Turn ship

[VirtualBrain]

Hello

I'm a new player, and I have a problem.

I can't turn my rocket before ~20000 meters, so I can't turn it at 45° at ~10000 meters.

Thanks for your answers!

[Snark]

Welcome to the forums!

First, just to make sure you're aware:  Nobody should be flying straight up to 10,000 meters and then suddenly turning 45 degrees.  That used to be the right behavior, before 1.0, before the new aero.  However, for the past more-than-a-year, that's not the case.  You want a gradual "gravity turn" that begins practically right off the pad.

Before I try to give any more specific advice, though, can you be a bit more specific?  What exactly do you mean when you say that you "can't" turn the rocket before 20,000 meters?  "Can't" as in "I push the W key and it won't pitch down, nothing happens"?  Or do you mean "can't" as in "I have to just go straight up because if I try to rotate before 20,000 it flips out of control and acts crazy"?  Or something else?

[Goody1981]

Hi and welcome to the forums

We definitely need to see pictures of your rocket to be able to help properly...

The only thing I can think of would be that you have a massively overpowered rocket with a TWR of like 7, and huge immobile fins at the bottom. That would make it hard to turn. 

With pics we will be able to help much more!

Edit: Ninja'd by the great @Snark himself 

Edited July 11, 2016 by Goody1981

[kBob]

Like they said, pics.  But one thing to watch is your speed.  Too fast and you can have a hard time turning.  Watch the g-force meter on your navball if it's over 2 than you're probably encountering this problem, however rocket designs vary--some may have trouble going much above 1.5 gee others may turn decently at 2g or more.  Of course once you're above most of the atmosphere it's no longer a problem. 

Edit here's a pic:

Edited July 11, 2016 by kBob

[bewing]

Turning is also only a problem if you want to end up in Kerbin orbit. If you want to go to Minmus or the Mun, then you don't need to turn. Ships that go fast straight up are very good for exploring the system.

Edited July 11, 2016 by bewing

[StarStryder]

16 hours ago, bewing said:

Turning is also only a problem if you want to end up in Kerbin orbit. If you want to go to Minmus or the Mun, then you don't need to turn. Ships that go fast straight up are very good for exploring the system.

Going straight up is not the most efficient trajectory, even if you're leaving Kerbin.  The most efficient way to the moons is a normal gravity turn up to LKO and just keep burning prograde.

[Firemetal]

Hmmmm. I would suggest adding reaction wheels which adds torque to your craft. Also turn gradually. You will flip if you turn to 45 degrees too fast at 10 km.

[septemberWaves]

The thing which helped me to learn to use gravity turns was actually MechJeb. It has (amongst other things) an ascent autopilot that will do the gravity turn for you. The only time it will fail is if a) your vessel doesn't have enough fuel to reach orbit or b) your vessel is badly designed - not streamlined, no fins, mass not centred above thrust vector, no engine gimballing or reaction wheels, and similar things which you probably will pick up fairly quickly as you progress with learning the game.

Here's an example of what your spacecraft should have to safely perform a gravity turn and ascent from Kerbin:

As you can see, my Mercury 1 spacecraft is streamlined and has fins at the bottom (fins without control surfaces). The engine at the bottom is modded, but the important thing about it is that it can gimbal (if you're unfamiliar with that term, it means that the engine can direct its thrust to help to turn the rocket). There is a fairing around all parts of the rocket that are not particularly streamlined in order to minimise drag (the less drag you have the safer your gravity turn is). Finally, in addition to the integrated reaction wheel in the command pod, there is also a 1.25m reaction wheel at the top of the booster. It is decoupled when the booster is decoupled, but on the ascent it aids in control of the rocket.

Like most of the rockets that I make are designed for, the Mercury 1 transport follows the following set of guidelines for a launch:

1. Engine at full throttle (I actually limit the thrust in the VAB to suit the payload mass but that's somewhat advanced); stability assist turned on
2. Straight up until speed is about 100m/s
3. Rotate so that North line is at the bottom of the navball whilst ascending directly up (this is a personal preference so that I use the s key instead of the d key to perform the gravity turn, it's not a requirement for this craft)
4. Begin gradual turn to East when speed passes 100m/s
5. Turn rocket by about two degrees every second or so at first, until 50 degree angle is reached by 8km altitude (your initial angle is 90 degrees)
6. Aim for 50 degrees by 8km, 45 degrees by 10km (once you reach this point it may be possible to set stability assist to point prograde, which may minimise needed control input until main engine cutoff), 30 degrees by 30km, and under 20 degrees by 40km
7. After 40km set stability assist to point prograde if not done already, and burn either until main engine cutoff or until the apoapsis of 100km is reached (with a good ascent there should be maybe 1% of the fuel for the main engine remaining by the time the desired apoapsis is reached; this remaining fuel is not necessary if the gravity turn was performed properly and can be jettisoned). This should happen when the vessel is pointing about 5 degrees above the horizon and is between 50 and 60km above sea level. At this point the fairing and launch escape tower are jettisoned (in that order because the fairing is attached to the launch escape tower) and then the main booster is separated. The service module engine can be ignited at this point but only if throttle is at zero.
8. Plot and execute maneuver to circularise orbit at apoapsis. There should be a significant amount of fuel remaining in the service module if the ascent was performed well (this vessel in particular is designed for orbital rendezvous with stations or large vessels in orbits up to 500km, hence the excessive delta-v).

