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Advanced Flight Model........?


Fish
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Would anyone like to have a go at explaining in what way/s are the FM of the Su25~'s are more 'Advanced' than the other aircraft in FC. I know that things like weapons inertia, and fuel load affect the center of gravity, and I also know that the plane behaves much different from say the A10. I presume it also means better damage modelling integrated with the other characteristics, However when i look other sims many boast of '....the most advanced flight model in a pc game. I do believe that this accolade goes hands down to the Su25~'s of FC, but would like to understand it in lay terms what makes it so better. Also I've flown the latest version of FB/ACE/PF, and some of the aircraft seem to have a similar feel on handling, slow speed, performance, and landing/cross wind, to the SU25. Would be intereested to hear comments.

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"To simulate accurate flight dynamics of the Su-25T, a very detailed physical model has been created. This model is a further development of the models used in Lock On. The model includes dynamics that partly control behavior in various flight regimes: standard, transitional supercritical, and damage modeling."

 

The Su-25T Physics Model

 

 

"The following new features have been introduced with the Su-25T:

 

Plane dynamics are always calculated on the basis of the same physics equations describing transnational and rotational motion of a solid body under the influence of external forces and moments disregarding the nature of their origin.

The center-of-gravity can change its location within the speed axis system;

When calculating aerodynamics characteristics, the plane is represented as a combination of airframe components (fuselage, outer wing panel, stabilizer, etc). Separate calculations of aerodynamics characteristics are performed for each of the above named components in the entire range of local angles of attack and sliding (including supercritical), local dynamic pressure and Mach number taking into consideration deviation and grade of destruction of control instruments and some airframe components.

The engine is represented as a complicated system of the main components models: compressor, combustion chamber, turbine and starter-generator.

 

When flying the Su-25T, the new physics model shines in the following ways:

 

Transition between flight modes is performed in a smooth manner, without abrupt changes of angle rotational speeds and attitude (for example, after tail-dive or when landing with angle of roll, on one of the landing-gear).

Gyroscopic effect of the plane's rotation is taken into account.

Asymmetric effect of external forces is considered as well as the effect of external forces not going through the center-of-gravity (for example, engine thrust and drag chute force). These forces are correctly calculated at any flight stage.

Recoil force when firing the cannon is taken into account.

A notion of lateral and longitudinal center of mass is introduced. This notion can change depending on fuel load and external loadout.

Asymmetrical pylon loading now influences the characteristics of lateral control (depending on flight speed and regular overload, etc) is also considered.

Aerodynamics are accurately modeled in the whole range of angles of attack and glide. This is especially noticeable when performing a tail-slide and aileron roll.

Efficiency of lateral control and degree of lateral and static lateral stability depend on angle of attack, longitudinal and lateral center-of-gravity.

Wing autorotation mode when performing a rolling rotation at great angles of attack is taken into consideration.

Kinematics, aerodynamic and inertial interaction of longitudinal, dihedral and lateral channels (yaw movement when performing a rolling turn, rolling motion at rudder pedal forward, etc).

Angle of glide availability is determined by the pilot's efforts and the plane's position.

In case of the airframe damage, the plane's motion is performed in a natural way by means of deletion of the damaged component from aerodynamics calculations fully or partially.

The model guarantees realistic stall characteristics of stall (rocking wings with simultaneous course oscillation).

Diverse effects of aerodynamic shaking depending on flight mode: exceeding the allowable angle of attack, Mach number, etc.

Engine thrust at idle corresponds to the real one.

Idle RPM depends on the speed mode: altitude and Mach number, weather conditions: pressure and temperature.

Short RPM over speeding is modeled at acceleration time.

Acceleration time, engine throttling and its controllability depends on rotation speed.

Gas temperature behind the turbine is dependent on engine operating mode, flight mode and weather condition.

Specific fuel consumption is non-linearly dependent on engine operating mode and flight mode.

Dynamics of engine operating parameters (gas speed and temperature) is accurately modeled in regards to engine start and shut down. The mode of engine autorotation from ram airflow, engine freeze-up (accompanied by continued temperature rise) when throttle position is in the wrong position at engine start up. Flight restart and windmill air restart.

