AVSIM Commercial FSX Aircraft Review

X-1A, B, C & D

Product Information

Publishers:  Xtreme Prototypes

Description: The X-1 rocket plane of second generation.

Download Size:
383 MB

Simulation Type:
Reviewed by: Xavier Noche AVSIM Staff Reviewer - March 10, 2010


Xtreme Prototypes proposes the second generation of Bell Aircrafts X1 rocket planes. This aircraft came after the first generation that broke mach 1, with the aim to reach beyond mach 2 and 90 000ft. The real aircraft reached Mach 2.44 and 90 440 ft. 3 of these airplanes X-1A, B and D were build and the 4th one X-1C was planned but never built.

The X-1 SG from Xtreme Prototypes simulates all 4 in overall 6 liveries, plus the B-29 used to launch them at high altitude. You are warned: it is an extreme prototype not an easy and forgiving airplane like the C-172.


The installation is straightforward and eventless. One minor regret is that the location of the 100 Mbyte+ documentation cannot be chosen. I just moved it away from the default C:\Program files that I try to keep as free as possible from applications.


The 85 pages documentation is excellent: complete and nice looking in a 1950s handbook style. It is provided in both English and French.

It provides ample data about history, precise technical explication of the chemical reactions involved in the rocket and of the various systems, and thorough exterior and cockpit description. The appendixes cover the reference data, the saved flights and other information. In addition, the documentation contains a chapter that explains where the various X-1 related files are located on the hard disk.

Sample from the supplied pdf documentation

The checklists are not available from the documentation but from the FS kneeboard only. I simply regret the lack of a quick starter chapter typically for someone who would like to reach 90 000 ft in the next 3 minutes after the software installation. That is technically possible, but you will most probably need a bit of time to browse though the documentation, if only to find out about the magic start button.

Exterior model

There are 4 models: X-1A or D without launch Boeing B-29, X-1A or D with launch B-29, X-1B without B-29 and X-1C without B-29. The X-1A and D models are the same. The X-1B is not very different from A and D.

The X-1C includes 2 specific large yaw damping fins in the middle of the wing, a retractable small ventral fin (that automatically deploys above 15 000 ft and retracts below this altitude) and a gun in the front.

All the models are nice and full of details. The model file size is typically 17 Mbyte, and 23 Mbyte for the model that includes the B29. That’s huge. The bmp files are 2 sets of 5 files of 2048 x 2048 pixel in DXT5.

Exterior model from the ground


Exterior model from the air


Details of the fuselage

The last 2 pictures show the simulated condensation of the ambient air water into frost outside the liquid oxygen tanks that last while this tank is not empty.

Details specific to the X-1C; note the reflections and metal effects on the lateral wing fin

Interior model

The interior model does include most of the exterior model. So there is no empty space in any direction. It contains a lot of details as well, including the worn paint of the seat and floor.

Interior model of the cockpit and surroundings

Samples of details of pipes, levers, canopy mechanism and (breathing) oxygen tank

As for frame rates, I got 15 to 20 frames per second on standard scenery with my mid-range system.


The panel is technically unique as all the gauge shapes are in the interior model, not in the panel. The full panel and gauges size is just 25 Kbyte! The xml gauges seem to just pass variables processed inside the interior model, which is a whopping 10 Mbyte.

This aircraft has a true 3D panel, meaning 3D gauges, not flat 2D gauges projected on a 3D panel: every single switch, nut, screw or washer is modeled in 3D! Even the needles of the gauges are 3D! The result is just astounding. I am not aware of any other FSX add-on software that has gone that far in this direction. So impressive, that you understand well that no 2D panel is provided.

Nonetheless, only a 3D panel means that you will typically fly with at least 60% of zoom because you need to carefully watch several gauges and as a result most of the cockpit will be hidden. Indeed remaining in control requires frequent glances at the attitude indicator and other gauges such as airspeed; as well, various fuel levels and pressures indications need to be monitored too.

From a pilot’s point of view, one absence is surprising: there is no VSI at all! I am sure this was the case in the real X-1, but given the typical flights of this aircraft, this would seem a very useful piece of in-flight information at high altitude. In addition, in the only phase of flight that somewhat resembles other aircraft is the landing. This would be useful too to help achieve not just smooth, but simply a non-destructive landings.

