AI starting speed: Possible to decrease?

[Manschy]

While watching the current visitors at Brüggen to check out and doing some fine tuning to my AFCAD, I noticed several aircraft getting very fast in the very beginning of their take off.
(Just an interest incidentally)
I would like to know if it is possible to decrease the starting speed of several AI aircraft.
Especially the C-17 or prop heavies seem to be very fast after a short distance. That way, they use less than half of the runway to take off.
Is the speed part of the air file or is it possible to change some minor entries inside the aircraft.cfg?

Thanks.

[hschuit]

You could try to reduce the Aircraft.cfg static_thrust value. Or reduce the flaps_up_stall_speed but that has the risk of the model going to pitch oscillate, specially on approach.

[hschuit]

Made a mistake: Do not reduce the flaps_up_stall_speed but increase it to make the take off run longer.

[Firebird]

As a principal do not reduce the power on its own, unless it is so vastly overpowered that it is an obvious thing to do.

What I mean here is that whilst you would decrease the acceleration and therefore increase the take off roll you will have a knock on effect. This will normally entail the aircraft not getting up to cruise speed or even worse it being so under powered that it ends up stalling before it gets to its operating height.

I, like many people dabble in fde work, will say frequently that quite often it is a balancing act. If you alter one thing you will need to alter one or more other parms to counteract parts of the first change. This is why it is not always possible to give a simple answer. Each fde has to be treated differently.

To give you an example I am currently working on Johns USN project. The land based, or dry, fde has met Johns satisfaction but to turn this in to a wet fde with a similar performance but with a quicker take off is really tough, slow going.

In essence my advice to you would be to assume the worse case and that not one thing will cure your issue. If you make any changes make only relatively small changes and test again. Again as an example altering the flaps_up_stall_speed will increase the nose lifting off the runway, increase the take off speed but might cause issues with the gear retraction.
Altering that parm also alters climb rate, climb speed, descent rate and approach speed.
Be prepared to alter others to counteract negative changes.

For your testing don't just look at take offs. You have to check circuits, VFR and IFR (if applicable), climb to height, cruise, descent and landing. Don't forget that if you increase the take off run for one base then it may not be able to operate out of others.

Now on the specific questions you asked, yes you can make changes to the cfg file to affect what you are looking to change. The fde consists of both the cfg and the air files. Normally what is in the cfg file will override the equivilent parm in the air file.
Rather than altering the thrust settings directly it would be better to alter the thrust_scalar parm for jets and turboprops. I would advise again that you start with small increments of .05 or at max .1 changes and view the changes.

If you have the inclination for the amending and testing of modifications then I would like to welcome you to the world of fde work

[Manschy]

Wow - thanks a lot for this exhaustive explanation, Steve.
Yes, I guessed as much - AI traffic is such a complex subject matter and I admire all experts here around for creating aircraft - flyable or AI likewise.
It's not worth to change some parameters, just to let some aircraft look fine at some place - but elsewhere, they crash or disappear.
So asked as a layman, I thought it maybe would be a simple number or minor entries inside the aircraft.cfg to change . This will reduce my pleasure in AI traffic not at all

[hgschnell]

Jan Martin did a great job with his AI FDEs, have a look at his tables of take off speed and runway length
http://janswebsites.altervista.org/flightsim/index.html

[Firebird]

His AI FDE Settings table is a gold mine for how the most common settings alter various stages of flight.

You have to know what you want to do, then look up what will make that happen. Then you note what else will change and then work out if you need to counter that by altering another parm. You will see that several parms will alter a specific attribute.

This is the reason why you make small changes, test them and then modify again.

What might help you is that he already created a modified fde for the C-17. You might like to try that to see if suits you better than the one that came with the model.

[Manschy]

Oh, that's a great hint! Thank you, Günther. Guys, so many things around without knowing of its presence.

[hgschnell]

I dont know if these FDEs are okay in FSX or P3D, but I am very happy with them in FS9