Each hydraulic system supplies its own group of hydraulic pressure systems (landing gear, aileron actuator, flaps, wing leading edge flaps, adjustable stabilizer, nose-wheel steering, brake system, etc).

Pressure in the left and right hydraulic systems depends on the balance of hydraulic pump efficiency and operating fluid consumption by hydraulic pressure users (boosters, actuators, etc). Hydraulic pumps' efficiency depends on the right and left engines speed respectively; operating fluid consumption depends on their state.

Both catastrophic and partial hydraulic actuators failure at pressure loss in a corresponding hydraulic system is modeled.

Pitch trimming, yaw model and aileron trimming mechanism models are included, each using a different logic. In particular, pitch trimming position does not influence rate controller position at near-zero flight speed. Trimming tab serviceability depends on electric power availability in aircraft electrical system.

Extension and retraction speed of high-lift wing devices and adjustable stabilizer depends on fuselage pressure.

Extension of wing high-lift devices for a more maneuvering configuration at a greater indicated airspeed leads first to partial and then to complete hydraulic actuator blocking. This causes fuselage pipe damage, hydraulic liquid leakage, and fuselage pressure drop.

Landing gear extension at a high indicated airspeed first leads to partial and then to complete hydraulic actuator blocking, causes fuselage pipes damage, hydraulic liquid leakage and fuselage pressure drop. "

Cheers.

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AFM takes in consideration centroids of aplied forces in each surface (including fuselage) or sub-surfaces (such as flaps). These forces are generated by calculated aerodynamic phenomena (fluid flow). It also takes in consideration masses and momends of Inertia. Sounds simple but its a real pain in the ass to make it.

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I didn't see a flight sim that can reproduce this

 

show single post

 

:icon_supe

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Thanks for the replies.

I can't say i understand all of this, or even most of it. but i get the jist. From the comments above there seems to be two levels of difficulty in achieving such an AFM for a simulated aircraft.

1. The complexity of the models, and the logic, and programming of these.

2. The attainment for the correct data parameters to put into the models.

 

So even if the models could be built for second world war planes or other modern military fighter planes, It might be very difficult to get the accurate data ?

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I was just exemplifieng Force_Feedback the AFM.

 

I am not that good at stunts. But how can be triming more resposive and efficient than actualy moving the control surfaces, knowing that you have to trim often and you don't have the exact trims that could reduce your problem (I mean eleron trims)?

 

Also did you managed to land?

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There was a very interesting thread at the Lockon (LOMAC)SimHQ forum just before Lockon1.0 went gold (in mid2003) concerning the "advance flight modeling"

Its now in the archives section,the link:

http://www.simhq.com/simhq3/sims/boards/bbs/ultimatebb.php?ubb=get_topic;f=106;t=001116

 

Here is a quote from Igor Tishin development manager at

Eagle Dynamics:

document.write(timestamp(new Date(2003,6,31,12,34,0), dfrm, tfrm, 0, 0, 0, 0)); July 31, 2003 12:34 posted July 31, 2003 12:34 Dear Sirs

Let me put some light to this subject

 

We are always working on improvement of Flanker(LockOn) FM and we have two approaches.

First is based on the existing concept which uses

few but very complicated dependencies, requires relatively small number of initial data. This approach is a very good since it was developed in a way that it can be improved any time we get more information. It is very convenient in situation, when whole product is complicated and we need to develop many aspects of it at the same time. We are using this approach in LockOn, improving flight models of all flyable planes as soon as we get the new information.

 

The second approach is an attemption to use much more aerodynamics data with bigger set of equations. This approach is normally used for professional simulators and it requires a lot of suphisticated initial official data. As soon as we got such data for one russian airplane we tryed that approach as well, but unfortunately found out that official initial data very rare suite to each other, in other words, that approach needs a lot of work to preprocess the initial data with no guarantee, that result is good. As a result for one year of work a very first tryal version of one airpalane was developed, but was not tested enough, and even nobody could say yet is it better than FM developed by old approach or even worse. So, not everithing what is complicated necessarily better smile.gif . Very often genius is in simplicity. But we continue working to provide you with the best of what is only possible on PC.

 

 

 

 

 

 

can be improve

The second one is an attemption to

 

--------------------

Igor Tishin, director of Eagle Dynamics/LockOn development manager

Hornet1a

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