KRMG T-6 Texan II Falls Over

[WingZ]

The RNZAF has taken delivery of its first Texan II's and so the updated AI needs to go to Woodbourne.
There is a single taxiway; on landing the plane slows to 26kt and then does the U-turn to taxi back. This is too fast, and the plane trips over its nosewheel.
I am hoping there is a quick fix?

[campbeme]

Yes that correct, it does not do 180 degree turns without falling over. I stumbled across it when I was making the East Sale package.




Magic Mike, is there a tweek you could do to the FDE?

[Stewart Pearson]

Magic Mike, is there a tweek you could do to the FDE?

Fit stabilizers, like we had on bikes?

[Chrisb]

Turn it off....and then on again.

Chris

[Firebird]

If I get a chance later I will see if I can recreate and at least come up with a temp fix until Mike has a chance to look into it.

[Firebird]

For my tests what scenery and afcad is that NZWB?

The reason I ask is that the 3 tests that I have done so far have not reproduced the error. I have also double-checked that both the fde and the air file that my T-6s are using is the same as the ones from the Greek Trainers package.

[WingZ]

At AVSIM: (You should really have this if you don't already: a classic scenery )
I've attached the custom AFCAD
The issue would be apparent for any T-bone taxi configuration forcing a 180 turn I imagine.

File Description:
The 'Real New Zealand' Marlborough scenery previously available as payware is now offered here as freeware (the scenery and installer are unaltered from the original payware version). Includes custom-built Woodbourne, Omaka and Picton airports, based on a photo scenery which covers much of the Marlborough area.
Filename: installrnzmarlfs9.zip
License: Freeware, limited distribution
Added: 2nd April 2012, 11:49:02
Downloads: 1340
Author: Robin Corn, Ian Warren
Size: 118898kb

[Firebird]

OK thanks I will try that scenery/afcad combi.

[JohnTenn]

Found a work around.

I have put a taxi lane on the runway, beyond the centre line. (cross over the centreline from the intersection.)
No lights and no lines.

Take the taxiway to the end of the runway, add a link to the runway line.

Beyond where the Texan does its manoeuvre add another link between the taxi-link and the runway link.
Move the taxiway link closer to the runway centreline.

Used also at Hamilton (NZHN) to stop large aircraft from using the GA taxiway.

Hope this helps.

John

[Firebird]

That is along the lines that I have found.
In my case what I did not get is that the aircraft tips over on landing, not once. However, it always tips over when manoeuvring for take off. The simplest thing I have found to slow it down for turning, on take off, is just to put a node on the runway.

It slows towards that point and starts to turn and stays upright. Two things I found here, one is that the taxy speed that you have set in your system must be key. If you have set too high a taxi speed then it will flip whilst trying to turn. I think that I have my limit set to 20. Try lowering your taxi speed, assuming that you have altered it. I believe that people that have set high taxi speeds are the ones having the problem.

The second is that although the node slows the aircraft down for the turn it doesn't slow it down quickly enough, to enable the aircraft to stay on the runway throughout it's 180.

Still working on this.

Incidentally, thanks for the link to the scenery. Very nice find. I admit that I had missed that.

[WingZ]

You're welcome Steve, it's an all-time favourite in this part of the world!
You are correct about taxispeed having an influence.
I use high speeds to clear the runways at the major airports: 35kt runway, 20 kt taxiway.
I didn't play long enough to decide the critical value, but winding them right down allowed everyone to come home!



John with my normal settings, the parallel taxiway will work for takeoffs but not landings.

It would be nice if the FDE could be tweaked a little, it is the only aircraft doing this.
Also: it does tend to turn rather wider than the runway, and it would be great if it could turn on a dime like the real thing!

Cheers
Charl
>>>>>>

[Firebird]

Hi Charl,
FDE's are complicated little beasties that are balancing acts and numerous parms interact with other features and changing one part nearly always leads to some aspect of the flight model changing.

I shall give you a specific answer in this case.
The sort of changes that you are talking about involves redistribution of weight. Quite often a model will tip over when making turns, especially if the aircraft fde is set lighter than the actual aircraft is. The sort of things you can do is to increase the weight overall, move weight further from the centre line, stiffen the undercarriage, turn the aircraft less aggressively or slow the plane down.

The obvious one of these that you can see will have the most drawbacks is increasing the weight overall. This will most obviously affect take off speed and distance, acceleration, climb rate, approach rate, turn performance. As you can see altering this means altering a lot more parms and some of those will alter others and quite quickly you get into a massive re-write situation.

With moving weight from the centre line a useful tool that AI fde guys have is the fuel load. the fuel load has no influence on an AI aircraft as it uses no fuel. If you give it no fuel it will still fly, but what you can do is place the fuel as far along the wings as you need. It seems strange but an aircraft is less stable with all the fuel in the fuselage.

You can increase steer angle of the nose wheel, but this really only has a great effect at very low speed plus if your aircraft is unstable increasing the nose steering will make it more unstable not less.

The other critical parm that you can alter for balance is the empty CG position. This could work but will also alter other factors like instability on take, rate of climb, how quickly the nose leg comes down on landing. The further forward the CG is set the better the look on take off but it is also normally the reason that an aircraft tips over, forwards, in a turn.

I will have a play and see if I can improve your situation w/o ruining what Mike was trying to create aerodynamically. In the mean time, I would try reducing your runway taxy speed a bit to see at what speed the problem stops. At 20kts it will not tip over on landing.

As you can see it is not a simple thing.

[WingZ]

I think I knew this was no simple thng
I do appreciate your having a look; meantime I will temporarily post the appropriate speed limit signs down the runway!

Cheers
Charl
>>>>>>>

[SeanG]

I think I knew this was no simple thng
I do appreciate your having a look; meantime I will temporarily post the appropriate speed limit signs down the runway!

Cheers
Charl
>>>>>>>

Hey Charl! Didn't know you hung out in these parts too

I'm working on an Ohakea package that you may be interested in too......

SeanG

[WingZ]

I hang out ... everywhere, Sean!
And for matters military and AI, can you think of a better place?

Yes I've seen bits of your NZFF posts about it, sounds good.

[WingZ]

Always a workaround...
Zolt painted the IRIS model, which I stripped of everything and made it AI.
Nothing ventured...
The landing flare is somewhat overdone, but at least they turn properly and don't fall over!

[Firebird]

Charl,
I have thought about this for a while and then came up with a kludge fix for the NZWB afcad.
Why I did this and not touch the fde is due to two considerations. One is to fix it would require a rewrite for one base, which seems a bit of overkill and two the problem isn't the fde it is the AI engine.

Simply put in real life no pilot would consider making a near 180 deg turn at 35 kts. He would slow to around 5-10kts before undertaking such a turn. The trouble is that the AI engine rules do not even go close to touching this aspect of flight. The engine looks for the nearest exit and slows down as you approach the node for the turn. The problem is that there is only one exit, in the middle-ish, and it makes a beeline for it at taxi speed as there is no node to slow it.

The solution I have created follows on from what John mentioned earlier. I created a taxiway the full length of the runway, close to the runway link and created a loop at either end of the runway for aircraft taking off which stopped the problem I had on takeoff.
The effect of adding exits at both ends means that the aircraft no longer creates an abrupt turn once it slows to taxi speed, 35 kts in your case, when it lands as it recognizes that there is an exit in front and continues forward.
In addition to this I added two earlier loops, one in each direction, after the runway exit to allow the aircraft to turn earlier than the end of the runway.

I have tested this out using your taxi speeds, 35 and 20, and found that it works.

The only issue will be if you get two landing within a minute of each other. Once the aircraft exits the runway to the parallel taxiway any others on approach will be cleared to land and you will get a collision. As this is not what you would call a high volume movements base this shouldn't be an issue.

I amended the afcad supplied with the scenery you mentioned. See if this meets your requirements. Let me know if it works or if you think it could be improved.

[WingZ]

It does indeed work as advertised; interesting that with very little change in taxi speed, the Texans will overshoot the first turnout and go to the end of the runway.

Of course in the RNZAF flightplan (previously for the CT4's) these 6 birds depart NZOH in pairs.
Arriving at NZWB #1 lands and 2 breaks away into the pattern.
3 goes missed (1 occupying the rwy); 1 faces off with in the returning taxi with 4 landing.
You need big attached round objects to taxi into an aircraft on short finals, but he makes it to the turnoff with maybe 5m to spare.
5 goes missed, but 6 and 4 - just - don't make it, and arrive at the scene of the accident at the same time.
I'm sure increasing taxi speed by a knot or so will sort that problem, and I may play with it a bit.
Quite entertaining to watch all the antics.

Thanks for your input, Steve and John.

[JohnTenn]

Hi Gents

Not to belabour the point.

A visual depiction should clarify the creation of taxiways along the runway to get aircraft to behave better.

An unintended consequence might be that the following aircraft land while the preceding aircraft is "backtracking" the runway.

I created narrow taxiways and then pushed them toward the centreline of the runway to hide them.

The entrance needs to be beyond the runway centreline otherwise the fillet, curved bits, is removed.

There are detailed tutorials on the net somewhere.

Have a look at the attached picture from ADE

[Firebird]

That is more or less where I started, John, and the unintended consequences are indeed what Charl was describing and what I warned about.

I did add the mod about creating earlier access to the pseudo taxiway to prevent taxying to the end, so as to try to eliminate most of the problems.

You are right about the curved bits but in this case the photo scenery makes up the ground texture not the afcad. Hopefully you will see what I mean.