The X-15 Experience

No ordinary airplane! (Prepar3D® v2 screenshot)

The flight model of the X-15A-2 SE addon was developed with the desktop pilot in mind so he/she can have fun while maintaining stability and control of the aircraft at all flight regimes allowed by the simulator. We do not pretend that the flight model reproduces the exact flight characteristics of the real X-15 rocket plane, which would be practically impossible to achieve on the currently available simulation platforms, but we tried our best to develop a unique addon that is fun to fly while pushing the simulator to its limits and simulating nearly every step and procedure that are required in a real, typical X-15 mission.

The X-15A-2 SE addon was designed to simulate rocket propulsion and its related fuel systems including, in the case of the X-15, the use of three different propellants and their pressurization methods. Therefore, "CTRL-E" (the standard auto-start command in the simulator) will not work with the X-15 as it does with conventional aircraft.

Instead, referring to the quick-start procedures, you must at the very least power the X-15 from an external source, refuel the aircraft from the service panel, start the APUs and generators, switch on the stable platform in order to have functioning instruments, pressurize the propellant tanks and follow the engine precool, prime and ignition procedures.

Remember: the X-15 is no ordinary airplane!

You can also use the (fictitious) automatic sequence start button [76, fig. 5-1] on the main panel to start the engine without going through the normal procedures or the quick-start procedures. However, following each step presented in the manual will make your overall X-15 experience much more realistic and enjoyable.

Since we are taking off from the ground, because there is no B-52 carrier in the simulator to fly our X-15 addon to a proper altitude and heading before launch, we should treat the X-15 as, well, a "B-52 addon" until we reach our intended launch point. This means that we should aim for a Mach .78/FL450 launch while respecting the X-15's limitations.

Whichever starting method you previously selected, the unlimited fuel option switch [27, fig. 5-3], on the service panel, should be moved to ON for this type of practice flight with a fictitious takeoff from the ground.

You can also use the slew mode or the map view to position the aircraft at launch altitude and speed. Taking off from the ground is rather fun however, and is something the real X-15 pilots could not do! Refer to your simulator's manual for more informations about the slew mode and the map.

We found that the best way to achieve takeoff is to accelerate on the runway centerline with the engine at about 75% and to use the throttle [12, fig. 5-4] as required until the actual launch (Mach .78/FL450).

The airspeed indicator [5, fig. 5-1] on the X-15 main instrument panel is provided with a "barberpole" (actually a small red pointer on the left upper side of the instrument) which limits the airspeed at low altitudes to around 690 KIAS. As the aircraft climbs through 26,000 feet, the barberpole pointer moves to allow higher airspeeds thus reflecting the lower air density. The important thing to remember is that the indicated airspeed must be kept below the barberpole indicated value. You may refer to "Aircraft Reference Information" for other airspeed vs altitude limitations.

Rotate at 260-280 KIAS in a smooth but swift pull-up to about 30 degrees nose-up while retracting the gear. You may want to use the pitch error pointer (the small horizontal pointer on the left side of the attitude indicator [9, fig. 5-1]) and the pitch angle set control knob [16, fig. 5-1] (a separate instrument located at the lower right corner of the attitude indicator) to fine tune your pitch angle.

Before takeoff, select the pitch angle you want with the pitch angle selector control knob (the small lever must be clicked to get positive angles). As you maneuver the aircraft to within +5 or -5 degrees of your selected pitch, the pitch error pointer on the left side of the eight-ball (attitude indicator) will act as a vernier pitch indicator which you can use for fine-tuning the pitch angle. Initial pitch-up and precise pitch angle control was an essential part in every X-15 mission. You should first approximate the desired pitch angle with the ball and then focus on the pointer for precise adjustments. The pointer moves in the same direction as the ball so it acts as a magnifying glass for pitch.

Be careful not to take too long to achieve the correct pitch or the airspeed may get out of hand. In this case, you may need to pitch up to very steep attitudes in order to regain airspeed control.

As you climb through FL450, check your IAS and try to maintain at least 350-400 KIAS by carefully adjusting your pitch. Remember that you should be flying trimmed and leveled at around Mach .78 and FL450 before fully opening the throttle.

Once the launch altitude and speed are attained, you may proceed with the launch itself, which in our case is merely a question of setting the throttle to 100% (with the unlimited fuel option switch [27, fig. 5-3], on the service panel, to ON) since the normal start-up procedures were performed on the ground.

