Launching Using Trim or: How I Learned to Stop Fighting Wild Oscillations and Love the New Aero

[Rhomphaia]

We all know by now that tall thin rockets that start a gravity turn very early on in the flight is the way to go to orbit.

But we have probably also all seen one of our tall thin rockets, that works fine going straight up, turn to spaghetti as soon as you touch the controls.

What I have been doing recently is rather than using WASD to steer my rockets only using ALT-WASDX for steering and leaving SAS off, setting a few notches of pitch down in the desired direction before I even fire my engines(I always rotate my command pods so pitch down is the direction i want to go), then restoring neutral trim once my gravity turn starts.

If the turn is too fast I can arrest it with a little pitch up trim, too slow and pitch down trim will sort it. If I find myself veering off course north or south I set up the appropriate yaw trim until I am back on course.

Any-one else doing this?

[JoCRaM]

Or use CAPS-LOCK to switch to fine control.

[EtherDragon]

We all know by now that tall thin rockets that start a gravity turn very early on in the flight is the way to go to orbit.

But we have probably also all seen one of our tall thin rockets, that works fine going straight up, turn to spaghetti as soon as you touch the controls.

So don't touch the controls. =)

Seriously, when you about 100m/s velocity use a little bit of control to get your rocket tipped over to about 5 or 10 degrees off of vertical. Then TURN SAS OFF. Don't touch it, leave it alone, you don't need it (any more). If you rocket is stable during ascent, it will keep itself pointed nose first into atmosphere. All you need to do is drive it with your throttle to let your rocket tip over naturally. Try to let your rocket fall over to about 45 degrees by 25km altitude - then go full throttle!

[falloutaddict]

So don't touch the controls. =)

Seriously, when you about 100m/s velocity use a little bit of control to get your rocket tipped over to about 5 or 10 degrees off of vertical. Then TURN SAS OFF. Don't touch it, leave it alone, you don't need it (any more). If you rocket is stable during ascent, it will keep itself pointed nose first into atmosphere. All you need to do is drive it with your throttle to let your rocket tip over naturally. Try to let your rocket fall over to about 45 degrees by 25km altitude - then go full throttle!

I have tried this about 50 times with maybe a 5% success rate but never tried it by steering with the throttle, so maybe that is what I was doing wrong. I'll have to give it a shot when i get home. I also didnt know about the Alt-WASD thing either, I swear I learn something new about this game every week. I played for a month before I realized you could quicksave.

[Rhomphaia]

So don't touch the controls. =)

Seriously, when you about 100m/s velocity use a little bit of control to get your rocket tipped over to about 5 or 10 degrees off of vertical. Then TURN SAS OFF. Don't touch it, leave it alone, you don't need it (any more). If you rocket is stable during ascent, it will keep itself pointed nose first into atmosphere. All you need to do is drive it with your throttle to let your rocket tip over naturally. Try to let your rocket fall over to about 45 degrees by 25km altitude - then go full throttle!

How do you turn your rocket 5-10 degrees off vertical without touching the controls?.. Use trim!

The rockets I am building are very tall. if they are nice and stable all i need is two notches of trim before launch, then hit alt-X when I am 5-10 degrees of vert and job done. If I try to turn when I hit 100m/s with SAS enabled then wild oscilations will occur as the SAS fights the aerodynamics and joints start to flex. SAS is completely unnecessary in lower atmo

[Voidryder]

So don't touch the controls. =)

Seriously, when you about 100m/s velocity use a little bit of control to get your rocket tipped over to about 5 or 10 degrees off of vertical. Then TURN SAS OFF. Don't touch it, leave it alone, you don't need it (any more). If you rocket is stable during ascent, it will keep itself pointed nose first into atmosphere. All you need to do is drive it with your throttle to let your rocket tip over naturally. Try to let your rocket fall over to about 45 degrees by 25km altitude - then go full throttle!

This is how I fly - nav-ball and throttle. I only find I need to slightly adjust to the type of launch vehicle I'm using. And this is why I'm loving the new aero -- gravity turns.

[Kerbart]

Reducing the gimbal range is another way. Oscillations are the result of SAS overcorrecting and turning into a positive feedback loop. Locking the gimbals on your boosters and reducing the gimbal range on your main engine is an easy way to achieve oscillation reduction without having to resort to adjusting the way you control the rocket.

[Tex_NL]

I've never launched rockets with just trim but I pretty much always fly my SSTO spaceplanes like that. Neither MechJeb nor the stock SAS has the required control skills to avoid potentially lethal oscillations.

[EtherDragon]

This is how I fly - nav-ball and throttle. I only find I need to slightly adjust to the type of launch vehicle I'm using. And this is why I'm loving the new aero -- gravity turns.

Yes, the accurately modeled gravity turn is one of my favorite new features of the new Aero. Also, SAS was added as a game benefit back when rockets would turn, yaw, and rotate unexpectedly because of the inaccurately modeled aerodynamic forces. Now that aero is much more accurate - SAS has largely lost its usefulness in the atmosphere. I routinely leave it off until I'm at 45km altitude, these days.

[Rhomphaia]

Reducing the gimbal range is another way. Oscillations are the result of SAS overcorrecting and turning into a positive feedback loop. Locking the gimbals on your boosters and reducing the gimbal range on your main engine is an easy way to achieve oscillation reduction without having to resort to adjusting the way you control the rocket.

Not exactly a resort. I now launch like this even with rockets that don't need it. Generally I do lock the gimbals when I have more than one gimballing engine. Honestly never noticed gimbal limits were tweakable before.

[Warzouz]

I don't use SAS except higher than 35km. but I still need to force it to turn before 45°(10/15km), and force it to hold back from going horizontal until 35km. If I let go I usually en horizontal at 22km and loose a lot of fuel by drag, because I need to throttle up to orbit.

Tested on 10 SSTO rockets able to orbit from 12T to 236T payloads

PS : I use Joint reinforcement Mod

[Two]

Another option is to raise the thrust vector above the center of mass, basically creating a front-accelerated rocket. This can be easily done with radial engines, just put them at the highest point possible.

While a front-pushed rocket can theoretically still rotate if the mass of it's 'tail' swings about, it will be a lot more stable than a back-pushed rocket. Only downside: you might burn equipment on the sides.

[JoCRaM]

Another option is to raise the thrust vector above the center of mass, basically creating a front-accelerated rocket. This can be easily done with radial engines, just put them at the highest point possible.

While a front-pushed rocket can theoretically still rotate if the mass of it's 'tail' swings about, it will be a lot more stable than a back-pushed rocket. Only downside: you might burn equipment on the sides.

Before people shout pendulum fallacy, this does work - but mostly because it moves the engines close to the probe core which "helps" the control software, and reduces compression flexing.

[Wolf Baginski]

Reducing the gimbal range is another way. Oscillations are the result of SAS overcorrecting and turning into a positive feedback loop. Locking the gimbals on your boosters and reducing the gimbal range on your main engine is an easy way to achieve oscillation reduction without having to resort to adjusting the way you control the rocket.

I can confirm that over control of this sort is part of such problems, whether with rockets or planes, and whether with manual, SAS, or MechJeb. In 1950s flight testing, a lot of work was in adjusting the control system to get the right amount of control movement.