AI Approach and Landing Speed

[aerogator]

Hey guys,

How do you change the approach speed and landing speed of AI aircraft? I have searched the forum and there's a lot of talk about it but can't find how to. Also searched the .cfg file and the .air file using AirEd of course but can't find any usable variables. I've got planes that approach way too slowly and too high then drop to the runway from about 75 feet.

I'm mainly just looking for the way to adjust the variables: I'll play with it from there.

Thanks,

[Firebird]

Jake,
Sorry to say that it is a whole host of variables that can alter the fde, not a simple one of two. In the case of the approach speed and landing speed there is no set parameter.

For example a real aircrafts approach speed is determined by lift/weight/drag/power. the AI model is no different and changing any one of those parms can altering some other aspects of the flight. Likewise other parms can affect the approach/landings speeds.

A useful guide you can see here, http://janswebsites.ja.funpic.de/fde/ai ... tings.html and download a pdf version if you want to. Jan describes the changes made to various parms in both the .cfg and .air files and what effect they have on the models flight characteristics.

Hopefully it is easy to follow but simply put you see what the changes were on the left hand side and it shows you how it affects the flight through a variety of conditions. Once you grasped what either the increase/decrease does and you want to apply that to your model then you apply a similar approach.

The bottom line is that it is a balancing act. You may find that you need to alter one parm to achieve what you want and tweak two others to counteract the effects that you didn't want from the first change.

[bismarck]

That link doesn't work, at least for me....

Giorgio

[aerogator]

Thanks for the quick reply Steve. I had a feeling this was what I would run into. No worries! I'll study it and see what I can come up with. That's what this is all about anyway, right?

Giorgio - You may have your web security settings too high. When I went there, I got a warning but went anyway. . If my computer crashes, I'll let you know.

[Trevytt2004]

Wondering if these parameters would also be responsible for the landing distance. I'm finding that the kc-135s are able to stop way to quickly. Maybe the breaking parameter could be tweaked to allow for a longer rollout.

[fishlips]

Often you can reduce the reverse thrust effects which helps a bit. Mike or Steve may be able to help further with this info.

[Firebird]

That link that I posted earlier gives you most of the things that the main parms alter. Like before, it can be a balancing act. A short landing can be due to a number of factors, not least the approach and touchdown speed. If it touches down slower than it should then it will, obviously, stop shorter than you think/want.

Having said that, what Mark says is correct and it may be the one time that you get a magic bullet. The reverse thrust will only apply to speed on the ground and above 30kts and so it is one parm that you can play around with.

The parm is min_throttle_limit, which can be found under the GeneralEngineData section.

In this circumstance this following parm means a reverse thrust of 10% full power :-
min_throttle_limit = -0.10

If you wanted to try 5% reverse thrust then alter the parm to :-
min_throttle_limit = -0.05

[aerogator]

Steve, I meant to thank you for that link. It has become a valuable tool for me and I have only scratched the surface. Like you said, it can be a balancing act, but once you get the hang of it it is not so hard to alter most basic things. I've been able to correct the original problem I had with the approach and landing problem.

Now I've got a crazy one and this has popped up before. (Steve, I think you helped me with it but I don't know what you did) I've got a large tail-dragger that begins to bounce and shake as soon as push-back is initiated and finally it just disappears through the pavement. I've tried a lot of things from weight, contact points, and CG in ACM, to adjustments with Aired, to manually changing things in the .cfg file. Any ideas of what causes this?

Thanks,

[Firebird]

No problem,Jake.
Without seeing it for myself it is difficult to be sure. What it does seem like is possibly a combination of balance and undercarriage issues. What I think is happening is that the aircraft crashes due to it's balance and gear damping. It starts bouncing and that leads to a crash through the floor.
What I mean by balance is where is the CofG in the model and how is the weight distributed. This is potentially one of the most difficult things to solve.
The main thing is where is the empty_weight_CG_position in relation to the aircraft and its undercarraige?, where is any additional weight?

Then there is the problem of the undercarriage. If the aircraft is light then it is quite easy for the aircraft to start bouncing around on quite soft gear compression, what I would do is look at the Damping Ratio of the gear and see if you can dampen it a touch more.

An obvious thing to try is to add more weight to try to stabilize it but as you see from that pdf if you do you will alter so many features that you may end up with one hell of a job on your hands. So if you think that the plane is too light be very careful that you don't add too much or you could end up basically re-writing the fde.

Oh nearly forgot, ACM is almost obligatory (IMHO) to try and sort out a balance issue.