Optional Procedures:

If you want a more realistic mission from this point on, with a limited engine burn time, you can shut down the engine by first retarding the throttle to 50%, then by moving the throttle outboard to OFF (right-clicking the throttle handle). Then, perform the following procedures:

Engine master switch [63, fig. 5-1] – OFF.

Unlimited fuel option switch [27, fig. 5-3] – OFF.

Engine timer [11, fig. 5-1] – Push knob for RESET.

Engine master switch [63, fig. 5-1] – ON.

Engine precool switch [61, fig. 5-1] – PRECOOL.

Engine prime switch [56, fig. 5-1] – PRIME.

Igniter idle switch [53, fig. 5-1] – IGNITER. Wait about 10 seconds.

Ready-to-launch switch [52, fig. 5-1] – ON.

Throttle [12, fig. 5-4] – START (click and then move inboard to 50%). Throttle must be moved to 50% by the time the idle-end (amber) caution light [2b, fig. 5-1] comes on. Note that combustion in the main thrust chamber of the XLR-99 engine will start almost instantaneously when the throttle lever is moved.

The previous steps would simulate a true high altitude launch with limited fuel.

Once again (as during most X-15 missions), you should pitch up to about 30-35 degrees (in reality, each mission called for a very accurate angle, which can be set with the attitude indicator's vernier pointer and the pitch angle selector knob), maintain the throttle to 100% and watch the X-15 accelerate. Mach 4.65 seems to be a hard limit of the simulator.

We recommend not exceeding 200,000 feet because the simulator has an unpredictable behavior beyond that point. Remember that the highest altitude attained by the real X-15A-2 rocket plane was 249,000 feet (August 3, 1966) and that most high speed flights were performed at even lower altitudes.

The main instrument panel is provided with a dynamic pressure gauge [10, fig. 5-1] which allows you to "see" how much air is actually hitting your wings and control surfaces. On the low side of the gauge (low airspeeds or very high altitudes) you see that not much control is possible below 250 psf (hence the high rotation speeds on takeoff). Unfortunately, the ballistic control rockets on the X-15 are not (yet) supported in the current flight simulation platforms, so control at very high altitudes and at very low dynamic pressure is kind of touchy. Be careful not to exceed the maximum dynamic pressure and acceleration values (again, you may refer to the "Aircraft Reference Information") or structural damage and/or "skin overheating" may occur!

During your mission, it is recommended to use an extra spot plane view, as visibility out of the cockpit is rather limited, especially at high pitch angles. It also makes for some great screenshots!

An engine timer [11, fig. 5-1] was installed in the X-15 equipped with the XLR-99 engine. The timer was automatically started during the ignition sequence and would tell the pilot when to shut down the engine, depending on the mission's objectives (altitude and speed to be attained). You can use the engine timer (located on top of the main instrument panel) for the same purpose.

If we exclude the climb to the launch altitude (during captive flight), a typical X-15A-2 mission would last for about 10 minutes, of which about 90 seconds (no external tanks) to 150 seconds (external tanks installed) saw the engine burning. The remainder of the flight was jettisoning the empty external propellant tanks, maintaining course while on a ballistic trajectory at several times the speed of sound, holding the correct angle of attack for reentry into the earth's atmosphere, decelerating with the speed brakes, jettisoning the remaining propellants, and finally, gliding your way back home. This is the way you should fly the X-15A-2 SE addon in the simulator as well.

Get to know the Mojave Desert and the emergency landing sites that this incredible landscape has to offer and try to make it back to Edwards or land on some dry lakes, as your simulation platform provides you with many strips and Air Force bases in the area. Be aware however that at X-15 speeds and altitudes, the distances between the landing areas appear quite short and therefore require accurate descent planning. Of course, flat sand does the trick as well, as long as it is not too soft.

You may want to switch to the trapezoidal windows for the final approach, as they provide more visibility, move your view point slightly to the left to better see the runway, make the engine timer invisible or use the invisible canopy mode.

Approach at 300 KIAS (flaps down, 100 feet AGL), drop the gear right before flare and touchdown at 174-200 KIAS. Don't forget to jettison the ventral (or ramjet) before landing.

Refer to "Landing" for complete approach and landing procedures.

Happy record breaking!