How do I prevent flipouts during a gravity turn with MechJeb and Ferram Aerospace?

[Petarski]

All my crafts will flipout shortly after going super sonic and doing a 10km/40% gravity turn. What is the best turn shape for the mod?

edit:

Tips are start gravity turn higher (10km or so), lessen turn angle (80%-100%), add more reaction wheels, add control surfaces. Thanks guys! Crafts work now.

Edited August 2, 2013 by Petarski

[nhnifong]

If you show some pictures, we can help you determine what's wrong. take screenshots with F1 (fn F1 with a mac keyboard). Upload them to imgur, then put the direct link in bbcode tags.

[Scorpi15]

Add more reaction wheels. Control surfaces aren't as effective after a certain altitude and have been the bane of many a craft. Reaction wheels, on the other hand, add more helping torque no matter how high up you are. Remember to add batteries and manage your power levels though.

[espm400]

With FAR you're going to have to keep your speed a bit lower than normal and keep your nose in, or very close to the prograde marker, at least until you're above 30,000m. I had this problem myself until I realized this.

EDIT: I can't speak for MechJeb, as I've not used the ascent guidance on it.

Edited August 1, 2013 by espm400

[Hovis]

I was saved by limiting acceleration to 20 m/s on the control thingy. Not sure on the exact science of how this made the critical difference, but it did. My understanding is that Ferram favours longer more controlled lift offs, rather than the Massive Power Blitz style that would traditionally work fine. Once I made that change Mechjeb was fine.

[Kaa253]

I have had the same issues with mechjeb since upgrading to 0.21 and I am not using FAR. I believe it is caused by mechjeb not being well tuned for the new attitude control system. I notice it particularly when the balance of my craft shifts as 2nd stage tanks are getting below half full. Typically I am around half way through my gravity turns at this point. As others have noted before me, limiting acceleration, adding more reaction wheels and keeping the nose in very close to the prograde marker (I use bursts of RCS for this) will all help to solve this problem for you. I kind of like the change as Hovis puts it the "Massive Power Blitz" style is not as successful as before which I think adds realism. I have never tried Ferram Aerospace, meybe I should...

[Tyren]

I had that Problem without mechjeb, i recommend reaction wheels AND RCS Thrusters near the bottom of your missile, too.

@Scorpi: The test in ur sig is lulz (i am slow in typing english )

[ploxus]

Does MechJeb take advantage of reaction wheels? I noticed MJ doesn't enable SAS when in auto-pilot. Or do reaction wheels work without SAS enabled?

[Guest]

I avoid control surfaces on rockets altogether due to random stalls. Lots of Reactions wheels like stated earlier seems to do me well. Correct me If I am wrong but the control surfaces on irl rockets produce no lift, they only redirect airflow.

[kofeyh]

I avoid control surfaces on rockets altogether due to random stalls. Lots of Reactions wheels like stated earlier seems to do me well. Correct me If I am wrong but the control surfaces on irl rockets produce no lift, they only redirect airflow.

Wings are only really useful below 30km. Above that and reaction wheels, RCS is the easiest option. As for wings on rockets, it varies, some are used for attitude control, others have fins to add stability. Guided missiles are a case in point.

The thing to remember in KSP, is that control and flight surfaces don't quite work the way one might expect.

[rryy]

You can't just suddenly turn 45º from prograde and expect to stay on course, especially with FAR. You have to do a more gradual gravity turn starting at around 5 km, keeping near the prograde vector.

[zerotwo]

In my experience the two mods do not react well together under most circumstances. The only way I have found to mitigate this is to launch using only one of the two. Disable all of the components in mechjeb you can and do a horizontal lift into orbit or shut off everything you can in FAR and do a vertical launch.

I went looking for a good mod to swap control computers but unsurprisingly it did not exist. (Kind of a rare need)

That flip may also be a result of your craft's centre of mass shifting too far backwards due to the way you are burning fuel in flight.

Engines always reach for the furthest source of fuel and aircraft designs tend to be heavy towards the rear already, if your craft burns all it's forward fuel in flight it becomes incredibly unstable and the aft weight imbalance can cause the craft to flip into and unrecoverable stall.

Try locking forward fuel tanks and draining from the rear first?

Hope this helps.