These instructions are perhaps a little specific, but hopefully should give you some insight into how to perform a gravity turn, and how to design your vessels so that they're capable of performing a gravity turn.

[pincushionman]

On July 11, 2016 at 2:34 PM, VirtualBrain said:

Hello

I'm a new player, and I have a problem.

I can't turn my rocket before ~20000 meters, so I can't turn it at 45° at ~10000 meters.

Thanks for your answers!

Is it because you have no controllable fins and no gimbal on your engines? And your ship is so large your wimpy reaction wheel can't do anything?

I've said it before (and others already have), and I'll say it again: Pictures man, pictures! We can't diagnose a problem we can't see.

[swjr-swis]

Guys, I see a lot of good advice, but are you considering that @VirtualBrain may be a console player?

Can console players 'press W', or use mods, or even something as taken for granted as providing logs/screenshots? I mean, for all I know they can, but we may need to drop some of our assumptions from now on when offering advice.

 

[bewing]

3 hours ago, swjr-swis said:

Guys, I see a lot of good advice, but are you considering that @VirtualBrain may be a console player?

Can console players 'press W', or use mods, or even something as taken for granted as providing logs/screenshots? I mean, for all I know they can, but we may need to drop some of our assumptions from now on when offering advice.

 

Well, if the game is actually out on console at this point, then one of us is going to have to be a guinea pig and find out what's possible -- or a Squad console version tester is going to have to tell us. But until then, we would be shooting blind by not making any assumptions at all.

[VirtualBrain]

This is my ship :

http://image.noelshack.com/fichiers/2016/28/1468417600-screenshot14.png

I want to put the upper part in orbit around Kerbin. I'm a PC player (I'm not english, sorry if it's a no correct sentence...)

Edited July 13, 2016 by VirtualBrain

[Snark]

39 minutes ago, VirtualBrain said:

This is my ship

Thanks, really helps to see it.  For the most part, that's a pretty reasonable early-career ship to get to orbit.  A couple of observations:

First, you have a lot of tanks vertically stacked in your first liquid-fueled stage.  That's going to tend to make your rocket flop and bend-- reduce the number of tanks if you can.  Fewer taller tanks = better than more, shorter tanks.  Even if the 1-ton LFO tank is the biggest one that you've got unlocked thus far, you can still use fewer than you've got.  I count four 1-ton tanks and four half-ton tanks, for a total of 6 tons of fuel capacity.  You could replace those four half-tonners with two one-tonners, reducing your tank count while keeping the same fuel capacity.

As for turning:  if that's a Reliant on the bottom, I can see why you'd have trouble.  There are basically only three ways you can turn a rocket during ascent:

1. Engine gimbal
2. Steerable aerodynamic control surfaces
3. Torque from reaction wheels

With a Reliant, you don't have any of #1 at all.  Your fins are fixed ones, so you don't have any of #2, either.  The only turning authority you have at all is #3, the reaction torque from your command pod, and it's pretty weak in comparison to #1 and #2.

So, how to solve this?

Three potential solutions.  Any one of these could help, but you could also do more than one of them-- they're not mutually exclusive.

• You can replace the Reliant with a Swivel.
  • The Swivel has engine gimbal, which will help you steer during ascent.
  • It also has slightly better fuel economy than the Reliant when air pressure is low (which it will be, after those SRBs have burned out), so it's basically a win all around. 
  • Potential drawback:  it's a higher tech level than the Reliant, I don't know if you've unlocked it yet.
• You can use steerable fins.
  • For example, replace the fixed fins you have now with the AV-R8 Winglet.  It's only slightly more expensive, and will give you a lot of steering power.
  • Personally, I almost never do this with small, early rockets like that-- it's kind of overkill, IMHO.  If you go with a Swivel, I don't think you need steerable fins.  I'm just mentioning it as an option.
  • Potential drawback:  As with the Swivel solution, I don't know whether you've got this unlocked yet or not.
• You can do a proper "gravity turn".
  • This is by far the most attractive solution, if you can do it.  It will work with your current rocket, as long as you're aerodynamically stable.  It will get you to orbit smoothly and efficiently, and save you a lot of fuel, and doesn't require any new technologies or design changes.
  • Potential drawback:  You'll probably find it hard to do at first; it's tricky to do right.  You'll get better with practice, but you'll probably have to repeat it many times to get it right.  Just be patient, keep at it, and remember that "Revert to Launch" is your friend.     Details below on how to do it.

