The flight model in Precision Simulator is -- similar to full motion simulators -- based upon thousands of data packages derived from real 744 test flights. All this data has been harmonized and combined with an accurate atmosphere model incorporating varying pressure altitudes and density altitudes.

Unlike other PC simulations, a “library” of several aircraft modules are not included in Precision Simulator as it would lead to compromises in the flight model (despite the fact that the simulation of the technical systems, too, would be too big to get several aircraft simulations of this complexity into one software title). Consequently, Precision Simulator is -- just like full motion sims -- specialized in one aircraft. It models the 744. (In fact, there are different airline specific airplanes included in Precision Simulator, but they are, of course, solely from the 747-4 series.)

Limitations in version 1.3: The simulation of the EPR read-outs is simplified using a fixed exponential algorithm. However, this does not affect the N1 indications nor the overall performance model. Also simplified is the cost index /economy speed ratio in the FMC. However, the feature itself is fully functioning.

Barometric pressure, OAT, density altitude, IAS/TAT/Mach, pitch/power/lift, drag/power curve, speed buffets, gross weight/inertia, fuel flow etc. -- all variables interact with each other and play an important role in a complicated, harmonic system. The result is a highly accurate model of the real 744 performance.

Basically, the performance data in Precision Simulator doesn't deviate more from the average real-world fleet data than any real 744 deviates from its average fleet data (due to normal system tolerances on the real aircraft). The following table shows some examples:

Sample Comparisons -
Real World v/s Precision Simulator

(CF6 powered, all-pax, ISA conditions)

CLIMB
290 KIAS, Max Climb Thrust, clean config.

200 000 kgs Gross Weight

300 000 kgs Gross Weight

390 000 kgs Gross Weight

LEVEL FLIGHT
Mach .84, FL350

DESCENT -
290 KIAS, TAI off, clean config.

350 000 kgs Gross Weight

250 000 kgs Gross Weight

OTHER CONFIGURATIONS

Also, in various flap/gear configurations and during low level flight, approach, holding etc. the performance/pitch tolerances between Precision Simulator and the real 744 are smaller than 3.4%. Since its introduction in 1997, Precision Simulator is the only PC simulation on the market that agrees that exactly with the real 744.

Drag, Fuel Flow & Economy

The optimum altitudes for best economy are incoporated in the flight model as well. Ignoring or following these altitudes lead to the respective consequences just like on a real flight. Whether you're using a flight plan from a professional airline dispatcher or the logs of an actual flight -- comprehensive tests have shown that if you put Precision Simulator into the same real-world scenario you'll get the same results within +/-5%. Even after a long 12 hour London - Hong Kong flight the fuel remaining and ETA in the simulator did not deviate more than 3% from the real flight data. This deviation is smaller than the average tolerance within a real 744 fleet!

Engine Models - CF6, RB211, PW4056

Additionally to the General Electric CF6 engines, Precision Simulator version 1.3 now models also the Rolls-Royce RB211 and Pratt&Wittney PW4056 engines. Engine specific fuel consumption, structural differences, engine control equipment, start-up behaviour, EICAS indications etc., are modelled according to the engine type selected. Please note that the EPR read-outs on the PW4056 are lower than on the RB211, i.e. if in doubt, check the FMC IDENT page which engine simulation is selected.

Engine Out Conditions

Assymetric flight -- the most difficult task for flight simulations of all categories -- is very accurately modelled in Precision Simulator. Even at the limits, e.g. two engines out on one side at MAX take-off weight, is that fine-tuned and well balanced in the flight model that you will get a good demonstration on how difficult it is to gain airspeed and altitude in such a scenario.

Ground Effect

The "ground effect", i.e. the additional lift that occurs when the aircraft is close to the ground  (on the 747 up to 200 ft AGL) is accurately modelled in Precision Simulator.

Airspeed Buffets & G-Forces

Precision Simulator models low-speed stalls in clean and landing configurations as well as high-speed stalls caused by excessive centrifugal forces. The required stall recovery procedures are very authentic. Overspeed effects such as aileron reversal are also included. Besides, the simulation can model pitot tube malfunctions caused by ice or volcanic ash.

Inertia

The flight model incorporates realistic inertia algorithms in all six degrees of freedom. The exact values depend on the simulated gross weight.

Airspeed Acceleration/Deceleration

The flight model incorporates the standard deceleration rate of 1 kt/sec when thrust is reduced to idle during level flight. Speedbrake drag in flight and autobrake deceleration rates on the ground are correctly reflected as well. Also the typical "power curve" effect that doesn't let the airplane accelerate from slow speeds at high pitch attitudes during high altitude level flights is exactly modelled.

Pitch Momentum By Thrust Changes

The 747 has a nose up tendency when the engines are spooling up -- and vice versa when spooling down. This pitch momentum is neutral when the thrust is stabilized. Precision Simulator models these effects very realistically. The speed trim feature of the stabilizer systems are taken into account as well.

Flaps & Gear Configurations

The drag caused by gear and flaps is, of course, modelled as well. The flap retraction/extension schedule during departue/approach requires the same timing as on the real 744. Pitch and/or thrust must be accordingly adjusted by the pilot or automation when the flap/gear configuration is changing. Precision Simulator models also the "balloon" effect during flap extension.

Turning Radius & Bank Angle & TAS

The flight model includes an accurate ratio between turning radius, bank angle and TAS. Precision Simulator also includes the correct elevator behaviour in steep turns, i.e. the steeper the bank angle the less elevator altitude control is available and the elevator will control the turning rate rather than the vertical speed (most "high end" IFR simulators don't model this effect at all and have, therefore, a very unrealistic feel when turning at a bank angle greater than 10°). Precision Simulator is also able to simulate aileron lockout malfunctions and yaw damper malfunctions which result into a noticeable negative roll/yaw momentum (Dutch Roll tendency).

Flight Control With PC Joysticks

PC joysticks -- both “high end” all-metal yokes and cheap plastic joysticks -- have one particular problem: The force required to move these sticks is much too small, i.e. you won’t get more than just 1 - 10% of the back pressure of a real aircraft yoke at the same deflection. For example, an average plastic joystick produces a force of approx. 0.4kgs/~0.9lbs at full deflection regardless of airspeed, while on a real airplane (whether Cessna or 747) that same deflection produces a force up to approx. 40kgs/~90lbs -- 100 times higher - depending on airspeed. This is the main reason why manual flying on PC sims is more difficult than on real aircraft. While a slight pressure on a real aircraft yoke will have no effect at all, the same slight pressure will instantaneously move the “PC joystick”, and the simulated aircraft will shoot away from the selected altitude.
Precision Simulator compensates this natural “PC problem” to a certain degree. The simulation takes the lack of back pressure into account by using a logarithmic rather than a linear translation of the incoming joystick signals. For example, when you rotate during the take-off roll you don’t need to care about how many millimeters you deflect the PC stick.
Instead, you will “feel” that a certain amount of “force” is required to rotate the aircraft.
The actual deflection on the PC stick may appear unusually large at first, but be aware that the relative travel distances available on PC sticks are not realistic anyway: The distances are too short (virtually a miniature model of a real yoke). In other words, Precision Simulator lets you focus more on the “stick force” rather than on the “stick deflection”. This is more realistic and provides a much better manual pitch control.

Summary...

Please note that this web page can only partially discuss the overall flight model included in Precision Simulator. Static stability and dynamic stability (phugoid effect), longitudinal, directional and lateral stability laws, dihedral effect, sweepback effect and many other mechanics and laws, too, are, of course, thoroughly incorporated in Precision Simulator in order to compute this highly realistic flight model at all.

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