Engine types, idle rpm FM related

[Fenrir]

Hi
A small sound project has grown outside the box and raised a few questions:

• Ground idle rpm vs flight idle rpm, does the F16(any engine you know) have different rpm? Ive tried to find info on this and it seems on rl vids it settles at about 70%. Or does it use its nozzle for this?

-Is there any way to get info on the different engine types in the FMs? What features they have etc?
-Or more specific, is there any engine type were ground idle rpm and flight idle rpm is modeled? And if so, any commands to set them?

Well, lets start with these

Cheers

[condor]

IIRC the engine computer calculates the idle depending on the situations… ie try reaching 15-20k ft @300kts and then dive(30-40 degrees) with idle… you will notice the change in rpm… when you are about 2000ft level out and notice the rpm variation as your speed bleeds… i think there is no official ground or flight idle…

[Fenrir]

As far as I understand the flight vs ground idle has to do with spool up times, the thing you describe has to do with pressure inside the engine or more specific the difference in pressure, right?

[Mav-jp]

i think the answer is in HFFM manual, if this is not…well i will need to elaborate but

1. yes all F16 variants have different engine logic

2. IDLE RPM varies with dynamics pressure from 100% (when you are in supersonic) down to 70%

3. nozzle behavior is also engine specific

[Fenrir]

Thanks Mav-jp, it was a interesting read but I couldn’t find the answer.
What I am really looking for is what the engine types in the FM.dat do. Maybe they aren’t used anymore but if they are.
What the feature for the different types would be.

Cheers

[Guest]

Max,

One of the F16 crew chiefs here has stated all that info at one point, can’t remember which one or where it is, but it’s buried here somewhere.

Hopefully they will see this thread and respond.

Take care,

Brian

[thunder]

Just to add to the conversation, consider also that windmilling has a role in idle RPM. Flying at 500kt will have your engine spinning just by the ram air coming through the intake, engine nozzle is meant to somewhat limit the effect by maintaining back pressure in the engine, but you will notice that idle at 70% is only possible below a certain speed.

$0.02

[Fenrir]

The RM8B engine, a Pratt & Whitney JT8D-22 with afterburner has a ground idle at 57% (7100rpm) and a flight idle at 70,5%(8950), so i wanted to see if there was any engine type in BMS that modeled this as i couldnt find any reference for the F16s to have this.

Cheers

[Mav-jp]

okay

forget about enginetypes, those were old coding style values, i am not even sure this is well supported anymore.

If you want to finely control your RPM / max / idle and nozzle Max Min you need to introduce the new tables that are controling those.

Those new tables are called with the key word

engopt AdvancedDynamics

that you have to put just after the

PROPULSION DATA

ENGINE OPTIONS MUST BE LISTED HERE

This key word allows you to introduce the following tables (here it is f16bk30 exemple):

###########################################################

IdleThrottle Chart

###########################################################

4 # mach breakpoints
0.5 0.6 1.1 1.4
2 # alt breakpoints
0 100000

alt 0

.7 .8 .8 1.03

alt 100000

.7 .8 .8 1.03

###########################################################

MilRPM Chart

###########################################################

2 # mach breakpoints
0 2.5
2 # alt breakpoints
0 100000

alt 0

1.03 1.03

alt 100000

1.03 1.03

###########################################################

MaxABRPM Chart

###########################################################

2 # mach breakpoints
0.0 2.5
2 # alt breakpoints
0 100000

alt 0

1.04 1.04

alt 100000

1.04 1.04

###########################################################

Nozzle Max Chart

###########################################################

2 # mach breakpoints
0.0 2.5
3 # alt breakpoints
0 35000 100000

alt 0

0.7 0.7

alt 35000

0.5 0.7

alt 100000

0.3 0.5

–-------

make a comparison between F16 dat files and others and you will understand where those tables are set

You can also introduce the fuel flow tables with the keyword:

engopt fuelflow

forget about
engopt AdvancedThrust

this is really F16 engine specific

[Mav-jp]

i forgot to mention

Nozzle pos in idle is harcoded

Nozzle pos in MIL is defined in auxaerodata section with the following parameter :

nozzleMil 0.13 (block 30 example)

for all those parameters (nozzle control) to work properly, you also need to define

complexnozzle 1

in the auxaerodata section

––

i hope this time i answer your question

[Fenrir]

Thanks Mav-jp!! This is what i asked:) I already introduced those charts for the .dat but I didn’t get the result I was looking for, I got a positive side effect though, but your answer gave me a hint what I might done wrong, need to try it tomorrow

Again, thanks!!
Cheers

[Guest]

Yes, seriously, Thanks Mav-jp!!

Max, some good info for ya. Good Luck,

Brian

[Fenrir]

The MilRPM chart and the MaxABRPM chart does what i thought, the rpm for MIL and AB can be set to the rl performance data.
The Idlethrottle chart work in a different way, it kind of moves your throttle idle “zero” position in relation to MIL, right? And the alt breakpoints are not AGL but ASL, is that correct?
The Idle RPM seems to be hardcoded, the idle rpm will not go lower than 70%, if i set the idlethrottle chart for example 0.57 the result will be a higher thrust at idle.

I had to use the “a Rate” and “function 66” charts with the “engopt AdvancedDynamics” , BMS ctd without them.
What do they represent?

Cheers

[Mav-jp]

@mAXpOWER:

The MilRPM chart and the MaxABRPM chart does what i thought, the rpm for MIL and AB can be set to the rl performance data.
The Idlethrottle chart work in a different way, it kind of moves your throttle idle “zero” position in relation to MIL, right? And the alt breakpoints are not AGL but ASL, is that correct?
The Idle RPM seems to be hardcoded, the idle rpm will not go lower than 70%, if i set the idlethrottle chart for example 0.57 the result will be a higher thrust at idle.

I had to use the “a Rate” and “function 66” charts with the “engopt AdvancedDynamics” , BMS ctd without them.
What do they represent?

Cheers

Altitude are of course ASL, AGL means nothing .

a ate and functoin 66 are handling the spool times of the engine as per NASA TP1538 (you will find detail explanation of if in this document)

[condor]

is it possible to change the idle rpm?? it should range between 62% - 80% rpm(main checklist rev 1107 BMS4.32 page 3/16) but it is on 70% constantly…
is it limited by code or it can be affected by ie Temprature/altitute (MSL) etc??

[Fenrir]

It varies with speed try to idle a 500kts and you see that it’s not 70-ish, it’s a bit different depending what f16 you fly as they have different engines.
Higher than 70 but not lower though.

Cheers

[condor]

i was refering to ground idle… but thanks for clearing that up…

[mvsgas]

@mAXpOWER:

Hi
A small sound project has grown outside the box and raised a few questions:

• Ground idle rpm vs flight idle rpm, does the F16(any engine you know) have different rpm? Ive tried to find info on this and it seems on rl vids it settles at about 70%. Or does it use its nozzle for this?

-Is there any way to get info on the different engine types in the FMs? What features they have etc?
-Or more specific, is there any engine type were ground idle rpm and flight idle rpm is modeled? And if so, any commands to set them?

Well, lets start with these

Cheers

Not sure in BMS but engine RPM is never a set number. Idle rpm is always a range for example GE 110 is 60 to 80% in the air it is not set. Many factor control RPM. Additionally N1 ( first compressor, in the F110, first three stages) is more affected by nozzle position. N2 ( core of the engine) is more affected by throttle movement of power lever angle (PLA) Speed, air density, etc. affect engine RPM. in the F-16 you can only see N2, N1 is not even monitored.

So the answer for one. Yes every single engine has its own RPM and above idle you only care for max rpm. example F110 on the ground idle is 60 to 80 % anything above is 106% max.
sorry don’t know the answer for the rest.

Information would be found in the 1F-16()-1, 1F-16()-2-70gs-1 if you can find any.

[Scorpion82]

Sorry for digging up this old thread, but it’s the only one suitable found via the search engine.

One question about the engoptfuel variable does it work for twin/multi engined aircraft or is it still limited to single engined aircraft?