Forcing a Runway into use at NZCH

[greaneyr]

After reading some comments in another post to this effect recently, I decided to sit down and try to figure out why FS just won't allow the use of Runways 11/29 at Christchurch. It appears FS has a formula for working out which runway should be designated as active, based on the wind direction (possibly derived from crosswind/tailwind components for each runway) and the ratio of length of longest to length of next longest runway.

At Christchurch, I set the wind to 110 degrees at 8 knots. Needless to say, it gave me runway 02/20. This is the behaviour we all hate and are trying to quash. So I increased the wind up and up and up. Still had RWY 02/20 at around 60 knots of crosswind. Then I tried playing with the AFCAD and lengthened RWY11/29 so it was longer than 02/20. Set wind to 110@8 and the runway in use became runway 11! It seems that as you shorten runway 11/29, the amount of wind necessary for it to be advertised as the duty runway increases considerably, since it's always compared to 02/20 at nearly 3300m.

I guess the behaviour they are TRYING to model is that "A shorter runway is always less desirable than a longer runway. Strong crosswinds render a longer runway unsafe, so under those circumstances, it's safer to land into a head wind on a shorter runway than land with a strong crosswind on a long runway." What's silly is the threshold. With runway 11/29 extended out to 2050m, the wind speed necessary for it to become the duty runway was 110@40. And to think there are airports like Gisborne with just over 1300m of runway that will happily become the duty runway with 1 knot of wind since there is nothing else longer. It seems a little silly really.

It also makes sense why New Plymouth is always so keen to dish out the grass vectors, since it's 1200m which is only 110m shorter than the seal runway. In this case, the wind would only have to favour the grass slightly in order to be classed as 'safer' than the seal. Remember, FS cares nothing about surfaces. A runway is a runway in it's opinion.

Anyway.... Can anyone think of any creative way we could exploit this and get our beloved Runway 11/29 to work at Christchurch?

[HardCorePawn]

Yep... its called the 'Star' method...

unfortunately, some of the links on that thread no longer work due to PAI redesigning their site... so try these:

http://www.fsdeveloper.com/forum/showthread.php?t=4965
http://www.projectai.com/forums/index.php?showtopic=54393
http://www.projectai.com/forums/index.php?...c=54913&hl=

Basically what you do is create a whole bunch of (closed, invisible) runways that have less than 8 degrees difference between their headings that go between the two 'real' runways... so you end up with a 'star' shape something like this:



and then place them far way, eg. the south pole, so that you cannot get vectored on to them and AI will not find them as they approach...

Apparently this works by tricking FS into thinking they are all parallel runways (due to the less than 8 degrees difference)... and will adjust for the winds accordingly...

[greaneyr]

Thanks for that. I figured there had to be a way around it?

QUOTE (HardCorePawn @ Feb 11 2008, 10:15 AM) <{POST_SNAPBACK}>

Apparently this works by tricking FS into thinking they are all parallel runways (due to the less than 8 degrees difference)... and will adjust for the winds accordingly...

I can pretty much follow those tutorials. I'm still not quite sure 'why' this particular behaviour is put right by this workaround. What's so magical about parallel runways that means FS will end up using a significantly shorter runway on a different heading?

[HardCorePawn]

Who knows... just another one of those 'MS Flight Sim Mysteries'™

[greaneyr]

Hmm, I tried the star method last night without success. Will give it another go when I get the chance.

The thing I got from reading about it is that it activates BOTH runways... which isn't necessarily what we want. I have another idea i might try too... Will keep you posted.