from today.

I think Milton Thompson and some of the other books I’ve read pretty much give high praise to the pilots that were also engineers, or that had mechanical thinking minds. I know I wouldn’t qualify as one of those types if I were magically transported back to that era.

Agreed - it is a different mindset, and the “kick the tires, light the fires” attitude died an appropriate death. That said, there are still vestiges of it around when you look at things like Scaled Composites and the Space Ship One project. Tragically…you can only simulate so much and even still we see things like what happened with Space Ship Two, and how human factors always find a way around safeguards, or people just do things you don’t expect them to do. I think @fearlessfrog can attest that somehow @beachav8r always manages to find a way to break something on the site despite specific instructions on how to do things. :rofl:

Thanks - your kind words mean a lot and I’m glad people are enjoying the article. And I’ve already got my idea for the next article. In doing the research for the X-15, there was a lot of crossover of project knowledge and now I have a new target of fascination - The Lifting Bodies…


Great read, Beach. I was a pup back in the X-15 days, and remember pictures and toys of the aircraft.

Fun X-15 trivia -
Launch platform NB-52B “Balls 8” only retired in 2004, is located at Wings Over the Rockies Air & Space Museum, Denver, CO

Here she is, from my recent visit -


That seems to be a recurring theme among fans of the X-15. Many of the people I’ve talked to about it that are fans had a toy X-15 they carried around…LOL…

Oh dear…I can see what I’ll be scouring eBay for this weekend…

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And I really encourage people to read that book/PDF I linked to in the article. Much of the fun stuff to read about is things like how they measured the lakebeds for landings, how they used other aircraft to simulate the X-15, and a lot of the interwoven research that was occurring at the same time at Edwards. By all accounts, Paul Bikle (Directory of NASA Dryden from 1959 to 1971) was THE man.

View It / Do It:

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Really interesting write up Chris, thanks for the excellent article and the link to the 644 page PDF.

I flew over Edwards today as I was climbing to FL450 where we cruise speed of M0.85. I always feel like I’m nothing more than a kid holding out his arms making airplane making airplane noises when I fly past this place.


What are we but dwarfs, standing on the shoulders of giants.


You’ve been pretty coy about what you’ve been up to! The result was a Masterpiece. Yeah, I said it! You didn’t just have an experience and then write about it. You sculpted that experince to match your research.


That’s SO typical @BeachAV8R!
All about having fun, and then tell us about it… :wink:


:blush: Like I said, it was VERY self-indulgent. And the more I got into it, the more I got into it. Putting the LR11 engine that JetManHuss provided on the X-15 was the highlight…it was really cool to get to fly that version. And of course, flying it in VR…

I really wish the XTreme Prototypes X-1A and X-15s were available for X-Plane, because they look like real masterpieces. And while FSX/P3D do some things really well…X-Plane really just feels good for dynamic aircraft like those X aircraft planes.

I’ll dive into the lifting bodies in a couple weeks. I have lots of good content for that…