In fact this lack is probably due to room taken by the needed chemical fuel levels and pressure monitoring gauges that represent more than half of the panel surface. As well there is no Nav instrument, except for a fictitious pop up compass and RMI that come in place of the accelerometer and hydrogen peroxide pump outlet pressure indicator.

The X-1A and D panels are the same. The X-1B panel differs with the location of a few gauges and of the engine switches. The X-1C panel is similar to the X-1B but with an added basic autopilot, which control is based on FSX native autopilot, like for most add-on software.

Panel Overview




X1-C with the gun in operation


The central panel


The 3D, panel, gauges, switches, bolts, needles...


The sound set seems realistic, although I never heard the real one. It includes rocket sounds and other engine sounds such as the oxygen release prior to ignition. In addition, there are the sounds of the tires contacting the ground and that of the gear and flaps moving.

The concept

Microsoft Flight Simulator X is designed to simulate piston or jet aircraft using avgas or jet fuel combustion with the oxygen of the outside air. The outside air oxygen density is modeled and bolted in the core of FSX.

The simulated jet engines as approximation for the rockets have 2 deviations compared to the real airplane:
• Starting time takes 30 to 45 seconds, whereas the rocket engine starts instantaneously
• The simulated rockets are overpowered at low altitude because the outside air oxygen density is not a factor for their thrust.
These limits are explained in the documentation.

I would add that the fuel consumption at altitude becomes extremely low. This is build into FSX as well. I remember a few years ago on FS 2002 having –after around 20 trials- successfully flown a classic 737-500 (Eric Cantu’s one as far as I remember) from Paris to beyond Auckland, flying at around 70,000 ft and 132 Kts, at the limit between max mach and stall.

In fact by the rocket design, the consumption should be less dependent from altitude –again because the outside air density is not a factor for the rocket engines; just for the air friction on the fuselage and wings. This does not apply to hydrogen peroxide and nitrogen that are consumed at what seems to be a regular rate.

By the nature of the rocket engine thrust is all or nothing, on engine per engine basis. So the real aircraft can just provide 0%, 25%, 50% 75% or 100% of the maximum power. This is selected using the thrust lever on the left that has 5 positions: 0-1-2-3-4.

The simulated aircraft adds more progressiveness with the availability of the yoke’s throttle that moderates the power selected by the thrust lever. This results in more control and this is welcome. Clicking on a 3D panel that can be moving in turbulences or accelerations is not easy, and it requires to have the lever on the screen, which is not always the case. If you absolutely want the real thing, leave your throttle at full power and that’s it.

Test System

AMD Athlon 6000+ Dual core
ATI Radeon HD4850 / 512 Mbyte (Graphic + sound)
Memory: 2 Gbyte.
Windows XP SP3

Flying Time:
25 hours

Flight behavior

For this aircraft to fly you need:
- Water alcohol (WALC) fuel
- Liquid oxygen (LOX) oxidizer reacting with the fuel above to produce thrust; it is stored under high pressure
- Hydrogen peroxide auto-reacting thanks to a catalyst, to drive a turbine that provide the force needed to pump the propellant into the rocket engines
- Nitrogen, used as a control gas for the hydrogen peroxide auto-reaction and various other functions such as fuel and oxidizer pressurization and driving the gyros then pressuring the cockpit, gear and flaps operation
- Oxygen, for the pilot to breath
- More fluids such as the dibromodifluoromethane used as fire extinguisher.

Running short of any of the first 4 elements stops the engines. The tanks can be (in fact have to be as there is no other means) filled up by pressing on fictional buttons or clicking on the level or pressure gauges.

Extreme Prototypes advises you to select unlimited fuel and ignore crashes. This is mere advice. I chose the opposite, as is helped me progress and learn more about handling the aircraft.

Take off

The X-1 can be either classically started by taking off from the ground, though that only happened once in 42 flights, or dropped from a B-29 at an altitude above 40 000 ft. On top of this, several pre-defined flights start at a high altitude without drop. I used the first method of classical take off most of the time.

