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Why do aircraft not go to the start of the runway for take off

G

ggeccles

Messages
85
Country
australia
Can anyone tell me why it is that at some airports with single runway entry points or entry points not at the runway start, aircraft taxi correctly along the runway to commence take off at the start of that runway while at others, the aircraft starts at the taxiway entry point even though there is very little runway left for take off at that point.

I've done searches on many forums but the answer to this issue eludes me. Anyone have any ideas?
 
danfoster

danfoster

Messages
359
Country
unitedkingdom
It is probably to do with the distance between the threshold and the runway entry point. If it is over a certain length, the aircraft will backtrack to the threshold. If it is under that length it won't - irrespective of how much runway is left in front of it to takeoff on.

I think?
 
R

rfields

Messages
823
Country
us-arkansas
Normally if the entry is less than 1,000 feet from the runway end, the aircraft will not back taxi to the end.
 
G

ggeccles

Messages
85
Country
australia
Thanks guys. I suspect the default length is a little more than 1,000ft but I think your rationale is correct.

I did some further testing and noticed that I was able to get the AI to back taxi once the first runway link node past the node at the entry point (not the actual runway end) is beyond about 1,400ft.

This means I was able to place the end node quite some distance beyond the actual end of the runway as once you allow for the aircraft to do a u-turn, it still remains within the runway limit.

Not completely satisfactory for shorter runways but at least I am now understanding why it is so.
 
danfoster

danfoster

Messages
359
Country
unitedkingdom
All you need to do is create a small turning loop at the threshold, using "Apron Path" taxiway links.

This will solve your problem.
 
G

ggeccles

Messages
85
Country
australia
danfoster said:
All you need to do is create a small turning loop at the threshold, using "Apron Path" taxiway links.

This will solve your problem.
Click to expand...

Spent many hours, no days experimenting with this setup and cannot make it work. The only real solution for these shorter runways seems to be to create a taxiway down the centre line to each end of the runway. Probably not suitable for a busy airport but does work ok provided only one AI aircraft is active at the airport at any one time.
 
R

rfields

Messages
823
Country
us-arkansas
YBUD -Is the airport still in the configuration of the default - Rwy 14/32 - 5358 ft x 98 Asphalt and Rwy 07/25 - 3701 ft x 98 Grass ?

Which runway and which runway entry point is the problem?

YMUI may be too short to make the aircraft takeoff from the ends unless the parking is at one end of the runway.
 
G

ggeccles

Messages
85
Country
australia
Sorry for being so slow in replying Reggie, been away enjoying some sun, sand and surf.

YBUD is still in roughly the same setup as the default, just a few minor adjustments to enable the airport to line up with the photoreal base. the only problem is with runway 14 and the nearest taxiway - unfortunately that is where the airliners enter when departing for takeoff to the South/East.

I did manage to force aircraft from that taxiway to go to the end of rwy 14 by extending the runway link well beyond the runway end point, but that just created a couple of new problems, notably the departing aircraft going beyond the runway end to turn around.

I've had to settle with aircraft entering the runway from that particular taxiway and departing to the South/East, starting their takeoff from that point.

Another issue I had with YBUD related to the grass strip. under normal circumstances, these crosswind runways are not used by AI aircraft but for YBUD, I had to specifically stop takeoff and landings in the runway setup to stop Dash 8 and B737 aircraft from landing on the grass. Why is this so when I can't get small AI aircraft to go anywhere near these smaller crosswind runways elsewhere.
 
R

rfields

Messages
823
Country
us-arkansas
Has the Airport file changed the offset threshold to a blast pad or overrun?

That would shorten Rwy 14 to be too short for a back taxi.

Landing on crosswind runways is really a function of the approach path from the takeoff airport. Too many of our AI aircraft flight dynamics make FS think our jets are very small, very light aircraft. That way the FS weight limits on runways do not come into use because the aircraft are too light.

The configuration of YBUD should make all aircraft be assigned to 14/32 for takeoff. The centerpoint of 7/25 is farther away than the centerpoint of 14/32 for the whole ramp area.

Normally we have to put small AI parking very near the extended runway centerline for 7/25 to have them assigned to that runway for takeoff.
 
G

ggeccles

Messages
85
Country
australia
I left the offset threshold in place as although it is not visible under the runway poly, it helps to force landing aircraft further down the runway so they don't clash with departing ones.

I'm still confused by the inconsistencies within FSX. As a test, I reduced the backup section of runway 15 at YBCS to about 100 mtrs and the departing aircraft still went to that newly shortened end to turn and take off. Mind you, even with that big chunk taken out of the YBCS runway, it is still 50% longer than YBUD.

There are also inconsistencies with cross wind runways. While AI aircraft will land and take off from 7/25 at YBUD where I do not want it to. Try as I may, I cannot get AI aircraft to use 12/30 at YBCS or 14/32 at YBBN. This of course is without deliberately setting up these airports with the crosswind runway 7.29 deg. modification.

I mention issues with these three airports however I’m making these observations after customising well over 100 FSX AFCAD files over the years. It's as though there is a built in code somewhere within the FSX engine that seems to determine different characteristics for separate airports.
 
jvile

jvile

Messages
8,893
It's as though there is a built in code somewhere within the FSX engine that seems to determine different characteristics for separate airports.
Click to expand...

Yes, you will see differences across airports in rare cases :)

Sometimes what works at one will not work at the other.
 
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