[BLEEP] Gravity Turns, How Do They Work?

[JakeGrey]

I aim to start mine around the 10-12km mark, partly because I use FAR and have found that even my best designs will go tumbling if I try and turn below that. I've also found it advisable to hold off until the booster stage is away to prevent mid-air collisions.

[BubbaWilkins]

I'd say most "efficient" turns start fairly low, below 10km.

Problem is that doesn't mean your craft can actually manage it. Most of mine tend to lose control unless sufficiently high in the atmosphere. I blame FAR and DRE.

[Epthelyn]

The atmosphere starts to thin out more and more at 10km, which is why it seems to be the 'recommended minimum' for gravity turns. The idea is that you're not wasting fuel trying to fight gravity (so the earlier the better to gain horizontal speed) but also not wasting fuel fighting against atmospheric drag (so the later the better). A balance of the two gives the best results.

I usually go for 10km, but only if I can or need to. For larger rockets which I dare not try to pitch before staging at least once or twice it can be anything up to 20km, and for smaller rockets just aiming for orbit it can be as low as 7 or 8km because I don't really need efficiency.

The 5-6km MechJeb guide seems a bit low, but I guess that depends on how sharply you turn.

[Oggula]

I commence turning at 9km (which made significant fuel savings in tests) and turn at a continuous rate until my velocity vector is 45 degrees at 30 km. I keep turning until by 60km I go below the horizon to keep my apoapsis around 68km as I circularize. My final orbit is always 70km.

I basically ran this off a tutorial Scott Manley did a while ago

[Cydonian Monk]

It really depend on where the center of mass will be as the first stage burns out. If I've got a heavy payload and a large first stage, I'll start the gravity turn much later to prevent "issues."

But generally I turn 2° to 5° once clear of the tower, slow turn once above the troposphere to 45°, then turn from there based upon my chosen ascent profile (burn-coast-burn vs direct injection vs "we're doing what!?!"). [Edit: My "usual" orbit is 130km, which is my station orbit. That affects the launch profile a bit vs a 70km orbit.]

I may just try a swig of your Munshine later to see how well it flies for me. And that launch efficiency exercise, too.

Edited September 9, 2013 by Cydonian Monk

[Giggleplex777]

It's really hard to do a proper gravity turn without FAR. If you can tip the rocket over a bit and turn SAS of, depending on how heavy the top of the rocket is, the rocket should follow the prograde.

For "Pitchover Maneuvers" on the other hand, I usually do this:

1. Pitchover to 5 degrees at 8.5km

2. I keep turning slowly. When my speed exceeds 400m/s, I should be at 45 degrees.

3. 80 degrees at 900m/s

4. At this point, I usually stay at 85 degrees until I past 1700 m/s

5. I turn slightly lower than 85 degrees and wait until my Apopasis is above 75km.

Edited September 9, 2013 by Giggleplex777

[Brofessional]

I lower my throttle until 7-10km, then pitch to 75 degrees at full throttle, then 45 degrees at 20km, 25 degrees at 30km, and zero degrees by 50km.

It all depends on the TWR and stability of your rocket really. Slower rockets can't turn as soon.

The smoother your turn is, the less fuel you'll waste on steering losses.

Edited September 9, 2013 by Brofessional

[theflyingfish]

With FAR, gravity turns should be much shallower than stock, beginning almost right off the pad. A good rule of thumb is that you want to be turned toward horizontal about 5 degrees every four kilometers. So if you're at 28 kilometers, you should be at about 55 degrees of pitch. Halfway up (to 70 km) you should be at 45 degrees. At 70 km, flat.

Keep in mind that these values are for FAR only. Stock has a much thicker atmosphere lower down.

[boxman]

For me it entirely depends on the launcher.. Sometimes i turn early, other times late and sometimes I burn straight up for solar orbit if i have a launcher that has enough thrust and fuel.

[nhnifong]

My basic launch profile is exactly the same as Wayfare's description in the OP. I never got the hang of FAR

[notfruit]

A perfect ascent is a continuous burn, with no coasting to Apoapsis to circularize. I almost had it but my Radical 2 Rocket only had 3517.8 m/s of delta-v and is designed for suborbital trajectories. I started leading the prograde marker east at about 8 km and by 15 km I was at like 45 degrees. It was beautiful.