Here's how to do a gravity turn:

It involves giving your rocket a slight eastward nudge-- just a few degrees-- right away, almost immediately when you leave the launch pad.  For example, as soon as you get up to, say, 20 m/s.  Launch, wait a couple of seconds for 20  m/s, then nudge it eastwards a "small angle".  There.  You're done.  If you get the correct "small angle", you don't need to do any more steering, your rocket will just fly itself on the curve it needs to go.  You can take your hands off the keyboard and let it fly itself (except for staging, of course).

So:  How much is the correct "small angle"?  I can't tell you, exactly, since that will depend on your rocket design (in particular, it depends on your TWR).

But here's a good way to check:  Just pick an amount and try it.  Then wait a minute and see what your rocket is doing when it reaches 10 km altitude.  If it's going something over 300 m/s and is tipped at about a 45 degree angle at that point, then congratulations, you nailed it!  If it's still climbing a lot more steeply than 45 degrees, then you didn't tip enough; revert to launch and try again, with a bit more tipping.  If it's going a lot more horizontal than 45 degrees, then you tipped too much; revert to launch and try again, with a bit less tipping.

It might take you a few tries to get it right.  It's really sensitive:  if the "small angle" is only slightly too big or too small, it'll have a big effect on the path that your rocket takes.  Don't give up, keep trying.  You'll find that you get a lot better at it with practice.

Does this help?

[kBob]

Did you check your g-force like I suggested?  You've got four SRB's there and unless you have set their throttle limiters (in the VAB right click on one of them), that thing probably goes pretty fast at the start until they burn out and the faster you go the harder it is to turn.  A gimbaling engine can help like Snark suggested but if you are going too fast it can still be hard to turn. 

Also you can add struts to make that tall stack more rigid at the beginning by running struts from the SRBs to the upper part of the stack (until you drop the SRB's then it can flex again but the higher you are the less this will effect you, though like Snark suggested always go with the tallest tanks you have rather than several shorter ones, you can use one shorter one if you need just a little more propellant but the fewer connections you have in a stack the better and again struts help a lot).

[pincushionman]

2 hours ago, VirtualBrain said:

This is my ship :

http://image.noelshack.com/fichiers/2016/28/1468417600-screenshot14.png

I want to put the upper part in orbit around Kerbin. I'm a PC player (I'm not english, sorry if it's a no correct sentence...)

 

1 hour ago, Snark said:

Three potential solutions.  Any one of these could help, but you could also do more than one of them-- they're not mutually exclusive.

• You can replace the Reliant with a Swivel.
• You can use steerable fins.
• You can do a proper "gravity turn".

49 minutes ago, kBob said:

Did you check your g-force like I suggested?  You've got four SRB's there and unless you have set their throttle limiters (in the VAB right click on one of them), that thing probably goes pretty fast at the start until they burn out and the faster you go the harder it is to turn.  A gimbaling engine can help like Snark suggested but if you are going too fast it can still be hard to turn.

Agree with the others here, and thanks for the picture. As @Snark said, if that center engine is a Reliant, you're pretty screwed for turning. I'd expect that to launch you high enough where the air is thin and fins are no longer effective, so a Swivel is called for.

If it is a Swivel…you're still kinda screwed for turning, since as @kBob noted, you have four un-steerable Hammers going right off the pad. Your Swivel won't help until you stage it. You need steerable fins for the stage right off the pad.

As he also said, it's harder to turn the faster you're going, especially if your ship is flexible (read: more smaller tanks). Four Hammers will get you going very fast, very quickly, and it may be too late for a good turn by the time you stage them off. I've never needed more than two Hammers on a ship of (roughly) that size, even when I'm flying badly (and I do, often). Three, tops.

[Snark]

33 minutes ago, pincushionman said:

If it is a Swivel…you're still kinda screwed for turning, since as @kBob noted, you have four un-steerable Hammers going right off the pad. Your Swivel won't help until you stage it. You need steerable fins for the stage right off the pad.

Except that he could stage the Swivel together with the Hammers and burn it at low throttle.  With a tall ship like that, even a slight amount of gimbaled thrust can make a big difference to steering.

But even that much shouldn't be necessary.  If he starts a gravity turn practically right off the pad, then the torque of the command pod should be plenty to nudge the nose of the ship a couple of degrees eastward when the ship is going low speed.