NBAI F-15C Eagles Misbehaving in Taxiing to Parking

[Janeway]

I was observing the landing and taxiing of some F-15 Eagles (Nick Black), both at Elmendorf AFB - PAED, and at Mountain Home AFB - KMUO. When the F-15 Eagle turned into the nearest taxiway, it halted for some seconds. Then, when it resumed taxiing, it suddenly reared up like a "horse"...sank into the ground, and vanished. It did NOT complete its trip to the parking spot. And this happens over and over again with my F-15 Eagles. I even installed the F-15C Eagle from the installer, as it was packaged by MAIW....and the same behaviour persisted.... So it's not something that is present on my setup, or some modification I might have inadvertently made on the F-15 Eagle.... because the original, unmodified version of the F-15C Eagle behaved identically...

Has anybody experienced this problem before??

[MIKE JG]

I'm guessing that somehow your aircraft.cfg file for that model is getting corrupted.

Is this the only model that behaves this way at PAED??

[Janeway]

Thanks for taking an interest Mike. Your tip was one thing I checked out....
After a couple of hours investigating this problem, I discovered the solution...!!!. Or at least One solution.

The "rearing up" of the F15s ater they enter the taxiway to vacate the runway affects all models: F15 A-B-C-D-E. As far as I can tell.
My attempts to solve this behaviour included: brand new installs of F15 air files and aircraft.cfg files. Switching airfiles of F15 with the F14 Tomcat. All to no avail.
Another experiment involved moving the C.G. forward: by changing the 'wing_pos_apex_lon' entry in the F15s aircraft.cfg files. I altered it from -31.5 to 1.5 and even to 0.0. But no effect! Problem still present.

After modifying aircraft parameters failed to produce any positive result, I turned my attention to the Afcad... And I started changing 'hold-short' nodes to 'normal' nodes at the problematic taxiway. The F15s started to move smoothly along THIS taxiway....but they ALL parked in the SAME parking-spot. All four F15s that landed consecutively. So the problem was not solved satisfactorily....

Finally, I decided to do one more alteration: I added more nodes to the problematic taxiway..... and presto, the problem was solved !!!
ALL the F15s now taxied properly and went on to park in separate parking-spots. Apparently, the extra nodes seemed to provide more "traction" to the wheels of the F15s and there's no more 'rearing-up' after vacating a taxiway.

This experiment was conducted at Mountain Home AFB (KMUO). But I first noticed this aberrant behaviour of the F15s while observing the landing of F15s at Elmendorf AFB. I wanted to check whether this flaw was limited to Elmendorf PAED or ANY airbase with F15s parking there.

Armed with this solution, I can now modify ANY afcad where F15s are stationed...IF the same problem repeats itself (which is highly probable). On my setup, anyway.

[MIKE JG]

That's weird as I have never had that problem at PAED but I have seen other people with that sort of problem. Glad you found a solution to it.

[mikewmac]

Another experiment involved moving the C.G. forward: by changing the 'wing_pos_apex_lon' entry in the F15s aircraft.cfg files. I altered it from -31.5 to 1.5 and even to 0.0. But no effect! Problem still present.

Finally, I decided to do one more alteration: I added more nodes to the problematic taxiway..... and presto, the problem was solved !!!ALL the F15s now taxied properly and went on to park in separate parking-spots. Apparently, the extra nodes seemed to provide more "traction" to the wheels of the F15s and there's no more 'rearing-up' after vacating a taxiway.

Janeway,

I have a couple of comments on your problem.

When I created the NBAI F-15 FDE I placed the CG as far back as practical to make the NBAI F-15's land with a high angle of attack (AOA) and appear to be using aerodynamic braking during their roll out. Unfortunately, although I have never experienced it in any of my testing, this has been reported by a few users to lead to the problem you experienced at a few airports and especially if one uses 2X or 4X acceleration to hurry the NBAI F-15's back to their parking spots.

To move the CG forward and reduce the risk of experiencing this problem, simply move the longitudinal position of the CG forward in the following line in the aircraft.cfg file:

empty_weight_CG_position = -4.00, 0, 1.0

I would suggest changing the -4.00 to -3.50 and see how that works. If the problem persists, try a smaller value until the problem disappears.

What I think the addition of nodes on that problematic taxiway is doing is slowing the taxi speed that the NBAI F-15's will attain on it and therefore reduce both their acceleration to this lower speed and their tendency to rear up.

I hope this helps you with understanding and dealing with your problem.

Mike M.