Thrust and Turbine Temperature gauges failure with afterburners?

[aleksaleks]

Hi,

 

thanks for the AFM in the f-15C!

 

However, since I'm not a real F15-c pilot I noticed something with the thrust and TT gauges when engaging/disengaging afterburners (AB) and I'm wondering if this is a feature or a bug (aka you're holding your phone wrong).

 

The thrust needle is stuck at 96/97 % i.e. max dry-thrust. When I engage AB it won't budge a bit. This is also true for the decimal display of the gauge, it stays at 97.

Same problem with the turbine temperature (TT) gauges below. They are stuck at max dry thrust setting and engaging AB does not change anything.

So, the only way I can tell from within the cockpit that I have AB engaged is FF (fuel flow).

Is this real? I can hardly believe that the real F-15C does that and I certainly did not have that issue with 1.2.7.

Have others noticed this too?

 

If it's not real please see that the next update or patch includes a fix for this.

 

Thanks!

[EtherealN]

Afterburner is an afterburner. There is no reason for it to affect turbine temps etcetera. The afterburner injects fuel AFTER the "normal" engine. ;) Think of it like placing a fuelguzzling rocket engine at the back of the normal engine.

[aleksaleks]

@EtherealN - O.K. but that does not explain the thrust gauges.

[cofcorpse]

This is not "thrust", it's RPM - revolutions per minute, in percents. 96% - is maximum steady RPM for this engine. Working AB does not affect RPM.

[mvsgas]

F-15, like the F-16, the RPM gauge is showing N2 speed of the second compressor, also known as the core. Every engine is different but PW-220 is around 90+, meaning it can be 92, 94 etc. The only thing most tech manuals say is that is should not exceed 96%. If it does, there is some thing wrong. As for the engine temp, in the PW engine is called Fan Inlet Turbine Temperature (FTIT). This means the sensor is taking temperature reading from the gases as they pass the High pressure turbine (HPT) and enter the low pressure turbine ( LPT). HPT drive or moves the core (N2) and LPT drive the Fan. So the sensor is far away from the AB flame holder, wish is where the AB flame sits ( causing most of the heat). The Flame holder is several inches behind the last LPT. If you look at picture of the exhaust of a PW-100,200,220 you will see the flame holder, It looks like rings.

 

The best way to tell if you are in AB is: Fuel flow increase, nozzle position increase ( meaning the nozzle is open or opening) and noise.

 

I take this info from the F-16, but it should hold true on the F-15 as well.

Edited May 10, 2014 by mvsgas

[EtherealN]

@EtherealN - O.K. but that does not explain the thrust gauges.

 

As mentioned: there are no "thrust" gauges.

 

Think of this as the engine RPM gauge on your automobile. It does not tell you how much power is presently being produced by your engine, only how fast the crankshaft turns. Seeing the engine RPM gauge in your automobile tells you very little if that's the only information you have (that is, no speed gauge, no gear indicator (if automatically shifted), no sound, etc).

 

In the case of the afterburner, it is literally happening "after" everything else, as previously mentioned. (Indeed, the earliest operational afterburners were modifications tacked on behind existing jet engines!) Due to that, you should not see any change in turbine RPM nor engine temperature when operating the AB. If you see it, something is most likely catastrophically wrong with your engine, since hot gases are apparently moving forwards past compressors and stuff. ;)

 

It really is like having a rocket motor on there, just in a sort of funky position. (And of course that it's still airbreathing, so it doesn't quite qualify as a rocket, but you get my drift.)

 

From wikipedia:

"A jet engine afterburner is an extended exhaust section containing extra fuel injectors. Since the jet engine upstream (i.e., before the turbine) will use little of the oxygen it ingests additional fuel can be burned after the gas flow has left the turbines. When the afterburner is turned on, fuel is injected and igniters are fired. The resulting combustion process increases the afterburner exit (nozzle entry) temperature significantly, resulting in a steep increase in engine net thrust."

 

 

Here, you can consider the engine design a bit closer: the turbine sectins are fairly obvious here, as is the afterburner section. Note what the wiki quite said about "extended exhaust section"; the RPM and temperature gauges are in the engine proper, amongst the turbines. Thus they get no information about what's happening "in the exhaust" - as far as they're concenrned, that stuff has already left the engine.