Afterburner Questions

[pstrany]

Hi;

okay, I'm in a mess. I am modeling a Me 262C-1a, a standard Me 262 with a rocket in its tail. This is for BOTH CFS2 and FS9, though I'm sure it should be done differently for each one. I want to simulate the thrust of the rocket motor using afterburner.

I went into air wrench, turned on the afterburner, and saved it. My aircraft, which had flown normally before, suddenly did cartwheels down the runway (okay, technically, it was backflips.) Even with the engine at idle, it did this. I checked the thrust on the afterburner, it is set at 1984 lbs (not sure why - this figure just showed up in the box. The thrust from the rocket unit was 3750lbs, I figure this has to be split in half as there are two engines, half being 1875lbs per engine. 1984 lbs seemed close enough.)

I've done a search both here and at FFDS, and come up with nothing that would explain this behavior. Any thoughts would be much appreciated. And bear in mind when you answer that I'm not even sure how to turn on afterburner in either CFS2 or FS9, so be kind and speak slowly in small words. I'm in this because I like to make polygons and color them.:icon_lol: :icon_lol:



Paul

[aeronca1]

The afterburner section is a multiplier I believe. Set it to the number that the normal thrust must be multiplied by to arrive at the total combined thrust of rocket and jet. If the normal thrust is say 1000lbs and with rocket 1250lbs then make the afterburner section 1.25.

[sparks]

Paul,

AirWrench uses the value input for 'Afterburner Thrust (lbs)' to calculate scalar values for air file table 1524. The value that 'just shows up' in that box is initially the same as 'Static Thrust'.

If there was one rocket, and it's thrust was 3750 lbs, add half of 3750 to 1984 and put the result (3859) in as 'Afterburner Thrust (lbs)'.

I'll bet your engines are located below the center of gravity. Set the vertical location of both your engines to zero and see if that helps.

[pstrany]

Hi Sparks;

Yup, engines are located at veritcal -0.3. I corrected that to 0.0, and now she sits on the runway okay when at low throttle, but any movement of the throttle, or attempting to put the aircraft into the air (via 'YAW') results in an immediate backwards tumble. This is true in both CFS2 and FS2004.

I'm using the "1%" air file as a source (this project is an update of the VB Planes Me 262, so the aircraft geometry SHOULD be very similar, if not identical) and so far have made no other modifications to the .AIR or aircraft.cfg files.

Just for fun, I went back to the original "1%" files then used AirEd to edit section 1501 (and also changed afterburner_available= from "0" to "1" in the .CFG file) and it flies okay (no tumbling) but I don't understand how to edit section 1524, so I get the same take-off run as without afterburner.

I don't know, all this flight model stuff is so- well, I don't know, either I'm going to end up with an aircraft that flies or a way of converting tin into gold. Maybe I should be wearing a robe and waving a wand?:costumes: :costumes:

Ah, the mysteries of life..........

Paul

[pstrany]

Okay, a quick addendum, I copied section 1524 from another aircraft (a Saab Draken) and now I have a speed increase which would seem to be an afterburner effect, though I have no control over how much extra thrust it delivers.

For those keeping score, I've changed the aircraft.cfg entry for afterburner_available= from "0" to "1", changed AIR file record 1501 to AFTERBURNER = TRUE, and copied section 1524 from another aircraft that actually had an afterburner, and now I have a working afterburner in both CFS2 and FS2004. I have no idea how to edit section 1524 to get the afterburner thrust I want, but it seems like I'm moving in the right direction.
But that leaves the BIG mystery. How do I edit section 1524 of the air file? It seems to some kind of a graph.........

Paul

[pstrany]

I can't seem to edit my previous post - no button to do it (I can do it in other forums though.)

Anyway, last (I hope) amendment, I also had to edit section 1521 to reheat available to TRUE (why does the AIR file have two different entries for this? Ah, the mysteries of life.......)


Paul

[sparks]

Paul,

I have no idea why you're having trouble with AirWrench. I cobbled up an Me-262 in FS9 using the air and cfg files I did for the CFS3 mudpond upgrades, then updated them with the current release of AirWrench (v1.01.38). I started with the basic engine without afterburner, then added afterburner. I never experienced any form of instability at any stage in the process. The air and aircraft.cfg files should be attached to this post. Feel free to install these files and continue from there. At a minumum you'll have to reset the contact points for whatever MDL you're using.

To edit table 1524 in AirEd, you need to change it's definition in aired.ini from type 'tbldb' to 'record':

;1524=Afterburner Thrust Scalars vs Mach,tbldb
1524=Afterburner Thrust Scalars vs Mach,record

Then add the 'record' definition for 1524:

[1524]
1=00,int32,No. of Table Pairs
2=04,double,m1
3=0C,double,s1
4=14,double,m2
5=1C,double,s2
6=24,double,m3
7=2C,double,s3
8=34,double,m4
9=3C,double,s4
10=44,double,m5
11=4C,double,s5
12=54,double,m6
13=5C,double,s6

I added this after the definition for [1522] in my aired.ini file.

Just remember that AirWrench will overwrite anything you do with AirEd.

[pstrany]

Hi Sparks;

Hey, I started with an AIR file that was 2+ years old, and I know these AIR files can be a little quirky sometime. I went back and processed it again through air wrench without adding the afterburner and it did the same thing, so there is a problem with the AIR file itself.
I know I've had problems with other AIR files before. My FSDS program won't even recognize some of them, so its not necessarily an air wrench bug in this case.

Thanks for all the pointers, and the AIR file (and CFG.) The contact points are extrememly close, must be a very good model you were working with:costumes:

Thanks for the pointers, off to play with the new toy.......

Paul