Gravity Turn Problems

[LukeTheZuke]

Hello guys, I've been trying for over 2 hours to understand why my rocket goes insane when I am trying to perform a gravity turn and it never seemed to fix. I read through tons of forums saying that you should put aerodynamic fins but none of that worked. I tried with tons of different rockets and it didn't work. I even downloaded a Mun Rocket and the gravity turn still isn't working. I even tried using MechJeb and still not working. Can anyone help me?

Edited May 11, 2015 by LukeTheZuke

[stibbons]

You need to add some pics of your craft, and describe how you're trying to fly it now. Pics of the ascent are probably helpful there too. But, at a guess, you're either going too fast, turning too hard and too late, or both.

[DeMatt]

The old rule-of-thumb of "turn 45 degrees at 10 kilometres" is invalid. You want to make an immediate turn off the launch pad of, oh, about 5 degrees, and then continue turning as your rocket flies. Never really getting out of the prograde circle, but continually getting further from the vertical as it moves, and thus approaching horizontal as you approach your desired orbital height.

Beyond that, we'll need to see the rocket you're having trouble with.

[Eric S]

What ascent profile are you trying to do? If it's the old "10km up then pitch 45 degrees" then that's not likely to work.

What ascent profile works is really a per-craft thing depending on the aerodynamic efficiency and TWR of the craft. Craft with a higher TWR have to turn more aggressively and also have greater aerodynamic forces applied, so a high TWR craft that isn't aerodynamic is actually rather hard to get into orbit efficiently because the only time you can safely turn more than a few degrees away from prograde is before you pick up too much speed.

For most of my craft that keep the TWR between 1.4 and 1.8, I find that tipping one degree when the craft reaches 35 m/s, a second degree at about 65 m/s, and a third at about 85 m/s. past 110m/s, I just follow the prograde marker. If I got the early part right, I tend to hit 10 degrees pitch from vertical at about 3500-4000m altitude, and 35 degrees pitch at about 9500-12000m. This is the ascent profile that tends to work best with my craft that like to flip.

If your craft can safely turn farther off of prograde, you can wait longer and pitch over farther, but I still wouldn't expect to be able to pitch over more than 10 degrees off of prograde.

[LukeTheZuke]

Thanks guys,it was actually the "old rule-of-thumb" that was screwing me over. I understand alot more about how to get in orbit now that I understood how you guys did it. I was so caught up into the "How to get into Orbit in Kerbal Space Program" videos that I didn't think about experimenting with the other stuff. I know Turn a good bit at 6,000 altitude and it gets me into orbit, longer than usual but I now know I can experiment to understand more about getting into Orbit and stuff. I thought I was quite good but then I saw the replies in my thread. Anyways thank you guys, I fixed the problem

[Invader Jim]

You want to make an immediate turn off the launch pad of, oh, about 5 degrees, and then continue turning as your rocket flies. Never really getting out of the prograde circle, but continually getting further from the vertical as it moves, and thus approaching horizontal as you approach your desired orbital height.

How do you correct a too steep launch? Sometimes I can't get the rocket to lean the 5 degrees and it seems really slow to drop the nose at all. Am I going too fast? Too slow?

I want a steady natural and gradual turn to 45 degrees and beyond but it feels like I have to fight it to pull the nose away from absolute vertical.

[Empiro]

If you add winglets or have a vectoring engine, it shouldn't be very difficult to get the degree turn. Also, I often turn off SAS after the turn, and let the natural aerodynamics take over (winglets really help here).

[Fishslap]

You can reduce the amount of boosters, scale them down by right clicking them or add fins to the bottom of the core launch engine for maneuverability. Occasionally it will also work to just keel over right above the launch pad like 5 -10 degrees so the excessive thrust at least goes somewhat in the right direction. It`ll then be easier to turn the rest of the way higher up. Early on I managed to get a few rockets up that way. The best ascent vector is entirely dependent on the craft. Ideally you want some initial altitude to get as much thrust out of the launch phase as possible. But the degrees don`t really matter so much, as long as you make a straight line somewhere. What matters is the curve of your beginning orbit, which is a function of your velocity and angle. If you have a slow second stage you need to keep your nose higher to gain altitude and if you have a fast engine you can just flop down to the equator and stay there as soon as the boosters drop. With the medium engines you can actually circularize your orbit directly from launch because you are able to keep up with the apogee of your orbit. Ideally you should be about 40-50 seconds behind it. Any less and you`re losing altitude. Any more and you`re too steep.

Anyway, if you`re too steep it`s either because you`re using the "Reliant" which doesn`t come with steering, because you`re not using fins at the bottom of the craft or because you`ve overdone it on boosters. But like I said, you can sometimes overcome it by leaning off the launchpad so you get started on the general angle you want as early as possible.

Edited May 15, 2015 by Fishslap