Why is this fighting me?

[Tex_NL]

18 minutes ago, Plusck said:

Yes, I agree.

Also, I noticed that people are talking about "surviving the [gravity] turn" and MechJeb ascent guidance.

It has been said many many times, but could perhaps be repeated again here:

The "gravity turn" is by definition, and must in reality always be, a gentle and gradual affair that cannot go against the airflow. The fact that old versions of KSP allowed sharp turns is regrettable. I don't have MechJeb but it sounds like MechJeb will try to force a sharp turn if you tell it to.

A sharp turn against the airflow will destroy rockets IRL and also (now) in KSP. While you're in the atmosphere, prograde is the direction of the airflow. Try suddenly turning 20° against the airflow at mach 1 in anything other than a fighter jet (and even then...) or air-to-air missile and see what happens.

Fairings are problematic because they are big empty shells. Whether they are "bugged" or not is actually far less important than the essential point about not turning a big, long empty shell at an angle to the airflow.

All very true. Yes, MechJeb can turn you away from the airflow if you tell it too. It also can keep you perfectly aligned with the airflow. But the same can be said about manual control. MechJeb has NOTHING to do with it!
The real problem is the body lift bug on the fairings. It is placed WAY to far forward. As soon as you veer even slightly off course (with or without MechJeb) this bug can generate a huge force too far in front of your rocket. So huge that it can be nearly impossible to correct. With Claws Stock Bug Fix the body lift vector is place back where it should be making the fairings behave as intended.
But with an improper flight profile (with or without MechJeb) it is still possible to screw up and destroy your rocket.

All that said only one question remains? Why bring in issues that have completely nothing to do with the problem at hand?

[Plusck]

4 minutes ago, Tex_NL said:

All that said only one question remains? Why bring in issues that have completely nothing to do with the problem at hand?

The OP said "I've been trying to get a scanner lauched and every time it starts a gravity turn, it either flips or breaks apart.".

The problem is right there in the question: "every time it starts a gravity turn". A rocket will only flp when "starting" a "gravity turn" if that gravity turn is going far off prograde.

The problem is exacerbated by the fairing problem. But the main issue is that either the player has "learnt" to do exactly the wrong kind of gravity turn, or MechJeb is causing the problem for them. Therefore telling the OP that it's all the fault of the "fairing bug" is misplacing the problem.

 

Edited March 19, 2016 by Plusck

[Tex_NL]

15 minutes ago, Plusck said:

...

Therefore telling the OP that it's all the fault of the "fairing bug" is misplacing the problem.

 

No. Because when the fairing bug is fixed a smooth gravity turn will not flip your rocket.

Starting the gravity turn requires you to deviate slightly from prograde. EVERY form of gravity turn will deviate slightly from perfect airflow. If you perfectly follow the airflow you will be travelling in a straight line and there will be no turn.

[Plusck]

1 minute ago, Tex_NL said:

No. Because when the fairing bug is fixed a smooth gravity turn will not flip your rocket.

Starting the gravity turn requires you to deviate slightly from prograde. EVERY form of gravity turn will deviate slightly from perfect airflow. If you perfectly follow the airflow you will be travelling in a straight line and there will be no turn.

Which is why the gravity turn must be initiated at a relatively low speed, to allow "gravity" to then induce the rest of the "turn".

A stable, top-heavy and rear-finned rocket will always make a gravity turn unless you (a) force it not to or (b) make a one-in-a-thousand launch that is actually perfectly straight up. Most people will only have RL experience with emergency flares or fireworks, both of which are top-heavy for a reason and both of which will (a) make a gravity turn and (b) naturally turn into the airflow. That is why you must fire flares slightly downwind - otherwise they turn into the airflow and continue their gravity turn into the ground.

Whether bugged or not, fairings in themselves make the top of a rocket light, and this needs careful attention.

The OP's rocket is essentially empty space in the top third, followed by a rapidly-draining small tank. With or without the fairing, it would not take kindly to any kind of deviation from prograde. It is also massively overpowered, making any kind of gravity turn difficult because it won't have time to dip towards the horizon if run at full thrust.

The main issues with the OP's problem with fliipping are therefore (a) trying to turn too late, going too fast, and too far away from prograde, (b) having far too high a TWR, which rules out a natural gravity turn, (c) possibly using MechJeb which sounds like it enforces the "old and wrong atmosphere" approach to gravity turns, (d) using a lightweight 2.5-to-1.25m adapter that is pointless and merely adds to the length of the fairing, and (e) allowing a smallish fuel tank just under the fairing to drain first.

These basic problems with design and ascent profiles are, indeed, exacerbated by the fairing. That added problem is certainly the final straw as far as the OP's design is concerned, but I and many other people manage to use fairings extensively as long as these major design and flightpath problems are eliminated.

I'm not saying there is no bug. I'm saying that the bug is merely highlighting problems that were there already, and sorting those will help the OP. Understanding the problems helps understand the mechanics that are at work.

And finally, I'm pretty sure that a realistic physics rendering of a realistic fairing, applied to the OP's rocket and in the OP's usage scenario, would give exactly the same problem as the OP is describing. If Claw's bug fix allows the OP to get away with a sharp gravity turn with that rocket, then I would wonder whether "fixing" the bug is actually positive for the game.

[Kryxal]

12 hours ago, Plusck said:

The "gravity turn" is by definition, and must in reality always be, a gentle and gradual affair that cannot go against the airflow. The fact that old versions of KSP allowed sharp turns is regrettable. I don't have MechJeb but it sounds like MechJeb will try to force a sharp turn if you tell it to.

Mechjeb will do a poor "gravity" turn if you set it that way ... but you can also tell it "go this far off prograde and no further in atmosphere" with a possible modifier of "widen the range below a certain pressure".

[kiwi1960]

Dump the fairings.....

 

Dump that silly engine configuration and go for a single engine... dump the multiple fins and add just four... ones that can actually steer the rocket in the atmosphere...

 

Also, I have found that you need RCS engines with fuel to help keep the rocket pointing the right way, need to say, using mechjeb, press the ascent button.... the R for the RCS and then launch....

 

[Tex_NL]

I just re-build and tested the OP rocket. With KerbalJointReenforcement and Claws StockBuxFix there is NOTHING preventing MechJeb from launching it into orbit. It blasted to a 100*100km equatorial orbit with over 560m/s to spare in the first stage.
I intentionally typed 'blasted' bold as it has an insane TWR. On the launchpad it starts at just over 4, going all the way up to 14! If MechJeb had not throttled back it would have burned on the way up. This might also be part of your problem, you might simply be going too fast.

Just a side note: You won't be travelling far on your ion stage. Without batteries four SP solar panels will not sustain an ion engine.

Edit:
Removed the Rocko adapter. You don't need it.
Replaced the reaction wheel with batteries. You don't need the reaction wheel  but you do need batteries.
Replaced the separator with a decoupler and the 8 canards with 4 winglets to save even more weight.
And narrowed down the fairing to reduce drag.
Still gets to orbit with fuel to spare. Over 380m/s in the first stage. And that's WITHOUT the Rocko X200 fuel tank. I removed that too.

Edit2:
And do no loose the fairings. Un-bug them instead. Launching my rebuild with the same launch profile without fairings (nothing else changed) it only had 255m/s left in the tanks.

Edited March 20, 2016 by Tex_NL

[Tex_NL]

This thread could not have come at a better time: