Afterburner Thrust

[brettt777]

Where is the thrust of the afterburner determined? I have some planes, like the Accel pack F-18, that the afterburner seems very realistic. When it kicks in, there is an obviously large increase in the thrust. But I have other planes where the AB makes very little difference if any. The only increase in thrust is the small amount the throttle is moved to go from 95% or 98% to 100%.

[tigisfat]

Where is the thrust of the afterburner determined? I have some planes, like the Accel pack F-18, that the afterburner seems very realistic. When it kicks in, there is an obviously large increase in the thrust. But I have other planes where the AB makes very little difference if any. The only increase in thrust is the small amount the throttle is moved to go from 95% or 98% to 100%.


The difference lies in each aircraft. Different aircraft have higher jumps in thrust in real life, and different FDSXS designers produce different flight dynamics.

[Wingnut172N]

I can tell you this; the large jump seen in the FSX Hornet is absolutely not realistic.

Having flown as a passenger twice in the F/A-18 (granted it was an F and not a C/D as modeled in Acceleration) the acceleration, while impressive in afterburner, wasn't nearly as monumental as FSX would have you believe.

The simulators the Navy uses also have much much less afterburner effect than FSX does.

Actually, we had full internal tanks and no stores or pylons and the acceleration without afterburners was pretty similar to a lightly loaded airliner at the beginning of the takeoff roll.

Point being, those jets you have that don't show a huge increase in thrust with afterburner are probably more realistic...

[viking3]

Older aircraft like the Voodoo and the F-106 just had one big valve which gave one hell of a kick where as more modern fighters have a mult-staged afterburner which opens a series of valves to dump the fuel into the exhaust which tends to make the effect less dramatic.

Regards, Rob:ernae:

[Dino Cattaneo]

In Acceleration planes afterburner "thrust gain" (with respect of the dry thrust) is controlled in the .air file.
There is a table in which you can specify the "gain" depending on the Mach no. (if I remember correctly). Editing this table allows a much more realistic behaviour.

For example, numbers in the air file of my Tomcat are almost exact - and I am quite happy with its behaviour (...but I need to fix other things as the "dry" engine responds too quickly to throttle)..

[jmig]

As mentioned above, modern fighters have soft ABs versus the hard ABs of older Century series aircraft.

During T/O in both the T-38 and F-4 you could feel the AB kick in, although you looked at the Nozzle swing to confirm good AB light.

Where you could really tell was going from say 0.75 mach to supersonic. It would really kick the airspeed up rapidly.

[rcbarend]

Where is the thrust of the afterburner determined? I have some planes, like the Accel pack F-18, that the afterburner seems very realistic. When it kicks in, there is an obviously large increase in the thrust. But I have other planes where the AB makes very little difference if any. The only increase in thrust is the small amount the throttle is moved to go from 95% or 98% to 100%.

The extra AB thrust is determined by the "Turbine Afterburner Thrust Factor vs. Mach No." table in the .air file.

Whether that is done realistically or not for any given aircraft: I don't know, since I've never flown them IRL nor have the exact figures.

But I DO know that there are many addons out there (even for FSX) in which the designer simply forgot to model this feature; hence, the AB is nothing more than a visual effect in that case (usually depending on throttle position).
My guess is that that is what you observe.

Rob

[brettt777]

The extra AB thrust is determined by the "Turbine Afterburner Thrust Factor vs. Mach No." table in the .air file.

Whether that is done realistically or not for any given aircraft: I don't know, since I've never flown them IRL nor have the exact figures.

But I DO know that there are many addons out there (even for FSX) in which the designer simply forgot to model this feature; hence, the AB is nothing more than a visual effect in that case (usually depending on throttle position).
My guess is that that is what you observe.

Rob

You are probably right because there are a couple aircraft where the AB definitely adds ALOT of thrust instantly and others add very little. Okay so next question, can this "Turbine Afterburner Thrust Factor vs. Mach No" table be added to an existing .air file. I have AirEd. Will this work?

[Sundog]

It also depends on the thrust to weight ratio. If one models the mass and aerodynamics properly and has accurate engine data, the rest should take care of itself. Of course, getting an accurate engine deck for a fighter engine and accurate aerodynamic data for modern aircraft is quite difficult, other than from anecedotal pilot reports.

[rcbarend]

You are probably right because there are a couple aircraft where the AB definitely adds ALOT of thrust instantly and others add very little. Okay so next question, can this "Turbine Afterburner Thrust Factor vs. Mach No" table be added to an existing .air file. I have AirEd. Will this work?
Depends; only if this is table entry (but not filled) is allready present in the airfile. Because I wouldn't know how to add a new table with AirEd.

Rob

[viking3]

Don't forget the fact that jet engines suffer from wear and tear and probably only reach their rated power for say 1000-2000 hrs. Turbine blades wear which then have turn faster to make power or compressor blades wear and can't gulp enough air. After that the mechs start adjusting Fuel Control Units to get the power which then plays hell with your fuel burn calcs. Throttle stagger problems and low EPRs follow that, and then it is time for an engine change. Been there, done that, and got the oil stains on my t-shirt.:kilroy:

Regards, Rob:ernae: