In praise of the new aerodynamics and rocket flipping

[Superfluous J]

I built a rocket the other day that ingenuously (I thought) siphoned the fuel from the payload into the main launcher, to give my side boosters about 30 more seconds of thrust on ascent. My trial runs with the rocket had shown that I'd save total dV if they could burn a little longer, and why add more fuel when I didn't actually need to? Once in orbit, I could just transfer fuel back from the remaining center stack before ditching it to fall back to Kerbin.

This rocket, which in early testing had been pretty rock solid on the ascent, started flipping like a baton no matter how well I kept it in the airflow, no matter how many fins I put on the bottom, and no matter how much I tried to correct manually.

Now at this point, from what I see in so many posts in this forum, most people would have thrown their arms up and complained that KSP was killing their fun. Instead, I looked at it, thought about it, and realized my problem. By emptying the fuel out of the top of the rocket, I was making the whole thing EXTREMELY bottom heavy. I was - to continue to overuse an overused analogy - throwing a dart backward. Putting the feathers on the arrow head won't make it fly backwards, to overuse another analogy.

So I undid my change, found a better way to add a little more time to my early boost stage, and the rocket made orbit with the payload intact. I could even deviate significantly from prograde very low in the atmosphere and at high speed, all because I (re)applied a little aerodynamics know-how.

So thank you, Squad, for introducing that sort of necessary thinking into the game.

[Xkay7]

A thousand and one threads complaining about rockets flipping for no reason and finally someone understands the problem. Hurrah!

[Green Baron]

I can't understand either why it's so hard to adapt to new conditions, but i must admit that sometimes i also feel like blaming everyone else except me. Usually a temporary feeling :-)

Finding a solution to a problem always is the more intelligent approach (no offense to noone !), even in a game. Or especially in a game ?

Always have the correct end pointed towards space

k

Edited May 16, 2015 by kemde

[Voidryder]

Nice job on figuring that out 5thHorseman. I have actually had better success with rockets, planes and ssto's with 1.0.2 then pre-1.0. Just makes more sense to me. Once Squad figures out the whole heating bit, I'll be golden.

[regex]

Nice work. It's still easy to launch ridiculous stuff into orbit in 1.0.x, just like it was before using FAR, there are just different things to worry about now.

[Parkaboy]

I just wish we had more tools to control fuel flow in the rockets. The way LFO flows in the tanks, it's as if they want the flips to happen. As if kerbal rockets were designed to fly doing stunts...

[Temeter]

Nice work. It's still easy to launch ridiculous stuff into orbit in 1.0.x, just like it was before using FAR, there are just different things to worry about now.

Yep, FAR/Stock never really stopped you from launching bricks into space. You just need a bigger rocket and lower speed. It's a bit easier, though, since the lack of FAR's destructive aerodynamic forces means complex constructions and unprotected equipment are less likely to break apart when coming close to sonic speed.

I just wish we had more tools to control fuel flow in the rockets. The way LFO flows in the tanks, it's as if they want the flips to happen. As if kerbal rockets were designed to fly doing stunts...

That's just the result of stacking tanks and usually also a lacking gravity cuve. The produceral parts mod allow you to avoid those issues, since you can make a single tanks as large as you want.

http://forum.kerbalspaceprogram.com/threads/106975-0-90-Procedural-Parts-Parts-the-way-you-want-em-v1-0-Jan-11

Edited May 16, 2015 by Temeter

[Bill Phil]

Yeah, people don't often realize that the old rules of thumb won't work anymore...

I'm glad some do.

[hellion13]

I'm actually flying rockets immensely better than before thanks to the new aero. Application of a little real world logic, and they launch to space 100% of the time.

I've even learned to be way more efficient than ever before. The game has become much more fun for me. Things actually work the way I expect them to.

Now I've just gotta be patient and wait for the memory leak hotfix, or whatever they have planned for that.

[Robotengineer]

Congrats! You just did real rocket engineering, which can be fun when approached as an interesting challenge.

[Eric S]

Nice work. It's still easy to launch ridiculous stuff into orbit in 1.0.x, just like it was before using FAR, there are just different things to worry about now.

To be fair, pre nuFAR never stopped me from launching ridiculous stuff, I just had to understand the forces at work. Haven't tried nuFAR yet.

[TK421d]

Well, what about staged rockets that still flip, that still have normal masses on upper stages that arent draining fuel?

[LordCurlyton]

I've come to the same conclusion, but sometimes it seems like I can launch the exact same rocket fine one time and then the next launch it flips in midair, which confuses me. I just attribute it to me going slightly further off prograde than I should compared to the last time. Still trying to figure out all the changes from pre-1.0.x, but having fun (mostly) doing so.

[Green Baron]

Well, what about staged rockets that still flip, that still have normal masses on upper stages that arent draining fuel?

If you show us the craftfile we'll tell you if it's a design or a piloting error ....

k

[Temeter]

I've come to the same conclusion, but sometimes it seems like I can launch the exact same rocket fine one time and then the next launch it flips in midair, which confuses me. I just attribute it to me going slightly further off prograde than I should compared to the last time. Still trying to figure out all the changes from pre-1.0.x, but having fun (mostly) doing so.

It's also important what speed you're flipping at. Around 340m/s a rocket will reach the most dangerous part of the sound barrier and around the highest level of drag you'll encounter.

I recommend activating the aerodynamic overlay via F12. You'll see a bunch of arrows which show exactly what part causes the flipping!

[Superfluous J]

That's actually exactly what I did. The arrows helped me deduce the problem.

Also, the rocket reached its most unstable state right about mach 1, which of course didn't help!

[N_Molson]

That's a simple matter of AoA (Angle of Attack). In surface mode, the yellow marker shows the direction of the airflow, while the eyeball shows you where the rocket is heading. The key is to keep that angle very low during the critical stage of the ascent (10,000 to 20,000 meters depending of the rocket design). Keeping the nose within the yellow cue should work. That's much, much more realistic, indeed !

[LordCurlyton]

I have noticed, oddly, that many of my rockets fly better without any sort of fins to assist in stability in atmosphere, which seems counter-intuitive to me. I dunno if its just me (probably) or what else, but it has been annoying at times. But I persevere. I'm by no means what I would call good at this in the first place, so when in doubt I presume myself as the source of failure.

[Temeter]

I have noticed, oddly, that many of my rockets fly better without any sort of fins to assist in stability in atmosphere, which seems counter-intuitive to me. I dunno if its just me (probably) or what else, but it has been annoying at times. But I persevere. I'm by no means what I would call good at this in the first place, so when in doubt I presume myself as the source of failure.

As I said, the points of failure heavily depend on speed and flight path. Possible there is just some part of your rockets/gravity turn where fins indeed cause trouble. When your rockets work well without fins, than that's maybe just what you should go for.

I found that my rockets tend to be very stable with fins. Not always the most efficient rockets, but reliable and able to make a comfortable gravity turn, even when the freight is an unhandly and draghappy mothership using a bunch of wings as connectors.

[tg626]

We need a center of pressure marker in the vab....

[Temeter]

We need a center of pressure marker in the vab....

Why, are you trying to fly your rocket sideways?

[Nathair]

I just wish we had more tools to control fuel flow in the rockets. The way LFO flows in the tanks, it's as if they want the flips to happen. As if kerbal rockets were designed to fly doing stunts...

Very much this. It's all well and good to say that the problem is tank stacks draining from top to bottom but what exactly is the alternative?

[Brotoro]

It's all well and good to say that the problem is tank stacks draining from top to bottom but what exactly is the alternative?

You could set up fuel lines and separators that cause your stack of fuel tanks to be drained from the bottommost tanks first. But this could involve a lot of long fuel lines.

[RainDreamer]

You can also use tanks of different sizes. Smaller tanks near engines and bigger tanks near top, even though it drains the same rate, the size can make a little bit of difference and may get you far enough.

[sal_vager]

I find craft that wobble/bendiness combined with hyperactive SAS and extreme gimbal makes craft more inclined to fall over, so I tweak gimbal down to .90 values and I use the basic fins with struts to add truss structures to my longer craft.

I swear decouplers and fairing bases are made of rubber.