Keep 90 degree heading and TWR

[Tripolith]

Hi everyone -

being a more casual KSP player, I am still trying to find may way in 1.02 and in particular trying to get things into orbit. Here are two questions and I am thankful for some advice:

1. When I do a gravity turn, how do I keep my rocket at a heading of 90 degrees?

I am trying to get into orbit applying the approach described in this video:

http://youtu.be/0pA1y5a5rnk

The problem I have, however, is that whenever I initiate my gravity turn by turning 5 to 10 degrees east my rocket does not stay on a 90 degree heading. Typically it moves to a 100 to even 130 degrees requiring a lot of of correction steering. I have tried to add fins, but the problem still exists. Is this normal given the new aerodynamic model or do I get something wrong? In this video the yaw, pitch, roll controls on the bottom left of the UI do not suggest that any corrections are required.

2. TWR

In pre 1.0 my rule of thumb was always that a rocket needs a TWR greater 1 to lift off. Since 1.0, however, it seems that rockets with a TWR of 1.3 to 1.5 would not lift off any more. I assume that this is due to the new aerodynamic model, correct? Is this because drag adds further thrust requirements?

Many thanks for helping me to better understand the new way of playing KSP!

Edited May 5, 2015 by Tripolith

[Gaarst]

About gravity turn, it depends on your rocket; please post a screenshot so that we can actually see the problem. Causes can be numerous.

And about TWR, 1.3 to 1.5 is the best ratio for KSP 1.0.x but be sure to account for the lack of thrust in low atmosphere.

[Chaos_Klaus]

When you say TWR, you probably mean vacuum TWR, right? In 1.0 they changed the way that the specific impulse of an engine works. In 0.90.0 engines would use more fuel in the lower atmo, because specific impulse decreases with high air pessure. 1.0 corrected that behaviour. Now thrust is reduced in atmospheres.

So if you see a vacuum TWR of 1.5, your atmospheric TWR could be way lower or (depending on the engine) even blow 1. You can righclick the engines in the parts menu to see more info on this. Some engines perform well in atmospheres, some are totally useless. The aerospike is the only engine that works ell for both.

If you are using Kerbal Engineer Redux: It has a button that sais "atmospheric".

As for the gravity turn: Use stability control by pressing T. Use fins at the bottom of your rocket. They will stabilize you just like the feathers on an arrow.

Start the turn when you have aquired some vertical speed. I always go for around 100m/s. That gives your fins some grip and you won't oversteer.

[Mastikator]

Putting fins at the bottom of the rocket will make it less likely to flip over, especially at high velocities. I've found that it's harder to do gravity turns with too many fins because it just won't turn.

Put fins at the very bottom of the rocket, at least 4. 6 or 8 if it's not enough, winglets if it's still not enough. Usually I can get away with breaking the sound barrier at 6000-7000m doing this, I immediately go for the 90 degree angle, preferable before 8000m. Once you're at 15km+ the Oberth effect becomes greater than the drag so you actually benefit from going maximum overdrive (also it's way more fun that way).

[Tripolith]

Thanks for all your responses. This is the rocket that wouldn't stay on a 90 degree heading. The first stage is a LV-T45 and the second, upper stage is a LV-909. I have also tried adding more fins at the bottom but the rocket would still not keep at 90 degrees turning to 100+ degrees.

Thanks for any help and advice!

http://steamcommunity.com/sharedfiles/filedetails/?id=437456296

[Pe-Ter]

Does your engine have a Gimbal + why don't you use fins that can move according to your keyboard input?

[Harry Rhodan]

It's that single small Ox-Stat on the back of your capsule. Just use two of them symmetrically.

[Alshain]

Does your engine have a Gimbal + why don't you use fins that can move according to your keyboard input?

Don't do both of these. Either use an engine that gimbals or use active fins, not both.

[Tripolith]

My engine has a gimbal and the reason I am not using active fins is because I am not advanced enough in the tech tree. The thing that looks like an Ox-Stat is in fact this one part from the KER plugin mod. Could that cause the unwanted turn? In the old pre 0.90 version these small massless parts didn't have much of an impact. Will indeed need to get used to the new KSP. I will try this tomorrow without that part and will see what happens! Thanks!

[Tripolith]

Ok! I removed that KER part and my rocket now keeps straight at 90 degrees! Thanks for all your help!