[BubbaWilkins]

In my experience the two mods do not react well together under most circumstances. The only way I have found to mitigate this is to launch using only one of the two. Disable all of the components in mechjeb you can and do a horizontal lift into orbit or shut off everything you can in FAR and do a vertical launch.

I went looking for a good mod to swap control computers but unsurprisingly it did not exist. (Kind of a rare need)

That flip may also be a result of your craft's centre of mass shifting too far backwards due to the way you are burning fuel in flight.

Engines always reach for the furthest source of fuel and aircraft designs tend to be heavy towards the rear already, if your craft burns all it's forward fuel in flight it becomes incredibly unstable and the aft weight imbalance can cause the craft to flip into and unrecoverable stall.

Try locking forward fuel tanks and draining from the rear first?

Hope this helps.

FAR and mechjeb work just fine together, but it takes far more fine tuning and experimentation to produce a craft that flies well. It is possible to manually fly some crafts that mechjeb can't handle, but more likely it's less frustrating to just fix the balance/performance of the craft first. If your craft is balanced, but you still fight instability mid flight, check to make sure that you are strutted sufficiently to remove ALL flex. It only takes a small amount of flex to upset an engines thrust vector and send your craft out of control.

All my crafts will flipout shortly after going super sonic and doing a 10km/40% gravity turn. What is the best turn shape for the mod?

first, expirement....

remove the gravity turn all together.

1) Does your craft stay straight up at 10/km? 15km?, 20km?, 25?

if so, move your gravity turn to a higher elevation and try again.

2) If your craft becomes unstable even in a straight up ascent with no turn, adjust your speed accordingly. Perhaps you're going too fast for that elevation and need to back off a touch. My original shuttle+launcher design was flawless as long as you didn't exceed 200 m/s below 10,000 feet.

3) If 1 or 2 get you close, perhaps activate RCS in the atmosphere to add that little additional bit of command authority.

4) Now add a gravity turn, but experiment with the altitude it initiates. Perhaps 10,000 is too low for your craft and you need to wait until it's higher up in the atmosphere and/or going faster. My current shuttle+launcher can not handle a gravity turn under 20km. For me this works out well because its just above this point that the solid boosters typically run dry.

5) All else fails, redesign the craft until you get something more stable to start with.

Edited August 1, 2013 by BubbaWilkins

[Eric S]

Basically, you're looking at two issues.

The first is the way FAR works. It removes the atmosphere so that the stock aerodynamics doesn't affect the craft, and then computes the aerodynamics as if the atmosphere were still there. This means that MJ can't compute terminal velocity and will merrily take the rocket past terminal velocity and even the speed of sound. Limiting the thrust to about 20-24 m/s is about the only way to deal with that other than manual throttle control.

The second issue is that rockets with too much aerodynamic drag (not the right term, can't remember the right one though) ahead of the center of mass tend to want to flip around and try to fly backwards. While you're aiming the craft directly prograde, it doesn't take much to overcome this force, but the farther away from prograde you're pointed, the harder it becomes to overcome it. Most of the reading I've done on FAR says that you shouldn't be more than 5 to 10 degrees off of prograde at any time below 30K. That's not "5-10 degrees is OK," it's more "some craft will flip out at 6 degrees, others can go farther."

[Petarski]

What I'm getting from all these posts is that I should lessen the gravity turn to a very low angle (80%/100%) and start higher up if I want to do a sharper turn. All my craft are good when vertical. Thanks guys.

[42BelowVodka]

the problem i have is that mechjabber wont start a gravity turn anymore when the SAS is active. before it would just turn it on and off by itself. when i turn it off at 10K the ship just swings out of control. sometime it will turn around a couple of time and than recover but thats a huge waste of fuel

[AndreyATGB]

the problem i have is that mechjabber wont start a gravity turn anymore when the SAS is active. before it would just turn it on and off by itself. when i turn it off at 10K the ship just swings out of control. sometime it will turn around a couple of time and than recover but thats a huge waste of fuel

MJ 2.0.9 removed SAS use because, according to the changelog, it's "no longer needed". I don't understand this logic, but there you go. 2.0.9 will just manually control it all the time completely ignoring SAS which actually makes autopilots be jerkier than before.

[42BelowVodka]

If i dont turn on SAS at launch the my rocket will crash in seconds