FAR and Mechjeb terminal velocity

[Ditchbuster]

Hi, while waiting for some of the mods i like to update i have been playing with mods I dont normally use that have been updated. And I have come across a question which I am sure has been answered but I havent found yet. I am sure there is a thread on this somewhere so a link to it will be fine. I am really not trying to waste anyones time.

Anyways my question: Does Far change the terminal velocity and if so does mechjeb then recognize this?

I have been playing around with some rockets and I was surprised at how fast mechjeb was taking my rocket to with the terminal velocity limiter turned on. it was defiantly way higher then the wiki recommends for velocity at the various altitudes.

Thanks!

[Nibb31]

Anyways my question: Does Far change the terminal velocity and if so does mechjeb then recognize this?

Yes and No.

FAR changes the aerodynamics completely, including terminal velocity. MechJeb gets its info from the default system, so it doesn't work properly with FAR.

[MennoLente]

Indeed, mechjeb relies purely on math, and uses as little variables as possible, as there are not many provided by the game. The question that remains unanswered is: how small is the difference?

[Ditchbuster]

Hmm I will check it a little later. right now mechjeb is letting the rocket go to 300m/s at 2500m. well thats is what i am hitting with the current rocket. and it is limiting the thrust based on overheating not terminal velocity at that point. Also getting reentry effects at around 5k or 6k altitude so i assume i am going too fast... if it is doing this based on the normal game wouldnt this be the same speed as normal even if FAR and now changed it?

Edit: Removed FAR and mechjeb does go back to limiting the rockets at the normal terminal velocity.

Edited May 27, 2013 by Ditchbuster

[stupid_chris]

I think it's because MechJeb calculates terminal velocity on the force air drag applies on the ship. If correctly made, I rocket can go pretty fast without too much drag in atmosphere. Maybe MechJeb is just not receiving a sufficient amount of drag from air resistance to slow you down. And FAR changing terminal velocity probably makes it that what would be so fast you would have re-entry effects in vanilla KSP becomes normal, but the game still sends the effects. This would also be logical that MechJeb calculates terminal velocity this way because I highly doubt it has the terminal velocities per altitude stored for Kerbin, Eve, Duna, Laythe AND Jool.

I'm also pretty interested at knowing these things because I've been considering getting FAR as I only use rockets and don't ever really go in the SPH, but I'm kinda unsure if it would make it easier to launch stuff up or completely throw my rockets off course, and I am in the dark for what concerns MechJeb's relations with FAR and calculating delta V and such.

Edited May 27, 2013 by stupid_chris

[Ditchbuster]

Well Ill keep playing around with it. I know it makes it harder with the gravity turn. Mechjeb seems to crank over too hard and flips the rocket sometimes. It is probably just my rocket design. I do like that FAR allows you to assign the axis the control surfaces are on.

[stupid_chris]

I think the spinning is due to air resistance. There probably too much air pressure when you do your grav turn and when you tilt your ship it causes sideways drag, spinning the crap outta your ship. Which means: with far, make your grav turn a lot higher. I guess.

[Ditchbuster]

Well actually I was reading a post by the creator of FAR and I think he said start earlier but way more gentle. That if you crank hard all of a sudden you will get that flip cause your angle of attack goes nuts. Also because you normally end up with most your weight in the back on rockets and that part wants to be forward (like a dart) they tend to want to flip around. So i think it was a combination of mechjeb not being designed for FAR assent and that I am not used to designing rockets with FAR.

[stupid_chris]

Makes sense. One thing though: Don't ever use FAR with the Deadly Re-entry plugin, FAR screws it up big time and make you explode for no reason all the time :l

[numerobis]

MechJeb calculates drag from the basic equation of drag, getting the coefficient from the part on your ship. It doesn't have tables to look up.

It is not impossible that FAR and MechJeb would interact correctly, but I wouldn't necessarily count on it.

[dlrk]

Makes sense. One thing though: Don't ever use FAR with the Deadly Re-entry plugin, FAR screws it up big time and make you explode for no reason all the time :l

Just ran across this post, and I'd like to point that that is inaccurate. FAR works fine with Deadly Reentry, I use the two together.

[stupid_chris]

Just ran across this post, and I'd like to point that that is inaccurate. FAR works fine with Deadly Reentry, I use the two together.

At the time of this post, the only version of Deadly Reentry available was 1.3 Since then, ialdabaoth took over the management of the plugin and version 2.0 works with FAR.

Now I posted this the exact same day that v2.0 came out for testers, but I hadn't noticed it by then. So at the time being, I wasn't really wrong because v1.3 didn't work at all with FAR.

[deepholecaver]

Currently, It looks like with 0.23, MechJeb 2.1.1.01, and FAR 0.1.2.3, MJ gets either a 0 (even at mach speeds), or NaN, for aerodynamic drag, and then calculates an infinite terminal velocity. I like MechJeb and having the terminal velocity available to get an efficient launch more than I like the idea of FAR, so I'm going to drop it until the problem gets fixed.

[almagnus1]

Alternatively, you can hold off on using MechJeb until you are out of the atmosphere, which will give you a decent compromise.

[numerobis]

Currently, It looks like with 0.23, MechJeb 2.1.1.01, and FAR 0.1.2.3, MJ gets either a 0 (even at mach speeds), or NaN, for aerodynamic drag, and then calculates an infinite terminal velocity. I like MechJeb and having the terminal velocity available to get an efficient launch more than I like the idea of FAR, so I'm going to drop it until the problem gets fixed.

You get a more efficient ascent by just adding more fuel so that your TWR is less than 2, at which point you will never reach terminal velocity.

[zinfinion]

You get a more efficient ascent by just adding more fuel so that your TWR is less than 2, at which point you will never reach terminal velocity.

With FAR + KIDS set to .55 Atm and Thrust varies with Isp I can set MechJeb to cap acceleration to 2.4G and it will only exceed terminal velocity for a few seconds.

So yeah, what you said.

[draeath]

Reminder that you can use ascent guidance and not actually have it fly for you... just tell you where you should be pointing. AFAIK the throttle during ascent guidance is really the only spot where the terminal velocity is useful in Mechjeb?

You can also adjust the ascent curve that mechjeb will guide you on.

[Taki117]

On another note, And I don't know if this has been pointed out or not, but with FAR the Terminal Velocity at sea level is approximately 350m/s, by the time you get up to 3km it's about 700m/s, once you get above about 10km it balloons to 3km/s. If you are getting reentry effects it's because the game is thinking that you are going super fast for your altitude, but in reality you are not (relatively speaking) and while MechJeb is actually limiting you to Terminal Velocity, your rocket might not actually be going that fast anyway.

[How2FoldSoup]

Holy mother of necro

Edit: I have no plans for content:sealed:

[Castun]

On another note, And I don't know if this has been pointed out or not, but with FAR the Terminal Velocity at sea level is approximately 350m/s, by the time you get up to 3km it's about 700m/s, once you get above about 10km it balloons to 3km/s. If you are getting reentry effects it's because the game is thinking that you are going super fast for your altitude, but in reality you are not (relatively speaking) and while MechJeb is actually limiting you to Terminal Velocity, your rocket might not actually be going that fast anyway.

Is there a chart for new terminal velocity in FAR?

[ferram4]

FAR has a terminal velocity readout in the Flight Data GUI if you want it. You'll have trouble reaching it though, and you'd be better off ignoring terminal velocity if you're using FAR.

[draeath]

It's not a hard wall with FAR anyways, if you're the least bit aerodynamic. You'll also get visible supersonic shock wave effects if you're pushing too hard.

[Roastduck]

If you use KER with FAR, you can control the throttle so that your TWR stays at 2. Fuel efficiency should see a noticeable boost if you do that.