X1-A take off from ground

Climbing after take off

Taking off from the ground, there are 2 ways to start the aircraft:
• The easy one: press the magic red button that fill all the tanks and starts all systems for you; lower the flaps; You just need to wait 45 seconds and start the take off toll out
• The real one. Using the switches and control individually in the proper order.

Manual ground start, step by step

I must say that even with the document in hand, I spent quite some time trying to successfully start the engines, as the documentation explains what should be done, but it does not include a complete step by step start procedure, like a rocket start check list. Given the well simulated variety and complexity of the systems involved, using intuition only does not succeed. As indicated in the documentation you cannot use Ctrl + E for the engines start.

Taxiing is possible, with just 1 engine, on idle throttle, and using heavy amounts of brake. The real aircraft was most probably never taxied!

The take off is typically made on 2 engines to simulate real power at low altitude. The flaps, of classic type, have just 2 positions: up or down, approximately 60°. Both take off and landing are made with flaps down. Whereas engine 1 is straight on the longitudinal axis, engine 2 is on the right. As a consequence, the aircraft has a tendency to veer to the left during take off. You also get a hint about the low roll stability on the ground at high (rolling) speed.

Apply power and rotate at 140 Kts. Given the speed limits for the gear and flaps that are relatively low compared to the rocket performance, you need to promptly retract both after lift off. Typically aim at 40° of pitch and watch speed increase.

Taking off on 4 engines and pitching close to 90° lifts you from Edwards ground at 2 300 ft to 90 000 ft in just 60 seconds. But then pitch (and roll, and yaw!!) management at high altitude become the challenge.

Indeed taking off is an easy action compared to high altitude cruise or descent and landing. The documentation mentions nowhere that the aircraft is easy to fly. And it is fine like this; the real X-1 was certainly a challenge to control.

Launch from B-29

This is only possible using the model of X-1A or D with B29. A simple described procedure has to be completed and a countdown is initiated and drop is performed:

The B-29 only appears when the drop switch is armed (middle position). This B-29 exterior is fairly detailed in the exterior. But due to FSX restrictions, the B-29 propellers are rotating but produce no thrust.

As a consequence the set is not powered at all, and so you need to proceed with the drop quickly by moving the drop switch up. This action initiates a 10 second countdown and releases the X-1, unless you move the switch back. The B-29 automatically disappears when the X-1 moves away from it. The X-1 engines must be started after the drop. This takes 30 to 45 seconds, as on the ground.

Dropping from the B-29

Jet altitude rocket engines start after drop

In addition, a few supplied pre-defined flights start from the air at 40 000 ft. The engines are not started, as the saved flights cannot store anything else other than the few Microsoft defined jet engines parameters. In other words, all flights begin with a cold start – even if from the air.

In flight

After the take off, the high altitude flight comes very quickly; even if you took off from a runway, you don’t stay a long time at low or medium altitudes with an X-1! If you stick to the recommended 2 engines only below 30 000 ft and maximum pitch of 40° and remain above 200 Kts IAS, staying in control is relatively easy up to 70 000 ft. Then roll stability becomes weak.

I deliberately pushed that envelope and I must admit that most of my flights ended up in spins that I was not able to control. This is due to the gap between my personal skills and what it takes to control an extreme prototype. Nonetheless in a few of my flights I remained in control and in a few others, I managed to recover. I could comfortably say that the same happened at least once to Chuck Yeager and that he recovered after a 60 000 ft drop!

In addition, watch your pitch control movements as the speed reached is such that anything else than a small adjustment creates a positive or a negative acceleration that exceeds what your virtual body can stand, and you continue to fly with a black or a red screen for a few seconds, or more if you do not correct back.

Lastly, in flight you have to monitor your gauge levels and pressures as there are 4 required chemical components that do not burn at the same rate depending on altitude and selected thrust level: Water alcohol fuel, liquid oxygen, hydrogen peroxide and nitrogen.

At high altitude, the last 2 are the ones that empty the quickest. Then you have 2 choices:
• Accept the fact and initiate a descent, to be followed by a power off landing.
• Click on the level or pressure gauges that will automatically replenish the tank(s).

And there is no light warning you of the low level (or pressure for the gases); just some needles that drift off their green area. I learned that the hard way!

Climb out from Edwards

High altitude, around 80 000 ft

The altitudes reached provide magnificent sights. Above, the physical geography of California shows very well.

In the real world, a spin is one way: down. In FSX, it can be down, but most of the times up (!) and the altitude continues to increase slowly, leading to surprising results. Thus very high altitudes can be reached, up to 16 000 000ft (!), after entering yet another spin and 1 or 2 minutes at a simulation rate of x128. This provides amazing sights of the earth, even though unrealistic.

Very high altitude spinning leads to pretty views


Provided that you managed to stay in control or recover from a spin, you need to descent. Descent planning is tough as no other aircraft behavior can be used as a reference. You need to cut all engines, or keep just number one at idle and maintain a nose down attitude of up to –30°.


Landing is difficult too! I crashed my first 10 attempts to landings, whereas the next 5 where not beautiful at all. Then my landings became not great, just acceptable even though with some more crashes from times to time.

In order to succeed, I practiced the short trip from Edwards AFB to the Mojave airport a few times, just 15 nm away. The maximum enroute altitude reached was typically 15 000 to 20 000 ft! This is followed by a steep nose down descent; you need to manage the rate of descent mostly visually and with the altimeter as no VSI is there.

After the visual approach with unusual rate of descent, once you get aligned on a high but still more conventional visual glide slope, this becomes more classical. The panel is not designed for landing and the somewhat narrow forward down angle of vision makes is not so easy. I confess that to get used to the aircraft I selected the “empty” 2D panel and pressed W to find the standard C172 panel.

What I found work well is to pick a long runway and not to have the constraint to touchdown right at the edge, and keep just the 1 engine as power is more than enough. Keep the engine on until after gear and flaps down, then cut (move thrust lever to 0) the engine 1000 ft before flare. Keeping even one engine on, even at idle throttle, makes it impossible to brake: the brakes cannot fight against a rocket engine! Indeed, just one engine at idle throttle on the ground without brakes makes the aircraft accelerate up to 110 Kts!

The only problem with this technique is that on flare, the aircraft has a tendency to bounce and balloon heavily. In this case to add power you need the mouse, which is not very handy. Failure to do so most often results in crash landing at the second touchdown. Not an issue of course, if you instructed FSX to ignore the crashes...

The noise of tire contact is characteristic, mixing tire noise and metal fuselage sounds and cannot be missed. Then keep concentrated while the airplane decelerates using the brakes because high speed roll stability on the ground is low, leading to a heavy rolling tendency.

If you land without power, for example after exhaustion of any of the 4 needed chemical components, then you have to make a very high approach around 250 Kts and only lower both flaps and gear once you are absolutely sure you are going to reach the runway. Once the gear and flaps are lowered, the airspeed bleeds rather fast.

Approaching Mojave visually


Landing in Mojave, view from the right


Landing in Mojave, trying to keep away from wing strike


The next level of challenge, after controlling the aircraft in all flight phases in normal operations, is to master the emergency situations. A handful of systems were incorporated in the aircraft to cope with emergencies and are simulated: fuel and liquid oxygen jettison, engine fire extinguishing...

Engine fire effect

Whereas I already struggled in normal operations, I spent little time –yet- in attempting tackling an emergency.

Summary / Closing Remarks

Xtreme Prototypes X-1 is a beautiful aircraft with unique performance and an amazing full 3D panel; a challenge to control in most phases of flight (but what else would you expect from an extreme prototype?). But it rewards you with beautiful pictures.

It pushes the limits of both your skills and FS capabilities. It is yours for 40 USD, which is in the middle range of the payware prices but you get a top product. Ready for a spin? Go for it!


Mojave desert upgraded airport and static stored aircraft by BC's Unofficial FSX Tweaks, now incorporated into High Flight Simulations. Screenshots capturing made with StageSoft SnapShot V4.


What I Like About Xtreme Prototypes X-1 SG

  • An original aircraft, that allows a unique vision of earth and landscape thanks to its performance
  • The true 3D panel and gauges
  • Very detailed model and texture metal features
  • The challenge to fly and yet more to discover in aircraft handling
  • The documentation


What I Don't Like About Xtreme Prototypes X-1 SG

  • A few minor details



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